Quantitative assessment of the midcarpal shift test

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.)