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Arab Orthopaedic Board MCQs - Part 12

27 Apr 2026 133 min read 81 Views
Arab Ortho Board MCQs - Part 11

Key Takeaway

For anyone wondering about Arab Orthopaedic Board MCQs - Part 12, Practice Arab Orthopaedic Board MCQs Part 12. Review orthopedic surgery questions 551 to 600 for your board exam preparation.

Arab Orthopaedic Board MCQs - Part 12

Comprehensive 100-Question Exam


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Question 1

Which of the following genetic or molecular factors is most strongly associated with the pathogenesis of Ossification of the Posterior Longitudinal Ligament (OPLL)?





Explanation

OPLL pathogenesis is heavily linked to genetic and mechanical factors, with overexpression of bone morphogenetic protein-2 (BMP-2) and transforming growth factor-beta (TGF-beta) playing a key role in the enchondral ossification of the posterior longitudinal ligament. FGFR3 is related to achondroplasia, type I collagen to osteogenesis imperfecta, and sclerostin deficiency to sclerosteosis/van Buchem disease.

Question 2

Romosozumab is currently utilized in the treatment of severe osteoporosis. What is the specific cellular mechanism of action of this medication?





Explanation

Romosozumab is a humanized monoclonal antibody that binds to and inhibits sclerostin. By inhibiting sclerostin, it disinhibits the Wnt/beta-catenin signaling pathway, leading to increased bone formation and decreased bone resorption (a dual-acting anabolic agent).

Question 3

A 4-year-old girl is diagnosed with neglected left developmental dysplasia of the hip. She is scheduled for an open reduction, femoral shortening osteotomy, and a Dega pelvic osteotomy. Which of the following correctly describes the anatomical cuts of a Dega osteotomy?





Explanation

The Dega osteotomy is an incomplete trans-iliac pelvic osteotomy. The outer table is cut, but the inner table and the greater sciatic notch are left intact to act as a posterior hinge. This allows the acetabulum to be hinged downward, providing anterior, lateral, and posterior coverage.

Question 4

A 30-year-old male sustains an APC-III pelvic ring injury in a motorcycle accident. He is hemodynamically unstable despite initial fluid resuscitation. A pelvic binder is applied, but he remains hypotensive. FAST exam is negative. What is the most appropriate next step in management?





Explanation

In a hemodynamically unstable patient with a pelvic ring injury and a negative FAST exam, the source of bleeding is presumed retroperitoneal (venous or arterial). Pre-peritoneal pelvic packing (PPP) and/or pelvic angiography with embolization are the mainstays of controlling retroperitoneal pelvic hemorrhage. Laparotomy releases the tamponade effect and is contraindicated for isolated retroperitoneal bleeding.

Question 5

A 28-year-old female presents with a destructive, expansile lytic lesion in the distal femur epimetaphysis. Biopsy confirms a Giant Cell Tumor of Bone. She is started on Denosumab preoperatively. Which of the following describes the primary histological effect of Denosumab on this tumor?





Explanation

Denosumab is a RANKL inhibitor. In Giant Cell Tumor of Bone, the neoplastic mononuclear stromal cells express RANKL, which recruits reactive multinucleated osteoclast-like giant cells. Denosumab inhibits this recruitment, leading to the rapid depletion of the giant cells and subsequent woven bone formation, but the neoplastic stromal cells often remain viable.

Question 6

The medial patellofemoral ligament (MPFL) is the primary restraint to lateral patellar translation at 0 to 30 degrees of knee flexion. Which of the following best describes the anatomical femoral attachment of the MPFL?





Explanation

Anatomically, the femoral origin of the MPFL is located in the saddle (or groove) between the adductor tubercle (which is proximal and posterior) and the medial epicondyle (which is distal and anterior). Schottle's point defines this radiographically.

Question 7

To optimize stability and minimize the risk of posterior dislocation in primary total hip arthroplasty, the combined anteversion (McKhann's or Ranawat's concept) of the acetabular and femoral components should ideally fall into which range?





Explanation

The concept of combined anteversion (the sum of cup anteversion and femoral stem anteversion) helps prevent impingement and dislocation. For a posterior approach, the widely accepted safe zone for combined anteversion is between 25 and 45 degrees.

Question 8

When performing a primary repair of a zone II flexor digitorum profundus (FDP) laceration, which of the following suture configurations provides the greatest tensile strength and resistance to gap formation during early active rehabilitation?





Explanation

The ultimate tensile strength of a flexor tendon repair is directly proportional to the number of core strands crossing the repair site. A 6-strand core provides excellent strength. The addition of a peripheral epitendinous suture significantly improves resistance to initial gap formation and adds approximately 20-30% to the overall strength of the construct.

Question 9

A 55-year-old male with poorly controlled diabetes presents with a swollen, erythematous foot. Radiographs reveal fragmentation of the navicular and cuneiforms with joint subluxation, but no consolidation. According to the Eichenholtz classification, what stage is this, and what is the primary pathophysiological driver according to the neurovascular theory?





Explanation

The patient is in Eichenholtz Stage 1 (Fragmentation), characterized by acute inflammation, subluxation, and bony fragmentation. The French/neurovascular theory states that autonomic neuropathy causes arteriovenous shunting and local hyperemia, which increases osteoclastic activity leading to bone resorption and structural collapse.

Question 10

During the incorporation of a cortical structural allograft, the process of 'creeping substitution' occurs. Which of the following correctly describes the sequence of cellular events in this process?





Explanation

Creeping substitution is the process by which a bone graft is slowly resorbed and simultaneously replaced with new living bone. For dense cortical grafts, this occurs via a 'cutting cone' mechanism, where osteoclasts lead the way by resorbing the Haversian canals, followed closely by osteoblasts laying down new osteoid.

Question 11

A 40-year-old male sustains a coronal plane fracture of the lateral femoral condyle (Hoffa fracture). Which surgical approach and fixation trajectory provides the most biomechanically stable construct for this specific fracture pattern?





Explanation

Hoffa fractures are coronal shear fractures. Biomechanical studies demonstrate that posterior-to-anterior directed lag screws placed perpendicular to the fracture plane offer superior stability compared to anterior-to-posterior screws. A direct lateral or swashbuckler approach allows optimal posterior access to the lateral condyle for this trajectory.

Question 12

A 12-year-old overweight boy presents with an antalgic gait. Radiographs confirm a mild left Slipped Capital Femoral Epiphysis (SCFE). Which of the following is an accepted and strongly supported indication for prophylactic in situ pinning of the contralateral right hip?





Explanation

Prophylactic pinning of the contralateral hip in SCFE is controversial but widely indicated in patients at high risk for a subsequent slip. Known strong risk factors for a contralateral slip include an open triradiate cartilage (indicating significant skeletal immaturity), underlying endocrine disorders (e.g., hypothyroidism), and very young age (girls <10, boys <12).

Question 13

A 16-year-old male undergoes neoadjuvant chemotherapy followed by wide resection of a distal femur osteosarcoma. Pathology reveals 95% tumor necrosis. According to the Huvos grading system, what grade is this, and what is its clinical significance?





Explanation

The Huvos grading system measures histologic response to chemotherapy in osteosarcoma. Grade I: <50% necrosis. Grade II: 50-90% necrosis. Grade III: >90% necrosis but with viable tumor cells. Grade IV: 100% necrosis (no viable cells). A finding of 95% necrosis falls into Grade III, which is considered a 'good response' and is highly prognostic of improved overall survival.

