Arab Orthopaedic Board MCQs: Part 27 (Qs 1301-1350)

Arab Orthopaedic Board MCQs - Part 27

Comprehensive 100-Question Exam

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Question 1

A 12-year-old boy presents with left hip pain and an obligate external rotation during passive hip flexion. Radiographs confirm a left Slipped Capital Femoral Epiphysis (SCFE). Under which of the following conditions is prophylactic pinning of the asymptomatic contralateral hip most strongly indicated?

Explanation

Prophylactic pinning of the contralateral hip in SCFE is highly recommended for patients with underlying endocrine disorders (such as hypothyroidism, panhypopituitarism, or renal osteodystrophy) or those who have undergone previous pelvic radiation. These patients have a significantly higher risk of developing bilateral disease compared to idiopathic cases.

Question 2

In the context of total hip arthroplasty (THA), osteolysis is a primary cause of aseptic loosening. Which mechanism of polyethylene wear is the primary generator of the submicron, highly reactive particles that incite the macrophage-mediated osteolytic cascade?

Explanation

Adhesive wear occurs when microscopic asperities on the bearing surfaces bond and then break off. In metal-on-polyethylene THA bearings, adhesive wear is the primary source of the billions of submicron-sized polyethylene particles generated annually, which are phagocytosed by macrophages, initiating the release of cytokines (TNF-alpha, IL-1, IL-6) and leading to osteolysis.

Question 3

During an ilioinguinal approach for open reduction and internal fixation of an anterior column acetabular fracture, massive hemorrhage occurs as the surgeon dissects over the superior pubic ramus. This bleeding is most likely originating from an anastomosis between which of the following vessels?

Explanation

The corona mortis ('crown of death') is a vascular anastomosis between the obturator vessels (internal iliac system) and the inferior epigastric or external iliac vessels. It lies on the posterior aspect of the superior pubic ramus at an average distance of 5 to 6 cm from the pubic symphysis and is at significant risk during the anterior approaches to the acetabulum.

Question 4

A 28-year-old male is brought to the emergency department after sustaining a traumatic knee dislocation (KD-III). Following closed reduction, neurologic examination reveals foot drop and absent sensation over the dorsum of the foot, including the first web space. Which structure was most likely injured?

Explanation

The common peroneal nerve is uniquely tethered at the fibular head and is frequently injured in multiligamentous knee injuries, particularly those involving posterolateral corner disruption. The clinical presentation of complete foot drop (weakness of both anterior and lateral compartments) and sensory deficit over the dorsum (superficial peroneal) and first web space (deep peroneal) confirms a lesion of the common peroneal nerve proximal to its bifurcation.

Question 5

A 65-year-old male presents with deteriorating hand dexterity and difficulty performing tandem gait. Physical examination reveals a positive Hoffmann sign. Magnetic resonance imaging demonstrates severe central canal stenosis at C5-C6. What is the precise pathophysiological mechanism indicating a positive Hoffmann sign?

Explanation

The Hoffmann sign (reflex finger flexion upon snapping the distal phalanx of the middle finger) is a reliable indicator of an upper motor neuron (UMN) lesion. It indicates pathology in the corticospinal tract above the spinal segment that supplies the hand, typically implying spinal cord compression or brain pathology proximal to the C5 level.

Question 6

In the evaluation of a patient with suspected pyogenic flexor tenosynovitis, which of Kanavel's four cardinal signs is generally considered the most sensitive and presents earliest in the course of the infection?

Explanation

Kanavel's signs for suppurative flexor tenosynovitis include: 1) flexed resting posture, 2) fusiform (sausage) swelling, 3) tenderness along the flexor sheath, and 4) pain with passive extension. Pain with passive extension is typically the earliest, most sensitive, and most clinically significant sign to manifest.

Question 7

A 22-year-old collegiate football player sustains an axial load to a plantarflexed foot. Weight-bearing radiographs reveal a 2.5 mm diastasis between the bases of the first and second metatarsals ('fleck sign'). The primary ligamentous disruption in this injury normally connects which two osseous structures?

