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Arab Orthopaedic Board MCQs - Part 14

27 Apr 2026 74 min read 81 Views
Arab Ortho Board MCQs - Part 13

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For anyone wondering about Arab Orthopaedic Board MCQs - Part 14, Practice Arab Orthopaedic Board MCQs Part 14. Review orthopedic surgery questions 651 to 700 for your board exam preparation.

Arab Orthopaedic Board MCQs - Part 14

Comprehensive 100-Question Exam


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Question 1

A 6-year-old boy falls on an outstretched hand and sustains an ulnar diaphyseal fracture associated with a radial neck fracture. According to the Bado classification equivalents, what type of Monteggia lesion does this represent?





Explanation

A Bado Type I equivalent involves an anterior dislocation of the radial head or a fracture of the radial neck combined with an ulnar diaphyseal fracture. Type I Bado injuries are the most common Monteggia lesions in children, traditionally characterized by anterior apex ulnar bowing or fracture combined with an anterior radial head dislocation.

Question 2

A 65-year-old man who underwent total hip arthroplasty 5 years ago presents with groin pain and a palpable anterior thigh mass. Plain radiographs show a well-fixed cementless implant without osteolysis. Joint aspiration yields cloudy, sterile fluid. Serum cobalt levels are markedly elevated, while chromium is normal. What is the most likely underlying pathophysiological mechanism?





Explanation

The presentation is classic for trunnionosis, which refers to mechanically assisted crevice corrosion at the modular head-neck junction (the trunnion). It typically presents with elevated serum cobalt (often discordant with chromium) and an adverse local tissue reaction (ALTR) resulting in a pseudotumor, even in patients with metal-on-polyethylene bearings.

Question 3

Bone morphogenetic protein-2 (BMP-2) is heavily utilized in spine surgery for its potent osteoinductive properties. Through which of the following intracellular signaling pathways does BMP-2 primarily exert its osteogenic effect?





Explanation

BMP-2 binds to a heterodimeric serine/threonine kinase receptor on the cell surface. This binding leads to the intracellular phosphorylation of receptor-regulated SMADs (SMAD 1, 5, and 8). These form a complex with the common-mediator SMAD 4, which then translocates to the nucleus to regulate the transcription of osteogenic genes such as Runx2.

Question 4

In the evaluation of a patient with suspected pyogenic flexor tenosynovitis, which of Kanavel's four classic signs is generally considered the earliest and most sensitive indicator of the condition?





Explanation

Kanavel's four signs of pyogenic flexor tenosynovitis are: 1) fusiform swelling (sausage digit), 2) flexed resting posture, 3) tenderness along the flexor tendon sheath, and 4) excruciating pain with passive extension. Pain with passive extension is widely recognized as the earliest and most sensitive clinical sign of a flexor sheath infection.

Question 5

A 25-year-old soccer player sustains a twisting injury to his knee. On physical examination, the dial test reveals 15 degrees of increased external rotation on the injured side compared to the contralateral normal knee at 30 degrees of knee flexion. However, at 90 degrees of knee flexion, the external rotation is equal bilaterally. Which anatomic structure(s) is/are injured?





Explanation

The dial test is used to differentiate isolated posterolateral corner (PLC) injuries from combined PLC and PCL injuries. An increase in external rotation of >10 degrees at 30 degrees of flexion, but not at 90 degrees, indicates an isolated PLC injury. If the asymmetry is present at both 30 and 90 degrees, it suggests a combined PCL and PLC injury.

Question 6

A 35-year-old male presents with chronic shoulder pain and a lytic lesion in the proximal humeral epiphysis. Radiographs show a well-defined geographic lytic lesion with central punctate calcifications. Histological examination reveals sheets of cells with abundant clear cytoplasm, distinct cell membranes, and areas of malignant hyaline cartilage intermixed with woven bone. What is the most likely diagnosis?





