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American Association of Hip and Knee Surgeons

Advocacy, Education, Research

Full vs. Partial Knee Replacement: What’s the difference?

While it may seem appealing to have half of a surgery compared to a full surgery, it is important to understand the differences between a unicompartmental (partial) and a total knee replacement surgery. Each type of knee replacement surgery is unique and has its own outcomes after surgery.

The knee is composed of three compartments: the inside (medial), outside (lateral) and underneath the knee cap (patellofemoral/anterior). Each of these compartments can be replaced individually in partial knee replacement surgery, or all three can be replaced in total knee replacement surgery*. A partial knee replacement is technically one-third of the surgery of a total knee replacement. If you have a partial knee replacement, you will find improvement in the function of your knee, but there are some long-term factors to consider.

Partial Knee Replacement

In the past, partial knee replacement was for patients over 60 years old whose ligaments were in good shape, had little knee deformity and could move their knee pretty well.1 Today, the procedure is being done on younger patients who have pain and other symptoms in one part of the knee.

Because a partial knee replacement is less surgery, it has often been reported to have an easier, quicker, more complete recovery and greater satisfaction than a full knee replacement.2  Complications during surgery like blood loss, transfusion and blood clots tend to be less with a partial replacement;3 however, long-term studies show the lifespan of partial knee replacement components is not as long as the lifespan of components used in a total knee replacement.4,5

Because partial knee replacement retains most of your knee tissue, you are still susceptible to meniscal tears and progression of arthritis in the rest of the knee. When a partial knee replacement fails, it can be converted to a full knee replacement with an excellent degree of success. The surgery and recovery may be more involved, but the overall outcomes are highly successful.6

Total Knee Replacement

This procedure has been revolutionary to orthopaedics giving many patients the ability to return to function and enjoy their lives with implants lasting about 10-15-years. While the surgery is longer, there is a higher rate of complications and greater cost, the lifetime of the implants is much greater than in partial knee replacements. Physical therapy is tougher early on, and the knee ultimately doesn’t quite feel the same as your own knee. Despite these potential limitations, patients who are good candidates for total knee replacement have greater patient satisfaction, higher functional scores and longer-lasting replacements. In the United States, over 90% of knee replacement surgeries are total knee replacements; while 10% or less are partial knee replacements.

Overall Outcomes

Both partial and total knee replacements can be highly successfully for patients who are good candidates. It is important to discuss the risks and benefits of each type of surgery with your surgeon so that your expectations are in line with the procedure you elect to have. Remember that both of these procedures are replacements, and you should follow the activity restrictions your surgeon provides you. Neither procedure is designed to hold up to the rigors of high-impact sports. If you take care of your total or partial knee replacement it will provide you with the greatest longevity possible.

*In some instances the undersurface of the patella may not be resurfaced as selected by your surgeon.

See also “Resuming Physical and Athletic Activity following Knee Replacement.”

  1. Kozinn SC, Marx C, Scott RD. Unicompartmental knee arthroplasty. A 4.5-6-year follow-up study with a metal-backed tibial component. J Arthroplasty. 1989;4 Suppl:S1-10.
  2. Kim MS, Koh IJ, Choi YJ, Lee JY, In Y. Differences in Patient-Reported Outcomes Between Unicompartmental and Total Knee Arthroplasties: A Propensity Score-Matched Analysis. J Arthroplasty. 2017;32(5):1453-1459.
  3. Siman H, Kamath AF, Carrillo N, Harmsen WS, Pagnano MW, Sierra RJ. Unicompartmental Knee Arthroplasty vs Total Knee Arthroplasty for Medial Compartment Arthritis in Patients Older Than 75 Years: Comparable Reoperation, Revision, and Complication Rates. J Arthroplasty. 2017.
  4. Dyrhovden GS, Lygre SH, Badawy M, Gothesen O, Furnes O. Have the Causes of Revision for Total and Unicompartmental Knee Arthroplasties Changed During the Past Two Decades? Clin Orthop Relat Res. 2017.
  5. Chawla H, van der List JP, Christ AB, Sobrero MR, Zuiderbaan HA, Pearle AD. Annual revision rates of partial versus total knee arthroplasty: A comparative meta-analysis. Knee. 2017;24(2):179-190.
  6. Thienpont E. Conversion of a unicompartmental knee arthroplasty to a total knee arthroplasty: can we achieve a primary result? Bone Joint J. 2017;99-B(1 Supple A):65-69.

This article has been written and peer reviewed by the AAHKS Patient and Public Relations Committee and the AAHKS Evidence Based Medicine Committee.
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