Full Question & Answer Text (for Search Engines)
Question 1:
A 4-year-old obese girl presents with bilateral genu varum. Radiographs reveal a distinct step-off and depression at the medial proximal tibial physis. She is diagnosed with Langenskiöld stage IV infantile Blount's disease. What is the most appropriate management?
Options:
- Observation and reassurance
- Treatment with Knee-Ankle-Foot Orthoses (KAFOs)
- Proximal tibial osteotomy with fibular osteotomy
- Hemiepiphysiodesis of the lateral proximal tibia
- Asymmetrical physeal distraction using an external fixator
Correct Answer: Proximal tibial osteotomy with fibular osteotomy
Explanation:
Infantile Blount's disease presenting as Langenskiöld stage III or greater in a child older than 3 years is an absolute indication for surgery. Bracing is generally only effective for stages I and II in children under the age of 3. Proximal tibial osteotomy combined with a fibular procedure is required to correct the complex multiplanar deformity (varus, internal rotation, and procurvatum).
Question 2:
A 25-year-old male sustains a high-energy Pauwels type III femoral neck fracture. Based on biomechanical studies of vertical femoral neck fractures, which of the following internal fixation constructs demonstrates the highest ultimate failure load against shear forces?
Options:
- Three parallel cancellous screws placed in an inverted triangle
- A sliding hip screw (SHS) alone
- A sliding hip screw (SHS) augmented with an anti-rotation cancellous screw
- A dynamic condylar screw
- A proximal femoral locking plate
Correct Answer: A sliding hip screw (SHS) augmented with an anti-rotation cancellous screw
Explanation:
Pauwels type III femoral neck fractures (fracture angle >50 degrees) experience very high shear forces. Biomechanical studies (such as Aminian et al.) have consistently shown that a fixed-angle sliding hip screw combined with a derotation screw provides superior biomechanical stability and the highest ultimate failure load compared to multiple cancellous screws or a proximal femoral locking plate in vertical fracture patterns.
Question 3:
A 14-year-old boy presents with progressive thigh pain. Radiographs demonstrate a permeative diaphyseal lesion in the femur with a multilaminated 'onion skin' periosteal reaction. A biopsy confirms Ewing sarcoma. Which of the following chromosomal translocations is most characteristic of this tumor?
Options:
- t(11;22)(q24;q12)
- t(9;22)(q34;q11)
- t(12;16)(q13;p11)
- t(X;18)(p11;q11)
- t(2;13)(q35;q14)
Correct Answer: t(11;22)(q24;q12)
Explanation:
Ewing sarcoma is classically associated with the t(11;22)(q24;q12) translocation, which leads to the fusion of the EWSR1 gene on chromosome 22 with the FLI1 gene on chromosome 11. t(9;22) is seen in CML; t(12;16) in myxoid liposarcoma; t(X;18) in synovial sarcoma; and t(2;13) in alveolar rhabdomyosarcoma.
Question 4:
In normal articular cartilage, which zone is characterized by having the highest concentration of proteoglycans, the lowest water content, and chondrocytes that are arranged in vertical columns?
Options:
- Superficial (tangential) zone
- Middle (transitional) zone
- Deep (radial) zone
- Calcified cartilage zone
- Tidemark
Correct Answer: Deep (radial) zone
Explanation:
The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils oriented perpendicular to the joint surface. It has the highest concentration of proteoglycans, the lowest concentration of water, and its chondrocytes are classically arranged in vertical columns parallel to the collagen fibers.
Question 5:
During a primary total knee arthroplasty using measured resection principles, the surgeon notes that the knee is well-balanced in extension but excessively tight in flexion. Which of the following is the most appropriate intraoperative adjustment?
Options:
- Increase the distal femoral resection
- Decrease the distal femoral resection
- Decrease the size of the femoral component using an anterior referencing system
- Upsize the femoral component
- Resect additional bone from the proximal tibia
Correct Answer: Decrease the size of the femoral component using an anterior referencing system
Explanation:
A knee that is tight in flexion but balanced in extension has an isolated flexion gap mismatch (flexion gap is too tight). To increase the flexion gap without altering the extension gap, the surgeon can decrease the size of the femoral component. When using an anterior referencing system, downsizing the femoral component results in more posterior condylar bone resection, effectively opening the flexion gap.
