Surgeon opinions differ on UKA indications and revision rates compared to TKA

Orthopaedic surgeons typically perform unicompartmental knee arthroplasty in a small percentage of patients with osteoarthritis in one compartment of the knee. But for patients who meet the criteria for the procedure, the procedure preserves the patient’s natural cartilage and bone and only replaces one knee compartment with a prosthesis, according to surgeons who spoke with Orthopaedics Today Europe.

Physicians who favor total knee arthroplasty (TKA) for its overall good outcomes and minimal risk of failure argue, however, the reasons for treating knee osteoarthritis with unicompartmental knee arthroplasty (UKA) are limited.

This sentiment is a dangerous one for orthopaedic surgeons to have, according to Per Wagner Kristensen, MD, of Vejle, Denmark, who has possibly done the most UKA surgeries after the original investigators in the United Kingdom who developed and champion the procedure.

“Why just not give everyone a revision prosthesis, a hinged knee, and you will never run into problems again? That is just not correct. We see in a TKA, in about 10% of patients, there is usually a problem, some kind of motion defect. But, if the prosthesis is placed correctly, we cannot help you. In the statistics, this goes down as a success because the prosthesis was placed correctly. But, the patient is not happy,” Kristensen told Orthopaedics Today Europe.

“If we put in a UKA, then we have the possibility of changing to a total knee. There is no reason in taking away normal bone if you can avoid it,” he said.

When the least amount of a patient’s knee is replaced by a prosthesis, the better it is for the patient, Kristensen said.

UKA for single-compartment arthritis

According to Kristensen, UKA offers a quicker recovery period for patients and also preserves a greater knee range of motion compared with TKA. Also, patients with partial knee replacements tend to be more satisfied with the procedure than patients who undergo TKA.

However, the procedure, he said, should be reserved for patients with arthritis in just one knee compartment. For patients with arthritis in several compartments, TKA is more appropriate.

Sébastien Parratte, MD, PhD, told Orthopaedics Today Europe a UKA is most successful in younger patients who want to maintain a certain level of physical activity and for older patients who exhibit unicompartmental knee arthritis.

“This works well with younger patients who have bone-on-bone, good stability, no bony deformity and are still active and who want to be involved in physical activity with a ‘normal’ knee. The second category of patients where this works well is an older patient, around 80 [years old], with unicompartmental arthritis. It is less aggressive than a TKA, and the rate of postoperative complications is lower than TKA. If they are medically fragile or have comorbidities, the procedure is less invasive and the complication rate is lower,” he said.

UKA helps patients feel as if they still have their natural knee because it preserves bone and the cruciate ligaments, according to Parratte.

Anteromedial osteoarthritis

However, surgeons have various philosophies concerning UKA. David W. Murray, MD, FRCS, told Orthopaedics Today Europe, he and his colleagues at the Nuffield Orthopaedic Centre in Oxford found about 50% of patients presenting to their clinic are eligible for UKA.

This is very different from the 5% to 10% generally recommended in the literature, Murray said.

“The reason is that we have a different philosophy for the mobile-bearing UKA. The primary indication is anteromedial osteoarthritis. If a patient has this condition and significant symptoms, we will do UKA and we will ignore the generally accepted contraindications proposed by Kozinn and Scott and others. If surgeons adhere to the Kozinn and Scott contraindications, then only 5% to 10% of patients are appropriate, whereas if you ignore them, then 20% to 50% are appropriate,” he said.

The study by Kozinn and Scott in the Journal of Bone and Joint Surgery in 1989 listed several contraindications for UKA. Among them were patients who were overweight, young, active or with damage to the patellafemoral joint.

Murray said, “We have always had the philosophy that if a patient has anteromedial osteoarthritis, we will do a mobile-bearing UKA. We have therefore operated on numerous cases with the Kozinn and Scott contraindications and when we have reviewed our long-term data we have found that not one of these contraindications compromises the results.”

Mobile vs. fixed bearings

A mobile bearing UKA is preferred to a fixed-bearing UKA, according to Murray, because it can be used in a greater proportion of patients. With fixed bearing UKA, if Kozinn and Scott contraindications are ignored, this will compromise the long-term results, so the proportion of cases in which a UKA can be used is restricted, whereas this is not the case with mobile bearing UKA. The results of UKA depend the number that a surgeon does. So if surgeons do UKA in a greater proportion of cases they are likely to get better results.

“UKAs have many advantages compared to TKAs. They provide a better functional outcome with higher levels of satisfaction, patients recover quicker, complications and reoperations occur less frequently and the morbidity and mortality is less. For example, the risk of major medical complications, such as stroke, heart attack, thromboembolism and infection is about half. The main disadvantage of UKA is it has a higher revision rate. To put this in perspective, a recent study based on data from the National Joint Registry of England and Wales and published in Lancet, showed that if 100 patients had a UKA rather than a TKA, then over an 8-year period one life would be saved and there would be three more revisions,” Murray said.

