Comparison of isometric and anatomical graft placement in synthetic ACL reconstructions: a pilot study

Correct graft placement is critical to the success of anterior cruciate ligament reconstructions (ACLR). Whilst current trend is to insert the graft in an anatomical location, synthetic grafts have shown to better perform when they are located in an isometric position. Placement, however, is largely dependent on the surgeon and no consensus has been reached for synthetic grafts. Kinematic flexion-extension data of four separate cadaveric knees was obtained using an optical tracking system. Knees were CT-scanned and computer models were developed for each specimen. Three different graft insertion techniques were simulated in each of the computer models. Kinematic data obtained from the optical tracking was applied to the 3D computer models to simulate knee flexion-extension, and virtual change in ACL graft length was measured over the cycle for each insertion technique. Length changes were plotted onto the Radiological-Quadrant. The isometric region on the femur was found to be a band spreading from the mid to deep end of the Blumensaat's line down to the shallow-inferior end of the femoral condyle. The JP Laboureau isometric point technique was consistently located in the isometric zone, with the following coordinates on the Radiographic-Quadrant: t=0.375 (SD 0.0066), h=0.227 (SD 0.0266). The Bernard-Hertel and Charlie Brown anatomical placement methods were located (13%, -6%) and (8%, -15%) away, from the JP Laboureau isometric point, respectively, based on t- and h- coordinates of the Radiographic-Quadrant. This study has determined the isometric region using three-dimensional analysis relative to the Radiographic-Quadrant. The JP Laboureau method best finds the isometric point. This information is useful for synthetic graft placement.