Question 6:
A 65-year-old male presents with deteriorating handwriting, generalized clumsiness, and frequent tripping. Neurological examination reveals an inverted brachioradialis reflex. This clinical finding is most indicative of spinal cord compression at which of the following neurologic levels?
Options:
- C3-C4
- C4-C5
- C5-C6
- C6-C7
- C7-T1
Correct Answer: C5-C6
Explanation:
An inverted brachioradialis reflex is characterized by spontaneous flexion of the digits when the brachioradialis tendon is struck. It indicates a lower motor neuron lesion at C5-C6 (abolishing the normal brachioradialis reflex) combined with an upper motor neuron lesion affecting the reflex arc below this level (causing hyperreflexia of the C8-innervated finger flexors). It strongly correlates with cervical myelopathy at the C5-C6 level.
Question 7:
Which of the following best represents the initial ultimate tensile strength of a 10-mm central third bone-patellar tendon-bone (BPTB) autograft compared to the native anterior cruciate ligament (ACL)?
Options:
- 50% of the native ACL
- 100% of the native ACL
- 160% of the native ACL
- 250% of the native ACL
- 300% of the native ACL
Correct Answer: 160% of the native ACL
Explanation:
Biomechanical studies by Noyes et al. demonstrated that a 10-mm bone-patellar tendon-bone (BPTB) graft has an ultimate tensile strength of approximately 2977 N, which is roughly 138% to 160% of the strength of the native ACL (which is approximately 2160 N). A quadrupled hamstring graft is even stronger, measuring around 200-250% of the native ACL strength.
Question 8:
The vascular supply to the proximal pole of the scaphoid is predominantly derived from retrograde flow via which of the following vessels?
Options:
- Superficial palmar branch of the radial artery
- Volar carpal branch of the radial artery
- Dorsal carpal branch of the radial artery
- Anterior interosseous artery
- Ulnar artery via the deep palmar arch
Correct Answer: Dorsal carpal branch of the radial artery
Explanation:
The major blood supply to the scaphoid (70-80%, including the entire proximal pole) comes from branches of the radial artery, specifically the dorsal carpal branch. These vessels enter the dorsal ridge of the scaphoid and flow in a retrograde direction (distal to proximal), which is why proximal pole fractures have a high risk of avascular necrosis and nonunion.
Question 9:
A 55-year-old male with poorly controlled diabetes mellitus presents with a massively swollen, erythematous, and warm foot. Radiographs demonstrate marked osteopenia, periarticular fragmentation of the tarsometatarsal joints, and early joint subluxation. According to the Eichenholtz classification, what stage does this represent and what is the primary management?
Options:
- Stage 0; immediate open reduction and internal fixation
- Stage 1; total contact casting and non-weight bearing
- Stage 2; custom-molded Charcot Restraint Orthotic Walker (CROW) boot
- Stage 3; corrective midfoot osteotomy
- Stage 4; below knee amputation
Correct Answer: Stage 1; total contact casting and non-weight bearing
Explanation:
The clinical and radiographic presentation is classic for Eichenholtz Stage 1 (Developmental/Fragmentation stage) Charcot arthropathy, characterized by acute inflammation, osteopenia, fragmentation, and joint subluxation/dislocation. The gold standard treatment in this acute stage is offloading and immobilization using a total contact cast (TCC) to prevent further deformity until the active inflammatory process resolves.
Question 10:
During the ilioinguinal approach for an anterior column acetabular fracture, the surgeon encounters massive hemorrhage from a vascular anastomosis crossing the superior pubic ramus. This vessel, commonly known as the 'corona mortis', connects which two vascular systems?
Options:
- External iliac and internal iliac systems
- External iliac vein and internal pudendal vein
- Femoral artery and obturator artery
- External iliac and obturator systems
- Inferior epigastric and superficial circumflex iliac systems
Correct Answer: External iliac and obturator systems
Explanation:
The corona mortis ('crown of death') is an anatomical variant where there is an anastomotic connection between the external iliac system (specifically the inferior epigastric vessels) and the obturator system (internal iliac system) crossing the superior pubic ramus. Injury to it during pelvic/acetabular surgery can cause severe, difficult-to-control bleeding.
Question 11:
In a patient presenting with a unilateral slipped capital femoral epiphysis (SCFE), which of the following is considered the strongest indication for prophylactic in situ pinning of the asymptomatic contralateral hip?
