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Orthopedic Surgery Board Review MCQs: Arthroplasty, Trauma & Spine Part 255

Orthopedic Board Review MCQs: Cartilage, Hip & Revision Surgery | Part 214

23 Apr 2026 150 min read 56 Views
OITE & ABOS Orthopedic Board Prep: Practice Exam Part 214

Key Takeaway

This page offers Part 214 of a comprehensive orthopedic surgery board review quiz series by Dr. Mohammed Hutaif. It features 100 high-yield multiple-choice questions, strictly audited and formatted like the OITE and AAOS board exams. Designed for orthopedic residents and surgeons, this interactive quiz facilitates effective preparation for certification.

Orthopedic Board Review MCQs: Cartilage, Hip & Revision Surgery | Part 214

Comprehensive 100-Question Exam


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Question 1

Which of the following best describes the biochemical composition and biomechanical function of the superficial zone of articular cartilage compared to the deep zone?





Explanation

The superficial zone of articular cartilage has the highest water content (80%) and the lowest proteoglycan content. The collagen fibers (mostly Type II) are arranged parallel to the joint surface to resist shear forces. The deep zone has the highest proteoglycan content, the lowest water content, and collagen fibers arranged perpendicular to the joint line to resist compressive forces.

Question 2

An 82-year-old female sustains a periprosthetic femur fracture around a cemented polished taper slip stem 5 years after total hip arthroplasty. Radiographs show a spiral fracture around the stem with fracture extension slightly distal to the tip. The stem is visibly subsided by 1.5 cm. The femoral bone stock is otherwise adequate. What is the most appropriate definitive management?





Explanation

This is a Vancouver B2 periprosthetic fracture (fracture around the stem, loose implant, adequate bone stock). The standard of care for a B2 fracture is revision of the femoral component to a long extensively porous-coated or modular fluted tapered uncemented stem. The new stem must bypass the most distal aspect of the fracture by at least two cortical diameters. ORIF alone is contraindicated when the stem is loose (Vancouver B1 vs B2).

Question 3

During a revision total hip arthroplasty, the surgeon encounters a severe acetabular defect. Radiographs and intraoperative findings reveal greater than 3 cm of superior component migration, destruction of the teardrop, and component medialization beyond Kohler's line. The superior hemipelvis remains mechanically in continuity with the inferior hemipelvis. According to the Paprosky classification, what is the defect grade and the most appropriate reconstructive option?





Explanation

A Paprosky IIIB defect is characterized by severe bone loss with >3 cm of superior migration, component medialization past Kohler's line, and destruction of the teardrop, indicating non-supportive superior and medial bone (<30% host bone contact). Management typically requires a custom triflange component, a cup-cage construct, or massive structural allografts with a support ring to achieve stability, as standard hemispherical cups will not achieve adequate fixation.

Question 4

A 24-year-old male presents with a symptomatic 4.5 cm² full-thickness chondral defect on the medial femoral condyle. He has failed conservative management. What is the primary advantage of Autologous Chondrocyte Implantation (ACI) over microfracture for this specific patient?





Explanation

For lesions >2 cm², ACI is preferred over microfracture. Microfracture relies on marrow stimulation and results in fibrocartilage repair (predominantly Type I collagen), which is less durable under shear and compressive loads. ACI (a two-stage procedure) results in the formation of hyaline-like cartilage (predominantly Type II collagen and aggrecan), providing superior long-term durability for larger defects.

Question 5

During a primary total hip arthroplasty, the surgeon intentionally medializes the acetabular component to the level of the true floor of the acetabulum. Which of the following best describes the biomechanical consequence of this maneuver?





Explanation

Medializing the center of rotation of the hip decreases the body weight lever arm (the distance from the body's center of gravity to the center of rotation of the hip). By reducing the body weight lever arm, the force required by the abductors to maintain a level pelvis is reduced, which consequently decreases the overall joint reaction force across the hip. This is an essential principle in reconstructing hip biomechanics.

Question 6

A 62-year-old male with a metal-on-polyethylene total hip arthroplasty presents with new-onset groin pain and a palpable mass 6 years postoperatively. Radiographs show a well-fixed implant with no osteolysis. Serum cobalt levels are markedly elevated, while chromium levels are normal. MARS MRI reveals a large cystic mass communicating with the joint. Which of the following implant characteristics is most strongly associated with this complication?





Explanation

The clinical presentation describes Adverse Local Tissue Reaction (ALTR) secondary to mechanically assisted crevice corrosion (MACC) at the head-neck junction (trunnionosis). This is characteristically associated with elevated serum cobalt levels out of proportion to chromium. Risk factors include larger diameter cobalt-chromium heads (which increase torque at the trunnion), high-offset necks, and a dissimilar metal pairing (e.g., CoCr head on a titanium stem).

Question 7

A surgeon is considering using a dual mobility articulation for an 80-year-old patient undergoing revision THA for recurrent instability due to severe abductor deficiency. Which of the following best describes the biomechanical mechanism by which a dual mobility implant increases stability?





Explanation

Dual mobility implants feature a smaller inner metallic or ceramic head that articulates within a larger, mobile polyethylene sphere, which in turn articulates within a metal acetabular shell. The primary mechanism of increased stability is the large effective head size of the outer polyethylene sphere, which significantly increases the 'jumping distance' (the distance the head must translate to dislocate) and maximizes the impingement-free range of motion.

Question 8

When evaluating a painful total hip arthroplasty for potential periprosthetic joint infection (PJI), a synovial fluid alpha-defensin test is ordered. What is the biological origin and significance of alpha-defensin in this context?





Explanation

Alpha-defensin is an antimicrobial peptide secreted primarily by neutrophils in response to the presence of pathogens. In the setting of periprosthetic joint infection (PJI), it serves as a highly sensitive and specific synovial fluid biomarker. Its levels are not significantly elevated in aseptic failure, ALTR, or inflammatory arthropathies, making it a valuable tool in diagnosing PJI.

Question 9

Histological examination of healthy adult articular cartilage reveals a basophilic line known as the 'tidemark'. What is the primary anatomical and functional significance of this structure?





Explanation

The tidemark is a highly visible basophilic line on histology that separates the uncalcified deep zone of articular cartilage from the calcified cartilage zone. It serves as an important mechanical tethering point where the collagen fibers from the deep zone securely anchor into the calcified layer, and it is a site of significant shear stress. The tidemark advances outward with age, thinning the uncalcified cartilage.

Question 10

During total hip arthroplasty for a patient with Crowe Type IV developmental dysplasia of the hip (DDH), a subtrochanteric shortening osteotomy is planned. Which of the following is the most critical reason for performing the shortening osteotomy in this specific patient population?





Explanation

In Crowe Type IV DDH, the femoral head is completely dislocated and migrated proximally. Bringing the femoral head down to the true acetabulum (which is biomechanically optimal) requires significant lengthening of the limb. Lengthening the leg by more than 4 cm poses a very high risk of stretch injury to the sciatic nerve. A subtrochanteric shortening osteotomy allows the component to be seated in the true acetabulum while protecting the sciatic nerve from excessive tension.

Question 11

A patient develops anterior groin pain and posterior hip instability following a primary total hip arthroplasty. Radiographs demonstrate the acetabular component is placed in 5 degrees of retroversion and the femoral stem is in 0 degrees of anteversion. Which of the following biomechanical phenomena is most likely occurring?





Explanation

The components are retroverted (acetabular cup in 5 deg retroversion, femoral stem in 0 deg anteversion). Combined retroversion predisposes the hip to anterior prosthetic impingement (the neck hits the front of the cup) when the hip is placed in flexion and internal rotation. This anterior impingement acts as a fulcrum, levering the femoral head out posteriorly, leading to posterior instability.

