This practice set contains high-yield board review questions covering key concepts in Pediatric Hip. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.
Question 321
Topic: Pediatric Hip
A 12-year-old obese boy presents with insidious onset of left knee pain and a limp. On physical exam, there is obligate external rotation of the left hip with passive hip flexion. What is the most likely diagnosis?
Correct Answer & Explanation
. Slipped capital femoral epiphysis
Explanation
Slipped capital femoral epiphysis (SCFE) classically presents in obese adolescents with hip or referred knee pain. Obligate external rotation during passive hip flexion is a hallmark physical exam finding due to the anterior and superior displacement of the metaphysis relative to the epiphysis.
Question 322
Topic: Pediatric Hip
When treating an infant for developmental dysplasia of the hip (DDH) using a Pavlik harness, prolonged hyperflexion of the hips places the patient at highest risk for which complication?
Correct Answer & Explanation
. Femoral nerve palsy
Explanation
Hyperflexion in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to transient femoral nerve palsy. In contrast, excessive abduction places the hip at higher risk for avascular necrosis of the femoral head.
Question 323
Topic: Pediatric Hip
A 4-month-old female infant is diagnosed with developmental dysplasia of the hip (DDH). Ultrasound confirms a dislocated left hip that is reducible. What is the most appropriate initial treatment?
Correct Answer & Explanation
. Pavlik harness
Explanation
The Pavlik harness is the gold standard initial treatment for reducible DDH in infants up to 6 months of age. It dynamically maintains the hip in flexion and mild abduction, promoting spontaneous deepening of the acetabulum.
Question 324
Topic: Pediatric Hip
An obese 12-year-old boy presents with left groin pain and a limp. On physical examination, as the affected hip is passively flexed, it demonstrates an obligatory motion. Which obligatory motion is classic for this condition?
Correct Answer & Explanation
. External rotation
Explanation
The patient has a Slipped Capital Femoral Epiphysis (SCFE). The classic physical exam finding is obligatory external rotation of the thigh as the hip is passively flexed.
Question 325
Topic: Pediatric Hip
Which of the following is the strongest clinical predictor for the development of avascular necrosis (AVN) following a slipped capital femoral epiphysis (SCFE)?
Correct Answer & Explanation
. Inability to bear weight on the affected limb
Explanation
Clinical instability, defined as the inability to bear weight even with crutches, is the strongest predictor of AVN in SCFE. Unstable slips have an AVN rate approaching 20 to 50 percent, whereas stable slips have an AVN rate of nearly zero.
Question 326
Topic: Pediatric Hip
A 12-year-old obese male presents with acute-on-chronic hip pain and an inability to bear weight. Radiographs confirm a severe Slipped Capital Femoral Epiphysis (SCFE). Why is forceful closed reduction of the slippage strictly contraindicated?
Correct Answer & Explanation
. It significantly increases the risk of avascular necrosis
Explanation
The standard of care for a SCFE is in situ pinning. Forceful closed reduction of the epiphysis severely compromises the fragile retinacular blood supply, exponentially increasing the risk of iatrogenic avascular necrosis.
Question 327
Topic: Pediatric Hip
A 13-year-old obese male presents with a left slipped capital femoral epiphysis (SCFE). Which of the following is an absolute indication for prophylactic pinning of the contralateral asymptomatic hip?
Correct Answer & Explanation
. Presence of an endocrine disorder such as hypothyroidism
Explanation
Prophylactic pinning of the contralateral hip in SCFE is highly recommended and considered an absolute indication in patients with underlying endocrine or renal disorders. These metabolic conditions carry an extremely high risk for bilateral involvement.
Question 328
Topic: Pediatric Hip
A 13-year-old obese boy presents with severe left hip pain and an inability to bear weight after a minor fall. Radiographs confirm an acute, unstable slipped capital femoral epiphysis (SCFE). What is the primary theoretical rationale for performing an urgent capsulotomy prior to percutaneous pinning?
