Peritrapezial osteoarthritis: Inter- and intraobserver reliability of the Allieu classification

The Allieu classification takes into consideration the distal and proximal joints of the trapezium. Trapeziometacarpal (TMC) joint arthritis, TMC joint instability (TMI) and scapho-trapezio-trapezoid (STT) joint arthritis are considered independently, which better corresponds to the anatomical examinations. The aim of the study was to evaluate the inter- and intraobserver reliability of the Allieu classification of the peritrapezial arthritis. This was a prospective, single-center study performed from May to September 2016 with 30 cases of primary thumb osteoarthritis. Five raters scored the X-rays twice. In the Allieu classification, TMC arthritis is scored as "0" when the TMC joint is normal, "1" when the TMC joint space is <50% narrowed, "2" when the TMC joint space is >50% narrowed, "3" when the joint space is loose with advanced degenerative changes. TMI is scored as "0" for reducible subluxation, painful and unstable joint, "1" for advanced reducible subluxation, "2" for chronic subluxation <1/3 of the surface, "3" for chronic subluxation >1/3 of the surface. STT joint arthritis is scored as "0" for normal joint space, "1" for joint space narrowing <50%, "2" for important joint space narrowing and "3" for advanced degenerative changes with sclerotic subchondral bone changes. Inter- and intraobserver reliability was assessed using the weighted Cohen's kappa coefficient. Additional analyses were undertaken to determine the intraclass correlation coefficient (ICC) for the overall raters. The interobserver reliability was "moderate" to "substantial" for the TMC arthritis; "fair" to "substantial" for STT arthritis and "fair" to "substantial" for TMI. The intraobserver reliability was "moderate" to "excellent" for TMC arthritis (2 "excellent", 2 "substantial", 1 "moderate"); "fair" to "excellent" for the STT (1 "excellent", 2 "substantial", 1 "moderate", 1 "fair") and "fair" to "excellent" for the TMI (1 "excellent", 2 "substantial", 1 "moderate", 1 "fair"). The worst reliability, either for intra- or interobserver, was for TMI. The ICC for TMC arthritis was 0.67 (95%CI, 0.28-0.83); for STT it was 0.47 (95%CI, 0.15-0.66) and for TMI it was 0.30 (95%CI, 0.23-0.70), which is "fair". This study confirms a large variation in X-ray staging for peritrapezial arthritis. It shows that the Allieu classification is moderately reliable. However, the interobserver reliability was better for evaluating the TMC than the STT and worse for TMI. The classification for TMC and STT is simple to apply, based principally on the joint narrowing. The intraobserver is better than the interobserver reliability.