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Contain bone loss in UKA to facilitate easy, future conversion to TKA when needed
Revisions of unicompartmental knee arthroplasty can achieve 'primary' results in the presence of a stable, well-aligned, well-balanced knee.
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ORLANDO, Fla., USA — Unicompartmental knee arthroplasty has become a popular procedure because it may delay the need for total knee arthroplasty. But, surgeons should take several factors into consideration when they perform unicompartmental knee arthroplasty to help achieve primary-type results later on, should revision to total knee arthroplasty be necessary, according to a presenter.
These factors include limiting bone loss and avoiding joint line changes, which along with other factors, can affect the success of revision of unicompartmental knee arthroplasty (UKA) to total knee arthroplasty (TKA), Emmanuel Thienpont, MD, MBA, said.
“Unicompartmental knee arthroplasties are revised more often because it is believed to be an easier and more straightforward revision. Surgeons should distinguish between a revision where we add another modular component, such as adding a patellofemoral joint to a UKA, a revision of a UKA presenting simple modes of failure allowing us to utilize a primary TKA or a revision of a complex failure of UKA. The latter one needs more hardware to reconstruct the joint, but the former ones can be difficult in the absence of sufficient surgical experience,” Thienpont told Orthopaedics Today Europe.
Understand the revision
Surgeons should make sure they use a bone-preserving UKA implant system that allows for conservative bone cuts. This can help any future revision to TKA achieve excellent outcomes, Thienpont, an Orthopaedics Today Europe Editorial Board member, said at the Current Concepts in Joint Replacement Winter Meeting, here.
Surgeons also must understand the reason for the revision and how it will affect outcomes. If polyethylene wear is the reason for the revision, a fixed-bearing implant with a conservative tibial cut is simple to revise to a TKA. If the UKA revision requires a TKA that involves stems, bone substitutes (cones and wedges), more constraint and there are joint line changes, then a primary result will likely not be obtained. Thienpont noted about two-thirds of patients with UKAs that are revised to TKA need stems or wedges.
The good news is that implant survival for a TKA revision of a UKA is often similar to that of a primary UKA procedure, based on the literature, he said.
Maximize outcomes
To maximize outcomes for a UKA that is revised to a TKA, it will help to select a TKA implant with full-size interchangeability between the tibia and femur, Thienpont said.
“If you have to cut under your UKA, you would be low on the tibia, and you will end up with a small tibial tray. In that case, if you had to adapt the femoral size to match the femur to the tibia, you will obtain that by downsizing the femur. This can lead to flexion gap mismatch, and this can lead to more constraint if you wanted to balance your flexion gap. But, it could also be solved by proximalizing your femur, which would bring down the patella, however,” he said.
The ability to revise a UKA with an implant that calls for minimal constraint is another strategy to help improve the chances of attaining a “primary” TKA result, according to Thienpont.
He noted a revision is still a revision procedure. Therefore, surgeons should keep their experience level in mind before deciding to proceed with any of these options.
“Even if you are able to do a revision with primary components, still remember it remains a revision. You will need the surgical experience and the surgical expertise to do this well. You will need to create a stable, well-aligned and well-balanced knee. That [requires] training and experience,” Thienpont said. – by Robert Linnehan
- Reference:
- Thienpont E. Paper #106. Presented at: Current Concepts in Joint Replacement Winter Meeting; Dec. 9-12, 2015; Orlando, Fla., USA.
- For more information:
- Emmanuel Thienpont, MD, MBA, can be reached at University Hospital Saint Luc, Avenue Hippocrate, 10 B-1200, Brussels, Belgium; email: emmanuel.thienpont@uclouvain.be.
Disclosure: Thienpont reports no relevant financial disclosures.