This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.
Question 4741
Topic: 1. General Principles & Basic Science
Articular cartilage is composed of multiple distinct histologic zones, each with unique biochemical properties. Which zone of articular cartilage contains the highest concentration of proteoglycans and the lowest concentration of water?
Correct Answer & Explanation
. Deep (radial) zone
Explanation
The deep (radial) zone of articular cartilage is characterized by the highest concentration of proteoglycans (which provide compressive resistance), the lowest concentration of water, and the thickest collagen fibrils oriented perpendicular to the joint surface. The superficial zone has the highest water content and collagen fibrils parallel to the surface.
Question 4742
Topic: 1. General Principles & Basic Science
A 45-year-old man with a painful varus knee is being considered for an upper tibial osteotomy. Which of the following factors is considered the most compelling argument against this procedure?
Correct Answer & Explanation
. Rheumatoid arthropathy
Explanation
Proximal tibial osteotomy is appropriate for the younger and/or athletic patient who has mild to moderate medial compartment osteoarthritis. Relative contraindications include limited range of motion (eg, flexion contracture of 15 degrees), anatomic varus of greater than 10 degrees, advanced patellofemoral arthritis, and tibial subluxation. Inflammatory arthritides involve all the compartments and are a contraindication to osteotomies around the knee.
Question 4743
Topic: Infection, Pharmacology & VTE
A 2-week-old infant has been referred for evaluation of nonmovement of the left hip. History reveals that the patient was delivered 6 weeks premature by cesarean section. Examination reveals no fever, and there is mild swelling of the thigh. Passive movement of the hip appears to elicit tenderness and very limited hip motion. A radiograph of the pelvis shows mild subluxation of the left hip. The next step in evaluation should consist of
Correct Answer & Explanation
. aspiration of the left hip.
Explanation
The diagnosis of bone and joint sepsis in a newborn is difficult because of the relative lack of obvious signs and symptoms. Fever is usually absent. A study of 34 newborns with osteomyelitis identified prematurity and delivery by cesarean section as predisposing factors. In that study, the most common clinical findings were pseudoparalysis, local swelling, and pain on passive movement. Because early diagnosis is so important, any infant who exhibits these findings should be suspected as having bone or joint sepsis. Once the area of involvement is identified, aspiration is mandatory. In newborns who have an infection about the hip, radiographs may reveal subluxation. In this patient, septic arthritis must be ruled out by aspiration of the hip. Developmental dysplasia of the hip is not painful and is not accompanied by localized swelling. If no purulent material is obtained at the time of hip aspiration, an arthrogram should be obtained to rule out epiphysiolysis of the proximal femur. Because the area of involvement has been identified by clinical examination, a gallium scan or MRI scan of the spine is not indicated. Knudsen CJ, Hoffman EB: Neonatal osteomyelitis. J Bone Joint Surg Br 1990;72:846-851.
Question 4744
Topic: Biology, Genetics & Bone Healing
A 75-year-old male with a known history of Paget's disease of bone involving the left femur presents with new onset severe pain in the affected thigh, refractory to NSAIDs and bisphosphonates. Radiographs show progressive cortical thickening and bowing of the femur, with a new, subtle transverse lucency in the lateral cortex. What is the most appropriate next diagnostic step?
Correct Answer & Explanation
. MRI of the femur.
Explanation
This patient has Paget's disease affecting the femur and presents with new, severe pain and a 'subtle transverse lucency in the lateral cortex' on radiographs. This radiographic finding, especially in a pagetic bone that is bowed and hypertrophied, is highly suspicious for an impending or incomplete pathologic fracture, often referred to as a 'fissure fracture' or 'stress fracture' of Paget's bone. These fractures typically start on the convex side (tension side) of the bowed bone.Option A (CT scan) can provide more detailed bony architecture but may not be as sensitive for early stress fractures or soft tissue changes.Option B (Bone scintigraphy) would show increased uptake in the pagetic bone (hot spots), but it's a very sensitive but non-specific test. It might light up more intensely at the site of increased metabolic activity due to a stress fracture, but it wouldn't characterize the fracture line or any surrounding soft tissue injury as well as an MRI.Option C (MRI of the femur) is the most appropriate next diagnostic step. MRI is highly sensitive for detecting stress fractures, subtle lucencies, and incomplete fractures that may be missed or poorly characterized on plain radiographs or CT. It can also differentiate between different causes of pain (e.g., stress fracture, malignant transformation to sarcoma, inflammatory changes, or simply exacerbation of Paget's activity) and assess soft tissue involvement. Confirming an incomplete fracture or impending fracture is crucial for guiding management, often leading to prophylactic fixation.Option D (Measurement of serum alkaline phosphatase levels) is useful for monitoring disease activity in Paget's disease and response to bisphosphonates. However, it's a biochemical marker of bone turnover and will not directly diagnose or characterize a fracture. While a flare-up of Paget's could cause pain and elevate ALP, a new focal lucency points to a mechanical issue.Option E (Biopsy of the lesion) would be indicated if there was suspicion of malignant transformation (e.g., osteosarcoma, which is a known but rare complication of Paget's disease). While a new, severe pain can sometimes raise this concern, a 'subtle transverse lucency' is more characteristic of an incomplete fracture. MRI would be the first step to better characterize the lesion before considering an invasive biopsy.
