1. General Principles & Basic Science MCQs

Which of the following mechanical and biological conditions must be strictly satisfied for primary (direct) cortical bone healing to occur without the formation of a visible intermediate cartilaginous callus?

A novel diagnostic test for a rare orthopedic condition is developed with a sensitivity of 95% and a specificity of 90%. If this test is utilized in a primary care population where the actual prevalence of the disease is very low (e.g., 0.1%), what is the most likely statistical effect compared to using it in an orthopedic specialty clinic where the prevalence is 40%?

Bone morphogenetic proteins (BMPs) play a pivotal role in osteoinduction during bone healing. Upon binding to their transmembrane serine/threonine kinase receptors, which specific intracellular signaling molecules are phosphorylated and translocate to the nucleus to act as transcription factors?

You are consulted regarding a diabetic patient requiring lower extremity amputation due to advanced gangrene.

You counsel the patient on the anticipated increased metabolic energy expenditure required for ambulation with a prosthesis. Based on classic orthopedic data, which of the following amputation levels is associated with the highest percentage increase in energy expenditure compared to normal baseline walking?

A 70-year-old woman with a T-score of -3.1 is prescribed Alendronate for the treatment of osteoporosis.

What is the precise intracellular mechanism by which this nitrogen-containing bisphosphonate inhibits osteoclast function and causes osteoclast apoptosis?

A 65-year-old dysvascular patient undergoes a transfemoral amputation. Compared to baseline normal human gait, what is the expected increase in energy expenditure for this patient during ambulation with a properly fitted prosthesis?

During the stance phase of a normal gait cycle, the hip abductors fire to stabilize the pelvis and prevent a Trendelenburg drop. In which specific phase of the gait cycle does maximal contraction of the gluteus medius occur?

During the incorporation of a cortical structural allograft, a process known as creeping substitution occurs. What physiological process characterizes the initial phase of creeping substitution in this setting?

Articular cartilage is structurally divided into four distinct zones to optimize its biomechanical properties. In which zone are the collagen fibers oriented primarily perpendicular to the joint surface to resist compressive forces?

A 55-year-old female with malabsorption presents with diffuse bone pain, muscle weakness, and a Looser zone on radiographs.

Laboratory studies reveal low serum calcium, low serum phosphate, elevated alkaline phosphatase, and elevated parathyroid hormone levels. What is the most likely diagnosis?

In the pathogenesis of periprosthetic joint infection, biofilm formation protects bacteria from host defenses and systemic antibiotics. What is the primary constituent of the extracellular polymeric substance (EPS) matrix in a mature staphylococcal biofilm?

A peripheral nerve injury results in complete disruption of the axons and their surrounding myelin sheaths, but the endoneurial tubes remain entirely intact. Wallerian degeneration occurs distally. Which Sunderland classification best describes this injury?

When evaluating the biomechanical holding power of a cortical bone screw, the pull-out strength is most directly proportional to which of the following screw characteristics?

The optimal low-friction environment of healthy articular cartilage during high-load, dynamic activities (such as the stance phase of running) is primarily maintained by which of the following mechanisms?