Orthopedics Hyperguide Review | Dr Hutaif General Ortho -...

Question 1

During biomechanical testing of a human anterior cruciate ligament (ACL) graft, the tissue is subjected to a constant deformation (length is held constant) over a period of time. The researchers note that the load required to maintain this constant deformation gradually decreases. Which viscoelastic property is being demonstrated?

Explanation

Stress relaxation is the property where less force (stress) is required over time to maintain a tissue at a constant length (strain). Creep is the opposite: continued deformation (increasing length/strain) over time when subjected to a constant load (stress). Hysteresis represents the energy lost (as heat) during the loading and unloading cycle of a viscoelastic material. Ligaments exhibit both creep and stress relaxation due to their viscoelastic nature.

Question 2

A 28-year-old male sustains a closed comminuted tibial shaft fracture. Two hours post-injury, he develops severe pain out of proportion to the injury and pain with passive stretch of his toes. Which of the following objective measurements is the most accepted threshold to indicate the need for an emergent fasciotomy?

Explanation

The most reliable objective criterion for diagnosing acute compartment syndrome is the delta pressure (Delta P), calculated as the diastolic blood pressure minus the intracompartmental pressure. A Delta P of less than 30 mm Hg is a widely accepted threshold indicating inadequate tissue perfusion, necessitating emergent fasciotomy. Absolute pressure alone (e.g., > 30 mm Hg) is less reliable as it does not account for the patient's systemic blood pressure.

Question 3

A 10-year-old girl presents with a unilateral slipped capital femoral epiphysis (SCFE). She is at the 15th percentile for weight and 10th percentile for height. Considering her atypical presentation for SCFE, she undergoes an endocrine workup. Which of the following underlying conditions is the strongest indication for prophylactic pinning of the contralateral asymptomatic hip?

Explanation

Patients with SCFE who present outside the typical age range (girls 11-13, boys 13-15) or who are not overweight should be evaluated for endocrine disorders. Hypothyroidism is the most common endocrine disorder associated with SCFE. Bilateral involvement is significantly higher in patients with endocrine disorders, and prophylactic pinning of the contralateral hip is highly recommended in this population to prevent a future slip.

Question 4

A 45-year-old unrestrained driver is involved in a high-speed motor vehicle collision. Radiographs demonstrate a traumatic spondylolisthesis of the axis (Hangman's fracture) with bilateral pars interarticularis fractures of C2. What is the classic mechanism of injury for this fracture pattern?

Explanation

A classic Hangman's fracture (traumatic spondylolisthesis of the axis) is typically caused by hyperextension and axial loading. This forces the pedicles/pars interarticularis against the superior articular facets of C3, resulting in bilateral fractures of the C2 pars. Historically, judicial hangings caused a similar fracture via hyperextension and distraction, but modern vehicular trauma causes it via extension and axial load.

Question 5

A 22-year-old professional soccer player undergoes an anatomic single-bundle anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone autograft. Based on the biology of graft incorporation, at what postoperative time frame is the graft mechanically at its weakest?

Explanation

An autograft ACL reconstruction goes through phases of incorporation: necrosis, revascularization, cellular repopulation, and remodeling (ligamentization). The graft undergoes significant biologic degradation during the early revascularization phase, causing it to be mechanically at its weakest roughly between 6 to 12 weeks postoperatively. This represents a critical vulnerability period where rehabilitation must balance protecting the graft with restoring range of motion.

Question 6

In total hip arthroplasty, the introduction of highly cross-linked polyethylene (HXLPE) has significantly reduced volumetric wear and secondary osteolysis. However, the manufacturing process of highly cross-linking the polyethylene results in an important mechanical trade-off. What is the primary negative mechanical consequence of this process?

Explanation

Highly cross-linking polyethylene significantly improves its resistance to adhesive and abrasive wear, dramatically lowering volumetric wear rates. However, the cross-linking process (and the subsequent remelting/annealing used to eliminate free radicals and prevent oxidation) fundamentally alters the polymer's mechanical properties, leading to decreased fatigue strength, reduced ductility (elongation to failure), and lower ultimate tensile strength. This makes HXLPE more susceptible to catastrophic failure/fracture, especially in thin liners or high-stress designs.

Question 7

A 14-year-old boy presents with progressive knee pain and swelling. Radiographs show a permeative, destructive diaphyseal lesion of the femur with a large soft tissue mass and an 'onion skin' periosteal reaction. Biopsy reveals small round blue cells. Which chromosomal translocation is the diagnostic hallmark of this tumor?

Explanation

The clinical and radiographic presentation is classic for Ewing sarcoma. Ewing sarcoma is characterized by the t(11;22)(q24;q12) chromosomal translocation in approximately 85-90% of cases, which results in the EWS-FLI1 fusion protein. Other options correspond to different tumors: t(9;22) is Philadelphia chromosome (CML/ALL); t(X;18) is synovial sarcoma; t(2;13) is alveolar rhabdomyosarcoma; t(12;16) is myxoid liposarcoma.

Question 8

A 25-year-old rugby player grabs an opponent's jersey and feels a sudden pop in his right ring finger. He presents unable to actively flex the distal interphalangeal (DIP) joint. MRI demonstrates a complete flexor digitorum profundus (FDP) avulsion. Which of the following Leddy-Packer classifications corresponds to the highest risk of tendon ischemia and requires the most urgent surgical intervention (within 7-10 days)?

Explanation

The patient has a 'Jersey finger'. The Leddy-Packer classification describes FDP avulsion injuries based on the level of tendon retraction. Type I is retraction into the palm. Because the vincula (blood supply) are completely ruptured, the tendon is ischemic. Type I requires urgent surgical repair (typically within 7-10 days) before the tendon undergoes severe contracture and necrosis. Type II retracts to the PIP joint (vincula intact, delayed repair possible). Type III is a large bony avulsion caught at the A4 pulley.

Question 9

A 24-year-old gymnast sustains an axial load injury to her plantarflexed foot. Weight-bearing radiographs demonstrate a 3 mm diastasis between the base of the first and second metatarsals. What is the anatomic origin and insertion of the primary ligamentous structure ruptured in this injury pattern?