Question 4745
Topic: Biology, Genetics & Bone Healing
Regarding bone graft substitutes, which of the following statements accurately describes the primary characteristic of an osteoinductive material?
Correct Answer & Explanation
. It stimulates mesenchymal stem cells to differentiate into osteoblasts.
Explanation
Osteoinductive materials have the ability to stimulate mesenchymal stem cells (MSCs) to differentiate into osteoblasts, thereby inducing new bone formation, even in heterotopic sites. The classic example is bone morphogenetic protein (BMP). An osteoconductive material, on the other hand, provides a scaffold or framework for existing bone to grow into (e.g., calcium phosphate ceramics, demineralized bone matrix (DBM) primarily). Mechanical support is the role of structural grafts or fixation. Acting as a reservoir for growth factors might be a component of some advanced materials, but the direct stimulation of MSC differentiation is the core definition of osteoinduction. Enhancing bone remodeling and resorption is a metabolic function, not the primary characteristic of an osteoinductive graft.
Question 4746
Topic: Biology, Genetics & Bone Healing
A 55-year-old female presents with widespread musculoskeletal pain, muscle weakness, and proximal leg cramps. She has a history of bariatric surgery 5 years prior. Biochemical tests reveal low serum calcium, low serum phosphate, elevated alkaline phosphatase, and elevated parathyroid hormone. Radiographs show Looser zones (pseudofractures) in the femoral neck and pubic rami. Which of the following is the MOST likely underlying diagnosis?
Correct Answer & Explanation
. Vitamin D deficiency osteomalacia.
Explanation
The constellation of symptoms (widespread pain, weakness, cramps), history of bariatric surgery (which can lead to malabsorption), and biochemical findings (low calcium, low phosphate, elevated ALP, elevated PTH) strongly suggests vitamin D deficiency osteomalacia. The presence of Looser zones (pseudofractures) on radiographs is pathognomonic for osteomalacia. Paget's disease typically presents with localized pain, bone enlargement, and isolated elevated ALP but normal calcium/phosphate. Osteoporosis involves low bone mineral density and fragility fractures but not typically Looser zones or these specific biochemical abnormalities. Primary hyperparathyroidism causes hypercalcemia and hypophosphatemia, which is inconsistent with the low calcium. Renal osteodystrophy is seen in chronic kidney disease, which is not indicated here, though it shares some biochemical features.
Question 4747
Topic: 1. General Principles & Basic Science
In evaluating a patient for chronic lower back pain with suspected facet joint arthropathy, which of the following imaging modalities is considered the 'gold standard' for diagnosing facet pain before considering invasive treatments?
Correct Answer & Explanation
. Diagnostic medial branch nerve block.
Explanation
For diagnosing facet joint pain, particularly prior to considering treatments like radiofrequency ablation or surgical fusion, a diagnostic medial branch nerve block is considered the 'gold standard'. Facet joint pain is often a clinical diagnosis with radiographic correlation, but imaging alone (X-rays, MRI, CT) cannot definitively diagnose the pain generator. MRI and CT can show degenerative changes, but these changes often do not correlate with symptoms. A positive response (significant pain relief) to a precisely performed diagnostic block of the medial branch nerves (which innervate the facet joints) confirms the facet joint as the source of pain. A bone scan can show increased metabolic activity in the facets but is not definitive for pain diagnosis.