Emmanuel Thienpont, MD, MBA, an Orthopaedics Today Europe Editorial Board member, said fixed bearing UKA can provide the same outcomes for patients as mobile bearing UKA. Furthermore, long-term survival of the fixed bearing implants is improving thanks to better surgical technique, better understanding of the procedure and the use of new materials.

“Fixed bearings have many advantages. The surgical technique is easier and you can use it on the lateral side of the knee where it is much more dangerous to use a mobile bearing, and therefore use the same device or system on any patient,” Thienpont said.

Bearing type

Thienpont discussed findings from a 2012 study by Parratte and colleagues that showed no statistical differences in long-term survivorship of UKA with fixed bearings or mobile bearings.

“The mobile bearing had more revisions in the first 2 years postoperative with more dislocations of the insert and with more over-corrections of the global alignment because the surgeon was afraid to have a bearing dislocation. Mobile bearings are interesting, but technically more demanding. In fixed bearings, we had a very low revision rate in the first 12 years, but with some wear appearing 12 years or 14 years after the procedure. I am going to say fixed bearings are initially reliable with potential wear after 12 years to 15 years, and mobile bearings are an interesting concept with more risks of early revisions due to technical issues,” Thienpont said.

Revision statistics to consider

The main drawback of UKA is its high rate of revision. However, according to Murray, revision is a biased endpoint when UKA and TKA are compared, which is misleading for patients and surgeons. UKA is much easier to revise than TKA so the threshold for revision is lower. Data from the New Zealand national registry support this and show that 60% of UKAs with a bad result will be revised whereas only 10% of TKAs with a similarly bad result will be revised.

“It is interesting to reflect on the effect of different thresholds on national registry data. Whether you do a UKA or TKA, some patients will have a poor outcome. If you have a patient with a poor outcome following a TKA, it will probably not be revised. So the registers will consider it a success, whereas the patient would consider it a failure. In contrast, if you have a UKA with a poor outcome it will probably be revised and hopefully have a good outcome, so the register would consider it a failure whereas the patient will consider it a success,” Murray said. “One of the advantages of UKA is that if a problem occurs it can be addressed with a conversion to a TKA. This does however result in a higher revision rate. So perhaps the high revision rate should not be considered to be a major problem.”

Experience is key

Thienpont, of Brussels, performs UKA procedures for about 40% of his patients, which is well above the 10% average, but does not reach the 50% utilization rate that Murray reports.

The absolute number of UKA procedures a surgeon can perform is related to his or her experience with the prosthesis. Experience is critical for completing these procedures, according to Thienpont. UKA has a steep learning curve, which can keep surgeons from performing this type of arthroplasty, but it is worth sticking to since UKA can offer ailing patient such good outcomes, he said.

“What is very interesting is that people who are using a lot of UKA see that this is the best operation we can use on patients. The more you do them, the better you get at them and you can find more and more indications. You see that you help your patients a lot with these procedures,” Thienpont said.

Patient-reported success

TKA has a success record with patients, but 30% of them still have some chronic knee pain and limited function, Thienpont said. On the other hand, patients report better outcomes with UKA and this is possibly because the knee feels “more natural” and they have a sense that it is “still their knee,” Thienpont said.

“I think this is because we keep the central pivot intact; the PCL and ACL stay. It is such a more natural feeling of the knee. That is the reason why we extended our indications. We do not do unis alone, but also bicompartmental arthroplasty, which means we replace the medial or lateral side and combine it with the patellofemoral joints, as two individual joints with modular implants, so we can keep the central pivot intact. We are able to replace two of the three compartments and those patients have extremely good results also, [which are] comparable to the unis,” Thienpont said.

A newer approach to UKA procedures, which involves navigation or robotics, does not offer many benefits, Thienpont said. The reason for this is the traditional approach is very straightforward and there is not much room for improvement.

Kristensen said surgeons he works with have used navigation in UKA in an experimental setting, but the benefits are not there. However, he believes navigation may have a place in TKA procedures to identify the cutting blocks, but this approach still needs to be perfected.

Parratte said robotic systems, such as those from MAKO Surgical Corp. or Blue Belt Technologies, are interesting options to consider for performing UKA, but the cost efficiency with them has yet to be proven. – by Robert Linnehan

• References:
• Arirachakaran A, et al. Eur J Orthop Surg Traumatol. 2015;doi:10.1007/s00590-015-1610-9.
• Kozinn SC, et al. J Bone Joint Surg Am. 1989;71:145-150.
• Parratte S, et al. Clin Orthop Relat Res. 2012;doi:10.1007/s11999-011-1961-4.

• For more information:
• Per Wagner Kristensen, MD, can be reached at Department of Orthopaedic Surgery, Section for Hip and Knee Replacement, Vejle Hospital, Kabbeltoft 25, 7100, Vejle, Denmark; email: per.wagner.kristensen@rsyd.dk.
• David W. Murray, MD, FRCS, can be reached at Windmill Rd., Oxford OX3 7LD, United Kingdom; email: david.murray@ndorms.ox.ac.ak.
• Sébastien Parratte, MD, PhD, can be reached at Department of Orthopedics and Traumatology, Institute for Locomotion, Hôpital St. Marguerite, 270 Boulevard Sainte Marguerite, BP 29, 13274, Marseille, France; email: sebastien@parratte.fr.
• Emmanuel Thienpont, MD, MBA, can be reached at University Hospital Saint Luc, Avenue Hippocrate, 10 B-1200, Brussels, Belgium; email: emmanuel.thienpont@uclouvain.be.

