Pediatric Orthopaedics High-Yield MCQs | ABOS Part 1 Review

Question 1

A 12-year-old obese boy presents with left groin pain and an obligatory external rotation of the hip during flexion. Radiographs confirm a stable slipped capital femoral epiphysis (SCFE). Which of the following is the strongest indication for prophylactic in situ pinning of the asymptomatic contralateral hip?

Explanation

Correct Answer: Endocrine disorder (e.g., hypothyroidism)

Patients with endocrine disorders (such as hypothyroidism, renal osteodystrophy, or growth hormone deficiency) have a significantly higher risk of developing bilateral SCFE, often presenting at an atypical age. Prophylactic pinning of the contralateral hip is highly recommended in this population to prevent future displacement and associated complications.

Question 2

A 6-week-old female is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During a follow-up visit, the parents report that the infant has stopped kicking her right leg. On examination, there is absent active knee extension on the right, but ankle and toe movements are normal. What is the most likely cause of this finding?

Explanation

Correct Answer: Excessive flexion of the anterior straps causing femoral nerve palsy

Femoral nerve palsy is a known complication of Pavlik harness treatment, typically caused by excessive hyperflexion of the hip due to the anterior straps being too tight. It presents with decreased or absent active knee extension. If this occurs, the harness should be adjusted to reduce flexion or temporarily discontinued until nerve function returns.

Question 3

A 6-year-old boy falls from monkey bars and sustains a widely displaced, extension-type pediatric supracondylar humerus fracture. The distal fragment is displaced posteromedially. Which nerve is most likely to be injured in this specific fracture pattern?

Explanation

Correct Answer: Radial nerve

In extension-type supracondylar humerus fractures, the direction of displacement dictates the nerve at risk. Posteromedial displacement of the distal fragment drives the proximal fragment anterolaterally, putting the radial nerve at greatest risk. Conversely, posterolateral displacement puts the anterior interosseous nerve (AIN) and median nerve at risk.

Question 4

When treating a newborn with idiopathic clubfoot using the Ponseti method, what is the correct sequence of deformity correction?

Explanation

Correct Answer: Cavus, Adduction, Varus, Equinus

The Ponseti method corrects clubfoot deformities in a specific, sequential order, remembered by the acronym CAVE: Cavus (corrected first by elevating the first ray to align the forefoot with the hindfoot), Adductus, Varus, and finally Equinus (which often requires a percutaneous Achilles tenotomy as the final step).

Question 5

A 7-year-old boy is diagnosed with Legg-Calvé-Perthes disease. Which of the following radiographic findings is considered a 'head-at-risk' sign according to Catterall, indicating a poorer prognosis?

Explanation

Correct Answer: Gage sign (V-shaped radiolucency in the lateral epiphysis)

Catterall described several 'head-at-risk' signs for Perthes disease that correlate with a poorer prognosis and potential for hinge abduction. These include Gage sign (a V-shaped radiolucency in the lateral portion of the epiphysis and adjacent metaphysis), lateral subluxation of the femoral head, calcification lateral to the epiphysis, and a horizontal growth plate.

Question 6

A 14-year-old boy sustains an ankle injury while playing soccer. Radiographs reveal a Salter-Harris III fracture of the anterolateral distal tibial epiphysis. What is the primary deforming force and the ligament responsible for this specific fracture pattern?

Explanation

Correct Answer: External rotation; Anterior inferior tibiofibular ligament (AITFL)

A juvenile Tillaux fracture is a Salter-Harris III fracture of the anterolateral distal tibial epiphysis. It occurs due to an external rotation force on the foot. Because the distal tibial physis closes from central to anteromedial, and finally anterolateral, the anterolateral portion remains vulnerable in adolescents. The anterior inferior tibiofibular ligament (AITFL) avulses this unfused anterolateral epiphysis.

Question 7

A 2-year-old girl is evaluated for bilateral genu varum. Which of the following radiographic parameters is most indicative of infantile Blount disease rather than physiologic bowing?

Explanation

Correct Answer: Metaphyseal-diaphyseal angle greater than 16 degrees

The metaphyseal-diaphyseal angle (Drennan angle) is a critical radiographic measurement used to differentiate physiologic bowing from infantile Blount disease (tibia vara). An angle greater than 16 degrees is highly predictive of Blount disease, whereas an angle less than 10 degrees strongly suggests physiologic bowing.

Question 8

In a child with cerebral palsy, which of the following factors is the most significant predictor for the development of hip displacement (subluxation or dislocation)?

Explanation

Correct Answer: Gross Motor Function Classification System (GMFCS) level

The GMFCS level is the most reliable and significant predictor of hip displacement in children with cerebral palsy. There is a direct linear relationship: children with higher GMFCS levels (IV and V), who are non-ambulatory, have the highest risk of hip subluxation and dislocation, necessitating strict and frequent radiographic surveillance.

Question 9

A 9-year-old Tanner stage I male sustains a mid-substance anterior cruciate ligament (ACL) tear. Non-operative management has failed due to recurrent instability. When planning surgical reconstruction, which technique minimizes the risk of growth arrest and angular deformity?

Explanation

Correct Answer: Iliotibial band extra-articular tenodesis combined with an all-epiphyseal reconstruction

In a skeletally immature patient with significant growth remaining (Tanner stage I or II), physeal-sparing techniques are recommended to avoid iatrogenic physeal injury, growth arrest, and angular deformity. An all-epiphyseal reconstruction, often combined with an IT band extra-articular tenodesis (such as the MacIntosh or Lemaire procedure), provides stability while respecting the open physes.

Question 10

A 13-year-old boy presents with knee pain and is diagnosed with conventional osteosarcoma of the distal femur. Genetic testing reveals a germline mutation in the RB1 gene. This patient is at the highest risk for having a history of, or developing, which of the following secondary malignancies?

Explanation

Correct Answer: Retinoblastoma

Patients with a germline mutation in the RB1 gene (hereditary retinoblastoma) have a significantly increased risk of developing osteosarcoma. The RB1 gene is a tumor suppressor gene located on chromosome 13q14. Survivors of hereditary retinoblastoma frequently develop osteosarcoma as a secondary malignancy, often in adolescence.

Question 11

A 12-year-old obese boy presents with left groin pain and an obligatory external rotation of the hip during flexion. Radiographs confirm a slipped capital femoral epiphysis (SCFE). Which of the following is the strongest indication for prophylactic pinning of the contralateral asymptomatic hip?

Explanation

Correct Answer: Underlying endocrine disorder

Prophylactic pinning of the contralateral hip in SCFE is highly recommended in patients with underlying endocrine disorders (such as hypothyroidism, panhypopituitarism, or renal osteodystrophy) due to the significantly increased risk of bilateral involvement. While obesity and young age (e.g., males < 12, females < 10) are also risk factors for bilaterality, an underlying endocrinopathy is the strongest absolute indication for prophylactic fixation.

