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 441
Topic: Biology, Genetics & Bone Healing
A patient with hypophosphatemic rickets presents with a severe bow-leg deformity consisting of both a diaphyseal bow and a metaphyseal varus deformity in the same femur. Which of the following principles must be applied to accurately identify the true CORAs in this multi-apical deformity?
Correct Answer & Explanation
. Divide the bone into individual segments, drawing separate anatomical axes for each segment to find their intersections.
Explanation
In multi-apical deformities, the bone must be divided into three or more segments. Anatomical or mechanical axis lines are drawn for each individual segment, and their intersection points dictate the multiple separate CORAs required for correction.
Question 442
Topic: Biology, Genetics & Bone Healing
Following a corticotomy for tibial lengthening, the surgeon prescribes a latency period before initiating distraction. What is the optimal latency period for a healthy young adult to optimize regenerate bone formation?
Correct Answer & Explanation
. 5-7 days
Explanation
A latency period of 5 to 7 days is generally recommended before beginning distraction. This allows for the initial inflammatory and soft callus phases of fracture healing to commence, optimizing the local biological environment for distraction osteogenesis.
Question 443
Topic: Biology, Genetics & Bone Healing
In distraction osteogenesis (Ilizarov method) for limb lengthening, what is the primary biological purpose of the 'latent period' prior to initiating distraction?
Correct Answer & Explanation
. To permit the initial organization of the fracture hematoma and formation of a mesenchymal bridge.
Explanation
The latent period (typically 5-7 days) allows for the inflammatory phase and early soft callus formation. This ensures a vascularized mesenchymal tissue bridge is present to form quality regenerate bone upon distraction.
Question 444
Topic: Biology, Genetics & Bone Healing
A 12-year-old patient with a history of rickets presents with a complex femoral deformity. A long-leg radiograph is obtained and the surgeon performs anatomic axis planning, identifying the axis lines as shown in Diagram 'd' of the image below.
Based on this finding, what is the most appropriate surgical strategy for correcting this deformity?
Correct Answer & Explanation
. Multiple osteotomies, with one at each identified CORA (CORA1 and CORA2).
Explanation
Correct Answer: CDiagram 'd' in the image clearly illustrates amultiapical deformity, characterized by more than one bend in the bone, resulting in multiple axis lines that do not intersect at a single point, thus creating two or more Centers of Rotation of Angulation (CORA1, CORA2). The text explicitly states: 'Attempting to correct a multiapical deformity with a single osteotomy is a catastrophic biomechanical error. It will correct the angulation at one localized level but will inevitably induce a secondary translation and malalignment, failing to restore the overall mechanical axis of the limb. Multiapical deformities strictly require multiple osteotomies, strategically planned for each individual CORA.' Therefore, options A, B, D, and E, which suggest a single osteotomy or a method not suitable for multiapical deformities, are incorrect.
Question 445
Topic: Biology, Genetics & Bone Healing
A 70-year-old patient with a history of childhood rickets presents with severe genu varum. A full-length standing AP radiograph is obtained, as shown below. The surgeon notes a significant medial mechanical axis deviation. Based on the principles of the Paley method, what is the most appropriate initial step to determine the *source* of this deformity?
Correct Answer & Explanation
. Analyze the joint orientation angles (e.g., mLDFA, MPTA) and compare them to normative values.
Explanation
Correct Answer: CThe case states, 'The MAD tells the surgeonthata deformity exists and quantifies its overall effect on the limb's weight-bearing status, but it does not tell youwherethe deformity originates. To pinpoint the anatomic source (femur vs. tibia vs. joint line), you must analyze the joint orientation angles.' Therefore, measuring angles like mLDFA and MPTA is the crucial next step after identifying the MAD, to localize the deformity to the femur, tibia, or both.Option A is incorrectbecause planning an osteotomy without localizing the deformity (femoral vs. tibial) could lead to iatrogenic malalignment or an incomplete correction.Option B is incorrectbecause MAD only quantifies the overall deformity; it doesn't provide the necessary information for precise surgical planning regarding the location of the osteotomy.Option D is incorrectbecause while rotational deformity is important, the initial focus for frontal plane malalignment (as indicated by genu varum and MAD) is on frontal plane angles. A CT scan for rotation would typically follow initial frontal and sagittal plane analysis.Option E is incorrectbecause physical therapy alone cannot correct a structural bony deformity causing severe genu varum and medial compartment osteoarthritis.
