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Arab Orthopaedic Board MCQs - Part 38

27 Apr 2026 87 min read 92 Views
Arab Ortho Board MCQs - Part 37

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Arab Orthopaedic Board MCQs - Part 38

Comprehensive 100-Question Exam


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Question 1

A 28-year-old male is brought to the emergency department after a high-speed motorcycle collision. Pelvic radiographs reveal an anteroposterior compression (APC) type III pelvic ring injury. Clinically, he has blood at the urethral meatus and a high-riding prostate on digital rectal examination. Which of the following is the most appropriate next step in the management of his suspected urologic injury?





Explanation

Blood at the urethral meatus, a high-riding prostate, and perineal bruising are classic signs of a posterior urethral injury, which is highly associated with pelvic fractures (especially those involving disruption of the pubic symphysis). A retrograde urethrogram (RUG) is the gold standard diagnostic test to evaluate the integrity of the urethra. Blind insertion of a Foley catheter is contraindicated as it may convert a partial urethral tear into a complete tear. A CT cystogram is useful for diagnosing bladder ruptures but should be performed only after the urethra has been cleared.

Question 2

A 10-year-old boy with a BMI in the 99th percentile and height in the 3rd percentile presents with bilateral knee pain and a waddling gait. Radiographs confirm bilateral Slipped Capital Femoral Epiphysis (SCFE). Given his age and height percentile, an endocrine workup is initiated. Which of the following is the most commonly associated endocrinopathy in this clinical scenario?





Explanation

Hypothyroidism is the most common endocrine disorder associated with Slipped Capital Femoral Epiphysis (SCFE). Patients with endocrine-related SCFE typically present at an atypical age (either younger than 10 or older than 16), often with short stature, and frequently have bilateral involvement. The combination of obesity and decreased height velocity strongly suggests hypothyroidism, distinguishing it from typical idiopathic SCFE where patients may be obese but are usually of normal or increased height.

Question 3

A 55-year-old active female undergoes a primary total hip arthroplasty using a ceramic-on-ceramic bearing surface. Two years later, she presents complaining of an audible 'squeaking' sound from the hip during walking, bending, and ascending stairs. There is no pain, and radiographs show well-fixed components. Which of the following factors is most strongly associated with the development of squeaking in ceramic-on-ceramic articulations?





Explanation

Squeaking is a specific complication associated with ceramic-on-ceramic (CoC) bearing surfaces, occurring in up to 10% of patients. The most consistent biomechanical factor linked to CoC squeaking is edge-loading, which typically results from malpositioning of the acetabular component—specifically high inclination (steep cup) and extreme anteversion or retroversion. Edge-loading disrupts the fluid film lubrication, leading to stripe wear and the subsequent squeaking phenomenon.

Question 4

A 22-year-old professional rugby player sustains a closed hyperextension injury to his right ring finger while grabbing an opponent's jersey. He is unable to actively flex the distal interphalangeal (DIP) joint. Radiographs show a small bony fragment at the level of the A4 pulley. Surgical exploration reveals that the flexor digitorum profundus (FDP) tendon has avulsed from the bony fragment and retracted into the palm. Which Leddy and Packer classification type does this injury represent?





Explanation

The Leddy and Packer classification describes FDP avulsion injuries (Jersey finger). Type I involves retraction into the palm (disrupting all vincula, requires repair within 7-10 days). Type II retracts to the PIP joint (held by intact vincula). Type III involves a large bony avulsion that catches at the A4 pulley, preventing further retraction. Type IV is a double avulsion, where the tendon avulses from the bony fragment; the bony fragment remains at the A4 pulley, but the tendon retracts into the palm. Type V involves a bony avulsion with an intra-articular fracture of the distal phalanx.

Question 5

A 45-year-old male presents with a 4-week history of radiating neck pain into his right arm. Physical examination reveals a diminished reflex, specific motor weakness, and sensory alterations. Which of the following constellations of physical examination findings is most consistent with a C6 radiculopathy?





Explanation

A C6 radiculopathy typically results from compression of the C6 nerve root (often due to a C5-C6 disc herniation). The classic clinical presentation includes weakness in wrist extension and elbow flexion (the latter shared with C5), sensory loss or paresthesias over the lateral forearm, thumb, and index finger, and a diminished or absent brachioradialis reflex.

Question 6

During an arthroscopic anterior cruciate ligament (ACL) reconstruction using a hamstring autograft, the surgeon elects to drill the femoral tunnel independently through an accessory anteromedial portal rather than using a transtibial technique. Which of the following is the most recognized anatomical risk or complication specifically associated with anteromedial portal femoral drilling?





Explanation

Drilling the femoral tunnel through an accessory anteromedial portal allows for more anatomic, independent placement of the tunnel compared to the transtibial technique. However, it requires acute knee flexion (hyperflexion to at least 120 degrees) to properly orient the drill. A major risk with this technique is drilling too posterior or shallow, leading to a critically short femoral tunnel or a posterior wall blowout of the lateral femoral condyle. Transtibial drilling is historically associated with tunnels that are placed too vertical and high in the notch.

