Legg-Calvé-Perthes: interobserver and intraobserver reliability of the modified Herring lateral pillar classification.

Background: The purpose of our study was to independently assess the reliability of the modified Herring lateral pillar classification.

Methods: Thirty-five standardized true anteroposterior radiographs of children in the fragmentation phase were independently assessed by 6 senior observers on 2 separate occasions (6 wk apart). The κ analysis was used to assess the interobserver and intraobserver agreement.

Results: Intraobserver analysis revealed at best only moderate agreement for 2 observers. Three observers showed fair consistency, whereas 1 remaining observer showed poor consistency between repeated observations (P < 0.01). The highest scores for interobserver agreement varying between moderate to good could only be established between 2 observers. For the remaining observers results were just fair (P < 0.01).

Conclusions: This study highlights the lack of agreement between senior clinicians when applying the modified lateral pillar classification. The results from the Herring group were significantly better than ours, but utilized a weighted κ for analysis, which may have given artificially high scores. To our knowledge, this is the first time the modified lateral pillar classification has been independently tested for its reproducibility by a specialist pediatric orthopaedic unit.