Unicompartmental knee arthroplasty – Partial Knee Replacement

If you have been suggested to a partial knee replacement or MAKOplasty (a specific type of robotic guided surgical procedure to resurface your knee), you will be told that this procedure would be a viable option because you are a good candidate for this surgery and that you would be able to enjoy these benefits of the procedure:

It is a partial knee replacement or Unicompartmental knee arthroplasty (UKA), it is not a whole knee replacement. Only a “Uni” or one compartment of the knee is replaced. Either the left side compartment, the right side compartment or the knee cap is replaced. The surgery is less complicated.
The partial knee replacement is a smaller incision, only the most damaged parts of your knee are removed. The viable parts of your knee remain.
For more precision in placing the replacement hardware, during the surgery the surgeon will bring in a robotic arm to place the knee implant into the areas where your knee bones were shaved down for proper alignment.

The great selling points are, “You can walk a few hours after the surgery,” and “Return to everyday activities in 1 to 4 weeks.”

Sounds great until you read what surgeons are reporting in the medical literature:

The pluses and minuses of partial or Unicompartmental knee arthroplasty

Orthopedist surgeons in Germany sell out the advantages and disadvantages of a partial knee replacement in their December 2020 paper titled: Unicompartmental knee arthroplasty – a solution? (1)

Here is what they wrote:

Unicompartmental knee arthroplasty (partial knee replacement) has various advantages over total knee arthroplasty; however, studies and paptient follow-ups have demonstrated significantly higher revision rate.
Nevertheless, good results with high patient satisfaction can be achieved by appropriate patient selection.
The good functional outcome may be due to the philosophy of the procedure, since the unicompartmental joint replacement is a pure resurfacing replacement, which aims to restore the individual, variable native, pre-arthrotic alignment, joint line and knee laxity, thus respecting the kinematics of the native knee joint. (Explanatory note: This means, and as it may have been explained to you by your orthopedist who has recommended a partial knee replacement, that this procure tries to restore your knee to a more knee function). In addition, important proprioceptive structures (natural structures that help you move naturally) such as ligaments are preserved. The advantages of unicompartmental joint replacement (minimally invasive procedure, preserving ligaments, cartilage and bone stock, more physiological kinematics, faster rehabilitation and easier revision surgery) outweigh the disadvantages of this procedure (technically more demanding, higher revision rate).

So there you have it, the good versus the not so good.

In the Journal of Orthopaedics.: August 2018 (2)

“Literature on Unicompartmental knee arthroplasty failure rates suggests that Unicompartmental knee arthroplasty may be a less forgiving procedure than total knee replacement (arthroplasty). Robotic-arm assisted surgery is reported to improve the accuracy of implant placement. Based on our prospectively collected positive patient outcomes, the authors have achieved good results from performing robotic-arm assisted UKA on select patients.”

How good?

Seventy-seven percent reported their knee always felt “normal,”
20% reported that there knee sometimes felt normal,
3% reported that it never felt normal.

These scores were not just on anybody, these scores were reported on highly selected patients. Those who had the best chance of the procedure working.

The reason partial knee replacement developed into a robot-guided procedure was that the problems associated with the partial implant and there are still problems for some

In the journal: The Orthopedic clinics of North America.

“Since its introduction, unicompartmental knee replacement has been controversial because of poor early clinical outcomes due to implant design, bony fixation, surgical instrumentation, and technique. Improvements in surgical technique and implant design have resulted in improved results and greater survivorship.

The ability to obtain accurate implant placement includes avoiding surgeon decisions leading to potential errors. These errors include alignment in the sagittal, coronal, and axial planes on each prepared condyle (the bony surface) as well as the preservation of the joint line and the resulting overall limb alignment as something critical to obtaining a successful outcome.”(3)

Basically, the implant was not put in right. It tilted too far to the front, the back, the right, the left, up and down. It was not put in right because too much or too little bone was shaved away. Clearly, you can now see why the words, “challenging,” and “unforgiving,” are used to describe when this procedure does not “feel normal.”

Your knee feels good today, how about tomorrow?

The goal of all medicine is to make people feel better. For some people partial knee replacement is the answer, for some, it may not be the best answer. But in the end, surgery is surgery and when key components or the entire joint is being replaced, the wear and tear that caused your natural joint to erode, will eventually cause components of your knee replacement to erode. This is something that should be considered.

We will now take a brief look at October 2018 research discussing the mobile bearing unicompartmental knee arthroplasty.

When knee ligaments are compromised or damaged or cut during the surgery, the knee component is less successful. Athletes take note.

