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Arab Orthopaedic Board MCQs - Part 10

27 Apr 2026 59 min read 77 Views
Arab Ortho Board MCQs - Part 9

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This article provides essential research regarding Arab Orthopaedic Board MCQs - Part 10. Practice Arab Orthopaedic Board MCQs Part 10. Review orthopedic surgery questions 451 to 500 for your board exam preparation.

Arab Orthopaedic Board MCQs - Part 10

Comprehensive 100-Question Exam


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Question 1

Which of the following bone morphogenetic proteins (BMPs) is actually a procollagen C-proteinase and does NOT belong to the transforming growth factor-beta (TGF-beta) superfamily?





Explanation

BMP-1 is unique among the bone morphogenetic proteins. While initially discovered alongside other BMPs, it was later identified as a metalloproteinase (specifically a procollagen C-proteinase) that facilitates cartilage and bone formation by cleaving the C-termini of procollagens I, II, and III. Unlike BMP-2, BMP-4, and BMP-7 (which are osteoinductive factors), BMP-1 does not belong to the TGF-beta superfamily and does not signal through SMAD pathways.

Question 2

A 35-year-old male is involved in a lateral impact motor vehicle collision. Pelvic radiographs demonstrate a lateral compression (LC) type II injury pattern with a 'crescent fracture' of the posterior ilium. The sacroiliac (SI) joint is disrupted anteriorly, but the posterior iliac fragment remains anchored to the sacrum. Which of the following ligaments is primarily responsible for maintaining this posterior attachment?





Explanation

In a lateral compression injury resulting in a crescent fracture of the ilium (Day classification), the anterior SI ligaments typically fail, but the strong posterior sacroiliac ligaments remain intact. The posterior SI ligament complex anchors the crescentic posterior iliac fragment to the sacrum. The fracture line predictably exits through the ilium, leaving the posterior SI joint intact.

Question 3

A patient presents 2 years after a posterior-stabilized (PS) total knee arthroplasty with anterior knee pain and a subjective feeling of the knee 'giving way' into recurvatum. Radiographs show no component loosening. Revision surgery is performed, and inspection of the polyethylene insert reveals advanced wear exclusively on the anterior aspect of the tibial post. Which of the following surgical errors most likely caused this specific wear pattern?





Explanation

Anterior post impingement in a PS total knee arthroplasty typically occurs in full extension or hyperextension. If the femoral component is placed in excessive flexion, the intercondylar box and cam mechanism can impinge on the anterior aspect of the tibial post as the knee reaches full extension. Other causes of anterior post impingement include inadequate posterior slope (or excessive anterior slope) of the tibial component and recurvatum deformity.

Question 4

Historically, the arcuate artery (ascending branch of the anterior humeral circumflex artery) was considered the primary blood supply to the humeral head. However, recent quantitative cadaveric and MRI studies have demonstrated that the principal arterial supply to the humeral head actually arises from which of the following?





Explanation

Recent anatomic and MRI studies (e.g., Hettrich et al.) have redefined the vascular anatomy of the proximal humerus, demonstrating that the posterior humeral circumflex artery (PHCA) provides approximately 64% of the blood supply to the humeral head. This paradigm shift highlights the importance of the PHCA, though preserving both vessels when possible during proximal humerus surgery remains ideal.

Question 5

A 24-year-old athlete sustains a twisting injury to his left knee. Physical examination reveals a positive Dial test with 15 degrees of increased external rotation at 30 degrees of knee flexion compared to the contralateral side. At 90 degrees of knee flexion, the external rotation is equal bilaterally. This examination finding is most consistent with an isolated injury to which of the following structures?





Explanation

The Dial test evaluates external rotation of the tibia relative to the femur. 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). If external rotation is increased at both 30 and 90 degrees, it indicates a combined injury to both the PLC and the posterior cruciate ligament (PCL).