Question 4748
Topic: 1. General Principles & Basic Science
A 30-year-old football player sustains a high-energy knee injury resulting in a Schenck KD-III-M knee dislocation. Clinical examination reveals gross laxity to varus and valgus stress at 0 and 30 degrees of flexion, with a positive posterior drawer test. Popliteal pulses are palpable, but a common peroneal nerve palsy is present. An MRI of the knee is shown. What is the most appropriate initial management strategy for this patient?
Correct Answer & Explanation
. Emergent reduction, application of an external fixator, and careful neurovascular observation.
Explanation
For a knee dislocation, emergent reduction is the top priority to minimize soft tissue tension and reduce the risk of neurovascular compromise, even if pulses are palpable initially (occult vascular injury can exist). Once reduced, temporary stabilization, often with an external fixator, is crucial to maintain alignment and allow swelling to subside. Continuous neurovascular observation is essential. While a nerve palsy is present, immediate nerve exploration is typically not indicated unless there is an open injury or a progressive deficit after reduction. Ligament reconstruction is usually performed in a delayed fashion (7-14 days after injury) once swelling has decreased and the patient's general condition allows. MRI angiography is not the first step and can be performed after reduction if clinical suspicion of vascular injury remains high or if pulses were initially absent.
Question 4749
Topic: Biology, Genetics & Bone Healing
In the context of promoting bone healing, various orthobiologic agents are utilized. These agents exert their effects through different mechanisms. Which of the following orthobiologics primarily acts by providing a demineralized osteoconductive scaffold rich in growth factors to stimulate local mesenchymal stem cells, rather than directly supplying viable osteoprogenitor cells?
Correct Answer & Explanation
. Demineralized bone matrix (DBM).
Explanation
Demineralized bone matrix (DBM) is processed allograft bone where the mineral component is removed, leaving behind the collagen matrix and non-collagenous proteins, including bone morphogenetic proteins (BMPs) and other growth factors. DBM primarily functions through osteoconduction (providing a scaffold for new bone formation) and osteoinduction (due to the retained growth factors that stimulate host mesenchymal stem cells). It does NOT contain viable osteoprogenitor cells, as these are destroyed during processing. Autogenous cancellous bone graft and Bone Marrow Aspirate Concentrate (BMAC) contain viable osteoprogenitor cells (osteogenesis). Platelet-rich plasma (PRP) primarily provides a high concentration of growth factors (osteoinduction) but does not provide a scaffold or viable cells. Fresh frozen allograft is primarily osteoconductive but lacks significant osteoinductive properties and viable cells.
Question 4750
Topic: Surgical Anatomy & Approaches
A 28-year-old female sustains a crush injury to her dominant right hand. She develops a complete radial nerve palsy at the forearm level. After 6 months of observation and physical therapy, there is no evidence of motor recovery, and electrodiagnostic studies confirm a complete nerve transection. What is the MOST appropriate next surgical step to restore hand function?
Correct Answer & Explanation
. Nerve grafting of the radial nerve.
Explanation
The patient has a complete radial nerve palsy from a crush injury, with no recovery after 6 months and electrodiagnostic evidence of transection. For a complete nerve transection, surgical intervention is necessary. Given 6 months have passed, primary repair is likely not feasible due to nerve gap and retraction. Tendon transfers are typically considered if nerve repair/grafting is not possible or has failed, and sufficient time has passed for reinnervation to occur or fail (usually 12-18 months post-injury).For a complete nerve transection with a gap, nerve grafting is the appropriate reconstructive technique. This involves harvesting a nerve graft (e.g., sural nerve) and coapting the ends to bridge the gap in the radial nerve. The goal is to provide a conduit for regenerating axons to cross the defect.Rationale for options:A. Nerve grafting of the radial nerve is the most appropriate surgical intervention for a complete radial nerve transection with a nerve gap, especially after 6 months where primary repair is unlikely due to retraction. This is the correct answer.B. Primary repair of the radial nerve would be ideal if performed acutely after injury with minimal gap. After 6 months, significant retraction makes primary repair without tension highly improbable.C. Tendon transfers are typically considered if nerve reconstruction (repair or graft) is not feasible, has failed, or if the time for reinnervation (usually 12-18 months) has passed without functional recovery. It is a salvage procedure, not the primary choice for an acute transection with a potentially reconstructible nerve.D. Dynamic splinting is supportive care; continued observation for a complete transection after 6 months is inappropriate without surgical intervention.E. Exploration and neurolysis are for nerve compression or scarring, not for complete transection.