Question 7

A 30-year-old construction worker drops a heavy steel beam on the midfoot. Non-weight-bearing radiographs are initially read as normal, but weight-bearing films demonstrate a 3 mm diastasis between the base of the first and second metatarsals. An MRI confirms a complete rupture of the Lisfranc ligament. Which of the following correctly describes the anatomical attachments of the primary Lisfranc ligament?





Explanation

The Lisfranc ligament is an essential stabilizing structure of the midfoot. It is an interosseous ligament that runs obliquely from the plantar-lateral aspect of the medial cuneiform to the plantar-medial aspect of the base of the second metatarsal. There is no direct transverse ligamentous connection between the bases of the first and second metatarsals, making the Lisfranc ligament the critical restraint to lateral displacement of the lesser metatarsals.

Question 8

A 16-year-old male presents with severe knee pain after minor trauma. Radiographs show a purely lytic, expansile lesion in the distal femoral metaphysis. MRI demonstrates multiple fluid-fluid levels within the lesion. An incisional biopsy is performed to differentiate between an aneurysmal bone cyst (ABC) and a telangiectatic osteosarcoma. Which of the following histological findings definitively confirms a diagnosis of telangiectatic osteosarcoma?





Explanation

Telangiectatic osteosarcoma mimics an aneurysmal bone cyst (ABC) both radiographically (lytic, expansile) and on MRI (fluid-fluid levels). Grossly, both appear as blood-filled, cystic spaces. The crucial differentiating factor is histological: while an ABC has benign septa containing fibroblasts, reactive woven bone, and multinucleated giant cells, a telangiectatic osteosarcoma is characterized by highly atypical, pleomorphic, and malignant sarcomatous cells with frequent mitoses located within the septations.

Question 9

Bone Morphogenetic Proteins (BMPs) play a critical role in osteoinduction and are members of the transforming growth factor-beta (TGF-beta) superfamily. Following the binding of a BMP ligand to its transmembrane serine/threonine kinase receptor, which intracellular signaling molecules are directly phosphorylated to translocate to the nucleus and initiate transcription of osteogenic genes?





Explanation

BMP signaling operates primarily through the canonical Smad pathway. When BMP binds to its type I and type II serine/threonine kinase receptors, it induces phosphorylation of the receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These phosphorylated R-Smads then form a complex with the common-partner Smad (co-Smad, Smad 4) and translocate to the nucleus to regulate the transcription of target genes necessary for osteoblast differentiation.

Question 10

A 40-year-old pedestrian is struck by a vehicle and sustains a high-energy fracture of the knee. Radiographs reveal a depressed, displaced fracture of the medial tibial plateau with an associated intercondylar eminence extension. According to the Schatzker classification, this is a Type IV fracture. Which of the following statements correctly describes the primary mechanism of injury and the most critical associated neurovascular risk?





Explanation

A Schatzker IV fracture involves the medial tibial plateau. The medial plateau is structurally denser and stronger than the lateral plateau, meaning fractures here require significantly higher energy, typically a varus force combined with axial loading. Because of this high-energy mechanism and the close anatomical proximity of the popliteal artery to the posterior aspect of the knee (tethered at the adductor hiatus and soleal arch), these fractures carry a notoriously high risk of popliteal artery injury and knee dislocation equivalents.

Question 11

A 3-month-old female infant is being treated with a Pavlik harness for Developmental Dysplasia of the Hip (DDH). During her 2-week follow-up, the mother reports that the infant is not kicking her left leg as much as the right. On examination, the infant exhibits absent active knee extension on the left side, although she withdraws to pain. Passive range of motion is full. Which of the following adjustments to the Pavlik harness is the most appropriate next step in management?





Explanation

The infant is presenting with a femoral nerve palsy, a known complication of the Pavlik harness. This occurs due to excessive hyperflexion of the hip, which compresses or stretches the femoral nerve against the inguinal ligament or pelvic brim. The clinical sign is a loss of active knee extension. The appropriate management is to temporarily loosen or release the anterior flexion straps to reduce the degree of hip flexion, allowing the nerve to recover. Abandoning the harness entirely is not immediately indicated unless the palsy fails to resolve.

Question 12

During a primary total knee arthroplasty in a patient with a fixed varus deformity of 15 degrees, a step-wise medial soft tissue release is undertaken. Following the release of the deep medial collateral ligament and osteophytes, the joint remains excessively tight medially in extension, but is balanced in flexion. What is the most appropriate next step in the soft tissue release sequence?





Explanation

In a varus knee undergoing TKA, medial releases should be targeted based on whether the knee is tight in flexion, extension, or both. The deep MCL affects both. If the knee remains tight specifically in extension (but balanced in flexion), the posteromedial corner structures must be released. This includes the posterior oblique ligament, the posteromedial capsule, and potentially the semimembranosus expansion. Releasing the superficial MCL (sMCL) predominantly affects the flexion gap more than the extension gap, and extensive release of the sMCL risks creating instability.

