A 14-year-old girl with a history of hypothyroidism presents with bilateral hip pain and a waddling gait of 6 months' duration. She reports pain in the groin and medial thigh, worse with activity. On examination, both hips show limited internal rotation and abduction. Pelvic radiographs reveal bilateral posteromedial displacement of the femoral heads with respect to the femoral necks, more pronounced on the right side. The right slip measures 40° on the lateral view. What is the most likely complication if this patient does not receive appropriate treatment?

Explanation

## Clinical Presentation and Risk Stratification **Key Point:** This patient has chronic bilateral SCFE (symptoms > 3 weeks), with the right side showing a moderate slip (40°). The presence of an endocrine disorder (hypothyroidism) increases the risk of bilateral involvement and complications. ## SCFE Severity Classification | Slip Severity | Angle (Lateral View) | Risk of AVN | Management | |---|---|---|---| | Mild | < 30° | Low (< 5%) | In situ pinning | | Moderate | 30–60° | Moderate (5–15%) | In situ pinning ± prophylactic contralateral pinning | | Severe | > 60° | High (15–50%) | In situ pinning ± derotation osteotomy | **High-Yield:** The right slip of 40° is moderate and carries a 5–15% risk of AVN. Without treatment, chronic SCFE leads to progressive deformity and early osteoarthritis. ## Pathophysiology of Complications ```mermaid flowchart TD A[Untreated Chronic SCFE]:::outcome --> B[Persistent Posteromedial<br/>Femoral Head Displacement]:::outcome B --> C[Altered Hip Biomechanics]:::outcome C --> D[Femoroacetabular Impingement<br/>and Cartilage Damage]:::outcome D --> E[Early-Onset Osteoarthritis<br/>by 3rd–4th Decade]:::urgent B --> F[Vascular Compromise<br/>if Severe Slip or Reduction]:::urgent F --> G[Avascular Necrosis<br/>of Femoral Head]:::urgent E --> H[Hip Arthroplasty<br/>in Young Adult]:::urgent ``` ## Why AVN and Early OA Are the Primary Concerns 1. **Avascular necrosis (AVN):** - Occurs in 5–50% of SCFE cases, depending on severity and whether reduction is attempted - The femoral head blood supply is tenuous; further displacement or manipulation compromises it - Presents with progressive hip pain and collapse of the femoral head 2. **Early-onset osteoarthritis:** - Results from chronic femoroacetabular impingement (FAI) due to the persistent posteromedial slip - The femoral head-neck junction becomes abnormal, causing cam-type impingement - Cartilage damage is progressive and irreversible - Patients develop symptomatic OA by the 3rd–4th decade of life **Clinical Pearl:** Chronic SCFE is the most common cause of secondary hip osteoarthritis in young adults. The combination of AVN risk and FAI-driven OA makes early recognition and treatment critical. ## Why Other Options Are Incorrect - **Femoral neck fracture:** While acute unstable SCFE can progress to complete separation, this is not the most common long-term complication. Fracture is an acute event; the question asks about untreated chronic SCFE. - **Contralateral progression:** Although bilateral involvement occurs in 20–40% of cases, the question specifies the right side is already affected. The complication being asked about is what happens to the existing slip if untreated. - **Coxa valga:** SCFE causes coxa vara (varus deformity), not valga. External rotation contracture may develop, but it is not the primary complication. [cite:Campbell's Operative Orthopaedics 13e Ch 32; Tuli's Textbook of Orthopaedics 9e Ch 15]