Question 12

A 6-week-old female is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During a follow-up visit, the parents report that the infant has stopped kicking her leg on the treated side. On examination, there is an absence of active knee extension. What is the most appropriate next step in management?

Explanation

Correct Answer: Remove the harness and observe

The clinical presentation is consistent with a femoral nerve palsy, a known complication of hyperflexion in a Pavlik harness. The femoral nerve becomes compressed against the rim of the pelvis. The most appropriate next step is to remove the harness and observe until neurologic function returns, which typically occurs within a few days to weeks. Continuing the harness or increasing flexion can lead to permanent nerve damage or failure of treatment.

Question 13

When treating a congenital idiopathic clubfoot using the Ponseti method, what is the correct sequence of deformity correction?

Explanation

Correct Answer: Cavus, Adductus, Varus, Equinus

The Ponseti method corrects the deformities of clubfoot in a specific sequence summarized by the acronym CAVE: Cavus (corrected first by elevating the first ray to align the forefoot with the hindfoot), Adductus, Varus, and finally Equinus. Equinus is corrected last, often requiring a percutaneous Achilles tenotomy if dorsiflexion to 15 degrees cannot be achieved through casting alone.

Question 14

A 6-year-old boy sustains an extension-type supracondylar humerus fracture. He is unable to make an 'OK' sign with his thumb and index finger. Which nerve is most likely injured, and what is its typical course of recovery?

Explanation

Correct Answer: Anterior interosseous nerve; typically recovers spontaneously within 2-3 months

The anterior interosseous nerve (AIN), a branch of the median nerve, is the most commonly injured nerve in extension-type supracondylar humerus fractures. It innervates the flexor pollicis longus and the flexor digitorum profundus to the index finger, which are required to make the 'OK' sign. These injuries are typically neuropraxias that resolve spontaneously within 2 to 3 months, and observation is the standard of care.

Question 15

A 14-year-old boy sustains an ankle injury while playing soccer. Radiographs reveal a Salter-Harris III fracture of the anterolateral distal tibial epiphysis. Which ligament is responsible for the avulsion of this fracture fragment?

Explanation

Correct Answer: Anterior inferior tibiofibular ligament

A Tillaux fracture is a Salter-Harris III fracture of the anterolateral distal tibial epiphysis. It occurs in adolescents because the distal tibial physis closes in a specific pattern: central, then anteromedial, then posteromedial, and finally lateral. An external rotation force causes the anterior inferior tibiofibular ligament (AITFL) to avulse the unfused anterolateral epiphysis.

Question 16

In the evaluation of Legg-Calve-Perthes disease, the lateral pillar classification is used to determine prognosis. During which stage of the disease is this classification most accurately applied?

Explanation

Correct Answer: Fragmentation stage

The Herring lateral pillar classification is most accurately applied during the early fragmentation stage of Legg-Calve-Perthes disease. It assesses the height of the lateral pillar of the capital femoral epiphysis on an AP radiograph. A lateral pillar height of >100% is Group A, >50% is Group B, and <50% is Group C. This classification correlates strongly with the long-term outcome and risk of aspherical femoral head development.

Question 17

A 13-year-old boy presents with recurrent ankle sprains and rigid flatfeet. Radiographs show an 'anteater nose' sign on the lateral view. Which of the following is the most likely diagnosis?

Explanation

Correct Answer: Calcaneonavicular coalition

The 'anteater nose' sign on a lateral radiograph of the foot is characteristic of a calcaneonavicular coalition. It represents an elongated anterior process of the calcaneus extending toward the navicular. In contrast, talocalcaneal coalitions often present with the 'C-sign' on lateral radiographs and are best visualized on a Harris axial view or CT scan.

Question 18

A 4-year-old girl with frequent fractures, blue sclerae, and dentinogenesis imperfecta is diagnosed with Osteogenesis Imperfecta. This condition is most commonly caused by a mutation affecting which of the following?

Explanation

Correct Answer: Type I collagen

Osteogenesis Imperfecta (OI) is primarily caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, which encode the alpha-1 and alpha-2 chains of Type I collagen. Type I collagen is the major structural protein in bone, sclerae, and dentin, explaining the classic triad of brittle bones, blue sclerae, and dentinogenesis imperfecta. FGFR3 mutations cause achondroplasia, and COMP mutations cause pseudoachondroplasia or multiple epiphyseal dysplasia.

Question 19

In a child with spastic quadriplegic cerebral palsy (GMFCS Level V), what is the most critical radiographic parameter to monitor during routine hip surveillance to prevent hip dislocation?

Explanation

Correct Answer: Reimer's migration percentage

Reimer's migration percentage is the most critical radiographic parameter used in hip surveillance for children with cerebral palsy. It measures the percentage of the femoral head that is laterally displaced outside the ossified acetabular roof (Perkin's line). A migration percentage greater than 30% indicates subluxation and often warrants closer monitoring or prophylactic surgical intervention (e.g., adductor release or varus derotational osteotomy).

Question 20

A 3-year-old girl presents with progressive bilateral genu varum. Radiographs reveal a sharp varus angulation at the proximal tibial metaphysis with medial beaking. According to the Langenskiold classification, which radiographic feature defines Stage IV infantile Blount disease?

Explanation

Correct Answer: Closure of the medial physis with an established bony bar

In the Langenskiold classification of infantile Blount disease, Stage IV is characterized by the closure of the medial physis and the formation of an established bony bar (epiphyseometaphyseal bridge). Stage I shows metaphyseal beaking, Stage II shows a sharp depression, Stage III shows 'stepping' of the metaphysis, Stage V shows a cleft in the epiphysis, and Stage VI shows a fully formed medial physeal bar with severe deformity.

Question 21

A 12-year-old boy with a BMI in the 99th percentile undergoes in situ pinning for a stable left slipped capital femoral epiphysis (SCFE). Which of the following is the most widely accepted indication for prophylactic pinning of the contralateral asymptomatic hip?

Explanation

Correct Answer: Presence of an endocrine disorder (e.g., hypothyroidism)

Prophylactic pinning of the contralateral hip in SCFE remains a topic of debate, but it is generally recommended for patients at high risk for bilateral involvement. High-risk factors include the presence of an endocrine disorder (such as hypothyroidism, renal osteodystrophy, or panhypopituitarism), previous radiation therapy, and young age at presentation (typically less than 10 years old for boys). Older age, severity of the initial slip, and presentation with knee pain do not independently mandate prophylactic contralateral pinning.

Question 22

A 6-week-old female is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During a follow-up visit, the parents report that the infant has stopped kicking her leg on the affected side. On examination, there is an absence of active knee extension. What is the most appropriate next step in management?

Explanation

Correct Answer: Discontinue the Pavlik harness immediately

The clinical presentation describes a femoral nerve palsy, which is a known complication of excessive hip flexion in a Pavlik harness. The femoral nerve becomes compressed against the rim of the pelvis or the inguinal ligament. The appropriate management is to discontinue the harness (or significantly loosen the anterior straps to reduce hip flexion) to relieve the pressure on the nerve. Most cases resolve spontaneously within a few days to weeks after removing the hyperflexion force. Continuing the harness or switching to a spica cast without allowing nerve recovery is contraindicated.

