Question 1

The recommended interval for changing wound vacuum assisted closure (VAC ) dressings is:

Explanation

The preferred interval for changing VAC dressings is every 2 days. Patients may have significant discomfort with initial dressing changes; however, the pain usually diminishes rapidly.

Question 2

In children with Ewingâ s sarcoma, the risk of local recurrence at the tumor site after treatment is greatest in which region:

Explanation

The risk of local recurrence is greatest for Ewings sarcomas arising in the pelvis. The prognosis is poor. Many centers attempt resection of the pelvis if there is a good response to chemotherapy.

Question 3

What is the histological difference between avascular necrosis of the femoral head in children versus adults:

Explanation

Avascular necrosis models of the femoral head in immature animals show more osteoclastic resorption, fibroblastic response, and little creeping substitution when compared to models of mature animals. Osseous collapse is common, and there are often longterm residual changes in the shape of the femoral head.

Question 4

Which of the following is a principle of the Ponseti technique for correction of a clubfoot:

Explanation

The Ponseti technique, which was developed and tested by Ignacio Ponseti, MD, involves slow, gradual correction of a clubfoot using casts, a tenotomy if necessary to release the Achilles tendon, and maintenance of correction using braces (foot abduction orthoses) for several years. The technique avoids dissection of the growing bones and joints of a childs foot because of the associated risks of stiffness and growth disturbance.

Question 5

Which of the following pulse sequences is best for showing anatomy on magnetic resonance imaging (MRI):

Explanation

T1-weighted images generally display the best anatomical detail. Fat is bright, and muscle is dark, giving excellent contrast. Cortical bone, tendons, and ligaments are low signal.

Question 6

Which of the following pulse sequences is best for imaging the pediatric growth plate:

Explanation

The gradient echo sequence involves a short relaxation and excitation time. It shows both fat and water as intermediate signals. The gradient echo sequence is excellent for imaging physeal and articular cartilage. When imaging for a physeal bar, the physician ordering the magnetic resonance imaging should specify this sequence.

Question 7

Motion artifact in magnetic resonance imaging of the pediatric spine is caused by all of the following except:

Explanation

Motion artifact affects magnetic resonance imaging of the spine and can result from patient movement (common in children under 8 years old), cardiac activity, respiration, and cerebrospinal fluid flow. Presence of a titanium rod in a childs femur, while causing a local signal void, does not affect spinal imaging.

Question 8

There are no internal moments in the lower extremity during which phase of gait:

Explanation

Preswing is the only phase of gait in which all muscle groups are silent in the ipsilateral lower extremity. In the next phase (initial swing), internal moments are generated at the hip and ankle to initiate swing.

Question 9

The protein neurofibromin normally acts in which of the following ways:

Explanation

If defective, neurofibromin is the protein that causes neurofibromatosis. Neurofibroma is coded on chromosome 17, and it acts as a tumor suppressor by downregulating Ras protein, which enhances cell growth and proliferation.

Question 10

According to National Institutes of Health (NIH) criteria, what is the minimum number of 15-mm cafa-au-lait macules required as a diagnostic criterion for neurofibromatosis in postpubertal patients:

Explanation

The NIH criteria require at least six 15-mm cafa-au-lait macules in postpubertal patients. Cafa-au-lait macules must be larger than 5 mm in prepubertal patients.

Question 11

A 7-year-old girl presents with an acute fracture of her proximal radial metaphysis. Although a line down the shaft of the radius intersects the center of the capitellum, the articular surface of the radial head is angled 20° from the anatomic position as compared with the other elbow. You recommend:

Explanation

Proximal radial fractures have excellent remodeling potential, especially if the angulation is less than 30°. Manipulation is not necessary, and the risk of stiffness from any invasive procedure is not worthwhile.

Question 12

Which of the following findings is typical in patients with Marfan syndrome as opposed to patients with Ehlers-Danlos syndrome:

Explanation

All of the findings presented, with the exception of lens dislocation, are seen in both syndromes at a frequency that exceeds the general population. Lens dislocation is common in patients with Marfan syndrome but not those with Ehlers-Danlos syndrome.

Question 13

Ehlers-Danlos syndrome is caused by a defect in which of the following:

Explanation

There are 11 subtypes of Ehlers-Danlos syndrome. Each of the subtypes is caused by defects in collagen types 1, 3, or 5, or their processing. Defects in a component of elastic microfibrils (fibrillin) are responsible for Marfan syndrome. Defects in dermatan sulfate processing cause Hurler syndrome. Defects in fibroblast growth factor cause achondroplasia. Defects in proteoglycan processing cause diastrophic dysplasia.

