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1. General Principles & Basic Science MCQs

Practice Set 390 of 789

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 7781

Topic: Biomechanics & Biomaterials

A 45-year-old female presents with acute onset of medial joint line pain after a deep squat. MRI reveals a medial meniscus posterior root tear. Which of the following best describes the biomechanical consequence if this tear is left untreated?

. Decreased contact pressure in the medial compartment
. Biomechanics equivalent to a total meniscectomy
. Increased anterior tibial translation during the Lachman test
. Decreased peak contact pressure in the lateral compartment
. Shift of peak contact stresses to the patellofemoral joint

Correct Answer & Explanation

. Biomechanics equivalent to a total meniscectomy

Explanation

A meniscal root tear completely disrupts the hoop stresses of the meniscus, rendering it functionally incompetent. Biomechanical studies have demonstrated that a posterior root tear leads to peak contact pressures and joint kinematics that are essentially equivalent to a total meniscectomy. This drastically accelerates the progression of medial compartment osteoarthritis if left untreated.

Question 7782

Topic: 1. General Principles & Basic Science

A 55-year-old female presents with acute medial knee pain and a feeling of 'giving way' after descending stairs. Physical examination reveals focal joint line tenderness. MRI shows an extrusion of the medial meniscus of 4 mm and a radial tear strictly adjacent to the posterior root attachment. What is the primary biomechanical consequence of this injury if left untreated?

. Increased contact area in the medial compartment
. Loss of hoop stresses leading to altered peak contact pressures equivalent to a total meniscectomy
. Increased anterior tibial translation isolated to 30 degrees of flexion
. Medial compartment distraction with secondary lateral compartment overload
. Decreased peak contact pressures in the medial compartment

Correct Answer & Explanation

. Loss of hoop stresses leading to altered peak contact pressures equivalent to a total meniscectomy

Explanation

A complete posterior root tear of the medial meniscus effectively detaches the meniscus from its anchor, resulting in a complete loss of circumferential hoop stresses. Biomechanically, this failure leads to decreased contact area and exponentially increased peak contact pressures in the medial compartment, which are virtually equivalent to the knee having undergone a total meniscectomy. This often accelerates joint space narrowing and osteoarthritis.

Question 7783

Topic: Biomechanics & Biomaterials

A 52-year-old female presents with sudden onset medial-sided knee pain and a feeling of a 'pop' while ascending stairs. Physical examination reveals a mild effusion and joint line tenderness. MRI demonstrates an extruded medial meniscus and a high signal defect at the posterior horn attachment of the medial meniscus on the coronal sequences. What is the most likely biomechanical consequence if this injury is treated nonoperatively?

. Decreased contact pressures in the medial compartment
. Anterior translation of the tibia during active quadriceps contraction
. Alteration of knee kinematics equivalent to a total meniscectomy
. Increased varus laxity in full extension
. Healing of the meniscus with progressive scar tissue formation

Correct Answer & Explanation

. Alteration of knee kinematics equivalent to a total meniscectomy

Explanation

The clinical scenario and MRI findings are consistent with a medial meniscus posterior root tear. The posterior root attachments are critical for converting axial loads into hoop stresses within the meniscus. A complete root tear leads to loss of these hoop stresses, resulting in meniscal extrusion and altered peak contact pressures that are biomechanically equivalent to a total meniscectomy. This significantly accelerates the progression of medial compartment osteoarthritis. Nonoperative treatment typically results in rapid joint degeneration rather than healing.

Question 7784

Topic: Biology, Genetics & Bone Healing

A 3-year-old boy presents with a femur fracture following minimal trauma. This is his fourth long bone fracture. Clinical examination reveals blue sclerae and dentinogenesis imperfecta. Genetic testing confirms a mutation in the COL1A1 gene. He is started on intravenous pamidronate. What is the primary mechanism of action of this pharmacological therapy?

. Stimulation of osteoblast proliferation and differentiation
. Inhibition of osteoclast-mediated bone resorption
. Supplementation of endogenous type I collagen synthesis
. Activation of the calcium-sensing receptor in the parathyroid gland
. Inhibition of sclerostin to promote uninhibited bone formation

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption

Explanation

The patient has Osteogenesis Imperfecta (OI), typically caused by an autosomal dominant mutation in type I collagen genes (COL1A1 or COL1A2). Intravenous bisphosphonates, such as pamidronate, are the standard of care for moderate to severe OI to reduce fracture frequency and improve bone density. Bisphosphonates function primarily by attaching to hydroxyapatite binding sites on bony surfaces, leading to the inhibition of osteoclast-mediated bone resorption. They do not repair the underlying genetic defect in collagen synthesis.