Question 12

A 75-year-old female undergoes revision THA for aseptic loosening. Intraoperatively, the surgeon notes independent motion between the superior and inferior halves of the acetabulum. Which of the following reconstructive techniques is most appropriate for achieving stable long-term fixation in this setting?





Explanation

Independent motion between the superior and inferior halves of the acetabulum is the hallmark of pelvic discontinuity. Standard hemispherical cups (even with screws) will fail because they cannot bridge and stabilize the discontinuity. Reconstructive options must mechanically bridge the defect and provide stability, typically requiring a highly porous metal cup with an ilioischial cage (cup-cage construct), a custom triflange component, or a distraction technique using a highly porous jumbo cup if acute.

Question 13

A 50-year-old male presents with an acutely painful, swollen hip 3 years after a primary THA. Synovial fluid is aspirated. The fluid is cloudy, has low viscosity, and a white blood cell count of 45,000 cells/µL with 92% neutrophils. The decrease in synovial fluid viscosity in this scenario is primarily due to the breakdown of which molecule?





Explanation

Synovial fluid viscosity is primarily determined by hyaluronic acid (hyaluronan), a glycosaminoglycan secreted by type B synovial cells. In infectious or highly inflammatory states (such as acute PJI with 45,000 WBCs and high PMN%), bacterial hyaluronidases and inflammatory enzymes degrade hyaluronic acid, resulting in watery, low-viscosity synovial fluid with poor string sign.

Question 14

A surgeon places a constrained acetabular liner in a patient undergoing revision THA for recurrent posterior dislocations. The patient has a well-fixed, horizontally positioned acetabular shell but severely deficient abductor musculature. Three months later, the implant fails. What is the most common mode of failure for a constrained liner in this setting?





Explanation

Constrained liners securely capture the femoral head, effectively linking the femur to the acetabulum. This dramatically decreases the range of motion before impingement occurs and transfers massive torque and shear forces to the acetabular bone-implant interface during extreme motion. Consequently, the most common mode of failure for constrained liners is aseptic loosening of the acetabular shell (pull-out from the bone) or dissociation of the liner from the shell.

Question 15

During the removal of a well-fixed, fully porous-coated stem in a revision THA, an extended trochanteric osteotomy (ETO) is performed. Which muscle's attachment must be meticulously preserved on the osteotomized fragment to ensure adequate blood supply and subsequent osteotomy healing?





Explanation

An extended trochanteric osteotomy (ETO) involves elevating the greater trochanter and the lateral diaphyseal cortex. The blood supply to this fragment, which is crucial for union, is predominantly provided by the vastus lateralis (and its muscular branches). Preserving the attachment of the vastus lateralis (as well as the gluteus medius/minimus proximally) ensures the fragment remains vascularized and stabilizes it against proximal migration.

Question 16

A 28-year-old male hockey player presents with anterior groin pain exacerbated by hip flexion and internal rotation. Radiographs reveal a cam-type femoroacetabular impingement (FAI). Which of the following radiographic measurements is most characteristic of this pathology?





Explanation

Cam-type FAI is caused by an aspherical femoral head-neck junction (loss of native concavity). It is most accurately quantified using the alpha angle, typically measured on a Dunn lateral or frog-leg lateral radiograph (or MRI). An alpha angle >50-55 degrees indicates cam morphology. A crossover sign indicates pincer-type FAI (acetabular retroversion). Lateral center-edge angle <20 and high Tonnis angle denote hip dysplasia.

Question 17

A 68-year-old female presents with acute onset of intense right hip pain, fever, and chills. She underwent an uncomplicated primary THA 4 years ago. Hip aspiration yields purulent fluid growing Methicillin-sensitive Staphylococcus aureus (MSSA). Her symptoms began 48 hours prior to presentation. Radiographs show well-fixed components. What is the most appropriate surgical management?





Explanation

The patient has an acute hematogenous periprosthetic joint infection (symptoms <3 weeks, well-fixed implants, mature prior THA). The standard of care for acute hematogenous infections (or acute postoperative infections <4 weeks) with well-fixed components is DAIR (Debridement, Antibiotics, and Implant Retention), which must include the exchange of modular components (polyethylene liner and femoral head) to optimally reduce biofilm load.

Question 18

One year following a primary total hip arthroplasty using a proximally porous-coated, tapered titanium stem, AP and lateral radiographs demonstrate radiodense lines bridging the endosteum to the distal extent of the porous coating. The patient is asymptomatic. What do these radiographic findings represent?





Explanation

Endosteal bone bridges joining the cortex to the distal aspect of the porous coating are commonly referred to as 'spot welds.' Their presence is a classic radiographic sign of secondary biological fixation (bone ingrowth or ongrowth) indicating a stable, functioning cementless implant. A pedestal at the distal tip without proximal ingrowth would suggest distal toggle and instability.

Question 19

A 30-year-old female has an isolated 1.2 cm² full-thickness osteochondral defect on the weight-bearing surface of the medial femoral condyle. She is undergoing Osteochondral Autograft Transfer System (OATS) procedure. From which of the following locations is the graft most appropriately harvested to minimize donor site morbidity?





Explanation

In the OATS procedure (mosaicplasty), cylindrical osteochondral grafts are harvested from a non-weight-bearing or low-contact-pressure area of the knee to treat a defect in a high-weight-bearing area. The ideal and most common donor sites are the periphery of the lateral trochlear ridge (superolateral margin of the lateral condyle) or the medial superomedial trochlear margin, as these areas experience minimal contact pressures.

Question 20

In patients with metal-on-metal total hip arthroplasty, the generation of systemic wear debris is a concern. Systemic accumulation of chromium ions is most heavily dependent on which primary route of elimination?





Explanation

Chromium and cobalt ions generated from the wear and corrosion of metal-on-metal implants or from trunnionosis are systemically absorbed. They are primarily cleared from the body via renal filtration and excretion in the urine. Therefore, patients with impaired renal function are at significantly higher risk for systemic metal ion toxicity (metallosis) and elevated serum levels.

Question 21

Which zone of normal articular cartilage contains the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibrils oriented parallel to the articular surface?





Explanation

The superficial (tangential) zone of articular cartilage is the thinnest layer but has the highest water content (approx. 80%) and the lowest proteoglycan content. Its collagen fibrils (primarily Type II and IX) are densely packed and oriented parallel to the joint surface to resist shear forces.

Question 22

An 82-year-old female presents with a periprosthetic femur fracture around a cemented total hip arthroplasty. Radiographs show a transverse fracture at the tip of the stem, gross loosening of the femoral component, and severe comminution and osteolysis of the proximal femur extending to the mid-diaphysis. Which of the following is the most appropriate surgical management?





Explanation

This is a Vancouver B3 fracture (loose stem with poor proximal bone stock). In an elderly, low-demand patient, proximal femoral replacement (PFR) is the most reliable option. It allows for immediate weight-bearing and avoids the high complication and nonunion rates associated with complex reconstructions like impaction allografting in this age group.

Question 23

A 65-year-old female with a metal-on-metal total hip arthroplasty presents with worsening groin pain. Advanced imaging demonstrates a solid and cystic soft tissue mass adjacent to the joint. If tissue from this pseudotumor were examined histologically, which of the following findings would be most characteristic of ALVAL (Aseptic Lymphocytic Vasculitis-Associated Lesion)?





Explanation

ALVAL represents a Type IV (delayed) hypersensitivity reaction to metal ions (cobalt and chromium). The classic histological feature is a dense, perivascular infiltrate of predominantly CD4+ T-lymphocytes, distinct from the macrophage-dominated response seen in standard polyethylene wear or the neutrophil-dominated response in acute infection.

