Orthopedic Board Review MCQs: Fracture, Knee & Tumor

Question 1

A 35-year-old male presents with chronic knee pain. Radiographs demonstrate a lytic lesion in the proximal tibial epiphysis with intralesional calcifications. Biopsy reveals cells with abundant clear cytoplasm, distinct borders, and chondroid matrix, alongside areas of woven bone. Which of the following is the most appropriate management?

Explanation

The clinical and histological presentation is characteristic of clear cell chondrosarcoma. Unlike conventional chondrosarcoma, it typically presents in the epiphysis of long bones and often in young to middle-aged adults. It is a low-grade malignant bone tumor. Standard treatment is wide surgical resection, as curettage carries an unacceptably high local recurrence rate. It is not highly responsive to chemotherapy or radiation.

Question 2

A 25-year-old male sustains a high-velocity knee injury. Clinical examination demonstrates a deep transverse furrow ('dimple sign') over the medial joint line, and the knee is irreducible by closed means. Which structural interposition is most likely preventing reduction?

Explanation

The 'dimple sign' or transverse furrow across the medial joint line in a posterolateral knee dislocation is pathognomonic for an irreducible dislocation. It occurs when the medial femoral condyle buttonholes through the medial capsule and extensor retinaculum. Closed reduction is contraindicated as it can cause further soft tissue and skin necrosis; open reduction is strictly mandated.

Question 3

According to the 2013 revised American Society for Bone and Mineral Research (ASBMR) Task Force criteria, which of the following is considered a 'major' diagnostic criterion for an atypical femoral fracture (AFF)?

Explanation

The 2013 ASBMR revised major criteria for AFF require all of the following: location anywhere from just distal to the lesser trochanter to just proximal to the supracondylar flare; associated with minimal or no trauma; a transverse or short oblique line originating at the lateral cortex; noncomminuted or minimally comminuted; and localized periosteal or endosteal thickening of the lateral cortex (beaking). Bilateral fractures and delayed union are considered minor criteria.

Question 4

A 12-year-old boy is diagnosed with Ewing sarcoma of the femoral diaphysis. Following his initial regimen of neoadjuvant chemotherapy, what is the single most important prognostic factor for his long-term survival?

Explanation

While tumor size, volume, and the presence of metastasis at diagnosis are significant prognostic factors, the percentage of tumor necrosis following neoadjuvant chemotherapy (histologic response) is one of the most powerful and reliable predictors of overall and disease-free survival in patients with localized Ewing sarcoma. Greater than 90% necrosis is generally considered a favorable histological response.

Question 5

During deep flexion of the knee in a patient with a functioning cruciate-retaining (CR) total knee arthroplasty, paradoxical anterior sliding of the femur on the tibia may occur. Which of the following is the primary consequence of this kinematic alteration?

Explanation

In a normal knee, the femur rolls back posteriorly on the tibia during deep flexion, clearing the posterior structures and allowing full flexion. In CR TKAs with deficient PCL function or specific kinematic designs, paradoxical anterior translation of the femur on the tibia can occur. This prevents normal posterior rollback, resulting in premature posterior impingement and significantly decreased maximum knee flexion.

Question 6

A 45-year-old trauma patient sustains a highly comminuted extra-articular scapula neck fracture. Which of the following radiographic parameters is generally considered an absolute indication for operative fixation to prevent altered shoulder biomechanics?

Explanation

Operative indications for extra-articular scapular neck fractures include severe medialization (e.g., >20 mm), severe angulation (e.g., >45 degrees), and a significantly decreased glenopolar angle (GPA). A normal GPA is between 30 and 45 degrees. A GPA <22 degrees alters the relationship of the glenoid to the rotator cuff line of pull, leading to poor functional outcomes and rotator cuff dysfunction, making it a strong indication for surgery.

Question 7

A 28-year-old male presents with chronic anterior tibial pain. Radiographs demonstrate a multilocular, expansile, eccentric osteolytic lesion in the anterior cortex of the tibial diaphysis. Histological analysis reveals nests of epithelial cells in a fibrous stroma. What is the most appropriate definitive management?

Explanation

The clinical, radiographic, and histological presentation is characteristic of an adamantinoma. It is a low-grade, slow-growing malignant bone tumor most commonly found in the anterior cortex of the tibial diaphysis. Because it is highly resistant to both chemotherapy and radiation therapy, and has an unacceptably high local recurrence rate following intralesional procedures, the standard of care is wide en bloc resection.

Question 8

When harvesting the central third of the quadriceps tendon for an anterior cruciate ligament (ACL) reconstruction, violating the deepest layer of the extensor mechanism risks entry into the suprapatellar pouch. The quadriceps tendon is composed of multiple layers. Which muscle's aponeurosis contributes exclusively to the deepest layer of the quadriceps tendon?

Explanation

The quadriceps tendon has three distinct anatomical layers. The superficial layer is formed by the rectus femoris. The middle layer is formed by the conjoined aponeuroses of the vastus medialis and vastus lateralis. The deep layer is formed entirely by the vastus intermedius. During graft harvest, careful dissection avoids violating the vastus intermedius and the underlying synovial joint capsule (suprapatellar pouch).

Question 9

A 38-year-old male sustains a severe hyperflexion injury to the knee, resulting in a tibial plateau fracture. CT imaging demonstrates a coronal primary fracture line with a large, displaced posteromedial shear fragment. According to Luo's three-column concept, which surgical approach and fixation strategy is biomechanically optimal for this specific fragment?

Explanation

A posteromedial shear fragment of the tibial plateau is notoriously difficult to reduce and stabilize from an anterior approach. Luo's three-column concept emphasizes direct mechanical support for the involved posterior column. A posteromedial approach with a posteriorly applied buttress or anti-glide plate provides the optimal biomechanical stability to counteract the vertical shear forces during knee flexion.

Question 10

An oncologist consults you regarding prophylactic fixation of a metastatic bone lesion in a 60-year-old female with breast cancer. According to Mirels' criteria, which of the following clinical scenarios yields a strict score of 9, strongly indicating the need for prophylactic fixation?

Explanation

Mirels' scoring system evaluates 4 categories (Site, Pain, Lesion Nature, Size), assigning 1 to 3 points each. Option 3: Site (Upper extremity = 1) + Lesion Nature (Lytic = 3) + Size (1/3 to 2/3 = 2) + Pain (Severe = 3). Total = 1 + 3 + 2 + 3 = 9. A score of 9 or greater carries a high risk of impending fracture (>15%), making it a strong indication for prophylactic fixation.

Question 11

During reconstruction of the medial patellofemoral ligament (MPFL), identifying the anatomic femoral footprint is critical. According to Schöttle's radiographic criteria on a true lateral knee radiograph, where is the anatomic femoral origin of the MPFL located?

Explanation

Schöttle's point for the femoral attachment of the MPFL is defined radiographically on a strict lateral view. It is precisely located approximately 1 mm anterior to a line extending the posterior femoral cortex, 2.5 mm distal to the posterior articular origin of the medial femoral condyle, and just proximal to the posterior projection of Blumensaat's line. Non-anatomic placement alters graft tension across the flexion arc.

