1. General Principles & Basic Science MCQs

Bone morphogenetic protein-2 (BMP-2) promotes osteoinduction primarily by signaling through which of the following intracellular pathways?

The pullout strength of a cortical bone screw is most significantly increased by which of the following design alterations?

During Wallerian degeneration following a peripheral nerve transection, which cells are primarily responsible for clearing myelin debris to allow for axonal regeneration?

Which structure in the muscle sarcomere contains ONLY thin (actin) filaments and shortens during muscle contraction?

A 35-year-old pregnant woman presents with an expansile, lytic lesion in the distal femur.

Histology reveals multinucleated giant cells distributed uniformly among mononuclear stromal cells. Denosumab therapy is considered. What is the mechanism of action of denosumab in this disease?

When designing an orthopedic implant for diaphyseal fracture fixation, minimizing stress shielding is a primary goal. Which of the following implant materials possesses a Young's modulus most closely approximating that of human cortical bone?

Normal articular cartilage is structurally divided into four distinct zones. Which zone is characterized by having the highest concentration of proteoglycans, the lowest water content, and collagen fibrils oriented perpendicular to the articular surface?

A diaphyseal radius fracture is treated with rigid internal fixation using a dynamic compression plate, achieving absolute stability and anatomic reduction. This construct primarily dictates which pathway of bone healing?

A 30-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic, epiphyseal lesion in the distal femur that extends to the subchondral bone. Histopathologic analysis shows multinucleated giant cells in a background of mononuclear cells. The targeted biologic therapy denosumab acts by inhibiting which of the following factors expressed by the neoplastic cells in this lesion?

Bone morphogenetic proteins (BMPs) are utilized in spine surgery for their potent osteoinductive properties. They primarily exert their effect by binding to cell membrane receptors, which subsequently phosphorylates which family of intracellular signaling proteins to transcribe osteogenic genes?

When optimizing the fixation of a pedicle screw in osteoporotic bone, the pullout strength of the screw is most significantly increased by maximizing which of the following screw design parameters?

In fracture fixation, utilizing a stainless steel screw through a titanium plate in a saline-rich environment can lead to accelerated degradation of the implant. This process is best described as which type of corrosion?

During the bone remodeling cycle, osteoclasts attach to the bone surface via integrins, creating an isolated resorption pit (Howship's lacuna). Which intracellular enzyme is critical for generating the protons needed to acidify this microenvironment and dissolve the inorganic bone mineral?

A surgeon applies a constant, continuous distraction force to a contracted joint capsule using a hinged external fixator. Over several days, the capsule gradually elongates without any increase in the applied force. What is the biomechanical term for this viscoelastic phenomenon?

Polymethylmethacrylate (PMMA) is widely used for implant fixation in joint arthroplasty. Which of the following statements accurately describes its biomechanical properties?

The menisci of the knee play a crucial role in load distribution and shock absorption. The predominantly circumferential orientation of type I collagen bundles within the meniscus is specifically adapted to resist which biomechanical force during axial loading?

A 65-year-old man sustains a pathologic fracture of the humerus. Radiographs show multiple "punched-out" lytic lesions. Laboratory work reveals hypercalcemia, anemia, and an IgG kappa monoclonal spike. The severe osteolysis seen in this condition is primarily mediated by the neoplastic cells secreting factors that heavily upregulate which pathway?

A trauma surgeon uses a stainless steel dynamic compression plate but places titanium alloy screws for fixation of a diaphyseal femur fracture due to lack of inventory. Which type of corrosion is most likely to occur at the screw-plate interface?

A 70-year-old female with osteoporosis is prescribed a nitrogen-containing bisphosphonate. This medication inhibits bone resorption primarily by inhibiting which of the following intracellular targets within the osteoclast?