Question 6

A 6-week-old female infant is placed in a Pavlik harness for developmental dysplasia of the hip (DDH). One week later, the parents report that the infant is no longer actively kicking her right leg. On examination, there is an absence of active knee extension on the right side. Which of the following is the most likely cause of this complication?





Explanation

Femoral nerve palsy is a known complication of the Pavlik harness, typically caused by excessive flexion of the hip. The hyperflexion causes the femoral nerve to become compressed against the inguinal ligament. Presentation includes loss of active quadriceps function (lack of active knee extension). The treatment is to temporarily remove or adjust the harness to reduce flexion, and the palsy almost always resolves spontaneously.

Question 7

A 45-year-old carpenter presents with forearm pain and an inability to make an 'OK' sign (unable to flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger). Sensation over the entire hand is intact. Given this clinical presentation, which of the following muscles will maintain NORMAL motor strength?





Explanation

The patient has Anterior Interosseous Nerve (AIN) syndrome, evidenced by the inability to make an 'OK' sign (loss of FPL and FDP to the index finger) with spared sensation. The AIN is a purely motor branch of the median nerve. It innervates the FPL, FDP to the index and middle fingers, and the pronator quadratus. The flexor carpi radialis (FCR) is innervated by the main trunk of the median nerve proximal to the branching of the AIN, so its strength will be normal.

Question 8

A 78-year-old male falls from a standing height and sustains a Type II odontoid fracture. Computed tomography reveals an anteriorly displaced fracture with an oblique fracture line running from anterior-inferior to posterior-superior. Which of the following is the most appropriate surgical management?





Explanation

In elderly patients with Type II odontoid fractures, conservative management (collar/halo) carries a high rate of nonunion and halo vests have significant morbidity/mortality. Surgical fixation is preferred. An anterior odontoid screw is contraindicated in this scenario because of the 'reverse obliquity' of the fracture line (anterior-inferior to posterior-superior), which would cause the fragment to shear anteriorly upon screw compression. Additionally, poor bone quality in an elderly patient is a relative contraindication for an anterior screw. Therefore, posterior C1-C2 fusion is the treatment of choice.

Question 9

A 25-year-old female presents with a painful, lucent, eccentrically located lesion in the distal femur metaphysis extending to the subchondral bone. Biopsy reveals a population of neoplastic mononuclear cells and reactive multinucleated giant cells. Which of the following describes the mechanism of action of the targeted medical therapy (Denosumab) used for severe or recurrent cases of this condition?





Explanation

Giant Cell Tumor (GCT) of bone is characterized by neoplastic mononuclear stromal cells that express high levels of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This recruits and activates reactive multinucleated giant cells (osteoclasts) that cause bone destruction. Denosumab is a humanized monoclonal antibody that binds to RANKL, preventing its interaction with the RANK receptor on the osteoclast precursor cells, thereby inhibiting their differentiation and activation.

Question 10

Articular cartilage is a highly specialized tissue divided into distinct structural zones. Which of the following zones contains the highest concentration of proteoglycans, the lowest water content, and collagen fibers oriented perpendicular to the articular surface?





Explanation

The deep (radial) zone of articular cartilage is responsible for resisting compressive forces. It has the highest concentration of proteoglycans (which provide compressive stiffness), the lowest water content, and thick collagen fibrils arranged perpendicular to the joint surface to anchor the uncalcified cartilage to the tidemark and calcified zone. The superficial zone has the highest water content and collagen oriented parallel to the joint.

Question 11

In the setting of a classic 'terrible triad' injury of the elbow (elbow dislocation, radial head fracture, and coronoid fracture), which of the following fracture patterns is most characteristic of the coronoid process injury?





Explanation

The typical coronoid fracture in a 'terrible triad' injury is a transverse fracture involving the tip of the coronoid (Regan-Morrey Type 1 or Type 2; O'Driscoll Tip fracture). This occurs due to the shearing force as the elbow subluxates/dislocates posterolaterally. In contrast, an anteromedial facet fracture is typical of a varus posteromedial rotatory instability (VPMRI) pattern.

