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Orthopedic Surgery Mock Exam - Set B29D06

Orthopedic Surgery Mock Exam - Set 407640

27 Apr 2026 31 min read 82 Views
Orthopedic Surgery Mock Exam - Set 407640

Key Takeaway

This mock exam provides 50 randomized questions derived from Arab Board and FRCS databanks to perfectly simulate testing environments.

Orthopedic Surgery Mock Exam - Set 407640

Comprehensive 100-Question Exam


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Question 1

A 12-year-old obese male presents with left groin pain and an altered gait.

Based on the presumed diagnosis of slipped capital femoral epiphysis (SCFE) shown in the representative radiograph, which of the following is the primary blood supply to the femoral head that is at highest risk for iatrogenic injury during percutaneous in situ pinning if the pin is placed in the posterosuperior quadrant?





Explanation

The primary blood supply to the capital femoral epiphysis in children over the age of 3 is the posterosuperior retinacular vessels (lateral epiphyseal artery), which are terminal branches of the medial circumflex femoral artery (MCFA). During in situ pinning for SCFE, placement of the pin in the posterosuperior quadrant of the femoral neck/head places these extracapsular vessels at extreme risk of injury, potentially leading to avascular necrosis (AVN). Pins should ideally be placed in the center-center position to minimize this risk.

Question 2

A 45-year-old female sustains a knee injury following a motor vehicle collision.

Assuming the representative image demonstrates a medial tibial plateau fracture with articular depression (Schatzker IV), what is the most likely mechanism of injury?





Explanation

A Schatzker IV fracture involves the medial tibial plateau. The medial plateau is structurally denser and stronger than the lateral plateau, meaning fractures here typically require higher energy. The classic mechanism is a varus force combined with an axial load. In contrast, lateral plateau fractures (Schatzker I-III) are typically caused by a valgus force with an axial load. High-energy trauma to the medial plateau is also highly associated with injury to the peroneal nerve, popliteal artery, and ligamentous structures (like the ACL or LCL).

Question 3

A 25-year-old male is involved in a high-speed motor vehicle collision.

Radiographs demonstrate a traumatic spondylolisthesis of the axis (Hangman's fracture) with an oblique fracture line through the pars interarticularis, minimal translation, but extreme angulation (>11 degrees). The C2-C3 disc space appears disrupted posteriorly. According to the Levine-Edwards classification, what is the most appropriate initial management for this specific injury pattern (Type IIa)?





Explanation

The scenario describes a Levine-Edwards Type IIa Hangman's fracture. This injury is caused by a flexion-distraction mechanism, leading to severe angulation with minimal initial translation. A critical point in management is that axial traction is STRICTLY CONTRAINDICATED, as it will exacerbate the distraction and worsen the deformity. The appropriate non-operative management involves the application of a halo vest under gentle compression and extension to reduce the angulation and stabilize the fracture.

Question 4

A 14-year-old male presents with worsening night pain in his distal femur.

The radiograph shows a mixed lytic/sclerotic lesion with a 'sunburst' periosteal reaction and Codman's triangle. A biopsy confirms conventional osteosarcoma. Which of the following genetic alterations is most classically associated with the pathogenesis of this tumor?





Explanation

Conventional osteosarcoma is highly associated with mutations in the p53 (associated with Li-Fraumeni syndrome) and Rb (retinoblastoma) tumor suppressor genes. Option A (t(11;22)) is characteristic of Ewing sarcoma (EWS-FLI1 fusion). Option C (t(X;18)) is seen in Synovial Sarcoma (SYT-SSX). Option E (t(2;13)) is associated with Alveolar Rhabdomyosarcoma (PAX3-FOXO1).

Question 5

A 55-year-old diabetic patient presents with a swollen, erythematous, and warm foot.

Assuming radiographs initially revealed midfoot fragmentation and subluxation, and follow-up radiographs 4 months later demonstrate absorption of fine bone debris and early fusion of large fragments. According to the Eichenholtz classification of Charcot arthropathy, which stage does this represent?





Explanation

The Eichenholtz classification describes the natural history of Charcot neuroarthropathy. Stage 0 is the inflammatory phase (erythema, edema, warmth, normal radiographs or mild osteopenia). Stage I (Fragmentation) is characterized by joint subluxation, debris formation, and fragmentation. Stage II (Coalescence) is marked by the absorption of fine debris, early sclerosis, and fusion of larger fragments as the acute inflammation subsides. Stage III (Consolidation/Remodeling) shows remodeling of the bone ends, decreased sclerosis, and a stable (though often deformed) joint.

Question 6

In the context of modularity in total hip arthroplasty (THA), which of the following is the primary mechanism of failure associated with trunnionosis at the head-neck junction?





Explanation

Trunnionosis refers to wear and corrosion at the modular head-neck junction of a THA. The primary mechanism is mechanically assisted crevice corrosion (MACC), which involves a combination of fretting (micromotion between the surfaces) that disrupts the passive oxide layer, and crevice corrosion (a localized drop in pH and oxygen depletion in the crevice) once the bulk material is exposed. While galvanic corrosion can contribute when mixed metals are used (e.g., CoCr head on Ti stem), fretting and MACC are the predominant driving factors.

