Prospective validation of mean metacarpophalangeal joint extension as a measure of flexor compartment fibrotic inflammation in diabetes-related hand manifestations

Introduction Hand conditions in diabetes, namely limited joint mobility (LJM), flexor tenosynovitis (FT), carpal tunnel syndrome (CTS), and Dupuytren disease (DD), share a common pathophysiological process involving pro-fibrotic inflammation in flexor structures. A unified, quantitative measure of disease severity across these conditions is lacking, limiting correlational research. We evaluated mean metacarpophalangeal (MCP) joint extension as a potential measure of severity. Methods We assessed 2405 adults, including individuals with type 1 diabetes (n=291), type 2 diabetes (n=877), prediabetes (n=326), and non-diabetic controls (n=911). MCP extension was calculated as the average maximum passive extension of the 2nd-5th fingers, measured with a protractor. Validity was determined by correlating MCP extension with physician-rated severity (convergent) and hand grip strength and the Duruoz Hand Index (DHI, both divergent). Inter-rater reliability was tested in 128 individuals, and sensitivity to change was evaluated in 143 participants over time and in 21 rheumatology patients with subacute noninfectious FT. Results Mean MCP extension was significantly lower in individuals with all hand conditions (42.4° LJM, 42.8° FT, 39.9° DD, 51.7° CTS) than in those without (58.6°, all p<0.05). MCP extension correlated with physician-rated severity (−0.5, p<0.01) and weakly with DHI (R 2 =0.03) and grip strength (R 2 =0.07). Inter-rater reliability was strong (ICC 0.72), and MCP extension demonstrated sensitivity to change, worsening over eight months (SRM -0.61) and improving after treatment in subacute FT (SRM 0.69). Conclusion Mean MCP extension is a valid, reliable, and responsive measure for assessing fibro-inflammatory hand conditions in diabetes, suitable for use in research studies.