Explanation

Clear cell chondrosarcoma is a rare, low-grade variant of chondrosarcoma that characteristically occurs in the epiphysis of long bones (typically proximal femur or humerus) in adults (third to fifth decade). It often mimics chondroblastoma radiographically (which also occurs in the epiphysis but usually in younger patients prior to physeal closure), but histologically features cells with clear cytoplasm and malignant hyaline cartilage.

Question 7

During the surgical approach to the posteromedial aspect of the tibial plateau for internal fixation of a Schatzker IV fracture, the primary internervous/intermuscular plane is utilized. Which structures define the borders of this interval?





Explanation

The posteromedial approach to the tibial plateau utilizes an interval between the medial head of the gastrocnemius (innervated by the tibial nerve) posteriorly, and the pes anserinus (innervated by the femoral and sciatic nerves) anteriorly. Retracting the gastrocnemius posteriorly and laterally protects the popliteal neurovascular bundle.

Question 8

According to the modified Hawkins classification, a Hawkins Type III fracture of the talar neck involves subluxation or dislocation of which of the following joints?





Explanation

The Hawkins classification for talar neck fractures is: Type I: Nondisplaced. Type II: Displaced with subluxation/dislocation of the subtalar joint. Type III: Displaced with subluxation/dislocation of both the subtalar and tibiotalar joints. Type IV: Displaced with subluxation/dislocation of the subtalar, tibiotalar, and talonavicular joints.

Question 9

In articular cartilage, which zone has the highest concentration of proteoglycans, the lowest water content, and collagen fibers oriented strictly perpendicular to the articular surface?





Explanation

The deep (radial) zone of articular cartilage represents about 30% of the cartilage volume. It provides the greatest resistance to compressive forces, possesses the highest proteoglycan concentration, the lowest water content, and features large diameter Type II collagen fibrils arranged perpendicular to the joint surface to anchor the cartilage to the underlying bone.

Question 10

A 6-week-old female infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). She has been strictly in the harness for 4 weeks, but a repeat ultrasound demonstrates that the hip remains persistently dislocated. What is the most appropriate next step in management?





Explanation

Prolonged use of a Pavlik harness in a persistently dislocated hip leads to 'Pavlik harness disease', characterized by erosion of the posterior acetabular wall, which makes future reduction significantly more difficult. If a hip remains dislocated after 3 to 4 weeks of strict Pavlik harness wear, the harness must be discontinued. The accepted next step is transitioning to a rigid abduction brace (e.g., Ilfeld) or proceeding to closed reduction and spica casting.

Question 11

A 45-year-old cyclist presents with isolated weakness of finger abduction and adduction, and an inability to cross his fingers. Sensation over the volar aspect of his small finger and the ulnar half of the ring finger is completely intact. Where is the most likely site of ulnar nerve compression?





Explanation

Guyon's canal is divided into three zones. Zone 1 is proximal to the nerve bifurcation and contains both motor and sensory fibers; compression here causes mixed deficits. Zone 2 surrounds the deep motor branch; compression here causes isolated motor deficits of the ulnar-innervated intrinsic hand muscles. Zone 3 contains the superficial sensory branch; compression here causes isolated sensory deficits. 'Cyclist's palsy' frequently presents as an isolated motor deficit due to Zone 2 compression.

Question 12

A 68-year-old female presents with catching and a painful 'pop' at the anterior aspect of her knee when extending her leg from a flexed position. She underwent a posterior-stabilized (PS) total knee arthroplasty 18 months ago. Which implant design factor is most strongly associated with the development of this specific complication?





Explanation

The patient is presenting with 'patellar clunk syndrome', characterized by the formation of a fibrous nodule at the superior pole of the patella that catches in the intercondylar notch of the femoral component during active extension. It is classically associated with early posterior-stabilized (PS) knee designs that featured a high, anteriorly placed intercondylar box ratio, leading to impingement of the quadriceps tendon.

