Slipped Upper Femoral Epiphysis (SUFE)

History:

• •Hip, groin, or thigh pain - typically insidious over weeks to months in chronic SUFE; aching and activity-related.
• •Knee or medial thigh pain referred from the hip via the obturator nerve - present in up to 15-25% as the sole complaint and the classic cause of missed SUFE. Rule: always examine the hip in any adolescent with knee or medial thigh pain.
• •Antalgic limp - progressive in chronic disease, sudden in acute unstable SUFE.
• •Unstable SUFE: sudden severe hip pain with inability to weight-bear, sometimes after minor trauma; surgical emergency.
• •Typical patient: overweight or obese adolescent during the growth spurt; boys greater than girls; mean age around 12-13 in boys and 11-12 in girls.
• •No systemic features (no fever, night sweats, or weight loss).

Examination:

• •Antalgic gait (stable) or inability to weight-bear (unstable).
• •OBLIGATE external rotation during hip flexion - the hallmark sign. The limb involuntarily externally rotates as the hip is flexed; the single most important clinical finding.
• •Reduced INTERNAL ROTATION - the most sensitive and first-restricted movement; test in both flexion and extension.
• •Reduced flexion and abduction.
• •Leg shortening on the affected side; the limb may rest in external rotation.
• •Bilateral examination is mandatory - always assess the contralateral hip given the 20-40% bilateral rate.

Atypical SUFE - when to suspect an endocrine cause: age under 10, normal or low BMI, bilateral (particularly simultaneous), short stature, delayed puberty, or known endocrine or renal condition. Hypothyroidism is the most important association; growth hormone deficiency and hypogonadism are also recognised.

Differential diagnoses: Perthes disease (younger, AVN of epiphysis with sclerosis and fragmentation); transient synovitis (younger, post-viral, self-limiting); septic arthritis (any age - fever, non-weight-bearing, raised markers - emergency); stress fracture; labral tear or FAI; malignancy (night pain, systemic features, abnormal bloods).

Plain X-rays are first-line and usually diagnostic. Both AP pelvis and lateral views of both hips are essential. Early or very mild SUFE may be radiographically subtle - persistent clinical suspicion warrants urgent specialist input even if initial films are not definitive.

Plain radiographs - AP pelvis and lateral:

AP pelvis findings:

• •Klein''s line is drawn along the superior border of the femoral neck on the AP view. In a normal hip it intersects a portion of the femoral epiphysis. When Klein''s line fails to intersect the epiphysis (or intersects less than the contralateral side) this is a positive Trethowan''s sign and indicates SUFE.
• •Physeal widening and irregularity.
• •Reduced epiphyseal height (foreshortening from posterior displacement).
• •Metaphyseal blanch sign of Steel - a crescent of double density at the metaphysis overlapping the posteriorly displaced epiphysis.
• •Compare with the contralateral hip - subtle slips may only be apparent on comparison.

Lateral views:

• •Frog-leg lateral is more sensitive than AP because the slip is posterior; the deformity is most obvious on this view.
• •IMPORTANT: do NOT perform a frog-leg lateral in suspected unstable SUFE - the positioning may worsen the slip. Use a cross-table (shoot-through) lateral with the patient supine and the limb in a neutral position.

Both hips must be imaged - AP pelvis covers both; frog-leg laterals of each hip individually in stable disease, or cross-table laterals in unstable disease.

MRI is not routinely needed when X-rays are diagnostic. Use when X-rays are normal or equivocal but suspicion persists (pre-slip or very early slip), to assess AVN risk in unstable SUFE, or to exclude other pathology.

Blood tests: inflammatory markers are typically normal in isolated SUFE and are mainly useful to exclude infection or malignancy. Endocrine screening when indicated: TFTs, bone profile, IGF-1, sex hormones.

Once SUFE is diagnosed or suspected: make NON-WEIGHT-BEARING immediately, do NOT attempt forceful reduction, and refer same day for orthopaedic assessment. Unstable SUFE requires urgent same-day operative stabilisation.

Immediate management:

• •Non-weight-bearing using crutches or a wheelchair. Do not walk on the affected limb until surgical stabilisation.
• •Do NOT attempt manual reduction of a stable chronic slip - this damages retinacular vessels and substantially increases AVN risk.
• •Same-day referral to paediatric orthopaedics. Unstable SUFE is a surgical emergency requiring urgent operative stabilisation.

Surgical management:

In situ fixation - the standard treatment for stable SUFE. A single cannulated screw is inserted percutaneously across the physis into the epiphysis under fluoroscopic guidance, without attempting to reduce the slip. The screw stabilises the epiphysis and allows physeal closure. In situ screw fixation is the standard treatment for most stable SUFE, particularly mild slips; management of moderate and severe stable slips may vary by specialist centre.

