Objective. An ability to predict accurately 'normal' grip strength in rheum
atoid arthritis (RA) patients would facilitate a more accurate assessment o
f the degree of their functional loss. This, in turn, would allow the setti
ng of more meaningful treatment goals aimed at restoring hand function towa
rds normal. This study carefully measures three modalities of hand grip str
ength 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 st
rength measurements were made using an MIE digital pinch grip analyser. The
se 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 vario
us general anthropometric parameters (weight, height and age). These normal
subjects had been chosen so as to be age and sex matched with 83 RA patien
ts (67 female) in whom the same strength and anthropometric parameters were
assessed and correlated. In patients, the grip strength results were addit
ionally 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 h
and grip strengths and all specific anthropometric variables, the strongest
correlation being with forearm and hand volume (I = 0.729 and 0.638 for do
minant and non-dominant hands, respectively; P < 0.01 for both). The patien
ts were considerably weaker than normal subjects. Markers of disease activi
ty showed a negative correlation with grip strength. In normal subjects, th
e 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% wea
ker on the dominant side.
Conclusion. Simple anthropometric measurements, and forearm and hand volume
in particular, would be useful at baseline for predicting 'normal' hand gr
ip strength in RA patients, both in the clinical setting and in research tr
ials aimed at improving grip strength and hand function.