Question 14

During shoulder arthroscopy, a surgeon visualizes tearing of the superior labrum with complete detachment of the biceps anchor from the superior glenoid tubercle. The labrum is not buckethandle-torn, and the tear does not extend into the biceps tendon. What type of SLAP lesion is this?





Explanation

According to the Snyder classification of SLAP tears: Type I is degenerative fraying with an intact biceps anchor. Type II is detachment of the superior labrum and biceps anchor from the glenoid. Type III is a bucket-handle tear of the labrum with an intact biceps anchor. Type IV is a bucket-handle tear that extends into the biceps tendon.

Question 15

A 35-year-old female falls from a height and sustains a T12 burst fracture. On examination, she has 4/5 weakness in her right ankle dorsiflexors. MRI reveals disruption of the posterior ligamentous complex (PLC). What is her Thoracolumbar Injury Classification and Severity (TLICS) score?





Explanation

TLICS score calculation: Morphology = Burst fracture (2 points). Neurological status = Incomplete spinal cord / cauda equina injury (3 points). PLC status = Disrupted (3 points). Total = 2 + 3 + 3 = 8 points. A score > 4 is considered a strong indication for operative stabilization.

Question 16

Idiopathic avascular necrosis of the scaphoid is known as Preiser disease. Which of the following vascular anatomical features most directly makes the scaphoid proximal pole susceptible to avascular necrosis?





Explanation

The scaphoid relies heavily on branches of the radial artery (predominantly the dorsal carpal branch). These vessels enter the bone at the dorsal ridge, which is distal to the waist, and course in a retrograde direction to perfuse the proximal pole. This retrograde blood supply is easily compromised by fractures at the waist or proximal pole, leading to avascular necrosis.

Question 17

Which of the following radiographic findings is considered pathognomonic for a Lisfranc injury?





Explanation

The 'fleck sign' is a small bony avulsion fragment seen in the intermetatarsal space between the medial cuneiform and the base of the second metatarsal. It represents an avulsion of the Lisfranc ligament and is pathognomonic for a Lisfranc joint complex disruption.

Question 18

During a primary total knee arthroplasty, the trial reduction reveals that the knee is excessively tight in flexion but symmetric and well-balanced in extension. Which of the following surgical steps is the most appropriate to correct this mismatch?





Explanation

When a knee is tight in flexion but balanced in extension, the flexion gap is too small relative to the extension gap. To increase the flexion gap without altering the extension gap, the surgeon must resect more posterior femoral condyle. Downsizing the femoral component (decreasing the AP size) and keeping the anterior flange flush (anterior referencing) will resect more posterior bone, enlarging the flexion gap.

Question 19

Osteoclasts are multinucleated giant cells that create a sealed zone to isolate the resorptive pit (Howship's lacuna) on the bone surface. Which of the following integrins is primarily responsible for forming this sealing zone by binding to osteopontin and bone sialoprotein?





Explanation

The alpha-v beta-3 (αvβ3) integrin is highly expressed on the osteoclast cell membrane. It binds specifically to RGD (Arg-Gly-Asp) amino acid sequences found in bone matrix proteins like osteopontin and bone sialoprotein. This interaction is essential for the tight attachment of the osteoclast to the bone and the formation of the actin sealing zone.

Question 20

Scapulothoracic dissociation is a devastating high-energy injury characterized by complete disruption of the scapulothoracic articulation. What is the most important determinant of long-term limb survival and overall functional prognosis in these patients?





Explanation

Scapulothoracic dissociation is essentially a closed forequarter amputation. While subclavian/axillary vascular injuries can be acutely life-threatening and require emergency repair, the ultimate functional survival and prognosis of the limb are dictated by the brachial plexus injury. Complete avulsions result in a flail, insensate limb that frequently requires eventual amputation.

Question 21

A 45-year-old patient undergoes revision osteosynthesis of a nonunion using a titanium locking plate and stainless steel screws. Which of the following best describes the likely electrochemical outcome at the implant interface?





Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution (e.g., bodily fluids). Stainless steel is anodic (less noble) relative to titanium. Therefore, when they are in direct contact, the stainless steel acts as the anode and preferentially corrodes, releasing ions, while the titanium acts as the cathode and remains protected.

Question 22

During a total knee arthroplasty for a patient with a severe, fixed varus deformity, the surgeon must perform a sequential medial release to achieve a balanced extension and flexion gap. Which of the following represents the most accepted sequence of release after osteophyte removal?





Explanation

In a severe varus knee, sequential release of the tight medial structures is necessary. Following the removal of medial osteophytes, the classic stepwise release begins with the deep MCL, followed by the posteromedial corner/capsule, then the superficial MCL (often subperiosteally off the tibia), and finally the pes anserinus tendons if further correction is required.

Question 23

A 4-week-old infant with developmental dysplasia of the hip (DDH) is treated with a Pavlik harness. Two weeks later, the parents notice the infant is no longer actively extending the knee on the affected side, although ankle and toe movements are normal. What is the most likely diagnosis and the most appropriate next step in management?





Explanation

The most common neurologic complication of a Pavlik harness is a femoral nerve palsy, typically resulting from hyperflexion of the hip which stretches or compresses the nerve. Clinical signs include a loss of active quadriceps function (knee extension). The standard management is to immediately remove the harness or significantly reduce hip flexion to allow the nerve to recover before resuming DDH treatment.

Question 24

A 60-year-old male presents with gait instability, hand clumsiness, and hyperreflexia in both the upper and lower extremities. Which of the following physical examination findings, if present, most specifically localizes his upper motor neuron lesion to a level cephalad to the foramen magnum?





Explanation

Hyperreflexia in the limbs indicates an upper motor neuron (UMN) lesion, which could be in the cervical spine or higher. The jaw jerk reflex assesses the trigeminal nerve (Cranial Nerve V). An exaggerated jaw jerk reflex localizes the UMN lesion to above the mid-pons (cephalad to the foramen magnum), helping differentiate cranial/brain pathology from cervical spondylotic myelopathy.

Question 25

The anterior cruciate ligament (ACL) is composed of two primary functional bundles. Which of the following best describes the specific biomechanical roles and tensioning patterns of the anteromedial (AM) and posterolateral (PL) bundles during knee range of motion?





Explanation

The ACL's two functional bundles are the anteromedial (AM) and posterolateral (PL) bundles. The AM bundle increases in tension during knee flexion and is the primary restraint to anterior tibial translation. The PL bundle is taut in extension and is the primary restraint to rotatory loads (pivot shift).

Question 26

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is used off-label in various nonunion surgeries. Following the binding of rhBMP-2 to its transmembrane serine/threonine kinase receptors, which of the following intracellular signaling pathways is primarily activated to upregulate osteogenic gene expression?





Explanation

Bone morphogenetic proteins (BMPs) belong to the TGF-beta superfamily. When BMPs bind to their specific heterodimeric receptors, they primarily signal through the canonical Smad pathway, specifically phosphorylating Smad 1, 5, and 8. These complex with Smad 4 and translocate to the nucleus to induce transcription of osteoblastic genes like Runx2.

Question 27

During surgical exposure for a complex zone II flexor tendon repair, the surgeon must decide which portions of the digital flexor sheath to vent. Preserving which of the following combinations of pulleys is biomechanically most critical to prevent digital bowstringing and loss of flexion work efficiency?