Unstable SUFE - urgent operative stabilisation: in situ screw fixation remains the standard approach. Gentle reduction may be attempted at surgery in some centres. The modified Dunn procedure (surgical hip dislocation allowing open anatomical reduction while protecting the retinacular blood supply) is increasingly used at specialist centres for unstable or severe slips (NICE IPG511). AVN risk remains substantially higher than for stable SUFE regardless of surgical approach.

Prophylactic contralateral fixation - controversial. Bilateral involvement occurs in 20-40%, and the contralateral hip may slip at presentation or subsequently. Some centres fix the contralateral hip prophylactically, particularly in endocrinopathy, younger age, open triradiate cartilage, or other high-risk features. Others observe with serial X-rays. The Modified Oxford Bone Age Score (MOBAS) is used by some UK centres to help predict contralateral slip risk and guide decision-making. No universal UK consensus - the decision is specialist-led and individualised.

Management of complications:

• •AVN (the most serious complication, substantially higher risk in unstable SUFE - up to ~50% historically): progressive pain, reduced ROM, femoral head collapse. Management is challenging - protected weight-bearing and, ultimately, hip replacement for severe cases. Prevention (avoiding forceful reduction and prompt stabilisation of unstable slips) is far better than treatment.
• •Chondrolysis: acute destruction of articular cartilage with rapid joint space narrowing, pain, and stiffness. Poor prognosis; supportive management.
• •Cam-type femoroacetabular impingement (FAI) - the most common LONG-TERM sequela. Residual bony prominence at the head-neck junction impinges against the acetabular rim during flexion and internal rotation, producing pain, labral tears, and accelerated OA in young adulthood. Highly relevant to SEM practice. Physiotherapy initially; surgical osteoplasty if symptomatic despite conservative management.

Post-operative recovery, restoration of function, return to activity, and long-term surveillance.

Post-operative rehabilitation:

• •Weight-bearing: for stable slips treated with in situ fixation, many surgeons allow weight-bearing as tolerated using crutches for comfort. For unstable or more severe slips, weight-bearing progression is more cautious. Specific protocols are specialist-directed.
• •ROM exercises: gentle active ROM; internal rotation and flexion are often limited by residual slip deformity - do not force.
• •Strengthening: hip abductors (Trendelenburg prevention), quadriceps, core; progressive and age-appropriate.
• •Gait re-education to address antalgic and Trendelenburg patterns.

Return to activity and sport is specialist-directed and depends on stability, severity, symptoms, and radiographic follow-up. Low-impact activity (swimming, cycling) typically resumes earlier; full return to sport including contact and high-impact activity follows later, guided by the treating surgeon.

Long-term follow-up: serial X-rays until physeal closure with monitoring for contralateral slip, screw position, AVN, and physeal closure. The contralateral hip must continue to be assessed and imaged. Screw removal is not routine and is considered if symptomatic after physeal closure. Moderate and severe SUFE patients are at risk of cam-type FAI and early OA - long-term hip surveillance is appropriate.

Weight management: obesity is the strongest modifiable risk factor; sensitive, age-appropriate weight counselling and paediatric dietetic input where available. Psychological support and family/school liaison matter through a developmentally significant period.

• •Loder stability classification - stable vs unstable; the most clinically important framework because it predicts AVN risk.
• •Klein''s line and Trethowan''s sign - the standard radiographic screening tool on AP pelvis.
• •NICE IPG511 - open reduction (modified Dunn) for slipped capital femoral epiphysis at specialist centres.
• •BSCOS consensus and NICE CKS limping-child pathway - the UK reference for assessment, investigation, and referral.
• •Modified Oxford Bone Age Score (MOBAS) - used by some UK centres to guide prophylactic contralateral fixation decisions.

• •SUFE: posterior-inferior epiphyseal slip through the hypertrophic zone; age 10-16; obesity strongest risk factor.
• •Loder: stable (can weight-bear, low AVN risk) vs unstable (cannot, surgical emergency, much higher AVN risk).
• •Hallmark sign: obligate external rotation on hip flexion; first restricted movement is internal rotation.
• •Klein''s line fails to intersect the epiphysis on AP (positive Trethowan''s sign); frog-leg lateral most sensitive.
• •Treatment: in situ percutaneous screw fixation; do NOT reduce a stable chronic slip; non-weight-bearing until surgery.
• •Always image BOTH hips; bilateral 20-40%; endocrine screen if atypical features.