Primary Knee Symposium: Biomechanical Considerations in the Knee

Knee Alignment: Important or Not? – Michael Manley, PhD

This presentation addressed the issue of knee alignment in total knee arthroplasty and whether impacts the longevity of knee replacement devices. The traditional belief is that alignment is critical for performance and function.

There are several measures for alignment. For flaxion/extension, mechanical testing one third with the PCL intact¹. PSlide A Cutting the PCL allows some, but not all, motion to be gained in this configuration. PSlide B Available flexion is also impacted by posterior offset. As reported by Bellemans et. al., in 72% of patients, deep flexion (squatting) was limited by direct impingement of the tibial insert against the back of the femur.²

Dr. Manley then presented opposing views on the importance fo the mechanical axis. In the clinical study published in 1991, Jeffrey et. al. showed that knees with coronal alignment within 3 degrees of mechanical alignment had a significantly lower revision rate than those that were malaligned.³ Recently, Pagnano, in a study published in Orthopaedics Today, concluded that mechanical axis was not important at 15 year survivorship.⁴

Dr. Manley's position was aligned with Jeffrey et. al. He argued that if components are malaligned, there will be adverse stress distribution in the polyethylene (due to very high contrast stresses). 1) View Knee Conformity Animation 2) View Knee Alignment Animation He concluded that maintenance of the joint line is important for the restoration of function, and mechanical alignment of components will minimize polyethylene damage and the stress on the fixation interfaces.^1,3