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Arab Orthopaedic Board MCQs - Part 36

27 Apr 2026 128 min read 86 Views
Arab Ortho Board MCQs - Part 35

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This article provides essential research regarding Arab Orthopaedic Board MCQs - Part 36. Practice Arab Orthopaedic Board MCQs Part 36. Review orthopedic surgery questions 1751 to 1800 for your board exam preparation.

Arab Orthopaedic Board MCQs - Part 36

Comprehensive 100-Question Exam


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Question 1

Which of the following is the recognized threshold of linear wear rate for conventional polyethylene in total hip arthroplasty above which the risk of pelvic osteolysis significantly increases?





Explanation

Osteolysis risk in THA is strongly correlated with polyethylene wear. A linear wear rate greater than 0.1 mm/year is the widely accepted threshold for the development of clinically significant periprosthetic osteolysis. Highly cross-linked polyethylene was developed to reduce wear rates below this critical threshold.

Question 2

During the ilioinguinal approach to the acetabulum, the 'corona mortis' is frequently encountered and must be ligated. This vascular structure represents an anastomosis between which two vascular systems?





Explanation

The corona mortis ('crown of death') is a vascular anastomosis between the obturator system (internal iliac) and the inferior epigastric or external iliac systems. It is located on the posterior aspect of the superior pubic ramus at an average distance of 5-6 cm from the pubic symphysis.

Question 3

In the Herring Lateral Pillar Classification of Legg-Calvé-Perthes disease, a Group B hip is defined by what percentage of lateral pillar height maintenance on an AP radiograph during the fragmentation stage?





Explanation

The Herring Lateral Pillar classification divides Perthes disease into three main groups based on the height of the lateral pillar of the capital femoral epiphysis. Group A has no involvement (100% height maintained). Group B has > 50% of the lateral pillar height maintained. Group C has < 50% height maintained.

Question 4

Which of the following stages of cancellous bone graft incorporation occurs first?





Explanation

The sequence of cancellous bone graft incorporation follows the general pattern of fracture healing: hematoma formation (inflammation) occurs first, followed by revascularization, osteoinduction (differentiation of mesenchymal stem cells into osteoblasts), osteoconduction (growth of capillaries and osteoprogenitor cells into the graft scaffolding), and finally creeping substitution.

Question 5

A 14-year-old girl presents with back pain and hamstring tightness. Radiographs show a Meyerding Grade IV L5-S1 isthmic spondylolisthesis. What is the most common neurological deficit observed if slip progression continues or during surgical reduction?





Explanation

In L5-S1 isthmic spondylolisthesis, the L5 nerve root is at greatest risk. As L5 slips anteriorly on S1, the L5 nerve root gets stretched over the posterior aspect of the sacral dome. It is also the most commonly injured root during surgical reduction of a high-grade slip.

Question 6

A 28-year-old rugby player sustains a knee injury. The dial test demonstrates 15 degrees of increased external rotation at 30 degrees of knee flexion compared to the uninjured side, but symmetric external rotation at 90 degrees. Which of the following structures is most likely injured?





Explanation

The dial test evaluates external rotation asymmetry. Increased external rotation (>10 degrees compared to the normal side) at 30 degrees of flexion, but not at 90 degrees, indicates an isolated injury to the posterolateral corner (PLC). Increased external rotation at both 30 and 90 degrees indicates a combined injury to the PLC and the posterior cruciate ligament (PCL).

Question 7

During surgical management of a 'terrible triad' injury of the elbow (coronoid fracture, radial head fracture, elbow dislocation), what is the most widely accepted sequence of repair according to the standard surgical algorithm?





Explanation

The standard surgical algorithm for a terrible triad injury emphasizes a deep-to-superficial repair from the lateral side. The sequence is typically: 1) Repair or fix the coronoid (to restore anterior stability), 2) Repair or replace the radial head, 3) Repair the lateral collateral ligament (LCL) complex. The medial collateral ligament (MCL) is only repaired if the elbow remains unstable after the lateral-sided and osseous repairs are complete.

Question 8

A 15-year-old boy presents with knee pain. Radiographs reveal a well-circumscribed, eccentrically located lytic lesion with sclerotic margins in the epiphysis of the distal femur. Histology shows polygonal mononuclear cells with longitudinal nuclear grooves and scattered multinucleated giant cells. What is the most likely diagnosis?





Explanation

Chondroblastoma typically occurs in the epiphysis or apophysis of long bones in skeletally immature patients. The classic histological appearance includes mononuclear cells with longitudinal nuclear grooves ('coffee bean' nuclei), multinucleated osteoclast-like giant cells, and 'chicken-wire' calcification. Giant cell tumor occurs in skeletally mature patients.

Question 9

A 32-year-old male sustains a Hawkins Type III talar neck fracture. This injury involves subluxation or dislocation of which of the following articulations?





Explanation

The Hawkins classification for talar neck fractures: Type I is nondisplaced; Type II is displaced with subtalar subluxation/dislocation; Type III is displaced with both subtalar and tibiotalar dislocation; Type IV (added by Canale and Kelly) involves subtalar, tibiotalar, and talonavicular dislocation.

Question 10

In total knee arthroplasty, excessive internal rotation of the femoral component will most likely lead to which of the following complications?





Explanation

Internal rotation of the femoral component in TKA medializes the trochlear groove, increasing the Q-angle and leading to lateral patellar maltracking, lateral patellar tilt, and potential lateral patellar dislocation. It also creates a tight medial flexion gap and loose lateral flexion gap.

Question 11

A patient presents with an inability to form an 'OK' sign with their thumb and index finger, instead forming a 'flat pinch'. Sensation in the hand is completely normal. Which of the following muscles is unaffected by this specific nerve palsy?





Explanation

The Anterior Interosseous Nerve (AIN) is a pure motor branch of the median nerve. It innervates the flexor pollicis longus (FPL), the radial half of the flexor digitorum profundus (FDP to index and middle fingers), and the pronator quadratus. The flexor carpi radialis is innervated by the main branch of the median nerve proximal to the AIN take-off.

Question 12

Which biomechanical property of tendons and ligaments is characterized by a decrease in stress over time when the tissue is held at a constant length?





Explanation

Stress relaxation is a viscoelastic property where the stress (force) within a material decreases over time when it is held at a constant strain (length). Creep is the increasing deformation (strain) over time under a constant load (stress). Hysteresis is the energy lost during a loading-unloading cycle.

Question 13

What is the most significant risk factor for the development of avascular necrosis (AVN) of the femoral head following a slipped capital femoral epiphysis (SCFE)?





Explanation

The Loder classification divides SCFE into stable (able to bear weight with or without crutches) and unstable (unable to bear weight). Unstable SCFE has a significantly higher rate of avascular necrosis (AVN), ranging from 20% to 50%, compared to stable SCFE which has an AVN rate of nearly 0%.

Question 14

A 45-year-old pedestrian is struck by a car and sustains a knee injury. Radiographs show a fracture of the medial tibial plateau with depression and extension into the metadiaphysis. According to the Schatzker classification, what type of fracture is this?





Explanation

Schatzker classification: I = Lateral split; II = Lateral split-depression; III = Lateral pure depression; IV = Medial plateau fracture (split or depression); V = Bicondylar plateau fracture; VI = Plateau fracture with meta-diaphyseal dissociation. A medial plateau fracture is Type IV, which typically results from a varus force and often involves higher energy.