Options:
- Patient age greater than 14 years in males
- Obesity (BMI > 95th percentile)
- Presence of an underlying endocrine disorder
- Severe (Grade III) slip on the affected side
- African American ethnicity
Correct Answer: Presence of an underlying endocrine disorder
Explanation:
The risk of developing a contralateral SCFE is significantly elevated in patients with an underlying endocrine or metabolic disorder (e.g., hypothyroidism, renal osteodystrophy, growth hormone deficiency). Bilateral involvement can approach 100% in these populations. Therefore, the presence of an endocrine disorder is a universally accepted indication for prophylactic prophylactic pinning of the unaffected hip.
Question 12:
Which of the following bearing surface combinations in Total Hip Arthroplasty (THA) is associated with the lowest linear wear rate, but carries a unique risk of catastrophic fracture and 'squeaking'?
Options:
- Cobalt-chrome on highly cross-linked polyethylene
- Oxidized zirconium on highly cross-linked polyethylene
- Ceramic on ceramic
- Ceramic on conventional polyethylene
- Cobalt-chrome on cobalt-chrome
Correct Answer: Ceramic on ceramic
Explanation:
Ceramic-on-ceramic (CoC) bearings have the lowest volumetric and linear wear rates among all bearing surfaces in THA. However, they carry specific complications not seen with metal-on-polyethylene, including the risk of catastrophic ceramic fracture and the phenomenon of 'squeaking' during range of motion.
Question 13:
Which of the following growth factors is highly osteoinductive, signals via cell-surface serine/threonine kinase receptors to activate the SMAD intracellular pathway, and is FDA-approved for use in open tibia fractures?
Options:
- Platelet-derived growth factor (PDGF)
- Vascular endothelial growth factor (VEGF)
- Fibroblast growth factor (FGF)
- Bone morphogenetic protein-2 (BMP-2)
- Transforming growth factor-beta (TGF-b)
Correct Answer: Bone morphogenetic protein-2 (BMP-2)
Explanation:
Bone morphogenetic proteins (specifically BMP-2 and BMP-7) are potent osteoinductive growth factors belonging to the TGF-beta superfamily. They bind to serine/threonine kinase receptors and signal intracellularly via the SMAD pathway. rhBMP-2 is FDA approved for use in open tibia fractures and anterior lumbar interbody fusions (ALIF).
Question 14:
A 45-year-old male presents with severe right leg pain radiating to the dorsum of the foot. Physical examination reveals intact knee and ankle reflexes, but marked weakness in extensor hallucis longus (EHL) function. Which nerve root is most likely compressed, and which reliable deep tendon reflex corresponds to it?
Options:
- S1 nerve root; Achilles reflex
- L5 nerve root; Achilles reflex
- L4 nerve root; Patellar reflex
- L5 nerve root; Medial hamstring reflex
- L5 nerve root; No consistent deep tendon reflex
Correct Answer: L5 nerve root; No consistent deep tendon reflex
Explanation:
Weakness in the extensor hallucis longus (EHL) and pain/sensory loss over the dorsum of the foot localize the lesion to the L5 nerve root. Unlike L4 (patellar reflex) and S1 (Achilles reflex), the L5 nerve root does not have a reliable, easily reproducible deep tendon reflex (though the tibialis posterior reflex is occasionally used, it is difficult to elicit and notoriously unreliable).
Question 15:
A 30-year-old female presents with a lytic, expansile lesion in the distal femur extending to the subchondral bone. A core needle biopsy confirms a Giant Cell Tumor of bone. If medical therapy is considered, it would typically involve Denosumab. What is the precise mechanism of action of this drug?
Options:
- Monoclonal antibody that binds to and inhibits RANK ligand (RANKL)
- Nitrogenous bisphosphonate that inhibits farnesyl pyrophosphate synthase
- Tyrosine kinase inhibitor targeting VEGF receptors
- Monoclonal antibody against CD20 on B-lymphocytes
- Recombinant antagonist of the parathyroid hormone (PTH) receptor
Correct Answer: Monoclonal antibody that binds to and inhibits RANK ligand (RANKL)
Explanation:
Denosumab is a fully human monoclonal antibody that binds directly to RANK Ligand (RANKL), preventing it from activating RANK on the surface of osteoclasts and their precursors. In Giant Cell Tumor of bone, the neoplastic stromal cells express high levels of RANKL, which recruits the giant cell osteoclasts that cause bone destruction. Denosumab effectively halts this osteoclastic bone resorption.
