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Biology, Genetics & Bone Healing MCQs

Practice Set 29 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 561

Topic: Biology, Genetics & Bone Healing
Figure 49 shows the radiograph of a 3-year-old child with progressive bowlegs. Laboratory studies show a calcium level of 9.5 mg/dL (normal 9.0 to 11.0 mg/dL), a phosphorus level of 4.2 mg/dL (normal 3 to 5.7 mg/dL), and an alkaline phosphatase level of 305 IU/L (normal 104 to 345 IU/L). What is the most likely diagnosis?
. Blountโ€™s disease
. Hypophosphatemic rickets
. Nutritional rickets
. Schmid metaphyseal dysostosis
. Jansen metaphyseal dysostosis

Correct Answer & Explanation

. Schmid metaphyseal dysostosis

Explanation

DISCUSSION: The patient has bowlegs associated with very wide physes, particularly noted at the hips. The widening of the growth plates is a classic sign of rickets; however, the normal levels of calcium, phosphorus, and alkaline phosphatase rule out both nutritional and hypophosphatemic rickets. Patients with nutritional rickets or hypophosphatemic rickets have hypophosphatemia and increased alkaline phosphatase levels. Jansen metaphyseal dysostosis has very severe radiographic findings that are not found in this patient; however, these radiographic findings are classic for Schmid metaphyseal dysostosis.

Question 562

Topic: Biology, Genetics & Bone Healing
What zone of the physis is widened in rickets?
. Reserve
. Proliferative
. Hypertrophic
. Maturation
. Primary spongiosa

Correct Answer & Explanation

. Hypertrophic

Explanation

DISCUSSION: Rickets causes widening of the hypertrophic layer of the physis because of the failure of mineralization and vascular invasion. The other zones of the physis may be altered in other disease conditions but remain relatively unchanged in rickets.

Question 563

Topic: Biology, Genetics & Bone Healing

What defect in collagen synthesis is caused by a lack of vitamin C?

. Impaired hydroxylation of proline
. Failure of cleavage in procollagen
. Defective binding sites for hydroxyproline
. Failure to incorporate glycine into the helix
. Diminished production of collagen through the rough endoplasmic reticulum

Correct Answer & Explanation

. Impaired hydroxylation of proline

Explanation

Scurvy results from vitamin C deficiency. Metabolically, vitamin C deficiency produces a decrease in chondroitin sulfate synthesis (enzymatic impairment of the conversion of glucose to galactosamine) and a deficiency in collagen synthesis by impaired hydroxylation of proline. The greatest problem in collagen synthesis is seen in the metaphysis. The metaphyseal bone becomes weakened and microfracture, hemorrhage, debris, and fibrous tissue accumulates. Collapse of the metaphysis and continued lateral growth produces the typical spurs associated with scurvy.

Question 564

Topic: Biology, Genetics & Bone Healing

In the pathogenesis of Charcot neuroarthropathy, the neurovascular theory suggests that autonomic neuropathy leads to which of the following physiologic changes?

. Decreased blood flow and subsequent avascular necrosis
. Increased sympathetic tone causing severe vasoconstriction
. Loss of sympathetic tone resulting in hyperemic bone resorption
. Ectopic bone formation due to chronic localized hypoxia
. Up-regulation of osteoprotegerin (OPG)

Correct Answer & Explanation

. Decreased blood flow and subsequent avascular necrosis

Explanation

The neurovascular theory of Charcot arthropathy postulates that autonomic neuropathy results in a loss of sympathetic control, leading to localized hyperemia and arteriovenous shunting. This hyperemia causes increased osteoclastic activity, active bone resorption, and subsequent osteopenia, making the bones highly susceptible to fracture and collapse with normal weight-bearing.

Question 565

Topic: Biology, Genetics & Bone Healing

Intermittent daily administration of recombinant parathyroid hormone (rhPTH) is an FDA-approved treatment for osteoporosis. Intermittent rhPTH treatment targets which of the following cells in osteoporotic patients?

