1. General Principles & Basic Science MCQs

Skeletal muscle contraction requires the transient elevation of intracellular calcium ions. To initiate cross-bridge cycling, calcium binds directly to which regulatory protein, resulting in the exposure of myosin-binding sites on the actin filament?

Parathyroid hormone (PTH) is a major regulator of calcium homeostasis that stimulates osteoclastic bone resorption. However, mature osteoclasts lack PTH receptors. To induce resorption, PTH primarily binds to receptors located on which cell type?

Surgeons often mix antibiotics into polymethylmethacrylate (PMMA) bone cement for local prophylaxis or treatment of periprosthetic joint infections. Which pharmacokinetic or physical characteristic is absolutely mandatory for an antibiotic to be effective in PMMA?

Various synthetic bone graft substitutes are utilized in orthopedic surgery to fill bone defects, acting purely as osteoconductive scaffolds. Among the following options, which material exhibits the most rapid rate of in vivo resorption?

A researcher applies a constant load to a human anterior cruciate ligament graft during biomechanical testing. Over several hours, the length of the graft progressively increases without any increase in the applied force. What viscoelastic property does this phenomenon represent?

A surgeon contemplates using a stainless steel screw to secure a titanium plate during fracture fixation. This combination is generally avoided due to the risk of galvanic corrosion. In this electrochemical process, which of the following accurately describes the interaction?

Retrieval analysis of a failed total hip arthroplasty shows microscopic scratches, plowing, and gouges on the cobalt-chromium femoral head caused by third-body bone cement particles. What specific type of wear does this represent?

During an active concentric muscle contraction, the sarcomere actively shortens. According to the sliding filament theory, which of the following statements regarding the structural bands is correct?

Osteoclasts degrade bone matrix within the highly specialized sealing zone known as Howship's lacuna. Which enzyme is primarily responsible for the intracellular production of protons required to acidify this resorptive pit?

According to Perren's strain theory of bone healing, the interfragmentary strain dictates the type of tissue that will form between fracture ends. What is the maximum interfragmentary strain threshold that permits primary (direct) cortical bone healing?

The compressive stiffness of articular cartilage is heavily reliant on its proteoglycan content. What biochemical characteristic of glycosaminoglycan (GAG) side chains primarily generates this compressive resistance?

A patient presents with persistent hypocalcemia following a radical thyroidectomy. Endogenous parathyroid hormone (PTH) secretion is normally triggered in this physiologic state. Which of the following best describes the direct effect of PTH on the kidneys?

Synovial fluid behaves as a non-Newtonian fluid, exhibiting decreased viscosity as the shear rate increases during rapid joint movement (thixotropy). Which specific macromolecule is primarily responsible for this vital rheological property?

When preparing antibiotic-loaded polymethylmethacrylate (PMMA) bone cement for a prosthetic joint infection spacer, which characteristic of the selected antibiotic is most crucial for successful incorporation, survival, and elution?

A structural cortical allograft is utilized to reconstruct a massive bone defect following tumor resection. Compared to the incorporation of a non-vascularized cancellous autograft, the incorporation of this cortical allograft is characterized by which of the following?