Explanation

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

Question 8

Following administration of neoadjuvant chemotherapy, a 15-year-old patient undergoes wide surgical resection for conventional high-grade osteosarcoma of the distal femur. According to the Huvos grading system, what is the minimum percentage of tumor necrosis required to classify the tumor as having a 'good histologic response'?

Explanation

The histologic response to neoadjuvant chemotherapy in osteosarcoma is the most important prognostic factor. A 'good responder' is defined by the Huvos criteria as having 90% or greater tumor necrosis (Grade III is 90-99% necrosis; Grade IV is 100% necrosis). Patients with <90% necrosis are considered poor responders.

Question 9

During the non-operative management of a clubfoot using the Ponseti method, serial casting gradually stretches the contracted medial ligaments. The viscoelastic property allowing the ligament to progressively elongate under a constant, prolonged load over time is termed:

Explanation

Creep is the progressive deformation (elongation) of a viscoelastic material when subjected to a constant load over time. In contrast, stress relaxation refers to the decrease in stress (force) within a material when it is held at a constant length/deformation. Serial casting utilizes both principles, but progressive elongation under constant tension is creep.

Question 10

A 6-week-old female infant with developmental dysplasia of the hip (DDH) is placed in a Pavlik harness due to a positive Ortolani sign and an ultrasound alpha angle of 45 degrees. After 3 weeks of strictly compliant harness wear, ultrasound confirms the hip remains persistently dislocated. What is the most appropriate next step in management?

Explanation

If a Pavlik harness fails to achieve reduction of a dislocated hip within 3 to 4 weeks, it must be discontinued to avoid 'Pavlik harness disease' (damage to the posterior acetabular wall) and to prevent femoral nerve palsy. The standard next step for a persistently dislocated hip failing Pavlik harness treatment in an infant is closed reduction under general anesthesia and application of a hip spica cast.

Question 11

During a primary posterior-stabilized total knee arthroplasty, trial reduction reveals that the knee is symmetric and balanced in extension, but symmetrically tight in 90 degrees of flexion. Which of the following technical adjustments is the most appropriate next step to balance the knee?

Explanation

A knee that is tight in flexion but balanced in extension requires an increase in the flexion gap without altering the extension gap. Downsizing the femoral component (using an anterior referencing system) translates the posterior condyles anteriorly, thereby resecting more posterior condylar bone and selectively increasing the flexion gap.

Question 12

Recent quantitative anatomical studies evaluating the vascularity of the proximal humerus have challenged historical teachings. In the context of a 4-part proximal humerus fracture, which artery is now recognized as providing the predominant blood supply to the humeral head?

Explanation

While classic literature (e.g., Laing) taught that the anterior humeral circumflex artery (via the arcuate artery) was the main blood supply, modern studies (such as those by Hettrich et al.) have demonstrated that the posterior humeral circumflex artery provides approximately 64% of the blood supply to the humeral head.

Question 13

A 28-year-old elite volleyball attacker presents with posterior shoulder pain and isolated weakness in external rotation. Magnetic resonance imaging demonstrates a multiloculated paralabral cyst located strictly within the spinoglenoid notch. Which muscle will exhibit neurogenic atrophy on the MRI?

Explanation

The suprascapular nerve innervates the supraspinatus before it passes through the spinoglenoid notch to innervate the infraspinatus. Entrapment of the nerve at the spinoglenoid notch (commonly by a cyst associated with a posterior labral tear) results in isolated denervation and atrophy of the infraspinatus, presenting clinically as isolated weakness in external rotation.

Question 14

A 45-year-old male presents with severe radicular leg pain. Magnetic resonance imaging reveals a large paracentral disc herniation at the L4-L5 level compressing the traversing nerve root. Physical examination is most likely to demonstrate which of the following focal deficits?