Question 12

A 55-year-old male with severe insertional Achilles tendinopathy and a prominent Haglund's deformity undergoes surgical debridement and exostectomy. Intraoperatively, it is determined that to adequately resect the calcaneal spur and debride the tendon, 60% of the Achilles tendon footprint must be detached. What is the most appropriate next step in the procedure?





Explanation

In the surgical management of insertional Achilles tendinopathy, if more than 50% of the Achilles tendon insertion is detached during debridement and ostectomy, primary repair alone carries a high risk of failure and weakness. Augmentation with a tendon transfer, most commonly the Flexor Hallucis Longus (FHL), is indicated to provide mechanical strength and a robust vascular supply to the healing area.

Question 13

When placing a single in situ screw for a slipped capital femoral epiphysis (SCFE), an incorrectly positioned starting point and trajectory can lead to catastrophic complications. Placement of the screw into which quadrant of the femoral head carries the highest risk of unrecognized joint penetration and damage to the primary blood supply, risking avascular necrosis (AVN)?





Explanation

The anterosuperior quadrant of the femoral head is the 'danger zone' during SCFE pinning. Because the epiphysis slips posteriorly and inferiorly, the anterior and superior aspect of the metaphysis becomes prominent. A screw directed anterosuperiorly is likely to exit the metaphysis and penetrate the joint space unrecognized. Furthermore, the lateral epiphyseal vessels, which provide the primary blood supply to the femoral head, enter in this region; injuring them significantly increases the risk of AVN. Screws should ideally be placed in the center-center position.

Question 14

In a patient with a high radial nerve palsy, tendon transfer surgery is planned to restore wrist and finger extension. To restore robust wrist extension, the pronator teres (PT) is most commonly transferred to which of the following tendons, and for what specific biomechanical reason?





Explanation

To restore wrist extension in radial nerve palsy, the pronator teres (PT) is universally transferred to the extensor carpi radialis brevis (ECRB). The ECRB inserts on the base of the 3rd metacarpal, providing a central, balanced wrist extension. If the PT were transferred to the ECRL (which inserts on the 2nd metacarpal), it would result in excessive and undesirable radial deviation of the wrist during extension.

Question 15

The 'peel-back' mechanism is a primary pathophysiologic etiology for superior labrum anterior-posterior (SLAP) tears in overhead throwing athletes. During which specific phase of the throwing motion does the peel-back mechanism place the greatest torsional stress on the biceps anchor?





Explanation

The 'peel-back' mechanism occurs during the late cocking phase of throwing, when the shoulder is in maximum abduction and external rotation. In this position, the vector of the biceps tendon changes, shifting posteriorly and creating a torsional force that 'peels' the superior labrum off the posterior glenoid rim.

Question 16

A patient with a ceramic-on-ceramic total hip arthroplasty (THA) complains of a loud squeaking noise during gait. This phenomenon is strongly associated with 'edge loading' of the ceramic components. Which of the following acetabular component position errors most significantly increases the risk of edge loading?





Explanation

Edge loading in a ceramic-on-ceramic THA occurs when the femoral head contacts the rim of the acetabular liner rather than the articulating concavity, leading to stripe wear, loss of fluid film lubrication, and squeaking. The risk of edge loading is markedly increased with suboptimal cup positioning, specifically increased cup inclination (a steep cup) and excessive anteversion or retroversion.

Question 17

A 32-year-old male sustains a T12 burst fracture after a fall. He is neurologically intact. MRI is obtained, and the status of the posterior ligamentous complex (PLC) is deemed 'indeterminate'. According to the Thoracolumbar Injury Classification and Severity (TLICS) score, how many points are assigned specifically to the PLC component in this scenario?





