Question 1

Fibrous dysplasia has been determined to be the result of a mutation in which gene:

Explanation

Fibrous dysplasia has been determined to be the result of a postzygotic mutation in the GNAS1 (stimulatory G protein of adenylyl cyclase) gene. All of the cells that are descended from the cell with the mutation manifest features of the disease. FGFR3 (fibroblast growth factor receptor-3 protein) is abnormal in achondroplasia. FBN1 (fibrillin 1) is abnormal in Marfan syndrome. C FBA1 is abnormal in cleidocranial dysplasia. COL1A1 (collagen, type 1, alpha 1) is abnormal in osteogenesis imperfecta.

Question 2

Which of the following conditions is not associated with congenital contractures:

Explanation

Down syndrome is the only condition listed that does not involve congenital contractures. Amyoplasia (or classic arthrogryposis) involves multiple contractures with normal intelligence and loss of flexion creases. Diastrophic dysplasia is a disorder of cartilage that includes contractures of many joints, as well as epiphyseal irregularity. Popliteal pterygium syndrome includes contractures with webbing across the flexor surfaces of the joints. Larsen syndrome involves multiple joint dislocations, as well as contractures.

Question 3

Diastematomyelia is best described as:

Explanation

A diastematomyelia is an osseous or fibrocartilaginous septum within the spinal canal that invaginates or splits the neural tissue. A diastematomyelia may or may not be associated with neurologic deficit. Surgical excision is indicated for the presence of symptoms or at the time of spinal deformity correction.

Question 4

Diastematomyelia is most common in which region of the spine:

Explanation

Several series of patients with diastematomyelia have shown the following anatomic distribution: 64% occur in the lumbar spine, 27% occur in the lower thoracic spine, 9% in the upper thoracic spine, and almost none occur in the cervical or sacral regions.

Question 5

Which of the following is the most common finding in diastematomyelia:

Explanation

Widened interpedicular distance is the most common finding (94% or greater) in patients with diastematomyelia. Neurologic deficit is present in 60% to 88% of patients with diastematomyelia. A cutaneous lesion, such as a dimple or hairy patch, is present in 55% to 79% of patients with diastematomyelia. Anisomelia is present in 53% to 58% of patients with diastematomyelia. Foot deformities are present in 32% to 52% of patients with diastematomyelia.

Question 6

In which of the following clinical situations would it be most appropriate to recommend an anterior and posterior hemiepiphyseodesis of the convex side of a congenital scoliosis:

Explanation

Hemiepiphyseodesis is most likely to produce progressive curve correction in patients under age 6. Hemiepiphyseodesis is not likely to result in improvement when there is no concave growth potential, as in the case of a congenital bar. In hemivertebra of the lumbosacral region, improvement is most likely when a hemivertebra resection is performed.

Question 7

Which of the following is the seating arrangement recommended for a 5- year-old in a family automobile:

Explanation

Children ages 4 to 8 (40 lbs to 60 lbs) are at risk for airbag injuries and should not be in the front seat. In addition, they require booster seats to allow proper fitting of the shoulder harness on the upper torso. Rear-facing seats are only appropriate for infants. Children should not be in the front seat until after age 12 and over 100 lbs.

Question 8

Immediate internal fixation of diaphyseal fractures in polytraumatized children has been shown to provide which of the following benefits:

Explanation

Acute internal fixation in children has not been shown to provide the same life-saving and morbidity-reducing benefits as in adults. However, it will ease the management of the polytraumatized patient.

Question 9

Which of the following statements is true about pin fixation of supracondylar humerus fractures:

Explanation

Pin fixation of supracondylar humerus fractures in children decreases the risk of compartment syndrome as well as malreduction. Use of medial and lateral pins has been shown to be the most stable construct in biomechanical studies. The use of medial and lateral pins carries a risk of iatrogenic injury to the ulnar nerve. No nerve injuries have been demonstrated after the use of two lateral pins.

Question 10

A 6-year-old boy who is treated for a type III supracondylar fracture has no neurovascular deficit on initial examination. His fracture is treated by anatomic closed reduction and percutaneous fixation with medial and lateral pins. A partial deficit in ulnar motor and sensory function is noted after surgery. The next step in treatment should be:

Explanation

The use of medial pins in treatment of supracondylar fractures of the humerus has been associated with a risk of ulnar nerve injury. However, in the largest reported series, 16 of 17 palsies resolved spontaneously and completely with observation after a mean of 18 weeks. There is no evidence that pin removal, exploration, or transposition is necessary at this stage. Hyperflexion in a splint may cause the nerve to be apposed to the pin and can be decreased.