Question 13

A 24-year-old male presents with radial-sided wrist pain after a fall onto an outstretched hand. Imaging reveals a displaced fracture of the proximal pole of the scaphoid. Surgical fixation with a headless compression screw is planned. Which of the following surgical approaches is most appropriate for optimal screw placement and preservation of the scaphoid blood supply in this specific fracture pattern?





Explanation

The blood supply to the scaphoid is primarily retrograde, entering the distal pole and dorsal ridge via branches of the radial artery. The proximal pole relies entirely on intraosseous blood flow from distal to proximal. For proximal pole fractures, a dorsal approach (typically between the 3rd and 4th extensor compartments) is preferred because it avoids damage to the dominant volar/distal blood supply (the palmar radiocarpal branches), prevents division of critical volar ligaments (e.g., radioscaphocapitate ligament), and provides direct, collinear access to the proximal pole for screw trajectory along the central axis of the scaphoid.

Question 14

A 68-year-old female presents with bilateral leg pain and cramping that worsens with prolonged standing and walking, but improves when she leans forward over a shopping cart. MRI demonstrates severe central lumbar spinal stenosis at L4-L5. Hypertrophy of which of the following ligaments is the primary contributor to dorsal compression of the thecal sac in this condition?





Explanation

The patient exhibits classic symptoms of neurogenic claudication ('shopping cart sign') secondary to lumbar spinal stenosis. Central canal stenosis in the degenerative spine is typically caused by a combination of anterior compression (disc bulging), lateral compression (facet joint hypertrophy), and dorsal compression. The ligamentum flavum, which spans the laminae posteriorly, undergoes age-related hypertrophy and buckling, acting as the primary dorsal compressive force on the thecal sac and nerve roots.

Question 15

A 19-year-old collegiate soccer player undergoes an MRI of the knee after a twisting injury, which demonstrates a 'ghost sign' on successive sagittal images through the mid-body of the lateral meniscus. This radiographic sign is pathognomonic for which type of meniscal tear?





Explanation

The 'ghost sign' (or empty meniscus sign) on a sagittal MRI is a characteristic finding of a complete radial tear of the meniscus. Because a radial tear runs perpendicular to the long axis of the meniscus, consecutive sagittal slices through the tear will show an absence of the normal low-signal meniscal tissue (the 'bow-tie' is missing), leaving a blank space or 'ghost'. This is crucial to identify as radial tears severely disrupt the hoop stresses of the meniscus, often requiring surgical repair in young athletes.

Question 16

A 35-year-old male sustains an acute, closed Achilles tendon rupture while playing basketball. He elects to undergo a percutaneous repair technique. During the placement of sutures into the proximal tendon stump, which of the following structures is at the highest risk of iatrogenic injury?





Explanation

The sural nerve courses distally down the posterior aspect of the calf. Approximately 10 cm proximal to the calcaneal insertion, it crosses from the midline to the lateral border of the Achilles tendon. During percutaneous or minimally invasive repair of the Achilles tendon, blind passage of sutures in the proximal stump (especially laterally) puts the sural nerve at high risk for entrapment or transection. To minimize this, careful blunt dissection or ultrasound guidance is often utilized laterally.

Question 17

A 55-year-old male is diagnosed with a massive conventional chondrosarcoma of the proximal femur. Staging shows no evidence of distant metastasis. The multidisciplinary tumor board recommends treatment. Which of the following constitutes the primary and most effective treatment modality for conventional intermediate to high-grade chondrosarcomas?





Explanation

Conventional chondrosarcomas are characterized by abundant extracellular cartilage matrix, poor vascularity, and slow division rates, rendering them highly resistant to both chemotherapy and radiation therapy. Therefore, the mainstay of treatment for intermediate (Grade II) to high-grade (Grade III) conventional chondrosarcomas is wide surgical excision with negative margins. Intralesional curettage is only considered for benign cartilage lesions (enchondromas) or very select low-grade (Grade I/atypical cartilaginous tumors) in the appendicular skeleton.

Question 18

Articular cartilage is structurally divided into four distinct zones: superficial, middle (transitional), deep, and calcified. Which of the following biochemical and structural descriptions is most accurate regarding the deep zone of normal adult articular cartilage?





Explanation

The deep (or radial) zone of articular cartilage represents the layer closest to the tidemark (which separates it from the calcified cartilage). It is characterized by having the lowest water content, the highest concentration of proteoglycans (which provides excellent resistance to compressive forces), and thick Type II collagen fibers that are oriented perpendicular to the joint surface. The superficial zone has the highest water content and parallel collagen fibers to resist shear stress.

Question 19

A 45-year-old woman falls on her outstretched hand and sustains a volar Barton's fracture (a displaced intra-articular fracture of the distal radius with volar subluxation of the carpus). The volar marginal fragment typically remains attached to the carpus due to the intact volar radiocarpal ligaments. Which specific ligaments are primarily responsible for this continued attachment?





