Perthes Disease

History:

• •Limp - the most common presenting feature. Often initially painless, progressing to painful and antalgic. Insidious onset over weeks.
• •Hip pain in the groin, anterior thigh, or lateral hip - activity-related, worse at the end of the day.
• •Knee pain - classic referred pain from the hip via the obturator nerve. The commonest cause of missed or delayed Perthes diagnosis - always examine the hip in a child with knee pain.
• •Reduced activity - the child avoids running and sits out of PE.
• •No systemic features: no fever, night sweats, or weight loss (these suggest infection or malignancy).

Examination:

• •Antalgic gait, sometimes with a Trendelenburg pattern (hip abductor weakness from pain inhibition).
• •Reduced ROM, with INTERNAL ROTATION the first and most limited movement (test in both flexion and extension; prone internal rotation in extension is the most sensitive test for early hip pathology in children). Abduction is often restricted; a fixed flexion deformity may develop (Thomas test).
• •Apparent leg shortening from adduction contracture or true shortening from collapse.
• •Quadriceps and gluteal wasting on the affected side.

Systematic hip examination follows the sequence: gait, then standing (Trendelenburg), then supine (ROM, Thomas test, leg length), then prone (internal rotation in extension).

Age-based differential for the limping child:

• •0-3 years: DDH, septic arthritis, toddler''s fracture, NAI.
• •4-8 years: Perthes, transient synovitis, septic arthritis.
• •9-16 years: SUFE, Osgood-Schlatter, apophysitis, stress fracture.
• •Any age: septic arthritis (emergency), osteomyelitis, malignancy, JIA.

Transient synovitis vs Perthes vs septic arthritis:

• •Transient synovitis: acute onset (often post-viral), absent or low-grade fever, weight-bearing, normal or mildly raised markers, resolves within 1-2 weeks.
• •Perthes: insidious onset over weeks, no fever, weight-bearing, normal markers; weeks to months.
• •Septic arthritis: acute over hours to days, high fever (>38.5 degrees C), refusing to weight-bear, systemically unwell, raised markers - urgent aspiration.

A presumed transient synovitis that does not improve over days or resolve within 1-2 weeks should prompt reconsideration for Perthes or other pathology.

Plain radiographs are first-line. MRI is the most sensitive investigation for early disease when X-rays are normal. A persistent limp with normal X-rays still warrants urgent referral.

Plain radiographs - AP pelvis AND frog-lateral are essential:

Waldenström-stage findings: Initial (sclerotic dense epiphysis, crescent/Caffey sign on frog-lateral); Fragmentation (fragmentation, lucencies, femoral head collapse and flattening, lateral extrusion, metaphyseal cysts); Reossification (progressive bone formation, contour redefining); Remodelling (residual deformity - coxa plana, coxa magna, coxa breva). X-rays may be NORMAL for the first 2-6 weeks; do not be reassured by a normal initial film in a child with persistent limp.

MRI:

• •The most sensitive investigation for early Perthes - detects marrow changes (loss of fatty marrow on T1, oedema on STIR/T2) before radiographic changes appear.
• •Defines the extent of epiphyseal involvement for prognostic assessment and surgical planning.
• •Differentiates Perthes from infection, malignancy, and transient synovitis.

USS detects hip effusion and is useful alongside X-ray for transient synovitis differentiation; it cannot diagnose Perthes itself.

Blood tests (FBC, CRP, ESR) should be NORMAL in Perthes and are used to exclude septic arthritis (raised WCC, CRP, ESR) and malignancy (abnormal FBC).

Classification systems:

• •Herring lateral pillar (applied during fragmentation): A = full lateral pillar height (good prognosis); B = >50% maintained (intermediate); B/C border = approximately 50% (poorer); C = <50% height (poor). Herring plus age at onset is the best prognostic predictor in current UK practice.
• •Catterall I-IV (extent of epiphyseal involvement): I = anterior epiphysis only; II = larger anterior involvement with intact lateral pillar; III = majority involvement with small intact posterior segment; IV = whole epiphysis. III/IV carries worse prognosis; less widely used than Herring in current UK practice.
• •Stulberg (at skeletal maturity): Class I (spherical, normal) - excellent; Class II (spherical with minor abnormalities, coxa magna) - good; Class III (ovoid, congruent) - fair, some OA risk; Class IV (flat, congruent) - poorer, earlier OA; Class V (flat, incongruent) - worst, early severe OA. Herring predicts the trajectory; Stulberg grades the final result.

Goal: maintain a spherical, congruent femoral head at skeletal maturity. The central principle is CONTAINMENT - keep the head within the acetabular mould during fragmentation. Management is age-stratified, classification-driven, and stage-dependent. UK practice follows BSCOS consensus and paediatric orthopaedic specialist pathways.