Question 11

Which of the following factors is associated with a decrease in the accuracy of measurement of congenital scoliosis:

Explanation

Measurement of congenital scoliosis has an intraobserver variation of 8°. Measurement accuracy decreases with decreased level of training, increased curve size, and decreased clarity of the endpoints. A coned and centered film would give better detail.

Question 12

Which of the following structures enables the growth plate to grow in diameter as the skeleton gets larger:

Explanation

The ossification groove of Ranvier contains chondrocytes that provide latitudinal growth of the growth plate. The groove of Ranvier may be thought of as â the growth ring of the growth plate.â The chondroepiphysis is the cartilage precursor of the epiphysis. The apophysis is a nonarticular growth region. The ring of LaC roix is a peripheral structure that reinforces the growth plate. The secondary spongiosa is mature lamellar bone after it has been remodeled.

Question 13

Which area of the growth plate has the lowest oxygen tension:

Explanation

The lowest pressure of oxygen is in the hypertrophic zone because it is poorly vascularized. This is one of the features that triggers cell death and calcificaton.

Question 14

How many major centers of ossification comprise the normal lumbar vertebral body:

Explanation

The normal lumbar and thoracic vertebrae are comprised of two posterior and one main anterior ossification center. These join at the neurocentral synchondrosis and the midline vertebal ossification center.

Question 15

The somite refers to which of the following features of embryologic development:

Explanation

The somite is a group of tissues that are bilaterally symmetric and repeated to comprise the axial skeleton. Each somite contains a dermatome, myotome, and sclerotome.

Question 16

Homeobox genes are best characterized by which of the following descriptions:

Explanation

Homeobox genes code for transcription factors involved in regulation of limb genesis in the embryonic period. Homeobox genes have a highly conserved 60-nucleotide sequence.

Question 17

Which of the following regions of the physis has the highest degree of proteoglycan aggregation in the matrix:

Explanation

The proteoglycan aggregation is greatest in the reserve zone and in the epiphysis. Proteoglycan concentration progressively decreases in the direction of the metaphysis. This phenomenon also enables calcification to occur.

Question 18

Which of the following categories of slipped capital femoral epiphysis (SC FE) is associated with the highest rate of bilaterality:

Explanation

Renal failure is associated with the highest risk (90%) of bilaterality. By contrast, idiopathic SC FE has a 20% risk of bilaterality initially and a further 10% to 20% risk until maturity.

Question 19

An African-American mother brings her 18-month-old baby in for examination because he has bowing of the legs. The child s past medical history is normal including height and weight. The child is still breast-fed. Radiographs reveal mild widening and irregularity of the physes. Which of the following conditions is likely to be found on laboratory examination:

Explanation

This patient has nutritional rickets because of a combination of decreased vitamin D intake and increased need for sunlight due to dark skin. The laboratory findings should include a lowâ normal calcium phosphate, elevated alkaline phosphatase and parathyroid hormone, and low vitamin D levels and precursors. Vitamin D supplementation without bracing is adequate treatment.

Question 20

The dose of acetaminophen for a child should be no more than:

Explanation

The dose of acetaminophen should be 10-15 mg/kg. The maximum daily dose should be no more than 75 mg/kg. Larger doses of acetaminophen pose a risk of hepatotoxicity over a long period of time.

Question 21

Opioids must be used with caution in infants younger than 3 months of age because of which of the following properties:

Explanation

Opioids must be used with caution in infants younger than 3 months of age because of decreased clearance and decreased protein binding. This results in greater bioavailability.

Question 22

The potency ratio of hydromorphone to morphine sulfate is:

Explanation

The potency ratio of commonly-used drugs is one of the factors that determines the appropriate dose of a drug. The potency ratio of hydromorphone to morphine sulfate is 7-10:1.

Question 23

The youngest age at which a number scale to quantitate pain (i.e., rating it as 1-10) can be appropriately used is:

Explanation

Pain measurement is becoming increasingly important for both children and adults. A number scale to quantitate pain can be appropriately used for most children over the age of 7 years. For younger children, the â faces scaleâ or a finger span scale (stretching the fingers as far apart as possible) is more accurate.

Question 24

Which of the following findings on a neuromuscular examination is not characteristic of spasticity:

Explanation

Spasticity is a hallmark of upper motor lesions. Spasticity is characterized by hyperreflexia, clonus, and velocity-dependent resistance. After early childhood, muscle contracture also develops. Writhing movements are characteristic of athetosis, not spasticity.

Question 25

Which of the following describes the mechanism of action of Botulinum toxin type A:

Explanation

Botulinum toxin type A acts by blocking the release of acetylcholine at the nerve terminal. Over time, new terminals sprout and the effect is lost. By contrast, alcohol and phenol denature proteins and disrupt nerve conduction.