Explanation

In the TLICS scoring system, the integrity of the Posterior Ligamentous Complex (PLC) is scored as follows: Intact = 0 points; Indeterminate (or suspected injury) = 2 points; Disrupted (definite injury) = 3 points. Total score dictates management (<=3 non-operative, 4 is surgeon's choice, >=5 operative).

Question 18

A 30-year-old male presents with a slow-growing, painful soft tissue mass near his knee. Biopsy confirms the diagnosis of synovial sarcoma. Which of the following cytogenetic translocations and resultant fusion genes is pathognomonic for this tumor?





Explanation

Synovial sarcoma is characterized by the pathognomonic balanced translocation t(X;18)(p11;q11), which results in the fusion of the SYT gene on chromosome 18 with one of the SSX genes on the X chromosome. t(11;22) is found in Ewing sarcoma, t(12;16) in myxoid liposarcoma, and t(2;13) in alveolar rhabdomyosarcoma.

Question 19

In orthopedic implant metallurgy, what specific type of corrosion occurs in restricted spaces, such as under the head of a bone screw, where the oxygen concentration becomes locally depleted compared to the surrounding fluid environment?





Explanation

Crevice corrosion occurs in shielded areas, such as the interface between a screw head and a plate. In these crevices, oxygen is quickly depleted, preventing the reformation of the protective passive oxide layer (passivation). The resulting oxygen concentration gradient between the crevice and the surrounding fluid causes the crevice to become anodic, leading to localized metal dissolution.

Question 20

A 28-year-old female sustains a Hawkins Type II talar neck fracture and undergoes open reduction and internal fixation. At the 8-week follow-up, an AP radiograph of the ankle reveals a subchondral radiolucent band extending across the dome of the talus (Hawkins sign). This radiographic finding indicates which of the following?





Explanation

The Hawkins sign is a subchondral radiolucent band seen in the dome of the talus 6 to 8 weeks following a talar neck fracture. It represents subchondral osteopenia (bone resorption) secondary to disuse atrophy. For this resorption to occur, the talar body must have an intact vascular supply. Therefore, a positive Hawkins sign is a highly reliable indicator that avascular necrosis (AVN) of the talar body will NOT occur.

Question 21

Which of the following cytokines is most directly responsible for the final activation of osteoclasts in the pathogenesis of aseptic loosening secondary to polyethylene wear debris?





Explanation

While macrophages phagocytose particulate wear debris and release inflammatory mediators such as IL-1, IL-6, and TNF-alpha, these cytokines act to stimulate osteoblasts and other local cells to express RANKL. RANKL then binds to RANK on the surface of osteoclast precursors, representing the final direct and necessary step for osteoclast differentiation, activation, and subsequent bone resorption (osteolysis).

Question 22

A 3-month-old infant in a Pavlik harness for developmental dysplasia of the hip (DDH) develops decreased active knee extension on the treated side. Which of the following harness positions is the most likely cause of this complication?





Explanation

Femoral nerve palsy is a known complication of Pavlik harness treatment, presenting as decreased active quadriceps function (lack of active knee extension). It is typically caused by hyperflexion of the hip, which impinges the femoral nerve against the inguinal ligament. Treatment involves temporary removal of the harness or adjusting the anterior straps to decrease hip flexion. Excessive abduction is associated with avascular necrosis (AVN) of the femoral head.

Question 23

During an anterior intrapelvic (modified Stoppa) approach for a localized anterior column acetabular fracture, significant hemorrhage occurs while dissecting over the superior pubic ramus. This bleeding is most likely originating from an anastomosis between which two vascular networks?





Explanation

The corona mortis ('crown of death') is a vascular anastomosis between the external iliac system (usually the inferior epigastric artery or vein) and the internal iliac system (obturator artery or vein). It is located over the posterior aspect of the superior pubic ramus, roughly 5-7 cm from the pubic symphysis, and is at high risk of iatrogenic injury during anterior intrapelvic approaches.