Question 24

In evaluating a patient with a painful total hip arthroplasty 4 years post-operatively, a joint aspiration is performed. According to the Musculoskeletal Infection Society (MSIS) criteria, which of the following synovial fluid profiles is the threshold most indicative of a chronic periprosthetic joint infection?





Explanation

For chronic periprosthetic joint infections (PJI) occurring >90 days after surgery, the accepted MSIS threshold for synovial fluid is WBC > 3,000 cells/µL and > 80% PMNs. Acute PJIs (within 90 days) have a higher threshold of WBC > 10,000 cells/µL and > 90% PMNs.

Question 25

A surgeon is performing an extended trochanteric osteotomy (ETO) via a posterior approach to facilitate femoral component extraction during a revision THA. To maintain the blood supply to the osteotomized fragment and prevent superior migration, which muscle attachments must be preserved?





Explanation

An extended trochanteric osteotomy (ETO) involves elevating the lateral third of the proximal femur. The gluteus medius and vastus lateralis must be left attached to the fragment. They provide an uninterrupted vascular supply to the bone flap and act as an antagonist muscle pair, maintaining the fragment's longitudinal position during healing.

Question 26

A 35-year-old male presents with severe groin pain. Radiographs reveal Ficat Stage III osteonecrosis of the left femoral head, characterized by a subchondral crescent sign but preservation of the articular joint space. Given the patient's age and stage, what is the most reliable surgical treatment to optimize pain relief and long-term functional outcomes?





Explanation

Once subchondral collapse has occurred (Ficat Stage III/crescent sign), head-preserving procedures like core decompression or osteotomies have high failure rates. Despite the patient's young age, Total Hip Arthroplasty (THA) provides the most reliable pain relief and functional improvement, and modern bearing surfaces have excellent long-term survivorship.

Question 27

In the basic science of articular cartilage, which structural component directly stabilizes the non-covalent interaction between the aggrecan monomer and the central hyaluronic acid (hyaluronan) backbone?





Explanation

Proteoglycan aggregates in cartilage are composed of many aggrecan monomers attached to a central hyaluronic acid (hyaluronan) backbone. This non-covalent binding is inherently unstable but is stabilized by Link protein, which binds to both the aggrecan core protein and the hyaluronan chain.

Question 28

A surgeon opts to use a high-offset femoral stem during a primary total hip arthroplasty. Compared to a standard offset stem, what is the expected biomechanical effect of this implant choice on the abductor force required to maintain a level pelvis, and on the joint reactive force?





Explanation

Increasing femoral offset moves the greater trochanter laterally, which increases the lever arm (moment arm) of the abductor muscles. A longer moment arm means less abductor muscle force is required to balance the pelvis. Because joint reactive force is largely determined by the muscle force acting across the joint, decreasing the required abductor force proportionally decreases the joint reactive force.

Question 29

What is the primary advantage of Matrix-Induced Autologous Chondrocyte Implantation (MACI) compared to traditional first-generation Autologous Chondrocyte Implantation (ACI) for treating full-thickness chondral defects?





Explanation

MACI utilizes a type I/III porcine collagen bilayer membrane seeded with the patient's cultured chondrocytes. A major advantage over first-generation ACI is that it does not require harvesting a periosteal patch to cover the defect. The use of a periosteal patch in traditional ACI was associated with a high rate of graft hypertrophy (up to 25%), which MACI significantly avoids.

Question 30

A 72-year-old female is undergoing a complex revision total hip arthroplasty for aseptic loosening. Radiographs demonstrate severe acetabular bone loss. Which of the following radiographic findings is most definitive for the diagnosis of an acetabular pelvic discontinuity?





Explanation

Pelvic discontinuity is defined as a separation of the superior hemipelvis (ilium) from the inferior hemipelvis (ischium and pubis). The most definitive radiographic sign is a transverse fracture line through the acetabulum, often accompanied by medial translation of the inferior hemipelvis relative to the superior hemipelvis, indicating independent movement of the two segments.

Question 31

Which of the following combinations of total hip arthroplasty components places the patient at the highest risk for mechanically assisted crevice corrosion (trunnionosis) at the head-neck junction?





Explanation

Trunnionosis (taper corrosion) is exacerbated by mixed metal junctions (e.g., CoCr head on Ti stem), large head diameters, and small/thin trunnions. A large CoCr head increases the lever arm and toggle at the head-neck junction, while a small titanium trunnion offers less surface area for interference fit, significantly increasing the risk of fretting and crevice corrosion.

Question 32

During a direct anterior approach for total hip arthroplasty, the surgeon develops the superficial internervous plane. The ascending branches of the lateral femoral circumflex artery are typically encountered and must be ligated. These vessels cross the operative field between which two muscles?





Explanation

The direct anterior approach (Smith-Petersen) utilizes the true internervous plane between the Sartorius (femoral nerve) and the Tensor fasciae latae (superior gluteal nerve). The ascending branches of the lateral femoral circumflex artery cross this interval transversely and must be identified and ligated to prevent significant postoperative hematoma.

Question 33

In a 14-year-old male with an osteochondritis dissecans (OCD) lesion of the medial femoral condyle, which of the following MRI findings is the most reliable indicator of lesion instability warranting surgical intervention over non-operative management?





Explanation

A high-intensity T2 signal line completely interposing between the OCD fragment and the underlying bone bed indicates that synovial fluid has tracked behind the fragment. This is a definitive sign of instability (a fluid cleft). Unstable lesions in both juveniles and adults generally require surgical stabilization, whereas stable lesions in juveniles with open physes may heal with rest.

Question 34

A total hip arthroplasty is performed using an uncemented acetabular component. If the cup is inadvertently placed in 60 degrees of abduction and 25 degrees of anteversion, which of the following complications is most likely to occur rapidly?





Explanation

Placing the acetabular cup in excessive abduction (e.g., >50 degrees) moves the contact patch of the femoral head to the superior rim of the liner. This results in edge loading, causing highly localized stress concentrations that lead to rapid, accelerated wear of polyethylene liners or 'stripe wear' and squeaking in ceramic-on-ceramic bearings.

Question 35

In evaluating a patient for recurrent instability following a primary total hip arthroplasty, the surgeon considers using a dual-mobility construct. What is the primary biomechanical mechanism by which a dual-mobility articulation reduces the risk of dislocation compared to a standard single-bearing articulation?





Explanation

A dual-mobility cup features a small inner head articulating within a large, mobile polyethylene liner that itself articulates against the metal acetabular shell. This creates a massive effective head size (the large poly liner), which significantly increases the jump distance (the distance the head center must travel laterally to dislocate) and maximizes the head-to-neck ratio, thereby increasing the impingement-free range of motion.

Question 36

A patient experiences a sciatic nerve palsy immediately following a complex revision total hip arthroplasty. Examination reveals a profound foot drop, weak extensor hallucis longus, and decreased sensation over the dorsal-lateral aspect of the foot, but intact plantar flexion. Which division of the sciatic nerve is injured, and what is its anatomic relationship to the other division within the sciatic sheath?





Explanation

The common peroneal division of the sciatic nerve is most frequently injured during THA because it is located more laterally and superficially within the sciatic nerve bundle. Its fibers are also larger and have less supporting connective tissue, making them more susceptible to stretch injuries. The resultant deficit is a foot drop (loss of dorsiflexion/eversion) and dorsal foot numbness.

Question 37

A 55-year-old female with severe rheumatoid arthritis presents for total hip arthroplasty. Radiographs show profound protrusio acetabuli (medial wall defect) with the femoral head migrated medial to Kohler's line. What is the optimal surgical strategy for managing the acetabulum to ensure long-term survivorship?





