1. General Principles & Basic Science MCQs

A patient recovering from a traumatic brain injury walks with a 'stiff-knee' gait, characterized by significantly diminished knee flexion during the swing phase. Overactivity of which muscle is the most common etiology of this specific gait abnormality?

A patient with a history of poliomyelitis walks with a forward lean of the trunk during the early stance phase of gait. Which underlying muscular deficit is this compensatory mechanism attempting to overcome?

Based on Paley's rules of deformity correction, if an osteotomy is created at a site distant from the center of rotation of angulation (CORA), but the hinge (axis of correction) is placed exactly at the CORA, what is the geometric result?

During the stance phase of normal human gait, the 'second rocker' mechanism involves forward translation of the tibia over a plantigrade foot. Which muscle group predominantly controls the rate of this progression via eccentric contraction?

A 45-year-old patient has a 4 cm true limb length discrepancy secondary to a remote femur fracture. What is the most common kinematic compensation observed in the shorter limb during the stance phase of gait?

Normal gait requires adequate knee flexion during the swing phase to ensure foot clearance. What is the maximum degree of knee flexion typically achieved during the normal human gait cycle?

According to Paley's rules of deformity correction, if an osteotomy is performed at a level distinct from the center of rotation of angulation (CORA), but the axis of correction (hinge) is placed exactly at the CORA, what is the resultant geometric effect on the bone?

During the initial swing phase of normal gait, which muscle group serves as the primary accelerator to advance the lower extremity forward?

A 45-year-old stroke patient exhibits a stiff-knee gait characterized by severely reduced knee flexion during the swing phase. Overactivity of which of the following muscles is the most common primary contributor to this specific gait abnormality?

A 35-year-old man presents with chronic, deep aching pain and limited range of motion in his left lower extremity. Radiographs demonstrate dense, irregular, eccentric hyperostosis along the cortex of the femur and tibia, resembling 'dripping candle wax'. Which of the following is the most likely diagnosis and its associated genetic mutation?

A 30-year-old female with polyostotic fibrous dysplasia complains of severe, persistent bone pain in her lower extremities that is refractory to simple analgesics. Radiographs show stable lesions without impending fractures. Which of the following pharmacological therapies is considered the first-line treatment to alleviate bone pain in this patient?

A 6-year-old child is diagnosed with Ollier disease. The parents are concerned about future limb length discrepancies and deformities. The deformities in Ollier disease are primarily caused by which of the following mechanisms?

Fibrous dysplasia is characterized by a somatic activating mutation in the GNAS gene. This specific mutation directly results in the constitutive activation of which of the following intracellular signaling pathways?

An 18-month-old presents with failure to thrive, recurrent infections, and hepatosplenomegaly. Radiographs reveal generalized increased bone density with a 'bone-within-bone' appearance. Which of the following is the only definitive curative treatment for the severe infantile form of this disease?

A newborn exhibits a prominently wide anterior fontanelle, midface hypoplasia, and an ability to bring the shoulders together across the midline. Radiographs reveal absent clavicles and delayed ossification of the pubic symphysis. This condition is caused by a defect in a transcription factor crucial for the differentiation of which cell type?

A 3-year-old child presents with bowing of the legs and a waddling gait. Radiographs show coxa vara and flaring of the metaphyses, primarily in the lower extremities. Laboratory tests reveal normal serum calcium, phosphorus, alkaline phosphatase, and vitamin D levels. Which of the following is the most likely diagnosis?

A 10-year-old boy presents with profound short stature, a wide, waddling gait, and deafness. Laboratory studies unexpectedly reveal severe hypercalcemia and hypophosphatemia with undetectable parathyroid hormone (PTH) levels. What is the underlying pathophysiology of this specific skeletal dysplasia?

A 14-year-old girl with a history of recurrent fractures is evaluated for progressive restriction of forearm pronation and supination. Radiographs reveal calcification of the interosseous membrane and a history of hyperplastic callus formation following a previous femur fracture. She lacks blue sclerae or dentinogenesis imperfecta. A mutation in which gene is responsible for her specific phenotype?