Question 26

Which of the following describes the mechanism of action of baclofen:

Explanation

Baclofen mimics the effect of gamma-aminobutyric acid, an inhibitory neurotransmitter in both the peripheral and central nervous system. Baclofen reduces peripheral spasticity. A major side effect of baclofen is sedation. The ratio of sedation to spasticity reduction may be enhanced by intrathecal administration.

Question 27

The migration index of Reimers is best described as:

Explanation

acetabulum. The migration index of Reimers is used to quantitate hip subluxation in cerebral palsy. It is defined as the ratio of the uncovered portion of the femoral head (lateral to a vertical line through the outer edge of the acetabulum) to the total width of the head.

Question 28

An appropriate indication for preoperative magnetic resonance imaging in adolescent idiopathic scoliosis is:

Explanation

The only absolute indication for preoperative magnetic resonance imaging in idiopathic adolescent scoliosis is an abnormal neurologic exam or abnormal curve pattern.

Question 29

The mean C obb measurement for idiopathic scoliosis curves with a 7Â° angle of trunk rotation (ATR) is:

Explanation

Although the angle of trunk rotation (ATR) does not convert directly to a C obb angle, there are population-based figures for mean curve at each ATR. The mean Cobb angle for curves having a 7° ATR is 20°.

Question 30

Using a 5° angle trunk rotation (ATR) as a positive screening threshold for detection of curves with a C obb angle over 20° is characterized by:

Explanation

Use of a 5° ATR threshold for detection of curves with a Cobb angle over 20° has a sensitivity of 98%, but a specificity of only 64%.

Question 31

The normal values (±2 standard deviations) for kyphosis in the general population of children and adolescents are:

Explanation

The normal values for kyphosis in the general population (2 standard deviations above and below the mean) are 20° to 50°.

Question 32

Which of the following is the most common cause of death in children with pelvic fractures:

Explanation

Head injury is the cause of virtually all mortality in children with pelvic fractures. The rarity of life-threatening intrapelvic hemorrhage is in marked contrast to adults. Pulmonary embolism and multisystem organ failure are rare in children.

Question 33

An 8-year-old pedestrian sustains a pelvic fracture when struck by a car. The injury consists of a posterior iliac fracture in which the iliac wing is rotated internally, although it is not vertically displaced. An anterior fracture of both ipsilateral pubic rami is present with 2 cm of overlap. Recommended treatment includes:

Explanation

A childs pelvis can absorb a significant amount of energy without serious displacement. There is rapid healing and good remodeling potential. Bedrest is the appropriate treatment for this patient because of the low risk of complications.

Question 34

Which of the following factors should prompt a workup for an underlying disorder in a patient with slipped capital femoral epiphysis:

Explanation

A positive age-weight test is defined as a patient who is under the 50th percentile of weight for age or older than 16 years of age at presentation with slipped capital femoral epiphysis. These patients should have a workup for underlying renal or endocrine disease. A positive family history is found in 5% to 10% of patients with slipped capital femoral epiphysis.

Question 35

Which of the following categories of slipped capital femoral epiphysis (SC FE) is associated with the highest risk of a grade III slip:

Explanation

A grade III slip refers to more than 50% displacement of the epiphysis. Renal failure is associated with the highest risk (43%) of progressing to a grade III slip. Fortunately, these slips are usually stable.

Question 36

Which of the following is the central element of Klippel-Feil syndrome:

Explanation

The essential feature of the definition of Klippel-Feil syndrome is congenital cervical fusion. Features other than congenital cervical fusion are sometimes seen but are not essential features of the syndrome. Features other than those listed above include scoliosis in different regions of the spine, congenital heart defects, a short neck, Sprengel deformity, and renal anomalies.

Question 37

The most common cause of neurologic deficit in patients with Down syndrome is:

Explanation

Basilar invagination is extremely rare in this syndrome, and problematic cervical kyphosis is equally uncommon. Atlanto-occipital translation and subaxial instability occur but rarely cause symptoms. Atlantoaxial instability is the most common of the cervical abnormalities listed to cause neurologic compromise in Down syndrome. Nevertheless, surgery is only indicated if the atlantoaxial interval exceeds 6 mm, or causes neurologic deficits.

Question 38

The timing of maximal progression of idiopathic scoliosis is most closely correlated with:

Explanation

The cause of scoliosis or its progression is still not known. However, the timing of the progression is most closely correlated with the peak velocity of growth. The other factors are more weakly correlated: a chronological or skeletal age of 10 to 12 years, Risser sign of 0, or Tanner sign of 0 to 1.

