A comparative study of 'isometric' points for anterior cruciate ligament graft attachment

Anterior cruciate ligament (ACL) reconstruction depends critically on isome tric graft placement. Unfortunately, different supposedly isometric points have been published, and no prior work has compared them to find out which are really isometric. The purpose of this study was to compare the isometry of previously published 'isometric' points for ACL reconstruction. The iso metric points and knee loadings of previous studies were reproduced accurat ely in 12 fresh cadaveric knees. The length changes were measured through 1 40 degrees knee flexion, using an intra-articular suture attached to a disp lacement transducer. Six points had less than 1 mm length change and were l ocated proximally in the natural ACL attachment at the posterior end of Blu mensaat's line. The other seven points had length change patterns that woul d cause ACL graft tightening or slackening with knee flexion if they were u sed as the sites of bone tunnels for graft placement. This study confirms t he existence of an isometric zone close to the posterior end of Blumensaat' s line under several loading conditions. Other graft attachment points are less suitable for ACL reconstruction.