What is the minimum clinically important difference in grip strength?

BACKGROUND

Grip strength reflects functional status of the upper extremity and has been used in many of the clinical studies regarding upper extremity disease or fracture. However, the smallest difference in grip strength that a patient would notice as an improvement resulting from treatment (defined as the minimum clinically important difference [MCID]), to our knowledge has not been determined.

QUESTIONS/PURPOSES: We asked (1) how 1-year postsurgery grip strength compares with preinjury values; (2) if grip strength correlated with patient's ratings; (3) what the MCID is in the grip strength; and (4) if these values are equivalent to or greater than what can be explained by measurement errors in patients treated for distal radius fracture.

METHODS

Fifty patients treated by volar locking plate fixation for a distal radius fracture constituted the study cohort. Grip strengths were measured 1 year after surgery on the injured and uninjured sides using a dynamometer. Grip strengths before injury were estimated using the grip strengths of the uninjured side with consideration of hand dominance. Patients were asked to rate their subjective level of grip strength weakness at 1 year postoperatively. Receiver operator characteristic curve analysis was used to determine MCIDs. Minimal detectable change in grip strength, which is a statistical estimate of the smallest change between two measurement points expected by measurement error or chance alone, also was determined using the formula 1.65 × √2 × standard error of measurement.

RESULTS

One year after surgery, grip strength (23 kg; 95% CI, 20-27) was less compared with calculated preinjury values (28 kg; 95% CI, 25-31; p < 0.001). Patients' rating of grip strength and measured grip strength changes correlated well (p = 0.56). MCIDs were 6.5 kg for grip strength and 19.5% for percentage grip strength. The MCID was not less than the minimum detectable change for grip strength (also 6.5 kg).

CONCLUSIONS

The MCID of the grip strength was a decrease of 6.5 kg (19.5%). We believe the MCID of grip strength is useful for evaluating effectiveness of new treatments and for determining appropriate sample size in clinical trials of distal radius fractures.

LEVEL OF EVIDENCE

Level III diagnostic study. See the Instructions for Authors for a complete description of levels of evidence.