Question 15

A 50-year-old male presents with neck pain radiating down his right arm. Examination reveals weakness in elbow extension, diminished triceps reflex, and numbness over the dorsum of the middle finger. Which cervical nerve root is most likely compressed?





Explanation

The C7 nerve root is the most commonly involved root in cervical radiculopathy. It manifests with weakness in elbow extension (triceps), wrist flexion, and finger extension; an abnormal triceps reflex; and sensory changes over the middle finger.

Question 16

A 25-year-old overhead athlete is diagnosed with a Type II SLAP lesion. He also demonstrates a 'peel-back' sign during arthroscopy. This pathology is most commonly associated with which of the following physical examination findings?





Explanation

Type II SLAP tears in overhead athletes are strongly associated with Glenohumeral Internal Rotation Deficit (GIRD) and a tight posterior capsule. The tight posterior capsule causes a posterosuperior shift of the humeral head during the late cocking phase of throwing, leading to the 'peel-back' mechanism that exacerbates the superior labral tear.

Question 17

A 60-year-old male who underwent a metal-on-metal total hip arthroplasty 8 years ago presents with groin pain and a palpable mass. Serum cobalt and chromium levels are elevated. MRI with MARS sequencing shows a cystic pseudotumor. Which type of hypersensitivity reaction is considered the primary mechanism for Adverse Local Tissue Reaction (ALTR) in metal-on-metal hips?





Explanation

ALTR or ALVAL (aseptic lymphocyte-dominated vasculitis-associated lesion) in metal-on-metal hip arthroplasty is primarily driven by a Type IV delayed-type hypersensitivity reaction to metal wear debris (specifically cobalt and chromium ions). This is a T-cell mediated response.

Question 18

The primary blood supply to the proximal pole of the scaphoid enters the bone at which anatomical location?





Explanation

The primary blood supply to the scaphoid is derived from the radial artery. The major vessels (providing 70-80% of the blood supply, including the entire proximal pole) enter the scaphoid via the dorsal ridge in a retrograde fashion. A smaller volar branch enters at the distal tubercle. This retrograde supply puts proximal pole fractures at high risk for AVN.

Question 19

In a standard Boyes tendon transfer for a high radial nerve palsy, which muscle is transferred to the extensor carpi radialis brevis to restore wrist extension?





Explanation

In standard tendon transfer algorithms for radial nerve palsy (such as the Boyes or Jones transfers), wrist extension is restored by transferring the Pronator Teres (PT) to the Extensor Carpi Radialis Brevis (ECRB). The PT is an ideal donor because of its synergistic action and adequate excursion.

Question 20

Which specific chromosomal translocation is pathognomonic for synovial sarcoma?





Explanation

Synovial sarcoma is characterized by the pathognomonic t(X;18)(p11;q11) translocation, which results in the SYT-SSX fusion gene. t(11;22) is seen in Ewing sarcoma. t(12;16) is seen in myxoid liposarcoma. t(2;13) is seen in alveolar rhabdomyosarcoma.

Question 21

A 4-month-old infant is placed in a Pavlik harness for the treatment of developmental dysplasia of the hip (DDH). Which of the following positions or strap adjustments places the infant at the highest risk for developing avascular necrosis (AVN) of the femoral head?





Explanation

Excessive abduction in a Pavlik harness places the hip at high risk for avascular necrosis (AVN) due to occlusion of the retinacular vessels against the acetabular rim. Excessive hip flexion places the infant at risk for femoral nerve palsy.

Question 22

A 19-year-old male presents with slowly progressive, unilateral weakness and atrophy of his right hand and forearm over the past 2 years. He denies sensory loss or lower extremity weakness. Cervical spine MRI in a neutral position is unremarkable, but a dynamic flexion MRI reveals anterior displacement of the posterior dura with flattening of the lower cervical cord. What is the most likely diagnosis?





Explanation

Hirayama disease (juvenile muscular atrophy of the distal upper extremity) is a cervical myelopathy predominantly affecting young males. It is caused by anterior displacement of the posterior dural sac during neck flexion, leading to cord compression and anterior horn cell ischemia, resulting in isolated distal upper extremity atrophy.

Question 23

A 35-year-old male sustains an isolated closed scapular body fracture following a motor vehicle collision. According to current evidence-based guidelines, which of the following radiographic parameters is an accepted indication for operative fixation of the scapular body?





Explanation

Operative indications for scapular body and neck fractures include medial/lateral displacement > 20 mm, angular deformity > 45 degrees, or a combination of displacement > 15 mm and angulation > 30 degrees. A glenopolar angle < 22 degrees is also an indication for surgery. Normal glenopolar angle is 30-45 degrees. Glenoid fractures typically require > 4 mm of step-off to indicate fixation.

Question 24

In a patient diagnosed with a 'skier's thumb', the mechanism of a Stener lesion involves the proximal stump of the torn ulnar collateral ligament (UCL) becoming anatomically trapped. Which structure interposes between the torn ends of the UCL?





Explanation

A Stener lesion occurs when the distal attachment of the thumb metacarpophalangeal (MCP) ulnar collateral ligament (UCL) avulses and displaces superficial to the adductor pollicis aponeurosis. This interposition prevents anatomical healing of the ligament and necessitates surgical repair.

Question 25

During a posterior-stabilized total knee arthroplasty, after making all initial bony cuts, the surgeon uses spacer blocks and notes that the joint is excessively tight in flexion but well-balanced in extension. Which of the following is the most appropriate intraoperative adjustment to balance the knee?





Explanation

A tight flexion gap with a balanced extension gap indicates that the posterior condylar offset is too large. Downsizing the femoral component decreases its anteroposterior dimension, effectively reducing posterior condylar thickness and opening the flexion gap. It often must be translated anteriorly to avoid notching the anterior femur.

Question 26

Sclerostin is a key negative regulator of bone formation that has become a therapeutic target for osteoporosis. Which of the following cells is the primary source of sclerostin, and which signaling pathway does it directly inhibit?





Explanation

Sclerostin is a glycoprotein encoded by the SOST gene and is primarily secreted by mature osteocytes. It inhibits bone formation by binding to LRP5/6 receptors on osteoblasts, thereby competitively antagonizing the canonical Wnt/beta-catenin signaling pathway.

Question 27

Which of the following genetic mutations is most frequently identified in patients with central chondrosarcoma and is also considered a hallmark of multiple enchondromatosis (Ollier disease and Maffucci syndrome)?





Explanation

Mutations in the isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) genes are found in up to 80% of central enchondromas and chondrosarcomas. They are hallmark mutations in Ollier disease and Maffucci syndrome. EXT1/2 mutations are seen in hereditary multiple exostoses. GNAS is mutated in fibrous dysplasia.

Question 28

A 55-year-old diabetic male presents with a unilaterally swollen, erythematous, and warm midfoot for the past 3 weeks. Radiographs show fragmentation of the navicular and cuneiforms with periarticular debris and subluxation. There is no open ulcer. According to the modified Eichenholtz classification, what stage is this, and what is the preferred initial management?