Question 12

During an ilioinguinal or Stoppa approach for open reduction and internal fixation of an acetabular fracture, the surgeon must identify the 'corona mortis' to prevent catastrophic hemorrhage. This structure is classically defined as a vascular anastomosis between which two systems?

Explanation

The corona mortis (crown of death) is a highly variable but frequent vascular anastomosis between the external iliac system (or its branch, the inferior epigastric artery/vein) and the obturator system. It typically crosses over the superior pubic ramus at an average distance of 5-6 cm from the pubic symphysis and is at significant risk of iatrogenic injury during anterior pelvic approaches.

Question 13

A 25-year-old female presents with a slow-growing, painful mass near her knee joint. MRI shows a soft tissue mass abutting the joint capsule, and plain films demonstrate punctate calcifications. Biopsy confirms a biphasic tumor with both epithelial and spindle cell components. Which chromosomal translocation is the hallmark of this malignancy?

Explanation

The clinical and histologic description is classic for synovial sarcoma. The hallmark cytogenetic abnormality is the t(X;18)(p11;q11) translocation, which results in the SYT-SSX fusion gene. It often presents in young adults as a slow-growing juxta-articular mass with calcifications seen on radiographs in ~30% of cases. Despite the name, it rarely involves the synovial tissue directly but rather arises in adjacent soft tissues.

Question 14

In revision total knee arthroplasty, the Anderson Orthopaedic Research Institute (AORI) classification is used to grade bone defects. A patient presents with a deficient medial tibial metaphysis requiring a structural augment, but has intact metaphyseal bone laterally and fully competent collateral ligaments. How is this specific tibial defect classified?

Explanation

The AORI classification evaluates bone loss. Type I indicates intact metaphyseal bone with minor joint line defects. Type II involves damaged metaphyseal bone requiring structural bone grafts or metal augments; Type IIA is isolated to one condyle or plateau (as in this case with medial deficiency only), whereas Type IIB involves both condyles/plateaus. Type III involves severe metaphyseal bone loss compromising the collateral ligaments or patellar tendon.

Question 15

Six weeks following open reduction and internal fixation of a Hawkins Type III talar neck fracture, a follow-up anteroposterior radiograph of the ankle demonstrates a subchondral radiolucent band in the talar dome. What does this specific radiographic finding indicate?

Explanation

The Hawkins sign is a subchondral radiolucent band that appears typically 6 to 8 weeks post-injury in the talar dome. It represents subchondral osteopenia secondary to disuse atrophy and active bone resorption. Because bone resorption requires an intact, active blood supply, the presence of the Hawkins sign is a highly reliable indicator that the talar body remains vascularized and avascular necrosis (AVN) is unlikely.

Question 16

A 15-year-old boy presents with right knee pain. Radiographs reveal an eccentric, lytic lesion strictly confined to the distal femoral epiphysis with a thin sclerotic rim. Histological examination reveals mononuclear cells with grooved nuclei and areas of fine, pericellular calcifications. What is the most likely diagnosis?

Explanation

Chondroblastoma is a rare, benign bone tumor that characteristically arises in the epiphysis or apophysis of skeletally immature patients. Histologically, it is uniquely defined by chondroblasts with grooved or indented nuclei (often described as 'coffee bean' nuclei), intermixed multinucleated giant cells, and distinctive pericellular calcifications known as 'chicken-wire' calcifications.

Question 17

During the physical examination of a patient with a multiple-ligament knee injury, the 'Dial test' is performed. The patient exhibits 15 degrees of increased external rotation of the tibia compared to the contralateral side at 30 degrees of knee flexion, and 15 degrees of increased external rotation at 90 degrees of flexion. Which structural injury pattern does this indicate?

Explanation

The Dial test evaluates external rotation asymmetry of the tibia. An increase of >10 degrees compared to the uninjured side is considered clinically significant. Increased external rotation at 30 degrees of flexion only indicates an isolated posterolateral corner (PLC) injury. Increased external rotation at both 30 degrees and 90 degrees of flexion strongly indicates a combined injury to both the PLC and the posterior cruciate ligament (PCL).

Question 18

During the surgical fixation of an intra-articular calcaneus fracture via an extensile lateral approach, the surgeon's goal is to reduce the lateral tuberosity and posterior facet fragments to the 'constant' medial (sustentacular) fragment. Which of the following best describes the anatomical structures that typically prevent displacement of this constant fragment?

Explanation

In calcaneus fractures, the sustentacular (anteromedial) fragment is considered the 'constant fragment' because it remains tightly bound in its anatomical position relative to the talus. This stability is maintained by the strong medial talocalcaneal ligaments, deep fibers of the deltoid ligament medially, and the robust talocalcaneal interosseous ligament located laterally within the tarsal canal.

Question 19

A 40-year-old female presents with recurrent, painful swelling of her knee. MRI demonstrates extensive synovial hypertrophy with nodular masses displaying low signal intensity on T1 and T2 sequences, and prominent 'blooming' artifact on gradient-echo sequences. Genetic testing reveals a translocation involving the colony-stimulating factor 1 (CSF1) gene. For severe, refractory cases, which targeted systemic therapy is FDA-approved?

Explanation

The clinical and MRI findings (hemosiderin blooming artifact) are diagnostic for diffuse tenosynovial giant cell tumor (TGCT), historically known as pigmented villonodular synovitis (PVNS). The pathogenesis relies on a t(1;2) translocation causing overexpression of CSF1. Pexidartinib is an orally administered tyrosine kinase inhibitor targeting the CSF1 receptor. It is the first FDA-approved systemic therapy for symptomatic, severe TGCT not amenable to surgical improvement.

Question 20

After intramedullary nailing of a femoral shaft fracture, a patient reports anterior knee pain. Lateral knee radiographs are obtained to assess for patellar height changes (patella baja/alta). Which of the following radiographic indices is most independent of the degree of knee flexion at the time the radiograph was taken?

Explanation

The Insall-Salvati ratio measures the length of the patellar tendon (from the lower pole of the patella to the tibial tubercle) divided by the longest diagonal length of the patella. Because both measurements are based solely on fixed anatomical landmarks of the extensor mechanism and do not rely on the articulation with the femur or the joint line, the ratio is relatively independent of the knee flexion angle compared to the Blackburne-Peel or Caton-Deschamps indices.

Question 21

A 22-year-old female undergoes medial patellofemoral ligament (MPFL) reconstruction for recurrent patellar instability. Postoperatively, she demonstrates severely restricted knee flexion but normal full extension. Patellofemoral contact pressures are noted to be abnormally high in deep flexion. What is the most likely error regarding the placement of the femoral tunnel?

Explanation

Correct placement of the MPFL femoral tunnel is critical for graft isometry. If the femoral tunnel is placed too proximal and anterior to the anatomic footprint (Schöttle point), the graft will be loose in extension but become excessively tight in flexion, leading to restricted knee flexion and increased patellofemoral contact pressures.