Question 24

A 65-year-old man undergoes a C3-C6 posterior cervical laminectomy and instrumented fusion for cervical spondylotic myelopathy. On postoperative day 2, he develops profound new-onset weakness in unilateral shoulder abduction and elbow flexion, but reports no pain and has normal lower extremity function. His preoperative MRI showed severe central canal stenosis but no significant foraminal stenosis. What is the most likely etiology of this complication?





Explanation

Postoperative C5 palsy is a well-documented complication of cervical decompression (laminectomy or laminoplasty), characterized by motor-dominant weakness in the deltoid and biceps. The most accepted mechanism is the posterior drift of the spinal cord following decompression, which stretches the relatively short C5 nerve roots (the 'tethering' effect). It typically presents within the first few days postoperatively and is treated conservatively.

Question 25

A 70-year-old man with advanced Paget's disease of the right hemipelvis and proximal femur is scheduled for a total hip arthroplasty (THA). Which of the following perioperative considerations is most accurate regarding THA in patients with Paget's disease?





Explanation

THA in Pagetic bone is challenging due to hypervascularity, altered bone mechanics, and deformity. Patients are at increased risk of bleeding, which can be mitigated by preoperative bisphosphonate therapy. Due to the poor structural quality and ongoing remodeling of Pagetic bone, uncemented stems have historically shown a higher risk of early aseptic loosening and subsidence compared to cemented stems, making cemented femoral fixation generally preferred, though modern highly porous components are closing this gap.

Question 26

Which of the following autografts used for anterior cruciate ligament (ACL) reconstruction possesses the highest ultimate tensile strength and stiffness compared to the native ACL?





Explanation

The native ACL has an ultimate load of approximately 2160 N. A quadrupled hamstring graft (semitendinosus and gracilis) is mechanically the strongest commonly used autograft, with an ultimate load exceeding 4000 N. A 10-mm bone-patellar tendon-bone (BPTB) graft has an ultimate load of around 2977 N. Despite biomechanical differences, clinical outcomes and stability between BPTB and quadrupled hamstring are generally equivalent.

Question 27

A 14-year-old boy presents with a permeative lytic lesion in the diaphysis of his femur with an associated 'onion-skin' periosteal reaction. Biopsy reveals sheets of uniform small blue round cells. Which of the following chromosomal translocations is most characteristic of this tumor?





Explanation

The clinical, radiographic, and histologic presentation is classic for Ewing sarcoma. The t(11;22)(q24;q12) translocation is present in 85-90% of Ewing sarcomas, resulting in the EWS-FLI1 fusion gene. 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 found in chronic myelogenous leukemia and mesenchymal chondrosarcoma.

Question 28

The Martin-Gruber anastomosis is a well-documented anatomical variant involving communicating neural branches. Which of the following best describes the most common neural transmission pathway in this anomaly?





Explanation

The Martin-Gruber anastomosis occurs in the proximal forearm and involves motor fibers crossing from the median nerve (often via the anterior interosseous nerve) to the ulnar nerve. These fibers typically travel down the ulnar nerve to innervate intrinsic muscles of the hand (such as the first dorsal interosseous, adductor pollicis, and hypothenar muscles) that are normally supplied by the ulnar nerve.

Question 29

A 55-year-old diabetic patient presents with a swollen, erythematous, and warm left foot. Radiographs reveal diffuse osteopenia, periarticular fragmentation, and early joint subluxation at the tarsometatarsal joints. According to the Eichenholtz classification, what stage of Charcot arthropathy does this represent, and what is the primary pathophysiological driver?





Explanation

The patient is in Eichenholtz Stage 1 (Development/Fragmentation stage), characterized clinically by a red, hot, swollen foot and radiographically by osteopenia, fragmentation, and joint subluxation/dislocation. The underlying pathophysiology involves autonomic neuropathy causing loss of sympathetic tone, arteriovenous shunting, hyperemia, and consequently increased osteoclastic bone resorption.

