1. General Principles & Basic Science MCQs

A patient with severe unilateral right hip osteoarthritis walks with a Trendelenburg gait, characterized by a lateral lurch of the torso over the affected right hip during the stance phase. What is the primary biomechanical effect of this compensatory gait pattern?

A 50-year-old female presents with persistent anterior groin pain 1 year after an uncemented THA. The pain is exacerbated by active hip flexion, such as getting into a car. Radiographs show a well-fixed acetabular component with 25 degrees of anteversion and prominent anterior overhang of 12 mm. Following a diagnostic local anesthetic injection into the iliopsoas bursa that provided temporary relief, what is the most appropriate definitive management?

A 55-year-old male with a metal-on-polyethylene THA presents with a 6-month history of progressive groin pain. Laboratory tests show significantly elevated serum cobalt levels with normal chromium levels. MRI with MARS reveals a large cystic mass communicating with the hip joint. Which of the following implant characteristics most strongly predisposes to this condition?

A surgeon is reviewing bearing surface options for a 50-year-old highly active patient and considers using highly cross-linked polyethylene (HXLPE). Which of the following manufacturing processes is critical to reducing the concentration of free radicals and preventing subsequent in vivo oxidation of HXLPE?

Following a primary right total hip arthroplasty, a patient demonstrates a profound foot drop. She is unable to actively dorsiflex or evert her foot, but plantar flexion and inversion remain completely intact. Which specific nerve structure is most commonly injured in this scenario and what anatomic feature accounts for this susceptibility?

Highly cross-linked polyethylene (HXLPE) is widely utilized in contemporary THA to decrease volumetric wear. Which of the following manufacturing steps is specifically utilized to eliminate free radicals and improve the long-term oxidation resistance of HXLPE?

A 64-year-old female undergoes a THA via the direct anterior approach utilizing the internervous plane between the sartorius and the tensor fasciae latae. Postoperatively, she reports a burning sensation and significant numbness over the anterolateral aspect of her thigh, but her motor function is intact. Injury to which of the following structures is the most likely cause?

What is the critical Space Available for the Cord (SAC) threshold at the C1-C2 level that signifies an absolute indication for surgical stabilization in a patient with Down syndrome, regardless of symptoms?

A 12-year-old girl with Down syndrome presents with habitual bilateral patellar dislocations. Which underlying anatomic abnormalities primarily drive patellofemoral instability in this population?

What is the primary early pathologic target of inflammation in psoriatic arthritis that leads to joint destruction, differentiating it from the primary target in rheumatoid arthritis?

A patient with severe psoriatic arthritis is started on secukinumab after failing methotrexate therapy. What is the precise mechanism of action of this biological medication?

The pathophysiology of psoriatic arthritis distinguishes it from rheumatoid arthritis by the primary anatomic site of initial inflammation. Which of the following structures is the earliest and primary target of the inflammatory process in psoriatic arthritis?

A 10-year-old boy with Down syndrome presents with a painless limp.

What is the primary underlying cause of recurrent hip instability and subluxation in this specific patient population?

A 50-year-old patient with long-standing psoriatic arthritis develops profound osteolysis of the phalanges, resulting in redundant overlying skin and telescoping digits (arthritis mutilans). What is the primary molecular driver of the massive bone resorption seen in this condition?

A 35-year-old male with psoriatic arthritis has predominantly axial disease (spondylitis and sacroiliitis) that has remained highly active despite maximum doses of NSAIDs. According to current treatment guidelines, what is the preferred next step in pharmacologic management?

A 4-year-old child with Down syndrome presents with severe, symptomatic, flexible pes planovalgus that causes frequent tripping. Which of the following is the most appropriate initial management?

A 50-year-old male with a long-standing history of generalized psoriasis develops progressive foreshortening of his digits, resulting in a "telescoping" phenomenon. Which of the following cytokines is most directly responsible for driving the extensive osteoclastogenesis and bone resorption seen in this specific presentation?

A 4-year-old girl with Down syndrome presents with a painless limp.

Radiographs demonstrate bilateral hip subluxation with an increased acetabular index. Which of the following underlying pathophysiologic factors most significantly contributes to the high rate of joint instability in this population?

The inability to feel a 5.07 Semmes-Weinstein monofilament on the plantar surface of the foot in a diabetic patient is clinically defined as the loss of:

In the evaluation of a diabetic patient, the inability to perceive the 5.07 Semmes-Weinstein monofilament specifically indicates the loss of which of the following?