Question 14

A 4-year-old boy with macrodactyly of the foot has involvement of the second and third rays. He undergoes debulking of the soft tissues of the phalanges and amputation of the distal phalanges. Two years later, he returns with a dramatic increase in the width and length of the involved regions. You recommend:

Explanation

The increase in width of the involved regions can be handled only by ray resection. Additional proximal levels of amputation are not required.

Question 15

A 14-year-old girl is kicking a soccer ball when she feels a â popâ in her hip. The most likely diagnosis is:

Explanation

This is a classic description of avulsion of the anterior inferior iliac spine. When this patient hyperextended her hip and flexed her knee simultaneously to kick a ball, the rectus femoris was stretched at both joints. In a skeletally immature patient, this apophysis is not fully ossified and is vulnerable to avulsion. Treatment is symptomatic, with return to sports in about 6 weeks.

Question 16

A 3-year-old boy has a progressive anterior bow of the right tibia. He experiences intermittent aching. His physical examination is otherwise unremarkable. Radiographs reveal 25° of anterior bow of the tibia just distal to the midshaft and 20° of lateral bow. There is some narrowing of the medullary canal around the bow and thinning of the anterior cortex. You recommend which course of action:

Explanation

This patient has a congenitally dysplastic tibia. The tibia is at risk for fracture, but orthotic protection is sometimes successful in preventing fracture. Operative intervention should be reserved for fracture because there is a significant risk of nonunion or delayed union.

Question 17

An 8-year-old patient with cerebral palsy has an equinovarus foot on the right side. The varus is worse during push-off. He also holds his right upper extremity stiffly when he walks. He is developing a pressure callus on the lateral side of his foot in the region of the calcaneocuboid joint. Passively, the foot can be corrected to a neutral position of varus-valgus but lacks 12Â° from neutral dorsiflexion. Your recommendation is:

Explanation

An equinovarus foot is commonly found in patients with hemiplegic cerebral palsy. The varus aspect is difficult to brace. In this patient with fixed equinus, an AFO would not be a successful treatment option. A lengthening of the triceps surae would be indicated, and it could be done at the level of the Achilles tendon or by a gastrocnemius-soleus recession, depending on the clinical examination. In addition, another procedure is necessary to deal with the varus. The best way to accomplish this would be by split posterior tibial tendon transfer. This patient is too young for a triple arthrodesis, as this procedure is appropriate in patients at or near skeletal maturity with rigid deformity.

Question 18

Hip subluxation is most commonly seen in which type of cerebral palsy:

Explanation

Neuromuscular subluxation of the hips is caused by muscle imbalance over time. It is most common in patients with greatest imbalance â total body involvement. Hip subluxation is rare in patients with spastic hemiplegia.

Question 19

Which group of cerebral palsy patients is most likely to sustain a pathologic fracture:

Explanation

Pathologic fracture is most common in cerebral palsy patients with total involvement, presumably because they have little stress on the bone from either muscle tone or standing.

Question 20

Which is the most common location of pathologic fracture in patients with cerebral palsy:

Explanation

Pathologic fracture is a common problem in patients with cerebral palsy. Pathologic fracture most commonly involves the femur, especially the shaft and distal metaphysis. This should be the first diagnostic consideration in a nonambulatory patient with a warm or swollen knee.

Question 21

Which of the following chromosomal translocations is most commonly associated with Ewing's sarcoma?

Explanation

Ewing's sarcoma is most commonly associated with the t(11;22) translocation, which results in the EWS-FLI1 fusion protein. Other classic translocations include t(X;18) for synovial sarcoma and t(9;22) for extraskeletal myxoid chondrosarcoma.

Question 22

In which of the following scenarios is prophylactic percutaneous pinning of the contralateral hip most strongly indicated in a patient with a unilateral slipped capital femoral epiphysis (SCFE)?

Explanation

Prophylactic pinning of the contralateral hip is highly recommended for patients with SCFE who have underlying endocrine disorders (e.g., hypothyroidism) or are younger than 10 years old, due to a significantly elevated risk of bilateral involvement.

Question 23

A 45-year-old farmer sustains an open tibia fracture with gross soil and manure contamination. Which of the following antibiotic regimens is most appropriate for initial management in the emergency department?

Explanation

Farm injuries with gross soil or manure contamination are at high risk for clostridial infection. The addition of high-dose penicillin to a first-generation cephalosporin and an aminoglycoside provides the necessary anaerobic coverage.

