Factors associated with hand-specific activity limitations in individuals with base-of-thumb osteoarthritis: a secondary cross-sectional analysis of the RHIBOT and RHIZORTHÈSE randomized trials

Technical Summary: Factors Associated with Hand-Specific Activity Limitations in Base-of-Thumb Osteoarthritis

Problem Statement
Base-of-thumb osteoarthritis, affecting the trapeziometacarpal joint, is a prevalent condition causing pain and functional limitations in daily activities. While the condition is well-documented, the specific clinical and functional factors driving hand-specific activity limitations remain insufficiently characterized. Most existing literature focuses on pain intensity or radiographic severity, leaving a gap in understanding which variables independently predict functional disability. Identifying these factors is crucial for clinicians to characterize patients at risk of functional decline and to tailor therapeutic interventions effectively.

Methodology
This study employed a secondary cross-sectional analysis of baseline data from two previously published, single-centered randomized controlled trials conducted in France: RHIBOT (N=60) and RHIZORTHÈSE (N=112).

• Participants: The analysis included 172 adults (mean age 63.8 years; 86% women) diagnosed with symptomatic base-of-thumb osteoarthritis according to American College of Rheumatology criteria. Exclusion criteria included prior thumb surgery, inflammatory rheumatic diseases, neurological disorders, and recent trauma or injections.
• Outcome Measure: Hand-specific activity limitations were assessed using the Cochin Hand Function Scale (CHFS), a validated questionnaire ranging from 0 to 90. Participants were dichotomized into two groups: those with "acceptable" limitations (CHFS ≤ 26/90) and those with "unacceptable" limitations (CHFS > 26/90), a threshold established by prior literature.
• Variables: Baseline demographic, clinical, and functional variables were collected, including age, sex, manual activity level, pain duration, pain intensity (0–100 numerical rating scale), and thumb mobility (Kapandji opposition score).
• Statistical Analysis: A multivariable binary logistic regression model was constructed to identify baseline variables independently associated with unacceptable hand-specific activity limitations. Statistical significance was set at a two-sided p-value < 0.05.

Key Results
Among the 172 participants, 59 (34.3%) exhibited unacceptable hand-specific activity limitations.

• Univariate Comparisons: Participants with unacceptable limitations reported significantly higher pain intensity (mean 64.0 vs. 45.0), longer pain duration, reduced strength on the affected side, and a higher prevalence of intense manual activity compared to those with acceptable function. No significant differences were observed regarding age, sex, or osteoarthritis duration between the groups.
• Multivariable Analysis: In the adjusted model, two factors were independently associated with unacceptable hand-specific activity limitations:
  1. Higher Pain Intensity: Associated with increased odds of unacceptable limitations (Odds Ratio [OR] 0.95 per unit increase on the 0–100 scale; 95% CI 0.93–0.97; p < 0.001). Note: The OR < 1 indicates that as the pain score increases, the likelihood of being in the "acceptable" group decreases, or conversely, higher pain correlates with higher disability.
  2. Reduced Thumb Opposition: Lower Kapandji opposition scores were independently associated with higher disability (OR 1.58 per unit decrease; 95% CI 1.03–2.41; p = 0.035).
• Non-Significant Factors: Age, sex, level of manual activity, and duration of osteoarthritis were not independently associated with hand-specific activity limitations in the multivariable model.

Significance and Claims
The authors conclude that in individuals with base-of-thumb osteoarthritis, pain intensity and thumb mobility are the primary factors associated with hand-specific activity limitations. The study highlights that while demographic factors and disease duration do not independently predict functional loss, the immediate clinical presentation of pain and the mechanical capacity for thumb opposition are critical.

The paper claims these findings underscore the necessity of therapeutic strategies that specifically target pain control and the preservation of thumb mobility. The authors suggest that interventions focusing on these two areas may be more effective in mitigating functional decline than those addressing other variables. However, the authors explicitly note the study's limitations: as a cross-sectional analysis, it identifies associations rather than causality; the sample size is moderate; and the findings are derived from a secondary analysis of specific trial populations, which may limit generalizability. Consequently, the authors state that prospective interventional studies are required to determine if optimizing these specific factors can meaningfully reduce hand disability.