Question 13

A 40-year-old male sustains an isolated thoracolumbar fracture at T12 following a fall. Neurological examination is completely normal. CT imaging demonstrates a burst fracture of T12 with 30% loss of anterior vertebral body height and splaying of the pedicles. MRI reveals the posterior ligamentous complex (PLC) is intact. According to the Thoracolumbar Injury Classification and Severity (TLICS) score, what is his total score and the generally recommended treatment pathway?





Explanation

The TLICS scoring system considers three parameters: injury morphology, neurological status, and integrity of the posterior ligamentous complex (PLC). Morphology: burst fracture = 2 points. Neurological status: intact = 0 points. PLC: intact = 0 points. Total score = 2. A score of less than 4 implies nonoperative management is indicated.

Question 14

A 28-year-old male presents with a slow-growing, painful mass in his left tibial diaphysis. Radiographs show a distinct, multi-loculated, expansile osteolytic 'soap-bubble' lesion within the anterior cortex of the tibia. Biopsy demonstrates a biphasic tumor with nests of basaloid epithelial cells dispersed within a fibrous stroma. What is the most appropriate definitive management for this lesion?





Explanation

The clinical, radiographic, and histologic presentation is classic for adamantinoma. Adamantinoma is a rare, low-grade malignant bone tumor that almost exclusively occurs in the anterior diaphyseal cortex of the tibia. It is biphasic, displaying both epithelial and osteofibrous components. It is notoriously resistant to both chemotherapy and radiation. The standard of care is wide surgical resection.

Question 15

During an anterior intrapelvic (modified Stoppa) approach to the acetabulum, severe hemorrhage is encountered just superior to the superior pubic ramus. This bleeding is most likely originating from the corona mortis, which is an anastomotic connection between which two vascular systems?





Explanation

The corona mortis ('crown of death') is an anatomical variant representing a vascular anastomosis between the external iliac (or its inferior epigastric branch) and the obturator vessels (a branch of the internal iliac). It crosses 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 exposures.

Question 16

In the context of preparing polymethylmethacrylate (PMMA) bone cement, which of the following modifications significantly decreases the mechanical strength and fatigue life of the cement mantle?





Explanation

Adding aqueous/liquid substances (like liquid antibiotics) or excessive fluid significantly increases porosity and radically decreases the ultimate mechanical strength and fatigue life of PMMA bone cement. Antibiotics should only be added in fine powder form. Vacuum mixing and centrifugation both decrease porosity and thereby increase fatigue life. Pre-chilling the monomer prolongs the working time but does not weaken the cement.

Question 17

A 13-year-old obese male presents to the emergency department complaining of right hip and thigh pain after slipping on ice. He is completely unable to bear weight on the right leg, even with crutches. Radiographs demonstrate a displaced Slipped Capital Femoral Epiphysis (SCFE) of the right hip. Based on the Loder classification, what is his primary risk regarding the natural history of this specific injury pattern?





Explanation

According to the Loder classification, SCFE is divided into stable and unstable. 'Unstable' is defined clinically as the inability to ambulate, even with assistive devices (crutches). The incidence of avascular necrosis (AVN) in unstable SCFE is extremely high (up to 47%), whereas it is nearly 0% in stable SCFE.

Question 18

The Lisfranc ligament is a critical stabilizing structure of the midfoot. What are the precise anatomic attachments of the primary Lisfranc ligament?





Explanation

The Lisfranc ligament is an oblique, stout plantar interosseous ligament that spans from 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 region uniquely vulnerable to disruption.

Question 19

A 55-year-old male sustains a traumatic anterior shoulder dislocation. After a successful closed reduction, he complains of profound weakness in shoulder abduction and external rotation. Electromyography (EMG) at 6 weeks confirms an isolated peripheral nerve injury. Which of the following nerve roots primarily contribute to the affected nerve?





Explanation

Anterior shoulder dislocations are frequently associated with axillary nerve palsy. The axillary nerve innervates the deltoid (shoulder abduction) and teres minor (external rotation). The axillary nerve arises from the posterior cord of the brachial plexus and carries nerve fibers primarily from the C5 and C6 nerve roots.

