Relationship between changes in length and force in in vitro reconstructed anterior cruciate ligament

The effect of tibial and femoral attachment site on the length change and force of an anterior cruciate ligament graft during unloaded flexion in eight cadaver speci mens was examined. Two tibial sites (anteromedial and central portion of the anterior cruciate ligament attach ment) and three femoral sites (anterior and central portions of the anterior cruciate ligament attachment, and over-the-top) were evaluated. Graft length changes between all combinations of attachment sites were measured from full extension to 150° of passive flexion at 15° intervals using the displacement of a 2-mm inextensible cord. The anterior cruciate ligament was then reconstructed using a Kennedy Ligament Aug mentation Device, and graft forces at the same angles of passive flexion were measured with a buckle trans ducer. Graft length change and force were more affected by the femoral attachment site than the tibial site. There was a close correlation between length change and force measurements in flexion, but not near extension. The pattern of force and length change versus flexion angle for a given combination of attachment sites some times varied over the knees tested. Our results suggest that intraoperative isometry measurements are worth while for indicating an overloaded graft in flexion; how ever, length changes near extension may not ade quately reflect graft force, creating the possibility that a graft may be more highly loaded than realized.