Explanation

The patient is in Eichenholtz Stage 1 (Development/Fragmentation stage), characterized by erythema, swelling, joint subluxation, bony fragmentation, and periarticular debris. The cornerstone of acute management for Charcot arthropathy without deep infection is strict immobilization and offloading, typically using a total contact cast (TCC). Surgery is generally contraindicated during the acute inflammatory stage.

Question 29

During an ilioinguinal approach for an anterior column acetabular fracture, the surgeon must be cautious to identify and ligate the 'corona mortis' to prevent life-threatening hemorrhage. This structure typically represents an anastomosis between which two vascular systems?





Explanation

The corona mortis (crown of death) is an important vascular anastomosis between the external iliac system (usually via the inferior epigastric artery or vein) and the internal iliac system (via the obturator artery or vein). It typically courses over the superior pubic ramus at the posterior aspect of the symphysis.

Question 30

A 42-year-old male presents with chronic wrist pain and a history of a scaphoid fracture 10 years ago. Radiographs reveal a scaphoid nonunion advanced collapse (SNAC) pattern with severe arthritis involving the radioscaphoid joint and the capitolunate joint. The radiolunate joint is perfectly preserved. What stage of SNAC wrist is this, and which procedure is most appropriate?





Explanation

SNAC staging: Stage 1 = Arthritis between the radial styloid and distal scaphoid. Stage 2 = Scaphocapitate arthritis. Stage 3 = Capitolunate arthritis. Stage 4 = Pancarpal arthritis (including radiolunate). This patient has capitolunate involvement (Stage 3). Scaphoid excision and four-corner fusion is the treatment of choice. Proximal row carpectomy (PRC) is contraindicated in Stage 3 SNAC/SLAC because PRC relies on a healthy proximal capitate articulating with the lunate fossa, which is destroyed in Stage 3.

Question 31

A 12-year-old obese male undergoes in-situ single screw fixation for a stable slipped capital femoral epiphysis (SCFE). Which of the following technical errors or clinical factors is most strongly associated with the development of postoperative chondrolysis?





Explanation

Chondrolysis is a devastating complication of SCFE characterized by acute loss of articular cartilage space. The most strongly associated iatrogenic cause is unrecognized intra-articular hardware penetration during pinning. To prevent this, the 'approach-withdraw' technique under fluoroscopy must be used to ensure the screw tip is fully within the epiphysis.

Question 32

Which of the following best describes the primary biomechanical mechanism by which Zirconia-toughened Alumina (ZTA) ceramics resist crack propagation in modern total hip arthroplasty?





Explanation

Zirconia in ZTA undergoes a phase transformation from a metastable tetragonal phase to a stable monoclinic phase when subjected to local stress (such as an advancing crack tip). This transformation is accompanied by a localized volume expansion (approximately 4%), which induces compressive stresses that close the crack tip and stop propagation. This is known as transformation toughening.

Question 33

A 14-year-old female gymnast presents with an insidious onset of lower back pain. Radiographs demonstrate a grade II L5-S1 spondylolisthesis, and oblique views reveal an obvious defect in the pars interarticularis. According to the Wiltse classification of spondylolisthesis, into which category does this patient fall?





Explanation

The Wiltse classification defines Type II as Isthmic, which involves a defect or lesion in the pars interarticularis. Subtype IIA is a stress fracture of the pars (most common in young athletes like gymnasts). Type I is dysplastic (congenital abnormalities of the upper sacrum or L5 arch). Type III is degenerative. Type IV is traumatic (fracture in areas other than the pars). Type V is pathologic.

Question 34

During reconstruction of the posterior cruciate ligament (PCL), the tibial inlay technique is theoretically designed to prevent which of the following mechanical complications associated with the traditional transtibial technique?





Explanation

The traditional transtibial PCL reconstruction technique requires the graft to bend sharply (often > 90 degrees) as it exits the posterior tibial tunnel to reach the femoral footprint. This acute angle is known as the 'killer turn' and is a site of significant mechanical stress, leading to graft abrasion, elongation, and potential failure. The tibial inlay technique secures the bone block directly to the posterior tibia, avoiding this turn.

Question 35

The Lisfranc ligament is essential for the stability of the midfoot and is often implicated in tarsometatarsal fracture-dislocations. Which of the following accurately describes the anatomical attachments of the Lisfranc ligament?





Explanation

The Lisfranc ligament is an interosseous ligament that connects the lateral aspect of the medial cuneiform to the medial base of the second metatarsal. There is notably no direct intermetatarsal ligament between the bases of the first and second metatarsals, rendering this articulation susceptible to disruption.

Question 36

Articular cartilage relies on its complex extracellular matrix to withstand compressive forces. While Type II collagen provides the primary structural fibril network, minor collagens also play critical structural roles. Which of the following describes the specific function of Type IX collagen in articular cartilage?





Explanation

In articular cartilage, Type II collagen forms the main structural network. Type IX and Type XI are minor collagens. Type IX collagen is located on the surface of Type II fibrils, where it covalently cross-links the fibrils to one another and interacts with matrix proteoglycans, providing critical structural stabilization and preventing fibril shear.

Question 37

A patient presents with a displaced posteromedial shear fracture of the tibial plateau. A direct posteromedial approach is chosen for open reduction and buttress plate fixation. During the deep dissection to expose the posteromedial surface of the tibia, which muscle must be identified and retracted laterally to safely access the fracture?





Explanation

In the posteromedial approach to the tibial plateau, the deep internervous plane is technically between the pes anserinus/semimembranosus (medial) and the medial head of the gastrocnemius (lateral). To expose the posteromedial tibia and protect the neurovascular structures of the popliteal fossa, the medial head of the gastrocnemius is retracted laterally, while the pes anserinus and hamstring tendons are retracted anteriorly/medially.

Question 38

A 28-year-old mechanic sustains a volar laceration to the proximal phalanx of his middle finger, completely transecting both the FDS and FDP tendons. This injury falls within flexor tendon Zone II. What is the anatomical landmark that defines the proximal boundary of Zone II?





Explanation

Flexor tendon Zone II (historically called 'no man's land' due to the poor outcomes of early repairs) extends from the proximal edge of the A1 pulley (at the level of the distal palmar crease) to the insertion of the Flexor Digitorum Superficialis (FDS) tendon on the middle phalanx. Both the FDS and FDP run together in a tight fibro-osseous sheath in this zone.

Question 39

A 32-year-old female presents with an extensive, locally aggressive Giant Cell Tumor of Bone (GCTB) in the distal femur that is not currently amenable to joint-sparing surgery. She is started on denosumab therapy. Which of the following best describes the cellular mechanism of action of this medication?





Explanation

Giant Cell Tumor of Bone consists of neoplastic mononuclear stromal cells that express high levels of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This RANKL recruits and activates reactive, multinucleated osteoclast-like giant cells that cause bone destruction. Denosumab is a fully human monoclonal antibody that binds to RANKL, preventing it from binding to the RANK receptor on osteoclasts/giant cells, thus halting their formation and bone resorption.

Question 40

A 6-year-old boy presents with a completely displaced, extension-type supracondylar humerus fracture (Gartland Type III). On initial examination, the hand is pale, pulseless, and cool. After a gentle closed reduction and percutaneous pinning in the OR, the hand becomes pink, warm, and has a capillary refill of 1.5 seconds, but the radial pulse remains absent on Doppler. What is the most appropriate next step in management?