Explanation

In protrusio acetabuli, the center of rotation is displaced medially and superiorly. The goal of reconstruction is to restore the anatomical center of rotation (lateralizing and inferiorizing the cup). This is best achieved by placing morselized (particulate) bone graft in the medial wall defect and securing a cementless hemispherical cup at the anatomic margin with rim fit.

Question 38

Following a microfracture procedure for a full-thickness chondral defect of the medial femoral condyle, a marrow-stimulating healing response occurs. The resulting repair tissue that fills the defect is predominantly characterized by the presence of which of the following?





Explanation

Microfracture penetrates the subchondral bone plate, releasing marrow elements (MSCs) that form a super-clot. This repairs the defect with fibrocartilage, which is predominantly composed of Type I collagen, unlike native hyaline articular cartilage, which is rich in Type II collagen. Fibrocartilage has inferior biomechanical properties and wear resistance compared to hyaline cartilage.

Question 39

In the field of cartilage tissue engineering, which of the following growth factors is most recognized for its potent ability to induce the chondrogenic differentiation of mesenchymal stem cells (MSCs) into chondrocyte-like cells?





Explanation

Members of the Transforming Growth Factor-beta (TGF-β) superfamily, particularly TGF-β1, TGF-β3, and certain Bone Morphogenetic Proteins (BMPs), are the primary chondroinductive factors used in vitro and in tissue engineering to drive undifferentiated mesenchymal stem cells toward a chondrogenic lineage.

Question 40

A 68-year-old male requires a revision total hip arthroplasty for a loose femoral stem. Radiographs demonstrate a Paprosky Type IIIB femoral defect. Which of the following best defines a Type IIIB defect and indicates the most appropriate femoral implant choice?





Explanation

In the Paprosky femoral defect classification, a Type IIIA defect has >4 cm of intact diaphyseal bone at the isthmus, allowing for reliable fixation with a fully porous-coated cylindrical stem. A Type IIIB defect has <4 cm of intact diaphysis, which is insufficient for cylindrical scratch fit. The standard of care for IIIB defects is a modular fluted tapered stem, which achieves rotational and axial stability in a shorter segment of distal bone.

Question 41

Which zone of normal articular cartilage contains the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibrils oriented parallel to the joint surface?





Explanation

The superficial (tangential) zone of articular cartilage is characterized by the highest water content (up to 80%), the lowest concentration of proteoglycans, and densely packed type II collagen fibers oriented parallel to the articular surface to resist shear forces.

Question 42

A 74-year-old female presents for revision total hip arthroplasty due to aseptic loosening. Radiographs demonstrate severe femoral osteolysis. Intraoperatively, the diaphyseal isthmus is severely expanded, providing less than 3 cm of intact diaphyseal bone available for scratch fit. According to the Paprosky classification, what is the most appropriate femoral reconstructive option?





Explanation

This patient has a Paprosky Type IIIB femoral defect, defined by an unsupportive metaphysis and less than 4 cm of diaphyseal isthmus available for fixation. A modular fluted tapered stem is the workhorse for this defect as the flutes provide rotational stability and the taper achieves axial stability in the distal diaphyseal bone.

Question 43

In normal hyaline articular cartilage, which of the following collagen types is primarily responsible for covalently cross-linking the Type II collagen fibrils to the surrounding proteoglycan network?





Explanation

Type IX collagen is a Fibril Associated Collagen with Interrupted Triple helices (FACIT) that covalently binds to the surface of Type II collagen fibrils. It plays a critical role in mediating the intersection and cross-linking of the fibril network with the proteoglycan-rich extracellular matrix.

Question 44

A 65-year-old male with a metal-on-polyethylene total hip arthroplasty presents with worsening groin pain 7 years postoperatively. Aspiration is negative for infection. A MARS MRI reveals a large cystic pseudotumor. Laboratory analysis demonstrates elevated serum cobalt levels with normal chromium levels. Which of the following is the most likely etiology?





Explanation

In a metal-on-polyethylene THA, a pseudotumor (Adverse Local Tissue Reaction - ALTR) accompanied by an isolated elevation in cobalt relative to chromium strongly indicates mechanically assisted crevice corrosion (MACC), commonly known as trunnionosis, at the modular head-neck junction.

Question 45

A 30-year-old female presents with persistent groin pain exacerbated by hip flexion. An AP pelvis radiograph demonstrates that the center of the femoral head is located medial to the ilioischial line. Which of the following is the most accurate diagnosis?





Explanation

Acetabular protrusio is diagnosed when the center of the femoral head (or the medial wall of the acetabulum) crosses medial to the ilioischial line on an AP pelvis radiograph. In coxa profunda, the acetabular fossa touches or crosses the ilioischial line, but the center of the femoral head remains lateral to it.

Question 46

During a revision total hip arthroplasty, the surgeon encounters an acetabular defect with 4 cm of superior migration of the hip center. Kohler's line is intact, but there is greater than 40% loss of the superior rim. A jumbo cup lacks adequate superior coverage and stability. What is the most appropriate reconstructive strategy?





Explanation

This is a Paprosky Type IIIA acetabular defect ('up and out', intact Kohler's line, >30% superior rim loss). Because the supportive superior rim is deficient, a highly porous cup combined with a superior porous metal augment (or structural allograft) is indicated to restore the hip center, provide initial stability, and allow for biologic ingrowth.

Question 47

The compressive stiffness of articular cartilage is heavily dependent on the presence of aggrecan molecules. Which of the following glycosaminoglycans represents the most abundant side chain covalently attached to the core protein of aggrecan?





Explanation

Chondroitin sulfate is the most abundant glycosaminoglycan (GAG) in articular cartilage. It binds to the aggrecan core protein. These aggrecan monomers then non-covalently bind to a long hyaluronic acid backbone via link proteins to form massive proteoglycan aggregates, which confer compressive stiffness by creating a high osmotic swelling pressure.

Question 48

An 82-year-old female sustains a fall and presents with a periprosthetic femur fracture around a cemented polished taper-slip stem placed 15 years ago. Radiographs show the fracture centered around the tip of the stem. The stem is grossly loose, and there is severe proximal femoral osteolysis with medial and lateral cortices measuring less than 2 mm in thickness. What is the recommended surgical treatment?





Explanation

This is a Vancouver B3 fracture (fracture around the stem, loose stem, severe proximal bone loss). In elderly, low-demand patients with inadequate proximal bone stock to support or heal a new stem, a proximal femoral replacement (tumor prosthesis) is the treatment of choice, allowing for immediate stability and early weight-bearing.

Question 49

During single-leg stance, the hip joint reaction force is determined by the balance of moments around the center of rotation of the hip. Which of the following surgical modifications will most effectively DECREASE the hip joint reaction force?





Explanation

Medializing the acetabulum brings the center of rotation of the hip closer to the body's center of gravity. This decreases the moment arm of the body weight. Consequently, less abductor muscle force is required to maintain a level pelvis, leading to an overall decrease in the hip joint reaction force.

Question 50

At the onset of joint movement under high contact loads, which lubrication mechanism is primarily responsible for reducing friction between the opposing articular cartilage surfaces?





Explanation

Boundary lubrication is the primary mechanism reducing friction under high loads and low speeds, such as at the onset of motion. It is mediated by molecules like lubricin (PRG4) that bind directly to the articular surface. Fluid-film mechanisms (like elastohydrodynamic and squeeze-film) predominate during continuous, higher-speed motion.

Question 51

A 70-year-old male with a history of multiple revision total hip arthroplasties presents with recurrent posterior dislocations. Intraoperative evaluation reveals that both the acetabular and femoral components are well-fixed and optimally aligned. However, the patient has profound and irreparable abductor deficiency. Assuming component modularity permits, what is the most reliable reconstructive option?





