So, what about that PCL? In most cases, in my experience, it’s degenerative, and it’s the Goldilocks effect. It’s too loose. It’s too tight. Ah, yes, it’s just right. Despite this though, let’s save the PCL. Michael has a bumper sticker on his car that says that.
Let’s assess TKR kinematics. Fluoroscopic and intraoperative sensor studies. Fluoroscopically it’s a loaded environment, reproducible by following the contact point through motion and the use of assessment to determine the impact of design variables on rollback.
In one prospective, randomized study—cruciate retaining versus posterior stabilized—at 5 years, taken through range of motion (Victor, et al., JBJS-Br 2005). The results showed greater rollback with the posterior stabilized. Greater amount of posterior translation. Forward displacement in the cruciate retaining knee. However, I will admit the clinical outcomes were similar.
What about more novel ways to assess this—intraoperative sensing? Michael, you’re familiar with this…right? I think you’ve actually written about this. Three pieces of work (J Arthroplasty 2017 and 2016).
Summary of Michael’s work … Early phenomena of lateral rollback equals better clinical outcomes in the cruciate retaining anterior lipped design. Getting a tighter grouping of the differences in the pressures on the medial and lateral sides yielded better UCLA scores. I think that’s important.
My problem with the cruciate retaining—with or without an anterior lip—is that the kinematics are unpredictable and you’ve got the risk for later dysfunction. Tearing. Stretching out.
What do you get with a posterior stabilized knee? You get a post-cam mechanism that’s durable. A post-cam mechanism that’s predictable. And a post-cam mechanism that’s reliable.
We started on the subject of vestigial structures. It is my suggestion, ladies and gentlemen, that the PCL in the total knee is the vestigial structure. That, in fact, the post lives on…long live the post.
Moderator Berry: Alright, gentlemen. Thank you both. You’ve made your points quite well. So, Mike people gradually have, not altogether, moved away from them to a PS design. Why? My guess is that it’s probably for two of the reasons Doug mentioned. One, is the PCL is kind of tough to balance and it’s easy to get a little too loose. There is unpredictability to that process. And then fluoroscopic data showed unpredictable kinematics once the PCL is gone. Can you address those two? Is the world different now? Or have you just decided it doesn’t matter?
Dr. Meneghini: To your first point, I think that the anterior lip gives those surgeons who want to try and retain the cruciate ligament a factor of safety. There is a factor of safety built in with modern designs that can help people transcend that. We’ll see if that maintains…if the world continues to be 60% PS, which it may do for the foreseeable future.
The second comment on the kinematic data…and its great fluoroscopic kinematic data…is that there is no correlation with that data and outcomes. We’ve talked about anterior paradoxical translation and femoral rollback for 30 years. Great work. But we have yet to correlate with outcomes. And our patients have changed. Our patients now come into our office with high-end activity levels.