Question 20

In the setting of massive posterosuperior rotator cuff tears, which muscle uniquely demonstrates a high degree of rapid fat accumulation and atrophy due to suprascapular nerve retraction and compression via the 'sling effect' at the spinoglenoid notch?





Explanation

While both the supraspinatus and infraspinatus are innervated by the suprascapular nerve, massive posterosuperior rotator cuff tears lead to severe medial retraction. The suprascapular nerve takes a sharp turn at the spinoglenoid notch to reach the infraspinatus. Medial retraction of the cuff causes traction on the nerve at this unyielding notch (the 'sling effect'), disproportionately causing profound denervation and rapid fatty infiltration in the infraspinatus compared to the supraspinatus.

Question 21

What is the most frequently injured nerve in an extension-type supracondylar fracture of the humerus in a pediatric patient?





Explanation

The anterior interosseous nerve (AIN), a branch of the median nerve, is the most frequently injured nerve in extension-type supracondylar fractures of the humerus. This is typically due to traction over the proximal fragment. AIN palsy presents with the inability to flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger (loss of the 'OK' sign).

Question 22

Which of the following is the most significant adverse prognostic factor for overall survival in a patient with conventional high-grade osteosarcoma?





Explanation

While high serum alkaline phosphatase and large tumor size are poor prognostic factors, the presence of macroscopic metastases (including skip lesions within the same bone or distant pulmonary metastases) is the most significant adverse prognostic indicator for overall survival in osteosarcoma.

Question 23

During an anterior cruciate ligament (ACL) reconstruction, the surgeon inadvertently places the femoral tunnel too anteriorly in the intercondylar notch. Which of the following kinematic abnormalities will most likely result?





Explanation

Placing the femoral tunnel too anteriorly in the intercondylar notch causes the ACL graft to be tight in knee flexion and loose in extension. This error restricts full knee flexion and may cause early graft failure or stretching.

Question 24

A 65-year-old female with adult degenerative scoliosis presents with intractable neurogenic claudication and low back pain. Corrective surgery is planned. Which of the following is the primary indication for extending a spinal fusion down to the pelvis rather than stopping at L5?





Explanation

Extending a long spinal fusion to the pelvis in adult spinal deformity is indicated when there is significant L5-S1 pathology, such as a fractional curve > 15 degrees, advanced L5-S1 disc degeneration, spondylolisthesis at L5-S1, or previous laminectomy at L5-S1. Stopping at L5 in the presence of these conditions often leads to rapid adjacent segment failure and pseudoarthrosis.

Question 25

The Pauwels classification for femoral neck fractures categorizes fractures based on which of the following parameters?





Explanation

The Pauwels classification is based on the angle of the fracture line relative to the horizontal plane. Type I is <30 degrees, Type II is 30-50 degrees, and Type III is >50 degrees. Higher angles indicate increased shear forces across the fracture site, which correlates with higher rates of nonunion and fixation failure.

Question 26

During an open carpal tunnel release, the transverse carpal ligament is systematically divided. Which of the following bony structures form the ulnar attachment of the transverse carpal ligament?





Explanation

The transverse carpal ligament (flexor retinaculum) forms the roof of the carpal tunnel. It attaches radially to the scaphoid tuberosity and the crest of the trapezium, and ulnarly to the pisiform and the hook of the hamate.

Question 27

Primary bone healing (contact healing via osteonal reconstruction) is achieved under which of the following mechanical and biological conditions?





Explanation

Primary bone healing requires absolute mechanical stability and precise anatomical reduction with a fracture gap of less than 0.01 mm. It occurs via direct Haversian remodeling (cutting cones advancing across the fracture site) without intermediate callus formation.

Question 28

According to modern Level I evidence regarding the management of acute Achilles tendon ruptures, which of the following statements is true when an accelerated functional rehabilitation protocol is employed?





Explanation

Recent high-quality Level I studies (such as the Willits trial) demonstrate that when an accelerated functional rehabilitation protocol (early weight-bearing and early mobilization) is used, there is no clinically important difference in re-rupture rates between operative and non-operative management. Operative treatment is, however, associated with higher risks of wound complications and nerve injury.

