Effects of notchplasty and femoral tunnel position on excursion patterns of an anterior cruciate ligament graft.

PURPOSE: Errors in femoral tunnel placement in anterior cruciate ligament (ACL) reconstruction can cause excessive length changes in the graft during knee flexion and extension, resulting in graft elongation during the postoperative period. To improve the accuracy of tunnel placement and to avoid graft impingement, a notchplasty is commonly performed. The purpose of this study was to determine the effects of varying the position of the femoral tunnel and of performing a 2-mm notchplasty of the lateral femoral condyle and roof of the intercondylar notch on excursion patterns of a bone-patellar tendon-bone graft. TYPE OF STUDY: Biomechanical cadaveric study. METHODS: A cylindrical cap of bone, containing the tibial insertion of the ACL, was mechanically isolated in 15 fresh-frozen cadaveric specimens using a coring cutter. The bone cap was attached to an electronic isometer that recorded displacement of the bone cap relative to the tibia as the knee was taken through a 90 degrees range of motion. After native ACL testing, the proximal end of a 10-mm bone-patella tendon-bone graft was fixed within femoral tunnels drilled at the 10-, 11-, and 12-o'clock (or 2-, 1-, and 12-o'clock) positions within the notch. The distal end of the graft was attached to the isometer. Testing was then completed at each tunnel position before and after notchplasty. RESULTS: Before notchplasty, mean graft excursions at the 10- or 2-, 11- or 1-, and 12-o'clock tunnels were not significantly different from the excursions of the native ACL or each other. After a 2-mm notchplasty, mean graft excursions at the 3 tunnel locations were not sigificantly different from each other but were greater than mean graft excursions before notchplasty. After notchplasty, all grafts tightened during knee flexion. CONCLUSIONS: Although errors in placement along the arc of the intercondylar notch did not significantly affect graft excursion patterns, the apparent graft tightening with knee flexion that was observed for all 3 tunnel positions after notchplasty suggests that graft forces would increase with knee flexion over this range. This would indicate that as little amount of bone as possible should be removed from the posterior portion of the intercondylar notch in ACL reconstruction.

Effects of femoral tunnel placement on knee laxity and forces in an anterior cruciate ligament graft.

The purpose of this study was to measure the effects of variation in placement of the femoral tunnel upon knee laxity, graft pretension required to restore normal anterior-posterior (AP) laxity and graft forces following anterior cruciate ligament (ACL) reconstruction. Two variants in tunnel position were studied: (1) AP position along the medial border of the lateral femoral condyle (at a standard 11 o'clock notch orientation) and (2) orientation along the arc of the femoral notch (o'clock position) at a fixed distance of 6-7 mm anterior to the posterior wall. AP laxity and forces in the native ACL were measured in fresh frozen cadaveric knee specimens during passive knee flexion-extension under the following modes of tibial loading: no external tibial force, anterior tibial force, varus-valgus moment, and internal-external tibial torque. One group (15 specimens) was used to determine effects of AP tunnel placement, while a second group (14 specimens) was used to study variations in o'clock position of the femoral tunnel within the femoral notch. A bone-patellar tendon-bone graft was placed into a femoral tunnel centered at a point 6-7 mm anterior to the posterior wall at the 11 o'clock position in the femoral notch. A graft pretension was determined such that AP laxity of the knee at 30 deg of flexion was restored to within 1 mm of normal; this was termed the laxity match pretension. All tests were repeated with a graft in the standard 11 o'clock tunnel, and then with a graft in tunnels placed at other selected positions. Varying placement of the femoral tunnel 1 h clockwise or counterclockwise from the 11 o'clock position did not significantly affect any biomechanical parameter measured in this study, nor did placing the graft 2.5 mm posteriorly within the standard 11 o'clock femoral tunnel. Placing the graft in a tunnel 5.0 mm anterior to the standard 11 o'clock tunnel increased the mean laxity match pretension by 16.8 N (62%) and produced a knee which was on average 1.7 mm more lax than normal at 10 deg of flexion and 4.2 mm less lax at 90 deg. During passive knee flexion-extension testing, mean graft forces with the 5.0 mm anterior tunnel were significantly higher than corresponding means with the standard 11 o'clock tunnel between 40 and 90 deg of flexion for all modes of constant tibial loading. These results indicate that AP positioning of the femoral tunnel at the 11 o'clock position is more critical than o'clock positioning in terms of restoring normal levels of graft force and knee laxity profiles at the time of ACL reconstruction.

