A METHOD FOR MEASURING TENSION IN SMALL LIGAMENTS - AN APPLICATION TOTHE LIGAMENTS OF THE WRIST CARPUS

A new technique has been devised for measuring the in situ tension in small ligaments. It is based on measuring the tension in an axially lo aded flexible cable with pinned endpoints by deflecting the cable late rally and measuring its lateral load and deformation. Studies were per formed in which nylon line and bone ligament bone preparations were pl aced in a materials tester and loaded in axial tension. Axial load as measured by lateral load and deformation was found to agree with the k nown load to within 8 percent. The method was sensitive to error in de termination of ligament length, nonperpendicularity of the laterally a pplied load to the long axis of the ligament, and when used in situ, i mpingement of the ligament on a third bone causing bending. A device, consisting of an LVDT mounted to a rigid frame with its core rod conne cted to a load cell, was developed. The position of the core rod was c ontrolled by a manual screw drive, and a hook on the other end of the core rod was used to deflect the ligament laterally. This device was a pplied to the study of tensions in five ligaments of the palmar wrist carpus, in seven cadaver specimens. Results showed that the radioscaph ocapitate (RSC) and radiolunate (RL) ligaments had significantly great er tensions than the lunotriquetral (LT), the triquetrocapitate (TC), and scaphocapitate (SC) ligaments. For the four positions of the hand tested, neutral, 14 deg radial and 14 deg ulnar deviation, and 28 deg of extension, ligament tensions were found to be unaffected by positio n. In all positions tested, all ligaments had measurable tension, demo nstrating the importance of ligaments in maintaining the integrity of the wrist carpus.