Abstract
Introduction
It is well known that total knee arthroplasty (TKA) does not preserve normal knee kinematics. This outcome has been attributed to alteration of soft-tissue balance and differences between the geometry of the implant design and the normal articular surfaces. Bicompartmental knee arthroplasty (BKA) has been developed to replace the medial and anterior compartments, while preserving the lateral compartment, the anterior cruciate ligament (ACL), and the posterior cruciate ligament (PCL). In a previous study, we reported that unicompartmental knee arthroplasty did not significantly change knee kinematics and attributed that finding to a combination of preservation of soft-tissue balance and minimal alteration of joint articular geometry (Patil, JBJS, 2007). In the present study, we analyzed the effect of replacing trochlear surface in addition to the medial compartment by implanting cadaver knees with a bicompartmental arthroplasty design. Our hypothesis was that kinematics after BCKA will more closely replicate normal kinematics than kinematics after TKA.
Methods
Eight human cadaveric knees underwent kinematic analysis with a surgical navigation system. Each knee was evaluated in its normal intact state, then after BKA with the Deuce design (Smith & Nephew, Memphis, TN), then after ACL sacrifice, and finally after implanting a PCL-retaining TKA (Legion, Smith & Nephew). Knees were tested on the Oxford knee rig, which simulates a quadriceps-driven dynamic deep knee bend. Tibiofemoral rollback and rotation and patellofemoral shift and tilt were recorded for each condition and compared using repeated measures ANOVA for significance.
Results
Statistically significant differences were noted in femoral rollback between TKA and Intact conditions but not between Intact and BKA or between Intact and BKA without ACL. Statistically significant differences were noted in tibiofemoral rotation between TKA and Intact conditions but not between Intact and BKA or between Intact and BKA without ACL. No significant differences in patellar lateral shift or lateral tilt were found among the four conditions tested.
Discussion & Conclusion
BKA prostheses that preserve the ACL and PCL allow for more normal knee kinematics than does conventional TKA. Our results supported our primary hypothesis that a bicompartmental approach would not significantly alter knee kinematics. These results also imply that replacement of the medial compartment and trochlear surface are not major factors contributing to altered knee function. The results that we observed may not necessarily apply to other BKA designs and should therefore not be extrapolated beyond the prosthesis designs in this study. Additionally, the current study was designed to only evaluate kinematics, and we can not make conclusions regarding implant wear, fixation, durability, ideal patient selection, and reproducibility of successful clinical outcomes. Lastly, the current study was undertaken using relatively normal cadaveric knees whereas in vivo arthroplasty is typically reserved for arthritic knees that are often affected by contracture and/or deformity. We therefore believe that clinical studies with well-defined measures of success need to be conducted before far-reaching conclusions can be drawn regarding the utility of these implants in clinical practice.
