Unicompartmental arthroplasty for osteonecrosis yielded low failure rate
Patients had small range of motion improvement, but high improvements in clinical and functional scores.
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Results published in the Journal of Bone and Joint Surgery showed an estimated 5-year survival rate of 94.7% for patients with advanced-stage focal osteonecrosis of the medial femoral condyle who underwent unicompartmental arthroplasty.
“Irrespective of either the width or depth of the lesion … there was only one patient that experienced a femoral component loosening despite having perceivably less bony contact and needing more cement to fill the defect and fixate the component,” Nicholas J. Greco, MD, co-author of the study and assistant professor in the department of orthopedics at the Wexner Medical Center at Ohio State University, told Orthopedics Today.
High survival rate
Greco and his colleagues from Joint Implant Surgeons in New Albany, Ohio, collected patient-reported outcome measures and data on the need for revision procedures among 64 patients with medial femoral condyle osteonecrosis who underwent unicompartmental knee arthroplasty (UKA) with the Oxford Partial Knee (Zimmer Biomet). Researchers classified lesion size according to the ratio of lesion width and depth to condylar width and depth, respectively.
Preoperatively, 82% of patients demonstrated subchondral collapse and the mean ratio of lesion width to condylar width was 64% and mean lesion depth was 1.11 cm. Although patients had a small improvement in range of motion with surgery, the clinical Knee Society Score (KSS) improved more than 50 points and the KSS for function and pain improved 25 points and 36 points, respectively. Researchers noted an increase in patient activity level measured by the University of California Los Angeles activity score.
With an end point of revision for any reason, the estimated 5-year survival rate was 94.7% and the failure incidence was 1.2% per person-year. During the study, 6% of patients required a revision, of whom one patient experienced aseptic loosening of the femoral component.
“From our study, we were not sure what we would find. But, we found the patients did thoroughly well without the need for revision surgery [due to] the femoral component loosening from those larger defects,” Greco said. “With patients [who] stayed active, they had high Knee Society Scores at follow-up which indicated they were doing well clinically and getting back to activity without increasing the rate of failure of that component.”
Additional implant designs
Since the researchers used a single type of mobile-bearing implant, Greco noted it is unclear whether outcomes would differ using another type of implant, such as one with a fixed bearing.
Greco and his colleagues are interested in reviewing whether cementless UKA components are as effective as cemented in the treatment of larger bone defects of the medial femoral condyle.
“That is probably sometime down the line from being investigated because they are not FDA approved yet, even for cases of osteoarthritis,” Greco said. “There is probably going to be a little lag before we figure out if it is, therefore, indicated in osteonecrotic lesions.” – by Casey Tingle
Reference:
Greco NJ, et al. J Bone Joint Surg Am. 2019;doi:10.2106/JBJS.18.00913.
For more information:
Nicholas J. Greco, MD, can be reached at 543 Taylor Ave., Columbus, OH 43203; email: alexis.shaw2@osumc.edu.
Disclosure: Greco reports no relevant financial disclosures.
Perspective
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Brian J. McGrory, MD, MS
Nicholas J. Greco, MD, and colleagues enhance the literature pertaining to UKA in their study. Introduced in the late 1950s,UKA has evolved and been used increasingly as an option for patients with localized articular knee disease and deformity, as well as a functional ACL. The authors’ reported single institution UKR implant survivorship for the diagnosis of focal femoral osteonecrosis exceeds that reported in a recent study for UKA used for all diagnoses. Primary osteonecrosis represented about 1.4% of medial UKAs performed at the investigators’ institution. The cemented Oxford Partial Knee (Zimmer Biomet) was implanted on an outpatient basis in all cases. The cementation protocol consisted of full cement curing with the knee at 45° flexion to prevent component rocking. Of the four revisions in the 65 knees studied, only one patient developed aseptic loosening of the femoral component. The authors have demonstrated UKA is effective for treatment of focal osteonecrosis of the medial femoral condyle and have shown that loosening was not a major concern, even for larger, advanced lesions, at a mean follow-up of 5.3 years. Longer term follow-up is warranted, but this report is encouraging for the subset of patients who have symptomatic focal femoral osteonecrosis.
Reference:
Hansen EN, et al. J Arthroplasty. 2019;doi:10.1016/j.arth.2019.04.004.
Maine Medical Center
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