Question 39

Which of the following events typically occurs first in adolescent girls:

Explanation

Typically, the peak height velocity is the first of these events to occur in adolescent girls. Skeletal maturity is the last event to occur.

Question 40

A 15-year-old with idiopathic scoliosis develops a temperature of 39.5Â° C 8 days after posterior spinal fusion with instrumentation. Blood and urine cultures show no growth, and chest X-ray is normal. Your next step should be which of the following:

Explanation

There is a significant likelihood of a deep wound infection, although other possibilities exist, including superficial wound infection, atelectasis, and drug-related fever. Therefore, confirmation of the diagnosis is the next step. The wound should be aspirated for culture next. If infection is confirmed, the wound should be opened and debrided.

Question 41

Nine days after surgery, a 16-year-old boy with idiopathic scoliosis has a temperature of 39.5° C . Wound aspiration reveals gram-positive cocci in clusters. Your next step in management is:

Explanation

Open debridement is the treatment of choice if an early deep wound infection is confirmed after spinal fusion. The instrumentation is left in place to stabilize the wound and promote fusion. The wound is closed as long as it can be cleaned up adequately during surgery, and muscle has a healthy appearance. If this cannot be achieved or if several debridements fail, the wound may be left open.

Question 42

A thoracic curve of more than 50Â° due to an idiopathic adolescent scoliosis curve has an increased risk of causing all except which of the following consequences in adulthood, when compared to the general population:

Explanation

Idiopathic adolescent scoliosis is likely to progress in adulthood if it exceeds 50°. The rate of progression in adults is slower than during adolescence; about 1° per year. Nevertheless, it is likely to have some effect on pulmonary function later during adulthood. The effect is one of restrictive rather than obstructive lung disease. There is an increase in the risk of back pain, although it is rarely disabling. Patients with idiopathic scoliosis as a group have a more negative body image, although it is not a serious life impairment. In all of these parameters, there are individual exceptions.

Question 43

A 13-year-old girl with idiopathic adolescent scoliosis has a 32° right thoracolumbar curve. Her Risser sign is 1. Her curve measured 29° 4 months ago. You recommend:

Explanation

Idiopathic scoliosis in skeletally immature patients should be braced if it is greater than 30° and significant growth remains (estimated by a Risser sign of 0, 1, or 2). Studies have shown that patients with idiopathic scoliosis without atypical findings do not need magnetic resonance imaging. Physical therapy and electrical stimulation have been shown not to have any effect on the progression of idiopathic scoliosis.

Question 44

Which of the following factors are not related to the success of brace treatment for idiopathic scoliosis?

Explanation

A lower chance of curve control with brace treatment has been shown with curves greater than 40Â°, correction of less than 50% in brace, brace worn fewer than 16 hours per day, or male gender. Positive family history has not been shown to be related to curve progression or chance of control.

Question 45

A 12-year-old patient has a rigid, 135° scoliosis. Gradually increasing halo- gravity traction is planned in correcting the curve. The maximum weight that should be used is:

Explanation

Halo-gravity traction is a safe and effective means of gradually correcting large curves. It allows balanced force application and continuous neurological monitoring. C ranial and peripheral nerves should be monitored. The weight can be increased gradually up to 35% to 45% of body weight, as documented in published series.

Question 46

In evaluating infants for Blount disease, which diagnostic parameter allows correct classification of the greatest number of children:

Explanation

The tibial metaphyseal-diaphyseal (M-D) angle, no matter what threshold is set, has a significant number of false-positives or false-negatives. Using the ratio of femoral to tibial M-D angle improves diagnostic accuracy significantly. The Langenskjold rating, tibiofemoral angle, and intercondylar distances, although conceptually important, have low diagnostic accuracy for an individual patient.

Question 47

Which of the following statements best characterizes a Dega osteotomy as a distinct osteotomy from a Salter osteotomy:

Explanation

The Dega osteotomy, originally described in Poland in 1964, is an incomplete transiliac osteotomy. The medial pelvic cortex is largely preserved, and the osteotomy hinges upon this point. Both osteotomies are best performed in young children, before triradiate cartilage closure. The Salter osteotomy is stabilized by pins, so the Dega needs no internal fixation. The Salter osteotomy lengthens the limb because it is a complete osteotomy.

Question 48

After the bone age of 15 years, boys will achieve the most growth from which of the following regions:

Explanation

After the age of 15 in boys (13 in girls), most of the growth (4.5 cm on average) occurs in the spine.