Correct Answer & Explanation
. To decompress an intracapsular hematoma and reduce the risk of osteonecrosis
Explanation
Unstable SCFE carries a high risk of avascular necrosis (AVN) due to kinking or compression of the delicate retinacular vessels. An urgent capsulotomy decompresses the intracapsular hematoma, which can lower intracapsular pressure, potentially restoring blood flow and reducing AVN risk.
Question 329
Topic: Pediatric Hip
A 12-year-old obese male presents with an acute-on-chronic slipped capital femoral epiphysis (SCFE). He is in severe pain and completely unable to bear weight. What is the most critical risk factor for the subsequent development of avascular necrosis (AVN) in this patient?
Correct Answer & Explanation
. The clinical instability of the slip (inability to bear weight)
Explanation
The clinical stability of the slip, defined strictly by the inability to bear weight even with crutches (an unstable SCFE), is the single most important risk factor for developing AVN. Rates of AVN in unstable SCFE can reach up to nearly 50%, whereas stable SCFE rarely results in osteonecrosis.
Question 330
Topic: Pediatric Hip
An infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During a follow-up visit, you notice the infant is lacking active knee extension on the treated side. This complication is most likely due to which improper positioning of the harness?
Correct Answer & Explanation
. Excessive hip hyperflexion.
Explanation
Excessive hyperflexion in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to a femoral nerve palsy characterized by a lack of active knee extension. Excessive abduction, conversely, increases the risk of avascular necrosis.
Question 331
Topic: Pediatric Hip
A 13-year-old obese male presents with acute severe groin pain and an inability to bear weight. Radiographs show a slipped capital femoral epiphysis (SCFE). He is diagnosed with an unstable SCFE. Which of the following is the most significant risk factor for the development of avascular necrosis (AVN) in this patient?
Correct Answer & Explanation
. The clinical instability of the slip (inability to bear weight)
Explanation
The defining feature of an unstable SCFE is the clinical inability to bear weight, even with crutches. This instability correlates with a significantly higher risk of AVN (up to 50%) compared to stable slips.
Question 332
Topic: Pediatric Hip
A 12-year-old obese male presents with left knee pain and an obligate external rotation of the hip during passive flexion. Radiographs confirm a mild stable slipped capital femoral epiphysis (SCFE). What is a primary indication for prophylactic pinning of the contralateral asymptomatic hip?
Correct Answer & Explanation
. Endocrine disorders such as hypothyroidism or renal osteodystrophy
Explanation
Endocrine disorders significantly increase the risk of developing bilateral SCFE. Prophylactic pinning of the contralateral hip is highly recommended in these specific metabolic populations.
Question 333
Topic: Pediatric Hip
A 6-month-old female with developmental dysplasia of the hip (DDH) is planned for closed reduction and spica casting. According to Ramsey's criteria, the 'safe zone' of reduction is defined by the arc between the angle of maximum abduction and the angle of:
Correct Answer & Explanation
. Redislocation (adduction)
Explanation
The safe zone of Ramsey is the arc of motion between maximum abduction and the angle of redislocation. Maintaining the hip within this zone minimizes AVN risk while preventing loss of reduction.
Question 334
Topic: Pediatric Hip
A 42-year-old patient presents with a painful varus knee deformity. A full-length standing radiograph is obtained, and the joint orientation angles are measured as shown in the diagram below. The measured Mechanical Lateral Distal Femoral Angle (mLDFA) is 95°, and the Medial Proximal Tibial Angle (MPTA) is 87°.
Based on Paley's principles and the provided normal values, where is the primary anatomical location of this patient's varus deformity?
Correct Answer & Explanation
. Distal femur.