Explanation

The flexor tendon pulley system prevents bowstringing of the tendons across the interphalangeal joints. The A2 pulley (located over the proximal phalanx) and the A4 pulley (located over the middle phalanx) are mechanically the most crucial. Loss of these pulleys leads to significant bowstringing, decreased range of motion, and decreased mechanical efficiency (increased work of flexion).

Question 28

A 55-year-old patient with poorly controlled diabetes mellitus presents with a swollen, erythematous, and warm right foot. Radiographs of the foot are completely normal. An MRI is obtained, demonstrating diffuse bone marrow edema across the midfoot without cortical disruption, subchondral cysts, or fragmentation. Which Eichenholtz stage of Charcot arthropathy does this represent?





Explanation

Eichenholtz Stage 0 (often added to the original 3-stage classification by Shibata et al.) represents the earliest, pre-radiographic phase of Charcot arthropathy. It is characterized by clinical inflammation (warmth, swelling, erythema) and normal radiographs. MRI will show early changes such as bone marrow edema and microfractures before gross structural collapse occurs.

Question 29

In patients undergoing total hip arthroplasty (THA) with a ceramic-on-ceramic bearing surface, the phenomenon of 'squeaking' is a known complication. Which of the following factors is most strongly and consistently associated with the development of this noise?





Explanation

Squeaking in ceramic-on-ceramic THA is multifactorial but is most strongly correlated with component malposition, specifically acetabular cup retroversion or steep (excessive) inclination. This malposition leads to edge loading, disruption of fluid-film lubrication, stripe wear on the ceramic head, and subsequent micro-vibrations that produce the audible squeak.

Question 30

During the ilioinguinal approach to the acetabulum, the surgeon must carefully identify and ligate the 'corona mortis' to prevent life-threatening hemorrhage. This vascular structure is an anastomosis between the obturator vessels and which of the following vascular systems?





Explanation

The corona mortis ('crown of death') is a retropubic vascular anastomosis between the obturator system and the external iliac or inferior epigastric systems. It is found traversing the superior pubic ramus at an average distance of 5-6 cm from the pubic symphysis and is at high risk of iatrogenic injury during anterior pelvic surgical exposures.

Question 31

A 12-year-old male is diagnosed with a unilateral slipped capital femoral epiphysis (SCFE) and undergoes in situ pinning. Which of the following represents the strongest absolute indication for prophylactic in situ pinning of the contralateral asymptomatic hip?





Explanation

Prophylactic pinning of the contralateral hip in SCFE is controversial but is universally recommended for patients with underlying endocrinopathies (such as hypothyroidism, panhypopituitarism, or renal osteodystrophy), previous radiation therapy, or presentation at an atypically young age (< 10 years). These populations have an exceptionally high risk of developing a contralateral slip.

Question 32

A 35-year-old male sustains a T12 burst fracture after a fall. Neurological examination is completely intact. Radiographs and an MRI demonstrate splaying of the spinous processes and complete disruption of the posterior ligamentous complex (PLC). Based on the Thoracolumbar Injury Classification and Severity (TLICS) score, what is his total score and the recommended treatment strategy?





Explanation

The TLICS score assigns points based on morphology, neurologic status, and PLC integrity. Burst morphology = 2 points. Intact neurologic status = 0 points. Disrupted PLC = 3 points. Total score = 5 points. A TLICS score of 3 or less is typically treated non-operatively, 4 is indeterminate (surgeon's choice), and 5 or more indicates surgical stabilization.

Question 33

In overhead-throwing athletes, a Type II Superior Labrum Anterior to Posterior (SLAP) tear is often propagated by the 'peel-back' mechanism during the throwing motion. In which of the following shoulder positions does the maximum peel-back force occur?





Explanation

The 'peel-back' mechanism is a primary contributor to SLAP tears in overhead athletes. During the late cocking phase of throwing, the shoulder is in abduction and maximum external rotation. This position causes the biceps vector to shift posteriorly, creating a torsional force that 'peels back' the superior labrum from the glenoid.

Question 34

A 52-year-old male presents with chronic wrist pain and is diagnosed with Scaphoid Nonunion Advanced Collapse (SNAC). Radiographs reveal advanced osteoarthritic changes in the radioscaphoid and capitolunate joints, while the radiolunate joint is completely spared. Which of the following salvage procedures is strictly contraindicated in this patient?





Explanation

Proximal row carpectomy (PRC) relies on a preserved, cartilaginous articulation between the head of the capitate and the lunate fossa of the distal radius. In this patient, the presence of capitolunate arthritis (a feature of advanced SNAC/SLAC stage III) makes PRC strictly contraindicated. A four-corner fusion or total wrist arthrodesis would be more appropriate.

Question 35

According to Mirels' criteria for evaluating the risk of a pathologic fracture in a long bone affected by a metastatic lesion, which of the following clinical scenarios yields the highest possible score and mandates prophylactic fixation?





Explanation

Mirels' criteria score four variables from 1 to 3: Site (Upper=1, Lower=2, Peritrochanteric=3), Pain (Mild=1, Moderate=2, Functional=3), Lesion Nature (Blastic=1, Mixed=2, Lytic=3), and Size (<1/3=1, 1/3-2/3=2, >2/3=3). A lytic lesion (3) in the lower extremity (wait, peritrochanteric is 3, but lower extremity generally is scored high; standard Mirels scores Lower limb as 2 and peritrochanteric as 3. Given the options, Lytic (3) + Lower extremity (at least 2) + >2/3 cortex (3) + functional pain (3) yields a score of 11 or 12, which is the highest among the choices and strictly indicates prophylactic fixation.

Question 36

Which of the following statements best describes the primary pathophysiologic mechanism leading to tissue ischemia in acute compartment syndrome?





Explanation

The pathophysiology of compartment syndrome is based on the arteriovenous (AV) gradient theory. As tissue pressure increases within a closed fascial space, it exceeds the venous pressure. This collapses the thin-walled venules, causing venous hypertension, which in turn decreases the local AV pressure gradient. When the gradient drops below a critical threshold, capillary perfusion ceases, leading to tissue ischemia well before arterial systolic occlusion occurs.

Question 37

What is the primary mechanism by which highly cross-linked polyethylene (HXLPE) achieves significantly reduced wear rates compared to conventional ultra-high-molecular-weight polyethylene (UHMWPE) in total hip arthroplasty?





Explanation

Highly cross-linked polyethylene is manufactured by exposing UHMWPE to high doses of gamma or electron beam irradiation. This radiation breaks carbon-hydrogen bonds, allowing free radicals to combine and form strong transverse covalent bonds (cross-links) between adjacent polymer chains. This highly interlinked network vastly improves resistance to adhesive and abrasive wear. Post-irradiation melting or annealing is then done to eliminate residual free radicals and prevent long-term oxidation.

Question 38

In normal articular cartilage, the collagen fibers in the superficial zone (lamina splendens) are tightly packed and oriented parallel to the articular surface. What is the primary biomechanical function of this specific structural alignment?





Explanation

Articular cartilage is divided into zones. The superficial zone (lamina splendens) contains densely packed Type II collagen fibers oriented parallel to the joint surface. This parallel orientation provides high tensile strength in the plane of the joint, which functions primarily to resist the extreme shear forces generated during joint articulation.