Question 24

During anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone autograft, incorporation of the bony ends into the tunnels occurs primarily via which of the following processes?

Explanation

Bone-to-bone healing in tunnels (such as with a BTB graft) occurs via creeping substitution, where osteoclasts resorb the grafted bone and osteoblasts lay down new bone. Conversely, soft tissue grafts heal via a fibrovascular interface.

Question 25

Which of the following is considered the most sensitive clinical indicator of early cauda equina syndrome?

Explanation

Urinary retention is the most sensitive early clinical sign of cauda equina syndrome, often evaluated objectively by measuring post-void residual volume. Saddle anesthesia and fecal incontinence are typically later findings.

Question 26

In severe carpal tunnel syndrome, which of the following electromyography (EMG) or nerve conduction velocity (NCV) findings is most indicative of irreversible axonal damage?

Explanation

Fibrillation potentials and positive sharp waves on EMG indicate active axonal denervation of the muscle, signifying significant and potentially irreversible damage. Prolonged latencies reflect demyelination but not necessarily permanent axonal loss.

Question 27

Which of the following molecules binds directly to RANK on the surface of osteoclast precursors to stimulate their differentiation into mature osteoclasts?

Explanation

Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), produced by osteoblasts, binds directly to RANK on osteoclast precursors to induce differentiation. Osteoprotegerin (OPG) is a decoy receptor that binds RANKL, inhibiting this process.

Question 28

A diabetic patient presents with a swollen, erythematous, but painless foot. Radiographs show extensive bone fragmentation, subluxation, and joint debris without significant sclerosis. According to the Eichenholtz classification, what stage of Charcot arthropathy does this represent?

Explanation

Eichenholtz Stage 1 (Development) is characterized by acute inflammation, joint laxity, subluxation, bone fragmentation, and debris formation. Stage 2 (Coalescence) shows absorption of fine debris and early sclerosis.

Question 29

Which of the following bearing surface combinations in total hip arthroplasty is most closely associated with the complication of "squeaking"?

Explanation

Squeaking is a well-documented specific complication associated with ceramic-on-ceramic bearings. Risk factors include impingement, edge loading, and component malposition.

Question 30

A 65-year-old male presents with bone pain and a lytic lesion in his proximal femur. Laboratory studies reveal hypercalcemia and a monoclonal spike on serum protein electrophoresis. Which imaging modality is most appropriate to evaluate the extent of skeletal involvement?

Explanation

Low-dose whole-body CT or whole-body MRI are the preferred imaging modalities for assessing skeletal involvement in multiple myeloma. Technetium-99m bone scans are notoriously unreliable because myeloma lesions typically lack osteoblastic activity.

Question 31

According to the Young-Burgess classification, an anteroposterior compression (APC) type III pelvic ring injury is characterized by which of the following?

Explanation

An APC type III injury involves disruption of the anterior ring along with complete disruption of both the anterior and posterior sacroiliac ligaments. This results in a globally unstable hemipelvis.

Question 32

During the Ponseti method of serial casting for idiopathic clubfoot, what is the first deformity that must be actively corrected?

Explanation

The cavus deformity must be corrected first by elevating the first ray to align the forefoot with the hindfoot. Correction of the remaining deformities (adduction, varus, and finally equinus) follows sequentially in subsequent casts.

Question 33

Which of the following annular pulleys are most biomechanically critical to prevent bowstringing of the flexor tendons in the finger?

Explanation

The A2 and A4 pulleys are the most robust and biomechanically critical for preventing bowstringing of the flexor tendons. They are located over the proximal and middle phalanges, respectively.

Question 34

The phenomenon whereby a ligament or tendon demonstrates increasing length over time under a constant applied load is known as:

Explanation

Creep is defined as the progressive deformation of a viscoelastic material over time when subjected to a constant load. Stress relaxation is the decrease in stress over time when the material is held at a constant length.

Question 35

In the setting of recurrent anterior shoulder instability, a large engaging Hill-Sachs lesion is best managed surgically by which of the following procedures?

Explanation

An engaging Hill-Sachs lesion can lever the humeral head out of the glenoid, causing recurrent instability. The remplissage procedure fills the defect with the infraspinatus tendon and capsule, preventing engagement when combined with a Bankart repair.

Question 36

When measuring intra-compartmental pressures to diagnose acute compartment syndrome, which of the following thresholds is the most widely accepted indicator for performing an emergent fasciotomy?

