The subjective, clinical midcarpal shift test was compared with a quantitat
ive measurement of carpel volar/dorsal translation versus ulnar deviation u
sing a mechanical testing system. Testing was performed on 19 healthy volun
teers (mean age, 33 years) and 3 patients (four wrists; mean age, 23 years)
who had been diagnosed with ulnar midcarpal instability, a nondissociative
form of carpal instability. During physical examination, each subject's wr
ist was graded I to V using the previously described classification of the
degree of laxity and clunk observed with the midcarpal shift test. Each sub
ject was also evaluated using a quantitative mechanical testing system that
simulates the subjective clinical test. The testing system measures displa
cement of the distal carpal row, more specifically, the capitate, as the wr
ist is moved from neutral to ulnar deviation under a constant axial load of
44 N directed volarly at the head of the capitate. Reflective markers were
attached to the skin above the proximal and distal ends of the third metac
arpal and at the point where the 44-N load was applied to the carpus. Motio
n of the markers was used to calculate ulnar deviation and dorsal/volar tra
nslation of the carpus. The maximum slope of the carpal translation versus
ulnar deviation curve was measured for each subject and compared with the r
esults of the clinical midcarpal shift test. Higher maximum slopes were see
n in subjects with the higher grades of carpal laxity. There were also diff
erences with regard to the point at which the clunk occurred; the higher th
e clinical grade of laxity, the greater the ulnar deviation of the wrist at
the point at which the clunk was observed. These differences were not sign
ificant, however. These data confirm the validity of the clinical test and
establish its usefulness as a diagnostic indicator of midcarpal nondissocia
tive carpal instability. The mechanized test also may be useful as a biomec
hanical marker, enabling the results of ligament sectioning to be effective
ly compared with defined clinical laxity. (J Hand Surg 1999;24A:977-983. Co
pyright (C) 1999 by the American Society for Surgery of the Hand.)