Question 7

A 6-week-old female is placed in a Pavlik harness for developmental dysplasia of the hip (DDH). At her 2-week follow-up, the mother notes the child is no longer kicking her right leg. On physical exam, there is an absence of active knee extension on the right side. What is the most appropriate next step in management?





Explanation

The infant is presenting with a femoral nerve palsy, which is the most common nerve palsy associated with the Pavlik harness. It is caused by hyperflexion of the hips, which compresses the femoral nerve against the inguinal ligament. The appropriate management is to adjust the anterior straps to decrease hip flexion, allowing the nerve to recover. Complete discontinuation is usually not necessary unless the palsy fails to resolve after adjustment. Posterior straps control abduction; hyperabduction can lead to avascular necrosis (AVN), not typically femoral nerve palsy.

Question 8

A 22-year-old male sustains a proximal pole scaphoid fracture. Which of the following best describes the predominant arterial supply to the scaphoid that makes this specific fracture pattern highly prone to avascular necrosis (AVN) and nonunion?





Explanation

The scaphoid is primarily supplied by the dorsal carpal branch of the radial artery (supplying 70-80% of the bone, including the proximal pole). These vessels enter the scaphoid distally at the dorsal ridge and flow in a retrograde fashion toward the proximal pole. Because of this retrograde blood supply, fractures at the proximal pole disrupt the vascularity to the proximal fragment, leading to high rates of AVN and nonunion.

Question 9

During a total knee arthroplasty (TKA) for a severe varus deformity, the surgeon resects the distal femur and proximal tibia. With spacer blocks inserted, the knee remains tight medially in both flexion and extension. To balance the gaps symmetrically, which structure should be released next?





Explanation

In a varus knee undergoing TKA, a tight medial gap in both flexion and extension indicates a symmetric medial soft tissue contracture. The standard medial release sequence typically begins with the deep medial collateral ligament (MCL) and the posteromedial capsule. If the gap remains tight, further releases may include the superficial MCL (often off the tibia, maintaining the periosteal sleeve) and the pes anserinus. Releasing the lateral structures (LCL, IT band, popliteus) would worsen the varus imbalance.

Question 10

A 30-year-old male presents in hypotensive shock following a motorcycle crash. Pelvic radiographs and CT demonstrate an anteroposterior compression type III (APC-III) injury according to the Young-Burgess classification. Which of the following ligamentous complexes are completely disrupted in this specific injury pattern?





Explanation

The Young-Burgess classification for APC injuries relies on progressive disruption of the pelvic ring from anterior to posterior. APC-I involves pubic diastasis <2.5 cm with intact posterior ligaments. APC-II involves diastasis >2.5 cm with disruption of the anterior sacroiliac (SI), sacrotuberous, and sacrospinous ligaments, but intact posterior SI ligaments (rotationally unstable, vertically stable). APC-III involves complete disruption of both the anterior and posterior SI ligaments, resulting in a globally (rotationally and vertically) unstable hemipelvis.

Question 11

Which of the following statements most accurately describes the vascular anatomy and healing potential of the meniscus?





Explanation

The blood supply to the menisci originates from the medial, lateral, and middle genicular arteries (predominantly the inferior genicular arteries). The vessels form a perimeniscal capillary plexus within the synovial and capsular tissues. Only the peripheral 10% to 30% of the menisci (the 'red-red' zone) is vascularized in adults, making this zone capable of healing after repair. The inner portions ('white-white' zone) are avascular and rely on diffusion from synovial fluid. Vascularity actually decreases with age.

Question 12

In healthy hyaline articular cartilage, which of the following macromolecular components is primarily responsible for providing the tissue with its compressive strength and stiffness?





Explanation

Aggrecan, a large proteoglycan, is the primary source of compressive strength in articular cartilage. It contains numerous negatively charged glycosaminoglycans (GAGs), such as chondroitin sulfate and keratan sulfate, which repel each other and attract water via the Donnan osmotic effect. This creates a swelling pressure that resists compressive loads. In contrast, the Type II collagen network provides the tensile strength and restrains the swelling pressure of the proteoglycans.

Question 13

A 65-year-old male with a history of neurogenic claudication undergoes a posterior lumbar decompressive laminectomy. Hypertrophy of which of the following anatomical structures is most directly responsible for the dorsal compression of the thecal sac in central lumbar spinal stenosis?





Explanation

Central lumbar spinal stenosis is typically caused by a combination of disc bulging anteriorly, facet joint hypertrophy laterally, and hypertrophy/buckling of the ligamentum flavum posteriorly. The ligamentum flavum forms the dorsal margin of the spinal canal and its hypertrophy is the primary dorsal contributor to canal narrowing. The posterior longitudinal ligament is ventral to the thecal sac.