Question 39

A 14-year-old male soccer player presents with chronic anterior knee pain and occasional mechanical catching. Radiographs and MRI confirm a stable osteochondritis dissecans (OCD) lesion. Statistically, what is the most common anatomical location for an OCD lesion in the knee?





Explanation

The most common location for osteochondritis dissecans (OCD) in the knee is the lateral aspect of the medial femoral condyle. This classic location accounts for approximately 70-80% of knee OCD lesions. A helpful mnemonic is 'LAME' (Lateral Aspect Medial Epicondyle/Condyle).

Question 40

A 30-year-old patient sustains a displaced intracapsular femoral neck fracture oriented at an angle of 75 degrees to the horizontal (Pauwels type III). The surgeon aims to optimize the biomechanical stability of the construct to prevent varus collapse. Which of the following fixation constructs provides the highest biomechanical resistance to the high shear forces inherent in this fracture pattern?





Explanation

Pauwels type III femoral neck fractures are highly vertical and experience massive shear forces, leading to high rates of varus collapse and nonunion when fixed with standard cancellous screws. Biomechanical studies have demonstrated that a fixed-angle device, such as a Dynamic Hip Screw (DHS), paired with an anti-rotation screw, provides superior construct stiffness and resistance to vertical shear compared to multiple cancellous screws.

Question 41

What is the primary mechanical and chemical advantage of incorporating Vitamin E (alpha-tocopherol) into highly cross-linked polyethylene (HXLPE) in total joint arthroplasty?





Explanation

Vitamin E is an antioxidant that acts as a free radical scavenger. By adding Vitamin E to highly cross-linked polyethylene (HXLPE), manufacturers can avoid the post-irradiation remelting or annealing steps that decrease mechanical strength. This provides a bearing surface that maintains high mechanical strength and fatigue resistance while effectively preventing long-term oxidative degradation.

Question 42

A 14-year-old boy presents with a diaphyseal femur lesion accompanied by an 'onion-skin' periosteal reaction. Biopsy reveals uniform small round blue cells. Molecular analysis demonstrates a t(11;22)(q24;q12) translocation. Which of the following fusion genes is pathognomonic for this tumor?





Explanation

The clinical scenario and t(11;22) translocation are classic for Ewing sarcoma, which is characterized by the EWS-FLI1 fusion gene in approximately 85% of cases. SYT-SSX is associated with Synovial Sarcoma; TLS-CHOP with Myxoid Liposarcoma; PAX3-FKHR with Alveolar Rhabdomyosarcoma; and COL1A1-PDGFB with Dermatofibrosarcoma protuberans.

Question 43

In a patient with negative ulnar variance, which of the following best describes the altered biomechanics across the radiocarpal joint that predisposes the patient to Kienbock's disease?





Explanation

Negative ulnar variance decreases the normal load borne by the ulnocarpal joint and triangular fibrocartilage complex (which is normally about 20%). This disproportionately increases the compressive forces transmitted from the distal radius to the lunate, leading to mechanical overload, microtrauma, and predisposing the lunate to avascular necrosis (Kienbock's disease).

Question 44

A 35-year-old male arrives in the emergency department intubated, sedated, and unexaminable following a high-speed motor vehicle collision. Radiographs reveal a C5-C6 bilateral facet dislocation. Which of the following is the most appropriate next step in management?





Explanation

In an obtunded or unexaminable patient with a cervical facet dislocation, an MRI is mandatory prior to closed or open reduction to rule out a herniated disc. If a disc herniation is present, a closed reduction could cause the disc material to be pushed into the spinal cord, leading to catastrophic neurologic injury. An anterior approach is generally required first in these cases.

Question 45

During a posterior-stabilized total knee arthroplasty, the trial reduction reveals that the knee is excessively tight in both flexion and extension. Which of the following is the most appropriate surgical step to balance the knee?





Explanation

When a knee is symmetrically tight in both flexion and extension, the overall joint space (global gap) is too small. The easiest and most appropriate first step is to decrease the thickness of the tibial polyethylene insert. If the thinnest poly is already being used, the proximal tibia should be recut to increase both the flexion and extension gaps equally.

Question 46

Which of the following radiographic parameters best evaluates the integrity of the distal tibiofibular syndesmosis on a standard AP view of the ankle?





Explanation

On standard AP and mortise radiographs of the ankle, the tibiofibular clear space should be less than 6 mm when measured 1 cm proximal to the tibial plafond. A measurement of 6 mm or greater indicates a high likelihood of syndesmotic injury. Tibiofibular overlap should be >6 mm on the AP view and >1 mm on the mortise view.

Question 47

During the 'ligamentization' process of a bone-patellar tendon-bone autograft following an ACL reconstruction, at which post-operative timeline is the graft at its weakest biomechanically?





Explanation

The autograft undergoes a process of necrosis, revascularization, and remodeling known as ligamentization. The graft is mechanically weakest during the revascularization and repopulation phase, which typically reaches its nadir around 6 to 8 weeks post-operatively. During this time, the graft is highly susceptible to elongation or rupture.

Question 48

According to the Herring Lateral Pillar Classification for Legg-Calve-Perthes disease, a patient whose lateral pillar maintains 60% of its original height falls into which group, and what is the typical prognosis for an 8-year-old child in this group?





Explanation

Herring Group B indicates that the lateral pillar maintains between 50% and 100% of its original height. In an 8-year-old child, Group B (and B/C border) hips generally have a fair to poor prognosis with non-operative treatment but show significantly improved outcomes with surgical containment (such as a proximal femoral varus osteotomy or pelvic osteotomy). Group C (<50% height) generally has a poor prognosis.

Question 49

A peripheral nerve injury is classified as a Sunderland Grade III. Which of the following structural components of the nerve remains intact?





Explanation

A Sunderland Grade III injury involves disruption of the axon and the endoneurium, but the perineurium and epineurium remain intact. Grade I is neurapraxia (focal demyelination). Grade II involves axon disruption with intact endoneurium. Grade IV involves disruption of the axon, endoneurium, and perineurium, leaving only the epineurium intact. Grade V is a complete nerve transection.

Question 50

According to Hertel's criteria, which of the following anatomic fracture characteristics is the strongest predictor of ischemia and subsequent avascular necrosis of the humeral head in proximal humerus fractures?





Explanation

Hertel described specific radiographic criteria that predict ischemia of the humeral head following proximal humerus fractures. The strongest predictors include a metaphyseal head extension (the length of the calcar attached to the articular segment) of less than 8 mm, disruption of the medial hinge, and a basicervical/anatomic neck fracture line. An intact medial hinge is protective.

Question 51

In adult spinal deformity surgery, achieving optimal sagittal balance is critical. The goal for restoring lumbar lordosis (LL) is typically based on the patient's pelvic incidence (PI). What is the generally accepted target relationship between PI and LL?





Explanation

In sagittal plane deformity correction, the target is a PI-LL mismatch of less than 10 degrees (ideally LL = PI +/- 9 degrees). This helps ensure that the patient can maintain an upright posture with minimal energy expenditure and reduces the risk of adjacent segment disease and mechanical failure.

Question 52

Following a Zone II flexor digitorum profundus (FDP) repair, which of the following rehabilitation protocols primarily relies on active extension and passive flexion utilizing rubber band traction attached to a dorsal blocking splint?