Explanation

A volar Barton's fracture involves a volar shear fragment of the distal radius. The carpus displaces volarly with this fracture fragment because of the strong, intact volar radiocarpal ligaments—specifically the short radiolunate and long radiolunate ligaments, which originate from the volar lip of the distal radius. Reduction and stabilization of this bony fragment via a volar buttress plate inherently reduces the carpus back to its anatomic position.

Question 20

A 6-year-old child presents with a completely displaced, extension-type supracondylar humerus fracture. Prior to intervention, the hand is pale and pulseless. The child is taken to the operating room, where an anatomic closed reduction is achieved and pinned with three divergent lateral Kirschner wires. Post-reduction, the radial pulse remains impalpable by Doppler, but the hand is now warm, pink, and has a capillary refill of less than 2 seconds. What is the most appropriate next step in management?





Explanation

The management of the 'pink, pulseless hand' following a successfully reduced and pinned supracondylar humerus fracture is observation. If the hand is well-perfused (warm, pink, brisk capillary refill < 2 seconds) despite the absence of a palpable pulse, it indicates adequate collateral circulation. Current pediatric orthopedic guidelines recommend admission and close monitoring. Surgical exploration of the brachial artery is indicated if the hand remains pale and poorly perfused (ischemic) after reduction.

Question 21

A 3-year-old girl is undergoing surgical treatment for developmental dysplasia of the hip (DDH). The surgeon performs a pelvic osteotomy that is described as an incomplete, pericapsular osteotomy that hinges on the triradiate cartilage, allowing the acetabular roof to be hinged downward to improve anterolateral coverage, thereby decreasing the volume of the acetabulum. Which osteotomy is being described?





Explanation

The Pemberton osteotomy is an incomplete transiliac osteotomy that hinges at the triradiate cartilage, altering the shape and decreasing the volume of the acetabulum. The Salter osteotomy is a complete osteotomy that hinges at the pubic symphysis without changing the acetabular volume. The Dega osteotomy also hinges at the triradiate cartilage but leaves the inner table of the ilium intact.

Question 22

A 65-year-old male presents with deteriorating handwriting, difficulty buttoning his shirt, and a broad-based, unsteady gait. Examination reveals a positive Hoffman's sign and hyperreflexia in the lower extremities. Which of the following physical examination tests specifically assesses upper extremity fine motor function in the setting of cervical myelopathy by counting repetitions?





Explanation

The 10-second grip and release test is used to evaluate fine motor coordination and hand function in patients with cervical myelopathy. A normal result is the ability to fully open and close the hand 20 or more times in 10 seconds. Spurling's test evaluates cervical radiculopathy, while Lhermitte's sign indicates posterior column irritation.

Question 23

A 55-year-old male presents with deep thigh pain. Radiographs of the proximal femur demonstrate a large, lucent lesion with intralesional "ring and arc" calcifications and endosteal scalloping involving more than 2/3 of the cortical thickness. Core needle biopsy confirms atypical chondrocytes with abundant hypercellular stroma, consistent with an intermediate-grade (Grade 2) conventional chondrosarcoma. What is the most appropriate management?





Explanation

Conventional chondrosarcomas (Grades 2 and 3) are treated with wide surgical resection to achieve negative margins. They are notoriously resistant to both chemotherapy and radiation therapy. Extended curettage is only appropriate for benign cartilage tumors or select low-grade (Grade 1) atypical cartilaginous tumors in the appendicular skeleton.

Question 24

In the Young-Burgess classification, an Anteroposterior Compression (APC) Type II pelvic ring injury is characterized by pubic symphysis diastasis and disruption of which of the following posterior ring structures?





Explanation

An APC II injury involves widening of the pubic symphysis and rupture of the anterior sacroiliac ligaments, sacrospinous, and sacrotuberous ligaments. The strong posterior sacroiliac ligaments remain intact, which prevents vertical displacement but allows the hemipelvis to "open like a book," resulting in rotational instability.

Question 25

A 45-year-old female sustains a completely detached posterior root tear of the medial meniscus. From a biomechanical perspective, what is the direct consequence of this injury on the knee joint?





Explanation

A complete tear of the medial meniscal root disrupts the transmission of circumferential hoop stresses. Biomechanical studies have shown that this results in a loss of meniscal function and an increase in peak contact pressures equivalent to that of a total meniscectomy, predisposing the knee to rapid medial compartment osteoarthritis.

Question 26

A patient presents with an irreversible high radial nerve palsy following a humerus fracture. The surgeon elects to perform a tendon transfer to restore wrist, finger, and thumb extension. The classic Boyes transfer specifically utilizes which of the following tendon transpositions to restore finger extension (Extensor Digitorum Communis)?





Explanation

The Boyes transfer relies on the flexor digitorum superficialis (FDS) of the middle finger transferred through the interosseous membrane to the EDC to restore finger extension. It also uses the FDS of the ring finger to the EIP and EPL. In contrast, standard transfers (like the modified Green transfer) use the FCU or FCR to EDC.

