Stulberg Classification of Perthes Outcome

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The Stulberg classification (1959, refined 1981) grades the radiographic appearance of the hip at skeletal maturity after Perthes disease. It uses two AP pelvic radiographs at maturity — one neutral and one in the weight-bearing phase — to assess femoral head sphericity and joint congruency.

The Stulberg system is rooted in two biomechanical principles:

• Sphericity of the femoral head determines contact area. A spherical head distributes load over the maximum articular surface, minimising peak contact stress. Loss of sphericity concentrates load on a smaller area, accelerating cartilage wear.
• Congruency between the femoral head and acetabulum determines whether the joint surfaces match. Congruent aspheric joints (Classes III–IV) redistribute load imperfectly but symmetrically, so OA develops more slowly. Incongruent joints (Class V) create edge-loading and rapid cartilage degeneration.

The Stulberg classification is applied retrospectively at maturity, but treatment during the active phase of Perthes disease aims to achieve the best possible Stulberg class. The clinical pathway is:

• Inter-observer reliability is moderate, particularly distinguishing Classes III from IV (both are non-spherical and congruent — the difference is ovoid versus flat). Some authors propose collapsing III and IV into a single category.
• Radiographic assessment only. The classification does not account for cartilage integrity (MRI-determined), labral pathology, or patient-reported outcomes — a patient with a Stulberg III hip may be asymptomatic while a Stulberg II patient may have pain from labral tearing.
• Age at onset matters independently. Children with onset before age 6 tend to achieve better Stulberg classes regardless of treatment, while those with onset after age 8 tend to do worse — the classification does not stratify by age.
• Stulberg was developed in the pre-MRI era and relies on plain radiographs. Modern MRI-based assessment of femoral head sphericity and cartilage health may provide more granular prognostication, but Stulberg remains the standard for outcome studies and exam purposes.
• Bilateral Perthes (in roughly 10–15 percent of cases) complicates classification because acetabular remodelling may be bilateral, and each hip must be classified independently.

• Perthes disease has no single universal guideline comparable to the NICE or AAOS pathways for arthroplasty. Management is guided by institutional protocols and expert consensus, primarily derived from the multicentre POSNA (Pediatric Orthopaedic Society of North America) studies and the European Paediatric Orthopaedic Society (EPOS) recommendations.
• Containment versus non-containment debate varies globally. North American practice historically favoured surgical containment (femoral varus osteotomy, Salter osteotomy) for head-at-risk patients, while some European centres (notably the UK and Scandinavia) have advocated non-operative management with physiotherapy and abduction bracing, citing that many lateral pillar B hips do well without surgery. The POSNA multicentre trial helped define the subgroup that benefits most from surgery.
• Age at onset drives practice variation. Most centres agree that children under age 6 with lateral pillar A or B disease can be managed non-operatively, while children over age 8 with lateral pillar B/C or C disease benefit from containment. The grey zone (age 6–8, lateral pillar B) is where practice varies most.
• Long-term follow-up recommendations differ: UK practice typically follows Perthes patients to skeletal maturity and then discharges if Stulberg I–II, while some centres in the US and Japan recommend lifelong periodic review for all Perthes patients regardless of outcome class, given the late OA risk.