Question 4751
Topic: 1. General Principles & Basic Science
A 7-year-old male with a history of recurrent osteomyelitis in his left tibia presents with increasing pain, swelling, and erythema localized to the anterior mid-tibia. Radiographs show a sclerotic bone lesion with a central lucency and periosteal reaction, consistent with Brodie's abscess. Despite broad-spectrum intravenous antibiotics administered for 4 weeks, his symptoms have not resolved, and inflammatory markers remain elevated. What is the MOST appropriate next step in management?
Correct Answer & Explanation
. Surgical debridement and curettage of the lesion with antibiotic bead placement.
Explanation
The patient has chronic osteomyelitis presenting as Brodie's abscess (localized subacute/chronic osteomyelitis) with persistent symptoms and elevated inflammatory markers despite prolonged intravenous antibiotics. Brodie's abscess is typically a walled-off intraosseous abscess. While antibiotics are part of the management, for persistent, symptomatic Brodie's abscess that fails medical management, surgical intervention is usually required.Surgical debridement, curettage of the abscess cavity, and removal of necrotic bone (sequestrum, if present) are the mainstays of treatment. Following debridement, the cavity can be packed with antibiotic-impregnated bone cement beads (e.g., PMMA beads with vancomycin/gentamicin) to provide high local concentrations of antibiotics. This is often followed by systemic culture-specific antibiotics.Rationale for options:A. Continuing intravenous antibiotics alone is unlikely to resolve the abscess, which is a walled-off lesion requiring surgical drainage and debridement.B. Switching to oral antibiotics is inappropriate given the failure of IV antibiotics and persistent inflammation.C. Surgical debridement and curettage of the lesion with antibiotic bead placement is the definitive treatment for a Brodie's abscess that has failed conservative management. This is the correct answer.D. While chronic osteomyelitis can sometimes mimic tumors (and vice versa), the imaging findings described (sclerotic bone lesion with central lucency and periosteal reaction) are classic for Brodie's abscess. A CT may provide more detail but the immediate concern is infection management. Malignancy should always be considered in persistent bone lesions, but given the history of recurrent osteomyelitis and classic radiographic appearance, addressing the infection is paramount.E. Amputation is a last resort for uncontrolled, limb-threatening infection or severe bone destruction, not for a localized Brodie's abscess.
Question 4752
Topic: Surgical Anatomy & Approaches
During the ilioinguinal approach for an acetabular fracture, significant hemorrhage is encountered upon dissecting over the superior pubic ramus. This bleeding is most likely originating from an anastomotic vessel connecting the obturator system and which of the following vessels?
Correct Answer & Explanation
. External iliac or deep inferior epigastric artery
Explanation
The vessel in question is the 'corona mortis' (crown of death), which is an anastomosis between the obturator artery/vein (from the internal iliac system) and the external iliac or deep inferior epigastric artery/vein. It crosses the superior pubic ramus and is highly vulnerable to iatrogenic injury during anterior pelvic approaches (like the ilioinguinal or Stoppa approaches), potentially leading to massive, life-threatening hemorrhage.
Question 4753
Topic: 1. General Principles & Basic Science
Which zone of articular cartilage contains the highest concentration of proteoglycans and the lowest concentration of water?
Correct Answer & Explanation
. Deep (radial) zone
Explanation
Articular cartilage is divided into distinct zones. The deep (radial) zone has the highest concentration of proteoglycans and the lowest concentration of water. The collagen fibers in this zone are oriented perpendicular to the articular surface to resist compressive forces. Conversely, the superficial zone has the highest water content and lowest proteoglycan content, with collagen fibers running parallel to the surface to resist shear stress.
Question 4754
Topic: 1. General Principles & Basic Science
Following a Zone II flexor tendon repair of the index finger in a 30-year-old construction worker, the surgeon opts for an early active motion protocol. Which of the following core suture techniques provides the highest initial tensile strength and resistance to gap formation?
Correct Answer & Explanation
. 6-strand Lim/Tsai
Explanation
The initial tensile strength of a flexor tendon repair is directly proportional to the number of core suture strands crossing the repair site. Therefore, a 6-strand repair (like the Lim/Tsai or modified combinations) provides greater initial strength and resistance to gap formation than 2-strand or 4-strand configurations, allowing for safer implementation of early active mobilization protocols. An epitendinous suture adds additional strength but is insufficient alone.