Question 16:
Following an uncomplicated Zone II flexor digitorum profundus (FDP) tendon repair, an early active motion rehabilitation protocol is initiated. What is the primary clinical advantage of early active motion over early passive motion protocols?
Options:
- Decreased risk of acute tendon rupture
- Increased ultimate tensile strength of the repair at 3 weeks
- Decreased formation of restrictive peritendinous adhesions
- Accelerated healing exclusively through secondary intention
- Elimination of the need for a protective orthosis
Correct Answer: Decreased formation of restrictive peritendinous adhesions
Explanation:
Early active motion protocols after flexor tendon repair generate differential glide between the FDP and FDS tendons. The primary advantage of this differential excursion is the decreased formation of restrictive peritendinous adhesions, resulting in improved final functional range of motion. It does not decrease the risk of acute rupture (which is actually higher if the repair isn't robust enough) and still requires a protective orthosis.
Question 17:
A 45-year-old female undergoes an MRI of the knee which reveals a complete radial tear at the posterior root of the medial meniscus, associated with 4 mm of meniscal extrusion. Biomechanically, this root injury alters knee joint loading in a manner most equivalent to which of the following?
Options:
- A stable longitudinal tear of the posterior horn
- A total meniscectomy
- A reducible bucket-handle meniscal tear
- A parameniscal cyst
- Normal age-related meniscal degeneration
Correct Answer: A total meniscectomy
Explanation:
The meniscal roots anchor the meniscus to the tibial plateau, allowing it to convert axial compressive loads into circumferential 'hoop stresses'. A root tear completely disrupts these hoop stresses, leading to meniscal extrusion. Biomechanical studies have proven that a posterior root tear effectively renders the meniscus non-functional, altering contact areas and peak contact pressures to a degree equivalent to a total meniscectomy.
Question 18:
In the evaluation of a patient with suspected acute compartment syndrome of the lower extremity, which of the following manometric pressure criteria is considered the most reliable threshold for performing a four-compartment fasciotomy?
Options:
- Absolute compartment pressure > 20 mm Hg
- Absolute compartment pressure > 30 mm Hg
- Delta P (Diastolic blood pressure - compartment pressure) < 30 mm Hg
- Delta P (Mean arterial pressure - compartment pressure) < 40 mm Hg
- Delta P (Systolic blood pressure - compartment pressure) < 50 mm Hg
Correct Answer: Delta P (Diastolic blood pressure - compartment pressure) < 30 mm Hg
Explanation:
Current evidence indicates that the Delta P—calculated as the patient's diastolic blood pressure minus the intracompartmental pressure—is the most reliable indicator for compartment syndrome. A Delta P of less than 30 mm Hg is the widely accepted threshold for surgical intervention (fasciotomy). Relying on absolute pressures alone can lead to overtreatment, particularly in hypertensive patients.
Question 19:
A 3-month-old female is being treated with a Pavlik harness for Developmental Dysplasia of the Hip (DDH). At her 2-week follow-up, the parents note that she has stopped kicking her left leg, and examination reveals a lack of active knee extension on the left side. This complication is most commonly caused by which of the following positioning errors?
Options:
- Excessive hip abduction
- Inadequate hip abduction
- Excessive hip flexion
- Inadequate hip flexion
- Excessive knee flexion
Correct Answer: Excessive hip flexion
Explanation:
The infant is exhibiting signs of a femoral nerve palsy (lack of active knee extension/quadriceps function), which is a known complication of Pavlik harness treatment. It is caused by hyperflexion of the hips, which causes compression of the femoral nerve against the inguinal ligament. Excessive hip abduction, by contrast, is associated with avascular necrosis (AVN) of the femoral head.
Question 20:
In the context of orthopedic biomaterials, galvanic corrosion is most likely to occur under which of the following specific conditions?
Options:
- Fretting wear occurring between two identical metals at a modular junction
- Exposure of a single metallic implant to highly acidic synovial fluid
- Physical contact between two dissimilar metals in an electrolytic solution
- Fatigue failure of a highly polished ceramic articulating surface
- Polyethylene wear debris activating a local macrophage response
Correct Answer: Physical contact between two dissimilar metals in an electrolytic solution
Explanation:
Galvanic corrosion is an electrochemical process that occurs when two dissimilar metals (having different anodic indices/electrochemical potentials) are placed in direct physical contact within a conductive electrolyte solution (such as human body fluid). The less noble metal acts as an anode and corrodes, while the more noble metal acts as a cathode.