Question 29

In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) compared to conventional ultra-high molecular weight polyethylene (UHMWPE) results in which of the following material property changes?





Explanation

Highly cross-linked polyethylene (HXLPE) is manufactured to significantly increase resistance to adhesive and abrasive wear, thereby reducing wear debris and subsequent osteolysis. However, the cross-linking process and subsequent thermal treatments decrease mechanical properties such as ultimate tensile strength, yield strength, and fatigue crack propagation resistance.

Question 30

What is the most devastating and rapid complication specifically associated with the surgical pinning of an unstable Slipped Capital Femoral Epiphysis (SCFE)?





Explanation

Osteonecrosis (AVN) is the most devastating complication of SCFE, occurring at a significantly higher rate in unstable SCFE (reported up to 47%) compared to stable SCFE (almost 0%). It is typically caused by disruption of the retinacular vessels, which can be exacerbated by forceful closed reduction or hematoma accumulation.

Question 31

In the Young-Burgess classification of pelvic ring injuries, an anteroposterior compression (APC) Type II injury is characterized by the rupture of which ligaments?





Explanation

An APC II injury involves symphyseal diastasis (usually >2.5 cm) with disruption of the anterior sacroiliac, sacrotuberous, and sacrospinous ligaments. The critical posterior sacroiliac ligament remains intact, making the pelvis rotationally unstable ('open book') but vertically stable.

Question 32

Denosumab is highly effective in the treatment of unresectable or metastatic Giant Cell Tumor of bone (GCTB). What is the specific molecular target of this medication?





Explanation

Denosumab is a fully human monoclonal antibody that binds to and inhibits RANK Ligand (RANKL). In GCTB, the neoplastic mononuclear stromal cells express high levels of RANKL, which recruits and activates the reactive multinucleated giant cells (osteoclast-like cells) that cause extensive bone osteolysis.

Question 33

During the physical examination of a patient with suspected cervical radiculopathy, the examiner applies downward axial compression to the patient's head while the neck is extended and laterally flexed to the symptomatic side. This provocative maneuver is known as:





Explanation

Spurling's test (foraminal compression test) is performed by extending and laterally bending the neck to the symptomatic side while applying axial compression. A positive test is the reproduction of radicular arm pain, indicating cervical nerve root compression within the neural foramen.

Question 34

Six months after open reduction and internal fixation of a distal radius fracture with a volar locking plate, the patient develops a sudden inability to actively extend the interphalangeal joint of the thumb. Which tendon is most likely injured, and what is the primary mechanism?





Explanation

The inability to actively extend the thumb interphalangeal joint indicates a rupture of the Extensor pollicis longus (EPL) tendon. In the setting of a previously placed volar plate, this complication is classically caused by excessively long screws protruding through the dorsal cortex, leading to attritional wear and eventual rupture of the EPL tendon.

Question 35

A 22-year-old athlete sustains a longitudinal tear in the peripheral one-third of the medial meniscus. This specific zone has the highest healing potential following a meniscal repair primarily because:





Explanation

The peripheral one-third of the meniscus (the 'red-red' zone) is highly vascularized by the perimeniscal capillary plexus, which arises from branches of the medial and lateral inferior genicular arteries. This rich blood supply affords this region excellent healing potential. The central zones are avascular and rely on diffusion.

Question 36

In standard mechanically aligned Total Knee Arthroplasty (TKA), the distal femoral cut is typically made at what angle relative to the anatomical axis of the femur to restore a neutral mechanical axis?





Explanation

The mechanical axis of the femur runs from the center of the femoral head to the center of the knee joint. The anatomical axis runs down the intramedullary canal of the femoral shaft. The angle between them represents the valgus cut angle, which averages 5 to 7 degrees of valgus for most patients to achieve a neutral overall mechanical alignment.