Question 22

A 35-year-old male presents with chronic knee pain. Radiographs reveal a secondary, eccentrically located, lytic lesion in the proximal tibial epiphysis. Biopsy reveals cells with distinct borders, abundant clear cytoplasm, and central nuclei, interspersed with areas of bland chondroid matrix. The lesion is graded as a low-grade malignancy. What is the most likely diagnosis?

Explanation

Clear cell chondrosarcoma is a rare, low-grade malignant cartilage tumor that classically occurs in the epiphysis of long bones in adults (3rd-4th decades). While chondroblastoma also occurs in the epiphysis, it typically affects younger patients (open physes) and features 'coffee bean' nuclei with 'chicken-wire' calcifications, lacking the distinctive clear cytoplasm seen in clear cell chondrosarcoma.

Question 23

During open reduction and internal fixation of a severe proximal humerus fracture using an extended deltopectoral approach, the surgeon decides to split the deltoid muscle longitudinally to improve distal exposure. Which of the following structures is at greatest risk, and what is its approximate distance from the lateral tip of the acromion?

Explanation

The axillary nerve runs transversely across the deep surface of the deltoid muscle, typically 5 to 7 cm distal to the lateral tip of the acromion. A longitudinal deltoid split should not extend more distal than this threshold to avoid denervating the anterior portion of the deltoid.

Question 24

A 28-year-old football player sustains a twisting injury to his knee. On physical examination, the dial test reveals +10 degrees of increased external rotation at 30 degrees of knee flexion compared to the contralateral side. At 90 degrees of knee flexion, the external rotation is symmetric bilaterally. What is the most likely injury pattern?

Explanation

The dial test assesses external rotation of the tibia. Increased external rotation (>10 degrees compared to the normal side) at 30 degrees of flexion, but symmetric at 90 degrees, indicates an isolated posterolateral corner (PLC) injury. If the asymmetry persists or increases at 90 degrees of flexion, it indicates a combined PLC and PCL injury.

Question 25

A 14-year-old boy presents with a painful, swollen thigh. Imaging demonstrates a permeative diaphyseal lesion of the femur with a prominent 'onion-skin' periosteal reaction. Biopsy reveals sheets of uniform small round blue cells that are strongly CD99 positive. Which specific chromosomal translocation is the diagnostic hallmark of this condition?

Explanation

The patient has Ewing sarcoma, characterized by CD99 (MIC2) positivity and a classic t(11;22) (q24;q12) translocation. This translocation fuses the EWSR1 gene on chromosome 22 with the FLI1 gene on chromosome 11. t(X;18) is seen in synovial sarcoma, t(12;16) in myxoid liposarcoma, and t(2;13) in alveolar rhabdomyosarcoma.

Question 26

During a modified Stoppa approach for the treatment of an anterior column acetabular fracture, the surgeon must carefully identify and potentially ligate the 'corona mortis' to prevent catastrophic hemorrhage. This structure represents a vascular anastomosis between which two systems?

Explanation

The corona mortis ('crown of death') is a critical vascular anastomosis connecting the external iliac or inferior epigastric system to the obturator system. It traverses the superior pubic ramus and is highly vulnerable to iatrogenic injury during the intrapelvic (modified Stoppa or ilioinguinal) approach to the acetabulum.

Question 27

An 18-year-old male with closed physes presents with knee pain. MRI reveals a 2 x 2 cm osteochondritis dissecans (OCD) lesion on the lateral aspect of the medial femoral condyle. A distinct high-signal T2 line is present behind the osteochondral fragment. Diagnostic arthroscopy shows the overlying cartilage is completely intact and ballotable, but without breach. What is the most appropriate surgical treatment?

Explanation

A high-signal T2 line behind an OCD fragment in an adult (closed physis) indicates an unstable lesion (fluid interposed between fragment and bed). Because it is unstable but the articular cartilage remains intact, the standard of care is internal fixation (with or without drilling) to compress the fragment and allow bony union. Retrograde drilling alone is reserved for stable lesions, while OATS/MACI are for unsalvageable fragments with significant cartilage loss.

Question 28

A 25-year-old male presents with anterior bowing of his tibia and insidious onset of pain. Radiographs demonstrate an eccentric, multilobulated osteolytic lesion in the anterior diaphyseal cortex of the tibia. Histologic analysis reveals epithelial-like cells arranged in nests surrounded by a bland spindle-cell osteofibrous stroma. Immunohistochemistry is strongly positive for cytokeratin. Which of the following is the standard of care?

Explanation

The diagnosis is Adamantinoma, a rare, low-grade malignant bone tumor that almost exclusively occurs in the anterior tibial diaphysis. It is characterized pathologically by biphasic histology (epithelial nests positive for cytokeratin in a fibrous stroma). Adamantinoma is largely chemo- and radioresistant and has a high local recurrence rate if treated with curettage; thus, wide en bloc resection is the definitive treatment.

Question 29

A 65-year-old female sustains a nondisplaced distal radius fracture and is treated non-operatively in a cast. Six weeks post-injury, she experiences a sudden, painless inability to actively extend her thumb at the interphalangeal joint. What is the primary pathophysiological mechanism of this specific complication?

Explanation

Rupture of the Extensor Pollicis Longus (EPL) tendon is a known complication of nondisplaced distal radius fractures. Because the fracture is nondisplaced, the third dorsal compartment sheath remains intact. Fracture hematoma and swelling increase pressure within the intact compartment, compromising the delicate vascular supply to the EPL tendon in its watershed zone around Lister's tubercle, leading to ischemic rupture.

Question 30

A surgeon performs a medial opening-wedge high tibial osteotomy (HTO) to correct varus deformity in a patient with medial compartment osteoarthritis. The surgeon fails to release the distal superficial medial collateral ligament (sMCL) and inadvertently opens the osteotomy gap predominantly at the anterior cortex. What unintended sagittal plane deformity is most likely to result?

Explanation

In a medial opening-wedge HTO, the tight posteromedial structures (specifically the sMCL) can act as a hinge. If the sMCL is not released, the osteotomy gap will preferentially open anteriorly. This anterior opening elevates the anterior tibial plateau relative to the posterior plateau, leading to an unintended increase in the posterior tibial slope. Releasing the sMCL and ensuring the gap is opened evenly (or slightly more posteromedially) prevents this.

Question 31

Which of the following bone tumors typically presents as a densely ossified mass on the posterior surface of the distal femur in young adults, is histologically characterized by low-grade spindle cells interspersed with well-formed woven bone trabeculae, and frequently demonstrates MDM2 and CDK4 gene amplification?

Explanation

Parosteal osteosarcoma is a low-grade surface osteosarcoma that classically arises on the posterior aspect of the distal femur. It is characterized pathologically by low-grade spindle cells and heavily ossified woven bone. Molecularly, it is distinguished by the amplification of MDM2 and CDK4 on chromosome 12q13-15.

