1. General Principles & Basic Science MCQs

A surgeon is performing a primary total hip arthroplasty utilizing the direct anterior approach. Which two nerves supply the muscles defining the superficial internervous plane of this approach?

In lower extremity deformity correction, an osteotomy is planned to correct a significant angular deformity. According to established osteotomy rules, if both the osteotomy cut and the hinge axis are placed away from the Center of Rotation of Angulation (CORA), what is the resultant geometric effect on the bone segments after angular correction?

A 14-year-old boy is undergoing complex multiplanar tibial deformity correction using a hexapod circular external fixator. Midway through the strut adjustment schedule, orthogonal radiographs demonstrate that angular correction is proceeding appropriately, but a new unintended 5 mm medial translation has developed at the osteotomy site. What is the most appropriate management?

A 28-year-old male sustains a closed midshaft humerus fracture. On examination, he demonstrates a 'wrist drop' and an inability to extend his metacarpophalangeal joints. Which of the following sensory deficits is most likely to accompany this motor finding?

A 28-year-old male presents to the emergency department after a motorcycle collision. Radiographs reveal a transverse midshaft humerus fracture. On physical examination, the patient is unable to extend his wrist or fingers, and he has decreased sensation over the dorsal web space of the hand. Which of the following nerves is most likely injured?

During the early stages of fracture healing via endochondral ossification, which transcription factor is considered the essential "master regulator" for the differentiation of mesenchymal stem cells into chondrocytes?

During biomechanical testing, a ligament is rapidly stretched to a specific, constant length and held rigidly in place. Over a period of minutes, the tensile force required to maintain this exact length is observed to gradually decrease. What specific viscoelastic property does this phenomenon represent?

Denosumab is an effective pharmacological treatment utilized in the management of unresectable or recurrent Giant Cell Tumor of Bone (GCTB). What is the precise molecular mechanism of action of this drug?

Normal articular cartilage is highly organized into four distinct structural zones. Which microscopic, basophilic feature definitively separates the deep (radial) uncalcified zone from the underlying calcified cartilage zone?

A 24-year-old rock climber sustains a closed flexor tendon pulley rupture while forcefully gripping a crimp hold. He presents with clinically evident bowstringing of the flexor tendons in the ring finger. Rupture of which two pulleys is most likely responsible for this significant bowstringing?

According to Perren's strain theory, what is the maximum interfragmentary strain that will still permit primary (direct) bone healing to occur via osteonal cutting cones without intermediate callus formation?

A 65-year-old man presents with progressive groin pain 12 years after undergoing a cementless total hip arthroplasty. Radiographs demonstrate eccentric wear of the polyethylene liner and expansive radiolucent lines around the femoral stem. What is the primary cellular mechanism driving this specific mode of failure?

In an orthopedic biomechanics laboratory, a viscoelastic tendon graft is subjected to a constant, sustained tensile load over a prolonged period. It is observed that the material continues to deform slowly over time despite the load remaining unchanged. Which biomechanical property does this phenomenon represent?

A 10-year-old boy presents with progressive hip pain and a waddling gait. His height is below the 5th percentile, primarily due to a short trunk. Radiographs show flattened vertebral bodies with central humps and dysplastic femoral heads. His father and paternal grandfather have normal stature, but his maternal uncle has early-onset osteoarthritis and short stature. What is the most likely genetic inheritance pattern and associated gene for this condition?

A newborn is noted to have short proximal limbs, cataracts, and ichthyosis. Radiographs reveal multiple punctate calcifications in the epiphyses of the long bones and the spine. Which of the following maternal exposures during pregnancy can produce a phenocopy of this genetic disorder?

A neonate presents with severe shortening of the proximal limbs, cataracts, and ichthyosis. Radiographs reveal multiple punctate calcifications in the epiphyses of the long bones and spine. Which of the following maternal exposures during pregnancy can produce a phenocopy of this genetic skeletal dysplasia?

A 10-year-old boy presents with progressive hip pain and a waddling gait. Physical examination reveals a short trunk but normal limb length. Radiographs reveal platyspondyly with a characteristic 'hump-shaped' buildup of bone on the central and posterior portions of the vertebral endplates. His maternal uncle has a similar condition. What is the most likely genetic inheritance pattern of this disorder?

A newborn is noted to have short proximal limbs, cataracts, and ichthyosis. Radiographs reveal multiple punctate calcifications in the epiphyses of the long bones and the cartilaginous portions of the spine. Which of the following maternal exposures during pregnancy can produce a phenocopy of this genetic skeletal dysplasia?

Pseudoachondroplasia and certain forms of Multiple Epiphyseal Dysplasia (MED) are caused by mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene. Which of the following best describes the cellular pathogenesis of these conditions?