Explanation
Correct Answer: BThe case provides the normal values for Paley's joint orientation angles: mLDFA (Mechanical Lateral Distal Femoral Angle) normal range is 85° to 90° (Avg 87°), and an mLDFA > 90° indicates distal femoral varus. The MPTA (Medial Proximal Tibial Angle) normal range is 85° to 90° (Avg 87°), and an MPTA < 85° indicates proximal tibial varus. In this patient, the mLDFA is 95°, which is significantly greater than 90°, indicating a distal femoral varus deformity. The MPTA is 87°, which falls within the normal range (85°-90°), indicating normal proximal tibial alignment. Therefore, the primary anatomical location of the varus deformity is the distal femur (Option B). Option A (proximal femur) would be indicated by an abnormal mLPFA. Option C (proximal tibia) would be indicated by an abnormal MPTA. Option D (distal tibia) would be indicated by an abnormal LDTA. Option E (intra-articular) would be indicated by an abnormal JLCA, or if both mLDFA and MPTA were normal despite a varus MAD.
Question 335
Topic: Pediatric Hip
A 45-year-old male presents with a severe adduction deformity of the left hip, causing significant pelvic obliquity and an apparent leg length discrepancy. His preoperative radiograph is shown in the left panel of the image below. Based on Paley's principles, what does the intersection point of the Proximal Mechanical Axis (PMA) and the Distal Mechanical Axis (DMA) represent, and what is its primary significance in planning the corrective osteotomy?
Correct Answer & Explanation
. The Center of Rotation of Angulation (CORA), representing the apex of the bony deformity and the ideal level for osteotomy.
Explanation
Correct Answer: CThe case clearly defines the Center of Rotation of Angulation (CORA) as 'the precise mathematical point in two-dimensional space where the deformity is centered.' For any angular deformity originating at the hip or within the proximal femur, the CORA is defined as 'the intersection point of the Proximal Mechanical Axis (PMA) and the Distal Mechanical Axis (DMA).' The text further states that 'accurately locating the CORA is the single most critical step in planning a mechanically sound osteotomy' and that 'if the CORA is located within the osseous boundaries of the proximal femur, it identifies the apex of the bony deformity and dictates the biomechanically ideal level for the corrective osteotomy.' The image visually demonstrates the divergence of the PMA and DMA in the preoperative film, and their intersection would define the CORA. Options A, B, D, and E describe other measurements or concepts that are not the primary significance of the intersection of PMA and DMA in this context.
Question 336
Topic: Pediatric Hip
A 38-year-old male presents with chronic right knee pain, worse with activity, and a noticeable Trendelenburg gait. Radiographs reveal a decreased Neck Shaft Angle (NSA) of 115 degrees on the right femur, with an otherwise normal knee joint line convergence angle (JLCA). Based on Paley's principles, what is the most likely biomechanical consequence of this proximal femoral deformity on the lower extremity?
Correct Answer & Explanation
. Medial shift of the mechanical axis, leading to varus deformity and medial compartment knee overload.
Explanation
Correct Answer: BThe patient presents with a decreased Neck Shaft Angle (NSA) of 115 degrees, which is indicative of coxa vara (normal NSA is 124° to 136°). According to Paley's principles, coxa vara causes the femoral head to sit lower and more horizontally. This biomechanically shifts the mechanical axis of the entire lower extremity medially. A medial shift of the mechanical axis at the knee joint results in a varus deformity, leading to increased compressive forces and overload on the medial compartment of the knee. This explains the patient's chronic knee pain and the Trendelenburg gait, which is often associated with the functional leg length discrepancy and abductor insufficiency seen with severe coxa vara.Option A is incorrectbecause a lateral shift of the mechanical axis and subsequent valgus deformity is characteristic of coxa valga (increased NSA), not coxa vara.Option C is incorrectbecause coxa vara typically causes a functional leg length discrepancy where the affected limb appears shorter, not longer, leading to the pelvis tilting down on the affected side.Option D is incorrectbecause increased femoral head elevation and associated ligamentous laxity are features of coxa valga, not coxa vara.Option E is incorrectbecause while a fixed pelvic obliquity can cause a Trendelenburg gait, the primary cause described in this vignette is a specific proximal femoral deformity (coxa vara) that directly impacts the mechanical axis and can induce a functional LLD, leading to compensatory pelvic tilt and gait abnormalities.