Question 446
Topic: Biology, Genetics & Bone Healing
A 14-year-old male is undergoing distraction osteogenesis for a 4 cm tibial limb length discrepancy. What is the optimal latency period and rate of distraction according to standard Ilizarov and Paley principles?
Correct Answer & Explanation
. 7-10 days latency; 1.0 mm/day distraction
Explanation
A latency period of 7-10 days allows for the initial formation of a fracture hematoma and early soft callus. The standard distraction rate is 1.0 mm per day, typically divided into four 0.25 mm increments.
Question 447
Topic: Biology, Genetics & Bone Healing
During an external fixation lengthening procedure, the term "Bone Healing Index" (BHI) is frequently used to assess patient progress. How is the BHI defined?
Correct Answer & Explanation
. The total time in the external fixator (in months) divided by the total length gained (in centimeters).
Explanation
The Bone Healing Index (BHI) quantifies the speed of consolidation in distraction osteogenesis. It is calculated by dividing the total time in the external fixator (months) by the length gained (centimeters).
Question 448
Topic: Biology, Genetics & Bone Healing
In distraction osteogenesis using the Ilizarov method, a latency period is maintained between the osteotomy and the initiation of distraction. What is the primary biological purpose of this latency period?
Correct Answer & Explanation
. To allow the hematoma to organize and mesenchymal stem cells to populate the gap
Explanation
A latency period of 5-7 days allows the initial fracture hematoma to organize and mesenchymal cells to proliferate. This ensures robust callus formation before distraction begins.
Question 449
Topic: Biology, Genetics & Bone Healing
What does the Bone Healing Index (BHI) commonly used in distraction osteogenesis represent?
Correct Answer & Explanation
. The total number of days the external fixator is worn divided by the total centimeters of lengthening achieved
Explanation
The Bone Healing Index (BHI) is a standardized measure of consolidation time, defined as the total days in the external fixator divided by the total lengthening in centimeters (days/cm).
Question 450
Topic: Biology, Genetics & Bone Healing
Osteopenia is defined by the World Health Organization (WHO) as a bone mineral density (BMD) that is
Correct Answer & Explanation
. within 1 and 2.5 standard deviations below age-matched normals.
Explanation
DISCUSSION: Osteopenia, decreased bone mass without fracture risk as defined by the WHO criteria for diagnosis of osteoporosis, is when a womanโs T-score is within -1 to -2.5 SD. The T-score represents a comparison to young normals or optimum peak density. The Z-score represents a comparison of BMD to age-matched normals. Measurements of bone mineral density (BMD) at various skeletal sites help in predicting fracture risk. Hip BMD best predicts fracture of the hip, as well as fractures at other sites. REFERENCE: Kanis JA, Johnell O, Oden A, et al: Risk of hip fracture according to the World Health Organization criteria for osteopenia and osteoporosis. Bone 2000;27:585-590.
Question 451
Topic: Biology, Genetics & Bone Healing
Receptor activator of nuclear factor kappa b (RANKL) and macrophage colony stimulating factor (MCSF) signaling pathways are necessary for the formation of multinucleated osteoclasts that resorb bone. Which of the following cells are known to produce RANKL?
Correct Answer & Explanation
. Osteoclasts
Explanation
Osteoclast differentiation and function depend on the establishment of specific patterns of gene expression achieved through networks of transcription factors activated by osteoclastogenic cytokines such as RANKL and MCSF. RANKL and MCSF are produced by osteoblasts and T cells. Key transcriptional factors responsible for osteoclatogenesis require activation of transcriptional factors such as PU.1, NF-kappaB, AP-1, NFATc1, Mitf, Myc, and Src in osteoclast precursors that are of monocyte/macrophage origin.
Question 452
Topic: Biology, Genetics & Bone Healing
An 11-year-old boy reports the acute onset of elbow pain and swelling after pushing his brother. The patient's mother and a younger sibling have experienced numerous fractures. You note that the patient and his mother have blue sclera and normal-appearing teeth. A radiograph of the elbow is shown in Figure 60. This patient's disorder is most likely the result of Review Topic
Correct Answer & Explanation
. a quantitative defect of type I collagen synthesis.