Question 27

A 24-year-old football player sustains a hyperplantarflexion injury to his midfoot. Weight-bearing radiographs reveal a subtle widening between the first and second metatarsal bases, and a "fleck sign" is present. The Lisfranc ligament, which is critical for midfoot stability and is avulsed in this scenario, connects which two anatomic structures?





Explanation

The Lisfranc ligament is a strong interosseous ligament that runs obliquely 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.

Question 28

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic environment, such as the human body. Which of the following combinations of orthopedic implants poses the highest risk for significant galvanic corrosion and is thus generally contraindicated?





Explanation

Stainless steel and Titanium (or Cobalt-chromium) have vastly different electrochemical potentials (anodic indices). Mixing stainless steel with Titanium or CoCr in the same construct leads to severe galvanic corrosion, preferentially degrading the more anodic metal (stainless steel). Titanium and Cobalt-chromium are frequently used together (e.g., modular THA) because their electrochemical potentials are similar, making the risk of clinical galvanic corrosion minimal.

Question 29

A 22-year-old male falls on an outstretched hand and sustains a displaced fracture through the waist of the scaphoid. He is at high risk for developing avascular necrosis of the proximal pole. This risk is primarily due to the retrograde intraosseous blood supply of the scaphoid, which is derived mainly from which vessel?





Explanation

The scaphoid receives 70-80% of its blood supply from branches of the radial artery, specifically via the dorsal carpal branch. These vessels enter the scaphoid distally and flow in a retrograde direction to supply the proximal pole. Thus, waist or proximal fractures interrupt this supply, leading to avascular necrosis.

Question 30

A 13-year-old boy presents with a limp and obligate external rotation of his left hip during passive flexion, indicative of a slipped capital femoral epiphysis (SCFE). Relative to the capital femoral epiphysis, in what direction does the femoral neck (metaphysis) displace in a typical SCFE?





Explanation

In a SCFE, the capital femoral epiphysis remains secured within the acetabulum while the femoral metaphysis (neck) displaces anteriorly and superiorly. This gives the radiographic appearance that the epiphysis has slipped posteriorly and inferiorly.

Question 31

A surgeon is performing a total hip arthroplasty using an approach that exploits the internervous plane between the superior gluteal nerve and the femoral nerve. Which of the following describes the muscles defining this surgical interval?





Explanation

The anterior approach to the hip (Smith-Petersen) uses the internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve) superficially.

Question 32

In the Thoracolumbar Injury Classification and Severity Score (TLICS), neurological status is a primary determinant of the final score and treatment recommendation. Which of the following neurological statuses is assigned the highest point value (3 points)?





Explanation

In the TLICS system, neurological status is scored as: Intact = 0; Nerve root injury = 2; Complete spinal cord injury = 2; Incomplete spinal cord injury or cauda equina syndrome = 3. Incomplete SCI scores highest because surgical decompression is most likely to result in neurological improvement.

Question 33

A 52-year-old male presents with advanced Scapholunate Advanced Collapse (SLAC) wrist following an untreated scapholunate ligament dissociation. As the predictable pattern of progressive articular degeneration occurs, which of the following joints is classically spared?





Explanation

In SLAC wrist, the radiolunate joint is characteristically spared from degenerative changes. This is because the lunate and the lunate fossa of the radius possess a concentrically spherical articulation that is maintained even when the lunate falls into a DISI deformity. The degeneration predictably occurs at the radial styloid, then the entire radioscaphoid joint, and finally the capitolunate joint.

Question 34

During fracture healing via endochondral ossification, undifferentiated mesenchymal stem cells are directed to differentiate along various lineages. Which of the following transcription factors is considered the essential "master regulator" for the differentiation of mesenchymal stem cells into osteoblasts?





Explanation

Runx2 (also known as Cbfa1) is the core transcription factor required for osteoblast differentiation and bone formation. A deficiency in Runx2 leads to cleidocranial dysplasia. SOX9 directs chondrogenic differentiation, PPAR-gamma directs adipogenesis, and MyoD directs myogenesis.

Question 35

During an anterior cruciate ligament (ACL) reconstruction, a surgeon places the femoral tunnel very high in the intercondylar notch, corresponding to the "12 o'clock" position in the coronal plane. What is the most likely biomechanical consequence of this vertically oriented graft placement?





Explanation

A vertical femoral tunnel (e.g., 12 o'clock position) produces a highly isometric graft that effectively limits anterior-posterior translation (Lachman) but biomechanically fails to reproduce the native ACL's oblique orientation, resulting in an inability to control rotational instability (evidenced by a persistent positive pivot-shift test).

Question 36

A 32-year-old male sustains a closed tibia fracture and develops worsening leg pain out of proportion to the injury. Suspecting acute compartment syndrome, the surgeon decides to measure tissue pressure. The modern threshold for performing a fasciotomy is defined by calculating the "delta P" (ΔP). Which of the following correctly defines the ΔP threshold used as an absolute indication for fasciotomy?