Explanation

A delta pressure (diastolic blood pressure minus intra-compartmental pressure) of less than 30 mmHg is the most reliable objective threshold for diagnosing acute compartment syndrome and indicates the need for emergent fasciotomy.

Question 37

Which of the following preoperative deformities in a patient undergoing total knee arthroplasty (TKA) carries the highest risk of postoperative peroneal nerve palsy?

Explanation

Severe fixed valgus deformities, especially when combined with a flexion contracture, place the peroneal nerve at significant risk of traction injury when the limb is surgically corrected to a neutral mechanical axis.

Question 38

On an infant hip ultrasound used to evaluate developmental dysplasia of the hip (DDH), the alpha angle is defined by the intersection of the baseline (iliac wing) and which other structure?

Explanation

The alpha angle measures the bony roof of the acetabulum and is formed by the intersection of the baseline (parallel to the iliac wing) and the bony roof line. An alpha angle greater than 60 degrees is considered normal.

Question 39

Which of the following best describes the mechanism of action of rivaroxaban, an oral anticoagulant commonly used for venous thromboembolism prophylaxis after total joint arthroplasty?

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants that work by directly inhibiting Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor, while low-molecular-weight heparins act indirectly via antithrombin III.

Question 40

A 30-year-old female presents with a destructive, eccentrically located lytic lesion extending into the epiphysis of the distal femur. Biopsy confirms a Giant Cell Tumor of bone. If medical therapy is considered for downstaging prior to surgery, which of the following agents is most appropriate?

Explanation

Denosumab, a monoclonal antibody against RANKL, is highly effective in treating Giant Cell Tumor of bone by inhibiting the RANKL-mediated osteoclast-like giant cells. It is frequently used to downstage large tumors or treat unresectable disease.

Question 41

In the treatment of extremity osteosarcoma, what percentage of tumor necrosis following neoadjuvant chemotherapy is defined as a "good response" and correlates with improved long-term survival?

Explanation

A "good response" to neoadjuvant chemotherapy in osteosarcoma is defined as greater than 90% tumor necrosis (Huvos grade III or IV). This is a strong independent prognostic factor for long-term survival.

Question 42

Denosumab is increasingly used in the management of unresectable Giant Cell Tumor of bone. What is its exact mechanism of action?

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL, preventing it from interacting with the RANK receptor on osteoclast precursors. This inhibits the maturation and function of the osteoclast-like giant cells, thereby reducing osteolysis.

Question 43

According to the Herring lateral pillar classification for Legg-Calve-Perthes disease, a patient in Group C has what characteristic radiographic finding?

Explanation

In the Herring lateral pillar classification, Group C is characterized by the maintenance of less than 50% of the normal lateral pillar height. This group has the poorest prognosis and highest risk of secondary osteoarthritis.

Question 44

While treating a 6-week-old infant with developmental dysplasia of the hip (DDH) using a Pavlik harness, you note the infant lacks active knee extension on the treated side. What is the most likely cause?

Explanation

Excessive hip flexion in a Pavlik harness can lead to compression of the femoral nerve against the rim of the pelvis, causing a transient femoral nerve palsy. Excessive abduction, on the other hand, is classically associated with avascular necrosis.

Question 45

Prophylactic pinning of the contralateral hip in a patient presenting with a unilateral slipped capital femoral epiphysis (SCFE) is most strongly indicated in which of the following scenarios?

Explanation

Prophylactic pinning of the contralateral hip in SCFE is recommended for patients with underlying endocrine or metabolic disorders (like hypothyroidism or renal osteodystrophy) due to the very high risk of bilateral involvement.

Question 46

According to Perren's strain theory, what level of tissue strain is required to allow for primary bone healing (direct Haversian remodeling) without callus formation?

Explanation

Primary bone healing requires absolute stability with an interfragmentary strain of less than 2%. Strains between 2% and 10% promote secondary bone healing with callus formation.

Question 47

In a patient with a tibial shaft fracture and suspected acute compartment syndrome, which of the following pressure measurements is the most reliable threshold for performing a fasciotomy?

Explanation

The delta P (diastolic blood pressure minus compartment pressure) is the most reliable indicator for compartment syndrome. A delta P of less than 30 mmHg represents critical tissue ischemia and is a strict indication for emergent fasciotomy.

Question 48

What is the most sensitive early clinical finding in patients developing cauda equina syndrome?

Explanation

Urinary retention is typically the first and most sensitive sign of cauda equina syndrome. A post-void residual volume of less than 100 mL practically rules out the diagnosis in suspected cases.

Question 49

In flexor tendon anatomy, Camper's chiasm refers to which of the following structures?

