Contact pressure and tension in anterior cruciate ligament grafts subjected to roof impingement during passive extension

Abstract

Contact between an anterior cruciate ligament graft and the intercondylar roof has been termed roof impingement. Grafts with impingement sustain permanent damage, and if the injury is extensive enough, then the graft may fail, causing recurrent instability. This study evaluated two mechanical factors that could be responsible for the graft injury associated with roof impingement: an increase in graft tension or elevated pressures between the graft and the roof, or both. An anterior cruciate ligament reconstruction was performed using an Achilles tendon graft in five fresh-frozen cadaveric knees. Using a six-degree-of-freedom load application system, the anterior displacement of the knee with the native anterior cruciate ligament was restored in the reconstructed knee at a flexion angle of 30 degrees and with an anterior force of 200 N applied. Pressure between the graft and intercondylar roof, graft tension, and flexion angle were measured during passive knee extension for three tibial tunnel placements (anterior, center, and posterior). Intercondylar roof impingement increased the contact pressure between the graft and the roof but had no significant effect on graft tension. Therefore, during passive knee extension, the contact pressure between the anterior cruciate ligament graft and the intercondylar roof is a more likely cause of graft damage than increased graft tension.

Comparison of the ACL and ACL graft forces before and after ACL reconstruction an in-vitro robotic investigation

“…Our study also found that the mean ACL graft forces were higher than the ACL forces at each flexion angle (significantly higher at 15° of flexion), even though the anterior tibial translation measured in the reconstructed knee was slightly larger than the translation of the intact knee. The difference in force between the ACL and graft measured in this study was not as large as those reported in the literature (Grontvedt et al 1996, Markolf et al 1996, Goss et al 1997. This may be due to the differences in surgical techniques used in these studies.…”

“…In previous studies, ACL graft forces were measured when the anterior tibial translation was matched to that of the intact knee under an anterior tibial load at 30° of flexion (Markolf et al 1996, Goss et al 1997). These graft forces were dramatically increased compared to the ACL forces under the anterior tibial load.…”

Analysis of forces of ACL reconstructions at the tunnel entrance: is tunnel enlargement a biomechanical problem?

“…Numerous studies have conducted displacement (Beynnon et al, 1992) or tension (Goss et al, 1997;Markolf et al, 1990;Goss et al, 1997) measurements of the ACLs or ACL substitutes. However, no study used the data to determine the redirecting forces that are caused by the angulation of the graft at the entrance of the bone tunnels.…”

Avoiding Posterior Cruciate Ligament and Roof Impingement With Transtibial Anterior Cruciate Ligament Reconstruction: Keys to Correct Tunnel Placement

“…Roof impingement disturbs the function of the knee because the contact pressure increases between the graft and the roof, which occurs prematurely before the knee reaches maximum hyperextension. 4 The premature increase in contact pressure causes symptoms of either a loss of extension or an increase in anterior laxity. 8,9,13 Avoiding roof impingement requires an understanding that the placement of the tibial tunnel in the sagittal plane determines whether the ACL graft impinges against the roof during extension.…”