Rotation of bone–patellar tendon–bone (BPTB) grafts during ACL reconstruction has been advocated for many reasons. Rotation of 180° has been theorized to improve fixation within the tibial tunnel and to prevent wear of the tendon at the edges of the tibial tunnel. External rotation may reproduce the natural rotation of the ACL and may improve graft isometry. More recently, rotation of the BPTB graft up to 540° has been used to shorten the graft to address graft length–tunnel mismatch.
The impact of rotation on the biomechanical properties of the BPTB construct, however, is largely undetermined. Several authors have found no effect of rotation. Using intraoperative measurements, Arnold cited changes in the force on the ACL with variable rotation. Cooper reported a statistically significant increase in ultimate load to failure in graft rotation from 0° to 90° (P < .05), with no additional increase with further rotation to 180°. Hame measured decreased AP laxity and increased graft tension at 90° and 180° of rotation. In our previous report, single-cycle load-to-failure testing of rotated grafts up to 540° found no difference in ultimate failure strength but noted a trend toward increasing strain at higher degrees of rotation.
The purpose of this study was to examine the biomechanical effects of various amounts of rotation on cyclic-loaded BPTB grafts. To our knowledge, a cyclic loading analysis of rotated grafts has not been previously reported. A secondary goal was to quantify the shortening achieved with external rotation of the graft. Our null hypothesis was that graft rotation does not meaningfully affect yield strength or modulus of elasticity of the construct.