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Biology, Genetics & Bone Healing MCQs

Practice Set 138 of 212

This practice set contains high-yield board review questions covering key concepts in Biology, Genetics & Bone Healing. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 2741

Topic: Biology, Genetics & Bone Healing
The normal intervertebral disc is anatomically composed of the nucleus pulposus and the surrounding annulus fibrosus, which withstand compressive and tensile forces, respectively. The outer lamellae of the annulus fibrosus are predominantly composed of which type of collagen?
. Type III collagen
. Type II collagen
. Type I collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

The annulus fibrosus functions to resist highly disruptive tensile 'hoop' stresses during axial loading and flexion. Consequently, its outer layers are primarily composed of strong, tension-resisting Type I collagen, unlike the Type II collagen in the nucleus pulposus.

Question 2742

Topic: Biology, Genetics & Bone Healing

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?

. Less than 2%
. 2% to 10%
. 10% to 20%
. 20% to 30%
. Greater than 30%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing requires absolute stability, which correlates to an interfragmentary strain of less than 2%. Strains between 2% and 10% permit secondary bone healing with callus formation.

Question 2743

Topic: Biology, Genetics & Bone Healing
Normal tendons exhibit a highly organized hierarchical structure designed to transmit immense mechanical forces from muscle to bone. Which of the following is the predominant collagen type found in the mid-substance of a healthy tendon?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

Type I collagen constitutes approximately 85-90% of the dry weight of normal tendons, providing robust tensile strength. Type III collagen is typically found in the epitenon and endotenon, and increases during the initial phases of tendon healing.

Question 2744

Topic: Biology, Genetics & Bone Healing

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?

. Rapid revascularization within 2 weeks
. Formation of a massive external bridging callus
. Initial osteoclastic resorption leading to temporary mechanical weakening
. Complete replacement by living host bone within 6 months
. High osteoinductive potential due to preserved viable osteoblasts

Correct Answer & Explanation

. Rapid revascularization within 2 weeks

Explanation

Cortical allografts heal via creeping substitution where osteoclastic resorption outpaces osteoblastic bone formation early on, leading to significant structural weakening for the first 1-2 years. It remains largely a mixture of necrotic graft and vital host bone long-term.

Question 2745

Topic: Biology, Genetics & Bone Healing

According to Perren's Strain Theory of fracture healing, lamellar bone formation (absolute stability) can only occur if the interfragmentary strain at the fracture site remains below what maximum threshold?

. 2%
. 10%
. 20%
. 30%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Perren's theory dictates that lamellar bone can only form when strain is less than 2%. Woven bone tolerates up to 10% strain, while granulation tissue can withstand up to 100% strain.

Question 2746

Topic: Biology, Genetics & Bone Healing

Denosumab is utilized in the medical management of giant cell tumor of bone and osteoporosis. What is the precise molecular target of this monoclonal antibody?

. RANK receptor
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Runx2 transcription factor

Correct Answer & Explanation

. RANK receptor

Explanation

Denosumab specifically binds to RANKL, preventing it from interacting with the RANK receptor on osteoclast precursors. This inhibits osteoclast differentiation, activation, and survival.

Question 2747

Topic: Biology, Genetics & Bone Healing

A 45-year-old female presents with diffuse bone pain and proximal muscle weakness. Laboratory workup reveals severe osteomalacia secondary to chronic malabsorption. Which of the following serum profiles is most consistent with this diagnosis?

. Low/normal Calcium, Low Phosphate, High PTH, High Alkaline Phosphatase
. High Calcium, Low Phosphate, High PTH, High Alkaline Phosphatase
. Normal Calcium, Normal Phosphate, Normal PTH, High Alkaline Phosphatase
. Low Calcium, High Phosphate, Low PTH, High Alkaline Phosphatase
. High Calcium, High Phosphate, Low PTH, Low Alkaline Phosphatase

Correct Answer & Explanation

. Low/normal Calcium, Low Phosphate, High PTH, High Alkaline Phosphatase

Explanation

Osteomalacia driven by Vitamin D deficiency results in reduced intestinal calcium absorption, triggering secondary hyperparathyroidism. This elevated PTH causes renal phosphate wasting (low phosphate) and increased bone turnover (high alkaline phosphatase).

Question 2748

Topic: Biology, Genetics & Bone Healing

Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is heavily utilized for its osteoinductive properties in spine fusion and trauma surgery. BMPs are members of which broader cytokine superfamily?

. Interleukins (IL)
. Tumor necrosis factor (TNF)
. Transforming growth factor-beta (TGF-beta)
. Platelet-derived growth factor (PDGF)
. Fibroblast growth factor (FGF)

Correct Answer & Explanation

. Transforming growth factor-beta (TGF-beta)

Explanation

Bone Morphogenetic Proteins (except BMP-1, which is a metalloproteinase) belong to the Transforming Growth Factor-beta (TGF-beta) superfamily. They bind to serine/threonine kinase receptors and signal intracellularly via the Smad pathway to induce osteoblastic differentiation.

