Abstract
CURRENT INDICATIONS
The ideal patient for unicompartmental arthroplasty has been described as an elderly sedentary individual with significant joint space loss isolated to either the medial or lateral compartment. Angular deformity should be no more than 5 or 10 degrees off a neutral mechanical axis. Ideal weight is below 180 pounds. Pre-operative flexion contracture should be less than 15 degrees. At surgery, the anterior cruciate ligament is ideally intact and there is no evidence of inflammatory synovitis. (Kozinn, Scott, 1989) Indications for the procedure have broadened today because of the availability of less invasive operative techniques and more rapid recovery with UKA. Because of its conservative nature, the procedure is being thought of as a conservative first arthroplasty in the middle-aged patient. Because of its less invasive nature with more rapid recovery and potentially less medical morbidity, it is being considered as the “last arthroplasty” in the octogenarian or older.
OUTCOMES OF UKA
Initial results reported for UKA in the 1970s were not as encouraging as they are today. This is most likely due to lessons that had yet to be learned about patient selection, surgical technique and prosthetic design. By the 1980s, reported results were improving with post-operative range of motion much higher than that reported for TKA. As longer follow-ups were reported, results were obtained that were competitive with those reported for TKA. Through the first post-operative decade, revision rates were being seen at approximately 1% failure per year or a 90% survivorship of the prosthesis at 10 years. More recently, however, some 10-year results have been reported that have survivorship well over 95% at 10 years. Modes of failure most often consist of problems with component wear or loosening or due to secondary degeneration of the opposite compartment. This latter complication is usually a late cause of failure, but can occur early if the alignment of the knee is over-corrected by the surgical technique.
UKA AS AN OPTION IN THE MIDDLE-AGED PATIENT
Although the classic selection criteria for UKA have emphasised the elderly patient as a candidate, the indications for UKA have been extended to a younger age group. The advantages of UKA in the middle-aged patient (especially female) are its higher initial success, few early complications, preservation of both cruciate ligaments and easier future conversion. Caution should be used, however, in advocating this procedure for the young, heavy, athletic person, as high levels of physical activity may be detrimental to the longevity of the procedure.
LATERAL UKA
Lateral UKA is performed much less often than medial UKA (approximately 10% of UKAs are lateral). It is technically more challenging than medial arthroplasty. Some surgeons perform the procedure through a small lateral arthrotomy while others advocate a medial approach with care to avoid injury to the medial meniscus. This medial approach still yields excellent results with a short recovery while allowing the surgeon wide exposure to assess the joint, accurately perform the procedure and intra-operatively convert to a total knee arthroplasty if indicated.
THE FUTURE
Research must continue in the areas of ideal patient selection, prosthetic design and surgical technique. Improvements in the durability of the polyethylene will enhance longevity. Mobile bearing articulations may improve long-term polyethylene wear by providing increased surface conformity without constraint.
