The effects of ACL injury on gait mechanics and the initiation of osteoarthritis [electronic resource]
Keywords: Mechanical Engineering.

Rupture of the anterior cruciate ligament (ACL) is one of the most common injuries to the knee. Unfortunately, individuals who experience this injury are likely to develop osteoarthritis of the knee much earlier than would be expected due to the normal ageing process, and this remains true even after surgical reconstruction of the ligament. Research has suggested that a major contributing factor to the development of premature osteoarthritis is altered knee mechanics which change the loading conditions of the cartilage in the joint. Furthermore, it has been shown that altered knee mechanics are present following rupture of the ACL and persist after reconstruction surgery. Despite initial reports, there still remains a need for a comprehensive understanding of both altered knee mechanics in both ACL deficient and ACL reconstructed knees as well as changes in cartilage morphology following ACL injury. Therefore, the goal of this dissertation is to address the question of the relationship between certain changes in knee mechanics and cartilage morphology as they relate to the development of osteoarthritis following both ACL injury and reconstruction. The first study presented involves an analysis of the knee mechanics in individuals with unilateral ACL deficiencies. This group was important in that they were free of knee pain and had no sign of osteoarthritis on MRI over a time frame that ranged up to three decades from injury. This provided a unique opportunity to explore the potential for a protective functional adaption. The results of this study suggest that alteration in knee mechanics may act as a protective mechanism against osteoarthritis development since when subjects were separated into "Short Term" and "Long Term", based upon the time from injury, only those in the "Long Term" group demonstrated a relationship between the external knee flexion moment, which is representative of the interaction between quadriceps and hamstrings muscle to control rotation and translation during walking. This is indicative of an adaptive control mechanism present in some subjects who were able to last many years after the injury without reconstruction surgery. These results suggest the potential for new methods for rehabilitation following ACL injury. The second study presented involves an analysis of the knee mechanics of individuals with unilateral ACL reconstructions during gait, stair ascent, and stair descent at two years from surgery. The results demonstrate a reduction in the external joint moments of ACL reconstructed knees and an increase in the joint moments of uninjured contralateral knees during each activity compared to healthy controls. This suggests two things: 1.) compensation for residual muscle weakness in the affected limb is needed by the contralateral knee during ambulation and 2.) a decrease in daily joint loading in ACL reconstructed knees and an increase in joint loading in contralateral knees. Decreased loading of the ACL reconstructed knee may seem counterintuitive to what was expected in patients who will likely develop premature osteoarthritis in this knee. However, this finding is consistent with the suggestion that changes in joint kinematics and even decreased joint loading following the injury may contribute to the initial cartilage breakdown. Note: Taken together the results of study 1 and 2 suggest that the interaction between muscle function and kinematics should be further considered in the development of knee OA in this population. The third and final study involves articular cartilage morphology analysis of individuals with unilateral ACL reconstructions at two and four years from surgery. The results illustrate differences between cartilage thickness of ACL reconstructed and healthy contralateral knees at both times of testing. The findings show significantly thinner cartilage in the lateral tibial compartment of ACL reconstructed knees at two years from surgery. These differences became more pronounced at four years from surgery and include the addition of a significantly thicker medial region of the tibia of ACL reconstructed knees compared to healthy contralateral knees. The results indicate that patterns of cartilage thickness change are detectable as early two years following ACL reconstruction, and these patterns become more pronounced at 4 years which suggests cartilage begins a degenerative pathway substantially in advance of clinically detectable OA. This finding is important since it provides a basis for assessing early interventions to reduce the risk of knee OA following ACL injury. This dissertation helps to further the understanding of altered knee mechanics following both ACL rupture and reconstruction. In addition, a possible pattern of OA initiation has been reported. Each of these studies will benefit future studies with the ultimate goal of a complete understanding of OA initiation and development in ACL ruptured and reconstructed knees.