Question 4755
Topic: Biology, Genetics & Bone Healing
A 55-year-old patient with long-standing, poorly controlled type 2 diabetes presents with an acutely swollen, red, and warm left foot. Radiographs demonstrate early fragmentation and periarticular debris at the tarsometatarsal joints. Which of the following pro-inflammatory cytokines/pathways is considered the primary driver of osteoclastogenesis and bone resorption in the acute phase of Charcot neuroarthropathy?
Correct Answer & Explanation
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
Explanation
The acute phase of Charcot neuroarthropathy is characterized by an exaggerated inflammatory response. The RANKL/OPG pathway is central to this process. Increased expression of pro-inflammatory cytokines (such as TNF-a and IL-1) stimulates the overexpression of RANKL. RANKL binds to RANK on osteoclast precursors, driving massive osteoclastogenesis and the rapid bone resorption/fragmentation pathognomonic of acute Charcot.
Question 4756
Topic: 1. General Principles & Basic Science
Which of the following classes of nerve injury, according to the Sunderland classification, represents a complete disruption of axons and endoneurium, while the perineurium and epineurium remain intact?
Correct Answer & Explanation
. Fourth-degree
Explanation
In the Sunderland classification of peripheral nerve injuries: First-degree is neuropraxia (myelin injury, intact axon). Second-degree is axonotmesis (axon disrupted, endoneurium intact). Third-degree involves disruption of the axon and endoneurium, but the perineurium is intact. Fourth-degree involves disruption of the axon, endoneurium, and perineurium (only epineurium intact). Fifth-degree is a complete nerve transection (neurotmesis).
Question 4757
Topic: Biology, Genetics & Bone Healing
Denosumab is increasingly utilized in the treatment of unresectable or recurrent Giant Cell Tumor (GCT) of bone. What is its exact mechanism of action?
Correct Answer & Explanation
. It binds to RANKL, preventing the activation of the RANK receptor
Explanation
Denosumab is a fully human monoclonal antibody that binds specifically to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding to RANKL, it prevents RANKL from interacting with the RANK receptor on the surface of osteoclast precursors and mature osteoclasts (and the giant cells in GCT), thereby inhibiting osteoclastogenesis and bone resorption.
Question 4758
Topic: Biology, Genetics & Bone Healing
Demineralized bone matrix (DBM) is widely used as a bone graft substitute in spinal fusions. Based on its biological composition, which of the following properties does DBM possess?
Correct Answer & Explanation
. Osteoinduction and osteoconduction
Explanation
DBM possesses both osteoinductive and osteoconductive properties. It is osteoinductive because the acid-demineralization process exposes growth factors, primarily Bone Morphogenetic Proteins (BMPs). It is osteoconductive because the remaining Type I collagen provides a structural scaffold for new bone growth. It is NOT osteogenic because it lacks living cells (osteoblasts/osteoprogenitor cells).
Question 4759
Topic: Biology, Genetics & Bone Healing
A 65-year-old female presents with severe thoracic back pain, fatigue, and anemia. Workup reveals multiple lytic bone lesions without sclerotic rims. Which cytokine is primarily responsible for the marked osteoclast activation and resulting osteolytic lesions in this disease process?
Correct Answer & Explanation
. Interleukin-6 (IL-6)
Explanation
The patient has Multiple Myeloma. The myeloma cells secrete high levels of Interleukin-6 (IL-6), which acts as a potent stimulator of osteoclastogenesis via the RANK/RANKL pathway, leading to massive bone resorption (lytic lesions). Additionally, osteoblast function is inhibited.
Question 4760
Topic: Biology, Genetics & Bone Healing
In the pathogenesis of aseptic loosening following total joint arthroplasty, submicron particulate polyethylene debris is generated and subsequently phagocytosed by local macrophages. Which of the following is the primary downstream effector cell directly responsible for the resulting periprosthetic bone resorption (osteolysis)?
Correct Answer & Explanation
. Osteoclast
Explanation
The biological response to wear debris is macrophage-mediated. Macrophages phagocytose the polyethylene particles and release pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6). These cytokines upregulate RANKL expression, which stimulates the final effector cell—the osteoclast—to resorb periprosthetic bone, leading to aseptic loosening.
Test Yourself
Switch to an interactive, timed exam simulation to truly master this topic.