1. General Principles & Basic Science MCQs

During the final 20 degrees of active knee extension, the 'screw-home' mechanism occurs to lock the knee in its most stable position. In an open kinetic chain (e.g., seated leg extension), which of the following best describes this obligatory kinematic coupling?

A surgeon is performing a primary total hip arthroplasty using the direct anterior approach. The superficial internervous plane is established between the sartorius and the tensor fasciae latae. During this specific stage of the superficial dissection, which of the following neurologic structures is at the highest risk of iatrogenic injury?

During a direct anterior approach for a total hip arthroplasty, the surgeon dissects through the superficial internervous plane between the tensor fasciae latae and the sartorius. In the distal extent of this field, a leash of vessels is encountered crossing the surgical field transversely, requiring ligation. These vessels are branches of which of the following arteries?

A 45-year-old active male with isolated medial compartment knee osteoarthritis and a varus deformity undergoes a medial opening-wedge high tibial osteotomy. To prevent an unintended increase in the posterior tibial slope during the procedure, how should the osteotomy gap be managed?

During the cementation of the femoral component in an 82-year-old patient undergoing a cemented hemiarthroplasty for a femoral neck fracture, the patient's end-tidal CO2 abruptly drops, followed by severe hypotension and hypoxia. Which of the following is the most likely pathophysiological mechanism of this intraoperative event?

A 70-year-old patient reports a feeling of instability and giving way when rising from a chair or using stairs 1 year after a TKA. Clinical examination demonstrates stability at 0 degrees and 90 degrees of flexion, but excessive varus-valgus laxity at 30 to 45 degrees of flexion. What is the primary cause of this presentation?

A 35-year-old man on chronic corticosteroids presents with bilateral groin pain. MRI reveals bilateral femoral head osteonecrosis without subchondral collapse (Ficat Stage II). What is the primary rationale for performing a core decompression in this patient?

A 62-year-old woman requires a TKA for severe osteoarthritis. She has a documented severe nickel hypersensitivity with previous blistering from inexpensive jewelry. What is the most appropriate implant choice to minimize the risk of a hypersensitivity reaction?

During a direct anterior approach for total hip arthroplasty, the surgeon develops the superficial internervous plane. Which of the following neurological structures is at greatest risk of injury during this specific stage of the dissection?

A surgeon is performing a primary total hip arthroplasty using the direct anterior approach, utilizing the internervous plane between the tensor fasciae latae and the sartorius. During the superficial dissection, a sensory nerve crossing the operative field is inadvertently transected. Damage to this specific nerve will most likely result in sensory loss to which of the following dermatomal distributions?

Periprosthetic osteolysis is the leading cause of late aseptic loosening following total joint arthroplasty, primarily driven by a biologic response to particulate wear debris. Following the phagocytosis of wear particles by macrophages, which of the following receptor-ligand interactions represents the terminal obligate pathway for the differentiation and activation of osteoclasts?

A 55-year-old male presents with groin pain and a progressive limp 6 years after an uncomplicated metal-on-polyethylene THA using a large-diameter cobalt-chromium head on a titanium stem. Radiographs show a well-fixed prosthesis. Aspiration yields fluid with a normal cell count and negative cultures. Serum cobalt levels are markedly elevated, while serum chromium levels are mildly elevated. What is the most likely source of the elevated metal ions?

A surgeon is performing a primary THA using the direct anterior approach (Smith-Petersen) on a standard operating table. The internervous plane is developed between the tensor fasciae latae and sartorius. To safely expose the anterior joint capsule without causing a postoperative hematoma, which of the following vascular structures typically must be identified and ligated?

Romosozumab is a monoclonal antibody utilized in the treatment of severe osteoporosis. What is the precise molecular target and subsequent downstream effect of this medication?

A surgeon places a stainless steel screw through a titanium plate. Which of the following best describes the resulting electrochemical interaction between these two implants?

Examine the following illustration of articular cartilage.

Which of the following characteristics accurately describes the superficial (tangential) zone of articular cartilage compared to the deeper zones?

Review the provided histological image demonstrating a multi-nucleated cell actively resorbing bone.

Which enzyme is primarily responsible for generating the acidic environment within the ruffled border (Howship's lacuna) required to dissolve the inorganic mineral phase of the bone?

During the late swing phase of the normal gait cycle, the hamstrings undergo an eccentric contraction to decelerate the advancing tibia. Which of the following proprioceptive organs is primarily stimulated by this excessive lengthening, acting to reflexively induce muscle contraction and prevent overstretching?