Question 30

A 12-year-old obese male presents with left hip pain and an obligatory external rotation of the thigh during passive hip flexion. Radiographs confirm a mild, stable slipped capital femoral epiphysis (SCFE) on the left. His contralateral right hip is asymptomatic and radiographically normal. Which of the following is the strongest indication for prophylactic in situ pinning of the asymptomatic right hip?





Explanation

Prophylactic pinning of the contralateral asymptomatic hip in SCFE is generally indicated in patients with an underlying endocrinopathy (e.g., hypothyroidism, renal osteodystrophy, growth hormone deficiency), as they have a significantly higher risk of developing a bilateral slip, approaching 100% in some series. Other accepted indications include an inability to follow up and presentation at an atypically young age (<10 years).

Question 31

A 40-year-old man sustains a closed, high-energy distal tibia intra-articular fracture (AO/OTA 43-C3). On presentation, he has massive soft tissue swelling and hemorrhagic fracture blisters over the medial ankle. A spanning external fixator is placed. Which of the following is the most reliable clinical indicator that the soft tissues are amenable to definitive open reduction and internal fixation?





Explanation

In high-energy pilon fractures, definitive open internal fixation should be delayed until the soft tissue envelope has recovered, to minimize the risk of wound breakdown and deep infection. The most reliable clinical sign of sufficient edema resolution is the return of normal skin wrinkles and a positive 'pinch test' (the ability to pinch the skin over the planned surgical approach). Hemorrhagic blisters represent a full-thickness epidermal injury and require extensive time to heal; incisions should ideally bypass them.

Question 32

A 68-year-old woman complains of bilateral calf and buttock pain that worsens with walking and prolonged standing. The pain is relieved by sitting or leaning forward over a shopping cart. During a bicycle stress test, her symptoms do not reproduce while pedaling. Which of the following best explains why spinal extension exacerbates her symptoms?





Explanation

The patient's presentation is classic for neurogenic claudication secondary to lumbar spinal stenosis. Extension of the lumbar spine exacerbates the stenosis by causing the hypertrophied ligamentum flavum to buckle into the spinal canal and by overriding the facet joints, thereby decreasing the cross-sectional area of the neural foramina and central canal. Flexion stretches the ligamentum flavum, increasing canal space and relieving symptoms.

Question 33

In the evaluation of a painful total knee arthroplasty for suspected periprosthetic joint infection (PJI), an alpha-defensin immunoassay of synovial fluid is obtained. Alpha-defensin is an antimicrobial peptide primarily secreted by which of the following cells in response to pathogens?





Explanation

Alpha-defensin is a biomarker widely used in the diagnosis of periprosthetic joint infection. It is an antimicrobial peptide released by active neutrophils in response to pathogens. Its measurement in synovial fluid is highly sensitive and specific for PJI and is included in the Musculoskeletal Infection Society (MSIS) and International Consensus Meeting (ICM) diagnostic algorithms.

Question 34

Articular cartilage is divided into distinct histomorphological zones. Which of the following characteristics best describes the superficial (tangential) zone?





Explanation

The superficial (tangential) zone of articular cartilage is characterized by the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibers (primarily Type II) oriented parallel to the joint surface. This parallel arrangement provides high tensile strength to resist shear forces during joint loading. The deep zone, conversely, has the highest proteoglycan content and collagen oriented perpendicular to the surface.

Question 35

A 25-year-old athlete sustains a twisting injury to the knee. On physical examination, the Dial test reveals 15 degrees of increased external rotation at 30 degrees of knee flexion compared to the uninjured side, but symmetric external rotation at 90 degrees of knee flexion. Which of the following structures is most likely injured?





Explanation

The Dial test evaluates external rotation of the tibia. Increased external rotation (>10-15 degrees compared to the normal side) isolated only at 30 degrees of knee flexion indicates an isolated injury to the posterolateral corner (PLC). If increased external rotation is present at both 30 degrees and 90 degrees of flexion, it indicates a combined injury to the PLC and the posterior cruciate ligament (PCL).