. Osteoclasts
. Macrophages
. Chondrocytes
. Osteoblasts
. Endothelial cells

Correct Answer & Explanation

. Osteoclasts

Explanation

PTH is an anabolic agent that enhances osteoblastic bone formation on both cortical and cancellous surfaces. It is synthesized in the parathyroid glands as a 115 amino acid precursor and is cleaved into the active 84 amino acid form. The biological activity in the clinically used recombinant PTH is in the 1-34 amino acid sequence at the N-terminus of the molecule. There are PTH receptors expressed by osteoblasts that mediate the anabolic bone response to intermittent PTH administration. Chronic elevation of PTH leads to stimulation of osteoclasts, producing bone loss.

Question 566

Topic: Biology, Genetics & Bone Healing

A tendon repair is thought to be weakest during which phase of tendon healing?

. Inflammatory
. Proliferation
. Maturation
. Remodeling

Correct Answer & Explanation

. Inflammatory

Explanation

Healing after a tendon repair or rupture has the following stages: inflammatory, cellular proliferation, and remodeling. During the inflammatory phase, neutrophils and macrophages migrate into the injury site and release chemotactic factors that recruit fibroblasts. A tendon is thought to be weakest 5 to 21 days after repair, which coincides with the inflammatory phase. During the proliferative phase, inflammatory cells secrete cytokines and growth factors (platelet-derived growth factor, insulin-like growth factor, bone morphogenetic protein (BMP)-12 and BMP 13, and transforming growth factor-beta) that promote differentiation of fibroblasts. Fibrosis and decreased cellularity are the hallmarks of the remodeling stage.

Question 567

Topic: Biology, Genetics & Bone Healing

A 45-year-old female develops severe post-traumatic arthrofibrosis of the knee following open reduction and internal fixation of a bicondylar tibial plateau fracture. At a cellular level, which cytokine is most strongly implicated in the pathogenesis of this excessive intra-articular scar formation?

. Interleukin-1 (IL-1)
. Tumor Necrosis Factor-alpha (TNF-alpha)
. Transforming Growth Factor-beta (TGF-beta)
. Interleukin-6 (IL-6)
. Bone Morphogenetic Protein-2 (BMP-2)

Correct Answer & Explanation

. Transforming Growth Factor-beta (TGF-beta)

Explanation

Transforming growth factor-beta (TGF-beta) is a potent profibrotic cytokine heavily implicated in the development of arthrofibrosis. It stimulates fibroblast proliferation and excessive collagen deposition within the joint capsule.

Question 568

Topic: Biology, Genetics & Bone Healing
Calcitonin acts as an antiresorptive agent by
. decreasing osteoblast number.
. decreasing osteoclast activity and number.
. increasing osteoclast activity.
. increasing osteoblast activity.
. increasing osteoblast number.

Correct Answer & Explanation

. decreasing osteoclast activity and number.

Explanation

DISCUSSION: Calcitonin is a hormone that binds to osteoclasts and acts to decrease both osteoclast activity and number. Calcitonin is most effective in reducing vertebral compression fractures in high-turnover osteoporosis. It is also effective in treating regional osteoporosis. Because of its analgesic effect, it is helpful in treating painful acute compression fractures associated with osteoporosis. REFERENCE: Lane JM, Nydick M: Osteoporosis: Current modes of prevention and treatment. J Am Acad Orthop Surg 1999;7:19-31.

Question 569

Topic: Biology, Genetics & Bone Healing

A minimally invasive plate osteosynthesis is seen in Figure 15. The resultant fracture healing can best be attributed to a fixation construct that was

. stiff and stable.
. flexible and stable.
. facilitating direct osteonal healing.
. inhibitory to endochondral ossification.
. stimulatory to intramembranous ossification.

Correct Answer & Explanation

. stiff and stable.

Explanation

Locked plating constructs with long-working lengths provide flexible but stable constructs that promote (not inhibit) endochondral ossification. Because of the longer working length they are not stiff, and these fractures do not heal with intramembranous ossification which occurs in bones like the calvarium. Direct osteonal healing is usually seen with constructs where absolute stability is achieved through interfragmentary compression, unlike in this case.

Question 570

Topic: Biology, Genetics & Bone Healing

Which of the following is not a cause of childhood osteomalacia (rickets)?

