There has been a renewed interest in unicompartmental arthroplasty, in part related to the advent of minimally invasive surgery. Because of this renewed interest, the authors undertook this study in order to compare the early failure rates and failure mechanisms of primary cemented unicompartmental knee replacements with those of primary cemented tricompartmental total knee replacements.
Furnes and colleagues present data from the Norwegian Arthroplasty Register for primary cemented unicompartmental and tricompartmental total knee replacements performed from January 1994 through December 2004. They found that patients who underwent unicompartmental knee replacement had an increased rate of revision due to pain, aseptic loosening, and periprosthetic fracture compared with patients who underwent total knee replacement. They also found that there was a lower risk of infection with unicompartmental knee replacement in comparison with total knee replacement.
A variety of unicompartmental designs were implanted, accounting for 12% of the arthroplasties performed during the eleven-year study period. Patients who received a unicompartmental replacement were younger and more often male in comparison with patients who received a total knee replacement. Almost 90% had a diagnosis of osteoarthritis. The volume of surgery averaged only four unicompartmental operations per hospital per year, but there was a large range. Very few lateral unicompartmental procedures were performed.
The major finding in the study was a revision rate that was two times greater for patients who received a unicompartmental replacement than it was for patients who received a total knee replacement, and this finding held true throughout all age categories. Furthermore, the authors found that the volume of surgery was associated with the revision rate. There was a 40% lower revision risk in hospitals at which twenty to forty-nine operations were performed per year in comparison with hospitals at which zero to nine operations were performed per year. The lower infection rate associated with use of the unicompartmental knee replacements confirmed earlier findings reported by the Swedish Knee Arthroplasty Register.
The authors concluded that, while unicompartmental arthroplasty, particularly when done through a minimal incision, has been reported by other authors to result in less pain-related morbidity, faster recovery, shorter length of hospital stay, less infection, and less thrombolic disease in comparison with total knee arthroplasty, these short-term advantages must be weighed against higher revision rates due to aseptic loosening, pain, and periprosthetic fractures.
Some advantages of deriving these data from a register are that the information is independent of the designers of an implant system, and the results represent surgeons who perform various volumes of surgery with varying abilities; hence, the findings reflect a very broad picture of surgical practice. It is quite impressive that the Norwegian Arthroplasty Register is able to capture 99% of primary knee arthroplasties performed in that country. In addition, various implant systems are utilized and a very large number of procedures are included.
In contrast, many of the reports in the literature include series from either a single surgeon or surgeons from a single practice group who typically utilized a single implant system, and, in many cases, the investigators are designers of the reported implant.
Indeed, some may consider the strengths of a register as their weakness; however, I believe that having a global picture of results implies that the findings will be meaningful to a large and broad body of orthopaedic surgeons.
In summary, I believe this study is unique from the standpoint of the data, which is long term and represents the results of multiple implants and multiple surgeons. I agree with the authors that one must consider the higher longer-term failure rate that is associated with a unicompartmental replacement when one is discussing surgical alternatives with a patient and not just focus on the short-term benefits as described above.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate family received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the author, or a member of his immediate family, is affiliated or associated.