Abstract
Purpose of the study: Anterior cruciate ligament (ACL) navigation systems are based on two underlying principles: «statistical» anatomic position and isometric anatomic (anatomometric) positioning. The purpose of this study was to demonstrate that an anatometric positioning of the transplant can be achieved, in other words, that the transplant can be positioned in the original anatomic air of the ligament insertion while preserving an optimal isometry without notch impingement. This study was also conducted to compare conventional systems with a computer-assisted system.
Material and methods: This study was conducted on thawed fresh-frozen cadaver knee specimens with > 120° flexion. The computer-assisted protocol for ACL surgery was applied to ten knee specimens. The original anatomic insertions of the ACL were dissected then inserted at the appropriate points into the computer display. The tibial and femoral insertion points of two classical aiming devices were recorded. These points were compared with the original anatomic insertion.
Results: For the tibia: classical aiming methods proposed a point of insertion posterior to the anatomic insertion for eight knees and within the frontiers of the anatomic insertion for two, in line with the anterior border of the posterior cruciate ligament. The computer-designated point of insertion for the tibial fixation was always within the anterior third of the ACL insertion, generally medially. For the femur, the transition (or isometric) line ran across the anatomic femoral insertion in all knees. It was observed that in all cases, the surgeon could choose an anatomic insertion with lesser anisometry by situating the insertion in the distal part of this line: for nine knees, the computer-designated femoral point was anatomic and with lesser anisometry. The Acufex aiming device produced better anisometry (my=4 mm) than the Arthrex device (my=6 mm) but with a less favorable anisometry curve.
Discussion: The notion of anatometry is compatible with computer-assisted surgery. This study demonstrated that the computer-designated tibial point of insertion is more anterior and medial than the conventional aiming points. This is a potential choice if the absence of a notch impingement can be visualized: Howel described a manual fluoroscopic method. In our opinion, at the present time, optimal choice of the femoral point to achieve the desired anisometric curve is strictly operator-dependent.
Correspondence should be addressed to SOFCOT, 56 rue Boissonade, 75014 Paris, France.