Explanation

The Delta P (ΔP) is calculated as the Diastolic Blood Pressure minus the intracompartmental pressure. A ΔP of 30 mmHg or less (e.g., Diastolic BP is 70 and compartment pressure is 45; 70-45 = 25) indicates inadequate tissue perfusion and is a strong indication for urgent four-compartment fasciotomy. Absolute pressure thresholds are less reliable because perfusion pressure is dependent on systemic blood pressure.

Question 37

A 28-year-old female undergoes curettage for a giant cell tumor (GCT) of the distal femur. The histology demonstrates multinucleated giant cells within a stroma of mononuclear cells. The neoplastic mononuclear cells express a specific ligand that promotes the recruitment and formation of the reactive osteoclast-like giant cells. What is this ligand?





Explanation

In Giant Cell Tumor of bone, the neoplastic cells are actually the spindled mononuclear stromal cells. These cells highly express RANKL, which binds to RANK on normal macrophages, driving them to fuse and differentiate into the massive, bone-destroying osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, is utilized therapeutically for unresectable GCT.

Question 38

An infant is being treated for congenital idiopathic clubfoot using the Ponseti casting technique. The sequence of correction of the individual deformities is critical to achieving a successful outcome. According to the Ponseti method, which specific component of the deformity must be corrected FIRST?





Explanation

In the Ponseti method, the mnemonic CAVE dictates the order of correction: Cavus, Adductus, Varus, Equinus. The cavus is corrected first by elevating (supinating) the first metatarsal to align the forefoot with the hindfoot. Only then is the foot abducted to correct the adductus and varus, followed finally by addressing the equinus (often requiring a percutaneous Achilles tenotomy).

Question 39

A 55-year-old poorly controlled diabetic patient presents with a swollen, warm, erythematous foot without an open ulcer or history of trauma. Radiographs show subluxation of the tarsometatarsal joints, osteopenia, and periarticular debris. According to the Eichenholtz classification, this stage of Charcot arthropathy is characterized primarily by which of the following?





Explanation

The Eichenholtz classification of Charcot arthropathy has three main stages: Stage I (Development/Fragmentation) is marked by active bone fragmentation, subluxation/dislocation, joint effusion, and debris formation. Stage II (Coalescence) is marked by absorption of fine debris and early fusion. Stage III (Consolidation/Reconstruction) is marked by remodeling, rounding of bone ends, and stable fusion/ankylosis.

Question 40

In modern total hip arthroplasty, the use of highly cross-linked ultra-high-molecular-weight polyethylene (HXLPE) has significantly reduced the rate of wear and subsequent osteolysis. However, the processes of cross-linking and subsequent thermal treatment (melting or annealing) primarily result in which of the following mechanical trade-offs?





Explanation

While highly cross-linked polyethylene substantially improves wear resistance (decreasing abrasive and adhesive wear), the higher cross-link density—along with thermal treatments to eliminate free radicals—makes the material more brittle. This results in decreased mechanical properties, specifically decreased fatigue strength, ultimate tensile strength, and fracture toughness, which can increase the risk of catastrophic liner fracture.

Question 41

A 25-year-old professional baseball pitcher presents with posterior shoulder pain during the late cocking phase of throwing. He is diagnosed with internal impingement. Which of the following physical exam findings is most characteristically associated with this condition?





Explanation

Internal impingement (posterosuperior impingement) occurs when the greater tuberosity abuts the posterosuperior glenoid during extreme abduction and external rotation. It is highly associated with Glenohumeral Internal Rotation Deficit (GIRD) in overhead athletes, driven by repetitive microtrauma leading to contracture of the posterior capsule and posterior band of the inferior glenohumeral ligament.

Question 42

A 45-year-old male is brought to the trauma bay after a crush injury. Radiographs reveal an Anterior-Posterior Compression type III (APC-III) pelvic ring injury. If the patient develops life-threatening arterial hemorrhage, which of the following vessels is most commonly the source and targeted for embolization?





Explanation

Arterial bleeding in APC pelvic fractures is typically from the anterior division of the internal iliac artery, most commonly the internal pudendal or obturator arteries. In contrast, Lateral Compression (LC) injuries more commonly compromise the superior gluteal artery, which is a branch of the posterior division.

Question 43

A 12-year-old obese male presents with knee and thigh pain. Radiographs demonstrate a classic 'ice cream slipping off a cone' appearance of the proximal femur, diagnostic of Slipped Capital Femoral Epiphysis (SCFE). The pathophysiology of this condition involves a mechanical failure primarily through which histological zone of the physis?





Explanation

Slipped Capital Femoral Epiphysis (SCFE) occurs due to mechanical shear forces across a susceptible physis. The slippage invariably occurs through the hypertrophic zone of the physis, which is structurally the weakest layer because it lacks collagen matrix and is composed of large, swollen chondrocytes.

Question 44

A 35-year-old female presents with an inability to make an 'OK' sign with her thumb and index finger, demonstrating flattening of the distal interphalangeal joint of the index finger and interphalangeal joint of the thumb. She has no sensory deficits. Which nerve is compressed, and what is the most common anatomic site of entrapment?





