SCFE — Loder Classification & Fixation

Slipped capital femoral epiphysis (SCFE) is the most common hip disorder in adolescents, characterised by displacement of the capital femoral epiphysis posteroinferiorly relative to the femoral neck through the hypertrophic zone of the proximal femoral physis. It is not a true fracture but a physeal stress failure — the epiphyseal plate in adolescence is weakened by the hormonal milieu of puberty and the increased mechanical loads of rapid body weight gain, predisposing it to failure. The femoral head (epiphysis) remains in the acetabulum while the femoral neck displaces anteriorly and superiorly relative to the head — which is counterintuitive but important: on clinical examination the limb is in external rotation and the hip is flexed into obligate external rotation (as the neck has moved anterior to the head).

• Epidemiology: incidence approximately 10.8 per 100,000 adolescents; peak age 10–16 years (boys slightly later than girls — correlating with physeal closure); male:female 2.4:1; obesity is the most important risk factor — present in approximately 50–80% of cases; Black and Hispanic children have higher incidence; bilateral SCFE occurs in approximately 20–40% of cases (may be simultaneous or sequential); the contralateral hip should always be assessed and monitored
• Underlying endocrine associations: SCFE occurring outside the typical age range (prepubertal child <10 years, or an older adolescent >16 years), in an underweight patient, or in the absence of obesity should trigger an endocrine workup; associated conditions include hypothyroidism, hypogonadism, growth hormone excess (acromegaly), panhypopituitarism, renal osteodystrophy, and radiation-induced growth plate damage; in these `atypical` SCFE cases, the physeal failure is attributable to an underlying hormonal or metabolic abnormality rather than mechanical overload alone; endocrine workup: TFTs, LH, FSH, IGF-1, renal function panel

The Loder classification (1993) classifies SCFE based on the ability of the patient to bear weight at the time of presentation. This simple clinical classification has powerful prognostic significance — specifically, it stratifies the risk of avascular necrosis of the femoral head.

• The critical rule: DO NOT reduce a stable SCFE; forced reduction dramatically increases AVN risk (the remodelled blood supply around a chronic slip is disrupted by acute reduction); in situ fixation preserves the current anatomy and allows remodelling; the apparent deformity (obligate external rotation) corrects with growth and remodelling of the femoral neck; even moderate SCFE degrees (Grade II) are treated with in situ fixation rather than reduction in stable cases

• Referred knee pain — the classic diagnostic pitfall: approximately 15–25% of SCFE patients present with knee pain rather than hip pain; the knee pain is referred from the obturator or anterior femoral cutaneous nerve distribution; a child with knee pain and no knee pathology on examination MUST have the hip examined and hip X-rays taken; failure to examine the hip in a child with knee pain is a recognised medicolegal error; always `look at the hip when the knee hurts in a child`
• Drehmann sign: the affected hip, when passively flexed, drifts into obligate external rotation; this is the pathognomonic clinical sign of SCFE — the posterior position of the femoral head (epiphysis) causes the femoral neck to abut the posterior acetabulum when flexion is attempted, forcing the hip into external rotation; the sign is strongly positive in moderate-to-severe SCFE
• Radiographic diagnosis: AP pelvis and frog-lateral or true lateral X-ray of the hip; key signs — (1) Klein`s line: on the AP view, a line drawn along the superior femoral neck (Klein`s line) should intersect the femoral head by at least 20%; in SCFE, Klein`s line passes above the epiphysis or intersects less than 20% — the epiphysis has slipped medially (posteriorly on lateral view); (2) `ice cream falling off a cone` appearance — the epiphysis (ice cream) has slipped off the femoral neck (cone); (3) `blanch sign of Steel` — a crescentic area of increased density in the metaphysis of the femoral neck on AP view, caused by overlapping bone of the slipped epiphysis
• MRI: the most sensitive imaging modality for pre-slip (physeal stress reaction) and early SCFE not visible on plain X-ray; shows physeal widening, surrounding oedema, and subtle epiphyseal displacement before plain X-ray changes are apparent; indicated when clinical suspicion is high and X-rays are equivocal; also identifies AVN early

