Up to 20 percent of patients remain dissatisfied after primary total knee arthroplasty (TKA) surgery. Understanding the reasons for dissatisfaction post TKA may allow for better patient selection and optimized treatment for those who remain dissatisfied. The association between function, mobility and satisfaction are not well understood. The purpose of this study was to investigate the association between post-TKA satisfaction and i) pre-operative, ii) post-operative, and iii) change in knee joint function during gait.

Thirty-one patients scheduled to receive primary TKA for knee osteoarthritis (OA) diagnosis were recruited and visited the Dynamics of Human Motion laboratory for instrumented walking gait analysis (using a synchronized NDI Optotrak motion capture system and AMTI force platforms in the walkway) at two time points, first within the week prior to their surgery, and second at approximately one year after surgery. At their post-operative visit, patients were asked to indicate their satisfaction with their knee prosthesis on a scale from zero to 100, with zero being totally unsatisfied and 100 being completely satisfied. Knee joint mechanics during gait at both time points were characterized by discriminant scores, the projection of their three-dimensional knee angles and moments during gait onto an existing discriminant model that was created to optimize separation of severe knee OA and healthy asymptomatic gait patterns. This discriminant model was created using data from 73 healthy participants and 73 with severe knee OA, and includes the magnitude and pattern features (captured with principal component analysis) of the knee adduction and flexion moment, and the magnitude of the knee flexion angle during gait. Larger discriminant scores indicate improved function toward healthy patterns, and smaller scores indicate more severe function. Associations between post-operative satisfaction and pre, post and change in discriminant scores were examined using Pearson correlation analyses. We also examined associations between satisfaction and pre-operative BMI, EQ5D and Oxford 12 scores, as well as changes in these scores from pre to post-TKA.

Discriminant scores representing knee joint function during gait significantly improved on average after surgery (P =0.05).

While overall knee joint function improved after primary TKA surgery, the amount of improvement in function was not reflected in post-operative patient satisfaction. However, the pre-operative function of the patient was negatively associated with satisfaction, indicating that patients with higher pre-operative function are overall less satisfied with their TKA surgery, regardless of any functional improvement due to the surgery. Interestingly, the only significant association with post-operative satisfaction was knee joint function, and the relationship between function and patient satisfaction following TKA appears to relate only to the baseline functional state of the patient, and not with functional improvement. This suggests that dissatisfaction post-surgery is more likely reflecting the unmet expectations of a higher functioning patient, and has implications for the need for improved understanding of pre-operative patient functional variability in TKA triage and expectation management.

Total knee arthroplasty (TKA) has been shown to improve knee joint function during gait post-operatively. However, there is considerable patient to patient variability, with most gait mechanics metrics not reaching asymptomatic levels. To understand how to target functional improvements with TKA, it is important to identify an optimal set of functional metrics that remain deficient post-TKA. The purpose of this study was to identify which combination of knee joint kinematics and kinetics during gait best discriminate pre-operative gait from postoperative gait, as well as post-operative from asymptomatic.

Seventy-three patients scheduled to receive a TKA for severe knee osteoarthritis underwent 3D gait analysis 1 week before and 1 year after surgery. Sixty asymptomatic individuals also underwent analysis. Eleven discrete gait parameters were extracted from the gait kinematic and kinetic waveforms, as previously defined (Astephen et al., J Orthop Res., 2008). Stepwise linear discriminant analyses were used to determine the sets of parameters that optimally separated pre-operative from post-operative gait, and post-operative from asymptomatic gait. Cross-validation was used to quantify group classification error.

Knee flexion angle range, knee adduction moment first peak, and gait velocity were included in the optimal discriminant function between the pre- and post-operative groups (P<0.05), with relatively equal standardised canonical coefficients (0.567, −0.501, 0.565 respectively), and a total classification rate of 74%. A number of metrics were included in the discriminant function to optimally separate post-operative and asymptomatic gait function, including the knee flexion angle range, peak stance knee flexion angle, minimum late stance knee extension moment, minimum mid-stance knee adduction moment, and peak knee internal rotation moment (P<0.05). The mid-stance knee adduction moment had the largest standardised canonical coefficients in the function, and 89.5% of cases were correctly classified.

Separation of pre and post-operative gait patterns included only three parameters, suggesting that current standard of care TKA significantly improves only walking velocity, knee flexion angle range, and the peak value of the knee adduction moment. A number of gait metrics, which were included in the discriminant function between post-operative and asymptomatic gait, could benefit from further improvement either through rehabilitation or design. With almost 90% classification, separation of post-operative gait function from asymptomatic levels is significant. The consolidation of knee joint function during gait into single, discrete discriminant scores allows for an efficient summary representation of patient-specific (or implant-specific) improvement in gait function from TKA surgery.