The contribution of the intrinsic muscles to grip and pinch strength

Profound deficiencies occur in the intrinsic minus hand with loss of the interossei, thenar, hypothenar, and adductor pollicis muscles. The purpose of this study was to define the load-generating deficiencies of grip and pinch after simulated low median and/or low ulnar nerve lesions. Twenty-one healthy volunteers underwent median and ulnar nerve blocks at the wrist level with mepivacaine HCI injection. Key pinch and grip data were recorded before injection and after each nerve block was determined to be effective. A computerized dynamometer that simultaneously recorded individual force data from each digit and cumulative grip was used to record grip strength. Grip strength data showed a significant decrease in total grasp at all 3 handle sizes after initial median or ulnar nerve block. The average decrease in grip strength was 38% after ulnar nerve block and 32% after median nerve block. The total grip loss after both injections averaged 49% compared with the preinjection strength. After ulnar or median nerve block there was a significant decrease in the force production of the long, ring, and small fingers but not the index finger. Pinch data revealed a significant decrease in key pinch of 77% after ulnar block and 60% after median block with a further significant change after combined block to decrease pinch 85%.