Question 7785

Topic: Biology, Genetics & Bone Healing

A 3-year-old girl with recurrent long bone fractures, blue sclerae, and dentinogenesis imperfecta is diagnosed with osteogenesis imperfecta. She is started on a medical therapy that aims to increase bone mineral density and reduce the fracture rate. What is the primary mechanism of action of this medication class?

. Inhibition of osteoclast-mediated bone resorption
. Stimulation of osteoblast proliferation
. Enhanced calcium absorption in the gastrointestinal tract
. Cross-linking of type I collagen
. Inhibition of parathyroid hormone secretion

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption

Explanation

The patient has osteogenesis imperfecta and is being treated with bisphosphonates (e.g., pamidronate or zoledronic acid). Bisphosphonates inhibit osteoclast-mediated bone resorption by inducing osteoclast apoptosis, which leads to increased bone mineral density, a reduced rate of fractures, and improvement in vertebral body shape in children with OI.

Question 7786

Topic: Biology, Genetics & Bone Healing

A 3-year-old child with a known diagnosis of Osteogenesis Imperfecta Type III is admitted to the hospital for elective placement of telescopic intramedullary rods in bilateral femurs. To decrease fracture burden and improve bone mineral density, the patient receives cyclical intravenous pamidronate therapy. What is the primary cellular mechanism of action of this pharmacological treatment?

. Stimulation of osteoblast-mediated bone formation
. Inhibition of osteoclast-mediated bone resorption
. Direct cross-linking of type 1 collagen fibrils in the extracellular matrix
. Inhibition of parathyroid hormone (PTH) secretion
. Enhancement of intestinal calcium and phosphate absorption

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption

Explanation

Pamidronate is a nitrogen-containing bisphosphonate. The primary mechanism of action of all bisphosphonates is the inhibition of osteoclast-mediated bone resorption. Specifically, nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase in the mevalonate pathway, leading to osteoclast apoptosis and decreased bone turnover. They do not primarily stimulate osteoblasts, alter collagen cross-linking (the primary structural defect in OI), or significantly affect PTH secretion or direct intestinal absorption.

Question 7787

Topic: 1. General Principles & Basic Science

A 6-week-old female infant is being treated with a Pavlik harness for an easily reducible dislocated left hip. At her 2-week follow-up appointment, the parents report that she is no longer kicking her left leg as much as her right. On physical examination, she demonstrates decreased active knee extension on the left, though she does not appear to be in pain. What is the most likely cause of this clinical finding?

. Avascular necrosis of the femoral head
. Progression to an irreducible hip dislocation
. Septic arthritis of the hip
. Femoral nerve palsy due to hyperflexion
. Sciatic nerve palsy due to hyperabduction

Correct Answer & Explanation

. Femoral nerve palsy due to hyperflexion

Explanation

Femoral nerve palsy is a known complication of Pavlik harness treatment and is typically caused by excessive hip flexion. It presents as an inability to actively extend the knee. The appropriate management is to temporarily discontinue the harness or adjust the anterior straps to decrease hip flexion until the palsy completely resolves.

Question 7788

Topic: Biology, Genetics & Bone Healing

A 5-year-old boy with a history of multiple low-energy fractures, blue sclerae, and dentinogenesis imperfecta is being evaluated for surgical intervention of a severely bowed femur. He receives intravenous bisphosphonate therapy every 3 months. What is the primary mechanism of action of bisphosphonates in this condition?

. Stimulation of osteoblast proliferation
. Inhibition of osteoclast-mediated bone resorption
. Direct enhancement of type I collagen synthesis
. Increased intestinal calcium absorption
. Promotion of chondrocyte hypertrophy

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption

Explanation

Osteogenesis imperfecta is most commonly caused by a genetic defect in type I collagen synthesis. Bisphosphonates are a mainstay of medical management to increase bone mineral density and reduce fracture rates. They function primarily by binding to hydroxyapatite crystals in bone and inhibiting osteoclast-mediated bone resorption, which leads to a relative increase in bone mass, despite the collagen matrix remaining abnormal.

Question 7789

Topic: Biology, Genetics & Bone Healing

A 2-year-old child with a known diagnosis of neurofibromatosis type 1 (NF1) presents with anterolateral bowing of the tibia that has progressed to a complete fracture. Radiographs confirm congenital pseudarthrosis of the tibia (CPT). Which of the following biological adjuncts is most strongly supported in the surgical management of this condition to improve bone union rates?

