Unicompartmental Knee Arthroplasty Could Be Right for 50% of Patients With Osteoarthritis

By Alvaro Ibaseta, MD, and Trevor G. Murray, MD

Prevalence of knee osteoarthritis is high and rising among U.S. adults, with demand for knee arthroplasty estimated to increase 600% by 2030.1 According to one study, 85% of cases present with isolated single-compartment degeneration, most commonly in the medial compartment.2

An alternative to total knee arthroplasty (TKA), unicompartmental knee arthroplasty (UKA) can preserve some ligaments and bone in patients with isolated single-compartment end-stage osteoarthritis. However, while an estimated 45%-50% of patients with knee osteoarthritis could be candidates for UKA, it is pursued in only 5%-8% of cases.2

Low adoption of UKA is attributed primarily to the long learning curve for surgeons as well as registry data that show high revision rates of UKA compared to TKA.3,4 However, recent data challenge conventional concerns and show that UKA is a safe and effective procedure that may be a better option for many patients.

Short- and long-term benefits

UKA is less invasive than TKA and spares noninvolved ligaments and bone. The approach requires limited exposure and no dislocation of the knee joint, which results in significantly less soft-tissue damage (Figure 1). Operative time is shorter, blood loss is reduced, and hospital stays are decreased compared to TKA.

In the immediate postoperative period, patients achieve greater range of motion and a higher overall level of activity. In the longer term, UKA offers significantly higher rates of forgettable joints due to preservation of knee kinematics, preservation of bone stock and overall lower morbidity.2

Indications have expanded

Patient selection is considered crucial for long-term success of UKA. Conventionally, indications for UKA have been narrow, with the ideal patient being younger than age 60 and weighing less than 180 lbs., with isolated medial, lateral or patellofemoral osteoarthritis or osteonecrosis; correctable angular deformity less than 15 degrees; flexion contracture less than 5 degrees; and range of motion greater than 90 degrees. Patients have been considered nonideal if they have a high level of activity, exposed bone in the patellofemoral compartment, anterior knee pain, chondrocalcinosis, osteophytes in the opposite compartment, inflammatory arthritis or ACL insufficiency.

However, these conservative criteria are poorly backed by evidence. Multiple recent studies report successful results in patients formerly considered suboptimal for UKA.5

Overall, UKA has become a valid option for the younger patient as an alternative to high tibial osteotomy, showing lower rates of complication and reoperation. UKA is also a valid option for older patients, who may not recover as readily from a more invasive TKA. UKA offers reduced operative time, blood loss and hospital stays, and enables higher levels of activity at discharge.

Why UKA revision rates seem high

As previously noted, early registry data showed high revision rates in UKA compared to TKA — a statistic that is frequently quoted when deciding against UKA. However, these data need careful interpretation. More recent cohort studies from high-volume centers report survivability of the modern UKA as similar to TKA.6

There are a number of factors that may explain this difference:

1. The threshold to revise UKA is often lower than TKA, even when outcome scores are similar. Among patients with Oxford knee scores less than 20, only 12% of TKAs were revised compared to 63% of UKAs.7
2. UKA is more easily revised. UKA conversion to TKA is less technically challenging than TKA revision, generally requiring fewer revision components and techniques.
3. Patients conventionally considered ideal for UKA are younger and more active than TKA patients. Thus, UKA patients have a higher likelihood of lifetime revision simply due to longevity.
4. UKA revision rates are reportedly four times higher by low-volume surgeons compared to high-volume surgeons.2 Volume is important because surgeons with UKA usage less than 5% have higher revision rates. Optimal outcomes in UKA are seen when surgeon usage is 40%-60%.

High-volume experience matters

For the appropriately indicated patient, UKA can be a more effective and less invasive surgical option than TKA. Modern implants and surgical techniques in the hands of high-volume surgeons result in outcomes comparable or superior to TKA.

Medial UKA (Figure 2) is the most commonly performed and best understood UKA procedure, but any compartment can be replaced. At Cleveland Clinic, we have performed single-stage bilateral patellofemoral UKA (Figure 3).

Overall, we have been able to report excellent short- and long-term outcomes, almost-universal same-day discharge, quick surgical recovery, a high level of activity at discharge, and a low rate of complications. While there is a risk of eventual conversion to TKA, our data agree with the latest cohort results, showing similar survivability between UKA and TKA.

Dr. Murray is staff in the Department of Orthopaedic Surgery and a high-volume unicompartmental knee arthroplasty surgeon. Dr. Ibaseta is a resident in the Department of Orthopaedic Surgery.

References

1. Kurtz S, Ong K, Lau E, Mowat F, Halpern M. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am. 2007 Apr;89(4):780-5.
2. Mittal A, Meshram P, Kim WH, Kim TK. Unicompartmental knee arthroplasty, an enigma, and the ten enigmas of medial UKA. J Orthop Traumatol. 2020 Sep 2;21(1):15.
3. Koskinen E, Eskelinen A, Paavolainen P, Pulkkinen P, Remes V. Comparison of survival and cost-effectiveness between unicondylar arthroplasty and total knee arthroplasty in patients with primary osteoarthritis: a follow-up study of 50,493 knee replacements from the Finnish Arthroplasty Register. Acta Orthop. 2008 Aug;79(4):499-507.
4. 10th Annual Report 2013. National Joint Registry for England, Wales and Northern Ireland.
5. Pandit H, Jenkins C, Gill HS, Barker K, Dodd CAF, Murray DW. Minimally invasive Oxford phase 3 unicompartmental knee replacement: results of 1000 cases. J Bone Joint Surg Br. 2011;93(2):198-204.
6. Lyons MC, MacDonald SJ, Somerville LE, Naudie DD, McCalden RW. Unicompartmental versus total knee arthroplasty database analysis: Is there a winner? Clin Orthop Relat Res. 2012;470(1):84-90.
7. Goodfellow JW, O’Connor JJ, Murray DW. A critique of revision rate as an outcome measure: re-interpretation of knee joint registry data. J Bone Joint Surg Br. 2010 Dec;92(12):1628-31.