Orthopedics Question Bank

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1. Which protein is the most abundant organic component of bone matrix?

Type I collagen constitutes roughly 90 percent of the organic matrix of bone and provides tensile strength. The inorganic hydroxyapatite mineral provides compressive strength. Non-collagenous proteins such as osteocalcin are present in much smaller amounts.

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2. The primary inorganic mineral component that gives bone its compressive strength is best described as which of the following?

Calcium hydroxyapatite is the crystalline mineral deposited within the collagen matrix and provides bone with its resistance to compressive loading. The organic collagen framework primarily resists tension. Together they create a composite material.

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3. Which cell is derived from the hematopoietic monocyte-macrophage lineage and is responsible for bone resorption?

Osteoclasts are multinucleated giant cells derived from the monocyte-macrophage hematopoietic lineage and resorb bone via acid and proteolytic enzymes in the ruffled border. Osteoblasts and osteocytes derive from mesenchymal stem cells. This distinction in lineage is a common exam concept.

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4. Osteoclast differentiation is primarily driven by RANKL binding to RANK, a process physiologically inhibited by which decoy receptor?

Osteoprotegerin (OPG) is a decoy receptor secreted by osteoblasts that binds RANKL and prevents it from activating RANK on osteoclast precursors. The RANKL/RANK/OPG axis regulates the balance of bone resorption. A high RANKL-to-OPG ratio favors resorption.

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5. An osteocyte communicates with neighboring cells and senses mechanical load primarily through which structures?

Osteocytes reside in lacunae and extend dendritic processes through canaliculi to form a syncytial network that senses mechanical strain and fluid flow. They are the primary mechanosensors of bone. Signals from osteocytes regulate osteoblast and osteoclast activity.

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6. Cortical bone is organized into structural units called osteons; the central channel of an osteon carrying vessels is termed which of the following?

The Haversian canal is the central longitudinal channel of an osteon that contains blood vessels and nerves. Volkmann canals connect adjacent Haversian systems transversely. Concentric lamellae surround the Haversian canal.

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7. Which type of bone healing occurs with rigid compression plating that provides absolute stability, and is characterized by the absence of visible callus?

Primary or direct bone healing occurs under absolute stability with anatomic reduction and interfragmentary compression, proceeding via cutting cones and Haversian remodeling without callus formation. Secondary healing occurs with relative stability and produces callus. Rigid plating aims for direct healing.

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8. Secondary bone healing with callus formation requires which mechanical environment at the fracture site?

Secondary bone healing proceeds through inflammation, soft callus, hard callus, and remodeling, and is stimulated by relative stability that permits controlled interfragmentary micromotion. Excessive motion causes nonunion, while absolute stability yields direct healing. Casts, intramedullary nails, and bridge plating provide relative stability.

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9. Place the phases of secondary fracture healing in correct order: which phase immediately follows the inflammatory (hematoma) phase?

After the initial inflammatory hematoma phase, the soft callus (fibrocartilaginous) phase forms, followed by the hard callus phase of endochondral and intramembranous ossification, and finally remodeling. The soft callus provides early stabilization. This sequence is a classic exam ordering question.

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10. During endochondral fracture healing, the soft cartilaginous callus is converted to woven bone through a process most analogous to which normal physiologic process?

Conversion of the cartilaginous soft callus to bone recapitulates endochondral ossification seen at the growth plate, where chondrocytes hypertrophy and mineralized cartilage is replaced by woven bone. Intramembranous ossification, by contrast, forms bone directly from mesenchyme without a cartilage intermediate. Both occur during fracture repair.