Explanation

In the setting of recurrent instability due to severe, unrepairable abductor deficiency with well-positioned and well-fixed components, a constrained acetabular liner is the most appropriate option. While dual-mobility constructs are excellent for instability, they rely on a functional dynamic soft-tissue envelope (abductors) and may still dislocate in profound abductor deficiency.

Question 52

A 45-year-old active male who underwent a total hip arthroplasty with a ceramic-on-ceramic bearing 3 years ago complains of a loud 'squeaking' noise when bending or rising from a chair. He denies pain, and standard radiographs appear unremarkable. Which of the following factors is the most significant contributor to this phenomenon?





Explanation

Squeaking in ceramic-on-ceramic THA is most commonly associated with edge loading of the bearing surfaces. Edge loading typically results from component malposition (e.g., a steeply inclined or excessively anteverted/retroverted acetabular cup), which causes loss of fluid film lubrication and highly concentrated focal stress.

Question 53

A 62-year-old male is evaluated for a painful THA 2 years postoperatively. Synovial fluid aspiration reveals a WBC count of 2,800 cells/µL and 60% polymorphonuclear neutrophils. To aid in confirming a periprosthetic joint infection based on the 2018 ICM criteria, which of the following synovial fluid biomarkers provides the highest specificity?





Explanation

Alpha-defensin is an antimicrobial peptide released by neutrophils that has exceptionally high sensitivity and specificity (often >95%) for diagnosing periprosthetic joint infection (PJI). It is included in the 2018 International Consensus Meeting (ICM) criteria as a heavily weighted biomarker for diagnosing PJI.

Question 54

A 24-year-old professional athlete undergoes Matrix-induced Autologous Chondrocyte Implantation (MACI) for a symptomatic 4 cm² full-thickness chondral defect on the medial femoral condyle. What histological type of tissue is predominantly expected to form in the defect at 2 years postoperatively?





Explanation

Autologous chondrocyte implantation techniques, including MACI, are designed to generate a repair tissue that closely resembles native hyaline cartilage ('hyaline-like'), which is predominantly composed of Type II collagen. In contrast, bone marrow stimulation techniques like microfracture produce primarily Type I collagen-rich fibrocartilage.

Question 55

During a complex revision THA to remove a well-fixed cementless stem, the surgeon performs an Extended Trochanteric Osteotomy (ETO). To preserve the primary vascular supply to the osteotomized fragment and minimize the risk of necrosis or nonunion, which of the following muscle attachments must be preserved distally?





Explanation

The Extended Trochanteric Osteotomy (ETO) fragment depends on the maintenance of its soft-tissue pedicle for vascularity. Proximally, the gluteus medius and minimus attachments are maintained, while distally, the vastus lateralis attachment must be preserved to ensure blood supply and distal stability of the fragment.

Question 56

Following insertion of trial components during a primary THA, the hip is stable. However, intraoperative measurement shows the operated leg is 15 mm longer than the contralateral side, and the global offset is 5 mm less than desired. Which of the following component adjustments will most effectively restore equal leg length while simultaneously increasing global offset?





Explanation

To correct an overly long leg, the neck length must be decreased (e.g., using a shorter modular head). However, this alone would further decrease offset. Changing from a standard stem to a high-offset stem increases offset independently of leg length. Therefore, using a high-offset stem with a shorter modular neck/head corrects both problems: it reduces leg length while maintaining or increasing the offset.

Question 57

In the pathogenesis of early primary osteoarthritis, enzymatic degradation of the articular cartilage extracellular matrix is a hallmark feature. Which of the following enzymes is predominantly responsible for the primary cleavage and degradation of the type II collagen network?





Explanation

Matrix metalloproteinase-13 (MMP-13), also known as collagenase-3, is the principal enzyme responsible for the cleavage and destruction of type II collagen in osteoarthritis. ADAMTS-4 and ADAMTS-5 are aggrecanases that primarily degrade aggrecan (proteoglycans), which usually precedes collagen degradation.

Question 58

In evaluating a patient with severe acetabular bone loss for a suspected pelvic discontinuity, which of the following radiographic findings on a standard AP pelvis radiograph is most indicative of this condition?





Explanation

Pelvic discontinuity occurs when there is a complete separation of the superior hemipelvis (ilium) from the inferior hemipelvis (ischium and pubis). Radiographically, this is best identified on an AP pelvis by a visible fracture line or gap that disrupts both the anterior column (iliopectineal line) and the posterior column (ilioischial line), often with medial translation of the inferior hemipelvis.

Question 59

When utilizing a polished, collarless, taper-slip cemented femoral stem during a primary THA, which of the following biomechanical principles governs its fundamental design and function?





Explanation

Polished, collarless, taper-slip stems (e.g., Exeter) are designed to subside slightly ('slip') within the cement mantle under axial loading. Because they are tapered, this subsidence wedges the stem into the cement, converting axial loads into radial compressive forces (hoop stresses) that strengthen the construct. They do not bond to the cement, unlike composite-beam stems.

Question 60

A 35-year-old male with early hip dysplasia is evaluated for a periacetabular osteotomy (PAO). To non-invasively assess the biochemical integrity of the hip articular cartilage, delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) is ordered. What is the physiological basis of this specific imaging modality?





Explanation

The contrast agent used in dGEMRIC (Gd-DTPA2-) is negatively charged. Glycosaminoglycans (GAGs) in normal healthy cartilage are also highly negatively charged. Due to electrostatic repulsion, the contrast agent distributes inversely proportional to the GAG concentration. High contrast uptake indicates low GAG content, signaling early cartilage degeneration.

Question 61

A 68-year-old female presents with a loose total hip arthroplasty. Radiographs show superior migration of the hip center by 3.5 cm and medial migration past Kohler's line into the pelvis. There is massive osteolysis of the ischium and the teardrop is obliterated. According to the Paprosky acetabular defect classification, what is the most likely defect type and the recommended reconstruction strategy?





Explanation

This patient has a Paprosky Type IIIB acetabular defect. Type IIIB is characterized by severe superomedial migration of the hip center (>3 cm superiorly) and medial to Kohler's line, with destruction of the teardrop and severe ischial lysis. Because less than 40% of the host bone is available for contact, standard hemispherical cups (even jumbo) fail to achieve stability. Advanced reconstruction techniques such as custom triflange components, cup-cage constructs, or massive structural allografts are required to bridge the defect and achieve fixation.

Question 62

Which of the following biochemical profiles most accurately distinguishes articular cartilage undergoing early osteoarthritic (OA) degeneration from articular cartilage undergoing normal physiologic aging?





Explanation

A hallmark difference between osteoarthritis (OA) and normal aging in articular cartilage is the water content. In early OA, the collagen network is damaged, allowing proteoglycans to swell, resulting in increased water content, accompanied by a decrease in total proteoglycan concentration. In contrast, normal aging cartilage exhibits decreased water content, decreased total proteoglycans, and increased chondroitin-6-sulfate relative to chondroitin-4-sulfate.

Question 63

A 75-year-old male sustains a periprosthetic femur fracture around a cemented total hip arthroplasty following a low-energy fall. Radiographs show a fracture at the tip of the stem. The stem demonstrates gross subsidence, but the proximal and distal diaphyseal bone stock remains thick and structurally sound. According to the Vancouver classification, what is the appropriate treatment?





Explanation

This is a Vancouver B2 periprosthetic fracture. The fracture is around or just below the tip of the stem (Type B), the stem is loose (2), but the bone stock is of good quality. The standard of care for a B2 fracture is revision arthroplasty utilizing a long uncemented stem (often fluted/tapered or fully porous-coated) that bypasses the most distal fracture line by at least two cortical diameters to ensure adequate diaphyseal fixation, supplemented with cerclage wiring or plating of the fracture.

