The lateral pillar classification (LPC) is a widely used tool in determining prognosis and planning treatment in patients who are in the fragmentation stage of Perthes disease. The original classification has been modified to help increase the accuracy of the classification system by the Herring group. The purpose of our study was to independently assess this modified Herring classification.

35 standardized true antero-posterior radiographs of children in various stages of fragmentation were independently assessed by 6 senior observers on 2 separate occasions (6 weeks apart). Kappa analysis was used to assess the inter and intraobserver agreement between observations made. The degrees of agreement were as follows: poor, fair, moderate, good and very good.

Intraobserver analysis revealed at best only moderate agreement for two observers. 3 observers showed fair consistency, whilst 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).

This study highlights the lack of agreement between senior clinicians when applying the modified LPC. This has clinical implications when applying the classification to the decision making process in treating patients at risk of developing adverse outcomes from the disease. To our knowledge, this is the first time the modified LPC has been independently tested for its reproducibility by another specialist paediatric orthopaedic unit.