Explanation

Camper's chiasm is the anatomical point in Zone II where the Flexor Digitorum Superficialis (FDS) tendon splits into two slips. This bifurcation allows the Flexor Digitorum Profundus (FDP) tendon to pass through and become superficial.

Question 50

A 72-year-old patient presents with severe shoulder pain, pseudoparalysis, and radiographs showing superior migration of the humeral head with "acetabularization" of the acromion. What is the most appropriate surgical treatment?

Explanation

The clinical and radiographic findings describe severe rotator cuff tear arthropathy (Hamada stage III or higher). Reverse total shoulder arthroplasty is the treatment of choice as it shifts the center of rotation medially and inferiorly, allowing the deltoid to effectively elevate the arm.

Question 51

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

Explanation

An anteriorly placed femoral tunnel in ACL reconstruction causes the graft distance to increase during knee flexion. This results in the graft being overly tight in flexion, causing restricted knee motion and potential graft stretching or rupture.

Question 52

The medial patellofemoral ligament (MPFL) is the primary restraint to lateral patellar translation. Where is its anatomic origin on the femur located (Schottle's point)?

Explanation

Radiographically, Schottle's point defines the femoral footprint of the MPFL. It is located just anterior to a line extending the posterior femoral cortex, between the adductor tubercle proximally and the medial epicondyle distally.

Question 53

Six weeks following a displaced talar neck fracture treated with open reduction and internal fixation, a radiograph reveals a subchondral radiolucent line in the dome of the talus (Hawkins sign). What does this finding indicate?

Explanation

A positive Hawkins sign is a subchondral radiolucent band in the talar dome seen at 6-8 weeks post-injury. It represents subchondral osteopenia from disuse and hyperemia, reliably indicating that the vascular supply to the talar body is intact.

Question 54

A patient undergoes volar plating for a distal radius fracture. Six months later, the patient cannot actively flex the interphalangeal joint of the thumb. What technical error during the initial surgery is the most likely cause?

Explanation

Rupture of the flexor pollicis longus (FPL) tendon is a known complication of volar distal radius plating. It most commonly occurs when the plate is placed too distally, crossing the "watershed line," causing mechanical attrition of the tendon.

Question 55

In the Denis classification of sacral fractures, fractures occurring in Zone III are most highly associated with which of the following complications?

Explanation

The Denis classification divides sacral fractures into three zones: alar (Zone I), foraminal (Zone II), and central canal (Zone III). Zone III fractures involve the central sacral canal and have the highest rate (up to 60%) of neurologic deficits, notably bowel, bladder, and sexual dysfunction.

Question 56

In the pathophysiology of chronic osteomyelitis, what is the term used to describe the segment of necrotic bone that has become separated from the surrounding viable bone?

Explanation

A sequestrum is a piece of dead, devascularized bone that separates from normal bone in chronic osteomyelitis. The involucrum is the new bone formation that surrounds the sequestrum.

Question 57

In a patient diagnosed with high-grade osteosarcoma of the distal femur, what is the most important prognostic factor for long-term survival?

Explanation

The histologic response to neoadjuvant chemotherapy (percentage of tumor necrosis) is the most critical prognostic factor in high-grade osteosarcoma. Greater than 90% necrosis indicates a favorable prognosis.

Question 58

A 35-year-old female presents with a recurrent giant cell tumor of the distal radius. She is treated with denosumab. What is the specific cellular mechanism of action of this medication?

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from binding to RANK on osteoclast precursors. This inhibits osteoclast-mediated bone resorption, which is heavily upregulated by the neoplastic stromal cells in giant cell tumors.

Question 59

A soft tissue mass is biopsied from the foot of a 25-year-old male. Histology shows a biphasic pattern of epithelial and spindle cells. Which of the following chromosomal translocations is characteristic of this tumor?

Explanation

Synovial sarcoma is characterized by the t(X;18) translocation, leading to the SYT-SSX fusion gene. It commonly presents in the extremities of young adults and can exhibit biphasic or monophasic histology.

Question 60

Which of the following clinical or radiographic features is most suggestive of malignant transformation of an enchondroma into a secondary chondrosarcoma?

Explanation

Deep endosteal scalloping (greater than two-thirds of the cortical thickness), cortical breakthrough, and new-onset pain are strong indicators of malignant transformation to chondrosarcoma. Lesions in the hand are typically benign despite active histologic appearance.

Question 61

A 30-year-old female presents with a slowly enlarging mass on the posterior aspect of her distal thigh. Radiographs reveal a heavily ossified, lobulated mass attached to the posterior cortex of the distal femur. What is the characteristic genetic mutation associated with this lesion?