Question 23

When treating a newborn with idiopathic clubfoot using the Ponseti method, what is the correct sequence of deformity correction?

Explanation

Correct Answer: Cavus, Adductus, Varus, Equinus

The Ponseti method corrects clubfoot deformities in a specific, sequential order summarized by the acronym CAVE: Cavus, Adductus, Varus, and Equinus. The first step is to correct the cavus by elevating the first ray to align the forefoot with the hindfoot. Subsequent casts correct the adductus and varus by abducting the foot around the head of the talus. Finally, the equinus is corrected, which often requires a percutaneous Achilles tenotomy.

Question 24

A 6-year-old boy sustains an extension-type supracondylar humerus fracture. On physical examination, he is unable to flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. Which nerve is most likely injured?

Explanation

Correct Answer: Anterior interosseous nerve

The anterior interosseous nerve (AIN), a motor branch of the median nerve, is the most commonly injured nerve in extension-type supracondylar humerus fractures. It innervates the flexor pollicis longus (FPL), the flexor digitorum profundus (FDP) to the index and middle fingers, and the pronator quadratus. Injury leads to the inability to make an 'OK' sign (loss of thumb IP and index DIP flexion). The radial nerve is the second most commonly injured, particularly with posteromedial displacement, while the ulnar nerve is more commonly injured in flexion-type fractures or iatrogenically during medial pin placement.

Question 25

A 5-year-old girl sustains a minimally displaced lateral condyle fracture of the humerus that is treated nonoperatively. She is lost to follow-up and presents 15 years later with progressive numbness and tingling in her ring and small fingers. What is the most likely underlying cause of her current symptoms?

Explanation

Correct Answer: Cubitus valgus deformity

Nonunion is a classic complication of lateral condyle fractures, particularly if displacement is missed or inadequately treated. A nonunion of the lateral condyle leads to a progressive cubitus valgus deformity as the medial physis continues to grow while the lateral side does not. Over time, this valgus alignment stretches the ulnar nerve behind the medial epicondyle, leading to a tardy ulnar nerve palsy. This presents with numbness, tingling, and potential intrinsic muscle weakness in the ulnar nerve distribution.

Question 26

In the evaluation of a 7-year-old boy with Legg-Calvé-Perthes disease, which of the following radiographic classification systems is most predictive of the long-term outcome and risk of early osteoarthritis?

Explanation

Correct Answer: Herring Lateral Pillar classification

The Herring Lateral Pillar classification, assessed during the fragmentation phase of Legg-Calvé-Perthes disease, is the most reliable and widely used prognostic indicator. It evaluates the height of the lateral pillar of the femoral head (Group A: >100% height maintained; Group B: >50% height maintained; Group C: <50% height maintained). The Stulberg classification is used at skeletal maturity to assess the final joint congruency, not during the active disease process. Waldenström describes the temporal stages of the disease.

Question 27

A 6-year-old child with spastic quadriplegic cerebral palsy (GMFCS Level V) is undergoing routine hip surveillance. An anteroposterior pelvis radiograph reveals a Reimers migration percentage of 45% bilaterally. What is the most appropriate management?

Explanation

Correct Answer: Bilateral varus derotational osteotomies (VDRO) and pelvic osteotomies

In a child with cerebral palsy, a Reimers migration percentage greater than 40-50% indicates significant hip subluxation with a high risk of progression to dislocation. In a 6-year-old child, soft tissue releases alone (such as adductor tenotomies) are generally insufficient to halt or reverse the progression when the migration percentage is this high. Bony reconstruction, typically consisting of a proximal femoral varus derotational osteotomy (VDRO) combined with a pelvic osteotomy (e.g., Dega or San Diego), is the standard of care to stabilize the hip and prevent painful dislocation.

Question 28

A 4-year-old boy presents with multiple fractures after minimal trauma, blue sclerae, and dentinogenesis imperfecta. Genetic testing is most likely to reveal a mutation affecting the synthesis of which of the following proteins?

Explanation

Correct Answer: Type I collagen

The clinical presentation of multiple fragility fractures, blue sclerae, and dentinogenesis imperfecta is classic for Osteogenesis Imperfecta (OI). OI is most commonly caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, which encode the alpha-1 and alpha-2 chains of Type I collagen. Type I collagen is the major structural protein in bone, sclera, dentin, and ligaments. Type II collagen mutations cause skeletal dysplasias like achondrogenesis or SED. Fibrillin-1 is associated with Marfan syndrome, FGFR3 with achondroplasia, and COMP with pseudoachondroplasia.

Question 29

A 14-year-old boy sustains an ankle injury while playing soccer. Radiographs reveal a Salter-Harris III fracture of the anterolateral distal tibia. Which of the following ligaments is responsible for the avulsion of this fracture fragment?

Explanation

Correct Answer: Anterior inferior tibiofibular ligament (AITFL)

A juvenile Tillaux fracture is a Salter-Harris III fracture of the anterolateral distal tibial epiphysis. It occurs in adolescents because the distal tibial physis closes in a specific pattern: central, then anteromedial, then posteromedial, and finally anterolateral. An external rotation force of the foot within the mortise causes the anterior inferior tibiofibular ligament (AITFL) to avulse the anterolateral epiphysis, which is the last portion of the physis to close.

Question 30

A 3-year-old girl presents with progressive bowing of her left leg. Radiographs demonstrate a sharp varus angulation at the proximal tibial metaphysis with beaking and fragmentation of the medial aspect of the epiphysis. She is diagnosed with infantile Blount disease. According to the Langenskiöld classification, at what stage is a proximal tibial osteotomy generally recommended to prevent permanent physeal damage?

Explanation

Correct Answer: Stage III

Infantile Blount disease is characterized by disordered endochondral ossification of the medial aspect of the proximal tibial physis. The Langenskiöld classification describes the radiographic progression from Stage I to VI. Bracing (KAFO) is typically attempted for Stages I and II in children under 3 years of age. However, by Stage III (characterized by a step-off in the metaphysis), or if the child is older than 3-4 years, surgical intervention with a proximal tibial valgus osteotomy is recommended. Surgery at this stage restores normal mechanical alignment and prevents irreversible physeal damage, which typically occurs in Stages V and VI with the formation of a physeal bar.

Question 31

A 9-year-old boy with a BMI in the 99th percentile presents with a stable slipped capital femoral epiphysis (SCFE) of the left hip. He has a known medical history of hypothyroidism. What is the most appropriate management for the contralateral right hip?

Explanation

Correct Answer: Prophylactic in situ pinning

Prophylactic pinning of the contralateral hip is highly recommended in patients with SCFE who have underlying endocrine disorders (such as hypothyroidism or panhypopituitarism), renal osteodystrophy, previous radiation therapy, or are under 10 years of age. These patients have a significantly higher risk of developing bilateral involvement compared to idiopathic cases.

