Choosing UKR vs TKR for Unicompartmental Knee Osteoarthritis

Jun 13, 2022

Osteoarthritis is a common disease

Osteoarthritis (OA) is the main cause of disability in the elderly; with individuals having a 50% lifetime risk of developing symptomatic knee arthritis (1). Surgical replacement of the knee joint, or “arthroplasty,” is an effective treatment for end-stage OA, however it is estimated that up to 47% of patients undergoing this procedure will have disease in only one compartment (medial, lateral, or patellofemoral) (2). Unicondylar knee replacement (UKR) and Total Knee Replacement (TKR) are two surgical options for unicompartmental knee OA. In UKR only the damaged knee compartment is replaced, while in TKR all three compartments are replaced.

An OA treatment Algorithm

The European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO) has suggested the following evidence-based algorithm for the stepwise management of knee OA (3):

Basic Principles & Core Set: education, weight loss, regular exercise program

Step I: Background Treatment = Paracetamol, topical NSAIDs, physiotherapy referral

Step 2: Pharmacological management = NSAIDs +/- intraarticular injections

Step 3: Last pharmacological attempts = Short-term weak opioids; duloxetine

Step 4: End-stage disease management and surgery = TKR or UKR

Arthroplasty indicated for end-stage OA – but what kind?

The choice of UKR vs TKR remains controversial in those patients suffering from only unicompartmental disease.

Traditionally, the indications for UKR have been narrow. The procedure has been classically reserved for older (>60yo) and thinner (<82kg) patients with minimal deformity (<10deg varus; <5deg valgus) or stiffness (ROM >90deg, flexion contractures <5-10deg), and no more than Outerbridge Grade 2 osteochondral wear in the contralateral compartment.

Considered alongside Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) results showing >91% TKR survivorship at 20yrs, most Australian surgeons have tended to recommend TKR for patients falling outside these strict parameters. Indeed, only 5.7% of the more than 62,624 knee replacement procedures performed in Australia during 2020 were UKRs (4).

UKR

TKR

Potential Benefits of UKR vs TKR

Yet research has demonstrated several potential benefits of UKR over TKR including:

1. Less expensive
2. Smaller Incision
3. Less blood loss
4. Less morbidity
5. Preservation of more normal knee kinematics (because ACL & PCL ligaments are retained)
6. Less postoperative pain
7. Shorter hospital stays
8. Quicker recovery
9. Faster rehabilitation

A recent Cochrane meta-analysis showed that UKR improved knee function and reduced post-operative pain and complications over TKR, with no increase in revision rate within 5 years of follow-up (5). Further, a recent comparative study of the UK’s National Joint Registry found that UKR resulted in increased Oxford Knee Scores vs TKR as well as significantly increased patient-reported quality of life measures (6). Finally, a study determining UKR candidacy from preoperative radiographs found 61% of patients <50yo and 36% of those >80yo were candidates for the procedure, and concluded “good outcomes could be expected in patients of all ages who were appropriate for UKR” (7).

Modest Australian Utilisation of UKR vs TKR

In view of potentially superior outcomes, then, why does UKR comprise only 5.7% of Australian knee replacement procedures when other registries show more robust uptake (Canada 9.2%, UK 10%, Sweden 10.8%, Germany 13.2%, Italy 16.4%)?

The answer is no doubt multifactorial, but Australian surgeons will be influenced by UKR’s higher revision rate vs TKR documented in the AOANJRR (4). Revision rates vary according to the prosthesis combination used, but overall the AOANJRR quotes a median UKR revision rate of 13% at 10 years and 30.7% at 20 years post implantation (4).

Interpreted another way, however, these figures imply 87% UKR implant survivorship after 10 years, and nearly 70% survivorship after 20 years. As UKRs tend to be implanted in younger patients, their increased revision rate vs TKR will reflect these patients’ longer, more active lifespans. The vast majority of UKR revision procedures are performed for either implant loosening or progression of OA and involve converting the UKR to a TKR.

Relieving Pain, Restoring Function, Reclaiming Mobility

In summary, the emerging body of evidence demonstrating UKR’s improved outcomes vs TKR and the validation provided by increased utilisation among our international colleagues must be balanced against the higher chance of requiring a revision procedure.

Patient selection will of course be key, and orthopaedic surgeons recommending arthroplasty to their patients with unicompartmental OA will ideally include a discussion of the risks, benefits and alternatives to UKR, as this procedure might ideally be suited for (and preferred by) some patients not satisfying the classical inclusion criteria.

Ultimately, the aim of arthroplasty is to relieve pain, restore joint function and enable patients to reclaim their mobility, and both TKR and UKR continue to be successful at achieving these aims in patients with unicompartmental disease.

88yo patient with unicompartmental OA, treated with UKR

References:

Dr Tad Gunkelman is a lower limb Orthopaedic Surgeon with special interests in Primary Hip and Knee Arthroplasty, Partial Knee Arthroplasty, Computer-assisted Navigation, Patient-specific Implants and Robotic Surgery.