. Systemic bisphosphonates
. Recombinant human bone morphogenetic protein-2 (rhBMP-2)
. Teriparatide (PTH 1-34)
. Non-steroidal anti-inflammatory drugs (NSAIDs)
. Vitamin C supplementation

Correct Answer & Explanation

. Recombinant human bone morphogenetic protein-2 (rhBMP-2)

Explanation

Congenital pseudarthrosis of the tibia (CPT) is extremely challenging to treat, with high rates of nonunion and refracture. Surgical management typically involves resection of the pseudarthrosis, rigid stabilization (often combining intramedullary fixation with an Ilizarov external fixator), and extensive bone grafting. The use of recombinant human bone morphogenetic protein-2 (rhBMP-2) as an adjunct has been shown in multiple studies to significantly increase union rates and decrease the time to union in children with CPT.

Question 7790

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with right hip pain, an acute limp, and refusal to bear weight for the past 24 hours. His oral temperature is 38.6°C (101.5°F). Laboratory tests show a WBC count of 13,500/mm3, an ESR of 45 mm/hr, and a CRP of 2.5 mg/dL. He has no history of recent trauma. Based on the Kocher criteria, what is the approximate predicted probability that this child has a septic arthritis of the hip?

. 3%
. 40%
. 75%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria differentiate septic arthritis from transient synovitis of the hip in children. The four classic criteria are: inability to bear weight, temperature > 38.5°C, ESR > 40 mm/hr, and WBC > 12,000/mm3. This patient meets all four criteria. The predicted probability of septic arthritis based on the number of positive criteria is approximately: 1 criterion = 3%, 2 criteria = 40%, 3 criteria = 93%, and 4 criteria = 99%.

Question 7791

Topic: Physiology & Rehabilitation
A 3-year-old boy, previously treated with serial casting and Achilles tenotomy for idiopathic clubfoot, presents with a relapsed deformity. On examination, he exhibits dynamic supination of the foot during the swing phase of gait. Passive dorsiflexion is 15 degrees past neutral. What is the most appropriate next step in management?
. Repeated serial casting
. Tibialis anterior tendon transfer to the lateral cuneiform
. Split tibialis posterior tendon transfer
. Cuboid decancellation
. Comprehensive posteromedial release

Correct Answer & Explanation

. Tibialis anterior tendon transfer to the lateral cuneiform

Explanation

Relapse of a clubfoot presenting as dynamic supination during the swing phase in a toddler with preserved passive dorsiflexion is best treated with a tibialis anterior tendon transfer (ATTT) to the lateral cuneiform. This addresses the muscular imbalance. Repeated casting is indicated if there is fixed stiffness or loss of dorsiflexion before tendon transfer.

Question 7792

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with a diaphyseal femur fracture after a minor fall. He has a history of multiple fractures, blue sclerae, and dentinogenesis imperfecta. This condition is most commonly caused by a mutation in genes coding for which of the following proteins?

. Fibroblast growth factor receptor 3 (FGFR3)
. Cartilage oligomeric matrix protein (COMP)
. Type I collagen
. Type II collagen
. Runx2

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta is most commonly an autosomal dominant disorder caused by mutations in the COL1A1 or COL1A2 genes, which encode Type I collagen. This defect leads to brittle bones, blue sclerae, and associated dental anomalies.

Question 7793

Topic: 1. General Principles & Basic Science

A 7-year-old girl presents with a painless "snapping" sensation in her lateral knee when extending her leg. MRI confirms a discoid lateral meniscus. If the meniscus completely lacks its normal posterior meniscotibial attachments, what specific variant is this?

. Complete variant
. Incomplete variant
. Wrisberg variant
. Ring variant
. Bucket-handle variant

Correct Answer & Explanation

. Wrisberg variant

Explanation

The Wrisberg variant of a discoid meniscus lacks normal posterior capsular and meniscotibial attachments, relying entirely on the meniscofemoral ligament of Wrisberg. This hypermobility leads to the classic snapping knee presentation.

Question 7794

Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with right hip pain, a limp, and a refusal to bear weight. He has a temperature of 38.6°C (101.5°F), an erythrocyte sedimentation rate (ESR) of 45 mm/hr, and a white blood cell (WBC) count of 13,000/mm³. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?
. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria for differentiating septic arthritis from transient synovitis include non-weight-bearing, temperature >38.5°C, ESR >40 mm/hr, and WBC >12,000/mm³. The presence of all four predictors yields a 99% probability of septic arthritis.

Question 7795

Topic: Biology, Genetics & Bone Healing

A 6-year-old boy with blue sclerae, dentinogenesis imperfecta, and a history of multiple low-energy fractures is being treated with intravenous pamidronate. What is the primary cellular mechanism of action of this medication in managing his condition?

