This is Part I of a landmark multicenter prospective study of Legg-Calvé-Perthes disease. It asks a methodological question that had to be answered before any treatment study could be trusted: can the lateral pillar and Stulberg classifications be defined precisely enough to be reliable across observers? The paper formalizes the modified lateral pillar classification (adding the B/C border group) and introduces quantitative Stulberg definitions, then validates both in blinded interobserver and intraobserver trials.
The Catterall classification dominated LCPD staging for decades, but this group abandoned it after repeated interobserver trials within their own multicenter cohort failed to achieve acceptable agreement. A reliable shared language was prerequisite for any meaningful treatment study.
When you stage an LCPD hip at early fragmentation, use the lateral pillar classification — and apply the B/C border criteria precisely. A thin or poorly ossified pillar that still retains 50% height is NOT a Group B hip by these definitions. That distinction matters because the companion Part II study showed surgical intervention (femoral or innominate osteotomy) significantly improves outcomes in B and B/C border hips for children older than 8 years, while Group C hips show no significant benefit from surgery regardless of age.
When assessing skeletal maturity radiographs, the Stulberg protractor technique is the validated method. A head that fails the 2-mm circle test on even one view is class III, not II. And class III carries a meaningfully different long-term prognosis than class II.
The B/C border group exists precisely because biology does not draw clean lines. Recognizing it as a distinct, intermediate category. Rather than forcing borderline hips into B or C. Is what makes this classification actionable in the clinic.
This is Part I of a landmark multicenter prospective study of Legg-Calvé-Perthes disease. It asks a methodological question that had to be answered before any treatment study could be trusted: can the lateral pillar and Stulberg classifications be defined precisely enough to be reliable across observers? The paper formalizes the modified lateral pillar classification (adding the B/C border group) and introduces quantitative Stulberg definitions, then validates both in blinded interobserver and intraobserver trials.
The Catterall classification dominated LCPD staging for decades, but this group abandoned it after repeated interobserver trials within their own multicenter cohort failed to achieve acceptable agreement. A reliable shared language was prerequisite for any meaningful treatment study.
When you stage an LCPD hip at early fragmentation, use the lateral pillar classification — and apply the B/C border criteria precisely. A thin or poorly ossified pillar that still retains 50% height is NOT a Group B hip by these definitions. That distinction matters because the companion Part II study showed surgical intervention (femoral or innominate osteotomy) significantly improves outcomes in B and B/C border hips for children older than 8 years, while Group C hips show no significant benefit from surgery regardless of age.
When assessing skeletal maturity radiographs, the Stulberg protractor technique is the validated method. A head that fails the 2-mm circle test on even one view is class III, not II. And class III carries a meaningfully different long-term prognosis than class II.
The B/C border group exists precisely because biology does not draw clean lines. Recognizing it as a distinct, intermediate category. Rather than forcing borderline hips into B or C. Is what makes this classification actionable in the clinic.