Question 2749

Topic: Biology, Genetics & Bone Healing

Which of the following intracellular signaling molecules is specifically phosphorylated following the binding of Bone Morphogenetic Protein 2 (BMP-2) to its cell surface receptor?

. JAK/STAT
. Smad 1/5/8
. Smad 2/3
. Beta-catenin
. c-Fos

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMP-2 binds to a serine/threonine kinase receptor. The canonical BMP signaling pathway involves the phosphorylation of Smad 1, 5, and 8, which then form a complex with the co-Smad (Smad 4) to translocate into the nucleus and regulate transcription of osteogenic genes. TGF-beta classically signals through Smad 2/3. Wnt signaling involves Beta-catenin.

Question 2750

Topic: Biology, Genetics & Bone Healing

Which of the following cell types is the primary effector responsible for recognizing polyethylene wear debris and initiating the biological cascade that leads to periprosthetic osteolysis?

. Osteoblasts
. Osteoclasts
. Macrophages
. T-lymphocytes
. Polymorphonuclear leukocytes

Correct Answer & Explanation

. Macrophages

Explanation

Macrophages phagocytose polyethylene particles (optimally sized between 0.1 and 10 micrometers) and release pro-inflammatory cytokines such as IL-1, IL-6, TNF-alpha, and PGE2. This stimulates osteoblasts to express RANKL, which subsequently activates osteoclasts, leading to bone resorption and periprosthetic osteolysis.

Question 2751

Topic: Biology, Genetics & Bone Healing

Denosumab is used in the treatment of osteoporosis and giant cell tumors of bone. It functions by mimicking the action of which naturally occurring molecule?

. RANK
. RANKL
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Sclerostin

Correct Answer & Explanation

. RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL, preventing it from binding to the RANK receptor on osteoclast precursors. This mechanism directly mimics the action of osteoprotegerin (OPG), a soluble decoy receptor produced by osteoblasts that competitively binds to RANKL to inhibit osteoclastogenesis.

Question 2752

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, primary (contact) bone healing without callus formation requires the interfragmentary strain to be kept below what percentage?

. 2%
. 5%
. 10%
. 15%
. 20%

Correct Answer & Explanation

. 5%

Explanation

Perren's strain theory dictates the type of tissue that can form in a fracture gap. Absolute stability with interfragmentary strain < 2% allows for primary bone healing (cutting cones) without visible callus. Strain between 2% and 10% promotes secondary bone healing via endochondral ossification (callus formation). Strain > 10% leads to nonunion (fibrous tissue).

Question 2753

Topic: Biology, Genetics & Bone Healing

Romosozumab is a bone-building medication that binds to and inhibits sclerostin. By inhibiting sclerostin, which intracellular signaling pathway is primarily disinhibited, leading to increased bone formation?

. Notch signaling pathway
. Hedgehog signaling pathway
. Wnt/Beta-catenin pathway
. Smad 1/5/8 pathway
. JAK/STAT pathway

Correct Answer & Explanation

. Wnt/Beta-catenin pathway

Explanation

Sclerostin, a glycoprotein secreted primarily by osteocytes, binds to LRP5/6 receptors on osteoblasts and inhibits the canonical Wnt/Beta-catenin signaling pathway. By inhibiting sclerostin with romosozumab, the Wnt pathway is activated, leading to the accumulation of Beta-catenin, which translocates to the nucleus to upregulate osteoblastic bone formation.

Question 2754

Topic: Biology, Genetics & Bone Healing

A 60-year-old female presents with diffuse bone pain and proximal muscle weakness. Laboratory studies reveal a low serum calcium, low serum 25-hydroxyvitamin D, elevated parathyroid hormone (PTH), and elevated alkaline phosphatase. What is the most likely pathological finding on a bone biopsy?

. Thickened woven bone with a mosaic pattern of lamellar bone
. Increased osteoid seam width and unmineralized bone matrix
. Empty lacunae with necrotic marrow architecture
. Massive replacement of marrow by plasma cells
. Hypermineralized bone with defective osteoclasts

Correct Answer & Explanation

. Increased osteoid seam width and unmineralized bone matrix

Explanation

The patient's clinical and laboratory profile is diagnostic of osteomalacia caused by severe Vitamin D deficiency (low Ca, low Vit D, secondary hyperparathyroidism, and elevated ALP). Histologically, osteomalacia is characterized by a defect in bone mineralization, leading to an accumulation of unmineralized osteoid (increased osteoid seam width/thickness). A mosaic pattern is seen in Paget's disease. Empty lacunae indicate osteonecrosis. Defective osteoclasts are seen in osteopetrosis.

Question 2755

Topic: Biology, Genetics & Bone Healing

A surgeon decides to use a synthetic bone graft substitute to fill a void after curettage of a benign bone cyst.

Which of the following bone graft substitutes is characterized as being purely osteoconductive without any native osteoinductive or osteogenic properties?