Explanation

Parosteal osteosarcoma is a low-grade surface osteosarcoma classically located on the posterior distal femur. It is driven by ring chromosomes leading to amplification of the MDM2 and CDK4 genes.

Question 62

In normal articular cartilage, which zone is characterized by the highest concentration of proteoglycans and vertically aligned type II collagen fibers?

Explanation

The deep (radial) zone of articular cartilage contains the highest concentration of proteoglycans. It has collagen fibers aligned perpendicular to the joint surface to resist high compressive loads.

Question 63

During the incorporation of a cortical bone allograft, the process of creeping substitution occurs. Which of the following accurately describes this mechanism?

Explanation

Creeping substitution in cortical bone involves osteoclastic resorption followed closely by osteoblastic bone formation via cutting cones. It is a significantly slower process compared to cancellous bone incorporation.

Question 64

Following a complete peripheral nerve transection, what is the earliest histologic change seen in the denervated skeletal muscle?

Explanation

The earliest histologic sign of denervation is the formation of target cells, which exhibit a central loss of myofibrils and oxidative enzymes. This precedes the eventual grouped atrophy seen in chronic denervation.

Question 65

During the remodeling phase of medial collateral ligament (MCL) healing, which biochemical transition is most prominent?

Explanation

During the remodeling phase of ligament healing, the initial, weaker Type III collagen produced during the proliferative phase is gradually replaced by stronger, more highly cross-linked Type I collagen.

Question 66

Which type of joint lubrication mechanism is most critical during low-load, low-speed activities such as standing or beginning to walk?

Explanation

Boundary lubrication, mediated by lubricin (PRG4) binding to the articular surface, prevents wear during high-load/low-speed or low-load/low-speed starting conditions. Fluid-film mechanisms dominate at higher speeds.

Question 67

In Legg-Calve-Perthes disease, the Herring Lateral Pillar classification is used to determine prognosis. At what stage of the disease is this classification most accurately applied?

Explanation

The Herring Lateral Pillar classification evaluates the height of the lateral third of the capital femoral epiphysis on an AP radiograph. It is most accurately and reliably applied during the early fragmentation phase.

Question 68

Which of the following is the primary pathophysiologic mechanism initiating skeletal muscle necrosis in acute compartment syndrome?

Explanation

Acute compartment syndrome occurs when elevated interstitial pressure decreases the local arteriovenous pressure gradient. This leads to compromised capillary perfusion and tissue ischemia, even while major arterial flow remains intact.

Question 69

Which enzyme is responsible for the conversion of 25-hydroxyvitamin D to its most active form, 1,25-dihydroxyvitamin D, and where is it predominantly located?

Explanation

The enzyme 1-alpha-hydroxylase, located in the proximal convoluted tubules of the kidney, converts 25-hydroxyvitamin D into the active hormone 1,25-dihydroxyvitamin D. This conversion is heavily stimulated by parathyroid hormone (PTH).

Question 70

According to the Kocher criteria, which combination strongly differentiates septic arthritis of the hip from transient synovitis in a pediatric patient?

Explanation

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

Question 71

A 13-year-old obese male presents with an unstable slipped capital femoral epiphysis (SCFE). Following in situ pinning, he develops severe, progressive restriction of hip motion without signs of infection. Radiographs show joint space narrowing. What is the most likely diagnosis?

Explanation

Chondrolysis involves rapid, progressive destruction of the articular cartilage. It is a known complication of SCFE, particularly associated with unrecognized intra-articular pin penetration, presenting with painful restriction of motion.

Question 72

A patient with osteopetrosis is found to have defective osteoclast function. The failure of osteoclasts to create an acidic environment for bone resorption is most commonly due to a mutation affecting which of the following?

Explanation

Osteopetrosis is often caused by a deficiency in Carbonic Anhydrase II, essential for generating protons. These protons are pumped into the ruffled border to create the acidic environment required to dissolve mineralized bone.

Question 73

Bone morphogenetic proteins (BMPs) initiate the osteoinductive cascade by binding to transmembrane receptors. This binding directly phosphorylates and activates which intracellular signaling molecules?

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, phosphorylating intracellular Smad proteins (1, 5, and 8). These form a complex with Smad 4 and translocate to the nucleus to regulate gene transcription for osteoblast differentiation.

Question 74

A patient is prescribed fondaparinux for DVT prophylaxis following total hip arthroplasty. What is the specific mechanism of action of this medication?