Question 36

Following a Zone II flexor tendon laceration, a multi-strand core suture repair is planned to allow for early active motion rehabilitation. According to biomechanical studies, which of the following factors has the greatest influence on the initial tensile strength of a flexor tendon repair?





Explanation

Biomechanical studies of flexor tendon repairs definitively demonstrate that the initial ultimate tensile strength of the repair is most directly proportional to the number of core suture strands crossing the repair site. For example, a 4-strand repair is substantially stronger than a 2-strand repair, and a 6-strand is stronger than a 4-strand. An epitendinous suture also adds significant strength, but the core strand count is the primary determinant of ability to withstand early active motion.

Question 37

A 30-year-old construction worker sustains a purely ligamentous Lisfranc injury involving the first, second, and third tarsometatarsal joints. Based on prospective randomized trials comparing primary arthrodesis versus open reduction and internal fixation (ORIF) for purely ligamentous Lisfranc injuries, which of the following statements is most accurate regarding primary arthrodesis?





Explanation

Level I randomized controlled trials (e.g., Ly and Coetzee, 2006) comparing ORIF to primary arthrodesis for purely ligamentous Lisfranc injuries have shown that primary arthrodesis yields better functional outcomes and a lower rate of secondary surgeries. ORIF of purely ligamentous injuries often results in progressive arch collapse or arthritis, and typically requires a planned secondary surgery for hardware removal, whereas primary arthrodesis provides a definitive, stable construct.

Question 38

A 19-year-old male presents with persistent dull back pain that is not relieved by ibuprofen. Radiographs and a CT scan reveal a 3.5 cm expansile, radiolucent lesion in the posterior elements of L3 with a thin sclerotic rim. Histologically, the lesion consists of interlacing trabeculae of woven bone lined by prominent osteoblasts. What is the most likely diagnosis?





Explanation

Both osteoid osteoma and osteoblastoma share identical histologic features (woven bone trabeculae lined by a single layer of osteoblasts with loose fibrovascular stroma). However, osteoblastomas are distinguished by being larger (>2 cm), being locally aggressive (expansile), and causing pain that is typically less responsive to NSAIDs compared to the classic nocturnal, NSAID-responsive pain of osteoid osteoma. The posterior elements of the spine are a classic location.

Question 39

An infant with a severe idiopathic clubfoot is being treated with serial casting according to the Ponseti method. After four casts, the cavus, adductus, and varus deformities have been fully corrected. The foot remains in 15 degrees of equinus. What is the most appropriate next step in management?





Explanation

In the Ponseti method for clubfoot, the deformities are corrected in a specific sequence: Cavus, Adductus, Varus, then Equinus (CAVE). Equinus is the final deformity addressed. In approximately 80-90% of cases, the Achilles tendon is too tight to be corrected by casting alone without causing a rocker-bottom deformity. The standard of care is a percutaneous Achilles tenotomy followed by a final cast in maximal dorsiflexion and abduction for 3 weeks.

Question 40

A 28-year-old man is admitted with a comminuted midshaft tibial fracture. Overnight, he complains of worsening leg pain out of proportion to his injury and increased pain with passive toe stretch. His blood pressure is 110/70 mmHg. Intracompartmental pressure monitoring of the anterior compartment reveals a pressure of 45 mmHg. What is his delta pressure, and what is the standard recommended management?





Explanation

Delta pressure is calculated as the Diastolic Blood Pressure minus the Intracompartmental Pressure (Delta P = DBP - ICP). In this patient, DBP is 70 mmHg and ICP is 45 mmHg, giving a Delta P of 25 mmHg. A Delta pressure of less than 30 mmHg, combined with strong clinical signs, is an absolute indication for an emergent four-compartment fasciotomy to treat acute compartment syndrome.

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