Explanation

The scenario describes a Lisfranc injury. The Lisfranc ligament is the primary stabilizer of the tarsometatarsal complex. It is a thick interosseous ligament that originates on the lateral aspect of the medial cuneiform and inserts onto the medial aspect of the base of the second metatarsal. There is no direct ligamentous connection between the base of the first and second metatarsals, making the Lisfranc ligament crucial for structural integrity.

Question 10

A 35-year-old male is struck by a car, sustaining an anteroposterior compression (APC) pelvic ring injury. According to the Young-Burgess classification, which specific ligamentous disruption differentiates an APC Type II injury from a highly unstable APC Type III injury?

Explanation

In the Young-Burgess classification, APC injuries involve varying degrees of diastasis of the symphysis pubis. APC II involves disruption of the symphysis, sacrotuberous, sacrospinous, and anterior sacroiliac ligaments, but the posterior sacroiliac ligaments remain intact (opening book injury). An APC III injury is characterized by the additional complete disruption of the posterior sacroiliac ligaments, resulting in complete hemipelvic instability (both rotational and vertical).

Question 11

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is utilized in spine fusion surgery to enhance osteoinduction. Following the binding of BMP-2 to its transmembrane serine/threonine kinase receptors, which intracellular signaling pathway is primarily activated to induce osteoblastic differentiation?

Explanation

Bone Morphogenetic Proteins (BMPs) belong to the Transforming Growth Factor-beta (TGF-beta) superfamily. When BMP-2 binds to its cell surface serine/threonine kinase receptors, it induces the phosphorylation of receptor-regulated SMADs (specifically SMAD 1, 5, and 8). These form a complex with the co-SMAD (SMAD 4), which translocates to the nucleus to act as a transcription factor, driving the expression of osteogenic genes like Runx2.

Question 12

A 72-year-old woman with a chronic massive, irreparable rotator cuff tear presents with severe pain and active forward elevation to only 45 degrees (pseudoparalysis). Her axillary nerve is intact. She is scheduled for a reverse total shoulder arthroplasty (rTSA). What is the primary biomechanical advantage provided by this implant design to restore active elevation?

Explanation

The Grammont design principles of a reverse total shoulder arthroplasty (rTSA) rely on moving the center of rotation of the glenohumeral joint medially and inferiorly. Medializing the center of rotation recruits more of the deltoid fibers for elevation, while lowering the center of rotation tensions the deltoid, significantly increasing its moment arm. This allows the deltoid to effectively compensate for the deficient rotator cuff.

Question 13

A 4-month-old female infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During follow-up, the mother notes the child is no longer kicking her right leg. Examination reveals decreased quadriceps tone and an absent patellar reflex on the right. What positioning error in the Pavlik harness typically leads to this complication?

Explanation

The clinical picture describes a femoral nerve palsy, a known complication of Pavlik harness treatment. This is caused by excessive flexion of the hip, which can compress the femoral nerve against the inguinal ligament. Excessive abduction, on the other hand, is associated with a different severe complication: avascular necrosis (AVN) of the femoral head due to compression of the posterior circumflex femoral artery.

Question 14

A 68-year-old man presents with bilateral lower extremity pain radiating down his posterior thighs when walking. He undergoes a stationary bicycling test in the clinic. The patient notes that his leg symptoms do not occur while leaning forward and pedaling on the bicycle. What is the anatomical rationale for this improvement, confirming the diagnosis of neurogenic claudication?

Explanation

The stationary bicycle test differentiates neurogenic claudication (lumbar spinal stenosis) from vascular claudication. Patients with neurogenic claudication typically experience symptom relief when seated or leaning forward (such as riding a bike or pushing a shopping cart). This forward-flexed posture decreases lumbar lordosis, which temporarily opens the intervertebral foramina and increases the cross-sectional area of the spinal canal, relieving pressure on the nerve roots.

Question 15

A 55-year-old male with a metal-on-metal total hip arthroplasty presents with groin pain and an expanding soft tissue mass. Aspiration yields sterile, cloudy fluid. Histology of the periprosthetic tissue reveals an Aseptic Lymphocyte-dominated Vasculitis-Associated Lesion (ALVAL). This pathological response is driven by which immunologic mechanism?

Explanation

Adverse local tissue reactions (ALTR) or ALVAL in metal-on-metal implants are driven by a delayed hypersensitivity response to metal ions (specifically cobalt and chromium). This is a Type IV (cell-mediated) hypersensitivity reaction. It is characterized by perivascular lymphocytic infiltration, tissue necrosis, and the formation of pseudotumors, distinct from the innate macrophage-driven response seen in typical polyethylene wear osteolysis.

Question 16

A 19-year-old male reports persistent nocturnal diaphyseal tibial pain that is dramatically relieved by aspirin. Radiographs reveal a cortically based sclerotic lesion with a central radiolucent nidus measuring 8 mm. What is the primary biochemical mediator produced in high quantities by the nidus responsible for the patient's specific pain pattern?

Explanation

The clinical and radiographic presentation is classic for an osteoid osteoma. The central nidus contains osteoblasts that produce high levels of Prostaglandin E2 (PGE2) and cyclooxygenase-2 (COX-2). PGE2 mediates profound perilesional vasodilation and directly stimulates sensory nerve fibers, causing severe pain (characteristically worse at night). Because NSAIDs and aspirin potently inhibit COX enzymes and thus PGE2 synthesis, they dramatically relieve the pain.

Question 17

A 35-year-old carpenter presents with the inability to form an 'OK' sign with his right hand. He maintains normal sensation over his entire hand and forearm. He is diagnosed with Anterior Interosseous Nerve (AIN) syndrome. Which of the following muscles will have normal function on physical examination?

Explanation

The Anterior Interosseous Nerve (AIN) is a purely motor branch of the median nerve. It innervates three muscles: the flexor pollicis longus (FPL), the radial half of the flexor digitorum profundus (FDP to the index and long fingers), and the pronator quadratus. Inability to pinch the thumb and index finger (loss of IP thumb flexion and DIP index flexion) yields a positive 'OK' sign test. The Flexor carpi radialis (FCR) is innervated by the main branch of the median nerve before the AIN branches off, so its function is preserved.