Disclosures: Kristensen reports no relevant financial disclosures. Murray reports he is a designer of the Oxford Knee. Parratte reports he is a consultant to and participates in the educational program for Zimmer and is a consultant to Arthrex, Adler Ortho, Stryker and Graftys. Theinpont receives royalties from Biomet, Medacta and Zimmer.

What is the rationale for performing unicompartmental knee arthroplasty when total knee arthroplasty has many proven advantages?

Lower reported infection rate

Unicompartmental knee arthroplasty (UKA) is technically more demanding than total knee arthroplasty (TKA), and most early failures may be explained by a technical mistake during implantation. Furthermore, a UKA is easier to revise than a TKA, even with no other reason for revision than persistent pain. But, these revisions may not be effective.

Because of this, UKA will definitely experience a higher revision rate than TKA, especially in register studies. However, UKA is less invasive than TKA since the skin incision is shorter, there is no violation of the quadriceps muscle and tendon, functional recovery is faster, patients may be discharged earlier and the procedure can be more easily performed as an outpatient case.

Many authors report a lower infection rate. Eventually, functional results are improved compared to TKA as the native knee remains mostly intact except for the partial prosthetic joint. Preservation of both cruciates, which are still present in most arthritic knees, is critical for a good proprioception, which can lead to improved function especially during sports activities. When the early failures (which can be avoided by an adapted implantation technique) are excluded, the long-term survival is at least as high as with TKA.

The late revision of a UKA may also be performed with primary TKA and will be easier than a TKA revision with a more extensive implant. All these points explain why we still consider UKA after adequate patient selection.

Jean-Yves Jenny, MD, practices at Hôpitaux Universitaires de Strasbourg, in Strasbourg, France.
Disclosure: Jenny reports no relevant financial disclosures.

UKA shows increased return to sport

We now have a large body of evidence to support the use of unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) in end-stage knee osteoarthritis. While a large proportion of patients (up to 50%) have a disease-pattern suitable for either procedure, most receive TKA, largely because UKA has a higher reported revision rate. However, UKA has a number of important advantages which support its continued and increasing use.

The resection of healthy joint surfaces, and importantly the ACL, in TKA renders it virtually impossible to recreate the normal, ligament-driven kinematics of the native knee. Perhaps as a result, few patients achieve a “normal” knee following TKA, up to half of patients report residual symptoms and up to 20% are dissatisfied. In UKA, pre-disease kinematics are restored, resulting in a higher rate of return to work and sport, greater satisfaction and improved patient-reported outcomes compared to TKA.

The amount of bone and soft tissue resection with TKA results in greater blood loss, a higher rate of prosthetic joint infection, longer hospital stays, slower recoveries and more medical complications compared to UKA.

Two recent papers in The Lancet independently reported significantly higher rates of perioperative mortality for TKA compared to UKA.

The reasons for a higher revision rate in UKA include a lower threshold for revision UKA (as revision of UKA is perceived to be a more straightforward procedure) and factors related to patient selection and surgical practice (high-volume centers report very low UKA revision rates). The difference in revision rates must be weighed against the proven advantages that UKA provides in eligible patients.

• References:
• Hunt LP, et al. Lancet. 2014;doi:http://dx.doi.org/10.1016/S0140-6736(14)60540-7.
• Liddle AD, et al. Lancet. 2015;doi:http://dx.doi.org/10.1016/S0140-6736(14)60419-0.

Alexander Liddle, BSc, MRCS, MBBS, is at the Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences at the University of Oxford, in Oxford, United Kingdom.
Disclosure: Liddle reports no relevant financial disclosures.

Functional results better

Both unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) are treatment options for medial osteoarthritis (OA) of the knee. UKA was introduced in the early 1970s but initially did not receive substantial support because TKA could show good functional results, patient satisfaction and long-term survival. As such, the question arises, why UKA still plays a role in the treatment algorithm of OA?

In recent years, the interest in UKA increased with the introduction of minimally invasive surgical approaches and the need to treat younger, more demanding patients. Multiple studies could show a superior functional outcome of UKA vs. TKA. In addition, UKA outperformed TKA with regard to patient satisfaction because of the restoration of the natural knee kinematics.

Most importantly, the mortality rate is lower after UKA, which the Oxford Group recently reported in The Lancet. They concluded if 100 patients receiving TKA had undergone UKA instead, there would have been one death and three reoperations less in the first 4 years after surgery. In comparison to UKA, studies could show a prolonged rehabilitation and increased bone loss associated with TKA. Opting for UKA, in particular for high-demand patients with OA, limits surgery to one compartment of the femorotibial joint.

Philipp von Roth, MD, practices at the Department of Orthopedic Surgery, Charité Universitätsmedizin Berlin, in Berlin.
Disclosure: Roth reports no relevant financial disclosures.