. Vitamin D deficiency
. Renal osteodystrophy
. X-linked hypophosphatemia
. Vitamin D malabsorption
. Vitamin K deficiency

Correct Answer & Explanation

. Vitamin D deficiency

Explanation

Rickets is caused by a decrease in calcium and phosphate that affects mineralization at the physes of the long bones. This disease is characterized by brittle bones; physeal widening is seen on radiographs with long-bone bowing, Looser's lines, enlargement of costal cartilages, and dorsal kyphosis. All of the above-mentioned choices are known causes of osteomalacia or rickets except vitamin K deficiency.

Question 571

Topic: Biology, Genetics & Bone Healing
When evaluating articular cartilage, what extracellular matrix component is most closely associated with the deep calcified cartilage zone?
. Collagen type I
. Collagen type II
. Collagen type X
. Proteoglycan aggrecan
. Hyaluronic acid

Correct Answer & Explanation

. Collagen type X

Explanation

Collagen type X is produced only by hypertrophic chondrocytes during enchondral ossification (growth plate, fracture callus, heterotopic ossification) and is associated with calcification of cartilage in the deep zone of articular cartilage. Collagen type I is the predominant collagen in bone, ligament, and tendon. Collagen type II is the predominant collagen in articular cartilage. Proteoglycan aggrecan and hyaluronic acid are components of the extracellular matrix and are involved in the compressive strength characteristics of articular cartilage.

Question 572

Topic: Biology, Genetics & Bone Healing
A 17-year-old cross country athlete runs 7 miles per day, 6 days per week. She has new-onset right groin pain. Passive flexion of her hip is normal, but internal rotation of the hip, resisted hip flexion, and knee extension reproduce the pain. Hip radiograph findings are normal. What is the best next step?
. Recommend decreasing her training regimen
. Obtain a bone scan
. Obtain an MRI
. Obtain a dual-energy x-ray absorptiometry (DEXA) scan

Correct Answer & Explanation

. Obtain an MRI

Explanation

A stress fracture of the femoral neck or pelvis should be ruled out in this patient. MRI is more accurate, more specific, and is superior to radionuclide bone scanning for the diagnosis of stress fracture in young endurance athletes. MRI detects early changes in osseous stress injury and allows precise definition of the anatomy and extent of injury.

Question 573

Topic: Biology, Genetics & Bone Healing

During the second stage of the Masquelet technique for an infected tibial nonunion, a surgeon plans to remove the antibiotic cement spacer and place bone graft. What is the optimal timing for this second stage to maximize the osteogenic potential of the induced membrane?

. 2 to 4 weeks
. 6 to 8 weeks
. 12 to 16 weeks
. 6 months
. 1 year

Correct Answer & Explanation

. 2 to 4 weeks

Explanation

The second stage of the Masquelet technique is ideally performed 6 to 8 weeks after spacer placement. At this time, the induced membrane has optimal vascularity and peak expression of osteogenic growth factors like VEGF and BMP-2.

Question 574

Topic: Biology, Genetics & Bone Healing

A 6-year-old girl is diagnosed with Klippel-Feil syndrome. Physical examination demonstrates a short neck, low posterior hairline, and severely limited cervical range of motion. Given the known associations of this syndrome, which of the following screening tests is mandatory?

. Pulmonary function tests
. Dual-energy x-ray absorptiometry (DEXA)
. Renal ultrasound
. MRI of the brain without contrast
. Barium swallow study

Correct Answer & Explanation

. Pulmonary function tests

Explanation

Klippel-Feil syndrome is characterized by congenital fusion of two or more cervical vertebrae. It is highly associated with other systemic anomalies, most notably renal abnormalities (such as unilateral renal agenesis or horseshoe kidney) in >30% of patients. Therefore, a renal ultrasound is a mandatory screening test. Cardiac and hearing evaluations are also routinely indicated.

Question 575

Topic: Biology, Genetics & Bone Healing

A 4-year-old girl is diagnosed with Klippel-Feil syndrome. She exhibits a low posterior hairline, short neck, and limited cervical range of motion. Because of known systemic associations with this syndrome, which of the following screening tests is most highly recommended?