Question 32

A 32-year-old male sustains a Hawkins Type III talar neck fracture and undergoes open reduction and internal fixation. At the 6-week postoperative visit, a well-defined subchondral radiolucent band is visible across the talar dome on the AP mortise radiograph. What is the clinical significance of this finding?

Explanation

This finding is the 'Hawkins sign'. The radiolucent band represents subchondral osteopenia, which occurs as a result of active hyperemia following the fracture. The presence of hyperemia definitively proves that the vascular supply to the talar body is intact, thereby serving as an excellent prognostic indicator that avascular necrosis (AVN) will not occur.

Question 33

During posterior cruciate ligament (PCL) reconstruction, graft attenuation and ultimate failure can occur due to the sharp angle the graft must navigate as it exits the proximal posterior tibia and heads toward the medial femoral condyle. This phenomenon is termed the 'killer turn'. Which surgical technique is most strongly associated with this biomechanical disadvantage?

Explanation

The 'killer turn' refers to the acute angle (approximately 90 degrees) the PCL graft makes as it exits the posterior aperture of a standard transtibial tunnel and courses anteriorly to the femur. This sharp turn creates high friction and stress on the graft, leading to attenuation. The tibial inlay technique was developed specifically to avoid this 'killer turn' by securing a bone block directly to the posterior tibial plateau.

Question 34

Denosumab is increasingly utilized to downstage unresectable or metastatic giant cell tumors of bone (GCT). Which of the following accurately describes the primary cellular mechanism by which Denosumab exerts its therapeutic effect in this specific tumor?

Explanation

In Giant Cell Tumor of bone (GCT), the true neoplastic cells are the spindle-shaped mononuclear cells, which express high levels of RANKL. This RANKL recruits and activates reactive, normal osteoclast-like giant cells that cause bone destruction. Denosumab is a monoclonal antibody that binds to RANKL on the neoplastic mononuclear cells, preventing them from activating the giant cells.

Question 35

In the surgical management of a high-angle, vertical femoral neck fracture (Pauwels type III) in a 30-year-old patient, construct choice is critical due to distinct deforming forces. Biomechanical studies comparing the use of a dynamic hip screw (DHS) with an anti-rotation screw versus three parallel cancellous screws suggest which primary advantage for the DHS construct?

Explanation

Pauwels type III fractures are highly vertical and experience significant vertical shear forces rather than compressive forces. Biomechanical studies have demonstrated that a fixed-angle construct, such as a Dynamic Hip Screw (DHS), provides superior resistance to these vertical shear forces compared to three parallel cancellous lag screws, reducing the risk of varus collapse and nonunion.

Question 36

A 45-year-old female undergoes anatomic repair of a complete posterior medial meniscal root tear. By restoring the anatomical insertion of the root, which of the following biomechanical consequences of the tear is most directly mitigated?

Explanation

The meniscal roots anchor the meniscus to the tibial plateau, converting axial loads into circumferential hoop stresses. A complete root tear disrupts this mechanism, making the meniscus biomechanically behave as if a total meniscectomy was performed, leading to radial extrusion of the meniscus and rapid onset of osteoarthritis. Root repair restores these hoop stresses.

Question 37

A 28-year-old male presents with a slowly enlarging, deep soft tissue mass in the popliteal fossa, not directly involving the joint. Radiographs show stippled calcifications within the soft tissue shadow. Core needle biopsy demonstrates a biphasic pattern of spindle cells and epithelial cells. Cytogenetic testing confirms a t(X;18) translocation. Which of the following best describes this tumor's diagnostic identity and characteristic behavior?

Explanation

The diagnosis is Synovial Sarcoma, characterized by the t(X;18) (p11;q11) translocation which results in the SYT-SSX fusion gene. It often presents in young adults near joints (but rarely intra-articular), shows calcification in up to 30% of cases, and has biphasic histology. It is a high-grade sarcoma with a significant rate of metastasis to lungs and a higher propensity for lymph node metastasis (approx 10-20%) compared to most other soft tissue sarcomas.

Question 38

A 35-year-old male sustains a high-energy trauma resulting in an isolated coronal plane fracture of the posterior aspect of the lateral femoral condyle (Hoffa fracture). Which of the following muscle combinations represents the primary deforming forces that pull the fracture fragment posteriorly and distally?

Explanation

A Hoffa fracture of the lateral femoral condyle creates a free posterior osteochondral fragment. The lateral head of the gastrocnemius originates from the posterior surface of the lateral condyle, and the popliteus originates from the lateral epicondyle. These muscles act as the primary deforming forces, displacing the free coronal fragment posteriorly and distally.

Question 39

A 25-year-old male is brought to the emergency department after a motorcycle collision. He sustained a complete multiligamentous knee dislocation (Schenck KD-IV), which was immediately reduced upon arrival. Post-reduction, he has no active bleeding or expanding hematoma, and distal pulses are palpable but slightly diminished. His ankle-brachial index (ABI) is measured at 0.85. What is the most appropriate next step in management?

Explanation

An ABI less than 0.90 after a knee dislocation is a 'soft sign' of vascular injury and mandates further advanced imaging, most commonly a CT angiogram (CTA). Immediate surgical exploration is reserved for 'hard signs' of vascular injury, such as an expanding or pulsatile hematoma, absent distal pulses, or active pulsatile bleeding.

Question 40

A 16-year-old male presents with chronic knee pain. Radiographs reveal a 2 cm eccentric, purely lytic lesion with a sclerotic rim located entirely within the proximal tibial epiphysis. The proximal tibial physis remains open. Histologic examination demonstrates mononuclear cells with longitudinal nuclear grooves ('coffee bean' nuclei) and a 'chicken-wire' pattern of pericellular calcification. What is the most appropriate surgical treatment?

Explanation

The clinical and histological presentation is classic for Chondroblastoma, a benign but locally aggressive bone tumor found in the epiphyses of skeletally immature patients. The standard treatment is intralesional extended curettage and filling the defect with bone graft or bone cement. Wide resection or amputation is overly aggressive, while observation is inappropriate due to the risk of joint destruction.

Question 41

A 60-year-old male presents with chronic, progressively worsening shoulder pain. Radiographs demonstrate a large lytic lesion with 'ring and arc' calcifications in the proximal humerus and endosteal scalloping involving greater than 2/3 of the cortical thickness. Biopsy confirms grade II conventional chondrosarcoma. Which of the following is the most appropriate management?

Explanation

Conventional chondrosarcoma (Grade II and III) is notoriously resistant to both chemotherapy and radiation therapy. The standard of care for intermediate and high-grade conventional chondrosarcoma is wide surgical resection. Endosteal scalloping >2/3 of the cortex is a strong radiographic indicator of chondrosarcoma rather than benign enchondroma.

Question 42

A 28-year-old male suffers a high-energy knee dislocation. Vascular examination is normal with an Ankle-Brachial Index (ABI) of 1.1. Post-reduction MRI reveals complete rupture of the ACL, PCL, and posterolateral corner (PLC) structures. Which nerve is most commonly injured in this specific injury pattern, and what is its primary motor deficit?

