Long-term follow-up of patients treated with pyrocarbon disc implant for thumb carpometacarpal osteoarthritis: the effect of disc position on outcomes measures

Pyrocarbon disc interposition arthroplasty is an effective treatment for thumb base osteoarthritis. However, as with all implant techniques, the disc can (sub)luxate over time. The relationship between disc position, the experienced pain, and the necessity for revision surgery is not known. This study evaluated the effect of radiographic pyrocarbon disc position on the Michigan Hand Questionnaire (MHQ) outcome measurement. In addition, the correlation between disc position and other factors, including pain intensity, thumb strength, and occupation, was assessed. In this retrospective study, we included 136 patients (161 thumbs) with a mean follow-up of 6.7 years (range 3.3-11). Radiographs were scored on disc position and classified as 'well aligned' (Grade 1) up to 'luxated' (Grade 4). A database used for outcome measures included MHQ scores, pain intensity, satisfaction, thumb strength, range of motion, occupation, and hand dominance. In bivariate analyses, we assessed any association between disc position and outcome measurements. Eighty of the 136 implants (59%) were well-positioned (not displaced), 41% were (slightly) displaced (grade 2-3). No relationship existed between the degree of disc displacement and MHQ scores. Manual labor occupation was the only factor that correlated with more severe disc displacement. We could not detect any association between disc position and other outcome variables including pain intensity, thumb strength, or hand dominance. In conclusion, our study suggests that radiographic disc displacement has little clinical consequences. Future studies must assess if there is a causality between heavy mechanical stress to the CMC1 joint and luxation of the pyrocarbon disc over time.