Explanation

The management of a 'pink, pulseless' hand following the successful reduction and pinning of a pediatric supracondylar humerus fracture is observation. If the hand is well-perfused (warm, pink, brisk capillary refill < 2 seconds), the limb is viable. The absence of a palpable or Doppler pulse is typically due to localized vasospasm, which resolves over hours to days. Emergent vascular exploration is indicated if the hand remains 'pale and pulseless' (poorly perfused) after reduction.

Question 41

An 11-year-old boy presents with a painful mass in the diaphysis of the femur. Biopsy reveals small round blue cells. Cytogenetic analysis is pending. Which of the following chromosomal translocations is most characteristic of this tumor and what is the corresponding fusion gene product?





Explanation

The clinical and histological presentation is highly characteristic of Ewing sarcoma. The most common cytogenetic abnormality in Ewing sarcoma is the t(11;22)(q24;q12) translocation, which results in the EWS-FLI1 fusion protein. t(X;18) is associated with synovial sarcoma; t(2;13) with alveolar rhabdomyosarcoma; t(12;16) with myxoid liposarcoma; and t(9;22) is the Philadelphia chromosome seen in CML.

Question 42

A 5-year-old child sustains a Gartland type III supracondylar humerus fracture. Post-injury examination reveals an isolated anterior interosseous nerve (AIN) palsy. What is the most characteristic clinical finding associated with this specific nerve injury?





Explanation

The anterior interosseous nerve (AIN) is the most commonly injured nerve in extension-type supracondylar humerus fractures. The AIN is a pure motor nerve that innervates the flexor pollicis longus (FPL), the radial half of the flexor digitorum profundus (FDP to the index and middle fingers), and the pronator quadratus. An AIN palsy presents with weakness in flexing the thumb IP joint and index finger DIP joint, clinically resulting in the inability to form an 'OK' sign. Because it is purely motor, there is no sensory deficit.

Question 43

During a posterior-stabilized (PS) total knee arthroplasty, the surgeon evaluates the gaps and notices that the knee is tight in flexion but balanced in extension. Assuming an anterior referencing system was used, which of the following intraoperative adjustments is the most appropriate next step to balance the knee?





Explanation

A knee that is tight in flexion and balanced in extension indicates an unequal gap where the flexion gap is smaller than the extension gap. To increase the flexion gap without affecting the extension gap, the posterior condylar offset must be reduced. In an anterior referencing system, downsizing the femoral component decreases the posterior condylar dimension, thus effectively opening the flexion gap. Resecting more distal femur would increase the extension gap. Releasing the PCL is not applicable here as a PS knee implies the PCL is already resected.

Question 44

A 65-year-old male presents with deteriorating hand dexterity, a broad-based gait, and hyperreflexia. MRI shows multilevel cervical spondylosis with cord compression from C3 to C6, but with well-preserved cervical lordosis. He denies any significant axial neck pain. Which of the following surgical approaches is most appropriate?





Explanation

The patient has cervical spondylotic myelopathy involving more than 3 levels (C3-C6). In a patient with well-maintained cervical lordosis and minimal axial neck pain, a posterior motion-preserving decompression such as cervical laminoplasty is ideal. It avoids the morbidity of multilevel anterior fusion (dysphagia, pseudoarthrosis) and prevents post-laminectomy kyphosis by preserving the posterior tension band.

Question 45

In order to prevent bowstringing of the flexor tendons in the fingers, which combination of pulleys is biomechanically the most critical to preserve during hand surgery?





Explanation

The flexor tendon sheath in the fingers consists of a series of annular (A) and cruciate (C) pulleys. The A2 and A4 pulleys are the major biomechanical pulleys that arise from the periosteum of the proximal and middle phalanges, respectively. They are the most critical in preventing bowstringing of the flexor tendons during digit flexion and must be preserved or reconstructed.

Question 46

A 60-year-old female presents with dorsal midfoot pain and stiffness in the first metatarsophalangeal (MTP) joint. Radiographs show advanced joint space narrowing, a large dorsal osteophyte, and flattening of the metatarsal head (Coughlin and Shurnas Grade 3 hallux rigidus). She has failed nonoperative management. What is the gold standard surgical treatment?





Explanation

For advanced (Grade 3 or 4) hallux rigidus with diffuse joint involvement and severe pain, the gold standard surgical treatment is a first MTP joint arthrodesis. It provides reliable and durable pain relief and restores walking ability. Dorsal cheilectomy is indicated for early stages (Grades 1 and 2) where the plantar joint space is preserved.

Question 47

A 22-year-old collegiate baseball pitcher complains of posterior shoulder pain during the late cocking phase of throwing. He has a positive apprehension test but no relief with the relocation test. MRI reveals articular-sided, partial-thickness tears of the supraspinatus and a superior labrum anterior-posterior (SLAP) lesion. What is the underlying pathophysiology of this condition?





Explanation

This presentation describes 'internal impingement' (posterosuperior impingement), classically seen in overhead throwing athletes. The underlying pathophysiology is driven by posterior capsular contracture, leading to a glenohumeral internal rotation deficit (GIRD). The tight posterior capsule causes an obligate posterosuperior shift of the humeral head in extreme abduction and external rotation (late cocking phase), pinching the undersurface of the rotator cuff and superior labrum between the greater tuberosity and the posterosuperior glenoid rim.

Question 48

During secondary (indirect) fracture healing, the transition from soft callus to hard callus is mediated primarily by which of the following processes?





Explanation

Secondary fracture healing involves the formation of a soft cartilaginous callus, which is subsequently mineralized and replaced by bone. This process, where bone replaces a cartilage template, is known as endochondral ossification. Intramembranous ossification (bone formation without a cartilage template) occurs during primary fracture healing and at the periosteal margins.

Question 49

A 4-month-old female infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During the follow-up visit, the parents report she has stopped kicking her right leg. Examination reveals decreased active extension of the right knee, but intact ankle and toe movements. What is the most likely cause?





Explanation

The most common nerve injury associated with the use of a Pavlik harness is femoral nerve palsy, typically caused by hyperflexion of the hips. This leads to an inability to actively extend the knee (quadriceps weakness). It usually resolves once the flexion is decreased or the harness is temporarily discontinued. Sciatic nerve palsy is exceedingly rare in this context.

Question 50

A 35-year-old male sustains an anteroposterior compression type III (APC-III) pelvic ring injury. He is hemodynamically unstable despite initial resuscitation and the application of a pelvic binder. A FAST scan is negative. What is the most appropriate next step in management?





Explanation

In a patient with a mechanically unstable pelvic ring injury and persistent hemodynamic instability despite a pelvic binder, if intraperitoneal bleeding has been ruled out (negative FAST), the source of bleeding is assumed to be the pelvic retroperitoneum. The standard algorithm involves either emergent preperitoneal pelvic packing (PPP) or pelvic angiography with embolization to address venous or arterial hemorrhage, respectively.

Question 51

A 68-year-old male presents with severe back pain. Radiographs reveal multiple punched-out lytic lesions in the skull and a compression fracture of L2. Laboratory tests show hypercalcemia and elevated total protein. Which of the following tests is most definitive for confirming the underlying diagnosis?





