1. General Principles & Basic Science MCQs

Which of the following enzymes is primarily responsible for generating the protons necessary for the acidic environment within the Howship lacuna during osteoclast-mediated bone resorption?

A patient presents with a symptomatic nonunion of a femoral shaft fracture initially treated with a stainless steel plate. The surgeon plans to revise the fixation using a titanium plate and the existing stainless steel screws. Why is this construct contraindicated?

When preparing antibiotic-loaded polymethylmethacrylate (PMMA) bone cement for a two-stage revision of an infected total hip arthroplasty, which of the following antibiotics is best suited for incorporation due to its thermal stability and elution profile?

A 32-year-old man undergoes open reduction and internal fixation of a transverse radial shaft fracture with a compression plate. Radiographs at 8 weeks show no visible callus, but the fracture line is disappearing. What is the primary mechanism of bone healing occurring in this scenario?

A 45-year-old patient with a tibial shaft fracture asks for a potent non-steroidal anti-inflammatory drug (NSAID) for pain control. The surgeon advises against prolonged use due to the risk of nonunion. NSAIDs impair fracture healing primarily by inhibiting which of the following processes?

In a standard stress-strain curve for a metallic orthopedic implant, what does the slope of the curve in the linear elastic region represent?

In response to hypocalcemia, parathyroid hormone (PTH) is secreted into the bloodstream. Which of the following best describes the direct effect of PTH on the kidneys to restore serum calcium levels?

A 72-year-old woman with a history of multiple osteoporotic vertebral compression fractures is started on teriparatide. Which of the following best describes the mechanism of action of this medication?

A surgeon uses demineralized bone matrix (DBM) to augment a posterolateral lumbar fusion. Which of the following properties is characteristic of DBM but absent in synthetic calcium phosphate ceramics?

The biphasic model of articular cartilage describes the tissue as a porous, permeable solid phase and an incompressible fluid phase. Under rapid loading of a joint, which mechanism primarily provides the tissue's initial stiffness?

During an ACL reconstruction, a hamstring tendon graft is tensioned and secured at a constant length. Over the first few minutes, the tension within the graft decreases. This viscoelastic phenomenon is known as:

Sclerostin is a key negative regulator of bone mass. It functions by antagonizing the Wnt signaling pathway. Which cell type is the primary source of sclerostin in the skeletal system?

Which of the following bone graft substitutes is considered exclusively osteoconductive and relies entirely on the host bed for cellular and inductive components?

On a standard stress-strain curve for a structural material such as metal or bone, the point at which the material transitions from completely reversible elastic deformation to permanent plastic deformation is known as the:

In a bridge plating construct for a comminuted diaphyseal fracture, increasing the working length of the plate (the distance between the closest screws on either side of the fracture) has what primary biomechanical effect?

Galvanic corrosion occurs when two dissimilar metals are in contact within a conductive fluid environment. Which factor primarily dictates the severity and direction of this corrosive process?

Bone Morphogenetic Proteins (BMPs) play a crucial role in osteoinduction. Following the binding of BMPs to their serine/threonine kinase receptors, which intracellular signaling molecules are directly phosphorylated to translocate to the nucleus?

The initial "toe region" of the load-elongation curve for a healthy ligament is primarily biomechanically explained by:

Osteoclasts resorb bone by creating an isolated extracellular microenvironment. Which enzyme is essential for generating the intracellular protons required to lower the pH within this sealing zone?