Background/Purpose: Osteoarthritis (OA) in the first carpometacarpal (CMC1) joint in the thumb base is frequent and has a large contribution in hand pain and disability. Previous ultrasonography (US) studies of hand OA have focussed on interphalangeal joints, showing inflammatory features that associate with clinical signs and symptoms. Until now, US studies specifically addressing the CMC1 joint have not been performed. We investigated the associations between inflammatory features, structural damage and pain in CMC1 OA.

Methods: Cross-sectional data of 87 hand OA patients according to ACR criteria who participated in the EChography in Hand OA (n=63) and the Etanercept in Hand OA (n=24) study at the Leiden University Medical Center were used in this analysis. Both CMC1 joints were assessed with US for synovial thickening, effusion and power Doppler signal (PDS) on a 0-3 scale by experienced ultrasonographers. Presence of pain upon palpation of the thumb base was assessed by trained research nurses on the same day as the US. Hand radiographs were scored blinded for clinical and US features, according to the Osteoarthritis Research Society International atlas for osteophytes (0-3), joint space narrowing (JSN, 0-3), sclerosis (0-1) and malalignment (0-1) in the CMC1 joint. Risk ratios (RRs) with 95% confidence intervals (CIs) were calculated using generalized estimating equations to investigate associations between US or radiographic features and thumb base pain on joint level.

Results: Of 87 patients (mean age 60.3 years, 82% women, mean BMI 27.2 kg/m²) 174 CMC1 joints were assessed, of which 54 (31%) were painful. The US features synovial thickening, effusion and PDS were found in 26%, 33% and 25% of the joints, respectively. Radiographic features were present in 55% (osteophytes), 79% (JSN), 20% (sclerosis) and 12% (malalignment) of the joints. No associations were seen between inflammatory US features and pain upon palpation of the thumb base (Table). However, osteophytes and sclerosis were associated with more pain (RR 2.5 [95% CI 1.4 to 4.6] for osteophytes grade 3 versus no osteophytes, and RR 2.0 [95% CI 1.3 to 3.2] for presence of sclerosis). Other radiographic features (JSN, malalignment) showed a trend for increased risk of pain on palpation, and for osteophytes and JSN a dose-response relation was apparent.

Conclusion: Radiographic features, especially osteophytes and JSN, were prevalent and more frequently present than US inflammatory features in the CMC1 joints of hand OA patients. In contrast to what is known from studies in interphalangeal joints, the presence of inflammatory US features was not associated with pain in the thumb base, but structural damage was. These results suggest differences in aetiology of pain in thumb base compared to interphalangeal OA, with a larger role for structural damage in thumb base OA.