Understanding the interaction between graft placement, gait mechanics, and cartilage morphology as a pathway to osteoarthristis in the ACL reconstructed knee [electronic resource]
Keywords: Mechanical Engineering

The overall goal of this dissertation was to address the question of the relationship between anterior cruciate ligament (ACL) graft function, changes in walking mechanics, and the morphology of the articular cartilage in the ACL reconstructed knee as a step towards filling critical gaps in the available knowledge of the association between ACL injury and premature osteoarthritis of the knee. ACL injury often leads to premature osteoarthritis of the knee even when the ACL is reconstructed and alterations in knee mechanics during walking have been identified as a potential mechanism of cartilage degeneration in the ACL deficient knee. This thesis provides the results of experimental studies using magnetic resonance (MR) imaging and gait analysis to understand the effect of ACL reconstruction on the mechanics of walking and articular cartilage morphology in the context of a potential mechanism for the initiation of osteoarthritis. These results provide a basis for improving the treatment and long-term prognosis of the ACL injured knee. Gait analysis of subjects after ACL reconstruction showed that during the stance phase of walking, their ACL reconstructed knee had significantly more external tibial rotation when compared to their contralateral knee. This kinematic alteration likely causes changes in normal cartilage contact mechanics and could contribute to the eventual degeneration of the articular cartilage. Analysis of ACL graft placement in this population revealed a potential mechanism for the observed alteration in ambulatory mechanics in the ACL reconstructed knee. Variations in graft placement were correlated with the magnitude of the peak external knee flexion moment (balanced by a net quadriceps moment) and the tibiofemoral rotational position of the reconstructed knee during walking. In both cases, non-anatomic graft placement resulted in greater deviations in the ambulatory mechanics of the ACL reconstructed knee. Since these results indicated graft placement plays a critical role in the restoration of normal ambulatory mechanics, MR imaging was utilized to develop a method to determine the three-dimensional location of native tibial and femoral ACL insertions to guide and evaluate anatomic ACL graft placement. Analysis of healthy and ACL reconstructed subjects revealed the presence of side-to-side symmetry in location of ACL insertions in healthy subjects but not after transtibial ACL reconstruction, indicating that conventional transtibial reconstruction frequently places the graft outside the center of the anatomical ACL footprint. Further examination of the effects of non-anatomic ACL graft placement revealed the unintended consequences of vertical sagittal orientation of the ACL graft. These results demonstrated that although vertical sagittal graft orientation was associated with less occurrence of an active knee extension deficit during walking (as intended), it was also associated with an increased anterior tibial neutral position in the ACL reconstructed knees. Finally, in order to investigate the mechanism of the proposed kinematic pathway to osteoarthritis after ACL reconstruction, the individual-specific femoral cartilage thickness distribution was related to knee flexion during walking in the reconstructed and healthy contralateral knees. The results of this study showed that although a relationship existed in both the reconstructed and contralateral knees, a shift in knee flexion at heel-strike without an adaptation in cartilage thickness distribution caused an alteration in the relationship in the ACL reconstructed knees. Thus failure of the ACL reconstruction to restore normal walking mechanics could contribute the breakdown of articular cartilage in the ACL reconstructed knee. The results of these studies provide a better understanding of the influence of ACL reconstruction on the subsequent changes in the mechanics of the ACL reconstructed knee. These findings present insights into the complex relationship between variations in ACL graft placement, changes in walking mechanics, and the distribution of cartilage thickness in the context of a potential kinematic mechanism for the development of premature osteoarthritis after ACL injury and reconstruction. Taken together, these results provide a basis for improving the standard of care for the ACL injured knee.