Question 14

Following a primary Zone II flexor tendon repair, which of the following biological processes characterizes the 'proliferation' phase of tendon healing (typically peaking between 1 to 4 weeks post-repair)?





Explanation

Tendon healing occurs in three phases: inflammatory (days 1-7), proliferative (days 7-21/28), and remodeling (weeks to months). During the proliferative phase, fibroblasts (from the epitenon and endotenon) migrate to the repair site and synthesize abundant Type III collagen, increasing the mass and strength of the repair. The inflammatory phase is characterized by hematoma and macrophage activity (where the tendon is weakest), and the remodeling phase is characterized by the conversion of Type III to Type I collagen and cross-linking.

Question 15

A 30-year-old female is diagnosed with a biopsy-proven giant cell tumor of the distal radius. Due to the extent of the lesion, she is treated with denosumab preoperatively. What is the precise mechanism of action of this pharmacological agent?





Explanation

Denosumab is a fully human monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). Giant cell tumors of bone consist of neoplastic mononuclear stromal cells that overexpress RANKL, which in turn recruits and hyperactivates multinucleated giant cells (osteoclast-like cells) expressing the RANK receptor. By binding RANKL, denosumab prevents it from interacting with RANK on osteoclasts, severely halting bone resorption and leading to ossification of the tumor matrix.

Question 16

According to the Seddon classification of nerve injuries, a peripheral nerve injury that involves complete disruption of the axon and myelin sheath, but preservation of the surrounding connective tissue framework (endoneurium, perineurium, and epineurium) is termed:





Explanation

In the Seddon classification: Neuropraxia is a local conduction block with intact axons (demyelination); recovery is fast and complete. Axonotmesis involves disruption of the axon and myelin sheath, resulting in distal Wallerian degeneration, but the connective tissue tubes (endoneurium, perineurium, epineurium) remain intact. This guides the regenerating axons, allowing for spontaneous recovery at ~1 mm/day. Neurotmesis is a complete transection of the nerve including the connective tissue framework, requiring surgical repair for any functional recovery.

Question 17

A 25-year-old male suffers a highly comminuted, closed tibial shaft fracture. Two hours later, he complains of severe leg pain out of proportion to the injury, worsening with passive stretch of the toes. Which of the following absolute or differential pressure readings is the most widely accepted and evidence-based threshold for diagnosing acute compartment syndrome and proceeding with fasciotomy?





Explanation

The threshold for diagnosing acute compartment syndrome is generally based on the differential pressure (Delta P), calculated as the Diastolic Blood Pressure minus the Absolute Compartment Pressure. A Delta P of less than 30 mmHg indicates that perfusion to the capillary beds is critically impaired, leading to muscle and nerve ischemia. Absolute pressures alone are less reliable because systemic blood pressure variations significantly affect tissue perfusion thresholds.

Question 18

A 6-year-old boy presents with a painless limp. Radiographs show sclerosis and early fragmentation of the capital femoral epiphysis, consistent with Legg-Calvé-Perthes disease. According to Catterall, which of the following is considered a radiographic 'head at risk' sign?





Explanation

Catterall described five clinical and radiographic 'head at risk' signs for Legg-Calvé-Perthes disease that correlate with a worse prognosis and higher risk of femoral head deformation. These include: 1) Gage's sign (a V-shaped radiolucent defect in the lateral epiphysis/metaphysis), 2) Calcification lateral to the epiphysis, 3) Lateral (not medial) subluxation of the femoral head, 4) A horizontal (not vertical) growth plate, and 5) Metaphyseal cysts.

Question 19

A 35-year-old female sustains a twisting injury to her ankle. Radiographs reveal a transverse fracture of the medial malleolus and a spiral fracture of the proximal third of the fibula (Maisonneuve fracture). For this specific fracture pattern to occur, which of the following ligamentous structures MUST be completely disrupted?





Explanation

A Maisonneuve fracture is a pronounced variation of a pronation-external rotation (PER) injury. The mechanism involves external rotation of the talus, which either avulses the medial malleolus or ruptures the deltoid ligament, then disrupts the anterior inferior tibiofibular ligament, tears up the interosseous membrane all the way to the proximal fibula, and exits as a high fibular fracture. Therefore, the syndesmotic complex and the interosseous membrane up to the level of the fracture are intrinsically disrupted.

Question 20

Which of the following surgical approaches for total hip arthroplasty (THA) uniquely utilizes a true internervous and intermuscular plane, dissecting superficially between the tensor fasciae latae and the sartorius, and deeply between the gluteus medius and the rectus femoris?





Explanation

The direct anterior (Smith-Petersen) approach exploits a true internervous plane. Superficially, the plane is between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve). Deeply, the plane is between the rectus femoris (femoral nerve) and the gluteus medius/minimus (superior gluteal nerve). The anterolateral (Watson-Jones) plane is between the TFL and gluteus medius (both superior gluteal nerve, thus not internervous). The direct lateral approach splits the gluteus medius and vastus lateralis.

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