Explanation

This injury pattern is a KD-IIIL (dislocation with ACL, PCL, and lateral-sided/PLC disruption). Due to the traction force on the lateral aspect of the knee, the common peroneal nerve is highly susceptible to stretch injury, resulting in a foot drop (loss of ankle dorsiflexion and eversion).

Question 43

A 35-year-old male involved in a motorcycle collision sustains a coronal plane fracture of the lateral femoral condyle (Hoffa fracture). Which surgical approach and fixation strategy is historically and biomechanically most appropriate for rigid fixation of this fracture?

Explanation

A Hoffa fracture (OTA 33-B3) of the lateral condyle is best addressed via a lateral approach (such as lateral parapatellar). Biomechanical studies show that anterior-to-posterior placed lag screws (often countersunk to avoid articular damage) are significantly stronger than posterior-to-anterior screws in resisting the shear forces at this fracture site.

Question 44

Which of the following MRI findings is the most reliable distinguishing feature to differentiate a low-grade chondrosarcoma of the proximal femur from a benign enchondroma?

Explanation

Differentiating enchondroma from low-grade chondrosarcoma is challenging. However, aggressive features such as peri-tumoral bone marrow edema, soft tissue mass, and deep endosteal scalloping (>2/3 of cortical thickness) strongly favor chondrosarcoma. Lobular growth, T2 high signal, and popcorn calcifications are seen in both.

Question 45

A 65-year-old female presents with a painful 'clunking' sensation in her knee 9 months after a posterior-stabilized total knee arthroplasty (TKA). The clunk occurs as the knee transitions from flexion into extension around 30 to 45 degrees. What is the most common anatomic etiology of this phenomenon?

Explanation

Patellar clunk syndrome occurs primarily in posterior-stabilized TKA. It is caused by the formation of a fibrous nodule at the superior pole of the patella. As the knee extends from flexion, the nodule catches in the femoral intercondylar box and then abruptly dislodges with a 'clunk' around 30-45 degrees of flexion.

Question 46

A 40-year-old skier sustains a Schatzker II tibial plateau fracture. Which specific soft tissue injury is most frequently associated with this fracture pattern?

Explanation

A Schatzker II fracture is a split-depression of the lateral tibial plateau. It is highly associated with lateral meniscus tears, particularly peripheral or meniscocapsular separations, occurring in up to 50% of these injuries as the meniscus is trapped or damaged by the depressed articular fragment.

Question 47

A 16-year-old male is diagnosed with non-metastatic conventional osteosarcoma of the distal femur. He undergoes standard neoadjuvant chemotherapy followed by wide surgical resection. Which of the following is the most important prognostic factor for his overall survival?

Explanation

The degree of tumor necrosis following neoadjuvant chemotherapy is the single most significant prognostic factor for overall and disease-free survival in conventional osteosarcoma. A 'good responder' is typically defined as having greater than 90% tumor necrosis in the resected specimen.

Question 48

During a single-bundle anterior cruciate ligament (ACL) reconstruction, if the surgeon inadvertently places the femoral tunnel too anteriorly (high in the notch at the 12 o'clock position) rather than in the anatomic footprint, what biomechanical consequence will the graft exhibit?

Explanation

A non-anatomic femoral tunnel placed too anteriorly (high in the intercondylar notch) results in an ACL graft that becomes excessively tight in flexion, significantly limiting knee flexion, and becomes excessively loose in extension, failing to control anterior translation near extension.

Question 49

A 29-year-old female sustains a Hawkins III talar neck fracture following a fall from height. What is the approximate rate of avascular necrosis (AVN) of the talar body associated with this injury, and which major vascular supply is primarily disrupted?

Explanation

A Hawkins III fracture involves a talar neck fracture with dislocation of both the subtalar and tibiotalar joints. This severe displacement disrupts all three major blood supplies to the talus, particularly the artery of the tarsal canal (branch of the posterior tibial artery), leading to an AVN rate approaching 80-100%.

Question 50

A 25-year-old male presents with a slowly enlarging, painful mass near his knee. MRI demonstrates a well-circumscribed soft tissue mass adjacent to the joint capsule. Biopsy confirms a biphasic tumor containing both epithelial and spindle cell components. Which chromosomal translocation is characteristically associated with this diagnosis?

Explanation

The clinical and histologic findings (biphasic epithelial and spindle cells) are classic for synovial sarcoma. Synovial sarcoma is characterized by the t(X;18)(p11;q11) chromosomal translocation, which results in the SYT-SSX fusion gene.

Question 51

A 6-year-old child is evaluated for a painless 'snapping' and 'popping' of the lateral knee during flexion and extension. MRI reveals a complete Wrisberg variant of a discoid lateral meniscus. What is the primary anatomical deficiency in this specific variant?

Explanation

The Wrisberg variant of the discoid lateral meniscus lacks the normal posterior coronary ligament (meniscotibial) attachments to the tibial plateau. The posterior horn is only stabilized by the meniscofemoral ligament of Wrisberg, allowing hypermobility and resulting in the classic 'snapping knee' syndrome.

Question 52

When assessing a displaced 4-part proximal humerus fracture, which of the following specific radiographic criteria (Hertel's criteria) is the most reliable predictor of subsequent humeral head ischemia?

Explanation

Hertel described predictors of ischemia for proximal humerus fractures. The most significant predictors include a metaphyseal head extension (calcar length attached to the articular segment) of < 8 mm, disruption of the medial hinge (> 2 mm displacement), and an anatomic neck fracture pattern.

Question 53

A 32-year-old female is diagnosed with a giant cell tumor of the distal femur. The lesion is eccentric, expansile, and lytic. Histology reveals multinucleated giant cells in a background of mononuclear stromal cells. If neoadjuvant targeted pharmacotherapy is utilized, what is its primary mechanism of action?

Explanation

Giant cell tumor of bone (GCT) consists of neoplastic mononuclear stromal cells that express RANKL. RANKL recruits and activates normal multinucleated osteoclast-like giant cells, causing extensive bone resorption. Denosumab, a monoclonal antibody against RANKL, inhibits this process and is an effective targeted therapy for GCT.

Question 54

A 45-year-old male with isolated medial compartment knee osteoarthritis and genu varum is undergoing a medial opening-wedge high tibial osteotomy (HTO). To maintain the patient's native posterior tibial slope during correction, how should the osteotomy gap be dynamically managed?

Explanation

The proximal tibia has a triangular cross-section, being narrower anteriorly than posteriorly. To maintain the native posterior tibial slope (~10 degrees) during a medial opening-wedge HTO, the gap must be opened in a roughly 2:1 ratio (posterior gap twice as wide as the anterior gap). Opening it equally will increase the posterior slope.

Question 55

A 38-year-old male sustains an anteroposterior compression type II (APC-II) pelvic ring injury. Based on the Young-Burgess classification, which of the following ligaments must be disrupted to define this specific injury pattern?

