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Arab Orthopaedic Board MCQs - Part 35

27 Apr 2026 25 min read 90 Views
Arab Ortho Board MCQs - Part 34

Key Takeaway

For anyone wondering about Arab Orthopaedic Board MCQs - Part 35, Practice Arab Orthopaedic Board MCQs Part 35. Review orthopedic surgery questions 1701 to 1750 for your board exam preparation.

Arab Orthopaedic Board MCQs - Part 35

Comprehensive 100-Question Exam


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Question 1

A 65-year-old male presents with groin pain 5 years after a primary total hip arthroplasty. Serum metal ion testing reveals elevated cobalt levels that are disproportionately higher than chromium levels. Radiographs demonstrate well-fixed components. MRI with metal artifact reduction sequence (MARS) shows a solid pseudotumor surrounding the joint. What is the most likely cause of failure in this patient?





Explanation

Trunnionosis (mechanically assisted crevice corrosion) occurs at the modular head-neck junction of total hip implants. It classically presents with elevated cobalt levels (often disproportionately higher than chromium) and adverse local tissue reactions (ALVAL/pseudotumor formation), even when the bearing surfaces are intact and components are well-fixed.

Question 2

During an ilioinguinal approach for internal fixation of an anterior column acetabular fracture, significant arterial bleeding is suddenly encountered on the posterior aspect of the superior pubic ramus near the symphysis. This vessel represents an anastomosis between which two vascular systems?





Explanation

The corona mortis is a vascular anastomosis between the external iliac system (via the inferior epigastric artery/vein) and the internal iliac system (via the obturator artery/vein). It is classically located over the superior pubic ramus and is at high risk of iatrogenic injury during the ilioinguinal approach.

Question 3

Which of the following is considered the strongest indication for prophylactic in situ pinning of the contralateral hip in a patient presenting with a unilateral Slipped Capital Femoral Epiphysis (SCFE)?





Explanation

Prophylactic pinning of the contralateral hip is strongly recommended in patients with an underlying endocrine disorder (e.g., hypothyroidism, renal osteodystrophy, or growth hormone therapy) due to a near 100% risk of developing bilateral SCFE. Routine prophylactic pinning in idiopathic cases remains controversial but is less indicated than in endocrine-related SCFE.

Question 4

A 75-year-old male presents to the emergency department after a mechanical fall from standing height, complaining of neck pain. CT scan of the cervical spine reveals a Type II odontoid fracture with 2 mm of posterior displacement. He is neurologically intact. What is the most appropriate initial management for this patient?





Explanation

In elderly patients (generally defined as >65 or >70 years) with a Type II odontoid fracture, treatment is debated, but a rigid cervical collar is often preferred as initial management. This is because halo vest immobilization and operative interventions carry disproportionately high morbidity and mortality in this population. Although nonunion rates are higher with a collar, the nonunions are frequently stable and asymptomatic (fibrous nonunion).

Question 5

In a patient with an isolated complete rupture of the posterior cruciate ligament (PCL), the most significant increase in posterior tibial translation on examination occurs at what degree of knee flexion?





Explanation

The anterolateral (AL) bundle of the PCL is the primary restraint to posterior tibial translation at 90 degrees of knee flexion. Therefore, a complete PCL rupture yields the maximum abnormal posterior translation at 90 degrees of flexion, which is the basis for the posterior drawer test.

Question 6

Highly cross-linked polyethylene (HXLPE) is widely used in total hip arthroplasty to reduce wear rates. What is the primary molecular mechanism by which irradiation improves the wear resistance of polyethylene?





Explanation

Cross-linking uses gamma or electron-beam irradiation to cleave carbon-hydrogen bonds, creating free radicals that subsequently combine to form covalent bonds between adjacent polyethylene chains. This dense three-dimensional network significantly reduces abrasive and adhesive wear, although it decreases certain mechanical properties such as ductility and fatigue crack propagation resistance.

Question 7

During an EMG/NCS for suspected carpal tunnel syndrome, the amplitude of the compound muscle action potential (CMAP) of the thenar muscles is paradoxically higher with proximal median nerve stimulation at the elbow than with distal stimulation at the wrist. What is the most likely anatomic explanation for this finding?





Explanation

A Martin-Gruber anastomosis involves anomalous motor fibers crossing from the median nerve to the ulnar nerve in the proximal forearm. Proximal median nerve stimulation at the elbow captures these fibers before they cross over, generating a robust thenar CMAP. Distal median nerve stimulation at the wrist misses these crossed fibers (which are now in the ulnar nerve), resulting in a lower CMAP amplitude.

Question 8

Which of the following structures is classically the last to be addressed or repaired during the step-wise surgical reconstruction of a 'terrible triad' injury of the elbow?





Explanation

The standard surgical algorithm for a terrible triad of the elbow (elbow dislocation, radial head fracture, and coronoid fracture) proceeds from deep to superficial and typically from lateral to medial (or via a single lateral approach). The sequence is: 1) Coronoid fixation, 2) Radial head fixation or replacement, 3) LUCL repair. The Medial Collateral Ligament (MCL) is only repaired (or augmented with an external fixator) if the elbow remains unstable in extension after the first three steps are completed.

Question 9

The primary Lisfranc ligament, critical for the stability of the midfoot, connects which two osseous structures?





Explanation

The Lisfranc ligament is an oblique, stout interosseous ligament that runs 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 first and second metatarsal bases, making this ligament vital for stabilizing the keystone of the midfoot.

Question 10

A 14-year-old boy presents with right knee pain. Radiographs reveal a well-circumscribed, eccentrically located lytic lesion with a sclerotic rim in the proximal tibial epiphysis. Biopsy demonstrates mononuclear cells with longitudinal nuclear grooves and pericellular 'chicken-wire' calcifications. What is the most likely diagnosis?