. Electrocardiogram (ECG)
. Renal ultrasound
. Pulmonary function tests
. Ophthalmologic slit-lamp exam
. DEXA scan

Correct Answer & Explanation

. Electrocardiogram (ECG)

Explanation

Klippel-Feil syndrome is associated with congenital anomalies due to abnormal embryogenesis. Genitourinary anomalies (e.g., unilateral renal agenesis) occur in approximately 30% of patients, making screening renal ultrasound mandatory.

Question 576

Topic: Biology, Genetics & Bone Healing
A 4-year-old child has droopy shoulders. Examination shows that the child has a large head, short stature, and a narrow chest. Radiographs of the spine and chest show absent clavicles, delayed ossification of the pubis and ischium, and mild coxa vara. What is the inheritance pattern for this condition?
. Autosomal dominant
. Autosomal recessive
. Sex-linked recessive
. Sex-linked dominant
. No inheritance pattern

Correct Answer & Explanation

. Autosomal dominant

Explanation

The child has the clinical and radiographic features of cleidocranial dysostosis. This is a disorder of bones formed by intramembranous ossification. It is inherited as an autosomal-dominant condition. About two thirds of cases are familial.

Question 577

Topic: Biology, Genetics & Bone Healing

A 28-year-old woman who is an avid runner reports pain about the left hip with activities. Nonsurgical management has failed to provide relief. An MRI arthrogram is shown in Figure 47. What is the most likely diagnosis? Review Topic

. Osteonecrosis
. Transient osteoporosis
. Loose chondral fragment
. Labral tear
. Femoral neck stress fracture

Correct Answer & Explanation

. Osteonecrosis

Explanation

The MRI arthrogram reveals dye extravasation into the labrum, consistent with a labral tear. The MRI findings are not typical of osteonecrosis, stress fracture, or transient osteoporosis. There is no increase in bone marrow edema in the neck or femoral head.

Question 578

Topic: Biology, Genetics & Bone Healing
Which treatment of the current fracture will provide the best long-term outcome?
. Casting it in its current position, which is acceptable alignment
. Closed reduction and casting
. Functional brace because this is a stable fracture
. Open reduction with revision of the current implants

Correct Answer & Explanation

. Open reduction with revision of the current implants

Explanation

This fracture is in unacceptable alignment with subluxation of the radiocapitellar joint. The plates are bent, so closed reduction will not solve the alignment problem. In early childhood, load-sharing implants (flexible rods or wires) should be used to solve the elasticity mismatch that contributed to the current fracture.

Question 579

Topic: Biology, Genetics & Bone Healing
Which of the following has been shown to have similar biochemical and clinical characteristics as iliac crest autograft?
. Femoral intramedullary reaming contents
. BMP-2
. BMP-7 with collagen matrix carrier
. Hydroxyapatite cement
. Platelet rich plasma with allograft cancellous bone carrier

Correct Answer & Explanation

. Femoral intramedullary reaming contents

Explanation

In multiple studies, femoral intramedullary reaming debris has been shown to have similar biochemical characteristics as iliac crest autograft. Intramedullary reaming products have osteogenic potential with viable cells while BMPs are osteoinductive cytokines. Hoegel et al found that the reamings had alkaline phosphatase activity, indicating living osteoblasts. The amount of activity was independent of the reamer sizes and reamer design. Frolke et al concluded that reaming debris supports callus building (healing) as much as conventional iliac crest bone grafting in an animal fracture gap model.

Question 580

Topic: Biology, Genetics & Bone Healing
What does Dual Energy X-ray Absorptiometry (DEXA) testing, as a technique, measure?
. Bone mineral content and soft-tissue composition
. Qualitative value of core bone mineral content
. Differentiation of trabecular and cortical bone content
. Core bone mineral density unchanged by osteoarthritis at or around the site
. Bone mineral content and density without need for cross-sectional dimension

Correct Answer & Explanation

. Bone mineral content and soft-tissue composition

Explanation

DEXA can provide data on bone mineral content and soft-tissue composition, and requires cross-sectional dimension for accuracy. DEXA provides a quantitative, not qualitative, measurement of bone mineral content and is incapable of differentiating between trabecular and cortical bone. Osteoarthritis falsely elevates the values, especially in the AP spinal analysis.

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