1. General Principles & Basic Science MCQs

During the excitation-contraction coupling of skeletal muscle, the unmasking of the myosin-binding sites on the actin filament is directly triggered by the binding of calcium to which of the following proteins?

When a constant tensile force is applied to a ligament over a prolonged period, the ligament gradually continues to elongate. Which biomechanical term best describes this time-dependent property?

A 35-year-old sustains a transverse radius shaft fracture that is treated with open reduction and internal fixation using a dynamic compression plate to achieve absolute stability. What is the primary mechanism of bone healing expected in this scenario?

A 55-year-old patient presents with diffuse bone pain and proximal muscle weakness. Laboratory evaluation reveals hypocalcemia, hypophosphatemia, elevated alkaline phosphatase, and elevated parathyroid hormone. Radiographs show Looser zones in the femoral neck. What is the primary histopathologic defect?

Articular cartilage is highly specialized to withstand distinct mechanical forces. In which histologic layer of articular cartilage are the type II collagen fibers oriented perpendicular to the joint surface to resist significant compressive loads?

Parathyroid hormone (PTH) plays a critical role in calcium homeostasis by modulating bone turnover. By what mechanism does PTH indirectly stimulate osteoclastic bone resorption?

A patient presents with a radial nerve palsy immediately following a closed midshaft humerus fracture. Electromyography at 4 weeks is consistent with a Sunderland Class II injury (axonotmesis). Which of the following best describes the microscopic pathology of the nerve at the injury site?

During the biomechanical loading of a normal human synovial joint, different lubrication mechanisms dominate depending on the applied load and velocity. During the initial high-load impact phase, such as heel strike during gait, which primary mechanism prevents immediate cartilage-to-cartilage contact?

A 65-year-old male with a history of advanced prostate carcinoma presents with severe back pain. Radiographs demonstrate multiple dense, osteoblastic lesions in the lumbar vertebrae. Prostate cancer cells predominantly stimulate this osteoblastic response by secreting which of the following factors?

A surgeon plans to utilize recombinant human bone morphogenetic protein-2 (rhBMP-2) on a collagen sponge carrier to augment healing in a tibial nonunion. At the cellular level, BMP-2 promotes osteoinduction primarily by initiating an intracellular signaling cascade mediated by which proteins?

A pediatric patient with frequent fractures and cranial nerve palsies is evaluated. Radiographs demonstrate a diffuse 'bone-within-bone' appearance. The primary pathophysiologic defect in this condition is characterized by a failure of which of the following?

When evaluating normal adult articular cartilage histology, in which zone are the collagen fibers oriented perpendicular to the joint surface and the highest concentration of proteoglycans found?

A 68-year-old woman sustains an atypical subtrochanteric femur fracture after taking alendronate for 10 years. What is the primary cellular mechanism of action of this class of medication?

During the pathogenesis of periprosthetic joint infection, which phase of biofilm formation is characterized by the secretion of extracellular polymeric substances (EPS) leading to irreversible bacterial attachment?

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is utilized to augment spinal fusion. BMPs primarily induce bone formation by binding to cell surface receptors and stimulating which of the following intracellular signaling pathways?

A 65-year-old male presents with bone pain and hypercalcemia. Radiographs demonstrate multiple 'punched-out' lytic lesions in the skull and long bones.

The profound lack of bone formation in the lytic lesions of this disease is primarily mediated by tumor cell secretion of which factor?