• In situ pinning — the standard treatment for stable SCFE (all grades): a single percutaneous cannulated screw is inserted in situ (without reduction) under fluoroscopic guidance; the screw is aimed toward the centre of the epiphysis (central third on AP and lateral views); the screw tip must be within 5 mm of the subchondral bone — the `5 mm rule`; the screw should NOT penetrate the articular cartilage (chondrolysis risk) and must cross the physis to achieve physeal closure; surgical technique — image intensifier in operating theatre; two fluoroscopic views confirm screw position; percutaneous stab incision; usually a single 7.3 mm or 8 mm cannulated screw
• Number of screws: one screw is standard for stable SCFE; two screws may be used for severe or unstable slips to provide additional stability and rotational control; two screws increase the risk of AVN from interference with the blood supply (the lateral epiphyseal vessels enter through the neck — avoid placing screws through this zone); most evidence supports one screw for stable cases
• Contralateral prophylactic pinning: highly controversial; the contralateral hip develops SCFE in 20–40% of cases over the subsequent years; prophylactic in situ fixation of the asymptomatic contralateral hip eliminates the risk of the second slip but exposes a potentially unaffected hip to the risks of surgery (AVN, chondrolysis, infection, secondary OA from screw penetration); indications for prophylactic pinning — endocrine abnormality (high risk of contralateral slip); young age (<10 years at first slip); marked obesity; difficult follow-up/compliance; the debate continues and practice varies between centres
• Unstable SCFE: surgical emergency; immediate gentle positioning (traction) to decompress the joint; capsular decompression (joint aspiration or capsulotomy/drilling) to reduce intracapsular pressure and potentially improve AVN risk; gentle reduction versus in situ fixation is debated — evidence suggests that gentle reduction (not forcible manipulation) followed by fixation may reduce AVN risk compared to in situ fixation in truly unstable cases, but this is not universally accepted; in situ fixation is still widely practised even for unstable slips by many surgeons
• Severe or persistent SCFE deformity: cam-type femoroacetabular impingement (FAI) develops after SCFE from the prominent posterior metaphyseal callus and deformity of the proximal femur; may cause early OA; surgical correction — subcapital realignment osteotomy (Dunn procedure or modified Dunn via surgical hip dislocation — the technique described by Ganz; allows anatomical correction of the epiphyseal position via an extended retinacular flap that preserves blood supply); base-of-neck osteotomy (Imhaüser osteotomy); intertrochanteric valgus-extension osteotomy

• SCFE: most common hip disorder in adolescents; obese boys 10–16 years; epiphysis displaces posteroinferiorly relative to neck; neck moves anteriorly relative to head — obligate external rotation on hip flexion (Drehmann sign)
• Loder classification: Stable (can bear weight, <10% AVN) vs Unstable (cannot bear weight, >47% AVN); critical prognostic distinction
• DO NOT REDUCE a stable SCFE — in situ fixation only; reduction increases AVN risk dramatically; the deformity remodels with growth
• Referred knee pain: 15–25% present with knee pain; always examine and X-ray the hip in any child with knee pain; a classic medicolegal pitfall — `the hip when the knee hurts`
• Klein`s line (AP view): line along superior femoral neck should intersect >20% of the epiphysis; in SCFE — passes above the epiphysis (intersects <20%); pathognomonic
• Screw tip within 5 mm of subchondral bone (`5 mm rule`); central third of epiphysis on AP and lateral; single screw standard; do NOT penetrate articular cartilage (chondrolysis)
• Atypical SCFE: prepubertal (<10 years) or underweight patient → endocrine workup (TFTs, LH/FSH, IGF-1, renal function); hypothyroidism, growth hormone abnormality, hypogonadism
• Unstable SCFE: orthopaedic emergency; joint aspiration/capsulotomy to decompress; gentle reduction vs in situ fixation debated; high AVN risk regardless of technique; some advocate Ganz surgical hip dislocation for correction
• Bilateral SCFE: 20–40% bilateral; monitor contralateral hip; prophylactic pinning controversial — consider in endocrine cases, young age, difficult follow-up
• Chondrolysis: screw penetrating articular surface; remove screw; NSAIDs; joint space narrowing on X-ray; distinguish from septic arthritis (fever, elevated WBC)