Another selling point of the partial knee replacement is the turn in who the partial knee replacement will be successful for. Initially, this surgery was reserved for patients in the 60s and older who lead sedentary lifestyles. The surgeons were doing as little surgery as possible because of the patient’s deteriorating health concerns.

Then the surgeons began to suggest these procedures to younger patients who still wanted to remain active. Especially with the development of the mobile bearing prosthesis. The keyword = MOBILE.

Mobile bearing sounds great. A plastic ball bearing sits in your knee and helps the replacement component mimic a more natural knee motion. The plastic bearing floats around in your knee in a more anatomical way. The mobile bearing replacement came in response to the fixed bearing unicompartmental knee arthroplasty which was considered more rigid and caused greater wear and tear on the knee prosthesis.

In the journal Public Library of Science one, University researchers in Thailand made these observations and they involve a problem with damaging ligaments during the surgery. As we will see, strong ligaments are a crucial part of the success of a partial knee replacement.

The medial (center) mobile bearing unicompartmental knee arthroplasty has shown excellent clinical outcomes and survivorship. But release of the medial collateral ligament (MCL) during entering joint is the cause of mobile bearing dislocation in short-term outcomes and lateral (side) compartment osteoarthritis may occur in the mid to long-term outcomes.(4)

It should also be noted that doctors will not recommend mobile bearing unicompartmental knee arthroplasty unless the patient has an intact anterior cruciate ligament ACL.

Arthroscopy to prevent total knee replacement following partial knee replacement when problems develop

In the October 2018 issue if The Journal of arthroplasty, (5) surgeons discuss the problems that would cause partial knee replacement to be cut out and replaced with a total knee replacement.

Arthroscopy to prevent total knee replacement following partial knee replacement when problems develop

Persistent pain after medial unicompartmental knee arthroplasty is a prevailing reason for revision to total knee replacement. Many of these knee pain causing problems can be addressed arthroscopically. The purpose of this study is to examine the outcomes of patients who undergo an arthroscopy for any reason after partial knee replacement.
Indications for arthroscopy were:
- acute anterior cruciate ligament tear
- arthrofibrosis (excessive scar tissue caused by the surgery),
- synovitis (Inflammation of the synovial fluid of the knee),
- recurrent hemarthrosis (blood in the knee),
- lateral compartment degeneration including isolated lateral meniscus tears (the side of your knee is collapsing and damaging the meniscus)
- and loose cement fragments. (The bits and pieces left behind after the knee replacement component is cemented into place)

What concerned the doctors most, long-term – was the degeneration to the side of the knee and subsequent meniscus damage. In fact, 6 of the 11 patients in this study who had a complication of lateral compartment degradation went on to have a total knee replacement FOLLOWING an arthroscopic procedure to fix the partial knee replacement procedure. These patients had:

Partial knee replacement
Arthroscopic surgery to repair the partial knee replacement
Total knee replacement

Three surgeries long-term.

The evidence for alternatives to partial or total knee replacement.

We have many articles on our website that offer non-surgical alternatives to degenerative knee disease and advancing knee osteoarthritis. These articles will offer research and clinical outcomes that will help you understand the possibilities of rebuilding your knee through regenerative medicine:

If you have questions and would like to discuss your knee pain issues with our staff you get help and information from our Caring Medical staff.

1 Blatter SC, Koch P. Teilprothesen am Kniegelenk – wann sinnvoll? [Unicompartmental knee arthroplasty – a solution?]. Ther Umsch. 2020;77(10):475-479. German. doi: 10.1024/0040-5930/a001226. PMID: 33272050.
2 Deese JM, Gratto-Cox G, Carter DA, Sasser Jr TM, Brown KL. Patient reported and clinical outcomes of robotic-arm assisted unicondylar knee arthroplasty: Minimum two year follow-up. Journal of orthopaedics. 2018 Sep 1;15(3):847-53. [Google Scholar]
3 Roche M. Robotic-assisted unicompartmental knee arthroplasty: The MAKO experience. Clinics in sports medicine. 2014 Jan 1;33(1):123-32. [Google Scholar]
4 Pongcharoen B, Chanalithichai N. Clinical outcomes of patients with residual medial osteophytes following mobile bearing unicompartmental knee arthroplasty. PloS one. 2018 Oct 11;13(10):e0205469. [Google Scholar]
5 Hurst JM, Ranieri R, Berend KR, Morris MJ, Adams JB, Lombardi AV. Outcomes after Arthroscopic Evaluation of Patients with Painful Medial Unicompartmental Knee Arthroplasty. The Journal of Arthroplasty. 2018 May 29. [Google Scholar]

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