Question 49

The most accurate way to monitor the motor tracts during spinal surgery is to stimulate which of the following regions:

Explanation

The most accurate way to monitor the motor tracts of the spinal cord is to stimulate the motor cortex. Stimulation at the level of the spinal cord conducts mainly antidromically through sensory pathways. Stimulation of the tibial and peroneal nerve is performed for monitoring sensory pathways only; these are an important indicator of spinal cord integrity but do not monitor the motor pathways per se. Stimulation of the gastrocnemius does not have any value for monitoring.

Question 50

Which of the following most definitively makes the diagnosis of Sever disease:

Explanation

There are no radiographic findings diagnostic of Sever disease. Sclerosis and irregularity are normal findings, although they are often mistakenly called evidence of disease. The diagnosis of Sever disease is made by tenderness over the calcaneal apophysis.

Question 51

Which of the following is the greatest risk factor for the progression of isthmic spondylolisthesis in a pediatric patient?

Explanation

A high slip angle, typically greater than 45 to 50 degrees, is the most significant radiographic predictor for the progression of isthmic spondylolisthesis. Other risk factors include young age at presentation, female gender, and dysplastic morphology.

Question 52

During an anterior cruciate ligament (ACL) reconstruction, inadvertently placing the femoral tunnel too anteriorly will result in which of the following postoperative complications?

Explanation

An anteriorly placed femoral tunnel causes the ACL graft to tighten excessively as the knee moves into flexion. This results in a mechanical block and significant loss of postoperative flexion.

Question 53

According to the Ponseti method for the treatment of congenital idiopathic clubfoot, which of the following deformities must be corrected first?

Explanation

The first step in the Ponseti technique is correcting the midfoot cavus, which is achieved by elevating the first ray to align the forefoot with the hindfoot. This provides a solid foundation for the subsequent correction of adduction, varus, and finally equinus (the CAVE sequence).

Question 54

The primary blood supply to the proximal pole of the scaphoid is derived from which of the following vessels?

Explanation

The dorsal carpal branch of the radial artery supplies the proximal 80% of the scaphoid via retrograde intraosseous blood flow. This retrograde supply makes the proximal pole highly susceptible to avascular necrosis following a fracture.

Question 55

What is the most important prognostic factor for long-term survival in a patient with localized, non-metastatic osteosarcoma of the distal femur?

Explanation

The percentage of histologic tumor necrosis after neoadjuvant chemotherapy is the most critical prognostic indicator in localized osteosarcoma. A good response, defined as greater than 90% necrosis, correlates strongly with improved disease-free and overall survival rates.

Question 56

In a hypotensive polytrauma patient suspected of having compartment syndrome of the lower leg, which of the following criteria is the standard threshold for performing a four-compartment fasciotomy?

Explanation

The delta P (Diastolic blood pressure minus compartment pressure) is the most accurate indicator for compartment syndrome, particularly in hypotensive patients. A delta P of less than 30 mmHg is the accepted threshold indicating the need for emergent fasciotomy.

Question 57

Which of the following radiographic findings is the hallmark of Eichenholtz Stage 1 (developmental stage) Charcot arthropathy of the foot?

Explanation

Eichenholtz Stage 1 is the fragmentation or developmental stage, characterized clinically by severe inflammation and radiographically by periarticular fragmentation, debris, and joint subluxation or dislocation. Stage 2 is coalescence, and Stage 3 is reconstruction/consolidation.

Question 58

Denosumab is an effective pharmacological treatment for Giant Cell Tumor of bone. What is its specific mechanism of action?

Explanation

Denosumab is a monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This prevents RANKL from binding to the RANK receptor, thereby inhibiting the recruitment and activation of osteoclast-like giant cells in the tumor.

Question 59

During a total knee arthroplasty, the surgeon evaluates the gaps and notes that the knee is excessively tight in extension but well-balanced in 90 degrees of flexion. Which of the following surgical steps is most appropriate?

Explanation

A knee that is tight in extension but balanced in flexion requires enlarging the extension gap without altering the flexion gap. Resecting more distal femur or releasing the posterior capsule selectively achieves this.

Question 60

Bone morphogenetic protein-2 (BMP-2) enhances spinal fusion through which of the following cellular mechanisms?

Explanation

BMP-2 is a potent osteoinductive protein that binds to cell surface serine/threonine kinase receptors on mesenchymal stem cells. This binding activates the intracellular SMAD signaling pathway, driving the differentiation of these cells into functioning osteoblasts.

Question 61

The primary stabilizing ligament of the Lisfranc joint complex connects which of the following osseous structures?

Explanation

The Lisfranc ligament is a strong interosseous ligament that runs from the lateral aspect of the medial cuneiform to the medial aspect of the base of the second metatarsal. It is the primary stabilizer of the second tarsometatarsal joint.