Explanation

In the lumbar spine, a paracentral disc herniation compresses the traversing nerve root. At L4-L5, the traversing root is L5. L5 radiculopathy is characterized by weakness in great toe extension (extensor hallucis longus) and ankle dorsiflexion (tibialis anterior), along with sensory changes over the dorsal aspect of the foot. Diminished patellar reflex implies L4 (exiting root), while diminished Achilles reflex implies S1.

Question 15

In the natural history of Scaphoid Nonunion Advanced Collapse (SNAC), degenerative arthritic changes progress through a predictable radiographic sequence. Which specific articulation is classically spared from this degenerative cascade due to its uniquely preserved concentric spherical kinematics?

Explanation

The radiolunate articulation is classically spared in both Scapholunate Advanced Collapse (SLAC) and Scaphoid Nonunion Advanced Collapse (SNAC) wrists. This is because the lunate maintains a congruent, concentric, spherical relationship with the lunate fossa of the radius, even when it assumes an extended (DISI) posture, thereby avoiding abnormal cartilage loading and shear stresses.

Question 16

A 55-year-old male with poorly controlled diabetes mellitus presents with a swollen, erythematous, and warm right foot. Radiographs demonstrate periarticular osteopenia, prominent bony fragmentation, and multiple subluxations at the Lisfranc joint complex. According to the Eichenholtz classification of Charcot arthropathy, this presentation represents which stage?

Explanation

Eichenholtz Stage 1 (Developmental/Fragmentation stage) is characterized clinically by the acute red, hot, swollen foot, and radiographically by periarticular fragmentation, debris formation, joint subluxation/dislocation, and osteopenia. Stage 2 (Coalescence) shows absorption of debris and early fusion, while Stage 3 (Reconstruction) shows rounding of bone ends and decreased sclerosis.

Question 17

Denosumab has revolutionized the medical management of Giant Cell Tumor of bone (GCTB), particularly for unresectable or metastatic lesions. What is the specific molecular mechanism of action of this agent?

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By neutralizing RANKL produced by the neoplastic stromal cells of a Giant Cell Tumor, it prevents RANKL from binding to the RANK receptor on osteoclast precursors, dramatically arresting the formation and function of the destructive giant osteoclasts.

Question 18

According to Perren's strain theory of bone healing, the mechanical environment dictates the type of tissue that forms within a fracture gap. What is the maximum theoretical amount of interfragmentary strain that can be tolerated to permit the formation of primary lamellar bone?

Explanation

Perren's strain theory postulates that a specific tissue can only form if the interfragmentary strain is lower than the strain at which that tissue yields. Lamellar bone can only form under very rigid conditions, tolerating less than 2% strain. Woven bone can form up to 10% strain, cartilage up to 30%, and granulation tissue up to 100%.

Question 19

A 30-year-old male sustains a closed tibial shaft fracture. Two hours post-admission, he develops severe pain out of proportion to the injury and tense leg compartments. Which of the following intracompartmental pressure measurements represents the most absolute and reliable indication for an immediate fasciotomy?

Explanation

The 'delta pressure' (Diastolic Blood Pressure minus the intracompartmental pressure) is the most accurate predictor for acute compartment syndrome. A delta pressure of less than 30 mmHg (e.g., DBP 70, Compartment Pressure 45 -> Delta = 25) indicates severe capillary bed occlusion and is an absolute indication for emergency fasciotomy.

Question 20

A 3-year-old girl is evaluated for worsening bilateral lower extremity bowing. Standing radiographs reveal a metaphyseal-diaphyseal angle (Drennan angle) of 18 degrees. Which specific radiographic feature is most pathognomonic for infantile Blount's disease (tibia vara)?

Lateral metaphyseal beaking of the distal femur
Medial metaphyseal beaking and fragmentation of the proximal tibia
Premature closure of the entire proximal tibial physis
Widening and irregularity of the distal femoral physis
Lateral subluxation of the patellofemoral joint

Correct Answer: Medial metaphyseal beaking and fragmentation of the proximal tibia

Arab Board Orthopedic B Review | Dr Hutaif General Orth -...

Arab Orthopaedic Board MCQs - Part 27

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Arab Orthopaedic Board MCQs - Part 27

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