Question 18

A 55-year-old poorly controlled diabetic male presents with a warm, erythematous, and swollen right foot without an open ulcer. Radiographs reveal periarticular fragmentation, subluxation, and joint debris at the midfoot. According to the Eichenholtz classification, he is in Stage 1 of Charcot neuroarthropathy. What is the gold standard initial non-operative treatment?

Explanation

The patient is in the acute fragmentation phase (Stage 1) of Eichenholtz Charcot neuroarthropathy, characterized clinically by a hot, swollen foot and radiographically by osteopenia, fragmentation, and joint subluxation. The gold standard treatment during this acute, destructive phase is strict immobilization and offloading, typically achieved with a total contact cast (TCC). Surgery is generally contraindicated during the acute inflammatory phase due to severe bone quality and high failure rates.

Question 19

Articular cartilage is a highly specialized tissue designed to distribute loads and minimize friction. Structurally, it is divided into distinct zones. Which zone possesses the highest concentration of proteoglycans, allowing it to provide the greatest resistance to compressive forces?

Explanation

The deep (radial) zone of articular cartilage contains the highest concentration of proteoglycans and the lowest water content. The collagen fibers here are oriented perpendicular to the joint surface. The high proteoglycan content binds water tightly, conferring the maximal resistance to compressive loads. In contrast, the superficial zone has the highest water and collagen content, with collagen fibers oriented parallel to the surface to resist shear stress.

Question 20

A 45-year-old skier sustains a Schatzker II tibial plateau fracture (split depression of the lateral plateau). He undergoes open reduction and internal fixation. During the procedure, the surgeon elevates the depressed articular fragment. What intra-articular pathology is most commonly associated with this specific fracture pattern and must be evaluated intraoperatively?

Explanation

Schatzker II fractures (lateral plateau split-depression) are highly associated with tears of the lateral meniscus. The lateral meniscus is frequently incarcerated within the fracture site or suffers a peripheral tear as the lateral femoral condyle drives into the tibial plateau. The surgeon must carefully inspect the lateral meniscus during arthrotomy or arthroscopy, often needing to elevate it (submeniscal arthrotomy) to visualize the joint surface and subsequently repair it.

Question 21

During a primary total knee arthroplasty, the surgeon notes that the knee is well-balanced in extension but unacceptably tight in 90 degrees of flexion. Which of the following technical adjustments is the most appropriate next step to balance the knee?

Explanation

A knee that is tight in flexion but balanced in extension requires an increase in the flexion gap without altering the extension gap. Decreasing the femoral component AP size, using anterior referencing to take more posterior condylar bone, effectively increases the flexion gap.

Question 22

Tranexamic acid (TXA) is frequently used in orthopedic surgery to reduce perioperative blood loss. Which of the following best describes its primary mechanism of action?

Explanation

Tranexamic acid is an antifibrinolytic agent that competitively binds to the lysine-binding sites on plasminogen. This prevents plasminogen from activating into plasmin, thereby inhibiting the degradation of fibrin clots.

Question 23

A 55-year-old male with a history of renal cell carcinoma presents with a large, solitary, highly destructive lytic lesion in the proximal diaphyseal femur with an impending pathologic fracture. What is the most critical step prior to proceeding with prophylactic intramedullary stabilization?

Explanation

Renal cell carcinoma metastases to bone are highly vascular and prone to massive intraoperative hemorrhage. Preoperative angiographic embolization is strictly recommended within 24-48 hours prior to surgical stabilization to reduce life-threatening blood loss.

Question 24

Denosumab is an effective pharmacological treatment for preventing skeletal-related events in patients with giant cell tumor of bone and metastatic bone disease. It exerts its effect by binding directly to which of the following targets?

Explanation

Denosumab is a human monoclonal antibody that specifically binds to and inhibits RANKL. By neutralizing RANKL, it prevents the interaction with RANK receptors on osteoclasts, severely impairing osteoclast formation, function, and survival.

Question 25

A 35-year-old male is brought to the trauma bay in hemorrhagic shock following a high-speed motorcycle collision. Pelvic radiographs reveal an anteroposterior compression type III (APC-III) pelvic ring injury. A circumferential pelvic binder is requested. Over which specific anatomic landmark should the binder be centered to be most effective?

Explanation

To effectively reduce pelvic volume and control venous bleeding in mechanically unstable pelvic ring injuries, a pelvic binder or sheet must be centered directly over the greater trochanters. Placing it higher (e.g., over the iliac crests) can paradoxically distract the pelvic brim.

Question 26

Highly cross-linked polyethylene (HXLPE) was developed to reduce wear rates in total hip arthroplasty. However, the cross-linking process introduces free radicals that can lead to long-term oxidation and material degradation. Which of the following manufacturing steps is used to eliminate or neutralize these free radicals?

Explanation

Free radicals generated during the gamma irradiation process of HXLPE are eliminated either by thermal treatment (remelting or annealing) or by the addition of antioxidants such as Vitamin E. This prevents oxidative degradation while maintaining wear resistance.

Question 27

A 6-year-old boy sustains a severe Gartland Type III supracondylar humerus fracture. Radiographs show the distal fragment is displaced posteromedially. Based on this displacement pattern, which neurovascular structure is at the greatest risk of injury?

Explanation

In a posteromedial displacement of a supracondylar humerus fracture, the proximal fragment is pushed anterolaterally, impaling the radial nerve. Conversely, posterolateral displacement puts the median nerve and brachial artery at greatest risk.

Question 28

According to Perren's strain theory of bone healing, primary (contact) bone healing via cutting cones requires which of the following mechanical environments?

Explanation

Primary bone healing occurs without callus formation and relies on direct Haversian remodeling (cutting cones). This biologic process can only occur under conditions of absolute stability, requiring an interfragmentary strain of less than 2%.

Question 29

A 32-year-old male presents 9 months after undergoing intramedullary nailing for a closed tibial shaft fracture. He reports persistent pain with weight-bearing. Radiographs demonstrate an "elephant foot" appearance at the fracture site with abundant bridging callus that fails to cross the fracture gap. What is the most appropriate management?

Explanation

An "elephant foot" nonunion is a hypertrophic nonunion, indicating excellent biological healing potential but inadequate mechanical stability. The treatment of choice is optimizing stability, most commonly through exchange nailing to a larger diameter implant.