Explanation

The clinical picture of 'punched-out' lytic lesions, hypercalcemia, and elevated total protein in an older adult is classic for multiple myeloma. The definitive diagnosis is made via bone marrow aspirate/biopsy (showing >10% clonal plasma cells) and demonstration of a monoclonal protein spike on serum or urine protein electrophoresis (SPEP/UPEP). Bone scans are typically cold in multiple myeloma because there is very little reactive osteoblastic activity.

Question 52

A 55-year-old male presents with a 'squeaking' sound coming from his total hip arthroplasty, which was performed 3 years ago. He is otherwise asymptomatic and radiographs are pristine. Which of the following bearing surfaces is most strongly associated with this phenomenon?





Explanation

Squeaking is a known complication almost exclusively associated with ceramic-on-ceramic (CoC) bearing surfaces in total hip arthroplasty. It is reported in up to 1-10% of cases and is thought to be multifactorial (e.g., stripe wear, edge loading from component malposition, or third-body debris). As long as the patient is asymptomatic, no surgical intervention is required.

Question 53

A 14-year-old female gymnast presents with persistent lower back pain exacerbated by extension. Lateral radiographs reveal a grade I isthmic spondylolisthesis at L5-S1. She has failed 6 months of conservative management including physical therapy, rest, and bracing. What is the most appropriate surgical treatment?





Explanation

For pediatric or adolescent patients with symptomatic isthmic spondylolisthesis who fail comprehensive nonoperative management, an in situ posterolateral instrumented fusion of the affected segment (L5-S1) is the gold standard surgical treatment. Laminectomy without fusion in a pediatric patient is contraindicated as it exacerbates instability. Interbody fusion is generally not required for low-grade slips in this age group.

Question 54

A cyclist complains of numbness in the ring and small fingers and weakness in hand grip. Examination reveals a positive Froment's sign and decreased sensation over the volar aspect of the fifth digit, but normal sensation over the dorsal ulnar aspect of the hand. Where is the most likely site of compression?





Explanation

The preservation of sensation over the dorsal ulnar hand indicates that the dorsal ulnar cutaneous nerve is spared, localizing the lesion distal to the forearm (i.e., at the wrist). Compression at Guyon's canal Zone 1 involves the main ulnar nerve trunk before it bifurcates, causing both motor weakness (positive Froment's sign, deep branch) and sensory deficits on the volar ulnar digits (superficial branch). Zone 2 compression is purely motor; Zone 3 is purely sensory.

Question 55

During open reduction and internal fixation of a tarsometatarsal fracture-dislocation, the surgeon must restore the anatomical integrity of the Lisfranc ligament. Which of the following accurately describes the anatomy of the Lisfranc ligament?





Explanation

The Lisfranc ligament is the strong, stout interosseous ligament that connects the lateral aspect of the medial cuneiform to the medial aspect of the base of the second metatarsal. There is no direct ligamentous connection between the bases of the first and second metatarsals, making this interval mechanically vulnerable.

Question 56

In articular cartilage, which structural zone has the highest concentration of water and the lowest concentration of proteoglycans?





Explanation

The superficial (tangential) zone of articular cartilage is characterized by chondrocytes that are flattened, collagen fibers oriented parallel to the joint surface, the highest water content, and the lowest proteoglycan content. As one moves toward the deep zone, water content decreases while proteoglycan concentration increases, allowing for compressive resistance.

Question 57

During an anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone autograft, an overly vertical femoral tunnel is drilled in the intercondylar notch. Which of the following complications is most likely to result from this specific technical error?





Explanation

An overly vertical femoral tunnel (often resulting from a transtibial drilling technique that does not reach low enough on the lateral wall of the notch) typically restores anteroposterior stability (Lachman test) but fails to restore the native anatomy of the ACL, leaving the knee with residual rotational instability (positive pivot shift test).

Question 58

A 13-year-old obese boy presents with left knee pain and an antalgic gait. Examination shows obligate external rotation of the left hip during passive flexion. Radiographs confirm a stable slipped capital femoral epiphysis (SCFE). What is the primary physiological reason to perform an in-situ pinning rather than attempting an aggressive closed reduction before pinning?





Explanation

The primary danger of forcefully reducing a slipped capital femoral epiphysis (SCFE) is the disruption of the fragile terminal branches of the medial femoral circumflex artery (retinacular vessels), which dramatically increases the risk of avascular necrosis (AVN) of the femoral head. Therefore, in-situ pinning without aggressive reduction is the standard of care for a stable SCFE.

Question 59

A 65-year-old female undergoes volar locked plating for a displaced distal radius fracture. Three months postoperatively, she presents with an inability to extend her thumb at the interphalangeal joint. What is the most likely iatrogenic cause of this complication in the setting of volar plating?





Explanation

Rupture of the extensor pollicis longus (EPL) tendon following volar plating of the distal radius is most commonly caused by prominent distal screws penetrating the dorsal cortex. The EPL runs in the third dorsal compartment, directly over the distal radius. Volar plate prominence or improper positioning on the watershed line typically causes flexor tendon ruptures (e.g., FPL), whereas dorsal screw prominence causes extensor tendon ruptures.

Question 60

A 32-year-old female presents with pain in her knee. Radiographs reveal an eccentric, lytic lesion in the distal femur that extends to the subchondral bone without a sclerotic margin. Biopsy shows multinucleated giant cells intermixed with mononuclear stromal cells. If surgical curettage is planned, which adjuvant systemic therapy can be used to downstage the tumor or treat unresectable disease?





Explanation

The diagnosis is Giant Cell Tumor (GCT) of bone. The neoplastic mononuclear stromal cells express RANKL, which recruits and activates the multinucleated osteoclast-like giant cells responsible for the aggressive bone resorption. Denosumab, a human monoclonal antibody against RANKL, halts this process, leading to tumor ossification and is highly effective as a neoadjuvant or primary treatment for aggressive or unresectable GCT.

Question 61

What is the most significant radiographic risk factor for the progression of a dysplastic (isthmic) spondylolisthesis in a skeletally immature patient?





Explanation

In skeletally immature patients with isthmic spondylolisthesis, a high slip angle (greater than 45-50 degrees) is the most significant radiographic risk factor for the progression of the slip. A high slip angle indicates a more vertical orientation of the L5-S1 disc space, placing higher shear forces across the lumbosacral junction. While high pelvic incidence is associated with the development of spondylolisthesis, the slip angle is the most predictive of progression.

Question 62

When performing a posteromedial approach to the tibia for open reduction and internal fixation of a Schatzker IV tibial plateau fracture, the surgical interval is developed between which two structures?





Explanation

The posteromedial approach to the proximal tibia utilizes the internervous/intermuscular interval between the medial head of the gastrocnemius (which is retracted posteriorly and laterally, protecting the neurovascular bundle) and the pes anserinus tendons (which are retracted anteriorly). This allows direct access to the posteromedial articular fragment commonly seen in Schatzker IV, V, and VI fractures.

Question 63

According to current guidelines, which of the following is considered the strongest indication for prophylactic in situ pinning of the asymptomatic contralateral hip in a patient presenting with a unilateral slipped capital femoral epiphysis (SCFE)?





Explanation

Prophylactic pinning of the contralateral hip in unilateral SCFE is strongly recommended in patients with endocrine or metabolic disorders (e.g., renal osteodystrophy, hypothyroidism, panhypopituitarism) due to the exceedingly high rate of bilateral involvement (up to 100% in some series). Other indications include young chronologic age or skeletal age (modified Oxford Bone Age score <16), and history of radiation therapy. A score of 22 and closed triradiate cartilage indicate a mature skeleton with low risk of subsequent SCFE.