Question 337
Topic: Pediatric Hip
A 60-year-old female presents with severe right hip pain and a history of childhood hip dysplasia. Full-length standing AP radiographs of her lower extremities reveal a Mechanical Lateral Proximal Femoral Angle (mLPFA) of 78 degrees. Her Neck Shaft Angle (NSA) is 128 degrees, and her Joint Line Convergence Angle (JLCA) is 1 degree. Based on these measurements and Paley's principles, what is the most accurate interpretation of her proximal femoral deformity?
Correct Answer & Explanation
. The patient has a varus deformity of the proximal femur, as indicated by the mLPFA.
Explanation
Correct Answer: CThe Mechanical Lateral Proximal Femoral Angle (mLPFA) is the primary angle for assessing varus or valgus of the proximal femur, relating the mechanical axis to the proximal joint line. A normal mLPFA ranges from 85° to 95°. The patient's mLPFA of 78 degrees is significantly less than 85 degrees, which definitively indicates a varus deformity of the proximal femur (coxa vara at the level of the metaphysis/diaphysis, even if the NSA is normal).Option A is incorrectbecause coxa valga is characterized by an increased neck-shaft angle (typically >136°), and the patient's NSA of 128 degrees is within the normal range. Furthermore, a valgus deformity would present with an mLPFA >95°.Option B is incorrectbecause while the NSA and JLCA are within normal limits, the mLPFA is clearly abnormal, indicating a significant proximal femoral deformity.Option D is incorrectbecause a valgus deformity would be indicated by an mLPFA greater than 95 degrees, not 78 degrees.Option E is incorrectbecause a JLCA of 1 degree is within the normal range (0° to 2°), suggesting that the knee joint itself is not the primary source of malalignment, although it could be secondarily affected over time by the proximal femoral varus.
Question 338
Topic: Pediatric Hip
In a patient undergoing a single-level pelvic support osteotomy (proximal valgus osteotomy only) for a chronically dislocated hip, which of the following long-term complications is most likely to develop if a second, distal osteotomy is NOT performed?
Correct Answer & Explanation
. Valgus osteoarthritis of the ipsilateral knee.
Explanation
A single-level proximal valgus osteotomy shifts the mechanical axis laterally, subjecting the lateral compartment of the knee to increased stress. Without a second, distal osteotomy to realign the mechanical axis, this lateral deviation leads to genu valgum and subsequent lateral compartment (valgus) osteoarthritis.
Question 339
Topic: Pediatric Hip
A 12-year-old boy with a history of Legg-Calvé-Perthes disease presents with a 2.5 cm LLD. His growth chart shows an initial period of increasing discrepancy, followed by a stable period where the discrepancy remained constant, and now a recent acceleration in discrepancy. This multi-phasic, erratic pattern of LLD progression is most consistent with which Shapiro type?
Correct Answer & Explanation
. Type 4: The Upward Slope Plateau Upward Slope Pattern
Explanation
The case describes the Type 4 pattern, which is characterized by an erratic, multi-phasic progression. The text states this pattern is 'most classically Legg-Calvé-Perthes disease.' It involves an initial upward slope (increasing LLD), followed by a plateau (stabilization), and then a second upward slope (accelerating discrepancy due to delayed physeal arrest).
Question 340
Topic: Pediatric Hip
A 4-year-old boy presents with right hip pain, a limp, and a temperature of 38.2°C. He refuses to bear weight. Laboratory tests reveal a WBC count of 11,500/mm3, an ESR of 35 mm/hr, and a CRP of 3.5 mg/dL. Based on the modified Kocher criteria (Caird et al.), what is the most appropriate next step in management?
Correct Answer & Explanation
. Urgent ultrasound-guided hip aspiration
Explanation
The addition of a CRP > 2.0 mg/dL to the Kocher criteria creates an excellent independent predictor of septic arthritis. With fever, inability to bear weight, and elevated CRP, the probability is high, necessitating urgent aspiration.
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