Question 32

During an open reduction of a developmental dysplasia of the hip (DDH) via a medial approach, the surgeon encounters resistance to concentric reduction. Which of the following structures is considered an intra-articular block to reduction?

Explanation

Correct Answer: Transverse acetabular ligament

Blocks to reduction in DDH are categorized as extra-articular or intra-articular. Extra-articular blocks include the iliopsoas tendon and adductor longus. Intra-articular blocks include the inverted limbus, hypertrophied pulvinar, ligamentum teres, and a contracted transverse acetabular ligament. The transverse acetabular ligament must often be incised to allow the femoral head to seat deeply within the true acetabulum.

Question 33

A 6-year-old boy sustains a displaced extension-type supracondylar humerus fracture after falling from monkey bars. Radiographs demonstrate that the distal fragment is displaced posteromedially. Which nerve is at the greatest risk of injury in this specific displacement pattern?

Explanation

Correct Answer: Radial nerve

In extension-type supracondylar humerus fractures, the direction of displacement dictates the nerve at risk. Posteromedial displacement of the distal fragment causes the proximal fragment to spike anterolaterally, putting the radial nerve at greatest risk. Conversely, posterolateral displacement puts the anterior interosseous nerve (AIN) and median nerve at risk. Flexion-type fractures place the ulnar nerve at risk.

Question 34

When treating a congenital idiopathic clubfoot using the Ponseti method, what is the correct sequence of deformity correction?

Explanation

Correct Answer: Cavus, Adductus, Varus, Equinus

The Ponseti method corrects clubfoot deformities in a specific, sequential order remembered by the acronym CAVE: Cavus (corrected first by elevating the first ray to align the forefoot with the hindfoot), Adductus, Varus, and finally Equinus. Equinus is corrected last, often requiring a percutaneous Achilles tenotomy once the other deformities are fully resolved.

Question 35

In the evaluation of a 7-year-old boy with Legg-Calvé-Perthes disease, which of the following radiographic classifications is considered the most reliable prognostic indicator for long-term hip outcome?

Explanation

Correct Answer: Herring lateral pillar classification

The Herring lateral pillar classification, assessed during the fragmentation phase of the disease, is the most reliable prognostic indicator for Legg-Calvé-Perthes disease. It evaluates the height of the lateral pillar of the capital femoral epiphysis. Group A has no lateral pillar involvement, Group B has >50% lateral pillar height maintained, and Group C has <50% lateral pillar height maintained. Group C has the poorest prognosis.

Question 36

The pathogenesis of infantile Blount disease (tibia vara) is best explained by which of the following biomechanical principles?

Explanation

Correct Answer: Hueter-Volkmann principle

The Hueter-Volkmann principle states that increased compressive forces on a physis inhibit growth, while decreased forces stimulate growth. In infantile Blount disease, excessive compressive forces on the medial proximal tibial physis (often due to early walking and obesity) lead to growth suppression medially, resulting in a progressive varus deformity.

Question 37

A 5-year-old child with spastic quadriplegic cerebral palsy (GMFCS Level V) is undergoing routine hip surveillance. Which of the following radiographic measurements is most critical for determining the need for surgical intervention to prevent hip dislocation?

Explanation

Correct Answer: Reimers migration percentage

Reimers migration percentage (or index) is the standard measurement used in cerebral palsy hip surveillance to quantify the lateral displacement of the femoral head out of the acetabulum. A migration percentage >30% indicates subluxation and warrants closer monitoring or soft tissue intervention, while a percentage >50% typically requires bony reconstructive surgery (VDRO and pelvic osteotomy) to prevent painful dislocation.

Question 38

A 14-year-old boy presents with rigid flatfeet and recurrent ankle sprains. Examination reveals restricted subtalar motion and peroneal spasticity. Radiographs show a 'C sign' on the lateral view. What is the most likely diagnosis?

Explanation

Correct Answer: Talocalcaneal coalition

The 'C sign' on a lateral foot radiograph is a classic radiographic finding indicative of a talocalcaneal coalition, specifically involving the middle facet. It is formed by the medial outline of the talar dome and the posteroinferior outline of the sustentaculum tali. Calcaneonavicular coalitions typically present earlier (ages 8-12) and are best visualized on a 45-degree internal oblique radiograph ('anteater sign').

Question 39

A 3-year-old girl presents with multiple fractures following minimal trauma, blue sclerae, and dentinogenesis imperfecta. Genetic testing is most likely to reveal a mutation affecting the synthesis of which of the following proteins?

Explanation

Correct Answer: Type I collagen

Osteogenesis imperfecta is primarily caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, which encode the alpha-1 and alpha-2 chains of Type I collagen. This structural defect leads to brittle bones, blue sclerae, hearing loss, and dentinogenesis imperfecta. Type II collagen defects cause spondyloepiphyseal dysplasia, FGFR3 mutations cause achondroplasia, and COMP mutations cause pseudoachondroplasia.

Question 40

A 3-year-old boy sustains an isolated, closed, diaphyseal spiral fracture of the right femur after a fall from a playground structure. Radiographs show 1.5 cm of shortening. What is the most appropriate definitive treatment?

Explanation

Correct Answer: Early spica casting

According to AAOS clinical practice guidelines, early spica casting is the treatment of choice for children aged 6 months to 5 years with diaphyseal femur fractures and less than 2-3 cm of shortening. A Pavlik harness is indicated for infants under 6 months. Flexible intramedullary nailing is typically indicated for children aged 5 to 11 years.

Question 41

A 13-year-old obese male undergoes in situ pinning for a stable slipped capital femoral epiphysis (SCFE). Postoperatively, he develops severe hip stiffness and pain. Radiographs show concentric joint space narrowing. What is the most likely cause of this complication?

Explanation

Correct Answer: Unrecognized hardware penetration into the joint

Chondrolysis is characterized by concentric joint space narrowing and severe stiffness following treatment for SCFE. The most common iatrogenic cause is unrecognized pin penetration into the joint space. Avascular necrosis typically presents with segmental collapse rather than concentric joint space narrowing.

Question 42

A 6-week-old female is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During a follow-up visit, the parents report that the infant has stopped kicking her leg on the affected side. On examination, there is absent active knee extension. Which of the following adjustments to the harness is most appropriate?

Explanation

Correct Answer: Decrease the flexion of the anterior straps

Hyperflexion in a Pavlik harness can lead to a compressive femoral nerve palsy, presenting as decreased active knee extension and a lack of kicking. The appropriate management is to decrease the flexion of the anterior straps or temporarily discontinue the harness until nerve function recovers.

Question 43

A 3-year-old boy who was successfully treated for idiopathic clubfoot with the Ponseti method and an Achilles tenotomy presents with a recurrent equinovarus deformity. What is the most common cause of relapse in this patient population?