Explanation
Osteogenesis imperfecta (OI) is a genetically determined disorder of type I collagen synthesis characterized by bone fragility. This patient sustained a displaced fracture of the olecranon apophysis after relatively minor trauma. Physical examination reveals distinctly blue sclera. His mother and younger sibling have experienced numerous fractures suggesting a family history of bone fragility. The patient's history, clinical features, and family history are consistent with a diagnosis of Sillence type I-A OI. Type I OI is the mildest and most common form. Inheritance is autosomal dominant.Type I is subclassified into the A type (absence of dentinogenesis imperfecta) and B type (presence of dentinogenesis imperfecta). These individuals have blue sclerae, and although the initial fracture usually occurs in the preschool years, it may occur at any age. Furthermore, olecranon apophyseal fractures that occur after relatively minor trauma have been associated with type I OI. Cells from individuals with type I OI largely demonstrate a quantitative defect of type I collagen; they synthesize and secrete about half the normal amount of type I procollagen. In this patient, there are no indications that the child has been subjected to abuse. Radiographs of the elbow show no evidence of osteopetrosis (due to abnormal osteoclast function) or rickets (due to a deficiency of vitamin D). Morquio syndrome (characterized by a defect of the enzyme N-Ac-Gal-6 sulfate sulfatase) is not associated with blue sclera.
Question 453
Topic: Biology, Genetics & Bone Healing
A 35-year-old male is undergoing tibial bone transport with a circular external fixator for a 6 cm segmental defect. The transport segment has successfully reached the docking site. After 8 weeks, radiographs show a persistent lucency at the docking site with no bridging callus. What is the most appropriate next step to stimulate union?
Correct Answer & Explanation
. Iliac crest bone grafting and compression at the docking site
Explanation
In distraction osteogenesis / bone transport, delayed union or nonunion at the docking site is a common complication. The standard of care to achieve union when the transport segment reaches the target but fails to consolidate is preparation of the docking site ends, autologous bone grafting (e.g., from the iliac crest), and applying compression across the docking site.
Question 454
Topic: Biology, Genetics & Bone Healing
A 40-year-old male is undergoing tibial lengthening via distraction osteogenesis using a circular Ilizarov external fixator. Following the corticotomy, there is a required waiting period before the commencement of distraction. What is the optimal 'latent period' in adults, and what is its primary biological purpose?
Correct Answer & Explanation
. 7-10 days; to allow early capillary ingrowth and primitive callus formation before applying tension
Explanation
The latent period is the time between the corticotomy/osteotomy and the initiation of distraction. In an adult undergoing tibial lengthening, the optimal latent period is typically 7 to 10 days. This allows the initial inflammatory phase to subside and permits the ingrowth of delicate capillaries and primitive mesenchymal tissue (early soft callus). If distraction begins too early (e.g., 0-3 days), the tissue is torn, leading to poor regenerate (hypotrophic). If it is too long, premature consolidation occurs.
Question 455
Topic: Biology, Genetics & Bone Healing
Smoking has been associated with lower fusion rates in both cervical and lumbar fusion. Which of the following statements best describes an explanation for these findings?
Correct Answer & Explanation
. The effects of smoking on bone healing are multifactorial and not yet fully understood.
Explanation
Tobacco smoking is now the leading avoidable cause of morbidity and mortality in the United States. The musculoskeletal effects of smoking have been implicated in osteoporosis, low back pain, degenerative disk disease, poor wound healing, and delayed fusion and fracture healing. A number of studies have demonstrated the relationship between smoking and development of pseudarthrosis. Numerous studieshave been performed to offer an explanation of the mechanism mediating this effect. Whereas all of the above have been postulated as explanations, more recent studies have demonstrated that nicotine delivered via a transdermal patch significantly enhanced posterior spinal fusion in rabbits. Thus it appears that the effects of smoking on fracture healing are multifactorial and not yet fully understood.
Question 456
Topic: Biology, Genetics & Bone Healing
Figure 11 shows the radiograph of a 2-year-old child with marked genu varum and tibial bowing. Based on these findings, what is the best initial course of action?
Correct Answer & Explanation
. Obtain serum phosphorous, calcium, and alkaline phosphatase levels.
Explanation
The radiograph shows multiple wide physes, consistent with a diagnosis of rickets. A low serum phosphorous level and an elevated alkaline phosphatase level are the hallmarks in diagnosing familial hypophosphatemic Vitamin D-resistant rickets. Serum calcium is usually normal or low normal. This disease is inherited as an X-linked dominant trait and usually presents at age 18 to 24 months. The disease results from a poorly defined problem with renal phosphate transport in which normal dietary intake of vitamin D is insufficient to achieve normal bone mineralization. Renal tubular dysfunction is associated with urinary phosphate wasting. Treatment involves oral phosphate supplementation, which can cause hypocalcemia and secondary hyperparathyroidism. To prevent associated problems, high doses of Vitamin D are administered. While obtaining a scanogram may be clinically indicated in an associated limb-length discrepancy, and subsequent corrective surgery may be indicated, either of these choices would not be the first course of action. An orthosis may slow the progression of genu varum in this disorder but is less important than establishing the correct diagnosis to begin pharmacologic treatment. This amount of varum and tibial bowing far exceeds the normal limits of physiologic genu varum. Skeletal dysplasias usually are not associated with abnormal laboratory values.