. Stimulation of osteoblast differentiation and bone formation
. Inhibition of osteoclast-mediated bone resorption
. Direct cross-linking of defective type 1 collagen fibers
. Increased intestinal calcium absorption via vitamin D pathways
. Stimulation of physeal chondrocyte proliferation

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption

Explanation

Pamidronate is a bisphosphonate used as the gold-standard medical therapy for osteogenesis imperfecta. It functions by inhibiting osteoclast-mediated bone resorption, thereby increasing bone mineral density and reducing fracture frequency.

Question 7796

Topic: Infection, Pharmacology & VTE

A 4-year-old girl presents with a 2-day history of right hip pain and a limp. Her temperature is 38.6 degrees Celsius (101.5 degrees Fahrenheit), ESR is 45 mm/hr, WBC is 13.5 x 10^9/L, and she is unable to bear weight. Based on the Kocher criteria, what is the approximate probability she has septic arthritis?

. 15%
. 40%
. 73%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria for septic arthritis of the hip include non-weight-bearing, ESR >40, fever >38.5C, and WBC >12,000. Having all 4 criteria predicts a 99% probability of septic arthritis.

Question 7797

Topic: Infection, Pharmacology & VTE

A 4-year-old girl presents with a 2-day history of right hip pain and refusal to bear weight. Which of the following sets of findings represents the classic Kocher criteria used to differentiate septic arthritis from transient synovitis?

. Fever > 38.5 C, inability to bear weight, ESR > 40 mm/hr, WBC > 12,000/mm3
. Fever > 38.0 C, limp, CRP > 10 mg/L, WBC > 10,000/mm3
. Fever > 39.0 C, inability to bear weight, ESR > 20 mm/hr, joint space widening on X-ray
. Fever > 38.5 C, hip held in flexion and external rotation, positive blood culture
. Fever > 38.5 C, history of trauma, CRP > 20 mg/L, ESR > 50 mm/hr

Correct Answer & Explanation

. Fever > 38.5 C, inability to bear weight, ESR > 40 mm/hr, WBC > 12,000/mm3

Explanation

The original Kocher criteria include fever > 38.5 C, non-weight-bearing status, ESR > 40 mm/hr, and serum WBC > 12,000/mm3. The presence of all four yields a 99% probability of septic arthritis.

Question 7798

Topic: Biomechanics & Biomaterials

A 55-year-old man receives a THA using a highly cross-linked polyethylene liner. What is the primary biochemical purpose of subjecting the polyethylene to a heating process (melting or annealing) immediately following gamma irradiation?

. To increase the ultimate tensile strength of the material
. To eliminate residual free radicals and reduce long-term oxidation
. To decrease the cross-link density for better elasticity
. To improve the elastic modulus of the bearing surface
. To increase the fatigue crack propagation resistance

Correct Answer & Explanation

. To eliminate residual free radicals and reduce long-term oxidation

Explanation

Heating highly cross-linked polyethylene after gamma irradiation eliminates residual free radicals trapped in the polymer chains. This critical step prevents long-term in vivo oxidation, which is a primary cause of polyethylene degradation and late wear.

Question 7799

Topic: Surgical Anatomy & Approaches

The direct anterior approach (DAA) to the hip is increasingly popular due to its internervous plane. This surgical approach exploits the interval between muscles supplied by which of the following nerve pairs?

. Femoral nerve and Sciatic nerve
. Superior gluteal nerve and Femoral nerve
. Superior gluteal nerve and Inferior gluteal nerve
. Femoral nerve and Obturator nerve
. Sciatic nerve and Obturator nerve

Correct Answer & Explanation

. Superior gluteal nerve and Femoral nerve

Explanation

The direct anterior approach to the hip uses the internervous plane between the tensor fasciae latae (supplied by the superior gluteal nerve) and the sartorius (supplied by the femoral nerve). Deep to this, the plane is between the rectus femoris (femoral nerve) and gluteus medius (superior gluteal nerve).

Question 7800

Topic: 1. General Principles & Basic Science

A 45-year-old man has medial compartment knee osteoarthritis and a 10-degree varus deformity. He is being evaluated for a medial opening wedge high tibial osteotomy (HTO). Which of the following is an absolute contraindication to this procedure?

. Age greater than 40 years
. Body mass index of 28 kg/m2
. Flexion contracture of 20 degrees
. Prior medial partial meniscectomy
. Kellgren-Lawrence grade 2 changes

Correct Answer & Explanation

. Flexion contracture of 20 degrees

Explanation

A flexion contracture of greater than 15 degrees is generally considered an absolute contraindication for a high tibial osteotomy. Other strict contraindications include inflammatory arthritis, lateral compartment arthritis, and severe symptomatic patellofemoral arthritis.

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