THE VALUE OF INTRAOPERATIVE ISOMETRY MEASUREMENTS IN ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION - AN IN-VIVO CORRELATION BETWEEN SUBSTITUTE TENSION AND LENGTH CHANGE

With the objective to evaluate an' ''isometry'' measurement in an ante rior cruciate ligament (ACL) substitute, in vivo measurements were tak en on 10 patients undergoing reconstruction due to chronic ACL deficie ncy. Change in intraarticular length of a 1.2-mm test ligament, measur ed with an isometer, was correlated to the tension created in the same test ligament after fixation, measured with a piezoelectric load cell . The knee was passively moved through the 0-100-degrees range with th e patient under general anaesthesia. Good statistical and visual corre lations between length change and tension curves were found in individ ual knees. A correlation between total length change and maximum tensi on, for all knees grouped, was also found. Individual knees showed lar ge variation in ability of the tissue to absorb load, resulting in a w ide range of N/mm ratios between length and tension. Three knees with an isolated ACL injury atl showed the least length change, implying a better restoration of kinematics in the absence of associated injuries . In nine of 10 knees the length change pattern could be used to ident ify the location of the femoral drill channel, as determined on an int raoperative lateral projection of the knee. Intraoperative isometry me asurement can be used to predict the tension pattern in the reconstruc ted knee, but not the magnitude of tension. It will be useful to the s urgeon in avoiding an anterior femoral ligament insertion site, which might threaten the integrity of the graft by tension rise in flexion.