A comparison of the validity and reliability of established bone stock loss classification systems and the proposal of a novel classification system.

The classification and management of aseptic loosening of total hip arthroplasty remains a distinct challenge to the modern orthopaedic surgeon. The aim of this study was to assess the inter-observer and intra-observer reliability of commonly used classification systems for the assessment of bone stock loss in revision hip surgery. Radiographs of 23 femoral and 32 acetabular components in 30 patients were assessed using the Paprosky, AAOS and Endo-Klinik classification systems. A novel classification system was introduced and also used to assess the radiographs. Assessment was undertaken by 3 surgeons on 2 separate occasions and the inter- and intra- observer reliability calculated. The novel classification system showed a good to very good intra-observer reliability for both femoral and acetabular components (0.77-1.0; p<0.001), performing better than the other systems assessed. The novel femoral system demonstrated moderate to good inter-observer agreement (0.46-0.73), performing as well as the Paprosky (0.63-0.80) and AAOS (0.63-0.68) femoral systems. The novel acetabular system demonstrated fair to moderate inter-observer reliability (0.35-0.51) performing better than the AAOS acetabular classification (0.07-0.10) and as well as the Paprosky acetabular classification system (0.59-0.60). We propose this novel system as an alternative method for assessing bone stock loss in revision hip surgery.