Observation and non-operative management:

• •Children under 6 years - generally better prognosis with greater remodelling potential; most are managed non-operatively.
• •Children 6-8 years with Herring A or B - intermediate risk, many do well with observation.
• •All children in the pre-fragmentation stage - classification cannot yet be applied; observe with serial X-rays.

Non-operative components:

• •Activity modification: avoid high-impact loading (running, jumping, competitive sport) during the active phase; encourage swimming and cycling (low-impact and ROM-preserving).
• •Physiotherapy: maintain ROM (particularly internal rotation and abduction - essential for containment; a stiff hip cannot be contained); strengthen hip abductors and core.
• •Analgesia (paracetamol, ibuprofen) for flares; short-term crutches if needed.
• •Serial X-rays every 3-4 months to monitor progression and apply Herring once fragmentation occurs.
• •Abduction bracing has historically been used to maintain containment, but modern UK practice has largely moved away from prolonged bracing in favour of activity modification and selective surgery.

Surgical containment (specialist-led):

Indications - decisions are specialist-led with some variation between centres:

• •Children over 8 years with Herring B/C border or Herring C (worst natural history) - the strongest indication.
• •Children 6-8 years with Herring B/C or C - offered at some centres.
• •Catterall III/IV with progressive deformity.
• •Progressive lateral subluxation despite non-operative management.
• •Persistent loss of ROM (particularly abduction and internal rotation) not improving with physiotherapy.
• •Hinge abduction - laterally extruded head impinges against the acetabular rim during abduction, indicating significant deformity.

Surgical options:

• •Femoral varus osteotomy: realigns the femoral shaft into varus, redirecting the femoral head deeper into the acetabulum - the most commonly performed containment procedure. Plate and screws are removed later.
• •Salter (innominate) pelvic osteotomy: redirects the acetabulum over the femoral head; used when acetabular coverage is deficient. May be combined with a femoral osteotomy.
• •Shelf acetabuloplasty: bone shelf added to the lateral acetabular margin.

Long-term monitoring: serial review to assess final femoral head shape (Stulberg classification), residual deformity (coxa plana, coxa magna, coxa breva), and early secondary OA. Total hip replacement may eventually be required in adult life for severe residual deformity.

Prognostic factors: better - younger age at onset (under 6), Herring A, maintained ROM, good containment throughout; worse - older onset (over 8), Herring B/C or C or Catterall IV, female sex, loss of ROM or containment, obesity, delayed diagnosis.

Rehabilitation focuses on maintaining ROM (internal rotation and abduction in particular - if ROM is lost, containment is compromised), preventing contracture, supporting wellbeing across a long disease course, and facilitating return to activity. Hip abductor, extensor, core, and quadriceps strengthening is age-appropriate and progressive. Gait re-education addresses antalgic and Trendelenburg patterns.

Swimming and cycling are encouraged throughout because they preserve ROM and fitness with reduced loading; high-impact loading is avoided during the active phase. Hydrotherapy is useful. The child should NOT be confined to bed rest or wheelchair unless there is a specific short-term post-operative indication.

Post-operative rehabilitation after femoral varus osteotomy typically involves 6-8 weeks of non- or partial weight-bearing followed by progressive weight-bearing, ROM, strengthening, gait re-education, and functional progression. Psychological support and school liaison (adjusted PE) are important across a 2-3 year disease course. Return to sport is guided by disease stage, ROM, pain, and specialist advice - full return to unrestricted sport is possible in many children with a good final head shape.

• •Waldenström radiographic stages - the framework for tracking Perthes disease through Initial, Fragmentation, Reossification, and Remodelling.
• •Herring lateral pillar classification - the dominant prognostic tool in current UK practice; combined with age at onset it best predicts outcome.
• •Catterall I-IV classification - the historical extent-of-involvement system; Catterall III/IV carry worse prognosis.
• •Stulberg classification - final femoral head shape at skeletal maturity (Class I-V), predicting long-term outcome and OA risk.
• •BSCOS consensus and NICE CKS limping-child pathway - the UK reference for assessment, investigation, and referral.

• •Perthes = idiopathic AVN of femoral head, age 4-8 (peak 5-7), M:F 4:1, bilateral 10-15%.
• •Always examine the hip in a child with knee pain; internal rotation is the first restricted movement.
• •Waldenström stages: Initial then Fragmentation then Reossification then Remodelling.
• •Herring B/C or C and age over 8 are poor prognostic markers and indications for containment surgery.
• •Initial X-rays may be normal; MRI is most sensitive for early disease.
• •Bilateral simultaneous Perthes suggests skeletal dysplasia or hypothyroidism.