Explanation

An APC-II injury is characterized by symphyseal diastasis and widening of the anterior SI joint. This requires rupture of the anterior sacroiliac ligaments as well as the pelvic floor ligaments (sacrotuberous and sacrospinous). The posterior sacroiliac ligaments remain intact, conferring vertical stability but leaving the pelvis rotationally unstable.

Question 56

A 19-year-old male presents with dull, aching pain in his right tibia that is worse at night and dramatically relieved by NSAIDs. CT scan shows a 7 mm radiolucent nidus surrounded by dense reactive sclerosis in the anterior tibial cortex. What is the most appropriate definitive, minimally invasive treatment?

Explanation

The clinical presentation (night pain relieved by NSAIDs) and CT findings (radiolucent nidus < 1.5 cm with surrounding sclerosis) are classic for osteoid osteoma. CT-guided radiofrequency ablation (RFA) is the standard of care, offering definitive treatment with minimal morbidity compared to open surgery.

Question 57

During an isolated posterior cruciate ligament (PCL) reconstruction using an anterolateral (AL) bundle single-bundle technique, at what knee flexion angle should the graft classically be tensioned to optimally restore its primary biomechanical function?

Explanation

The native PCL consists of a larger anterolateral (AL) bundle and a smaller posteromedial (PM) bundle. The AL bundle is tightest in flexion and is the primary restraint to posterior tibial translation at 90 degrees. Therefore, single-bundle AL reconstructions are traditionally tensioned and fixed at 90 degrees of knee flexion.

Question 58

A 25-year-old male sustains a vertically oriented, displaced intracapsular femoral neck fracture (Pauwels Type III). If closed reduction and internal fixation is planned, which of the following constructs provides the greatest biomechanical stability against shear forces and varus collapse?

Explanation

Pauwels Type III femoral neck fractures have a vertical fracture line (>50 degrees), subjecting them to high shear forces and a high risk of varus collapse. Biomechanical studies have demonstrated that a fixed-angle device, such as a sliding hip screw (DHS), combined with a derotation screw, provides superior stability against shear compared to multiple parallel cancellous screws.

Question 59

A 55-year-old male presents with chronic sacral pain and mild bowel dysfunction. MRI demonstrates a destructive midline mass in the lower sacrum. Biopsy reveals lobules of vacuolated, bubbly cells in a myxoid stroma. Which specific immunohistochemical marker is characteristically positive and diagnostic for this tumor?

Explanation

The clinical scenario and histology (physaliferous cells) are pathognomonic for a chordoma, a rare primary bone tumor arising from notochordal remnants. Chordomas are uniquely characterized by the nuclear expression of Brachyury, a transcription factor critical for notochord development.

Question 60

In anatomic reconstruction of the posterolateral corner (PLC) of the knee, precisely understanding the attachments to the fibular head is critical. Which of the following accurately describes the insertions of the fibular collateral ligament (FCL) and the popliteofibular ligament (PFL)?

Explanation

For anatomic PLC reconstruction (e.g., the LaPrade technique), the exact footprint locations are essential. The FCL (LCL) attaches to a depression on the anterolateral aspect of the proximal fibular head. The popliteofibular ligament (PFL) attaches at the posteromedial aspect of the fibular styloid tip.

Question 61

A 35-year-old male presents with a slow-growing soft tissue mass in his popliteal fossa. Biopsy reveals a biphasic tumor with both epithelial and spindle cell components. Which of the following chromosomal translocations is most characteristic of this diagnosis?

Explanation

The clinical and histologic presentation (biphasic tumor with epithelial and spindle cells in a peri-articular location) is classic for synovial sarcoma. Synovial sarcoma is uniquely characterized by the t(X;18)(p11;q11) chromosomal translocation, which creates the SYT-SSX fusion gene.

Question 62

A 65-year-old female presents with knee pain 12 years after a primary posterior-stabilized total knee arthroplasty. Radiographs show a large osteolytic lesion in the medial tibial metaphysis. Fluoroscopy confirms well-fixed tibial and femoral components without radiolucent lines at the cement-bone interface. Aspiration is negative for infection. What is the most appropriate management?

Explanation

In the setting of isolated polyethylene wear and osteolysis with well-fixed, well-aligned components and no evidence of infection, an isolated polyethylene exchange combined with bone grafting (or curettage) of the osteolytic defect is an acceptable, less morbid procedure compared to a full component revision.

Question 63

In the surgical management of a coronal plane shear fracture of the lateral femoral condyle (Hoffa fracture), which of the following screw configurations is biomechanically most stable?

Explanation

Biomechanical studies have demonstrated that posterior-to-anterior (PA) directed lag screws provide significantly greater construct stiffness and load to failure compared to anterior-to-posterior (AP) directed screws for Hoffa fractures, as they engage the denser bone of the anterior metaphysis and sit perpendicular to the primary shear forces.

Question 64

A 25-year-old male presents with chronic anterior leg pain. Radiographs demonstrate a multi-loculated, eccentric, osteolytic lesion in the anterior cortex of the tibial diaphysis. Biopsy reveals islands of epithelial cells surrounded by a spindle cell stroma. What is the treatment of choice?

Explanation

The clinical, radiographic, and histologic presentation is classic for adamantinoma, a low-grade malignant bone tumor that predominantly affects the anterior cortex of the tibia. It does not respond well to chemotherapy or radiation. Wide surgical resection is the treatment of choice to minimize recurrence risk.

Question 65

During an anatomic reconstruction of the posterolateral corner (PLC) of the knee, the surgeon is preparing the femoral tunnels for the popliteus tendon and the fibular collateral ligament (FCL). What is the anatomic relationship of the popliteus insertion relative to the FCL insertion on the lateral femoral epicondyle?

Explanation

On the lateral femoral epicondyle, the popliteus tendon inserts in the anterior fifth of the popliteal sulcus, which is located 18.5 mm distal and anterior to the insertion of the fibular collateral ligament (FCL).

Question 66

A 28-year-old male sustains a high-energy Pauwels type III (vertical) femoral neck fracture. To maximize biomechanical stability and reduce the risk of varus collapse, which of the following internal fixation constructs is considered superior?

Explanation

Pauwels type III fractures are highly vertically oriented and experience significant shear forces. Biomechanical studies consistently show that a fixed-angle device, such as a Sliding Hip Screw (DHS), provides superior resistance to varus collapse and a higher load to failure compared to multiple parallel cancellous screws for vertically oriented femoral neck fractures in young adults. A derotational screw is often added to control rotational instability.

Question 67

A 42-year-old male is diagnosed with a large, deep intramuscular myxoid liposarcoma of the thigh. Molecular analysis of the tumor is most likely to reveal which of the following genetic alterations?

Explanation

Myxoid liposarcoma is characterized by the t(12;16)(q13;p11) translocation, which creates the FUS-DDIT3 fusion protein. It is uniquely highly sensitive to radiation therapy. MDM2 amplification is characteristic of well-differentiated and dedifferentiated liposarcomas.

