This week’s Orthopaedic Crossfire® debate was part of the 35th Annual Current Concepts in Joint Replacement® (CCJR®), Winter meeting, which took place in Orlando. This week’s topic is “Patient Specific TKA Provides Improved Satisfaction.” For is Mary I. O’Connor, M.D., Yale School of Medicine, New Haven, Connecticut. Opposing is David G. Lewallen, M.D., Mayo Clinic, Rochester, Minnesota. Moderating is Fares S. Haddad, M.D., F.R.C.S., University College Hospital, London, United Kingdom.
Dr. O’Connor: My disclosure is that my institution receives support from ConforMIS, Inc., which is the company that manufactures the custom total knee I’ll be referring to.
A lot of our patients sing this song…”I Can’t Get No Satisfaction.” Right? Numerous studies show that a high percentage of our patients are dissatisfied with their total knees. They complain of lower than anticipated functional improvement potentially related to subtle instability and suboptimal kinematics. Incomplete pain relief – component malrotation and suboptimal fit can cause that. We know improper fit leads to residual pain. Femoral overhang can cause pain (Mahoney, et al., 2010; Bonnin, et al., 2013).
Component malrotation and internal rotation errors are 5 times more likely to cause anterior knee pain (Nicoll, et al., 2010; Bonnin, et al., 2013; Berger, et al., 1998, Barrack, et al., 2001; Martin, et al., 2012).
Poor kinematics, we know, lead to suboptimal function and there is a high frequency of paradoxical motion (Dennis, et al., 2003).
Let’s talk about anatomy. In a series of 24,000 patients, the variation in distal offset ranged from 1mm up to 6mm with 1/3 of the patients neutral, 1/3 moderate, and 1/3 with a high degree of joint line varus (Beckmann, et al., 2017).
So, can a custom total knee that takes that into account variation in anatomy produce a better result?
How is a custom total knee made? Patient gets a CT scan from the hip to the ankle. That’s sent to the company. They use that information to create a custom implant. They set alignment at the neutral mechanical axis. They recreate each patient’s individual J-curves.
An off-the-shelf component cannot do that.
A custom knee can give you offset polys, different thicknesses medial and lateral that allow you to maintain normal offset while having a horizontal tibial resection. And the medial insert is more conforming to facilitate rollback.
How do these implants perform clinically? Are patients better satisfied?
Looking at survivorship data, the UK Registry (Beyond Compliance iTotal G2 XE 11-Feb-2018; Northgate Publish Services (UK) Limited) found that ConforMIS knees at a 0.5% revision rate at 4 years which compares favorably to off-the-shelf implants at 1.9%.