Explanation

The patient has Anterior Interosseous Nerve (AIN) syndrome, evidenced by weakness in the flexor pollicis longus (FPL) and flexor digitorum profundus (FDP) to the index finger. The AIN is a purely motor branch of the median nerve. Compression most commonly occurs at the deep head of the pronator teres or the fibrous arcade of the flexor digitorum superficialis (FDS).

Question 45

A 14-year-old male presents with chronic left knee pain. Radiographs show a well-defined, eccentric, lytic lesion localized entirely within the proximal tibial epiphysis, with a thin sclerotic margin. Biopsy reveals mononuclear cells with scattered multinucleated giant cells and areas of 'chicken-wire' calcification. What is the most likely diagnosis?





Explanation

Chondroblastoma is a rare benign cartilage tumor that characteristically arises in the epiphysis or apophysis of long bones in skeletally immature patients (open physis). Histologically, it is defined by chondroblasts, osteoclast-like giant cells, and distinctive pericellular ('chicken-wire') calcifications.

Question 46

A 60-year-old male presents with bilateral neurogenic claudication that improves when leaning forward on a shopping cart. MRI of the lumbar spine confirms severe central canal stenosis at L4-L5. Hypertrophy of which of the following ligaments directly contributes to the reduction in the cross-sectional area of the central canal?





Explanation

Lumbar spinal stenosis is commonly caused by a combination of disc bulging anteriorly, facet joint hypertrophy laterally, and ligamentum flavum hypertrophy posteriorly. The ligamentum flavum spans the interlaminar space and its infolding or hypertrophy directly encroaches on the posterior aspect of the central spinal canal.

Question 47

A 65-year-old female undergoes a primary total hip arthroplasty via a posterior approach. On post-operative day one, she is noted to have a profound foot drop and absent sensation over the dorsum of her foot, though sensation on the plantar aspect of the foot is intact. What structure was most likely injured during the procedure?





Explanation

The sciatic nerve consists of the common peroneal and tibial divisions. During a posterior approach to the hip, the peroneal division is uniquely vulnerable to injury (often from excessive traction or retractor placement) because it is tethered at the fibular head and sits more laterally. Injury results in foot drop (loss of dorsiflexion) and numbness over the dorsum of the foot.

Question 48

A 28-year-old male cyclist sustains a middle-third clavicle fracture after a fall. Radiographs show significant displacement with the medial fragment pulled superiorly and posteriorly. Which muscle is primarily responsible for the displacement of the medial fragment?





Explanation

In fractures of the midshaft clavicle, the medial fragment is typically displaced posterosuperiorly by the unopposed pull of the sternocleidomastoid muscle. The distal fragment is displaced inferiorly and medially by the weight of the arm and the pull of the pectoralis major and latissimus dorsi.

Question 49

A 40-year-old male presents with a long-standing, rigid, and painful flatfoot deformity. Examination reveals an inability to perform a single-leg heel rise and rigid hindfoot valgus. Radiographs show advanced osteoarthritis of the subtalar, talonavicular, and calcaneocuboid joints. What is the gold standard surgical intervention?





Explanation

The patient has a Stage III adult acquired flatfoot deformity (rigid flatfoot with degenerative changes). The gold standard treatment for a rigid deformity with arthritis involving the subtalar, talonavicular, and calcaneocuboid joints is a triple arthrodesis. Tendon transfers and osteotomies are reserved for flexible, earlier-stage deformities (Stage II).

Question 50

In the principles of internal fixation, several design parameters of a screw influence its biomechanical performance. Which of the following factors is the primary determinant of a screw's pullout strength from bone?





Explanation

The pullout strength of a bone screw is directly proportional to the outer (major) diameter of the screw, the length of thread engagement, and the shear strength of the bone. The inner (minor) diameter determines the screw's tensile and torsional strength (resistance to breakage/fatigue), not its pullout strength.

Question 51

A 6-year-old boy falls from monkey bars and sustains a widely displaced, extension-type supracondylar humerus fracture. After closed reduction and percutaneous pinning, the patient demonstrates an inability to flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. Which nerve is injured?





Explanation

The Anterior Interosseous Nerve (AIN) is the most frequently injured nerve in extension-type supracondylar humerus fractures (often contused by the proximal fragment). It innervates the flexor pollicis longus (FPL) and flexor digitorum profundus (FDP) to the index and long fingers. The radial nerve is the second most common, particularly in posteromedial displacement.

Question 52

During a primary total knee arthroplasty (TKA), the surgeon inserts the trial components and assesses the gaps. The knee is perfectly balanced and symmetrical in full extension, but it is too tight in flexion, preventing full range of motion. What is the most appropriate surgical modification to correct this specific mismatch?





Explanation

A knee that is tight in flexion but balanced in extension requires an isolated increase in the flexion gap. Downsizing the femoral component (smaller Anterior-Posterior dimension) shifts the posterior condyles anteriorly, effectively increasing the flexion gap without altering the extension gap. Resecting more distal femur or releasing the posterior capsule affects the extension gap. Resecting more tibia or changing the poly affects both gaps equally.