Question 68

A 62-year-old female presents with a painful catching sensation in her knee 9 months after a posterior-stabilized total knee arthroplasty. The catching occurs reliably at 30-45 degrees of flexion as she extends the knee. What is the most likely etiology of her symptoms?

Explanation

This is the classic presentation of 'patellar clunk syndrome,' which occurs after posterior-stabilized TKA when a fibrosynovial nodule forms at the junction of the quadriceps tendon and the superior pole of the patella. As the knee extends, the nodule gets caught in the intercondylar box of the femoral component and then 'clunks' out.

Question 69

A 45-year-old male sustains a high-energy trauma resulting in a Schatzker type IV tibial plateau fracture. Which of the following associated injuries is most strongly correlated with this specific fracture pattern?

Explanation

Schatzker type IV is a fracture of the medial tibial plateau. Because the medial plateau is robust, fractures here require high-energy trauma (often a varus force) and are considered knee dislocation equivalents. This fracture pattern carries a significantly higher risk of popliteal artery injury and peroneal nerve injury compared to lateral plateau fractures.

Question 70

A 17-year-old male presents with night pain in the proximal femur that is dramatically relieved by NSAIDs. CT scan shows a 7 mm radiolucent nidus surrounded by dense sclerotic bone in the femoral neck, located 3 mm from the articular cartilage. What is the most appropriate definitive management?

Explanation

The diagnosis is osteoid osteoma. While radiofrequency ablation (RFA) is the standard of care for most osteoid osteomas, lesions located within 1-1.5 cm of critical structures such as articular cartilage or major nerves are generally considered contraindicated for RFA due to the high risk of thermal necrosis to the cartilage. In this case, surgical curettage or excision is the preferred treatment.

Question 71

The anterolateral ligament (ALL) of the knee has been increasingly recognized for its role in controlling rotational laxity. During an anatomic reconstruction, what are the precise origins and insertions of the ALL?

Explanation

The anterolateral ligament (ALL) originates on the lateral femoral epicondyle, slightly posterior and proximal to the origin of the fibular collateral ligament (FCL). It runs distally and anteriorly to insert on the proximal tibia, midway between Gerdy's tubercle and the fibular head, deep to the iliotibial band.

Question 72

Following an open reduction and internal fixation of a distal femur fracture (AO/OTA 33-C3) using a lateral locked plate, the patient develops a varus collapse. Which of the following technical errors is most strongly associated with this complication?

Explanation

Varus collapse after fixation of a distal femur fracture with a lateral locking plate is frequently associated with medial cortical comminution and failure to recognize or adequately stabilize a coronal plane (Hoffa) fracture. Unrecognized coronal shear fractures severely compromise the stability of the distal block, leading to hardware failure or varus collapse.

Question 73

A 60-year-old female with breast cancer presents with moderate thigh pain. Radiographs reveal a lytic lesion in the peritrochanteric region of the proximal femur that occupies less than 1/3 of the cortical diameter. What is her Mirels' score and the corresponding recommendation?

Explanation

Mirels' criteria for impending pathologic fracture: Site (Peritrochanteric = 3), Pain (Moderate = 2), Lesion (Lytic = 3), Size (<1/3 = 1). Total score = 3+2+3+1 = 9. A score of 9 or greater carries a high risk of fracture (>=33%), and prophylactic surgical fixation is strictly recommended.

Question 74

A 22-year-old male presents with persistent mechanical knee pain. MRI reveals a 4 cm² full-thickness osteochondral defect on the weight-bearing surface of the medial femoral condyle with an uncontained, loose fragment. He is very active and wishes to return to high-impact sports. Which of the following surgical interventions offers the most durable long-term outcome for this specific defect?

Explanation

For a large (>2-3 cm²), uncontained, full-thickness osteochondral defect (involving bone loss) in an active, skeletally mature patient, osteochondral allograft transplantation is the most appropriate treatment. It restores both the articular cartilage and the subchondral bone with mature, viable hyaline cartilage in a single stage.

Question 75

A 35-year-old male sustains a displaced transverse patella fracture. The surgeon elects to perform an open reduction and internal fixation using a tension band wiring technique. To optimize the biomechanical properties of the construct, how should the K-wires and cerclage wire be positioned?

Explanation

In a tension band wiring construct for a transverse patella fracture, the K-wires should be placed parallel to each other in the center (mid-substance) of the patella to prevent displacing the fragments when tightened. The figure-of-eight cerclage wire must be placed as anteriorly as possible to convert the tensile forces generated by the extensor mechanism into compressive forces across the articular surface during knee flexion.

Question 76

A 55-year-old male presents with chronic sacral pain and bowel dysfunction. Imaging reveals a large, destructive, midline mass in the sacrum. Histological examination shows physaliferous cells with vacuolated cytoplasm in a myxoid background. The tumor is positive for brachyury. What is the most important factor in determining the patient's overall survival?

Explanation

The diagnosis is a sacral chordoma, which is positive for the transcription factor brachyury. Chordomas are locally aggressive malignant tumors notoriously resistant to conventional chemotherapy and radiation. The single most important factor determining local recurrence and overall survival is obtaining wide, en bloc surgical margins during the initial resection.

Question 77

In total knee arthroplasty, the concept of kinematic alignment has gained popularity. Compared to traditional mechanical alignment, kinematic alignment aims to position the femoral component by matching which of the following patient-specific axes?

Explanation

Kinematic alignment in TKA aims to restore the patient's pre-arthritic constitutional alignment by co-aligning the transverse axis of the femoral component with the primary transverse axis of the knee, which is the cylindrical axis of the femoral condyles. It achieves this by resurfacing the condyles with equal thicknesses of metal matching the resected bone and cartilage.

Question 78

A 24-year-old male sustains an anteroposterior compression type II (APC-II) pelvic ring injury. According to the Young-Burgess classification, which posterior pelvic ligaments are disrupted and which remain intact in an APC-II injury?

Explanation

In an APC-II pelvic ring injury ('open book' pelvis), the symphysis pubis is diastatic (>2.5 cm). Posteriorly, the anterior sacroiliac ligaments, as well as the sacrotuberous and sacrospinous ligaments, are disrupted, causing rotational instability. The robust posterior sacroiliac ligaments remain intact, maintaining vertical stability.

Question 79

A 14-year-old male is diagnosed with Ewing sarcoma of the femoral diaphysis. He undergoes neoadjuvant chemotherapy, followed by wide surgical excision. Pathology of the resected specimen reveals 95% tumor necrosis. Which of the following statements best describes the significance of this finding?

Explanation

In Ewing sarcoma (and osteosarcoma), the degree of tumor necrosis following neoadjuvant chemotherapy is one of the most powerful independent prognostic indicators. A good histologic response (defined as >=90% or >=95% tumor necrosis) is strongly correlated with improved local control, disease-free survival, and overall survival.

