“Both lateral and medial unicompartmental knee arthroplasty (UKA) are safe and effective,” said Keith R. Berend, MD, during The Knee Society/American Association of Hip and Knee Surgeons Specialty Day program. “I was asked to discuss whether lateral UKA is better than medial UKA, and I should disclose that I’m a big fan of medial UKA, which comprises more than half of my knee practice.”

Lateral UKA is used in less than 1 percent of all knee arthroplasty procedures performed in the United States. It is, according to Dr. Berend, a true resurfacing procedure, requiring anatomic reconstruction of the original joint line. But performed properly in the right patient, lateral UKA can have excellent results.

Lateral UKA is more technically demanding than either total knee arthroplasty (TKA) or medial UKA, explained Dr. Berend, due to the more complex kinematic profile on the lateral side of the knee. In addition, the lateral compartment must be balanced differently compared to performing medial UKA or TKA. The complexity of the procedure may contribute to what Dr. Berend described as “a paucity of literature” describing techniques and outcomes for lateral UKA.

According to Dr. Berend, fixed bearing devices are recommended for lateral UKA, due to the high range of motion, femoral posterior subluxation, screw-home mechanism, and significant laxity of the lateral compartment in flexion.

Similar data
To compare the two procedures (medial and lateral UKA), Dr. Berend first reviewed information from his own practice.

Between June 2005 and September 2010, he performed lateral UKAs on 98 consecutive patients (104 knees), using a lateral parapatellar approach.

“Indications were complete lateral bone-on-bone arthrosis with a correctible deformity and maintenance of the medial joint space on varus stress radiographs,” he said. “The average age of the patients was relatively young—57 years. Overall, 69 percent of the cohort was women, and the average body mass index (BMI) was 30.0 kg/m2.”

At an average 28-month follow-up (range: 6 weeks to 6.2 years), Dr. Berend found that the average Knee Society pain, clinical, and function scores had improved from 10.0, 48.8, and 53.3 preoperative respectively, to 41.6, 89.6 and 73.6 at most recent follow-up.

“There was 99 percent survivorship of lateral UKAs out to 4 years, and 97 percent of those patients were free from reoperation at final follow-up,” he said.

Dr. Berend compared those findings against data from a study on medial UKAs that he coauthored. The study, published in the March 2013 issue of the Journal of Arthroplasty, reported on survivorship and failure modes for 1,000 consecutive medial mobile bearing UKA surgeries performed at a single center. Among the 839 patients who met the inclusion criteria, 40 revisions were performed at an average of 23.1 months after surgery, resulting in a 95.2 percent survivorship rate.

“The average age of that group was a little older, and the average BMI was slightly higher,” said Dr. Berend. “However, if we compare the medial UKA group to the lateral UKA group, with relatively similar follow-up, we find that the pain and knee scores were nearly identical between groups, but both range of motion and survivorship were better in the lateral cohort. Based on those two series, over a 5-year period, lateral UKA was truly better.”

Dr. Berend concluded, “To summarize, we found that lateral UKA patients tend to be younger, lighter, and achieve better range of motion than medial UKA patients. The indications for lateral UKA were isolated lateral bone-on-bone arthrosis with maintenance of medial joint space and no radiographic signs of patellofemoral disease.”

Dr. Berend lists the following disclosures: Biomet, Stryker, Clinical Orthopaedics and Related Research, Journal of Arthroplasty, Journal of Bone and Joint Surgery—American, Orthopedics, American Association of Hip and Knee Surgeons, AAOS Board of Specialty Societies.

Peter Pollack is a staff writer for AAOS Now. He can be reached at ppollack@aaos.org

References

1. Bergeson AG, Berend KR, Lombardi AV Jr, Hurst JM, Morris MJ, Sneller MA: Medial mobile bearing unicompartmental knee arthroplasty: Early survivorship and analysis of failures in 1000 consecutive cases. J Arthroplasty 2013 Mar 19. pii: S0883-5403(13)00132-0. doi: 10.1016/j.arth.2013.01.005.

Bottom Line

• Lateral UKAs account for just 1 percent of all knee arthroplasties and are technically more difficult than medial UKAs.
• Indications for lateral UKA include loss of joint space laterally, maintenance of medial joint space on varus stress radiograph, and no significant radiographic or arthroscopic patellofemoral disease .
• In this report, patients with lateral UKA had a 99 percent survivorship at 4 years, while patients with medial UKA had a 95 percent survivorship at minimum 2 years.
• Both lateral and medial UKA are safe and effective, with similar clinical outcomes.