Question 64

What is the primary clinical and biological advantage of utilizing Matrix-induced Autologous Chondrocyte Implantation (MACI) compared to first-generation Autologous Chondrocyte Implantation (ACI) for focal full-thickness chondral defects?





Explanation

First-generation ACI utilized a harvested periosteal patch sutured over the defect to contain the injected cultured chondrocytes. This periosteal patch was highly associated with symptomatic graft hypertrophy, often requiring reoperation for debridement. MACI seeds the cultured chondrocytes onto a biodegradable porcine collagen membrane (Type I/III), which can be glued or sutured into the defect, eliminating the need for periosteal harvest and significantly reducing the risk of graft hypertrophy.

Question 65

A 55-year-old female with a metal-on-metal total hip arthroplasty presents with groin pain and a palpable anterior mass. MRI with metal artifact reduction sequence (MARS) reveals a large, cystic periarticular lesion. Histological analysis of the periprosthetic tissue is most likely to demonstrate which of the following primary immune responses?





Explanation

The patient has an adverse local tissue reaction (ALTR) / aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL), commonly referred to as a 'pseudotumor' in the setting of a metal-on-metal THA. The pathophysiology is primarily a Type IV (delayed) hypersensitivity reaction to metal ions (cobalt and chromium). Histologically, this is characterized by a dense, perivascular infiltration of T-lymphocytes and macrophages, distinct from the innate macrophage-driven particulate disease seen in classic osteolysis.

Question 66

During a primary total hip arthroplasty via a posterior approach, the surgeon inadvertently utilizes a femoral component with significantly less offset than the patient's native anatomy, while maintaining equal leg lengths. Which of the following biomechanical consequences is most likely to occur?





Explanation

Decreasing the femoral offset brings the femur closer to the pelvis. This shortens the abductor lever arm, decreasing the mechanical advantage of the abductor muscles. To maintain a level pelvis during single-leg stance, the abductors must fire with significantly greater force, which in turn increases the total joint reactive force across the hip. Additionally, the decreased clearance between the femur and pelvis increases the risk of bony or soft tissue impingement, which can precipitate dislocation.

Question 67

A 62-year-old male with a metal-on-polyethylene (MoP) total hip arthroplasty (large cobalt-chromium head on a titanium stem) presents with new-onset hip pain 5 years post-operatively. Workup reveals a cystic mass and normal inflammatory markers. If mechanically assisted crevice corrosion (trunnionosis) is the primary pathology, serum metal ion testing will most likely demonstrate:





Explanation

In metal-on-polyethylene (MoP) THA utilizing a cobalt-chromium (CoCr) head on a titanium (Ti) alloy stem, mechanically assisted crevice corrosion can occur at the head-neck taper (trunnionosis). This specific galvanic and mechanical corrosion process preferentially releases cobalt over chromium. Therefore, serum analysis typically shows significantly elevated cobalt levels with normal or only slightly elevated chromium levels. This contrasts with wear in metal-on-metal (MoM) articulations, where both Co and Cr are typically elevated.

Question 68

A 14-year-old male presents with knee pain. MRI reveals an osteochondritis dissecans (OCD) lesion on the lateral aspect of the medial femoral condyle. Which of the following MRI findings is the most specific indicator that the OCD lesion is unstable and requires surgical fixation rather than non-operative management?





Explanation

The most specific and reliable MRI sign of instability in an OCD lesion is a high T2-signal line that completely surrounds the fragment, indicating fluid interposition between the fragment and the native bone bed (a true non-union/separation). Subchondral cysts and edema can be present in stable lesions, but a complete rim of fluid beneath the fragment confirms mechanical instability requiring surgical intervention.

Question 69

Alpha-defensin is an increasingly utilized biomarker for the diagnosis of periprosthetic joint infection (PJI) from synovial fluid aspirates. What is the precise biological origin and function of this molecule?





Explanation

Alpha-defensins are small, cysteine-rich antimicrobial peptides that are primarily stored in the azurophilic granules of neutrophils. In response to infection, neutrophils degranulate and release alpha-defensins into the synovial fluid, where they insert into and disrupt bacterial cell membranes. Because its release is heavily tied to the massive neutrophil influx during a true bacterial infection, it is highly sensitive and specific for diagnosing PJI.

Question 70

In a patient presenting with isolated Pincer-type femoroacetabular impingement (FAI), characterized by focal acetabular overcoverage, what is the classic pattern of chondral damage encountered during hip arthroscopy?





Explanation

Pincer FAI occurs due to acetabular overcoverage (e.g., retroversion, coxa profunda). The femoral neck linearly impacts the acetabular rim, causing damage to the labrum and a narrow strip of adjacent peripheral cartilage. As the neck levers against the anterior rim, the femoral head is driven backwards, creating a 'contre-coup' chondral lesion on the posteroinferior aspect of the acetabulum or posterior femoral head. In contrast, Cam FAI (nonspherical femoral head) causes sheer stress leading to deep, broad delamination of the anterosuperior acetabular cartilage.

Question 71

A revision total hip arthroplasty is planned for a patient with a loose femoral stem. Preoperative templating and intraoperative findings demonstrate severe proximal bone loss with less than 3 cm of intact diaphyseal bone available for distal fixation. According to the Paprosky femoral defect classification, which of the following stem designs is most appropriate for reliable fixation?





Explanation

This is a Paprosky Type IIIB femoral defect. It is characterized by severe proximal bone loss and an unsupported diaphysis with less than 4 cm of scratch fit available for a cylindrical stem. A fully porous-coated cylindrical stem (which requires at least 4 cm of intact diaphysis, i.e., Type IIIA) has a high failure rate in this setting. The treatment of choice for a Type IIIB defect is a fluted, tapered uncemented stem (often modular), which relies on a 3-point bending fit and axial splining rather than pure cylindrical diaphyseal scratch fit.

Question 72

Articular cartilage is divided into distinct anatomical zones. Which of the following accurately describes the 'Deep Zone' of normal mature articular cartilage?





Explanation

The deep (basal) zone of articular cartilage contains the highest concentration of proteoglycans (and correspondingly the lowest water content). The collagen fibers (Type II) are oriented perpendicular to the articular surface, crossing the tidemark to anchor into the calcified cartilage. The chondrocytes in this zone are distinctly arranged in vertical columns parallel to the collagen fibers. The superficial zone has the highest water content and parallel collagen fibers.

Question 73

A 70-year-old female with a history of a long posterior spinal fusion from T10 to the pelvis for adult spinal deformity is scheduled for a primary total hip arthroplasty. Her spinopelvic parameters indicate a 'stiff' spine. How does this condition biomechanically alter her risk for dislocation during activities such as sitting?





Explanation

In a normal patient moving from standing to sitting, the lumbar spine flexes and the pelvis tilts posteriorly. This posterior pelvic tilt effectively increases acetabular anteversion, allowing the femoral neck to clear the anterior rim of the socket. In patients with a stiff spine (e.g., long spinal fusion to the pelvis), the pelvis fails to tilt posteriorly upon sitting. Consequently, the acetabulum remains relatively 'closed' anteriorly. When the hip is flexed during sitting, the femoral neck strikes the anterior rim of the cup, levering the femoral head out posteriorly. Thus, they are at significantly higher risk for posterior dislocation.

Question 74

Femoral impaction bone grafting is a technique utilized in revision total hip arthroplasty for patients with severe cavitary femoral bone loss. To ensure appropriate initial stability and long-term graft incorporation via auto-compression, which type of femoral stem design is strictly required for this technique?





