Predicting 'normal' grip strength for rheumatoid arthritis patients.

OBJECTIVE: An ability to predict accurately 'normal' grip strength in rheumatoid arthritis (RA) patients would facilitate a more accurate assessment of the degree of their functional loss. This, in turn, would allow the setting of more meaningful treatment goals aimed at restoring hand function towards normal. This study carefully measures three modalities of hand grip strength and their correlation with multiple simple anthropometric parameters in normal subjects. We aim to determine which of these parameters are best correlated to grip strength, and whether this correlation is strong enough to allow the accurate prediction of what normal grip strength should be in RA patients.
METHODS: In 81 normal subjects (67 female), power, pinch and tripod grip strength measurements were made using an MIE digital pinch grip analyser. These strength data were correlated with specific local forearm anthropometric measurements: forearm circumference, forearm length, forearm volume, hand circumference, hand length, hand volume, hand and forearm volume, and various general anthropometric parameters (weight, height and age). These normal subjects had been chosen so as to be age and sex matched with 83 RA patients (67 female) in whom the same strength and anthropometric parameters were assessed and correlated. In patients, the grip strength results were additionally correlated with two markers of disease activity: a modified Ritchie Articular Index local to the hand and forearm (mRAI) and a visual analogue scale (VAS) assessing subjective pain severity.
RESULTS: In normal subjects, clear correlations were demonstrated between hand grip strengths and all specific anthropometric variables, the strongest correlation being with forearm and hand volume (r = 0.729 and 0.638 for dominant and non-dominant hands, respectively; P < 0.01 for both). The patients were considerably weaker than normal subjects. Markers of disease activity showed a negative correlation with grip strength. In normal subjects, the dominant hand was significantly stronger than the non-dominant hand, and on average by 8%, while the opposite was true in patients, who were 20% weaker on the dominant side.
CONCLUSION: Simple anthropometric measurements, and forearm and hand volume in particular, would be useful at baseline for predicting 'normal' hand grip strength in RA patients, both in the clinical setting and in research trials aimed at improving grip strength and hand function.