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.