Explanation

Chondroblastoma is a rare benign, cartilage-producing bone tumor that characteristically arises in the epiphysis or apophysis of skeletally immature patients. Histological hallmarks include chondroblasts with longitudinal nuclear grooves ('coffee bean' nuclei) and fine, lace-like pericellular 'chicken-wire' calcifications.

Question 11

Which of the following is an essential radiographic criterion for the definitive diagnosis of typical Scheuermann's kyphosis (Sorensen criteria)?





Explanation

The classic Sorensen criteria for the diagnosis of Scheuermann's kyphosis require the presence of thoracic kyphosis greater than 40 degrees and at least three consecutive vertebrae demonstrating a minimum of 5 degrees of anterior wedging each.

Question 12

A patient diagnosed with Osteogenesis Imperfecta Type I, the most common and mildest form of the disease, has a genetic mutation that predominantly results in which of the following?





Explanation

Osteogenesis Imperfecta (OI) Type I is typically caused by a null allele mutation resulting in haploinsufficiency—a decreased amount of structurally normal Type I collagen. In contrast, the more severe forms (OI Types II, III, and IV) typically involve structural (qualitative) mutations, such as glycine substitutions in the collagen chains, which disrupt triple helix formation.

Question 13

In a 30-year-old patient with a displaced, vertically oriented femoral neck fracture (Pauwels type III, shear angle >50 degrees), what is the most biomechanically stable construct for internal fixation?





Explanation

Pauwels Type III femoral neck fractures have a high shear angle (vertical fracture line), which makes them highly unstable and prone to varus collapse and nonunion if fixed with standard parallel cannulated screws. Biomechanical studies have shown that a fixed-angle device, such as a Dynamic Hip Screw (DHS), supplemented with an anti-rotation (derotational) screw, provides superior biomechanical stability against shear forces in young adults.

Question 14

The vincula brevia and vincula longa are critical for providing the vascular supply to the flexor tendons within the digital fibrous sheath. These vincula are direct branches originating from which of the following vessels?





Explanation

The proper digital arteries run longitudinally along the digits and give off small transverse branches that penetrate the flexor sheath to supply the flexor tendons via the vincula longa and vincula brevia.

Question 15

During the Ponseti casting technique for the treatment of idiopathic clubfoot, the initial step of manipulation involves correcting the cavus deformity by elevating the first ray. In the subsequent stages of casting to correct the adductus and varus deformities, which bony structure acts as the essential fulcrum for lateral abduction of the foot?





Explanation

In the Ponseti method, after correcting the cavus by supinating the forefoot to align it with the hindfoot, the entire foot is abducted around the lateral aspect of the head of the talus, which serves as the fulcrum. Direct pressure should never be applied to the calcaneus or the cuboid, as this blocks normal subtalar kinematics and can cause a midfoot break.

Question 16

During a primary Total Knee Arthroplasty (TKA), placing the femoral component in excessive internal rotation relative to the transepicondylar axis will most likely lead to which of the following patellofemoral complications?





Explanation

Internal rotation of the femoral component relative to the surgical transepicondylar axis shifts the trochlear groove medially. This effectively increases the Q-angle and relative lateral pull on the patella, resulting in lateral patellar maltracking, tilt, lateral subluxation, and an increased risk of patellar component wear or failure.

Question 17

The 'peel-back' mechanism is a well-described etiology for creating SLAP (Superior Labrum Anterior to Posterior) lesions in overhead athletes. In which specific shoulder position does this mechanism maximally tension the long head of the biceps anchor?





Explanation

The 'peel-back' mechanism occurs primarily during the late cocking phase of throwing, where the shoulder is positioned in abduction and maximal external rotation. In this position, the vector of the long head of the biceps shifts posteriorly, creating a torsional force that 'peels' the superior labrum off the posterior-superior glenoid rim.

Question 18

A 22-year-old male sustains a severe closed tibial shaft fracture and rapidly develops tense swelling over the anterolateral leg with excruciating pain on passive toe flexion. If this anterior compartment syndrome is left untreated, which specific sensory deficit is most expected to manifest?





Explanation

The anterior compartment of the leg contains the tibialis anterior, extensor hallucis longus, extensor digitorum longus, peroneus tertius, the anterior tibial artery, and the deep peroneal nerve. Ischemia to the deep peroneal nerve from anterior compartment syndrome classically results in a sensory deficit in its autonomous zone, which is the first dorsal web space of the foot.

Question 19

A 25-year-old male presents with a slow-growing, painful mass adjacent to his left knee joint, clearly outside the joint capsule on MRI. Histological evaluation of a biopsy reveals a biphasic tumor comprised of spindle cells and epithelial cells. Molecular testing demonstrates a t(X;18)(p11;q11) translocation. What is the most accurate diagnosis?





Explanation

Synovial sarcoma classically presents in young adults as a painful mass near large joints (especially the knee), though it rarely originates from actual synovial tissue. It is characterized pathologically by either a biphasic (epithelial and spindle cells) or monophasic spindle cell morphology. The hallmark cytogenetic abnormality is the t(X;18) translocation, resulting in the SYT-SSX fusion gene.

Question 20

According to the Thoracolumbar Injury Classification and Severity Score (TLICS), which is used to guide treatment for thoracolumbar trauma, a total score of 5 points generally indicates which of the following management strategies?





Explanation

The TLICS system guides treatment based on three categories: injury morphology, neurological status, and integrity of the posterior ligamentous complex (PLC). A total score of 3 or less suggests non-operative management; a score of 4 is indeterminate (surgeon's choice); and a score of 5 or greater indicates that operative management is generally recommended due to instability or neurological compromise.

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