Explanation

The Kleinert protocol utilizes a dorsal blocking splint with dynamic rubber band traction attached to the involved finger's nail. This allows the patient to perform active extension (pulling against the rubber band) while flexion is entirely passive (via the recoil of the rubber band). The Duran protocol relies on passive flexion and extension exercises performed by the patient or therapist without dynamic traction.

Question 53

Which of the following clinical or radiographic features most reliably differentiates an osteoblastoma from an osteoid osteoma?





Explanation

Osteoblastoma and osteoid osteoma are histologically identical, both featuring woven bone lined by prominent osteoblasts. The primary differentiating feature is size; osteoblastomas have a nidus greater than 2 cm (some sources use >1.5 cm), whereas osteoid osteomas are smaller. Additionally, the pain of osteoblastoma is often not predictably relieved by NSAIDs/aspirin, unlike osteoid osteoma.

Question 54

The spring ligament complex is a critical static stabilizer of the medial longitudinal arch. Which of its components is most frequently degenerated or torn in adult acquired flatfoot deformity associated with posterior tibial tendon dysfunction?





Explanation

The superomedial calcaneonavicular ligament is the most robust portion of the spring ligament complex and serves as a critical sling for the talar head. It is the most commonly torn or attenuated component in adult acquired flatfoot deformity associated with posterior tibial tendon dysfunction (PTTD).

Question 55

A 68-year-old female experiences recurrent anterior dislocations following a right total hip arthroplasty performed via a posterior approach. Radiographs show the acetabular component has 55 degrees of inclination and 35 degrees of anteversion. The femoral stem is in neutral version. Which of the following is the most appropriate definitive management?





Explanation

The acetabular component is excessively anteverted (35 degrees) and over-inclined (55 degrees). The normal target (Lewinnek safe zone) is typically 15-20 degrees of anteversion and 40-45 degrees of inclination. Excessive anteversion strongly predisposes to anterior dislocation. The appropriate definitive treatment is revision of the malpositioned acetabular component to restore appropriate anteversion and inclination.

Question 56

Demineralized bone matrix (DBM) is commonly used as a bone graft extender in orthopedic surgery. Which of the following best describes its primary biologic properties?





Explanation

Demineralized bone matrix (DBM) is osteoinductive (due to the release of bone morphogenetic proteins [BMPs] during the acid demineralization process) and osteoconductive (providing a collagen scaffold for bone growth). It is not osteogenic, because the sterilization and processing steps destroy all viable cells (osteoblasts and osteoprogenitor cells).

Question 57

A 22-year-old rugby player undergoes stabilization for recurrent anterior shoulder instability. Arthroscopy reveals 15% anterior glenoid bone loss and a large, engaging Hill-Sachs lesion. An arthroscopic Bankart repair is planned along with a 'remplissage' procedure. What structure is transferred or tenodesed into the humeral defect during a remplissage?





Explanation

The remplissage procedure involves tenodesis of the infraspinatus tendon and the underlying posterior joint capsule into a large, engaging Hill-Sachs defect. This essentially converts an intra-articular defect into an extra-articular one and acts as a posterior checkrein, preventing the humeral head defect from engaging the anterior glenoid rim during external rotation.

Question 58

In a 12-year-old boy presenting with a unilateral slipped capital femoral epiphysis (SCFE), which of the following endocrine disorders is the strongest indication for prophylactic in situ pinning of the asymptomatic contralateral hip?





Explanation

Atypical SCFE occurs in patients with endocrine disorders (such as hypothyroidism, growth hormone deficiency, and panhypopituitarism) or in children outside the typical age range. These patients have a significantly higher rate of bilateral involvement, approaching 100% in some series for certain endocrinopathies. Hypothyroidism is a classic and strong indication for prophylactic pinning of the contralateral hip.

Question 59

When performing a fasciotomy for suspected compartment syndrome of the hand, how many dorsal incisions are typically required to decompress the interosseous compartments, and where are they optimally placed?





Explanation

There are 10 compartments in the hand (4 dorsal interossei, 3 volar interossei, adductor pollicis, hypothenar, thenar). The standard dorsal approach for decompressing the interosseous compartments involves two longitudinal incisions: one placed over the 2nd metacarpal and one over the 4th metacarpal. This allows access to both the dorsal and volar interossei via the intermetacarpal spaces.

Question 60

During an anterior intrapelvic (modified Stoppa) approach for fixation of an acetabular fracture, life-threatening hemorrhage is encountered just posterior to the superior pubic ramus. This is most likely due to an iatrogenic injury to the 'corona mortis,' which represents an abnormal vascular anastomosis between which two systems?





Explanation

The corona mortis ('crown of death') is a common and clinically significant anatomical variant representing an anastomosis between the external iliac system (or its inferior epigastric branch) and the obturator system (a branch of the internal iliac). It crosses the superior pubic ramus approximately 4-5 cm lateral to the symphysis pubis and is at high risk of injury during anterior pelvic and acetabular exposures.

Question 61

In modern metal-on-polyethylene total hip arthroplasty, the development of an adverse local tissue reaction (ALTR) often referred to as 'trunnionosis' is most commonly driven by which of the following mechanisms at the head-neck taper?





Explanation

Trunnionosis in modern modular total hip arthroplasty is primarily caused by mechanically assisted crevice corrosion (MACC). The micromotion at the modular head-neck junction (fretting) destroys the protective passivation layer of the metal, and the local restricted fluid environment (crevice) becomes highly acidic, leading to accelerated localized corrosion and the release of metal ions that trigger an adverse local tissue reaction (ALTR).

Question 62

According to the Denis classification of sacral fractures, a Zone 3 fracture is anatomically located central to the neural foramina. This fracture pattern carries the highest risk of injury to which of the following neural structures?





Explanation

Denis classified sacral fractures into three zones based on their relationship to the neural foramina. Zone 1 (alar) fractures are lateral to the foramina. Zone 2 (foraminal) fractures involve the foramina and have the highest risk of radiculopathy, typically L5 or S1. Zone 3 (central) fractures involve the spinal canal medial to the foramina and carry the highest risk (over 50%) of cauda equina syndrome, resulting in bowel, bladder, and sexual dysfunction.

Question 63

A 3-month-old infant is being treated for developmental dysplasia of the hip (DDH) with a Pavlik harness. During a follow-up visit, the parents note that the infant is no longer actively extending the knee on the affected side. What is the most appropriate immediate management?





Explanation

Decreased active knee extension in an infant wearing a Pavlik harness is the classic presentation of a femoral nerve palsy, typically caused by excessive hip flexion. The standard of care is the immediate cessation of the Pavlik harness and observation. The palsy usually resolves within days to a couple of weeks, after which alternative bracing or casting can be considered.

Question 64

A 45-year-old construction worker presents with chronic wrist pain. Radiographs reveal a scaphoid nonunion advanced collapse (SNAC). Which of the following findings is an absolute contraindication to performing a proximal row carpectomy (PRC)?





Explanation

Proximal row carpectomy (PRC) relies on creating a new articulation between the lunate fossa of the distal radius and the proximal pole of the capitate. Therefore, any pre-existing degenerative changes or arthritis at the proximal pole of the capitate (or the lunate fossa) are an absolute contraindication to PRC. In such cases, a four-corner fusion (which relies on an intact radiolunate joint) is typically the preferred salvage procedure.

