Unicompartmental knee arthroplasty versus total knee arthroplasty


When should a surgeon opt for unicompartmental knee arthroplasty (UKA) versus total knee arthroplasty (TKA) to treat knee osteoarthritis (OA)? UKA may be associated with higher revision rates but there are situations when UKA offers benefits over TKA. Should orthopedic surgeons make efforts to increase the number of UKAs they perform?


Knee OA is a common problem. There is a 50% lifetime risk of developing symptomatic arthritis in the knee [1]. In the US alone, it was estimated in 2016 that close to 14 million people were afflicted with symptomatic knee OA, and there is a growing trend for this condition to develop in younger persons (< 65 years of age) [2].

The associated knee pain, aching, loss of range of motion (ROM) and function, as well as stiffness are all symptoms driving the increasing arthroplasty rates, with predictions of “a four-fold demand for knee arthroplasty in OECD countries by 2030.” [3] Coupled with risk factors such as obesity, gender, injury, and genetics, [4, 5] knee arthritis has been on orthopedic surgeons’ radar for many years…and will continue to be so.

Figure 1. End stage medial compartment osteoarthritis (MOA). Used under CC Attribution 4.0 International License. Source: Mancuso F, Dodd CA, Murray DW, et al. Medial unicompartmental knee arthroplasty in the ACL-deficient knee. J Orthop Traumatol. 2016 Sep;17(3):267–275.


Knee arthroplasty is an accepted surgical treatment to address knee OA. Ideally, patients, together with their surgeons, consider treatment options and prioritized patient-specific considerations, to make fully informed decisions. When asked, patients take into account how fast they could recover and return to work, the potential for revision and complications, functional outcomes, and mortality likelihood [6–8]. It has also been suggested that patients also consider length of the surgical scar when making treatment modality decisions [8].

Typically, depending on the location and progression of the OA, patient characteristics such as age, comorbidities, activity level, and the condition of the anterior cruciate ligament (ACL), a surgeon is presented with several treatment options after conservative management has been exhausted [9]. Simply put, the presence of single compartment (unicondylar) OA is the primary indicator that UKA should at least be considered, [10] together with other factors; this is a special subset of OA patients [11]. Approximately a third of knee OA patients will have the disease confined to a single compartment [12].

This article compares UKA and TKA and asks, “In which situations would you opt for these procedures?” Caution: This decision may not be as straightforward as it appears;[13] both UKA and TKA are accepted and established treatment options for OA of the knee [9, 14, 15]. 


Jean-Noël Argenson

University Hospital of Marseille
Marseille, France

Jean-Noël Argenson, Professor and Chairman of the University Hospital of Marseille’s Orthopaedics Department, France, explains that, “For many years, TKA has been considered the standard of surgical treatment for knee OA due to demonstrated reproducibility and effectiveness for relieving pain and restoring function; however UKA has increased in popularity over the last twenty years as shown in national orthopedic registries [16]. The indications for UKA are relatively strict with fewer indications compared to TKA since the OA should be limited to one femorotibial compartment of the knee with intact ACL.”


Lateral or medial compartment: Which is more common in UKA?

The lateral compartment is usually involved in 10% of unicompartmental femorotibial arthroplasty cases due to the natural history of OA preferentially loading the medial femorotibial compartment and the higher proportion of “knees in varus” among the general population [17]. Both the anatomical and the biomechanical characteristics are different in each of the knee femorotibial compartments, and similar surgical treatment may not give reproducible results when applied to a different compartment [18, 19]. Jean-Noël Argenson notes that, “UKA in the lateral compartment has been described as technically more challenging and is performed ten times less frequently than medial UKA,” for the reasons explained above.

“However, published studies have suggested that lateral UKA is a reasonable alternative to TKA for isolated lateral femorotibial compartment disease. The mid- and long-term results of lateral UKA have shown satisfying clinical and radiological results. The specific anatomical and biomechanical characteristics of the lateral compartment should be accommodated at the time of surgery when performing lateral UKA. Improvements in patient selection and surgical ancillaries over time have also decreased the failure rate, allowing similar survival for medial and lateral UKA,” says Argenson.


Read the full article with your AO login

  • Treatment options: TKA or UKA?
  • Kozinn and Scott contraindications
  • Patient selection: Oxford indications
  • Should a patient’s age, body mass index, or activity level preclude them from a UKA?
  • Revision rates influence surgeon procedure selection
  • Why are UKA revision rates higher than in TKA?
  • Increase the practice proportion of UKA to 20%?
  • Benefits of UKA
  • In summary
  • References

Part 2 | Unicompartmental knee arthroplasty versus high tibial osteotomy

Part 3 | Unicompartmental knee arthroplasties: Tips and tricks

More AO resources

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Contributing experts

This series of articles was created with the support of the following specialists (in alphabetical order):

Jean-Noël Argenson

University Hospital of Marseille
Marseille, France

Robert Hube

OCM—Orthopedic Surgery Center Munich
Munich, Germany

Georg Matziolis

Waldkliniken Eisenberg—German Center of Orthopedics
Eisenberg, Germany

This issue was created by Word+Vision Media Productions, Switzerland



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