A Biomechanical Evaluation of Transcondylar Femoral Fixation of Anterior Cruciate Ligament Grafts

Abstract

Background Interference screw fixation of the graft in anterior cruciate ligament reconstruction is considered the gold standard, but limited clinical experience suggests that transcondylar fixation is equally effective. Purpose To compare transcondylar and interference screw fixation. Study Design Ex vivo biomechanical study. Methods Twenty pairs of unembalmed knees underwent anterior cruciate ligament reconstruction with patellar tendon autografts. In 1 knee of each pair, the bone plug was stabilized in the femoral tunnel with standard interference screws; in the other knee, transcondylar screws were used. Testing to failure occurred immediately or after 1000 cycles of sinusoidal loading (30 to 150 N) (20 paired reconstructions each). Fixation stiffness, strength, graft creep, displacement amplitude, and change in amplitude were measured and compared (repeated measures anaylsis of variance with Tukey test; P < .05). Results There was no significant difference in acute strength, maximum load within 3 mm, or stiffness between transcondylar fixation (410 ± 164 N, 183 ± 93 N, and 49.6 ± 28 N/mm, respectively) and interference fixation (497 ± 216 N, 206 ± 115 N, and 61 ± 37.8 N/mm, respectively). Similarly, there was no significant difference in cyclic strength, maximum load within 3 mm, or stiffness between transcondylar fixation (496 ± 214 N, 357 ± 82.9 N, and 110 ± 27.4 N/mm, respectively) and interference fixation (552 ± 233 N, 357 ± 76.2 N, and 112 ± 26.8 N/mm, respectively). Predominant modes of failure were bone plug pullout (transcondylar fixation) and tendon failure or bone plug fracture (interference fixation). Conclusions Transcondylar screw fixation of the patellar tendon autograft into the femoral tunnel performed mechanically as well as interference screw fixation. Clinical Relevance The results suggest that transcondylar and interference screws provide similar fixation for anterior cruciate ligament reconstruction.