Explanation

Fondaparinux is a synthetic pentasaccharide that binds to antithrombin III, causing a conformational change that indirectly and selectively inhibits Factor Xa. Unlike Rivaroxaban, it is not a direct Factor Xa inhibitor.

Question 75

According to the Seddon classification, which type of peripheral nerve injury involves complete disruption of axons and myelin sheaths, but preservation of the endoneurium, perineurium, and epineurium?

Explanation

Axonotmesis involves the interruption of axons and their myelin sheaths with preservation of the surrounding connective tissue framework (endoneurium). This architectural preservation allows for spontaneous recovery as regenerating axons are guided to their original targets.

Question 76

Which sterilization technique for bone allografts provides the greatest reduction in viral transmission risk but significantly reduces the structural and biomechanical integrity of the graft?

Explanation

High-dose gamma irradiation (>3.0 Mrad) is highly effective at eradicating HIV and other viruses from allografts. However, it severely degrades collagen cross-links, drastically reducing the structural and biomechanical properties of the bone.

Question 77

Which histological feature is most characteristic of Grade 2 chondrosarcoma when differentiating it from Grade 1?

Explanation

Grade 2 chondrosarcomas demonstrate increased cellularity, nuclear atypia, and often prominent myxoid stroma compared to Grade 1. Host bone entrapment is a classic feature used to differentiate benign enchondroma from low-grade chondrosarcoma.

Question 78

A 3-month-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip. During a follow-up visit, the infant is noted to have a femoral nerve palsy. What is the most appropriate next step in management?

Explanation

Femoral nerve palsy in a Pavlik harness is typically caused by excessive hip flexion. The standard management is to remove the harness temporarily until the nerve recovers, which usually resolves spontaneously.

Question 79

In a hemodynamically unstable patient with an Anteroposterior Compression Type III (APC-III) pelvic ring injury, what is the most common anatomical source of major retroperitoneal hemorrhage?

Explanation

While arterial bleeding (such as the superior gluteal artery in APC/LC fractures) can be life-threatening, up to 80-90% of pelvic hemorrhage in trauma is venous in origin, primarily from the presacral and prevesical venous plexuses. Arterial bleeding accounts for a smaller percentage of cases.

Question 80

During the soft callus phase of secondary fracture healing, which type of collagen is primarily synthesized by the proliferating chondrocytes?

Explanation

During the soft callus phase, chondrocytes proliferate and primarily synthesize Type II collagen (cartilage matrix). As the callus matures into hard bone, osteoblasts replace this with Type I collagen.

Question 81

Which bearing surface combination in Total Hip Arthroplasty (THA) is associated with the lowest linear wear rate but carries the highest risk of catastrophic implant fracture?

Explanation

Ceramic-on-ceramic bearings offer the lowest wear rates of all combinations, making them appealing for young patients. However, they carry a unique, albeit low, risk of catastrophic brittle fracture of the ceramic components.

Question 82

What is the most significant prognostic factor for long-term survival in a pediatric patient treated for a high-grade intramedullary osteosarcoma of the distal femur?

Explanation

The degree of tumor necrosis following neoadjuvant chemotherapy is the most critical prognostic indicator in osteosarcoma. Greater than 90% tumor necrosis is associated with significantly higher long-term survival rates.

Question 83

A zone II flexor tendon laceration involves both the flexor digitorum profundus (FDP) and superficialis (FDS). Repairing both tendons, rather than the FDP alone, specifically helps prevent which of the following postoperative deformities?

Explanation

The FDS acts as a primary dynamic stabilizer of the PIP joint against hyperextension. Failing to repair the FDS can lead to PIP joint hyperextension and a subsequent swan neck deformity.

Question 84

In a 12-year-old boy presenting with a unilateral slipped capital femoral epiphysis (SCFE), prophylactic pinning of the contralateral asymptomatic hip is most strongly indicated if the patient has which of the following concomitant conditions?

Explanation

Endocrine disorders, such as hypothyroidism or renal osteodystrophy, significantly increase the risk of bilateral SCFE. Prophylactic pinning of the contralateral hip is strongly recommended in these atypical or syndromic cases.

Question 85

Which of the following continuous intracompartmental pressure criteria is the most reliable threshold for diagnosing acute compartment syndrome in a hypotensive trauma patient?

Explanation

The differential pressure (Delta P), calculated as Diastolic Blood Pressure minus Compartment Pressure, is the most accurate diagnostic threshold. A Delta P of less than 30 mmHg reliably indicates compromised tissue perfusion requiring fasciotomy.