Question 62

Which zone of articular cartilage is characterized by the lowest water content, the highest concentration of proteoglycans, and collagen fibers oriented perpendicular to the joint surface?

Explanation

The deep (radial) zone of articular cartilage has the highest proteoglycan concentration and the lowest water content, with collagen fibers running vertically to resist compressive forces. Conversely, the superficial zone has the highest water content and lowest proteoglycan concentration.

Question 63

A rupture of the ulnar collateral ligament (UCL) of the thumb metacarpophalangeal (MCP) joint primarily leads to instability when which of the following forces is applied?

Explanation

The UCL of the thumb prevents excessive abduction at the MCP joint. Therefore, injury to this structure (commonly known as Gamekeeper's or Skier's thumb) results in instability and laxity when a valgus stress is applied.

Question 64

An 8-year-old female presents with bilateral slipped capital femoral epiphysis (SCFE). Given her age and presentation, which of the following laboratory investigations is most appropriate?

Explanation

Patients presenting with SCFE outside the typical age range (under 10 or over 16) or with bilateral involvement should be screened for underlying endocrine disorders. Hypothyroidism is the most common associated endocrinopathy, making TSH the best initial screening test.

Question 65

A 40-year-old male sustains a bicondylar tibial plateau fracture with a large posteromedial shear fragment. Which surgical approach is most appropriate for rigid fixation of this specific fragment?

Explanation

A posteromedial shear fragment in a tibial plateau fracture cannot be adequately reduced or buttressed from an anterior or lateral approach. A posteromedial approach is required to directly visualize the fragment and place an anti-glide or buttress plate.

Question 66

A 25-year-old male sustains a closed, completely displaced midshaft humerus fracture. In the emergency department, he is noted to have a complete radial nerve palsy that was present immediately after the injury. What is the most appropriate initial management?

Explanation

A primary radial nerve palsy in the setting of a closed humeral shaft fracture is not an absolute indication for immediate surgical exploration. The initial management is functional bracing and observation, as the majority of these neuropraxias resolve spontaneously.

Question 67

A positive Finkelstein's test in a patient with De Quervain's tenosynovitis is caused by irritation of which of the following tendon groups as they pass through the first dorsal compartment?

Explanation

De Quervain's tenosynovitis involves stenosing inflammation of the first dorsal compartment of the wrist. This compartment contains the tendons of the abductor pollicis longus (APL) and the extensor pollicis brevis (EPB).

Question 68

During posterior spinal fusion for severe adolescent idiopathic scoliosis, a sudden drop in somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) is noted following deformity correction. What is the most likely neurologic syndrome if the cord becomes ischemic?

Explanation

Spinal cord ischemia during scoliosis surgery, typically due to over-distraction or hypotension, preferentially affects the anterior spinal artery watershed areas. This leads to anterior cord syndrome, which presents with motor paralysis and loss of pain/temperature sensation but preserved dorsal column function (proprioception).

Question 69

Aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) is a known complication of metal-on-metal total hip arthroplasty. This localized tissue reaction is primarily mediated by which of the following immune responses?

Explanation

ALVAL is an adverse local tissue reaction to metal debris (typically cobalt and chromium) seen in metal-on-metal implants. It is characterized histologically by a perivascular lymphocytic infiltrate, representing a Type IV (cell-mediated) delayed-type hypersensitivity reaction.

Question 70

According to the modified Gartland classification for pediatric supracondylar humerus fractures, which of the following best describes a Type III injury?

Explanation

In the Gartland classification, a Type I fracture is nondisplaced, and a Type II fracture is displaced but has an intact posterior hinge. A Type III fracture is completely displaced with no cortical contact, presenting a higher risk for neurovascular compromise.

Question 71

In the Levine-Edwards classification of traumatic spondylolisthesis of the axis, which mechanism is associated with a Type IIA fracture?

Explanation

Type IIA Hangman's fractures are caused by flexion and distraction, resulting in severe angulation with minimal translation. Traction is strictly contraindicated as it can exacerbate the deformity and cause neurologic injury.

Question 72

Articular cartilage is divided into distinct zones. Which of the following best describes the organization of collagen fibers in the superficial (tangential) zone?

Explanation

In the superficial zone, collagen fibers are packed tightly and oriented parallel to the articular surface. This arrangement is highly specialized to resist shear stresses and provide a low-friction gliding surface.

Question 73

A 32-year-old male sustains a closed tibial shaft fracture. Which of the following pressure measurements is considered the most reliable threshold for diagnosing acute compartment syndrome?