Biomechanical effects of femoral notchplasty in anterior cruciate ligament reconstruction.

Notchplasty is frequently performed in conjunction with anterior cruciate ligament reconstruction. Bench loading tests were performed on 26 fresh-frozen knee specimens to measure excursion of a bone-patellar tendon-bone graft, anterior-posterior laxity of the knee, and graft forces before and after performing a 2-mm and a 4-mm notchplasty. The mean intraarticular pretension required to restore normal anterior-posterior laxity at 30 degrees of flexion (laxity-matched pretension level) was 27 N before notchplasty, 48 N after 2-mm notchplasty, and 65 N after 4-mm notchplasty. The mean graft pretension decreased 53% and 58%, respectively, on completion of a loading test series involving anterior-posterior and constant tibial loading forces. Mean laxity increased 1.4 mm at full extension and decreased 1.8 mm at 90 degrees of flexion after a 2-mm notchplasty. Mean graft forces increased markedly between 30 degrees and 90 degrees of passive flexion after notchplasty. Our results show that after a notchplasty, a higher level of graft pretension will be necessary to restore normal laxity at 30 degrees of flexion. This increased level of pretension, combined with changes in graft excursion, produced dramatic increases in graft force when the knee was flexed to 90 degrees. These relatively high forces would be detrimental to a remodeling graft and could lead to subsequent failure of the reconstruction.

The effect of anterior cruciate ligament graft rotation on knee laxity and graft tension: An in vitro biomechanical analysis.

PURPOSE: The purpose of this study was to determine the effects of rotating a bone-patellar tendon- bone allograft during anterior cruciate ligament reconstruction on anteroposterior (AP) knee laxity and forces developed within the graft. TYPE OF STUDY: In vitro biomechanical study using human cadaveric knees. METHODS: Thirteen fresh-frozen knee specimens received bone-patella tendon-bone allografts that were pretensioned at 30 degrees of flexion to restore AP laxity to that of the intact knee. AP laxity was then measured at 0 degrees, 30 degrees, and 90 degrees of knee flexion with the graft in neutral rotation and in 90 degrees and 180 degrees of internal and external rotation. Five specimens received allografts that were rotated to 90 degrees internally and externally and then tensioned. Two knee specimens were used to measure the effects of graft rotation on graft force at full extension; 1 received 7 separate allografts and the other received 10 allografts. During testing, the potted end of the allograft that was connected to a tibial load cell was rotated. RESULTS: In specimens tensioned and then rotated, AP laxity at 30 degrees of knee flexion decreased an average of 0.9 mm with 90 degrees of graft rotation in either direction. At 180 degrees of external rotation, the mean decrease in laxity of 1.8 mm was significantly greater than that for 180 degrees of internal rotation (P <.05). When significant, all mean laxity reductions at 0 degrees and 90 degrees of flexion were less than those at 30 degrees of flexion. In specimens where the graft was rotated and then tensioned, rotation had no significant effect on laxity. With the exception of 90 degrees of external rotation, rotation of the graft increased graft tension at full extension; 90 degrees of internal rotation increased mean graft force by 11 N (P <.05). Rotating the graft 180 degrees in either direction increased mean graft force at full extension by 25 N (P <.05). CONCLUSIONS: Although minor, rotating the graft had significant effects on knee laxity and graft tension. In general, AP laxity decreased and graft tension increased with increasing rotation of the graft. The direction of rotation did not seem to be important. As a result, clinicians who choose to rotate their patellar tendon grafts can expect that the biomechanical changes in the graft with rotation will have little clinical importance.