Question 53

A 35-year-old male undergoes intramedullary nailing for a severely comminuted diaphyseal tibia fracture. Twelve hours post-operatively, he complains of intractable leg pain exacerbated by passive toe flexion. If compartment syndrome is developing, which compartment is historically the most susceptible and contains the deep peroneal nerve?





Explanation

The anterior compartment of the leg is the most commonly affected compartment in acute compartment syndrome following tibia fractures. It contains the tibialis anterior, extensor hallucis longus, extensor digitorum longus, peroneus tertius, the anterior tibial artery, and the deep peroneal nerve.

Question 54

A 45-year-old male sustains a T12 burst fracture after a fall. He is neurologically intact. In calculating the Thoracolumbar Injury Classification and Severity (TLICS) score, which of the following radiographic findings is most specifically indicative of an unstable Posterior Ligamentous Complex (PLC) injury that would push the score toward surgical management?





Explanation

The Thoracolumbar Injury Classification and Severity (TLICS) score relies heavily on the status of the Posterior Ligamentous Complex (PLC). Widening of the interspinous distance is a direct radiographic sign of PLC disruption. A disrupted PLC scores 3 points on the TLICS system, heavily weighing the treatment algorithm toward surgical stabilization, even in the absence of neurologic deficit.

Question 55

A 25-year-old athlete undergoes anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone autograft. If the surgeon inadvertently places the femoral tunnel too far anteriorly (away from the isometric footprint), what is the most likely biomechanical consequence during postoperative range of motion?





Explanation

Placement of the femoral tunnel too anteriorly (shallow) in ACL reconstruction causes the graft to tension excessively as the knee flexes. This leads to a graft that is tight in flexion (often restricting flexion or stretching out the graft) and loose in extension. A tunnel placed too far posteriorly will result in a graft that is tight in extension.

Question 56

A 40-year-old carpenter sustains a puncture wound to the volar aspect of his index finger and presents 48 hours later with severe throbbing pain. Which of the following is NOT one of Kanavel's cardinal signs of acute flexor tenosynovitis?





Explanation

Kanavel's four cardinal signs of flexor tenosynovitis are: 1) fusiform swelling of the digit, 2) resting flexed posture, 3) tenderness along the flexor tendon sheath, and 4) disproportionate pain with passive extension. While dorsal pitting edema can occur in hand infections due to the loose dorsal skin and venous/lymphatic drainage, it is not one of the cardinal signs.

Question 57

The osteoinductive properties of bone grafts are heavily mediated by Bone Morphogenetic Proteins (BMPs). Which of the following BMPs is an FDA-approved recombinant product specifically indicated for the treatment of acute open tibial shaft fractures treated with an intramedullary nail?





Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA approved for acute open tibial shaft fractures (and anterior lumbar interbody fusions). rhBMP-7 (also known as Osteogenic Protein-1 or OP-1) previously held a Humanitarian Device Exemption for recalcitrant tibial nonunions.

Question 58

A 6-year-old boy is diagnosed with Legg-Calvé-Perthes disease. During the radiographic evaluation of the hip, the earliest sign of the fragmentation stage represents a subchondral fracture of the femoral head. What is the eponym or term for this specific radiographic finding?





Explanation

The 'crescent sign' in Legg-Calvé-Perthes disease (or avascular necrosis) represents a subchondral fracture and marks the beginning of the fragmentation stage. Waldenström's sign is an increase in the medial joint space seen very early. Trethowan's sign and Klein's line are associated with SCFE. The sagging rope sign is a late sign indicating a widened femoral neck and coxa magna.

Question 59

A 65-year-old male presents with indolent pain and stiffness 2 years after a primary anatomic total shoulder arthroplasty. His inflammatory markers (ESR, CRP) are within normal limits, but an aspirate is suspicious for infection. Intraoperative tissue cultures are sent. Which organism is classically associated with this type of insidious periprosthetic shoulder infection?





Explanation

Cutibacterium acnes (formerly Propionibacterium acnes) is a slow-growing, anaerobic, Gram-positive bacillus that resides in the sebaceous glands, predominantly around the shoulder. It is the classic organism responsible for insidious, culture-negative or late-presenting periprosthetic joint infections of the shoulder. Cultures must be held for up to 14 days to detect it.

Question 60

A 65-year-old female sustains a distal radius fracture treated with closed reduction and casting. Four weeks later, she complains of severe burning pain in the hand. On exam, the hand is swollen, erythematous, profoundly stiff, and demonstrates abnormal sweating and allodynia. What is the most likely diagnosis?





Explanation

The clinical picture of burning pain out of proportion, sudomotor/vasomotor changes, allodynia, and stiffness following trauma (like a distal radius fracture) is classic for Complex Regional Pain Syndrome (CRPS). It is classified as Type I (formerly Reflex Sympathetic Dystrophy) when there is no definable major nerve injury. Type II (formerly Causalgia) requires a distinct, identified nerve injury.

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