Explanation

Correct Answer: Noncompliance with bracing

The most common cause of clubfoot relapse after successful Ponseti casting and tenotomy is noncompliance with the foot abduction orthosis (bracing). Strict adherence to the bracing protocol (full-time for 3 months, then nights/naps until age 4) is critical to maintaining the correction.

Question 44

A 6-year-old boy sustains a displaced extension-type supracondylar humerus fracture. Which nerve is most commonly injured in this specific fracture pattern, and what is the typical clinical finding?

Explanation

Correct Answer: Anterior interosseous nerve; inability to flex the interphalangeal joint of the thumb

The anterior interosseous nerve (AIN) is the most commonly injured nerve in extension-type supracondylar humerus fractures. It is a motor nerve, and injury results in the inability to flex the IP joint of the thumb and the DIP joint of the index finger (inability to make an 'OK' sign).

Question 45

A 7-year-old boy is diagnosed with Legg-Calvé-Perthes disease. Which of the following factors is considered the most significant predictor of the final radiographic and clinical outcome?

Explanation

Correct Answer: Age at the time of clinical onset

Age at the onset of symptoms is the most critical prognostic factor in Legg-Calvé-Perthes disease. Children who develop the disease at a younger age (typically under 6-8 years) have a better prognosis due to greater potential for remodeling of the femoral head before skeletal maturity.

Question 46

The pathogenesis of infantile Blount disease is best explained by which of the following biomechanical principles?

Explanation

Correct Answer: Hueter-Volkmann principle

The Hueter-Volkmann principle states that increased compressive forces on a physis inhibit growth, while decreased forces stimulate growth. In Blount disease, excessive compressive forces on the medial aspect of the proximal tibial physis (often due to early walking and obesity) lead to growth suppression and progressive varus deformity.

Question 47

A 6-year-old child with spastic quadriplegic cerebral palsy (GMFCS Level V) is undergoing routine hip surveillance. Radiographs reveal a Reimers migration percentage of 45% bilaterally. What is the most appropriate management?

Explanation

Correct Answer: Bilateral varus derotational osteotomies (VDRO) and pelvic osteotomies

In children with CP, a Reimers migration percentage >40% indicates significant hip subluxation that is unlikely to respond to soft tissue releases alone. Bony reconstruction, typically involving a proximal femoral varus derotational osteotomy (VDRO) and often a pelvic osteotomy (e.g., Dega or San Diego), is indicated to stabilize the hip and prevent painful dislocation.

Question 48

A 4-year-old girl with a history of multiple low-energy fractures, blue sclerae, and dentinogenesis imperfecta is diagnosed with osteogenesis imperfecta (OI). The most common genetic mutations associated with this condition affect the synthesis of which of the following proteins?

Explanation

Correct Answer: Type I collagen

Osteogenesis imperfecta is primarily caused by mutations in the COL1A1 or COL1A2 genes, which encode the alpha-1 and alpha-2 chains of Type I collagen. This leads to quantitative or qualitative defects in Type I collagen, the major structural protein in bone.

Question 49

A 14-year-old boy presents with recurrent ankle sprains and a rigid, painful flatfoot. On examination, he has decreased subtalar motion and peroneal spasticity. A CT scan confirms a talocalcaneal coalition. Which facet of the subtalar joint is most commonly involved in this type of coalition?

Explanation

Correct Answer: Middle facet

Talocalcaneal coalitions most commonly involve the middle facet of the subtalar joint. They typically present in adolescence (ages 12-16) as the coalition ossifies, leading to a rigid flatfoot, peroneal spasticity, and pain.

Question 50

A 15-year-old male gymnast presents with a 3-month history of low back pain that worsens with extension activities. Neurological examination is normal. Plain radiographs, including oblique views, are negative for a fracture. What is the most appropriate next imaging modality to evaluate for an acute or stress reaction of the pars interarticularis?

Explanation

Correct Answer: Magnetic resonance imaging (MRI) of the lumbar spine

MRI is the preferred advanced imaging modality for evaluating suspected early spondylolysis (pars stress reaction) in pediatric patients when plain radiographs are normal. It can detect bone marrow edema in the pars interarticularis (indicating an acute stress reaction) without exposing the child to ionizing radiation, unlike CT or SPECT.

Question 51

A 4-year-old boy presents with a displaced lateral condyle fracture of the humerus. Radiographs show a Milch Type II fracture with 3 mm of displacement. Which of the following is the most appropriate definitive management?

Explanation

Lateral condyle fractures with >2 mm of displacement are generally treated with ORIF to ensure anatomic reduction of the articular surface and physis. Closed reduction and pinning may be attempted, but typically requires an arthrogram to confirm perfect articular alignment.

Question 52

A 24-month-old girl recently emigrated from a developing country and is evaluated for a painless limp. Examination reveals a positive Galeazzi sign and asymmetric thigh folds. Radiographs confirm an untreated unilateral developmental dysplasia of the hip (DDH) with a dislocated left hip. What is the most appropriate initial management?

Explanation

For children over 18-24 months of age with a completely dislocated hip, open reduction is generally the initial treatment of choice. Closed reduction and Pavlik harness have unacceptably high failure and AVN rates in this older age group.

Question 53

An infant with a severe idiopathic clubfoot is undergoing serial manipulation and casting using the Ponseti method. According to the principles of this method, which of the following deformity components is corrected last?

Explanation

The Ponseti method corrects the components of clubfoot in a specific sequence summarized by the acronym CAVE: Cavus, Adductus, Varus, and finally Equinus. Equinus is typically corrected last and often requires a percutaneous Achilles tenotomy.

Question 54

A 14-year-old gymnast presents with severe back pain and a waddling gait. Lateral radiographs show a Grade IV isthmic spondylolisthesis at L5-S1 with a slip angle of 55 degrees. She has failed 6 months of conservative management. What is the most appropriate surgical treatment?

Explanation

High-grade spondylolisthesis (Grade III-V) with a high slip angle generally requires instrumented fusion, often extended to L4 to obtain adequate fixation. In situ fusion is historically used for lower grades, but high-grade slips typically need instrumentation and sometimes partial reduction.

Question 55

A 7-year-old boy with spastic quadriplegic cerebral palsy presents with worsening right hip pain. Radiographs reveal a Reimer's migration percentage of 55% on the right and 15% on the left. The right hip has broken the Shenton line. What is the most appropriate surgical intervention?

Explanation

In children with cerebral palsy, a migration percentage >50% generally indicates a progressive subluxation or dislocation that requires comprehensive bony reconstruction. This typically involves a femoral VDRO combined with a pelvic (Dega or San Diego) osteotomy to stabilize the hip.

Question 56

A 3-year-old child presents with a history of recurrent long bone fractures after minimal trauma, blue sclerae, and dentinogenesis imperfecta. A genetic defect in which of the following is most likely responsible for this condition?

Explanation

The clinical presentation is classic for Osteogenesis Imperfecta (OI). Approximately 90% of OI cases are caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, which encode Type I collagen.

