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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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').

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.