Question 65

A 55-year-old male with cervical myelopathy secondary to ossification of the posterior longitudinal ligament (OPLL) is evaluated for surgery. Imaging shows a 'K-line negative' cervical spine. What is the most appropriate surgical approach?





Explanation

The K-line is a straight line connecting the midpoints of the spinal canal at C2 and C7 on a lateral radiograph. If the OPLL mass crosses this line anteriorly, the patient is 'K-line negative'. In K-line negative patients, a posterior-only decompression (laminectomy or laminoplasty) is ineffective because the spinal cord will not sufficiently drift dorsally away from the anterior compressive mass. An anterior approach (like ACCF) or a combined anterior-posterior approach is required for adequate decompression.

Question 66

A 72-year-old patient sustains a periprosthetic femur fracture around a total hip arthroplasty following a mechanical fall. Radiographs demonstrate a fracture around the stem. The stem is radiographically loose, but there is adequate proximal bone stock. According to the Vancouver classification, what is the standard treatment for this injury?





Explanation

This is a Vancouver B2 fracture (fracture around the stem, loose stem, adequate bone stock). The standard of care for a Vancouver B2 fracture is revision arthroplasty using a cementless long bypass stem (such as a fully porous-coated or fluted tapered modular stem) that bypasses the most distal fracture line by at least two cortical diameters. ORIF alone is contraindicated for a loose stem and is associated with high failure rates.

Question 67

During an anatomical reconstruction of the posterolateral corner (PLC) of the knee, accurate tunnel placement is critical. Which of the following accurately describes the femoral attachment site of the fibular collateral ligament (FCL)?





Explanation

The femoral footprint of the fibular collateral ligament (FCL) is situated slightly proximal and posterior to the lateral epicondyle. The popliteus tendon (PLT) femoral attachment is located slightly anterior and distal to the FCL attachment, within the popliteal sulcus. Identifying the lateral epicondyle is a key surgical landmark for accurate isometric reconstruction of the PLC.

Question 68

A 60-year-old male undergoes wide resection of a massive pelvic tumor. Pathology confirms a diagnosis of dedifferentiated chondrosarcoma. Which of the following is the hallmark histological finding for this tumor?





Explanation

Dedifferentiated chondrosarcoma is characterized by a distinctive 'biphasic' histological pattern. It consists of a low-grade hyaline cartilage tumor that abruptly juxtaposes against a high-grade, non-cartilaginous spindle cell sarcoma (such as osteosarcoma, fibrosarcoma, or undifferentiated pleomorphic sarcoma) without a transitional zone. This entity carries a very poor prognosis.

Question 69

A 55-year-old poorly controlled diabetic patient presents with a swollen, erythematous, and warm right foot. Radiographs show fragmentation, debris, and subluxation of the midfoot joints. Pulses are bounding. According to the Eichenholtz classification, this is Stage 1 Charcot arthropathy. What is the most appropriate initial management?





Explanation

Eichenholtz Stage 1 (development/fragmentation) of Charcot neuroarthropathy presents with active inflammation (red, hot, swollen foot) and radiographic evidence of osteopenia, fragmentation, and joint subluxation. The gold standard of treatment during this acute, active phase is strict offloading and immobilization, typically achieved with a Total Contact Cast (TCC). Surgery in Stage 1 is generally avoided due to profound hyperemia, severe osteopenia, and high failure rates.

Question 70

A 35-year-old unrestrained driver sustains a highly comminuted distal femur fracture, including a coronal plane fracture of the lateral femoral condyle (Hoffa fracture). Which of the following muscle groups exerts a deforming force that typically displaces the lateral Hoffa fragment posteriorly and inferiorly?





Explanation

A Hoffa fracture is a coronal shear fracture of the femoral condyle, most commonly involving the lateral condyle. The lateral head of the gastrocnemius and the popliteus tendon attach to the posterior and lateral aspects of the lateral femoral condyle. Their origin on the fragment creates a deforming force that pulls the lateral Hoffa fragment posteriorly and inferiorly, necessitating secure internal fixation (often with AP or PA lag screws).

Question 71

An 11-year-old boy presents with an acute-on-chronic slipped capital femoral epiphysis (SCFE) of the left hip. Prophylactic in situ pinning of the asymptomatic contralateral right hip is most strongly indicated in patients with which of the following clinical profiles?





Explanation

Prophylactic pinning of the contralateral hip in a patient with a unilateral SCFE is highly recommended for patients with endocrine disorders (such as hypothyroidism, panhypopituitarism, or renal osteodystrophy), patients who have had prior radiation therapy, or patients who are relatively young (often defined as <10 years for girls and <11-12 years for boys) or have open triradiate cartilages. These factors significantly increase the risk of a subsequent contralateral slip.

Question 72

In bone biology, the Wnt signaling pathway is crucial for osteoblastogenesis and bone formation. Sclerostin is a key negative regulator of this pathway. By binding to which of the following receptors does sclerostin exert its inhibitory effect?





Explanation

Sclerostin, a glycoprotein secreted primarily by osteocytes, acts as a potent inhibitor of the canonical Wnt signaling pathway. It does so by binding to the LRP5 and LRP6 coreceptors on the osteoblast surface, preventing Wnt ligands from binding. This inhibition reduces intracellular accumulation of beta-catenin, thereby decreasing bone formation. Monoclonal antibodies targeting sclerostin (e.g., romosozumab) exploit this mechanism to treat osteoporosis.

Question 73

A patient presents with a chronic Boutonniere deformity following an untreated injury to the extensor mechanism of the finger. The development of this deformity is mechanically driven by the rupture or attenuation of the central slip, followed by which of the following biomechanical shifts?





Explanation

A Boutonniere deformity is characterized by proximal interphalangeal (PIP) joint flexion and distal interphalangeal (DIP) joint hyperextension. It is initiated by the disruption of the central slip of the extensor tendon (Zone III). This failure allows the triangular ligament to attenuate, leading to the volar (palmar) subluxation of the lateral bands past the axis of rotation of the PIP joint. The lateral bands then become flexors of the PIP joint while continuing to exert a hyperextension force on the DIP joint.

Question 74

A 40-year-old female sustains a Levine-Edwards Type IIa Hangman's fracture (traumatic spondylolisthesis of the axis) following a motor vehicle collision. Radiographs demonstrate severe angulation with minimal translation. What is the effect of applying acute cervical traction in the management of this specific fracture subtype?





Explanation

The Levine-Edwards Type IIa Hangman's fracture is caused by a flexion-distraction mechanism, resulting in severe angulation but minimal translation. Because the primary injury involves significant posterior soft tissue and intervertebral disc disruption with an element of distraction, the application of cervical traction is strictly contraindicated. Traction can lead to extreme overdistraction of the fracture site and catastrophic neurologic deficit. Management involves closed reduction with slight extension and compression, followed by halo vest immobilization.

Question 75

A 68-year-old patient who underwent a primary posterior-stabilized (PS) total knee arthroplasty 18 months ago presents with anterior knee pain and a palpable 'catch' or 'clunk' in the knee. The classic patellar clunk syndrome occurs during which of the following phases of knee range of motion?





Explanation

Patellar clunk syndrome is a complication most commonly associated with posterior-stabilized (PS) total knee arthroplasty designs. A fibrosynovial nodule forms at the superior pole of the patella. As the knee is flexed, the nodule drops into the intercondylar box of the femoral component. As the knee is actively extended, typically between 45 and 30 degrees of flexion, the nodule catches on the superior edge of the intercondylar box and pops out, producing a painful 'clunk'.