Question 30

Articular cartilage relies on a highly organized structure for its biomechanical properties. Which zone of articular cartilage is characterized by collagen fibrils oriented perpendicular to the joint surface and contains the highest concentration of proteoglycans?

Explanation

The deep (radial) zone of articular cartilage is responsible for resisting compressive forces. It is characterized by perpendicularly oriented collagen fibers and the highest concentration of proteoglycans (and lowest water content) of any uncalcified zone.

Question 31

A 14-year-old boy presents with a painful, swollen mass on his left diaphyseal femur. Radiographs reveal a permeative, destructive lesion with an "onion-skin" periosteal reaction. Biopsy confirms small round blue cells. Immunohistochemistry is most likely to be strongly positive for which of the following markers?

Explanation

The clinical and radiographic presentation is classic for Ewing sarcoma, a small round blue cell tumor. Ewing sarcoma is characterized by the t(11;22) translocation and strongly expresses the cell surface marker CD99 (MIC2).

Question 32

A 40-year-old agricultural worker sustains an open tibia fracture (Gustilo-Anderson Type IIIA) after his leg is caught in a tractor mechanism. Soil and manure contamination are present. According to established guidelines, what is the most appropriate initial empiric antibiotic regimen?

Explanation

For severe open fractures (Type III) in a highly contaminated agricultural setting, standard prophylaxis historically includes a first-generation cephalosporin, an aminoglycoside (for Gram-negative coverage), and Penicillin to cover anaerobic organisms such as Clostridium species.

Question 33

A 25-year-old male presents to the emergency department after a diving accident. He is awake, alert, and cooperative. Examination reveals weakness in his hands and intrinsic muscles, but intact lower extremity function. Imaging shows a bilateral C6-C7 jumped facet. What is the most appropriate next step in management?

Explanation

In an awake, alert, and examinable patient with cervical facet dislocations, emergent closed reduction with skeletal traction is indicated and safe without a prior MRI. MRI is required prior to reduction primarily in comatose or unexaminable patients to rule out an extruded disc.

Question 34

During flexor tendon repair in the hand, preservation of the annular pulley system is critical to maintain the biomechanics of digital flexion. Which two pulleys are mechanically the most important to preserve in order to prevent bowstringing of the flexor tendons?

Explanation

The A2 (located over the proximal phalanx) and A4 (located over the middle phalanx) pulleys are mechanically the most crucial for maintaining the tendon closely apposed to the bone. Disruption of these pulleys leads to significant flexor tendon bowstringing and loss of mechanical advantage.

Question 35

According to the Musculoskeletal Infection Society (MSIS) and International Consensus Meeting (ICM) criteria, which of the following is considered a "major" criterion, sufficient on its own to definitively diagnose a periprosthetic joint infection (PJI)?

Explanation

The major criteria for diagnosing PJI include a sinus tract communicating with the joint or the isolation of the exact same organism from two separate tissue/fluid cultures. The other options listed are minor criteria.

Question 36

A 72-year-old female presents with severe shoulder pain and inability to actively elevate her arm above 30 degrees. Passive range of motion is full. MRI reveals a massive, retracted, full-thickness tear of the supraspinatus and infraspinatus with Goutallier stage 4 fatty infiltration. What is the most appropriate surgical treatment?

Explanation

This patient exhibits pseudoparalysis secondary to a massive, irreparable rotator cuff tear with severe fatty infiltration (Goutallier stage 4). Reverse total shoulder arthroplasty is the treatment of choice in an elderly patient to restore active forward elevation.

Question 37

An orthopedic surgeon utilizes a stainless steel screw to secure a titanium plate during open reduction internal fixation of a diaphyseal fracture. Postoperatively, the patient develops localized failure and rapid degradation at the screw-plate interface. This failure is primarily due to which phenomenon?

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic/cathodic indices (e.g., stainless steel and titanium) are placed in direct physical contact within a conductive fluid environment like the human body. This accelerates the electrochemical breakdown of the less noble metal.

Question 38

A 6-week-old female infant is undergoing treatment for developmental dysplasia of the hip (DDH) utilizing a Pavlik harness. Ultrasound evaluation at 4 weeks into treatment demonstrates that the left hip remains persistently dislocated. What is the most appropriate next step in management?

Explanation

If a dislocated hip fails to reduce after 3 to 4 weeks of proper Pavlik harness treatment, the harness should be abandoned to prevent "Pavlik harness disease" (damage to the posterior acetabular wall). The next step is a closed reduction and spica casting or a rigid orthosis.

Question 39

Fluoroquinolone antibiotics are known to carry a black box warning for an increased risk of tendon ruptures, particularly involving the Achilles tendon. What is the primary molecular mechanism underlying this adverse effect?

Explanation

Fluoroquinolones increase the expression of matrix metalloproteinases (MMPs) and decrease collagen synthesis in tenocytes. This combination leads to a net degradation of the extracellular matrix, compromising tendon strength and increasing the risk of rupture.

Question 40

A 65-year-old male presents with worsening hand clumsiness, difficulty buttoning his shirt, and a broad-based gait. Physical examination reveals a positive Hoffmann sign bilaterally. Elicitation of the brachioradialis reflex results in isolated flexion of the fingers without elbow flexion. This specific reflex finding strongly localizes a cervical spine lesion to which neurologic level?

Explanation

The "inverted radial reflex" (or inverted brachioradialis reflex) is a hallmark of cervical spondylotic myelopathy. It localizes the lesion specifically to the C5-C6 level, demonstrating lower motor neuron absence at C6 (no elbow flexion) and upper motor neuron hyperreflexia below this level (finger flexion).

Question 41

A 65-year-old male undergoes a total hip arthroplasty using a highly cross-linked polyethylene liner. Which of the following best describes the primary mechanism by which highly cross-linked polyethylene reduces wear compared to conventional polyethylene?

Explanation

Highly cross-linked polyethylene reduces wear by restricting polymer chain mobility, which minimizes plastic deformation and alignment under stress. This significantly decreases both adhesive and abrasive wear, though it also reduces fatigue strength.

Question 42

A 15-year-old boy presents with a destructive diaphyseal lesion of the femur with a large soft tissue mass. Biopsy reveals small round blue cells. Which of the following chromosomal translocations is most pathognomonic for this tumor?