Question 86

In a patient with cervical spondylotic myelopathy, the "finger escape sign" is characterized by the inability to maintain which digits in a fully extended and adducted position?

Explanation

The finger escape sign is a classic myelopathic finding where the patient cannot keep the ulnar digits (ring and small fingers) extended and adducted. They spontaneously drift into flexion and abduction.

Question 87

During an anterior cruciate ligament (ACL) reconstruction via an anteromedial portal, placing the knee in hyperflexion (greater than 110 degrees) while drilling the femoral tunnel primarily prevents which complication?

Explanation

Hyperflexing the knee when drilling the femoral tunnel through an anteromedial portal directs the drill trajectory more anteriorly. This prevents violating the posterior cortex of the lateral femoral condyle (posterior blowout).

Question 88

According to the Eichenholtz classification of Charcot arthropathy, which of the following radiographic findings characterizes the Coalescence stage (Stage II)?

Explanation

Stage II (Coalescence) is characterized by the absorption of fine bone debris, early fusion of larger fragments, and sclerosis. Stage I is fragmentation, and Stage III is consolidation and remodeling.

Question 89

Which element is specifically added to stainless steel alloys (e.g., 316L) to improve their resistance to pitting corrosion in the chloride-rich environment of the human body?

Explanation

Molybdenum is added to 316L stainless steel specifically to enhance resistance to pitting and crevice corrosion. Chromium provides the general passivation layer, while carbon is kept low (the "L" in 316L) to prevent intergranular corrosion.

Question 90

A patient presents with an inability to flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. Sensation in the hand is intact. Which nerve is most likely compressed, and at what anatomical site?

Explanation

The anterior interosseous nerve (AIN) innervates the FPL, FDP to the index/middle fingers, and pronator quadratus. It is purely motor, hence normal sensation; compression frequently occurs at the tendinous edge of the deep head of the pronator teres.

Question 91

An open tibial shaft fracture features a 12 cm laceration with extensive periosteal stripping. The wound requires a free latissimus dorsi flap for coverage, but distal pulses are palpable with adequate capillary refill. What is the Gustilo-Anderson classification?

Explanation

Type IIIB open fractures are characterized by extensive soft tissue loss, periosteal stripping, and bone exposure requiring a local or free flap for coverage. Type IIIC is reserved for open fractures requiring arterial repair for limb salvage.

Question 92

A patient with multiple myeloma has a massive impending pathological fracture of the proximal femur (subtrochanteric region) and a life expectancy greater than 6 months. What is the most appropriate prophylactic surgical stabilization technique?

Explanation

A cephalomedullary nail is the treatment of choice for impending proximal femur/subtrochanteric fractures in myeloma. It protects the entire length of the femur and provides biomechanically stable fixation into the femoral head and neck.

Question 93

What is the most common cause of early failure (within the first 2 years) requiring revision of a total knee arthroplasty?

Explanation

Periprosthetic joint infection and instability are the leading causes of early revision total knee arthroplasty (within 2 years). Aseptic loosening and polyethylene wear are primarily mechanisms of late failure.

Question 94

In a 6-year-old child with Legg-Calve-Perthes disease, which of the following radiographic "head-at-risk" signs is most indicative of a poor prognosis?

Explanation

The Gage sign, a V-shaped radiolucency in the lateral portion of the epiphysis and adjacent metaphysis, is one of Catterall's "head-at-risk" signs. It indicates lateral extrusion and carries a poor prognosis.

Question 95

A 65-year-old man sustains a first-time anterior shoulder dislocation. After a successful closed reduction, he is noted to have profound weakness in active external rotation and abduction. What is the most likely structural pathology causing this weakness?

Explanation

In patients older than 40-50 years, weakness in external rotation and abduction following an anterior shoulder dislocation is highly suspicious for an acute rotator cuff tear. This should be evaluated promptly with an MRI.

Question 96

Which of the following antibiotics is most frequently added to polymethylmethacrylate (PMMA) bone cement due to its broad-spectrum efficacy and thermal stability during the exothermic polymerization process?

Explanation

Tobramycin, gentamicin, and vancomycin are the most common antibiotics mixed into PMMA. They are chosen because they are available in powder form, have broad-spectrum coverage, and are thermostable during the high-heat curing of cement.

Orthopedic Prometric MCQs - Chapter 3 Part 1

Orthopedic Prometric MCQs - Chapter 3 Part 4

Orthopedic Prometric MCQs - Chapter 3 Part 4

Chapter Index