Intra-rater reliability of grip strength measurements in severely restricted hands

Introduction Grip strength (GS) is a crucial indicator of hand function; however, its reliable assessment in individuals with severe hand dysfunction remains a clinical challenge. This study evaluated the intra-rater reliability of GS and grip pressure (GP) using the Jamar dynamometer and a modified sphygmomanometer (ModSp) in patients with complex bilateral hand dysfunction. Secondary objectives included determining the correlation between the instruments and exploring patient preferences. Method Fifty-two individuals with severe bilateral hand dysfunction due to systemic sclerosis were assessed as a representative model. A standardized measurement protocol was followed for both instruments. Intra-rater reliability was analyzed using intraclass correlation coefficients (ICCs), and linear regression was used to derive conversion formulas. Patient preferences were recorded using standardized open-ended questions and analyzed via thematic content analysis. Results Both instruments demonstrated excellent ICCs (0.96–0.98). Strong positive correlations were found between instrument scores (r = 0.88–0.91, p < 0.001), and regression models explained 78–82% of the variance. However, Bland–Altman analysis revealed systematic bias and relatively wide limits of agreement, indicating the methods are not interchangeable. Regarding preferences, 69.2% of participants favored the ModSp, citing greater comfort, better adaptation to deformities, and reduced pain during grasp, while 17.3% preferred the Jamar dynamometer and 13.5% reported no preference. Conclusion The Jamar and ModSp devices demonstrated excellent intra-rater reliability for grip assessment in severe hand dysfunction. While strongly correlated, they are not directly interchangeable for precise monitoring. The ModSp offers a practical, patient-centered alternative when standard dynamometry is hindered by physical constraints.