Question 76

During a Latarjet procedure for recurrent anterior shoulder instability with significant glenoid bone loss, the transferred coracoid block provides both a static bony block and a dynamic 'sling effect'. Which anatomical structure is primarily responsible for generating this dynamic sling effect?





Explanation

The Latarjet procedure provides stability through three distinct mechanisms: 1) the static bony block of the transferred coracoid, 2) the dynamic 'sling effect' of the conjoint tendon (comprising the short head of the biceps and the coracobrachialis), and 3) the capsular repair (usually the CA ligament stump to the capsule). When the arm is abducted and externally rotated, the conjoint tendon tightens and acts as a sling against the lower subscapularis and anterior-inferior capsule, reinforcing anterior stability.

Question 77

A 24-year-old female presents with a slow-growing, painless mass on the posterior aspect of her distal femur. Radiographs show a densely ossified mass attached to the posterior cortex by a broad base. Biopsy suggests a low-grade parosteal osteosarcoma. Which of the following molecular alterations is pathognomonic and critical in distinguishing this lesion from benign mimics like myositis ossificans?





Explanation

Parosteal osteosarcoma is a low-grade, surface-based osteosarcoma that typically arises on the posterior aspect of the distal femur. It is characterized at the molecular level by the amplification of the MDM2 and CDK4 genes (located on chromosome 12q13-15). Identification of MDM2 amplification via FISH or immunohistochemistry is highly sensitive and specific, helping distinguish parosteal osteosarcoma from benign reactive conditions like myositis ossificans or osteochondromas.

Question 78

A 22-year-old elite soccer player presents with acute lateral foot pain after an inversion injury. Radiographs show a fracture at the base of the fifth metatarsal. To be accurately classified as a true 'Jones fracture' (Zone 2), the fracture line must anatomically involve which of the following regions?





Explanation

Fractures of the proximal fifth metatarsal are divided into three zones. Zone 1 is a pseudo-Jones fracture, an avulsion at the tuberosity involving the peroneus brevis and plantar fascia. Zone 2 is a true Jones fracture, which occurs at the metaphyseal-diaphyseal junction and intra-articularly extends into the fourth-fifth intermetatarsal articulation. Zone 3 is a proximal diaphyseal stress fracture. Zone 2 and 3 fractures have a high risk of nonunion due to an interosseous watershed blood supply.

Question 79

A 28-year-old male is evaluated for acute compartment syndrome following a high-energy tibial plateau fracture. Clinical examination is equivocal, so intra-compartmental pressure monitoring is performed. Which of the following thresholds is universally considered the most reliable indicator for emergent fasciotomy?





Explanation

The diagnosis of acute compartment syndrome using continuous or absolute pressure measurements has largely been replaced by the concept of 'delta P' (ΔP). Delta P is calculated as the Diastolic Blood Pressure minus the Intra-compartmental Pressure. A ΔP of less than 30 mmHg indicates inadequate capillary perfusion pressure, signifying tissue ischemia, and is an absolute indication for emergent fasciotomy.

Question 80

Infantile tibia vara (Blount's disease) is a developmental condition resulting in progressive varus deformity. Which of the following combinations represents the most significant risk factors for the development of infantile Blount's disease?





Explanation

Infantile tibia vara (Blount's disease) is characterized by an abnormal ossification of the medial aspect of the proximal tibial physis, leading to a progressive varus deformity. It is mechanically driven by excessive compressive forces on the medial physis. Early walking (before 1 year of age) and clinical obesity are the two most strongly associated risk factors, as they subject the immature medial physis to disproportionately high mechanical loads. It is also more common in children of African descent.

Question 81

A 25-year-old male presents with a slow-growing soft tissue mass in his foot. Biopsy confirms synovial sarcoma. Which of the following cytogenetic abnormalities is most characteristically associated with this tumor?





Explanation

Synovial sarcoma is characterized by the t(X;18)(p11;q11) translocation, resulting in the SYT-SSX fusion gene. This is tested frequently on board exams. t(11;22) is associated with Ewing sarcoma, t(12;16) with myxoid liposarcoma, and t(2;13) with alveolar rhabdomyosarcoma.

Question 82

A 6-week-old female is being treated with a Pavlik harness for developmental dysplasia of the hip. At a follow-up visit, the mother notes the infant is no longer actively kicking her affected leg. Physical examination reveals decreased active knee extension but normal sensation. Which of the following is the most likely cause?





Explanation

Femoral nerve palsy is a known complication of Pavlik harness treatment and is caused by excessive hip flexion. The anterior strap should be adjusted to decrease flexion. Excessive abduction in the harness is classically associated with an increased risk of avascular necrosis (AVN) of the femoral head.

Question 83

In the acute management of a hemodynamically unstable patient with an anterior-posterior compression (APC) pelvic ring injury, what is the correct anatomic landmark for the placement of a circumferential pelvic sheet or binder?





Explanation

A pelvic binder or sheet must be placed at the level of the greater trochanters to effectively reduce the pelvic volume and close an 'open book' pelvis. Placement over the iliac crests is less mechanically effective and may paradoxically open the pelvis further or cause dangerous abdominal compression.

Question 84

A 50-year-old construction worker presents with chronic wrist pain and a history of remote trauma. Radiographs reveal scapholunate advanced collapse (SLAC). According to the predictable progression of SLAC, which articulation is characteristically spared from degenerative changes, allowing for salvage procedures such as a four-corner fusion?





Explanation

In SLAC wrist, arthritis predictably progresses from the radial styloid-scaphoid (Stage I) to the entire radioscaphoid joint (Stage II), and then to the capitolunate joint (Stage III). The radiolunate joint is characteristically spared because of its concentric, congruent articulation, which makes motion-preserving salvage procedures like proximal row carpectomy or four-corner fusion possible.

Question 85

During a primary total knee arthroplasty, after making the standard bony cuts, the surgeon uses spacer blocks and notes that the knee is tight in extension but balanced in flexion. Which of the following is the most appropriate next step to balance the knee?





Explanation

If a knee is tight in extension but balanced in flexion, the extension gap needs to be increased without affecting the flexion gap. Resecting more distal femur or releasing the posterior capsule will achieve this. Resecting additional proximal tibia would increase both gaps symmetrically.

Question 86

An 82-year-old male sustains a Type II odontoid fracture after a low-energy ground-level fall. He is neurologically intact. When discussing non-operative vs. operative management, what is the most significant concern regarding the use of a halo vest immobilizer in this specific patient demographic?





Explanation

The use of a halo vest in the elderly (generally >65, and especially >80 years old) is associated with high rates of morbidity (pneumonia, respiratory distress, dysphagia) and significantly increased mortality compared to rigid cervical collars or surgical fixation. Therefore, its use is largely contraindicated in this demographic.

Question 87

Following an anterior cruciate ligament (ACL) reconstruction, a patient complains of a loss of terminal knee extension. A sagittal MRI reveals the tibial tunnel is positioned significantly anterior to the Blumensaat line with the knee in full extension. What is the most likely complication associated with this tunnel malposition?





Explanation

If the tibial tunnel is placed too anteriorly, the ACL graft will impinge against the roof of the intercondylar notch (the Blumensaat line) during terminal knee extension. This leads to a loss of extension (extension deficit), localized pain, and potential graft attrition or failure.