Question 57

An infant is diagnosed with achondroplasia shortly after birth. Which of the following evaluations is most critical to perform during the first year of life to prevent sudden death?

Explanation

Infants with achondroplasia are at high risk for foramen magnum stenosis, which can cause cervicomedullary compression leading to central sleep apnea and sudden infant death. Screening with MRI or sleep studies is critical in the first year.

Question 58

A 3-year-old boy in the 99th percentile for weight presents with bilateral genu varum. Standing AP radiographs show a metaphyseal-diaphyseal angle (Drennan angle) of 18 degrees bilaterally, with medial metaphyseal beaking. What is the most appropriate initial treatment?

Explanation

The patient has infantile Blount disease (Drennan angle >16 degrees is highly predictive). For children under the age of 4 with Langenskiöld Stage I or II Blount disease, KAFO bracing is the recommended initial non-operative treatment.

Question 59

A 13-year-old girl twists her ankle and sustains a juvenile Tillaux fracture. Which of the following ligaments is responsible for avulsing the anterolateral distal tibial epiphysis in this fracture pattern?

Explanation

A juvenile Tillaux fracture is a Salter-Harris III fracture of the anterolateral distal tibia. It is caused by an external rotation force, resulting in the AITFL avulsing the epiphyseal fragment as the physis closes from central to anterolateral.

Question 60

A 2-year-old toddler falls from a low bed and sustains a closed, isolated, spiral midshaft fracture of the femur with 2 cm of shortening. What is the most appropriate treatment?

Explanation

For children aged 6 months to 4-5 years with an isolated femur fracture and <2-3 cm of shortening, early spica casting is the gold standard treatment. Pavlik harnesses are reserved for infants <6 months old.

Question 61

Which of the following factors is considered the most significant prognostic indicator for the long-term outcome in a child diagnosed with Legg-Calvé-Perthes disease?

Explanation

Age at disease onset is the most important prognostic factor in Legg-Calvé-Perthes disease, alongside the lateral pillar classification. Children who develop the disease before age 6 to 8 generally have better remodeling potential and long-term outcomes.

Question 62

A 12-year-old boy presents with a painful, rigid flatfoot and recurrent ankle sprains. CT imaging confirms a calcaneonavicular coalition. He has failed 6 weeks of short leg cast immobilization and NSAIDs. What is the most appropriate surgical intervention?

Explanation

Symptomatic calcaneonavicular coalitions that fail conservative management are primarily treated with resection of the coalition and interposition of a material (fat or extensor digitorum brevis) to prevent recurrence. Arthrodesis is reserved for cases with severe degenerative changes or failed resections.

Question 63

A 13-year-old boy undergoes in situ single-screw fixation for a stable slipped capital femoral epiphysis (SCFE). At his 6-week follow-up, he complains of severe, constant hip pain and profound loss of hip motion in all planes. Radiographs show a significant reduction in the joint space compared to the immediate post-operative films. What is the most likely diagnosis?

Explanation

Chondrolysis is a devastating complication of SCFE characterized by acute narrowing of the joint space and severe, painful restriction of motion. It is strongly associated with unrecognized pin penetration into the joint space.

Question 64

A 4-year-old girl is brought to the emergency department refusing to bear weight on her right leg. She has a temperature of 38.8°C, an ESR of 55 mm/hr, and a serum WBC of 14,000 cells/mm3. According to the classic Kocher criteria, what is the probability that this child has septic arthritis of the hip?

Explanation

This patient meets all four of the classic Kocher criteria: fever >38.5°C, non-weight-bearing status, ESR >40 mm/hr, and WBC >12,000/mm3. The presence of all four predictors indicates a 99% probability of septic arthritis.

Question 65

A 14-year-old girl with adolescent idiopathic scoliosis (AIS) has a proximal thoracic curve of 20 degrees (bends to 10 degrees), a main thoracic curve of 55 degrees (bends to 20 degrees), and a thoracolumbar curve of 30 degrees (bends to 15 degrees). Based on the Lenke classification system, what is her curve type?

Explanation

In the Lenke classification, a Type 1 curve is defined by a structural main thoracic curve, while the proximal thoracic and thoracolumbar curves are non-structural (bend out to <25 degrees). Since only her main thoracic curve is structural, she has a Type 1 curve.

Question 66

A 2-month-old infant is diagnosed with congenital muscular torticollis affecting the right sternocleidomastoid (SCM) muscle. Which of the following best describes the typical posturing of the infant's head?

Explanation

In right-sided congenital muscular torticollis, the tight right SCM muscle causes the head to tilt toward the affected side (right) and rotate toward the contralateral side (left).

Question 67

A 9-year-old boy with wide-open physes sustains a complete, mid-substance anterior cruciate ligament (ACL) tear with objective instability. To minimize the risk of growth arrest while restoring stability, which of the following surgical techniques is most appropriate?

Explanation

For prepubescent patients with significant remaining growth (Tanner stage 1 or 2), physeal-sparing techniques like the all-epiphyseal reconstruction or the iliotibial band extra-articular tenodesis (MacIntosh/Micheli) are recommended to avoid crossing the physes and causing growth arrest.

Question 68

A 6-year-old boy presents with a painless clicking and snapping in his lateral knee. MRI confirms an isolated, complete discoid lateral meniscus with no evidence of tearing. What is the most appropriate management?

Explanation

An asymptomatic or incidentally found discoid meniscus without a tear should be managed with observation. Surgical intervention (saucerization) is reserved for symptomatic patients with mechanical symptoms, pain, or confirmed tears.

Question 69

A 5-year-old girl is evaluated after a minor fall. Lateral cervical spine radiographs show a 3 mm anterior translation of C2 on C3. Swischuk's line (spinolaminar line) from C1 to C3 passes exactly through the anterior cortex of the posterior arch of C2. What is the most likely diagnosis?

Explanation

Pseudosubluxation of C2 on C3 is common in children under 8. It is distinguished from true injury using Swischuk's line; if the line passes within 2 mm of the anterior aspect of the posterior arch of C2, the subluxation is considered physiologic.

Question 70

A 10-year-old girl presents with back pain. Oblique lumbar radiographs reveal a "Scotty dog" sign with a "collar" around the neck. This radiographic finding is pathognomonic for a defect in which anatomic structure?

Explanation

The "collar" on the neck of the "Scotty dog" seen on oblique lumbar radiographs represents a radiolucent defect or fracture in the pars interarticularis, indicating spondylolysis.

Question 71

An 8-year-old boy with Legg-Calve-Perthes disease presents for follow-up. Radiographs reveal a V-shaped radiolucent defect in the lateral portion of the proximal femoral epiphysis. What is the name of this specific radiographic finding, and what does it indicate?

Explanation

The Gage sign is a V-shaped radiolucency in the lateral epiphysis and adjacent metaphysis. It is one of Catterall's "head at risk" signs in Legg-Calve-Perthes disease, which correlate with a poorer prognosis and progressive deformity.