Explanation

Femoral impaction bone grafting (e.g., the Exeter technique) involves tightly packing washed cancellous allograft chips into the femoral canal. A collarless, highly polished, double-tapered cemented stem must be used. The taper and lack of a collar allow the stem to act as a wedge, subsiding slightly within the cement mantle under physiological loading. This controlled subsidence converts axial loads into radial hoop stresses, auto-compressing the bone graft, which is essential for construct stability and long-term graft incorporation.

Question 75

A 24-year-old athlete undergoes a microfracture procedure for a 1.5 cm² full-thickness chondral defect on the medial femoral condyle. Six months later, a second-look arthroscopy with biopsy is performed. The repair tissue filling the defect is predominantly characterized by which of the following?





Explanation

Microfracture is a marrow-stimulating technique that relies on the influx of bone marrow-derived mesenchymal stem cells into the chondral defect. These cells differentiate and produce fibrocartilage, rather than native hyaline cartilage. Fibrocartilage is predominantly composed of Type I collagen (unlike the Type II collagen of hyaline cartilage). It is biomechanically inferior, possessing lower compressive stiffness and wear resistance, which can lead to deterioration of the repair over time.

Question 76

A 40-year-old female with bilateral Crowe IV developmental dysplasia of the hip (DDH) presents for primary total hip arthroplasty. To bring the acetabular component down to the true anatomical hip center and avoid permanent sciatic nerve injury from excessive lengthening, a femoral shortening osteotomy is planned. What is the primary anatomical advantage of performing this shortening osteotomy in the subtrochanteric region rather than the supracondylar region?





Explanation

In Crowe IV DDH, the native femur is typically characterized by a narrow intramedullary canal and excessive anteversion. Bringing the hip to the true center often requires >4 cm of lengthening, risking severe sciatic nerve palsy, necessitating a shortening osteotomy. A subtrochanteric shortening osteotomy is preferred because it allows the surgeon to derotate the distal fragment to correct the excessive femoral anteversion while preserving the proximal metaphysis for secure fixation of the femoral stem.

Question 77

During a complex revision THA requiring removal of a well-fixed porous-coated stem, the surgeon decides to perform an Extended Trochanteric Osteotomy (ETO). To optimize the probability of bony union of the osteotomized fragment, meticulous care is taken to preserve its vascular pedicle. The primary blood supply to the ETO fragment is maintained by the attachments of which of the following muscles?





Explanation

The Extended Trochanteric Osteotomy (ETO) is a highly reliable technique for extraction of fixed femoral components. The osteotomy involves the greater trochanter and a lateral strut of the femoral diaphysis. To ensure healing, the vascular supply to the lateral diaphyseal bone must be preserved. This is primarily provided by the vastus lateralis muscle (which receives its blood supply from the descending branch of the lateral femoral circumflex artery). The gluteus medius provides some supply to the proximal tip, but the extensive diaphyseal portion relies on the vastus lateralis.

Question 78

A 20-year-old male develops rapid and devastating glenohumeral chondrolysis within 6 months following an arthroscopic Bankart repair. A review of the intraoperative and postoperative records suggests a highly implicated iatrogenic cause. Which of the following factors has been most definitively linked to postoperative chondrolysis in this setting?





Explanation

Postarthroscopic glenohumeral chondrolysis (PAGH) is a devastating complication characterized by rapid destruction of articular cartilage. A vast body of literature has definitively linked this complication to the use of continuous intra-articular pain pumps infusing local anesthetics, particularly bupivacaine (often combined with epinephrine). Bupivacaine has been shown in vitro and in vivo to be directly cytotoxic to chondrocytes, leading to widespread cellular necrosis and subsequent cartilage loss.

Question 79

A 71-year-old male with highly active Paget's disease of the right hemipelvis and proximal femur requires a primary total hip arthroplasty due to severe secondary osteoarthritis. To minimize perioperative complications specific to the active phase of this disease, preoperative optimization with intravenous bisphosphonates is performed. This therapy is primarily intended to reduce the risk of which of the following intraoperative or early postoperative complications?





Explanation

Paget's disease has three phases: osteolytic, mixed, and osteosclerotic. In the active (osteolytic/mixed) phase, the bone is highly vascular due to massive increases in osteoclastic and osteoblastic activity. Surgery during this hypervascular phase can result in profound, sometimes life-threatening intraoperative hemorrhage. Preoperative administration of bisphosphonates (or calcitonin) decreases disease activity, significantly reducing bone vascularity and thereby mitigating the risk of massive intraoperative bleeding.

Question 80

A two-stage exchange arthroplasty is planned for a chronic periprosthetic hip infection. The surgeon debates between utilizing an articulating versus a static antibiotic-loaded polymethylmethacrylate (PMMA) spacer. Which of the following represents an absolute contraindication to the use of an articulating spacer in this scenario?





Explanation

Articulating spacers offer the advantages of maintained soft tissue tension, improved patient mobility, and easier reimplantation. However, they require sufficient bone stock to remain stable. Massive, uncontained acetabular bone loss (e.g., Paprosky 3B) or severe abductor mechanism deficiency are contraindications to an articulating spacer because the spacer will dislocate or migrate into the pelvis, causing severe pain and further bone/soft tissue destruction. In these scenarios, a static block spacer (or dowel) is mandatory.

Question 81

Which zone of articular cartilage has the highest concentration of water and the lowest concentration of proteoglycans?





Explanation

The superficial (tangential) zone of articular cartilage has the highest water content (approx. 80%), the lowest proteoglycan content, and densely packed collagen fibrils aligned parallel to the joint surface to resist shear stress.

Question 82

In revision total hip arthroplasty (THA), intentionally utilizing a "high hip center" (superiorly and medially displaced compared to the native anatomic center) achieves which of the following biomechanical changes compared to a high and lateralized center?





Explanation

A high, medialized hip center shortens the body weight moment arm, which decreases the total joint reaction force compared to a lateralized position. However, to maintain abductor tension and leg length, the surgeon must compensate on the femoral side (e.g., using a high-offset stem or increasing neck length).

Question 83

A 65-year-old male presents with new-onset groin pain 8 years after a primary THA utilizing a large-diameter metal head on a titanium stem with a highly cross-linked polyethylene liner. Serum inflammatory markers are normal. A MARS MRI demonstrates a thick-walled cystic mass communicating with the joint space. What is the most likely primary source of the wear debris causing this presentation?





Explanation

This clinical picture describes an adverse local tissue reaction (ALTR) or pseudotumor due to mechanically assisted crevice corrosion (MACC), commonly known as trunnionosis. This is highly associated with large-diameter metal heads on titanium stems, leading to metal ion release even in metal-on-polyethylene bearings.

Question 84

Boundary lubrication of articular cartilage is primarily mediated by which of the following molecules?





Explanation

Boundary lubrication is crucial for reducing friction between apposing cartilage surfaces under high loads and low velocities. It is primarily mediated by lubricin (proteoglycan 4 or PRG4), a glycoprotein synthesized by superficial zone chondrocytes and synoviocytes.

Question 85

A patient undergoing revision THA is found to have an acetabular defect with severe ischial osteolysis, superior migration of the acetabular component greater than 3 cm, and the radiographic "teardrop" is completely absent on the AP pelvis radiograph. The Kohler line remains intact. What is the Paprosky classification of this acetabular defect?





Explanation

Paprosky IIIA represents severe bone loss with >3 cm of superior migration (often measured from the obturator foramen), severe ischial lysis, and an absent teardrop, but the Kohler line is intact (meaning no medial migration). Paprosky IIIB defects involve medial migration past the Kohler line.

Question 86

A 72-year-old female sustains a fall 5 years after an uncemented THA. Radiographs show a periprosthetic fracture around the distal tip of the femoral stem. The stem is radiographically loose with subsidence, but there is adequate proximal diaphyseal bone stock remaining. According to the Vancouver classification, what is the most appropriate surgical treatment?





