The in vivo relationship between anterior neutral tibial position and loss of knee extension after transtibial ACL reconstruction

Background: Restoration of anterior tibial stability while avoiding knee extension deficit are a common goal of anterior cruciate ligament (ACL) reconstruction. However, achieving this goal can be challenging. The purpose of this study was to determine whether side-to-side differences in anterior tibial neutral position and laxity are correlated with knee extension deficit in subjects 2 years after ACL reconstruction. Methods: In the reconstructed and contralateral knees of 29 subjects with transtibial reconstruction, anterior tibiofemoral neutral position was measured with MRI and three-dimensional modeling techniques; terminal knee extension at heel strike of walking and during a seated knee extension were measured via gait analysis; and anterior laxity was measured using the KT-1000. Results: Knees that approached normal anterior stability and anterior tibial position had increased extension deficit relative to the contralateral knee. On average the reconstructed knee had significantly less (2.1 +/- 4.4 degrees) extension during active extension and during heel strike of walking (3.0 +/- 4.3((0) under bar)), with increased anterior neutral tibial position (2.5 +/- 1.7 mm) and anterior laxity (1.8 +/- 1.0 mm). There was a significant correlation between side-to-side difference in anterior neutral tibial position with both measures of knee extension (walking, r = -0.711, p < 0.001); active knee extension, r = -0.544, p = 0.002). Conclusion: The results indicate a relationship between the loss of active knee extension and a change in anterior neutral tibial position following non-anatomic transtibial ACL reconstruction. Given the increasing evidence of a link between altered kinematics and premature osteoarthritis, these findings provide important information to improve our understanding of in vivo knee function after ACL reconstruction. (C) 2013 Elsevier B.V. All rights reserved.