Question 457
Topic: Biology, Genetics & Bone Healing
Which of the following growth factors binds and activates the lipoprotein receptor-related protein 5/6 (LRP5/6) during bone development? Review Topic
Correct Answer & Explanation
. Wnt protein
Explanation
Wnt and Hedgehog (Hh) signaling pathways are key regulators of bone formation. Mutations in the Wnt and Hh pathways result in skeletal malformations as well as osteoarthritis. Wnts are a large family of secreted proteins (19 different members in the human genome) that transduce their signal through several pathways. The most studied of these pathways is the Wnt/beta-catenin pathway, in which Wnt protein binds to the LRP5/6 receptor at the cell surface and activates an intracellular cascade. This cascade leads to translocation of beta-catenin into the nucleus to activate transcription of genes that control osteoblast differentiation. Agents that stimulate this pathway are under investigation for treatment of osteoporosis.
Question 458
Topic: Biology, Genetics & Bone Healing
What is the primary intracellular signaling mediator for bone morphogenetic protein (BMP) activity?
Correct Answer & Explanation
. SMADS
Explanation
BMPs signal through the activation of a transmembrane serine/threonine kinase receptor that leads to the activation of intracellular signaling molecules called SMADs. There are currently eight known SMADs, and the activation of different SMADs within a cell leads to different cellular responses. The other mediators are not believed to be directly involved with BMP signaling.
Question 459
Topic: Biology, Genetics & Bone Healing
What is the most likely cause of the lesion shown in Figures 35a and 35b?
Correct Answer & Explanation
. Contusion
Explanation
DISCUSSION: The most common cause of myositis ossificans is contusion. Certain regions, including the quadriceps and brachialis, are more commonly affected. The mechanisms of development have not been clearly established. REFERENCES: Beiner JM, Jokl P: Muscle contusion injuries: Current treatment options. J Am Acad Orthop Surg 2001;9:227-237. Jarvinen TA, Jarvinen TL, Kaariainen M, et al: Muscle injuries: Biology and treatment. Am J Sports Med 2005;33:745-764.
Question 460
Topic: Biology, Genetics & Bone Healing
Which of the following treatments for osteoporosis is a direct inhibitor of RANK ligand (RANK-L)?
Correct Answer & Explanation
. Romosozumab
Explanation
Prolia, or denosumab, is a newly approved drug used to treat osteoporosis and has a mechanism of action similar to osteoprotegerin (inhibits binding of RANKL to RANK).RANKL (Receptor activator of nuclear factor kappa-B ligand) is a key molecule for osteoclast differentiation and activation. Inhibition of RANKL activity with anti-RANKL antibody reduces osteoclastogenesis, resulting in inhibition of bone resorption.Capozzi et al. author a review article on denosumab. They state the medication confers improved bone mineral density and prevents new fragility fractures similar to alendronate. However, denosumab presents less risk of atypical femoral fractures andosteonecrosis of the jaw.Yasuda et al. present a review that details the creation of three elegant animal models to mimic metabolic bone disease and how the animal models can create a template to help cure human metabolic bone disease. These enable modeling of osteoporosis, hypercalcemia, and osteopetrosis by treating normal mice with soluble RANKL (sRANKL), adenovirus expressing sRANKL, and anti-mouse RANKL neutralizing antibody, respectively. They report that these animal models can be established in about 14 days using normal mice.Illustration A demonstrates the mechanism of action of bisphosphonates and denosumab.Incorrect Answers:1: Romosozumab is the first humanized anti-sclerostin monoclonal antibody that has been demonstrated to increase bone formation. 2: Zoledronic acid (Reclast) is a nitrogen containing bisphosphonates that inhibits osteoclast resorption by inhibiting the enzyme farnesyl diphosphate synthase. 4: Teriparatide (Forteo) comprises the first 34 amino acids of the 84 amino acid parathyroid hormone (PTH) and can reproduce the primary effects of PTH by activating adenyl cyclase. 5: Blosozumab is an investigational monoclonal anti-sclerostin antibody showing osteoanabolic properties with the potential to improve clinical outcomes in patients with osteoporosis.
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