Question 64

A 45-year-old male laborer presents with chronic wrist pain and is diagnosed with a scaphoid nonunion advanced collapse (SNAC) pattern. Radiographs reveal osteoarthritis involving the radial styloid, the entire scaphoid facet, and the capitolunate joint. The radiolunate joint is preserved. Which of the following surgical options is relatively contraindicated in this patient?





Explanation

This patient has a Stage III SNAC wrist (involvement of the capitolunate joint). Proximal row carpectomy (PRC) relies on a preserved cartilage articulation between the lunate fossa of the radius and the proximal head of the capitate. Because the capitolunate joint is arthritic, the capitate head is damaged, making PRC contraindicated as it would result in a painful capitate-radius articulation. Scaphoid excision with four-corner fusion is the appropriate motion-preserving procedure in this setting, as it spares the radiolunate joint.

Question 65

A 60-year-old female presents with groin pain and swelling three years following a metal-on-metal total hip arthroplasty. Aspiration is negative for infection, but MRI demonstrates a cystic pseudotumor. Histological examination of the periprosthetic tissue is most likely to reveal which of the following?





Explanation

The clinical presentation is highly indicative of an adverse local tissue reaction (ALTR) or aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL), commonly seen with metal-on-metal implants. Histologically, ALVAL is characterized by a delayed type IV hypersensitivity reaction, demonstrating prominent diffuse perivascular lymphocytic infiltrates (predominantly T-cells and macrophages). Polyethylene debris produces macrophage-mediated osteolysis without massive lymphocytic infiltrates.

Question 66

A 12-year-old boy presents with a permeative lytic lesion in the diaphysis of the femur with an associated 'onion-skin' periosteal reaction. Biopsy reveals small round blue cells. The most likely diagnosis is associated with a fusion gene resulting from which of the following chromosomal translocations?





Explanation

The clinical and radiographic presentation is classic for Ewing sarcoma. Ewing sarcoma is classically characterized by the chromosomal translocation t(11;22)(q24;q12), which results in the EWS-FLI1 fusion protein. CD99 (MIC2) is a highly sensitive immunohistochemical marker for this tumor. t(X;18) is seen in synovial sarcoma, t(2;13) in alveolar rhabdomyosarcoma, and t(12;16) in myxoid liposarcoma.

Question 67

A 19-year-old collegiate soccer player is undergoing primary anterior cruciate ligament (ACL) reconstruction. The surgeon discusses graft choices. Compared to bone-patellar tendon-bone (BPTB) autograft, the use of a non-irradiated BPTB allograft in this specific patient demographic is associated with which of the following?





Explanation

Multiple studies (such as those by the MOON group) have demonstrated that the use of allograft tissue for ACL reconstruction in young, active patients (typically defined as under 25 years of age) is associated with a significantly higher clinical failure and re-rupture rate compared to autograft. Allografts undergo a slower incorporation and remodeling process (ligamentization) and are not recommended for young, high-demand athletes.

Question 68

A 55-year-old patient with poorly controlled diabetes mellitus presents with a red, hot, and swollen foot. Radiographs demonstrate fragmentation of the midfoot bones, subchondral cysts, and early joint subluxation. There are no skin ulcerations. Which of the following is the most appropriate initial management?





Explanation

The patient is presenting with acute Stage I (Development/Fragmentation stage) Charcot arthropathy, characterized by a red, hot, swollen foot with radiographic evidence of osteopenia, fragmentation, and joint subluxation. In the absence of an open ulcer or signs of systemic infection, the standard of care for acute Charcot neuroarthropathy is immobilization and offloading, typically achieved via a total contact cast (TCC), to halt the progression of deformity until the active inflammatory stage resolves.

Question 69

Calcium phosphate ceramics are frequently used as bone graft substitutes in orthopedic surgery. Which of the following accurately describes their primary biologic property during bone healing?





Explanation

Calcium phosphate ceramics (along with calcium sulfates and hydroxyapatite) are purely osteoconductive. They provide a three-dimensional scaffold for host bone cells to migrate into and deposit new bone. They do not contain living cells (therefore are not osteogenic) and do not contain proteins like BMPs that stimulate mesenchymal stem cell differentiation (therefore are not osteoinductive).

Question 70

In the Young-Burgess classification of pelvic ring injuries, a Lateral Compression Type II (LC-2) fracture pattern is classically defined by which of the following posterior ring injuries?





Explanation

In the Young-Burgess classification, an LC-2 injury involves a lateral compression force that results in an anterior ring injury (e.g., rami fractures) and a posterior injury characterized by an iliac wing fracture that extends into the sacroiliac joint. The dense posterior sacroiliac ligaments remain intact, holding the posterior iliac fragment to the sacrum, while the anterior portion of the iliac wing hinges inward. This is commonly referred to as a 'crescent fracture'.

Question 71

During the Ponseti method for correction of idiopathic clubfoot, what is the critical first manipulative step performed before applying the initial cast?





Explanation

The Ponseti method corrects the deformities of clubfoot in a specific sequence (CAVE: Cavus, Adductus, Varus, Equinus). The very first step is to correct the cavus deformity. This is achieved by supinating the forefoot and elevating the first ray (first metatarsal), which aligns the forefoot with the hindfoot. Pronating the forefoot is a common error that worsens the cavus.

Question 72

A 24-year-old avid golfer presents with weakness of the intrinsic muscles of the hand. Sensation is perfectly normal over the entire volar and dorsal aspect of the hand and digits. A fracture of the hook of the hamate is identified. In which zone of Guyon's canal is the ulnar nerve compression most likely occurring?





Explanation

Guyon's canal is divided into 3 zones. Zone 1 is proximal to the bifurcation and contains both motor and sensory fibers. Zone 2 surrounds the deep motor branch of the ulnar nerve after it bifurcates and passes adjacent to the hook of the hamate; compression here causes isolated motor weakness of the ulnar-innervated intrinsics. Zone 3 encompasses the superficial sensory branch; compression here causes isolated sensory deficits. Hook of the hamate fractures typically compress Zone 2.

Question 73

Based on classic indications for a medial unicompartmental knee arthroplasty (UKA), which of the following is considered an absolute contraindication to the procedure?





Explanation

Inflammatory arthropathy (such as rheumatoid arthritis) is considered an absolute contraindication to unicompartmental knee arthroplasty (UKA) because the systemic, pan-articular nature of the disease will eventually destroy the unresurfaced compartments. Classic Kozinn and Scott indications include non-inflammatory OA, intact ACL, correctable deformity (<15 deg flexion contracture, <5-10 deg varus/valgus), and no significant anterior knee pain.

Question 74

A 45-year-old male presents with severe neck pain radiating down his right arm. Physical examination reveals weakness in wrist flexion and finger extension, and an absent triceps reflex. Sensation is diminished over the volar aspect of the middle finger. Which cervical nerve root is most likely compressed?