. Demineralized bone matrix (DBM)
. Calcium phosphate
. Recombinant human bone morphogenetic protein-2 (rhBMP-2)
. Autologous iliac crest bone graft
. Bone marrow aspirate concentrate (BMAC)

Correct Answer & Explanation

. Calcium phosphate

Explanation

Calcium phosphate ceramics provide a three-dimensional scaffold for bone ingrowth (osteoconduction) but lack the cells (osteogenic) and native proteins (osteoinductive) necessary to stimulate de novo bone formation. Demineralized bone matrix (DBM) contains varying levels of inherent osteoinductive proteins depending on processing, while autologous bone graft provides osteoconductive, osteoinductive, and osteogenic properties.

Question 2756

Topic: Biology, Genetics & Bone Healing
The intervertebral disc is a complex structure designed to withstand both tensile and compressive loads. The structural integrity of the nucleus pulposus relies heavily on its ability to attract and hold water. Which of the following collagen types predominates in the nucleus pulposus?
. Type I collagen
. Type II collagen
. Type III collagen
. Type X collagen
. Type XI collagen

Correct Answer & Explanation

. Type II collagen

Explanation

The nucleus pulposus is rich in proteoglycans (primarily aggrecan) and Type II collagen, which together provide excellent resistance to compressive loading (similar to articular cartilage). The annulus fibrosus, which resists tensile hoop stresses, is composed predominantly of Type I collagen.

Question 2757

Topic: Biology, Genetics & Bone Healing

A 12-year-old patient presents with recurrent fractures, severe anemia, and bilateral cranial nerve palsies. Radiographs demonstrate a striking diffuse sclerosis with a 'bone-within-a-bone' appearance.

The pathogenesis of this specific disease variant is most frequently due to a genetic deficiency in which of the following?

. Cathepsin K
. Tissue non-specific alkaline phosphatase
. Type I procollagen
. Carbonic anhydrase II
. Core binding factor alpha-1

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

The patient has osteopetrosis, a condition marked by defective osteoclast function leading to dense, brittle bones that obliterate the medullary cavity (causing anemia). One of the most common identifiable genetic causes of autosomal recessive infantile osteopetrosis is a deficiency of Carbonic anhydrase II, which is essential for generating the protons needed to acidify the Howship's lacuna for bone resorption.

Question 2758

Topic: Biology, Genetics & Bone Healing

A malnourished adult presents with perifollicular hemorrhages, swollen gums, and poor wound healing. Which specific step in collagen synthesis is primarily impaired in this patient's condition?

. Cleavage of procollagen extensions to form tropocollagen
. Hydroxylation of proline and lysine residues
. Cross-linking of tropocollagen molecules by lysyl oxidase
. Glycosylation of hydroxylysine residues
. Assembly of three alpha chains into a triple helix

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

The patient has clinical signs of scurvy (Vitamin C deficiency). Vitamin C (ascorbic acid) is an essential co-factor for the enzymes prolyl hydroxylase and lysyl hydroxylase. Without hydroxylation of proline and lysine, the collagen triple helix is unstable and rapidly degrades, leading to weakened connective tissue.

Question 2759

Topic: Biology, Genetics & Bone Healing

A 45-year-old immigrant presents with diffuse bone pain, proximal muscle weakness, and a waddling gait. Laboratory studies reveal low serum calcium, low phosphorus, and elevated alkaline phosphatase. A bone biopsy would most likely show which of the following histologic hallmarks?

. Accumulation of unmineralized osteoid
. Disorganized woven bone with prominent reversal lines
. Empty osteocyte lacunae with marrow fat necrosis
. Increased numbers of multinucleated osteoclasts in cutting cones
. Replacement of marrow space with loose fibrous tissue and giant cells

Correct Answer & Explanation

. Accumulation of unmineralized osteoid

Explanation

The patient has osteomalacia (the adult equivalent of rickets), typically due to severe Vitamin D deficiency. The histologic hallmark of osteomalacia is defective mineralization of newly formed bone matrix, resulting in significantly widened, unmineralized osteoid seams.

Question 2760

Topic: Biology, Genetics & Bone Healing

A 65-year-old man with increasing hat size and bowing of the tibiae undergoes a bone biopsy to rule out malignancy. Histopathology reveals a specific pattern indicative of the mixed phase of Paget's disease. Which of the following best describes this finding?

. Mosaic pattern of lamellar bone with haphazard cement lines
. Sheets of plasma cells with eccentric nuclei and clock-face chromatin
. Extensive woven bone lacking osteoclasts
. Fibrous replacement of the medullary cavity with spindle cells
. Dense sclerotic cortical bone with extremely narrow haversian canals

Correct Answer & Explanation

. Mosaic pattern of lamellar bone with haphazard cement lines

Explanation

Paget's disease of bone is characterized by excessive and disorganized bone remodeling. In the mixed (active) phase, rampant osteoclastic resorption and disorganized osteoblastic bone formation occur simultaneously. This results in the classic 'mosaic' or 'jigsaw puzzle' pattern of lamellar bone interspersed with prominent, haphazard cement (reversal) lines.

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