This week’s Orthopaedic Crossfire® debate was part of the 34th Annual Current Concepts in Joint Replacement® (CCJR®), Winter meeting, which took place in Orlando. This week’s topic is “Kinematic Alignment Optimizes Patient Outcome.” Affirming is Michael J. Dunbar, M.D., F.R.C.S.(C), Dalhousie University, Halifax, Nova Scotia, Canada. Opposing David G. Lewallen, M.D., Mayo Clinic, Rochester, Minnesota. Moderating is Daniel J. Berry, M.D., Mayo Clinic, Rochester, Minnesota.
Dr. Dunbar: I do have trepidation debating Dave, he’s such a thoughtful and learned knee surgeon. I’ll do my best.
To start, neutral mechanical axis is a paradigm of remarkable evolution of total knee arthroplasty. Millions of patients around the world and all of us in this room owe a great debt of gratitude to those who brought us this standard of care.
But I would ask…is it really the end of the road for evolution of TKAs [total knee arthroplasty]? Are we at a dead end when we consider that we’ve made no substantial improvement over the last 15 years of survivorship in total knee arthroplasty?
Arguably, our results in 2003 are as good or better than they were in the most recent reported rounds.
The human condition is individual variation. When we were first exposed to statistics our teacher would line up our classmates and show how height can fall into a bell curve.
Which brings me to the Bellemans, et al. award-winning paper (CORR 2012) that looked at the alignment (using 3-foot standing films) of 500 Belgium patients, aged 20-29 years. They found—go figure—a frequency distribution approximating normal distribution of a bell curve.
Importantly, this normal, healthy population had an average varus of 1.3 degrees and if you took the males out of those, they were at 1.8 or 2 degrees of varus. Healthy individuals. More importantly looking at plus/minus 3 degrees, a full one-third of that population was outside of that window. So, clearly, not one target fits all.
Adolph Lombardi, world-class knee surgeon and president of the Knee Society, said that “Aiming for neutral provides the safest margin for error, but the foremost objective of total knee arthroplasty is a durable joint, and this is important. Not necessarily one that replicates normal or the patient’s native condition.”
If you want to make something last, make it straight. Go back, look at the most promulgated paper (Jeffery et al, JBJS-Br 1991), it’s based on old designs and old implants. They found that a large portion of patients who were outside the 3 degrees of varus window failed—but this was a rheumatoid patient population. Mostly females, using implants that we clearly don’t use today on a population we’re not operating on today.
A very important paper from Barrack’s group (J Arthroplasty 2016) found more or less the same findings that if you’re plus or minus 3 degrees outside this window you have an increased risk of failure.
But my most important argument against this is short leg films, one implant, single center. When long leg films were looked at in a single series over a 15-year follow-up, (Parrette et al. JBJS-Am 2010) a post-operative mechanical axis of plus or minus 3 degrees did not improve 15-year survivorship.
