CONTACT PRESSURE AND TENSION IN ANTERIOR CRUCIATE LIGAMENT GRAFTS SUBJECTED TO ROOF IMPINGEMENT DURING PASSIVE EXTENSION

Contact between an anterior cruciate ligament graft and the intercondy lar roof has been termed roof impingement. Grafts with impingement sus tain permanent damage, and if the injury is extensive enough, then the graft may fail, causing recurrent instability. This study evaluated t wo mechanical factors that could be responsible for the graft injury a ssociated with roof impingement: an increase in graft tension or eleva ted pressures between the graft and the roof, or both. An anterior cru ciate ligament reconstruction was performed using an Achilles tendon g raft in five fresh-frozen cadaveric knees. Using a six-degree-of-freed om load application system, the anterior displacement of the knee with the native anterior cruciate ligament was restored in the reconstruct ed knee at a flexion angle of 30 degrees and with an anterior force of 200 N applied. Pressure between the graft and intercondylar roof, gra ft tension, and flexion angle were measured during passive knee extens ion for three tibial tunnel placements (anterior, center, and posterio r). Intercondylar roof impingement increased the contact pressure betw een the graft and the roof but had no significant effect on graft tens ion. Therefore, during passive knee extension, the contact pressure be tween the anterior cruciate ligament graft and the intercondylar roof is a more likely cause of graft damage than increased graft tension.