Explanation

A delta pressure (diastolic blood pressure minus compartment pressure) of less than 30 mmHg is the most reliable objective indicator for fasciotomy. Absolute pressure thresholds are less reliable due to variations in patient hemodynamics.

Question 74

Which of the following is an absolute indication for prophylactic in situ pinning of the contralateral asymptomatic hip in a patient with a unilateral slipped capital femoral epiphysis (SCFE)?

Explanation

Prophylactic contralateral pinning is highly recommended in patients with endocrine or metabolic disorders, as they have a significantly higher rate of bilateral involvement. Other relative indications include previous radiation therapy and young age (<10 years).

Question 75

A 14-year-old boy presents with a diaphyseal femur lesion showing an 'onion skin' periosteal reaction. A biopsy is planned. Which specific chromosomal translocation is most characteristically associated with this pathology?

Explanation

Ewing sarcoma is classically characterized by the t(11;22)(q24;q12) translocation, resulting in the EWS-FLI1 fusion protein. Synovial sarcoma is t(X;18), and myxoid liposarcoma is t(12;16).

Question 76

Following an anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone autograft, at what postoperative time frame is the graft biomechanically at its weakest?

Explanation

The graft is at its weakest during the remodeling phase, typically around 6 to 8 weeks postoperatively. This corresponds to the period where revascularization and cellular repopulation actively degrade the initial graft tissue before new collagen synthesis predominates.

Question 77

A 25-year-old rugby player sustains a flexor digitorum profundus (FDP) avulsion from the distal phalanx of the ring finger. Radiographs show a large bony fragment retracted to the level of the A4 pulley. What is the Leddy and Packer classification of this injury?

Explanation

Leddy and Packer Type III injuries involve a large bony avulsion that catches at the A4 pulley, preventing further proximal retraction of the tendon. Type I retracts into the palm, and Type II retracts to the PIP joint level (A3 pulley).

Question 78

Which ligament is the primary stabilizing structure of the Lisfranc joint complex?

Explanation

The Lisfranc ligament is a strong plantar interosseous ligament that connects the medial cuneiform to the base of the second metatarsal. There is no direct ligamentous connection between the bases of the first and second metatarsals, making this area inherently vulnerable to injury.

Question 79

In total hip arthroplasty, which of the following mechanisms is primarily responsible for osteolysis induced by ultra-high molecular weight polyethylene (UHMWPE) wear debris?

Explanation

Polyethylene wear debris measuring 0.1 to 10 micrometers is phagocytosed by macrophages, which then release pro-inflammatory cytokines such as TNF-alpha, IL-1, and IL-6. This cascade stimulates osteoclast differentiation and activity, leading to periprosthetic osteolysis.

Question 80

Bone morphogenetic proteins (BMPs) initiate intracellular signaling leading to osteoblast differentiation primarily through which of the following pathways?

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, which phosphorylate Smad 1, 5, and 8. These receptor-regulated Smads then form a complex with Smad 4 to enter the nucleus and regulate the transcription of osteogenic genes.

Question 81

In the lateral pillar classification of Legg-Calvé-Perthes disease described by Herring, which portion of the femoral head is evaluated on the anteroposterior radiograph to determine the prognosis?

Explanation

The Herring lateral pillar classification evaluates the height of the lateral third of the capital femoral epiphysis on an AP radiograph during the fragmentation stage. Maintenance of lateral pillar height is the most significant prognostic indicator for long-term hip congruency.

Question 82

Which of the following vascular structures provides the primary blood supply to the humeral head, and is at greatest risk in a displaced surgical neck fracture of the humerus?

Explanation

Recent anatomical studies and quantitative analyses have demonstrated that the posterior humeral circumflex artery provides the predominant blood supply (up to 64%) to the humeral head. This refutes classical teaching that heavily emphasized the anterolateral branch of the anterior humeral circumflex artery.

Question 83

A 55-year-old diabetic patient presents with progressive back pain, fever, and lower extremity weakness. MRI reveals a spinal epidural abscess. What is the most common causative organism and the most frequent mechanism of spread?

Explanation

Staphylococcus aureus is the most common organism responsible for spinal epidural abscesses. The most frequent mechanism of infection is hematogenous dissemination from a distant source, such as skin, respiratory, or urinary tract infections.

Question 84

A 32-year-old male presents with a slowly enlarging, painful mass near his knee joint. MRI reveals a soft tissue mass adjacent to the joint space. Biopsy demonstrates a biphasic pattern of spindle cells and epithelial cells. Which of the following chromosomal translocations is most characteristic of this lesion?