Explanation

The patient has Ewing sarcoma, characterized by the t(11;22)(q24;q12) translocation resulting in the EWS-FLI1 fusion protein. t(X;18) is seen in synovial sarcoma, and t(12;16) is associated with myxoid liposarcoma.

Question 43

A 45-year-old smoker presents with a hypertrophic nonunion of the tibial shaft 8 months after intramedullary nailing. Laboratory markers (WBC, ESR, CRP) are normal. What is the most appropriate next step in management?

Explanation

Hypertrophic nonunions are primarily biologically viable but mechanically unstable. Exchange nailing with a larger diameter nail provides the necessary mechanical stability to allow the already present biologic response to bridge the fracture.

Question 44

A 13-year-old overweight boy is diagnosed with an unstable slipped capital femoral epiphysis (SCFE). Which of the following factors most significantly increases his risk of developing avascular necrosis (AVN) following treatment?

Explanation

An unstable SCFE, defined clinically by the inability to bear weight even with crutches, carries a significantly higher risk of AVN (up to 50%) compared to stable slips. Capsulotomy may actually reduce intracapsular pressure, potentially lowering AVN risk.

Question 45

In the early stages of osteoarthritis, which of the following represents the most characteristic biochemical change in the articular cartilage matrix?

Explanation

The earliest biochemical change in osteoarthritis is the disruption of the collagen network, which allows the tissue to swell, resulting in increased water content. Concurrently, there is a depletion of proteoglycans as they are degraded and lost into the synovial fluid.

Question 46

A 25-year-old male is brought to the emergency department after a high-speed motor vehicle collision. He is hypotensive, bradycardic, and lacks motor or sensory function below the C6 level. Which of the following best explains his cardiovascular presentation?

Explanation

Neurogenic shock presents with hypotension and bradycardia due to the loss of sympathetic vasomotor tone following a high cervical or high thoracic spinal cord injury. This loss leaves vagal parasympathetic tone unopposed.

Question 47

A patient presents with pain and a sterile effusion 5 years after receiving a modular total hip arthroplasty with a cobalt-chromium head and a titanium femoral stem. Aspirate reveals dark fluid and metal debris. What type of corrosion is most likely occurring at the head-neck junction?

Explanation

Fretting corrosion occurs at modular junctions like the head-neck taper due to micromotion disrupting the protective oxide layer. This is often combined with crevice corrosion in a process termed mechanically assisted crevice corrosion (MACC).

Question 48

Following a crush injury to the forearm, a patient develops acute compartment syndrome. The fundamental pathophysiologic mechanism leading to muscle necrosis in this condition is primarily driven by an increase in:

Explanation

Acute compartment syndrome is initiated by a rise in tissue pressure that exceeds the local venous pressure. This collapses the venules, halting capillary perfusion, and leading to anoxic muscle necrosis despite continued arterial inflow initially.

Question 49

A 4-month-old infant is being treated for developmental dysplasia of the hip (DDH) with a Pavlik harness. During a follow-up ultrasound, the hip remains dislocated, and the infant demonstrates decreased active knee extension on the affected side. What is the most likely cause of this neurologic finding?

Explanation

Femoral nerve palsy in a Pavlik harness is typically caused by excessive hip flexion pressing the nerve against the inguinal ligament. It presents with decreased active knee extension and requires immediate loosening or removal of the harness.

Question 50

During arthroscopic rotator cuff repair, a surgeon aims to optimize tendon-to-bone healing. Which of the following describes the ideal biologic progression of primary healing at the repair site?

Explanation

Tendon-to-bone healing after rotator cuff repair typically occurs via secondary healing, initially forming a fibrovascular scar that remodels over months. Direct regeneration of the native four-zone enthesis is rarely fully achieved.

Question 51

A 22-year-old male sustains a proximal pole scaphoid fracture. Which of the following anatomical characteristics most directly explains the high rate of avascular necrosis associated with this specific injury?

Explanation

The primary blood supply to the scaphoid enters the dorsal ridge distally and supplies the proximal pole in a retrograde intraosseous fashion. Fractures of the proximal pole frequently disrupt this supply, leading to a high rate of avascular necrosis.

Question 52

Bone morphogenetic proteins (BMPs) induce bone formation primarily by signaling through which of the following intracellular pathways?

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, which subsequently phosphorylate and activate intracellular Smad proteins (specifically Smad 1, 5, and 8). These form a complex to enter the nucleus and regulate transcription of osteogenic genes.

Question 53

A 60-year-old female with a history of breast cancer presents with severe thigh pain. Radiographs reveal a 3 cm lytic lesion in the peritrochanteric region of the femur involving 50% of the cortical diameter. What is her Mirels' score, and what is the recommended treatment?

Explanation

Her Mirels' criteria score is 10: Lower limb (2), Severe pain (3), Lytic lesion (3), and Size 1/3-2/3 of cortex (2). A score of 9 or greater indicates a high risk of impending fracture and strongly warrants prophylactic internal fixation.

Question 54

A 40-year-old male ruptures his Achilles tendon. If he opts for non-operative management utilizing an early functional rehabilitation protocol, which of the following is the most likely outcome compared to surgical repair?

Explanation

Recent high-level evidence demonstrates that non-operative management with early functional rehabilitation yields similar re-rupture rates and functional outcomes compared to surgery. It also completely avoids the risk of surgical wound complications.

Question 55

A polytrauma patient presents with an anteroposterior compression (APC) type III pelvic ring injury. After pelvic binder application and aggressive fluid resuscitation, the patient remains hemodynamically unstable. FAST exam is negative. What is the most appropriate next step?

Explanation

In a hemodynamically unstable patient with a stabilized pelvic fracture and no other source of bleeding (negative FAST), the primary source of hemorrhage is pelvic retroperitoneal bleeding. Preperitoneal pelvic packing and/or angiography with embolization are the life-saving interventions of choice.

Question 56

Metal hypersensitivity after joint arthroplasty is most commonly mediated by which type of immune reaction?

Explanation

Metal hypersensitivity is a Type IV, cell-mediated (delayed-type) hypersensitivity reaction. T-lymphocytes become sensitized to metal ions acting as haptens, subsequently releasing cytokines that recruit macrophages and cause tissue damage.