Question 37

During the descent phase of a squat exercise, the quadriceps muscle actively lengthens while remaining under tension to control knee flexion. What type of muscle contraction does this describe?





Explanation

An eccentric contraction occurs when the muscle lengthens while actively producing force (e.g., the quadriceps during the descent phase of a squat acting as a brake). Concentric contractions occur when the muscle shortens, and isometric contractions occur when there is no change in muscle length.

Question 38

When treating an infant for Developmental Dysplasia of the Hip (DDH) using a Pavlik harness, hyperflexion of the hips beyond 120 degrees places the child at significant risk for which specific complication?





Explanation

Excessive hip flexion (typically >120 degrees) in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to an iatrogenic femoral nerve palsy. Excessive hip abduction, on the other hand, compromises the medial circumflex femoral artery and leads to avascular necrosis.

Question 39

A 30-year-old man with a comminuted tibial shaft fracture presents with severe pain out of proportion to the injury. Clinical suspicion for acute compartment syndrome is high. Which of the following pressure measurements strongly supports the need for an emergent fasciotomy?





Explanation

The most reliable indicator for diagnosing acute compartment syndrome in a borderline clinical scenario is the delta pressure, calculated as Diastolic Blood Pressure (DBP) minus Intracompartmental Pressure (ICP). A delta pressure of less than 30 mmHg (indicating critically compromised tissue perfusion) is an absolute indication for emergent fasciotomy.

Question 40

A distal chevron osteotomy is generally considered the most appropriate surgical intervention for a patient with symptomatic hallux valgus possessing which of the following radiographic profiles?





Explanation

The distal chevron osteotomy is indicated for mild to moderate hallux valgus deformities. This corresponds to an Intermetatarsal (IM) angle of less than 13 to 15 degrees and a Hallux Valgus Angle (HVA) of less than 30 to 35 degrees. Severe deformities (IM > 15) or hypermobility typically require a proximal osteotomy or Lapidus procedure, and advanced MTP arthritis is a contraindication.

Question 41

A 24-year-old gymnast presents with ulnar-sided wrist pain. Examination reveals a positive ballottement test (Reagan test). Radiographs show a volar flexed scaphoid and lunate with a dorsally extended triquetrum. What is the most likely diagnosis?





Explanation

Lunotriquetral (LT) ligament tears lead to Volar Intercalated Segment Instability (VISI). The lunate flexes with the scaphoid while the triquetrum extends. The Reagan test (LT ballottement) is positive. Scapholunate tears lead to DISI (Dorsal Intercalated Segment Instability).

Question 42

A 15-year-old boy presents with progressive thoracic kyphosis. Lateral spine radiographs are obtained. According to Sorensen's criteria, which of the following is required for the definitive radiographic diagnosis of Scheuermann's disease?





Explanation

Sorensen's criteria for the diagnosis of Scheuermann's kyphosis require the presence of anterior wedging of >5 degrees in at least three consecutive (adjacent) vertebrae. Schmorl's nodes and endplate irregularities are commonly seen but are not the primary defining criteria.

Question 43

In Posterior Cruciate Ligament (PCL) anatomy, which of the following statements accurately describes the biomechanical function of its bundles?





Explanation

The PCL has two main bundles: the larger anterolateral (AL) bundle and the smaller posteromedial (PM) bundle. The AL bundle is tight in flexion and lax in extension, serving as the primary restraint to posterior tibial translation at 90 degrees of flexion. The PM bundle is tight in extension and lax in flexion.

Question 44

A 60-year-old patient undergoes revision of a metal-on-metal total hip arthroplasty due to an adverse local tissue reaction (ALTR). Which of the following histological findings is most characteristic of this specific implant-related failure?





Explanation

Adverse local tissue reactions (ALTR) or adverse reactions to metal debris (ARMD) in metal-on-metal hips are characteristically associated with an Aseptic Lymphocyte-dominated Vasculitis-Associated Lesion (ALVAL), which represents a Type IV delayed hypersensitivity reaction to metal ions.

