A total knee arthroplasty (TKA) or knee replacement is considered successful to the extent that it relieves the pain caused by knee osteoarthritis (OA). While the aim is to restore function limited by the pain of OA, functional deficits may still persist postsurgery. Anterior Cruciate Ligament (ACL) injuries are a common cause of functional deficit in athletes, and anterior cruciate ligament reconstruction (ACLR) surgery is the surgical intervention to restore function and allow for participation in sport (Warren R Dunn et al. 2013).

In the case of both TKA and ACLR, patients’ recovery is aimed at restoring function following the surgery. Unfortunately, several complications unique to each patient population beleaguer patients’ recovery, even when the normal course of therapy is followed and despite achieving metrics and milestones set forth by physical therapists and guidelines. In the case of TKA, persistent disability, especially performing tasks of daily living like stair-climbing, dissatisfaction, instability, and failure requiring revision are among the outcomes. For patients following ACL reconstruction, complications can include a failure to return to preinjury levels of sport participation, increased risk of a subsequent ACL injury in the ipsilateral or contralateral limb. These complications and issues often manifest clinically within two years of surgery.

These problems raise the questions of how current guidelines for rehabilitation, whether it is the length of time spent, the goals and metrics against which we measure patients or even perhaps the way we group and categorize patients, can be reexamined, and updated to improve outcomes and reduce the incidence of these complications. A way to begin to do that is a biomechanical analysis of patients who undergo these surgeries at two years post-surgery to examine what measures of function, namely limb strength, and biomechanics can tell us about the surgery itself or prognosis of outcomes. The works described in this dissertation are examinations of two patient cohorts, one at different timepoints until two years post total knee arthroplasty, and one cohort of patients who were two years post ACL reconstruction, to begin to characterize how measures of lower limb strength evolve until two years and correlate with intraoperative biomechanics as well as two-year stair climbing biomechanics in the case of TKA and how proximal joint strength correlates with single landing biomechanics and force attenuation strategies after ACL reconstruction.

This dissertation is comprised of three studies. The first study examines quadriceps strength of a cohort of patients undergoing TKA. At 30 days pre-TKA and 6 months and two years post-surgery, participants’ isometric quadriceps strength was measured using stationary dynamometry. Participants were separated into three groups based on the difference between 6-month and pre-TKA recorded knee extension strength. When compared, the trends of the course of knee extension strength between the three groups showed different patterns of progression.

The second study examines seven sagittal-plane post-implantation intraoperative passive knee kinematics that define the femur position and translation with respect to the tibia through angles of passive knee flexion and their correlation with peak stair ascent knee extension moments two years post-surgery. Of the seven potential predictors investigated, only intraoperative anterior-most position of the femur with respect to the tibia during passive flexion was selected as a significant positive predictor in the forward regression.

Finally, we evaluated the sagittal-plane single-leg landing kinetics of participants who were two years-post ACL reconstruction and examined their correlations between hip abduction and extension strength. Peak vertical ground reaction force, loading rate, peak total support moment and joint sagittal plane moments at peak total support moment were considered. Hip strength significantly correlated with peak vertical ground reaction force as well as hip sagittal plane moments and showed a negative correlation with knee sagittal plane moment. The same degree of correlation between hip strength and single-limb landing kinetics was not shown in participants’ uninvolved limb. The results of this study suggest that hip strength may be an indicator of persistent functional deficits of the knee following ACL reconstruction.