Question 57

During the Ponseti method for correcting idiopathic clubfoot, what is the correct order of deformity correction?

Explanation

The Ponseti method follows the CAVE sequence: Cavus is corrected first by elevating the first ray. This is followed by correcting Adductus and Varus simultaneously via gradual abduction, with Equinus corrected last (often requiring a tenotomy).

Question 58

A rock climber experiences a sudden 'pop' in his ring finger while crimping. He exhibits bowstringing of the flexor tendons. Which pulley system is most critical to reconstruct to restore biomechanical function and prevent significant bowstringing?

Explanation

The A2 (located on the proximal phalanx) and A4 (on the middle phalanx) pulleys are the most mechanically critical annular pulleys. Their incompetence leads to severe bowstringing and a profound loss of mechanical advantage during digit flexion.

Question 59

Which of the following best describes the incorporation process of a structural cortical bone allograft compared to a cancellous autograft?

Explanation

Structural cortical allografts undergo initial osteoclastic resorption causing temporary mechanical weakness before new bone formation. Cancellous grafts incorporate faster via creeping substitution with early osteoblastic activity.

Question 60

In articular cartilage, which zone is responsible for the highest resistance to shear stress due to its specific collagen fiber orientation?

Explanation

The superficial (tangential) zone contains collagen fibers arranged parallel to the joint surface. This specific orientation provides the highest resistance to shear forces within the joint.

Question 61

A surgeon plans to use a stainless steel plate with titanium screws for fracture fixation. Which of the following types of corrosion is most likely to occur at the screw-plate interface?

Explanation

Galvanic corrosion occurs when two dissimilar metals, such as stainless steel and titanium, are placed in contact within an electrolytic solution (body fluid). The less noble metal (stainless steel) acts as an anode and preferentially corrodes.

Question 62

A 14-year-old boy presents with a diaphyseal femur lesion with an "onion skin" periosteal reaction. Biopsy reveals small round blue cells. Which of the following chromosomal translocations is most pathognomonic for this tumor?

Explanation

Ewing sarcoma is a small round blue cell tumor commonly affecting the diaphysis of long bones. It is classically characterized by the t(11;22) chromosomal translocation, resulting in the EWS-FLI1 fusion protein.

Question 63

A 65-year-old male presents with increasing hat size and bilateral thigh pain. Laboratory studies show markedly elevated alkaline phosphatase with normal calcium and phosphorus. What is the primary cellular defect in this condition?

Explanation

Paget disease of bone is driven by primary hyperactive, multinucleated osteoclasts leading to chaotic bone resorption. This is followed by disorganized osteoblastic bone formation, resulting in weak woven bone.

Question 64

A 45-year-old farmer sustains a highly contaminated Gustilo-Anderson Grade IIIA open tibia fracture from a tractor rollover. According to evidence-based guidelines, which antibiotic regimen is most appropriate for initial management?

Explanation

For farm injuries with gross soil contamination, high-dose penicillin is added to a first-generation cephalosporin and an aminoglycoside. This provides necessary coverage for Clostridium species to prevent gas gangrene.

Question 65

A 4-month-old infant with developmental dysplasia of the hip (DDH) is treated with a Pavlik harness. Two weeks later, the parents report the infant has stopped kicking the affected leg. Examination reveals absent active knee extension. What is the most likely cause?

Explanation

Femoral nerve palsy is a known complication of Pavlik harness treatment caused by excessive hip flexion. It typically resolves spontaneously when the hyperflexion is corrected or the harness is temporarily removed.

Question 66

A 60-year-old male presents with a swollen, acutely painful knee. Synovial fluid aspiration reveals a white blood cell count of 65,000 cells/mm3 with 85% polymorphonuclear leukocytes. Crystals are absent. What is the most likely diagnosis?

Explanation

A synovial fluid WBC count greater than 50,000 cells/mm3 with a high percentage of PMNs strongly suggests septic arthritis. The absence of crystals further lowers the likelihood of gout or pseudogout.

Question 67

During the remodeling phase of ligament healing, which biochemical transition is most responsible for the gradual increase in tensile strength?

Explanation

During the remodeling phase, the initially deposited disorganized Type III collagen is gradually replaced by stronger, highly cross-linked Type I collagen. This transition is essential for restoring the ligament's tensile strength.

Question 68

In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) primarily reduces which type of wear compared to conventional polyethylene?

Explanation

Highly cross-linked polyethylene significantly reduces adhesive wear at the articular bearing surface. However, cross-linking decreases the material's mechanical toughness, making it theoretically more susceptible to fatigue wear.

Question 69

A polytrauma patient arrives hemodynamically unstable with an "open book" anterior-posterior compression (APC) pelvic ring injury. A pelvic binder is ordered. To maximize mechanical reduction of the pelvic volume, over which anatomic landmark should the binder be centered?

Explanation

A pelvic binder must be centered directly over the greater trochanters to effectively provide internal rotation forces to the innominate bones. Placing it higher over the ASIS or iliac crests is less effective and can inappropriately flare the pelvis.

Question 70

A patient presents with weakness in ankle plantarflexion and a diminished Achilles tendon reflex. Which nerve root is most likely compressed?

Explanation

The S1 nerve root primarily provides motor innervation to the gastrocnemius-soleus complex for ankle plantarflexion. It is also the primary root tested by the Achilles deep tendon reflex.

Question 71

A 6-year-old boy presents with a painless limp and limited hip internal rotation. Radiographs show fragmentation and sclerosis of the proximal femoral epiphysis. Which vascular structure's compromise is primarily implicated in the pathogenesis of this disease?

Explanation

The presentation is classic for Legg-Calve-Perthes disease. The blood supply to the femoral head at this age depends heavily on the lateral epiphyseal branches of the medial femoral circumflex artery.

Question 72

A 35-year-old male is involved in a motor vehicle collision and sustains a traumatic spondylolisthesis of the axis (Hangman's fracture). The mechanism of injury typically involves which of the following forces?

Explanation

A Hangman's fracture (traumatic spondylolisthesis of C2) is classically caused by hyperextension and axial loading forces. This leads to bilateral fractures of the pars interarticularis of the axis.

Question 73

Following a peripheral nerve transection injury, Wallerian degeneration occurs distal to the injury site. Which cell type is primarily responsible for clearing myelin debris and guiding regenerating axons in the peripheral nervous system?