Question 45

During the evaluation of a suspected Lisfranc injury, a 'fleck sign' is noted on the AP radiograph of the foot. This radiographic sign represents an avulsion of the Lisfranc ligament from which of the following osseous structures?





Explanation

The 'fleck sign' is an avulsion fracture at the attachment of the Lisfranc ligament. The Lisfranc ligament connects the lateral aspect of the medial cuneiform to the medial base of the second metatarsal. The avulsion fragment most commonly originates from the medial aspect of the second metatarsal base.

Question 46

A 6-week-old female infant is undergoing an ultrasound evaluation for Developmental Dysplasia of the Hip (DDH). According to the Graf classification, what does the alpha angle measure and what is considered a normal value (Type I hip)?





Explanation

In the Graf classification for DDH ultrasound, the alpha angle measures the bony roof of the acetabulum (formed by the ilium). A normal alpha angle (Graf Type I) is > 60 degrees. The beta angle measures the cartilaginous roof.

Question 47

A 45-year-old patient presents with a painful cartilaginous lesion in the proximal femur. Which of the following histological features most reliably differentiates a low-grade (Grade 1) chondrosarcoma from a benign enchondroma?





Explanation

Distinguishing enchondroma from low-grade chondrosarcoma can be challenging. The most reliable histological feature of low-grade chondrosarcoma is its infiltrative growth pattern, demonstrating permeation of the marrow space and entrapment of pre-existing host lamellar bone trabeculae.

Question 48

In the pathogenesis of periprosthetic joint infection (PJI), bacteria establish a biofilm on the implant surface. Which molecular mechanism allows these bacteria to communicate and coordinate the gene expression necessary for biofilm maturation?





Explanation

Quorum sensing is a cell-to-cell communication mechanism used by bacteria to regulate gene expression in response to fluctuations in cell-population density. It is essential for the coordination and maturation of biofilms in periprosthetic joint infections.

Question 49

A 35-year-old man sustains a 'terrible triad' injury of the elbow following a fall. When performing surgical stabilization, what is the generally accepted and most biomechanically sound sequence of repair?





Explanation

The standard surgical algorithm for a terrible triad injury (elbow dislocation, radial head fracture, coronoid fracture) works from deep to superficial and typically from medial to lateral: 1) Coronoid repair or fixation, 2) Radial head repair or replacement, 3) Lateral collateral ligament (LCL) repair. If the elbow remains unstable, MCL repair or an external fixator may be considered.

Question 50

Adult acquired flatfoot deformity is often initiated by posterior tibial tendon dysfunction, leading to attenuation of the spring ligament complex. Which component of the spring ligament is the thickest, most clinically significant, and provides the primary static support to the talar head?





Explanation

The spring ligament complex consists of three main bands. The superomedial calcaneonavicular ligament is the thickest and most crucial component, providing primary static support to the talar head. Its attenuation allows plantar and medial migration of the talar head in adult acquired flatfoot deformity.

Question 51

A 16-year-old gymnast with an L5-S1 isthmic spondylolisthesis develops progressively worsening radicular leg pain. Imaging reveals an L5 pars defect with a Grade II slip and significant foraminal stenosis. Which nerve root is most likely compressed, and where does the compression occur?





Explanation

In L5-S1 isthmic spondylolisthesis, the exiting L5 nerve root is most commonly compressed within the neural foramen. The compression is typically caused by the hypertrophic fibrocartilaginous mass at the pars interarticularis defect (the 'Gill lesion').

Question 52

During a total knee arthroplasty, after making standard bony cuts and inserting trial components, the surgeon notes that the joint is tight in full extension but perfectly balanced in 90 degrees of flexion. Which of the following is the most appropriate corrective action?





Explanation

A knee that is tight in extension but balanced in flexion indicates an asymmetric extension gap. To increase the extension gap without affecting the flexion gap, the surgeon should resect more distal femur or release the posterior capsule.

Question 53

A 6-year-old boy sustains a completely displaced, extension-type supracondylar humerus fracture with posterolateral displacement of the distal fragment. On examination, he is unable to make an 'OK' sign. Which nerve is most likely injured?