Question 72

An 18-month-old girl undergoes closed reduction for developmental dysplasia of the hip (DDH). Intraoperative arthrography reveals an hourglass-shaped capsular constriction preventing the femoral head from seating concentrically in the acetabulum. Which anatomical structure is responsible for creating this extra-articular constriction?

Explanation

The iliopsoas tendon crosses the anterior aspect of the hip capsule, creating an hourglass capsular constriction that can physically block concentric closed reduction in DDH. The transverse ligament, ligamentum teres, and limbus are intra-articular blocks.

Question 73

An infant with idiopathic clubfoot is undergoing the first stage of the Ponseti casting method. Which manipulative maneuver is required to correctly address the initial component of the deformity?

Explanation

The first step in the Ponseti method is correcting the cavus deformity by elevating the first ray to supinate the forefoot. This aligns the forefoot with the hindfoot, preventing the creation of a midfoot break.

Question 74

A 7-year-old boy weighing 25 kg sustains a closed, isolated transverse midshaft femur fracture. What is the most appropriate surgical treatment modality associated with the best clinical outcomes for this patient?

Explanation

For children aged 5 to 11 years (or weight <50 kg), flexible intramedullary nailing is the standard of care for diaphyseal femur fractures. Rigid nailing is contraindicated due to the risk of avascular necrosis of the femoral head.

Question 75

A 6-year-old boy with spastic quadriplegic cerebral palsy presents for evaluation. Pelvic radiographs demonstrate a left hip migration percentage of 50%, with breaking of the Shenton line. Which surgical intervention is most appropriate to provide a durable hip reconstruction?

Explanation

In children with cerebral palsy and a hip migration percentage >40%, soft-tissue releases alone are inadequate. Comprehensive bony reconstruction with a proximal femoral VDRO and a concomitant pelvic osteotomy is the gold standard.

Question 76

A 14-year-old boy underwent in situ single-screw fixation for an unstable slipped capital femoral epiphysis (SCFE). Six months later, he complains of severe hip stiffness. Radiographs show a marked reduction in the joint space to <3 mm without femoral head collapse. What is the most likely diagnosis?

Explanation

Chondrolysis presents with acute joint space narrowing and severe stiffness following a SCFE, often associated with unrecognized articular pin penetration. Unlike AVN, chondrolysis does not typically involve structural collapse of the femoral head.

Question 77

A 2-year-old obese girl presents with bilateral progressive genu varum. Radiographs reveal metaphyseal beaking and a Langenskiold stage II classification. What is the most appropriate initial management?

Explanation

In infantile Blount disease (children <3 years old) with Langenskiold stage I or II, bracing with KAFOs is the initial treatment of choice. Surgical intervention is reserved for older children, failed bracing, or higher Langenskiold stages.

Question 78

A 13-year-old boy presents with a rigid, painful flatfoot and a history of recurrent ankle sprains. A lateral foot radiograph demonstrates an "anteater nose" sign. What is the most likely diagnosis?

Explanation

The "anteater nose" sign on a lateral foot radiograph is pathognomonic for an anterior elongation of the calcaneus, indicating a calcaneonavicular coalition. Talocalcaneal coalitions are classically identified by the "C sign".

Question 79

A 14-year-old girl sustains a Salter-Harris III fracture of the anterolateral distal tibia. Which specific biomechanical mechanism is responsible for this fracture pattern?

Explanation

A juvenile Tillaux fracture is a Salter-Harris III injury caused by external rotation of the foot, which tensions the anterior inferior tibiofibular ligament (AITFL). It occurs precisely during the period when the medial physis has closed but the lateral physis remains open.

Question 80

A 15-year-old gymnast has persistent low back pain unresponsive to 6 months of physical therapy and bracing. Radiographs confirm a Grade II isthmic spondylolisthesis at L5-S1. What is the most appropriate surgical intervention?

Explanation

For a symptomatic low-grade (Grade I or II) isthmic spondylolisthesis in an adolescent that fails conservative care, a posterolateral in situ fusion is the standard of care. Direct pars repair is generally reserved for isolated spondylolysis without a slip.

Question 81

An 11-year-old boy sustains a Meyers and McKeever Type III fracture of the tibial eminence during a bicycle fall. Which ligamentous structure is directly involved in this avulsion injury?

Explanation

A tibial eminence fracture in the pediatric population is a bony avulsion of the anterior cruciate ligament (ACL) insertion. A Type III fracture is completely displaced and requires surgical reduction and internal fixation.

Question 82

A 6-year-old boy with blue sclerae, dentinogenesis imperfecta, and multiple prior long bone fractures is diagnosed with a quantitative defect in Type I collagen. Which pharmacological agent is the gold standard to decrease fracture incidence in this patient?

Explanation

Intravenous bisphosphonates, such as pamidronate or zoledronic acid, are the standard of care for moderate to severe Osteogenesis Imperfecta. They inhibit osteoclastic bone resorption, significantly increasing bone mineral density and reducing fracture rates.

Question 83

A 12-year-old male with open physes presents with knee pain. MRI reveals an intact, stable osteochondritis dissecans (OCD) lesion. What is the most common anatomical location for this lesion?

Explanation

The lateral aspect of the medial femoral condyle is the classic and most common location for osteochondritis dissecans (OCD) lesions in the knee. Stable lesions in patients with open physes generally heal with conservative activity modification.

Question 84

A 5-year-old boy is evaluated after a minor motor vehicle collision. A lateral cervical spine radiograph shows 3 mm of anterior displacement of C2 on C3. Swischuk's line passes 1 mm anterior to the anterior aspect of the C3 spinous process. What is the appropriate next step in management?

Explanation

In young children, physiologic pseudosubluxation of C2 on C3 is common. If Swischuk's line passes within 1.5 mm of the anterior aspect of the C3 spinous process, it confirms pseudosubluxation rather than true ligamentous injury, requiring no treatment.

Question 85

An 8-year-old girl is brought in for an audible, painless snapping in the lateral aspect of her right knee. She has no history of trauma, and her physical exam is otherwise completely normal. What is the most appropriate management for her condition?

Explanation

The clinical presentation is classic for an asymptomatic snapping discoid lateral meniscus. Observation is the standard of care, as prophylactic meniscectomy in asymptomatic patients accelerates early joint degeneration and osteoarthritis.

Question 86

A 3-year-old boy presents with anterolateral bowing of his left tibia and a radiographically confirmed pseudarthrosis. Which systemic disorder is most strongly associated with this orthopaedic condition?

Explanation

Anterolateral bowing of the tibia with congenital pseudarthrosis (CPT) is highly associated with Neurofibromatosis type 1 (NF1). Management is notoriously difficult and typically requires excision of the hamartomatous tissue with rigid fixation.

Question 87

A 5-year-old boy sustained a lateral condyle fracture of the humerus that was treated nonoperatively. Two years later, he presents with a nonunion. Which of the following is the most common long-term neurological complication associated with this specific nonunion?