Question 80

A 38-year-old male presents with a chronic, retracted patellar tendon rupture sustained 3 months ago. Primary repair is attempted but the tendon ends cannot be apposed without excessive tension, and the tissue is heavily degenerated. Which of the following is the most reliable reconstructive technique for restoring the extensor mechanism in this setting?

Explanation

Chronic, retracted patellar tendon ruptures present a significant challenge due to soft tissue contracture, quadriceps atrophy, and poor quality of the residual tendon. Primary repair frequently fails. The gold standard for reconstructing a massive defect or chronic retraction is an Achilles tendon allograft with a calcaneal bone block fixed into a trough in the tibial tubercle. The tendon is then woven through or sutured to the patella and quadriceps tendon.

Question 81

A 45-year-old male sustains a Schatzker IV tibial plateau fracture following a high-energy fall. CT imaging reveals a significant posteromedial shear fragment. Which surgical approach and fixation strategy is most biomechanically appropriate for this specific fragment?

Explanation

Schatzker IV fractures frequently involve a posteromedial shear fragment. A posteromedial approach with an anti-glide (buttress) plate applied at the apex of the fracture is required to prevent distal displacement and provides the most stable construct.

Question 82

A 30-year-old female presents with chronic recurrent bloody knee effusions without any history of trauma. MRI of the knee demonstrates a nodular intra-articular mass with low signal intensity on both T1 and T2 sequences, accompanied by a 'blooming' artifact on gradient-echo sequences. What is the most likely diagnosis?

Explanation

Tenosynovial giant cell tumor (formerly known as Pigmented Villonodular Synovitis or PVNS) classically presents with recurrent hemarthrosis. The MRI pathognomonic finding is low T1/T2 signal with 'blooming' artifact due to hemosiderin deposition within the tumor.

Question 83

A 55-year-old female experiences a 'pop' in her posterior knee while squatting. MRI demonstrates a medial meniscus posterior root tear with 4 mm of meniscal extrusion. Which of the following best describes the biomechanical consequence of this injury?

Explanation

A complete tear of the medial meniscus posterior root disrupts the circumferential hoop stresses of the meniscus. Biomechanically, this results in altered kinematics and elevated peak contact pressures that are nearly equivalent to those seen following a total meniscectomy.

Question 84

A 14-year-old boy is diagnosed with osteoblastic osteosarcoma of the distal femur. Following neoadjuvant chemotherapy, he undergoes wide surgical resection. According to the Huvos grading system, what percentage of tumor necrosis defines a 'good responder' and indicates a better long-term prognosis?

Explanation

The Huvos grading system categorizes the histologic response of osteosarcoma to chemotherapy. A 'good response' (Grade III or IV) is defined as having greater than 90% tumor necrosis, which is a major prognostic indicator for improved survival.

Question 85

A 40-year-old male sustains a transverse patella fracture with 4 mm of displacement. He is treated surgically with tension band wiring. What is the primary biomechanical principle underlying this specific fixation technique?

Explanation

The tension band principle relies on placing the fixation construct on the tension side (anterior surface) of the bone. During knee flexion, it converts the disruptive tensile forces at the anterior cortex into dynamic compressive forces at the articular surface.

Question 86

A 68-year-old female presents with medial-sided knee pain 3 years after a primary posterior-stabilized total knee arthroplasty. Radiographs show progressive varus collapse and a symmetric radiolucent line greater than 2 mm in all zones around the tibial component. Serum CRP and ESR are normal, and joint aspiration is negative for infection. What is the most likely cause of failure?

Explanation

Progressive, symmetric radiolucent lines greater than 2 mm involving all zones of a tibial component strongly indicate aseptic loosening. With a negative workup for periprosthetic joint infection, aseptic loosening is the primary diagnosis requiring revision.

Question 87

A 32-year-old male presents with a purely lytic, expansile lesion extending into the subchondral bone of the distal femur. Biopsy reveals multinucleated giant cells intermixed with mononuclear stromal cells. Which targeted medical therapy directly inhibits the specific molecular pathway driving this pathology?

Explanation

Giant Cell Tumor of Bone (GCTB) is driven by neoplastic mononuclear stromal cells that overexpress RANKL, recruiting reactive osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, directly targets this pathway and is highly effective in treating GCTB.

Question 88

A 75-year-old female with severe osteoporosis sustains a comminuted distal femur fracture (OTA 33-C2) immediately proximal to a well-fixed posterior-stabilized total knee arthroplasty. Which of the following surgical constructs provides the greatest biomechanical stability for this specific fracture pattern?

Explanation

In severely comminuted periprosthetic distal femur fractures with poor bone stock, an isolated lateral plate is at high risk of varus collapse. Dual plating (lateral locking plate plus a medial plate) provides superior biomechanical stability and prevents medial column failure.

Question 89

During reconstruction of the medial patellofemoral ligament (MPFL) for recurrent patellar instability, the surgeon inadvertently places the femoral tunnel 5 mm proximal and anterior to the anatomic footprint (Schottle point). What is the expected clinical consequence of this technical error?

Explanation

A femoral tunnel placed proximal and anterior to the anatomic MPFL footprint results in non-isometric graft behavior. The graft will be relatively loose in extension and excessively tight in flexion, leading to restricted knee flexion and increased medial patellofemoral cartilage pressure.

Question 90

A 55-year-old male presents with an incidental 6 cm intraosseous lesion in the proximal tibia. Radiographs show classic ring-and-arc calcifications. A biopsy demonstrates a low-grade (Grade 1) central chondrosarcoma confined strictly to the medullary canal without cortical breakthrough. What is the standard surgical management?

Explanation

Low-grade (Grade 1) central chondrosarcomas, also termed atypical cartilaginous tumors, that are confined to the medullary canal can be safely managed with extended intralesional curettage, high-speed burring, and local adjuvants. This avoids the morbidity of wide resection while maintaining excellent local control.

Question 91

A 28-year-old male is admitted with a closed tibial shaft fracture. Eight hours later, he develops excruciating leg pain out of proportion to the injury and new-onset paresthesias isolated to the first dorsal web space of the foot. Which compartment of the lower leg is most likely experiencing critically elevated pressure?

Explanation

The deep peroneal nerve courses through the anterior compartment of the leg and provides sensory innervation to the first dorsal web space. Paresthesias in this specific distribution are a hallmark early neurologic sign of anterior compartment syndrome.

Question 92

A 24-year-old athlete sustains a multi-ligament knee injury involving the posterolateral corner (PLC). Based on clinical biomechanics, which of the following structures acts as the primary restraint to varus stress when the knee is tested at 30 degrees of flexion?

Explanation

The lateral collateral ligament (LCL) is the primary restraint to varus stress at all angles of knee flexion. However, it is most accurately isolated and tested clinically at 30 degrees of flexion, where the cruciate ligaments are relatively relaxed.

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

Orthopedic Surgery Board Review MCQs: Fracture, Knee & Tumor - Part 19

Key Takeaway

Orthopedic Surgery Board Review MCQs: Fracture, Knee & Tumor - Part 19

Chapter Index