A Comparison of the Validity and Reliability of Established Bone Stock Loss Classification Systems and the Proposal of a Novel Classification System

Abstract

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.

Classifications In Brief: Paprosky Classification of Acetabular Bone Loss

“…Many different classification schemes have been proposed to describe the extent of periacetabular bone loss in revision THA including those proposed by Paprosky et al [11], D'Antonio [2] (also known as the American Academy of Orthopaedic Surgeons system [AAOS]), Saleh et al [13], Gustilo and Pasternak [6], Gross et al [5], Parry et al [12], and Engh et al [3]. These classification schemes differ in that some aim to simplify classification to improve communication and reproducibility [3,5,7,12], whereas others seek to provide detailed anatomic information for defectspecific preoperative planning [2,6,7,11,13].…”

“…These classification schemes differ in that some aim to simplify classification to improve communication and reproducibility [3,5,7,12], whereas others seek to provide detailed anatomic information for defectspecific preoperative planning [2,6,7,11,13]. Other fundamental differences include the presence or absence of standard anatomic landmarks compared with pure volumetric bone loss independent of the structures affected and the focus on bone stock remaining in contrast to bone stock required for revision [7].…”

“…This classification is anatomically oriented and assesses specific osseous structures for deficiency, rather then being geared toward generalized volumetric bone loss, which is the basis of several other systems [3,5,12]. The Paprosky system uses preoperative radiographs to classify defects by the amount of acetabular component migration and the status of the acetabular supporting structures including the anterior and posterior columns, the superior weightbearing dome, and the medial wall (Table 1).…”

“…The kappa (j) analysis is a representation of the proportion of agreement beyond that expected by chance [10]; a value of zero indicates no agreement better than chance and a value of 1 indicates agreement between two scorers is perfect [10]. Intraobserver reliability for the Paprosky classification has varied with reported j values ranging from 0.14 to 0.75 [1,4,12,19]. Most of the time the values were between 0.3 and 0.6, indicating poor to good agreement.…”

“…Most of the time the values were between 0.3 and 0.6, indicating poor to good agreement. Interobserver reliability has shown even greater variability with reported j values ranging from 0.02 to 0.79 [1,4,12,19] with the majority of values between 0.4 and 0.6, suggesting anything from good agreement to essentially no agreement better than that is the result of chance. The source of this heterogeneity is likely multifactorial and includes the loosely defined and relatively subjective categories of mild, moderate, and severe used by the Paprosky system, the partial obstruction of acetabular features by the radiopaque cup on routine radiographs, and potential discrepancies in the measurement of hip center migration between reviewers which is a major differentiating feature between Types 1 and 2 defects.…”