Explanation

In the peripheral nervous system, Schwann cells are crucial for clearing myelin debris and forming the Bands of Büngner. These bands create a supportive microenvironment that guides regenerating axonal sprouts.

Question 74

In a posterior approach to the hip for total hip arthroplasty, the "safe zone" for acetabular cup placement to minimize dislocation risk is traditionally described by Lewinnek. What are these target parameters?

Explanation

The Lewinnek safe zone for acetabular component positioning is historically defined as 40 degrees (± 10 degrees) of abduction (inclination) and 15 degrees (± 10 degrees) of anteversion. Deviation from this zone increases the risk of postoperative impingement and dislocation.

Question 75

In the management of flexor tendon lacerations in the hand, Zone II represents a distinct surgical challenge. What anatomic boundaries define Zone II?

Explanation

Zone II, historically called "no man's land," extends from the proximal edge of the A1 pulley to the insertion of the flexor digitorum superficialis (FDS). It is notorious for poor healing and adhesions due to the tight fibro-osseous canal.

Question 76

A 22-year-old male sustains a scaphoid waist fracture. The risk of avascular necrosis of the proximal pole is notoriously high due to retrograde blood supply. Which artery provides the predominant blood supply to the scaphoid?

Explanation

The dorsal carpal branch of the radial artery provides 70-80% of the blood supply to the scaphoid, entering distally and flowing retrograde to the proximal pole. Fractures at the waist disrupt this flow, leading to proximal pole AVN.

Question 77

A 70-year-old female presents with severe back pain and a purely lytic lesion in the L3 vertebral body. Laboratory tests show anemia and hypercalcemia. Which of the following mechanisms is responsible for the bone destruction in this disease?

Explanation

Multiple myeloma cells secrete osteoclast-activating factors such as RANKL, MIP-1 alpha, and IL-6, which stimulate rampant osteoclastic bone resorption. Concurrently, they inhibit osteoblast activity, resulting in purely lytic bone lesions.

Question 78

Following uncemented total hip arthroplasty with an extensively porous-coated cobalt-chromium femoral stem, a patient develops proximal femoral cortical osteopenia. Which biomechanical principle best explains this phenomenon?

Explanation

Wolff's Law states that bone remodels in response to mechanical stress. A stiff femoral stem bears most of the load (stress shielding), bypassing the proximal femur and leading to adaptive bone resorption and osteopenia.

Question 79

A 55-year-old female undergoes a revision total hip arthroplasty. During the procedure, the surgeon utilizes a stainless steel cerclage wire around a titanium femoral stem. Which type of corrosion is most likely to occur at the interface of these two different metals?

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct contact within a conductive fluid environment, leading to an electrochemical gradient. The less noble metal (stainless steel) acts as the anode and corrodes preferentially.

Question 80

A 35-year-old male is brought to the trauma bay after a severe motorcycle crash. He is hemodynamically unstable despite initial fluid resuscitation. A pelvic binder is in place. Radiographs demonstrate an anteroposterior compression (APC) type III pelvic ring injury. A FAST exam is negative. What is the most appropriate next step in acute management?

Explanation

In a hemodynamically unstable patient with a mechanically unstable pelvic ring injury and a negative FAST exam, the primary source of bleeding is usually venous or from cancellous bone. Preperitoneal pelvic packing and external fixation provide rapid hemorrhage control.

Question 81

A 65-year-old male presents to the emergency department after a high-speed rear-end motor vehicle collision. He sustained a hyperextension injury to his cervical spine. On examination, he exhibits severe motor weakness in his upper extremities with relative sparing of his lower extremities, alongside patchy sensory deficits. Which of the following is the most likely diagnosis?

Explanation

Central cord syndrome typically occurs after hyperextension injuries in older patients with pre-existing cervical spondylosis. It affects the centrally located cervical tracts of the upper extremities more severely than the peripherally located tracts of the lower extremities.

Question 82

A 6-year-old boy presents with a persistent right leg limp and anterior thigh pain. Radiographs reveal a fragmented, sclerotic proximal femoral epiphysis consistent with Legg-Calve-Perthes disease. Which of the following is considered the most significant prognostic factor at the time of initial presentation?

Explanation

Age at clinical onset is the most critical prognostic factor in Legg-Calve-Perthes disease. Patients who develop the disease before the age of 6 generally have a better prognosis and greater potential for spherical remodeling of the femoral head.

Question 83

A 45-year-old female with a history of breast cancer presents with progressively worsening proximal femur pain. Radiographs demonstrate a large lytic lesion. You calculate a Mirels score to determine the need for prophylactic fixation. Which of the following is NOT a parameter used in the Mirels scoring system?

Explanation

The Mirels score determines the risk of pathologic fracture and guides the need for prophylactic fixation based on four parameters: site, size, nature of the lesion, and pain. Primary tumor histology is not a component of the score.

Question 84

A 22-year-old male sustains a direct blow to the anteromedial proximal tibia while his knee is extended. A posterolateral corner (PLC) injury is suspected. Which of the following physical examination findings specifically isolates an injury to the PLC?

Explanation

The dial test assesses for posterolateral corner injury. Increased external rotation at 30 degrees of flexion (but not at 90 degrees) indicates an isolated PLC injury. If it is increased at both 30 and 90 degrees, a combined PLC and PCL injury is present.

Question 85

A 3-month-old infant is being treated in a Pavlik harness for developmental dysplasia of the hip (DDH). The mother brings the child in because she notices the baby is no longer actively kicking the affected leg, although the toes continue to move. What is the most likely complication occurring in this patient?

Explanation

Femoral nerve palsy is a known complication of Pavlik harness treatment, typically caused by hyperflexion of the hip which compresses the nerve against the rim of the pelvis. Treatment requires immediate adjustment or removal of the harness until active quadriceps function returns.

Question 86

A 70-year-old female with a 12-year history of alendronate use presents with sudden onset thigh pain after a minor misstep. Radiographs demonstrate lateral cortical thickening and a transverse fracture with a medial spike in the subtrochanteric region. What is the primary pathophysiologic mechanism of this specific fracture type?