Question 88

A 55-year-old patient with poorly controlled diabetes presents with a red, hot, swollen right foot. Radiographs reveal periarticular osteopenia, osseous fragmentation, and subluxation at the tarsometatarsal joints. According to the Eichenholtz classification of Charcot arthropathy, what stage is this, and what is the primary pathophysiologic process occurring?





Explanation

Eichenholtz Stage 1 is the 'development' or 'fragmentation' stage, characterized clinically by a red, hot, swollen foot and radiographically by bony debris at articular margins, fragmentation, joint subluxation/dislocation, and loss of joint space. Stage 2 is coalescence, and Stage 3 is consolidation/remodeling.

Question 89

Recombinant human bone morphogenetic protein-2 (rhBMP-2) stimulates osteoblastic differentiation primarily through binding to cell surface serine/threonine kinase receptors. Upon activation, which intracellular signaling molecules are phosphorylated and translocated to the nucleus to regulate gene transcription?





Explanation

Bone Morphogenetic Proteins (BMPs) signal through cell surface serine/threonine kinase receptors. Once bound, they phosphorylate receptor-regulated Smads (R-Smads), specifically Smads 1, 5, and 8. These complex with Smad 4 to translocate to the nucleus and upregulate osteogenic genes like Runx2.

Question 90

A 34-year-old male presents with a closed spiral fracture of the distal third of the humeral shaft (Holstein-Lewis fracture). On initial examination, he has an intact radial nerve. Following a closed reduction maneuver and application of a coaptation splint, he develops a complete radial nerve palsy. What is the most appropriate next step in management?





Explanation

A secondary (post-reduction) radial nerve palsy in the setting of a humeral shaft fracture is a widely accepted absolute indication for immediate surgical exploration. The primary concern is that the nerve may have become entrapped between the fracture fragments during the reduction.

Question 91

A 65-year-old male with a metal-on-polyethylene total hip arthroplasty presents with new-onset groin pain 8 years postoperatively. Radiographs show a well-fixed stem and cup. Joint aspiration yields fluid with elevated cobalt levels but normal chromium levels. MRI with MARS sequencing shows a large cystic mass adjacent to the joint. What is the most likely diagnosis?





Explanation

Elevated serum or synovial fluid cobalt levels out of proportion to chromium levels in the setting of a non-metal-on-metal THA strongly suggests mechanically assisted crevice corrosion (MACC) at the modular head-neck junction (trunnionosis). This causes an adverse local tissue reaction (ALTR), frequently presenting as a pseudotumor or cystic mass.

Question 92

A 12-year-old obese male presents with a left slipped capital femoral epiphysis (SCFE). Which of the following patient profiles most strongly indicates the need for prophylactic in situ pinning of the asymptomatic contralateral hip?





Explanation

Prophylactic pinning of the contralateral hip in SCFE is generally recommended in patients with endocrine disorders (e.g., hypothyroidism, growth hormone deficiency, renal osteodystrophy) or prior radiation therapy due to a very high risk (often >50%) of developing a bilateral slip.

Question 93

During a zone II flexor digitorum profundus (FDP) tendon repair, the surgeon elects to increase the number of suture strands crossing the repair site from two to four. What is the primary biomechanical advantage of this technique?





Explanation

The ultimate tensile strength and resistance to gap formation of a flexor tendon repair are directly proportional to the number of core suture strands crossing the repair site. Increasing from a 2-strand to a 4-strand repair provides the necessary strength to withstand the forces of early active mobilization protocols.

Question 94

A 14-year-old female gymnast presents with chronic lower back pain. Radiographs reveal a Grade II isthmic spondylolisthesis at L5-S1. What is the pathognomonic finding associated with this condition on oblique lumbar radiographs?





Explanation

The 'Scotty dog with a collar' (or decapitated Scotty dog) on an oblique lumbar radiograph represents a defect in the pars interarticularis (spondylolysis), which is the underlying cause of an isthmic spondylolisthesis. The 'inverted Napoleon hat sign' is seen on AP radiographs in severe (Grade III/IV) spondylolisthesis.

Question 95

A 25-year-old female presents with a slowly enlarging mass on the posterior aspect of her distal femur. Plain radiographs show a heavily ossified, juxtacortical mass with a broad base on the surface of the bone, and a radiolucent cleft separating portions of the tumor from the underlying cortex. Medullary involvement is minimal. What is the most likely diagnosis?





Explanation

Parosteal osteosarcoma is a low-grade surface osteosarcoma typically found on the posterior distal femur. Radiographically, it appears as a heavily ossified mass with a broad base and a characteristic 'string sign' (a radiolucent cleft separating the tumor from the underlying cortex). It is distinct from periosteal osteosarcoma, which has a sunburst or hair-on-end appearance and is more chondroblastic.

Question 96

In the pathophysiology of acute compartment syndrome, the initial microvascular event that initiates the cascade toward ischemic necrosis of muscle is a critical reduction in which of the following pressures?





Explanation

Compartment syndrome occurs when increased tissue pressure within a closed fascial space compromises local circulation. The initial event is that tissue fluid pressure rises above capillary perfusion pressure (or venous pressure, thereby backing up the capillary bed). This leads to capillary collapse, hypoxia, and a vicious cycle of further edema and muscle necrosis.

Question 97

Articular cartilage is divided into distinct structural zones. Which zone contains the highest concentration of collagen, with fibrils aligned strictly parallel to the articular surface to resist shear forces?





Explanation

The superficial (tangential) zone of articular cartilage contains the highest concentration of collagen (primarily Type II) and the lowest concentration of proteoglycans. The collagen fibrils in this zone are aligned parallel to the joint surface specifically to resist shear forces.

Question 98

A 24-year-old elite skier presents with lateral ankle pain and a snapping sensation behind the lateral malleolus. Physical examination confirms subluxation of the peroneal tendons with resisted eversion and dorsiflexion. Which anatomical structure is primarily responsible for preventing this condition, and is likely deficient or torn?





Explanation

The superior peroneal retinaculum (SPR) is the primary static restraint to subluxation and dislocation of the peroneal tendons out of the retromalleolar groove. Disruption, stripping, or avulsion (e.g., 'fleck sign') of the SPR is the hallmark of peroneal tendon instability.

Question 99

In a patient with anterior shoulder instability, a bipolar bone loss lesion is identified. The 'glenoid track' concept is utilized to determine the risk of engagement. A Hill-Sachs lesion is considered 'engaging' (off-track) if its medial margin falls in which of the following locations relative to the glenoid track?





Explanation

The glenoid track represents the contact area of the glenoid on the humeral head during abduction and external rotation. If the medial margin of the Hill-Sachs lesion extends more medial than the medial margin of the glenoid track, it is considered 'off-track' and will engage the anterior glenoid rim, necessitating a procedure like Remplissage or a bone block.

Question 100

During the Ponseti method for the conservative correction of idiopathic clubfoot (talipes equinovarus), the components of the deformity are addressed in a specific sequence. What is the very first component of the deformity that must be corrected during the initial casting phase?





Explanation

The Ponseti method dictates a specific order of correction summarized by the acronym CAVE: Cavus, Adductus, Varus, Equinus. The first step is to correct the Cavus by elevating the first ray to align the forefoot with the hindfoot, establishing a solid lever arm for subsequent correction.

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