Explanation

Synovial sarcoma is characterized by the t(X;18) translocation, which results in the SYT-SSX fusion gene. It commonly presents in young adults as a calcified soft tissue mass near, but rarely within, a joint.

Question 85

A 45-year-old falls on an outstretched hand and sustains a "terrible triad" injury of the elbow. During surgical reconstruction, what is the most appropriate sequence of repair to restore elbow stability?

Explanation

The standard surgical sequence for a terrible triad injury is to reconstruct from deep to superficial: coronoid fixation first, followed by radial head repair or replacement, and finally LUCL repair. If the elbow remains unstable, the medial collateral ligament may be addressed last.

Question 86

A 12-year-old obese male presents with acute-on-chronic left hip pain and an inability to bear weight. Radiographs confirm an unstable slipped capital femoral epiphysis (SCFE). Which of the following represents the most significant risk associated with urgent, aggressive closed reduction of this injury prior to pinning?

Explanation

Forceful or aggressive closed reduction of an unstable SCFE significantly increases the risk of avascular necrosis (AVN) of the femoral head. Gentle, incidental reduction during patient positioning is acceptable, but intentional forceful manipulation is contraindicated.

Question 87

When planning a tendon transfer procedure for a patient with radial nerve palsy, the surgeon must consider muscle mechanics. Muscle excursion is primarily determined by which of the following characteristics?

Explanation

Muscle excursion, which is the distance a muscle can contract, is proportional to the length of its resting muscle fibers. In contrast, a muscle's force-generating capacity is determined by its physiological cross-sectional area.

Question 88

A 55-year-old diabetic patient presents with a swollen, erythematous, and warm foot with no systemic signs of infection. Radiographs show fragmentation, joint subluxation, and extensive osseous debris in the midfoot. According to the Eichenholtz classification, what is the most appropriate initial management?

Explanation

The patient is in Eichenholtz Stage I (Developmental/Fragmentation) of Charcot arthropathy. The gold standard of initial management is immediate immobilization with a total contact cast and strict non-weight bearing until the active inflammatory phase subsides.

Question 89

An 82-year-old male sustains a Type II odontoid fracture after a ground-level fall. He is neurologically intact. Which of the following radiographic parameters is the strongest predictor of nonunion for this injury if treated conservatively with a rigid cervical collar?

Explanation

Major risk factors for nonunion in Type II odontoid fractures include initial displacement greater than 5 mm, angulation greater than 10 degrees, and age over 50 years. Fracture extension into the C2 body describes a Type III fracture, which has a much higher rate of union.

Question 90

A 24-year-old athlete sustains a severe knee twist. Physical examination reveals an isolated increase in external tibial rotation of 15 degrees compared to the contralateral knee at 30 degrees of flexion, but symmetrical rotation at 90 degrees of flexion. Injury to which of the following structures is most likely responsible?

Explanation

A positive dial test showing increased external rotation at 30 degrees of flexion that reduces at 90 degrees indicates an isolated injury to the posterolateral corner (PLC). The popliteofibular ligament is one of the three primary static stabilizers of the PLC.

Question 91

A 65-year-old male presents with groin pain three years after a total hip arthroplasty utilizing a metal-on-polyethylene bearing. Aspiration reveals dark fluid negative for infection, and serum cobalt levels are significantly elevated compared to chromium levels. What is the most likely etiology of his symptoms?

Explanation

Elevated cobalt levels out of proportion to chromium levels in a metal-on-polyethylene THA is highly suggestive of mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck junction. This leads to an adverse local tissue reaction (ALTR) presenting with pain and soft tissue damage.

Question 92

A 35-year-old carpenter sustains a puncture wound to his index finger. He presents 48 hours later with severe pain and swelling. Which of the following Kanavel signs is generally considered the most reliable and earliest indicator of acute suppurative flexor tenosynovitis?

Explanation

Kanavel's four cardinal signs of flexor tenosynovitis include flexed resting posture, fusiform swelling, tenderness along the flexor tendon sheath, and pain with passive extension. Exquisite pain with passive extension is typically the earliest and most sensitive clinical indicator of this surgical emergency.

Question 93

Which of the following bone graft or bone graft substitute materials simultaneously possesses osteoinductive, osteoconductive, and osteogenic properties?

Explanation

Autologous bone graft, such as from the iliac crest, is considered the gold standard because it provides all three properties necessary for bone healing. It supplies an osteoconductive scaffold, osteoinductive growth factors, and live osteogenic progenitor cells.

Orthopedic Prometric Exam Preparation MCQs - Part 1

Orthopedic Prometric Exam Preparation MCQs - Part 19

Orthopedic Prometric Exam Preparation MCQs - Part 19

Chapter Index