Explanation

Long-term bisphosphonate use heavily suppresses osteoclast function, leading to a suppression of targeted bone remodeling. This prevents the normal repair of skeletal microdamage, resulting in the accumulation of microcracks and eventual atypical femur fractures.

Question 87

A 25-year-old male sustains a closed, isolated midshaft humerus fracture and is treated non-operatively with a functional fracture brace. At his 12-week follow-up, the fracture is radiographically healing, but he demonstrates an inability to actively extend his wrist or digits. Finger flexion and intrinsic function are normal. What is the most appropriate next step in management?

Explanation

Secondary radial nerve palsy or palsy failing to recover by 12 weeks during conservative management warrants an EMG/NCS to establish a baseline and determine if reinnervation is occurring. Continued observation is generally appropriate for up to 3 to 6 months before considering surgical exploration.

Question 88

A 14-year-old male gymnast presents with lower back pain that is exacerbated by extension activities. Oblique lumbar radiographs show a 'scotty dog with a collar' sign at L5. A lateral radiograph reveals a 15% anterior translation of L5 on S1. What is the most appropriate initial management?

Explanation

The patient has a Grade 1 isthmic spondylolisthesis. Initial management for symptomatic low-grade spondylolisthesis is conservative, consisting of activity modification, NSAIDs, and targeted physical therapy focusing on core and hamstring stretching.

Question 89

A 30-year-old male presents after falling onto an outstretched hand. Wrist radiographs demonstrate a perilunate dislocation. According to Mayfield's stages of perilunate instability, what structural failure corresponds with the final stage (Stage IV)?

Explanation

Mayfield's stages describe a progressive perilunate instability. Stage I is scapholunate failure, Stage II involves the space of Poirier (capitate dislocation), Stage III is lunotriquetral failure, and Stage IV occurs when the lunate dislocates volarly into the carpal tunnel.

Question 90

A 55-year-old male with a 5-year-old total hip arthroplasty presents with worsening hip pain. Aspiration of the hip joint yields fluid with a white blood cell count of 45,000 cells/mcL and 95% polymorphonuclear leukocytes. Culture grows Staphylococcus epidermidis. What is the most widely accepted definitive surgical management?

Explanation

The patient meets MSIS criteria for a chronic periprosthetic joint infection. In North America, the gold standard treatment for a chronic PJI (usually > 4 weeks post-op) is a two-stage revision arthroplasty utilizing an antibiotic-eluting spacer.

Question 91

When a diaphyseal fracture is treated with an interfragmentary lag screw and a neutralization plate to achieve absolute stability, which mode of bone healing predominates?

Explanation

Absolute stability virtually eliminates interfragmentary strain, bypassing the callus formation phase. The fracture heals via primary (Haversian) bone healing, utilizing cutting cones composed of osteoclasts followed by osteoblasts to directly bridge the fracture.

Question 92

A 40-year-old male complains of severe midfoot pain after falling from a ladder. Weight-bearing radiographs reveal a widened space between the first and second metatarsal bases and a small avulsion fracture (fleck sign) in the interspace. Which ligament is primarily injured?

Explanation

The fleck sign is highly specific for a Lisfranc injury. It represents a bony avulsion of the Lisfranc ligament, which originates from the lateral aspect of the medial cuneiform and attaches to the medial base of the second metatarsal.

Question 93

A 60-year-old male with a known massive, irreparable rotator cuff tear develops progressive superior migration of the humeral head and advanced glenohumeral osteoarthritis. He has pseudoparalysis with active elevation only up to 40 degrees. What is the most reliable surgical option for this patient?

Explanation

The patient has severe rotator cuff tear arthropathy (Hamada classification) with pseudoparalysis. Reverse total shoulder arthroplasty is the treatment of choice, as it medializes and distalizes the center of rotation, recruiting the deltoid to restore forward elevation.

Question 94

A 10-day-old infant is diagnosed with idiopathic clubfoot (talipes equinovarus). The orthopedic surgeon plans to initiate the Ponseti method of serial casting. What is the correct sequence of deformity correction in this method?

Explanation

The Ponseti method systematically corrects clubfoot deformities using the 'CAVE' sequence: first Cavus (by elevating the first ray), then Adductus, then Varus, and finally Equinus (often requiring a percutaneous Achilles tenotomy).

Question 95

A 25-year-old female athlete undergoes primary anterior cruciate ligament (ACL) reconstruction. Understanding the native biomechanics is crucial for anatomic tunnel placement. Which of the following statements accurately describes the biomechanical function of the native ACL bundles?

Explanation

The native ACL consists of two main bundles. The anteromedial (AM) bundle is tightest in flexion and is the primary restraint to anterior translation in a flexed knee. The posterolateral (PL) bundle is tightest in extension and provides rotational stability.

Question 96

A 32-year-old male presents with a severely displaced diaphyseal fracture of the radius and ulna. During his neurological examination, he demonstrates an inability to actively flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. Sensation is intact. Which nerve is most likely injured?

Explanation

The anterior interosseous nerve (AIN), a pure motor branch of the median nerve, innervates the flexor pollicis longus (FPL), the flexor digitorum profundus (FDP) to the index and middle fingers, and the pronator quadratus. Injury results in the 'OK sign' deficit.

Question 97

A 15-year-old male complains of a dull aching pain in his mid-thigh that is typically worse at night but dramatically relieved by ibuprofen. Radiographs demonstrate a small (<1.5 cm) radiolucent nidus surrounded by intense reactive cortical sclerosis in the femoral diaphysis. What is the most likely diagnosis?

Explanation

Osteoid osteoma classically presents in adolescents with severe night pain completely relieved by NSAIDs. Imaging typically shows a radiolucent nidus smaller than 1.5 cm surrounded by thickened, sclerotic reactive bone.

Question 98

A 45-year-old male sustains a displaced talar neck fracture with associated subtalar and tibiotalar dislocations (Hawkins Type III). Which of the following arteries provides the predominant blood supply to the body of the talus, rendering the body at exceptionally high risk for avascular necrosis in this injury pattern?

Explanation

The artery of the tarsal canal, a branch of the posterior tibial artery, supplies the majority of the talar body. In a Hawkins Type III fracture-dislocation, the three major blood supplies (tarsal canal, sinus tarsi, and deltoid branches) are heavily disrupted.

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