Explanation

Nonunion of a lateral condyle fracture typically results in a progressive cubitus valgus deformity. This progressive valgus stretch on the medial side of the elbow commonly leads to a tardy ulnar nerve palsy years later.

Question 88

A 9-year-old boy presents with mild, vague shoulder pain. A radiograph of the proximal humerus reveals a centrally located, completely radiolucent metaphyseal lesion with a "fallen leaf" sign. The cortices are thinned but intact. What is the most appropriate initial management?

Explanation

The "fallen leaf" sign is pathognomonic for a unicameral bone cyst (UBC). For an asymptomatic or mildly symptomatic UBC in the upper extremity without an impending fracture risk, observation is the most appropriate initial step.

Question 89

A 2-month-old infant is brought to the clinic holding his head persistently tilted to the right and rotated to the left. A firm, painless mass is palpated in the right side of the neck. Because this condition is part of the "packaging disorders," what other screening is unequivocally indicated?

Explanation

Congenital muscular torticollis is caused by unilateral contracture of the sternocleidomastoid muscle. It is highly associated with developmental dysplasia of the hip (up to 20%), making routine hip screening mandatory.

Question 90

An infant presents with a rigid equinovarus foot deformity characterized by a deep transverse plantar crease, a shortened first metatarsal, and severe equinus. Initial attempts at standard Ponseti casting result in cast slippage and worsening of the deformity. What is the most appropriate modification in the management of this specific condition?

Explanation

This presentation is classic for atypical (complex) clubfoot. Management requires a modified Ponseti technique that limits hyperabduction, utilizes knee flexion to approximately 110 degrees to prevent cast slippage, and emphasizes early Achilles tenotomy.

Question 91

A 35-year-old man presents with progressive intrinsic hand weakness, clawing of the small and ring fingers, and numbness on the ulnar aspect of his hand. He reports a history of a childhood elbow fracture treated non-operatively. Physical examination reveals a profound cubitus valgus deformity. Which of the following pediatric fractures did he most likely sustain?

Explanation

Nonunion of a pediatric lateral condyle humerus fracture frequently leads to a progressive cubitus valgus deformity over many years. This late valgus deformity stretches the ulnar nerve, predictably causing a tardy ulnar nerve palsy in adulthood.

Question 92

A 13-year-old girl sustains an ankle injury. Radiographs demonstrate a Salter-Harris III fracture of the distal tibial epiphysis, isolated to the anterolateral quadrant. This specific fracture pattern is dictated by the physiological closure sequence of the distal tibial physis. Which portion of the distal tibial physis is the last to close?

Explanation

The distal tibial physis closes in a predictable sequence: central, anteromedial, posteromedial, and finally anterolateral. Because the anterolateral physis remains open longest, it is selectively vulnerable to an avulsion fracture (Tillaux fracture) via the anterior inferior tibiofibular ligament.

Question 93

A 4-year-old boy is evaluated for a painless waddling gait. Pelvic radiographs demonstrate a unilateral decreased femoral neck-shaft angle with a vertically oriented proximal femoral physis. What specific radiographic parameter is the strongest indication for a valgus-producing proximal femoral osteotomy in this patient?

Explanation

In developmental coxa vara, a Hilgenreiner-epiphyseal angle (HEA) greater than 60 degrees indicates a high risk of progression and pseudarthrosis, serving as a strong indication for a subtrochanteric valgus osteotomy. An HEA of less than 45 degrees generally portends spontaneous resolution.

Question 94

A 9-year-old boy with known Legg-Calve-Perthes disease presents with increasing hip pain and decreased range of motion. A dynamic hip arthrogram reveals hinge abduction, demonstrating the anterolateral femoral head impinging on the acetabular rim. What is the most appropriate surgical management?

Explanation

Hinge abduction occurs when the enlarged, extruded anterolateral femoral head impinges against the lateral acetabular rim during abduction. A valgus-extension proximal femoral osteotomy is indicated to redirect the impinging segment away from the rim, improving congruency and relieving pain.

Question 95

A 7-year-old boy presents for follow-up 1 year after non-operative treatment of a Gartland Type II supracondylar humerus fracture. He has full range of motion but complains of an unsightly "gunstock" deformity of the elbow. What is the primary pathophysiological cause of this deformity?

Explanation

Cubitus varus (gunstock deformity) is the most common long-term complication of a pediatric supracondylar humerus fracture. It is predominantly caused by mechanical malreduction characterized by medial column comminution/collapse and residual internal rotation, rather than physeal growth arrest.

Question 96

A 6-month-old infant presents with a left thoracic curve of 28 degrees. Radiographs demonstrate a rib-vertebral angle difference (RVAD) of 26 degrees at the apical vertebra. MRI of the neuroaxis is completely normal. What is the most appropriate initial management?

Explanation

Infantile idiopathic scoliosis with a curve >20 degrees and an RVAD (Mehta's angle) >20 degrees is highly likely to progress. Serial Mehta casting is the gold standard for progressive infantile curves, as it can successfully control or even cure the deformity while allowing thoracic growth.

Question 97

A 14-year-old elite gymnast presents with severe, persistent low back pain. Radiographs reveal an L5-S1 isthmic spondylolisthesis with a 65% forward translation (Meyerding Grade III). Which of the following radiographic parameters is most predictive of further slip progression?

Explanation

In high-grade isthmic spondylolisthesis (Meyerding Grade III or higher), a high slip angle (lumbosacral kyphosis typically >40-50 degrees) is the most critical radiographic predictor of further forward translation and poor clinical outcomes.

Question 98

A 4-year-old girl with a BMI in the 99th percentile presents with progressive bilateral genu varum. Clinical exam shows a prominent lateral thrust during gait. Radiographs exhibit a sharp metaphyseal beak medially and a metaphyseal-diaphyseal angle of 18 degrees. What is the most appropriate management?

Explanation

This child has infantile Blount's disease. Because she is over the age of 3 and has advanced radiographic changes (high metaphyseal-diaphyseal angle and sharp medial beak), orthotic management will likely fail; thus, surgical realignment via proximal tibial valgus osteotomies is definitively indicated to prevent joint destruction.

Question 99

A 7-year-old child with spastic quadriplegic cerebral palsy (GMFCS level V) is evaluated for hip surveillance. Anteroposterior pelvic radiographs reveal bilateral hip subluxation with a Reimers migration percentage of 55%. The hips are currently painless, but abduction is symmetrically limited to 15 degrees. What is the most appropriate surgical treatment?

Explanation

In severe spastic cerebral palsy (GMFCS IV/V) with a Reimers migration percentage >40%, soft tissue releases alone have an unacceptably high failure rate. Bony reconstruction with varus derotational femoral osteotomies (VDRO), often combined with an acetabular procedure (e.g., Dega osteotomy), is required to achieve stable concentric reduction.

Orthopedic Pediatric Review | Dr Hutaif Pediatric Ortho -...

Pediatric Orthopaedic Board Review MCQs | ABOS & OITE

Pediatric Orthopaedic Board Review MCQs | ABOS & OITE

Chapter Index