Explanation

The clinical findings are classic for a C7 radiculopathy. The C7 nerve root supplies the triceps (elbow extension), wrist flexors (flexor carpi radialis), and finger extensors (extensor digitorum communis). The primary reflex tested is the triceps reflex, and the dermatomal sensory distribution is the middle finger. C6 radiculopathy would affect wrist extension and the brachioradialis reflex with numbness in the thumb/index finger.

Question 75

Biomechanical studies of the knee demonstrate that a complete radial tear adjacent to the posterior root of the medial meniscus results in contact pressures that are most similar to which of the following conditions?





Explanation

A complete radial tear near the posterior root of the medial meniscus completely disrupts the circumferential continuity of the meniscus. Biomechanically, this results in a complete loss of 'hoop stresses', leading to meniscal extrusion under load. Studies have shown that this creates peak contact pressures and altered kinematics in the medial compartment equivalent to those of a total meniscectomy.

Question 76

Which of the following bone tumors is characterized as a low-grade, surface-originating malignancy that is heavily ossified, commonly arises on the posterior aspect of the distal femur, and frequently exhibits amplification of MDM2 and CDK4?





Explanation

Parosteal osteosarcoma is a low-grade surface osteosarcoma that typically arises on the posterior surface of the distal femur. Radiographically, it appears as a heavily ossified, broad-based mass 'stuck on' the cortex, sometimes with a radiolucent string sign separating it from the underlying bone. Cytogenetically, it is characterized by ring chromosomes leading to amplification of MDM2 and CDK4.

Question 77

In adult acquired flatfoot deformity (posterior tibial tendon dysfunction), what is the primary static stabilizing ligament of the medial longitudinal arch that classically attenuates and fails?





Explanation

While the posterior tibial tendon provides dynamic support to the medial longitudinal arch, the primary static stabilizer is the plantar calcaneonavicular ligament, commonly known as the spring ligament. In adult acquired flatfoot deformity, the posterior tibial tendon fails, leading to increased stress on the static stabilizers. Attenuation and ultimate failure of the spring ligament leads to severe talonavicular subluxation (peritalar subluxation) characteristic of Stage 2b/3 disease.

Question 78

A 30-year-old male sustains a comminuted tibia fracture. He develops severe pain out of proportion to the injury. Which of the following objective compartment pressure measurements is the most accepted indication for performing a four-compartment fasciotomy?





Explanation

The diagnosis of acute compartment syndrome relies on the concept of 'delta pressure' (the difference between the diastolic blood pressure and the intracompartmental pressure). A delta pressure of 30 mmHg or less (i.e., compartment pressure comes within 30 mmHg of the diastolic BP) indicates inadequate capillary perfusion and is an absolute indication for emergency fasciotomy. Absolute pressures can be misleading, especially in hypotensive patients.

Question 79

When examining the ultrastructure of mature articular cartilage, which zone is characterized by having the highest concentration of proteoglycans, the lowest water content, and collagen fibrils aligned perpendicular to the joint surface?





Explanation

The deep (radial) zone of articular cartilage is responsible for resisting compressive loads. It has the highest concentration of proteoglycans, the lowest concentration of water, and thick type II collagen fibrils aligned perpendicularly to the articular surface. The superficial zone, by contrast, has the highest water content, lowest proteoglycan content, and collagen fibers aligned parallel to the surface to resist shear forces.

Question 80

An infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). At the 2-week follow-up, the parents report the infant is not kicking the left leg. On exam, there is an absent patellar reflex and profound weakness in knee extension on the left side. What specific positional error of the Pavlik harness is the most likely cause of this complication?





Explanation

The infant is presenting with an iatrogenic femoral nerve palsy, a known complication of Pavlik harness treatment. This is caused by excessive flexion of the hip (typically greater than 120 degrees), which causes the anterior strap to compress the femoral nerve against the pelvic brim. Treatment involves loosening the anterior straps to reduce flexion. Conversely, excessive abduction is associated with avascular necrosis of the femoral head.

Question 81

A 4-year-old child presents with disproportionate short stature, a waddling gait, and normal facial features and intelligence. Radiographs demonstrate delayed epiphyseal ossification and platyspondyly with anterior tongue-like projections. What is the primary genetic mutation responsible for this condition?





Explanation

The clinical scenario describes Pseudoachondroplasia. Unlike achondroplasia (which is caused by an FGFR3 mutation and presents with distinctive craniofacial features), pseudoachondroplasia patients have normal intelligence and normal faces. It is caused by a mutation in the Cartilage Oligomeric Matrix Protein (COMP) gene.

Question 82

During an ilioinguinal approach for an anterior column acetabular fracture, significant hemorrhage is encountered behind the superior pubic ramus near the symphysis. This bleeding is most likely originating from the 'corona mortis', which represents an anastomosis between which of the following vascular systems?





Explanation

The corona mortis ('crown of death') is a vascular anastomosis between the obturator and external iliac or inferior epigastric systems. It courses over the superior pubic ramus and is highly susceptible to iatrogenic injury during anterior pelvic surgical approaches.

Question 83

During arthroscopic evaluation of a baseball pitcher's shoulder, a Type II SLAP (Superior Labrum Anterior and Posterior) tear is identified. The 'peel-back' mechanism, which dynamically exacerbates this lesion during the throwing motion, occurs primarily in which of the following shoulder positions?





Explanation

The 'peel-back' mechanism describes the dynamic shift of the biceps vector during the late cocking phase of throwing, which places the shoulder in abduction and maximum external rotation. This force peels the superior labrum off the posterior glenoid rim.

Question 84

According to the Wiltse classification of spondylolisthesis, which subtype is characterized by an elongated, but intact, pars interarticularis resulting from repeated micro-fractures and subsequent healing?





Explanation

The Wiltse classification categorizes spondylolisthesis. Type II is isthmic (pars defect). Type IIA is a stress fracture (lytic). Type IIB represents an elongated pars interarticularis secondary to repetitive micro-fracture and healing without complete separation. Type IIC is an acute fracture.

Question 85

A patient with a chronic low ulnar nerve palsy presents with a classic claw hand deformity. During physical examination, the examiner blocks the metacarpophalangeal (MCP) joints in flexion, and the patient is then able to actively extend the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints. This finding indicates:





Explanation

This is a positive Bouvier test. In an intrinsic-minus hand, the extrinsic extensors hyperextend the MCP joint, dissipating the force needed to extend the IP joints. By blocking MCP hyperextension, the test proves the extensor digitorum communis (EDC) can successfully extend the IP joints, meaning the patient may benefit from a simple MCP flexion block procedure (e.g., Zancolli lasso).

Question 86

A 25-year-old female presents with a painless, slow-growing mass on the posterior aspect of her distal thigh. Radiographs demonstrate a dense, lobulated, ossified mass attached to the posterior cortex of the distal femur with a 'string sign' visible at its base. Histology reveals low-grade spindle cells with well-formed bony trabeculae. Which of the following cytogenetic abnormalities is most characteristic of this lesion?





Explanation

The clinical and radiographic presentation is classic for a parosteal osteosarcoma (surface osteosarcoma, typically low-grade, located on the posterior distal femur). It is characterized genetically by the amplification of MDM2 and CDK4 genes on chromosome 12q13-15.

Question 87

Demineralized bone matrix (DBM) is widely used in orthopedic surgery as a bone graft substitute. Which of the following best describes its innate biological properties prior to being mixed with any marrow elements?





