Paper 80: Biomechanical Analysis of Tibial Motion and ACL Graft Forces After ACLR With and Without LET at Varying Tibial Slopes

Abstract

Objectives:Lateral extra-articular tenodesis (LET) is being performed more frequently with anterior cruciate ligament reconstruction (ACLR) to decrease graft failure rates. Posterior tibial slope (PTS) affects ACL graft failure rates.2 The impact of LET plus ACLR on tibial motion and graft forces with increasing PTS has not been elucidated. We hypothesized LET will decrease anterior tibial translation (ATT), tibial rotation, and ACL graft force versus ACLR alone with increasing tibial slope throughout knee range of motion.Methods:Twelve cadaveric knees (40.5 mean age, all female) were tested in four conditions (intact, ACL cut, ACLR, ACLR + LET) with varying PTS (5°, 10°, 15°, 20°) at three flexion angles (0°, 30°, 60°). Specimens were mounted to a load frame which applied a 500-N axial load with 1 Nm of internal rotation (IR) torque (Figure 1). The amount of tibial translation, IR, and graft forces were measured.Results:Increasing PTS revealed a linear and statistically significant increase in graft force at all flexion angles. LET reduced graft force by 8.3% (6N) compared to ACLR alone at 30° of flexion. At the same position, slope-correcting osteotomy reduced graft force by 17-22% per 5° of slope correction, with a 46% reduction seen from 20° to 5°slope correction. For ATT, ACLR returned tibial translation to pre-injury levels, as did ACLR + LET at all flexion angles, except full extension where ACLR + LET over-reduced ATT by 2.47mm (p<0.05).Conclusions:Increased PTS was confirmed to increase graft forces linearly. Additionally, while the ACLR + LET reduced graft force compared to ACLR alone, slope correcting osteotomies are a more powerful method to minimize graft force. No other clinically significant differences were noted between ACLR with or without LET in regards to graft force, ATT, or IR. Many authors have proposed LET in the setting of ACLR, revision surgery, hyperlaxity, high grade pivot shift and elevated PTS, but the indications remain unclear. The biomechanical performance of LET plus ACLR at varying PTSs may impact daily practice and provide clarity on these indications.