Explanation

This is a Vancouver B2 fracture (fracture around the stem, stem is loose, but with adequate bone stock). The gold standard of treatment is revision of the femoral component to a long stem that bypasses the fracture by at least two cortical diameters, typically utilizing a distally fixing cementless stem (e.g., modular fluted tapered stem).

Question 87

Which of the following components of the articular cartilage extracellular matrix is responsible for creating the Donnan osmotic swelling pressure that imparts compressive stiffness?





Explanation

The high density of fixed negative charges on the sulfated glycosaminoglycans (chondroitin and keratin sulfate) repels adjacent charges and attracts cations (like Na+) and water. This creates a strong osmotic gradient (the Donnan effect) that exerts a swelling pressure. The tension of the collagen network constrains this swelling, providing articular cartilage with its compressive stiffness.

Question 88

In the setting of recurrent instability after THA, a dual-mobility articulation is often utilized. Which of the following describes the primary tribological mechanism that increases stability in this design?





Explanation

Dual-mobility constructs feature two articulations: a smaller inner articulation (metal/ceramic head in polyethylene) for primary daily motion, and a larger outer articulation (polyethylene liner in a highly polished metal shell) that engages at extremes of motion. This larger outer diameter increases the "jump distance" required for the head to dislocate, significantly reducing the risk of instability.

Question 89

During a complex revision total hip arthroplasty, the surgeon performs an extended trochanteric osteotomy (ETO) to remove a well-fixed, extensively porous-coated stem. Which of the following is true regarding the typical ETO fragment?





Explanation

The standard extended trochanteric osteotomy (ETO) fragment includes the greater trochanter and the anterolateral portion of the proximal femoral diaphysis. Crucially, it retains the continuous soft tissue sleeve consisting of the gluteus medius/minimus insertions proximally and the vastus lateralis origin distally, preserving the blood supply and facilitating excellent healing when reattached with cables.

Question 90

Which transcription factor is considered the master regulator of chondrogenesis and is essential for the expression of Type II collagen and aggrecan during skeletal development?





Explanation

SOX9 is the master regulatory transcription factor for chondrogenesis. It directly binds to and activates enhancer elements of key cartilage matrix genes, including COL2A1 (Type II collagen) and ACAN (aggrecan). RUNX2 and Osterix are key regulators of osteogenesis. Scleraxis is associated with tenogenesis/ligamentogenesis.

Question 91

A 78-year-old female presents for revision THA. Radiographs demonstrate a complete transverse separation of the superior and inferior hemi-pelves through the acetabulum. Which of the following surgical constructs is currently considered the most reliable method for achieving initial mechanical stability and long-term biologic fixation in this setting (chronic pelvic discontinuity)?





Explanation

For chronic pelvic discontinuity, bridging the discontinuity with a construct that provides immediate rigid mechanical stability and allows for biologic ingrowth is the gold standard. Modern techniques heavily favor highly porous metal constructs, such as a cup-cage system, distraction techniques with jumbo tantalum cups, or custom triflange components.

Question 92

Which of the following extracellular matrix changes differentiates early osteoarthritic cartilage from normally aging articular cartilage?





Explanation

In normally aging cartilage, water content decreases. In early osteoarthritis, however, the collagen network is disrupted and degraded, allowing the constrained proteoglycans to expand and draw in more fluid, leading to an paradoxical increase in water content (cartilage swelling). Proteoglycan content generally decreases as OA progresses.

Question 93

You are evaluating a painful THA for possible periprosthetic joint infection (PJI). Joint aspiration yields synovial fluid with a white blood cell (WBC) count of 4,000 cells/µL with 85% polymorphonuclear neutrophils (PMNs). According to the 2018 International Consensus Meeting (ICM) criteria, how are these synovial fluid results categorized in the diagnostic scoring system?





Explanation

Under the 2018 ICM criteria, a synovial fluid WBC >3,000 cells/µL and PMN% >80% are both considered positive minor criteria that contribute points toward the diagnosis of PJI. They do not constitute major criteria (major criteria are a sinus tract communicating with the joint or two positive cultures of the same organism).

Question 94

When utilizing the impaction bone grafting (IBG) technique for femoral revision, which of the following mechanical conditions is an absolute biomechanical prerequisite for a successful outcome?





Explanation

Impaction bone grafting (IBG) on the femoral side relies on the radial expansion of the cement and graft mantle under compressive load to "lock" the construct. This biomechanical concept (slip-subsidence) absolutely requires a highly polished, collarless, double-tapered stem (such as the Exeter stem) that can predictably subside slightly into the cement/graft mantle and generate the necessary hoop stresses.

Question 95

A 24-year-old athlete undergoes marrow stimulation (microfracture) for a 2 cm² full-thickness chondral defect on the medial femoral condyle. The resultant repair tissue generated by this procedure is primarily characterized by the presence of which of the following?





Explanation

Microfracture allows marrow elements to fill the chondral defect, resulting in a fibrocartilage repair. Unlike native hyaline cartilage (which is primarily Type II collagen and rich in proteoglycans), fibrocartilage is predominantly composed of Type I collagen, has a lower proteoglycan content, and exhibits inferior mechanical properties and wear characteristics.

Question 96

During the stance phase of the normal human gait cycle, the joint reaction force across the hip joint typically peaks at approximately what multiple of body weight?





Explanation

During normal walking, the hip joint reaction force peaks at approximately 2.5 to 3 times body weight during the stance phase. This force is the vector sum of body weight acting on a longer lever arm and the substantial counterbalancing pull of the abductor musculature acting on a shorter lever arm.

Question 97

Wear particles generated from metal-on-metal hip implants or from trunnion corrosion predominantly stimulate an inflammatory response driven by which of the following cell types?





Explanation

Unlike polyethylene wear debris, which primarily elicits a macrophage-driven response leading to osteoclast activation and osteolysis, metal wear particles and ions (cobalt and chromium) characteristically elicit a lymphocyte-dominated, delayed-type hypersensitivity reaction (Type IV). This is termed ALVAL (aseptic lymphocyte-dominated vasculitis-associated lesion) and is a hallmark of adverse local tissue reactions (ALTR) or pseudotumors.

Question 98

In total hip arthroplasty, combined excessive anteversion of both the acetabular component and the femoral component primarily increases the risk of which sequence of impingement and subsequent dislocation?





Explanation

Combined excessive anteversion of the cup and the stem moves the femoral neck closer to the posterior rim of the acetabulum during external rotation and extension. This leads to early posterior impingement. The femoral head then levers out of the acetabulum in the opposite direction, causing an anterior dislocation.

Question 99

In the early pathogenesis of osteoarthritis, the initial degradation and depletion of the aggrecan molecule from the extracellular matrix is primarily mediated by which of the following enzyme families?





Explanation

The aggrecanases, specifically ADAMTS-4 and ADAMTS-5 (A Disintegrin And Metalloproteinase with Thrombospondin motifs), are the primary enzymes responsible for the early proteolytic cleavage and degradation of aggrecan in osteoarthritis. MMPs (like MMP-13) are more heavily involved in the subsequent degradation of the Type II collagen network.

Question 100

When considering the use of a "jumbo" hemispherical acetabular cup during revision THA to bridge cavitary defects and achieve rim fit, what is the traditionally accepted minimum diameter threshold that defines an uncemented cup as "jumbo" in a female patient?





Explanation

In revision total hip arthroplasty, a "jumbo" cup is traditionally defined in the literature as an uncemented hemispherical acetabular component with an outer diameter of ≥ 62 mm in men and ≥ 58 mm in women. These implants are utilized to achieve secure rim fixation when large segmental or cavitary defects are present.

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