Explanation

Demineralized bone matrix (DBM) provides a collagenous scaffold (osteoconductive) and contains bone morphogenetic proteins (BMPs) exposed by the demineralization process (osteoinductive). However, it contains no living cells, so it is not osteogenic.

Question 88

A 55-year-old diabetic patient presents with a swollen, warm, and erythematous right foot. Radiographs show periarticular debris, fragmentation of the navicular, and early subluxation of the talonavicular joint. According to the Eichenholtz classification of Charcot arthropathy, what stage does this represent?





Explanation

The Eichenholtz classification describes the natural history of Charcot arthropathy. Stage 0 is inflammation with normal radiographs. Stage 1 is the Developmental/Fragmentation stage characterized by periarticular debris, fragmentation, and subluxation. Stage 2 is Coalescence (absorption of debris, early fusion). Stage 3 is Consolidation (remodeling and rounded bone edges).

Question 89

Highly cross-linked polyethylene (HXLPE) is utilized in total hip arthroplasty to reduce volumetric wear. The manufacturing process involves irradiation followed by thermal treatment (remelting or annealing). What is the primary purpose of this thermal treatment step?





Explanation

Irradiation generates free radicals that cross-link the polyethylene chains (improving wear resistance) but leaves residual free radicals. Thermal treatment (remelting or annealing) extinguishes these residual free radicals, which prevents subsequent in vivo oxidation and embrittlement.

Question 90

During a volar Henry approach to the distal radius, an incision is made over the flexor carpi radialis (FCR) sheath. Which of the following neural structures is at greatest risk of iatrogenic injury if the dissection mistakenly proceeds ulnar to the FCR tendon?





Explanation

The palmar cutaneous branch of the median nerve arises approximately 5 cm proximal to the wrist crease and travels ulnar to the FCR tendon. Incising the FCR sheath and retracting the tendon ulnarly protects this nerve. Straying ulnar to the FCR during superficial dissection places the nerve at high risk.

Question 91

A 28-year-old female presents with chronic wrist pain and is diagnosed with Kienböck's disease. Radiographs reveal increased sclerosis of the lunate without fragmentation, no carpal collapse, and an ulnar variance of -3 mm. According to the Lichtman classification, what is the most appropriate surgical intervention?





Explanation

The patient has Lichtman Stage II Kienböck's disease (sclerosis, no collapse) with negative ulnar variance. Joint leveling procedures, such as a radial shortening osteotomy, are the treatment of choice to decompress the lunate and halt disease progression.

Question 92

In the management of a patient with a unilateral Slipped Capital Femoral Epiphysis (SCFE), prophylactic in situ pinning of the contralateral asymptomatic hip is most strongly indicated in which of the following scenarios?





Explanation

Prophylactic contralateral pinning is highly recommended for patients with endocrine or metabolic disorders (e.g., hypothyroidism, renal osteodystrophy) due to the extremely high risk of bilateral involvement. Other relative indications include open triradiate cartilage or age <10 years.

Question 93

Which of the following alterations to the geometric design of a cortical bone screw will most significantly increase its pullout strength?





Explanation

Screw pullout strength is directly proportional to the outer (thread) diameter, the length of thread engagement, and the shear strength of the host bone. It is inversely proportional to the thread pitch. Therefore, increasing the outer diameter will significantly increase pullout strength.

Question 94

During a posterior-stabilized total knee arthroplasty, trial components are placed. The knee is found to be perfectly balanced and stable in full extension, but it is excessively tight in flexion, preventing range of motion beyond 70 degrees. Which of the following is the most appropriate intraoperative step to balance the knee?





Explanation

A knee that is tight in flexion but balanced in extension requires an increase in the flexion gap without affecting the extension gap. This can be achieved by increasing the posterior slope of the tibial cut, or by using a smaller femoral component with an anterior referencing guide (which moves the posterior condyles anteriorly). Downsizing with a posterior referencing guide does not increase the flexion gap. Since this is a PS knee, releasing the PCL is not an option as it is already resected.

Question 95

Cervical spondylotic myelopathy (CSM) classically presents with a combination of upper motor neuron signs in the lower extremities and lower motor neuron signs in the upper extremities. Which of the following spinal cord tracts is compressed anteriorly, resulting in the upper motor neuron signs seen in the legs?





Explanation

The upper motor neuron signs in the lower extremities (hyperreflexia, spasticity, positive Babinski) in CSM are caused by compression of the lateral corticospinal tracts, which are located in the lateral and anterior aspects of the spinal cord.

Question 96

The concept of a 'floating shoulder' historically involves a double disruption of the Superior Suspensory Shoulder Complex (SSSC). Which of the following injury combinations constitutes a classic double disruption of the SSSC?





Explanation

The Superior Suspensory Shoulder Complex (SSSC) is a ring composed of the glenoid, coracoid, CC ligaments, distal clavicle, AC joint, and acromion. A classic 'floating shoulder' represents a double disruption of this complex, most commonly a fracture of the clavicle shaft combined with an ipsilateral fracture of the scapular neck.

Question 97

A 45-year-old female presents with painful, progressive flattening of her left foot. Clinical examination reveals a 'too many toes' sign and inability to perform a single-leg heel raise. Radiographs demonstrate significant talonavicular uncoverage (>40%) without evidence of osteoarthritis. According to the Johnson and Strom classification, what is the stage and the most appropriate surgical treatment?





Explanation

The inability to perform a single-leg heel raise with flexible deformity indicates Stage II adult acquired flatfoot deformity. The presence of significant forefoot abduction (talonavicular uncoverage >30-40%) sub-classifies it as Stage IIB, which necessitates a lateral column lengthening (Evans osteotomy) in addition to soft tissue transfers and medial displacement calcaneal osteotomy.

Question 98

A 35-year-old male presents with chronic hip pain. Radiographs reveal a radiolucent lesion strictly contained within the epiphysis of the proximal femur with subtle intralesional calcifications. Histology shows cells with abundant clear cytoplasm, well-defined borders, and interspersed areas of mature bone formation. Which of the following is the most likely diagnosis?





Explanation

Clear cell chondrosarcoma is an atypical low-grade malignant cartilage tumor that classically arises in the epiphysis of long bones (especially the proximal femur) in adults (third to fifth decades). It is frequently misdiagnosed as chondroblastoma, but chondroblastoma typically occurs in skeletally immature patients.

Question 99

In Dupuytren's disease, the spiral cord is frequently responsible for proximal interphalangeal (PIP) joint flexion contractures. As the spiral cord matures and contracts, how does it anatomically displace the digital neurovascular bundle?





Explanation

The spiral cord in Dupuytren's contracture consists of the pretendinous band, spiral band, lateral digital sheet, and Grayson's ligament. As it contracts, it wraps around the neurovascular bundle, displacing it superficially (volar) and centrally (towards the midline), placing it at severe risk during surgical fasciectomy.

Question 100

Following primary surgical repair of an acute flexor tendon laceration in the hand, the tendon undergoes distinct phases of healing. During which time frame is the repair mechanically at its weakest, making it most susceptible to iatrogenic rupture?





Explanation

Tendon repair strength dips below its initial surgical holding strength between 5 and 21 days postoperatively. This occurs during the transition from the inflammatory phase to the early fibroblastic phase, where collagen degradation outpaces new collagen synthesis, causing the tendon ends to soften.

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