Explanation

The anterior interosseous nerve (AIN), a branch of the median nerve, is the most commonly injured nerve in extension-type supracondylar humerus fractures, particularly those with posterolateral displacement. The inability to flex the IP joint of the thumb and DIP joint of the index finger (the 'OK' sign) indicates AIN palsy.

Question 54

According to the Young-Burgess classification of pelvic ring injuries, which of the following ligamentous disruptions distinguishes an Anteroposterior Compression III (APC III) injury from an APC II injury?





Explanation

In the Young-Burgess classification, an APC II injury involves disruption of the pubic symphysis, anterior sacroiliac (SI) ligaments, and the sacrotuberous/sacrospinous ligaments, but the posterior SI ligaments remain intact. An APC III injury involves complete disruption of both the anterior and posterior SI ligaments, resulting in complete spinopelvic dissociation.

Question 55

A 42-year-old female presents with volar forearm pain and numbness in her thumb, index, and middle fingers. The physician suspects Pronator Syndrome rather than Carpal Tunnel Syndrome (CTS). Which clinical finding strongly supports a diagnosis of Pronator Syndrome over CTS?





Explanation

The palmar cutaneous branch of the median nerve provides sensation to the thenar eminence and branches off proximal to the carpal tunnel. Sensation over the thenar eminence is preserved in Carpal Tunnel Syndrome but is decreased in proximal median nerve entrapment neuropathies like Pronator Syndrome.

Question 56

A 20-year-old man presents with nocturnal thigh pain that is completely relieved by ibuprofen. Imaging shows a 1 cm radiolucent nidus with surrounding sclerosis in the femoral diaphysis. What is the primary biochemical mechanism underlying the effectiveness of NSAIDs for this specific lesion?





Explanation

Osteoid osteomas characteristically cause severe nocturnal pain that is relieved by NSAIDs. This is because the nidus cells produce high levels of prostaglandins (specifically PGE2) due to marked expression of cyclooxygenase-2 (COX-2) enzymes. NSAIDs inhibit this COX-2 activity, directly eliminating the source of the pain.

Question 57

During biomechanical testing of a tendon graft, the graft is rapidly stretched to a specific length and held at that constant length. Over time, the force required to maintain that length progressively decreases. This viscoelastic property is termed:





Explanation

Stress relaxation is the decrease in stress (force) over time when a viscoelastic material is held at a constant strain (length). Creep is the progressive increase in strain (length) over time when the material is held at a constant stress (load).

Question 58

In the Snyder classification of Superior Labrum Anterior and Posterior (SLAP) lesions, a Type II tear is defined by which of the following characteristics?





Explanation

The Snyder classification describes SLAP tears: Type I is fraying of the superior labrum with an intact 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 anchor. Type IV is a bucket-handle tear extending into the biceps tendon.

Question 59

According to the American Society for Bone and Mineral Research (ASBMR) criteria, which of the following is a REQUIRED major radiographic feature for the diagnosis of an atypical femur fracture (AFF) associated with prolonged bisphosphonate use?





Explanation

ASBMR major criteria for an atypical femur fracture include: location along the femoral diaphysis from just distal to the lesser trochanter to just proximal to the supracondylar flare, a transverse or short oblique fracture line originating at the lateral cortex, noncomminuted or minimally comminuted, and often a localized periosteal reaction of the lateral cortex ('beaking').

Question 60

A 35-year-old recreational athlete sustains an acute Achilles tendon rupture. The injury most commonly occurs in a hypovascular 'watershed' region. Where is this region anatomically located relative to the calcaneal insertion?





Explanation

The Achilles tendon receives its blood supply from the paratenon and osseous insertions, but it has a relatively hypovascular 'watershed' zone located approximately 2 to 6 cm proximal to its insertion on the calcaneus. This is the most common site for degenerative changes and acute ruptures.

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Consultant Orthopedic & Spine Surgeon
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