The purpose of this paper is to emphasize lateral compartment arthroplasty as efficient method and to discuss postoperative problems by investigating mid-term results (over 5 years)

Two hundred and twenty two consecutive unicompartmental knee arthroplasties (UKA) were performed in our hospital between August 1977 and December 1999. Thirty eight joints of 37 patients underwent lateral UKA. There were 8 male and 29 female patients with an average of 65.1 years old. The following prostheses were used: Marmor in 5 patients, Oxford in 1, PCA in 11, and Omnifit in 21. Out of them, 24 joints had follow up over 5 years after replacement. Three patients died of unrelated illness and 3 were lost to follow up. The remaining 18 joints could be followed from 60 to 189 months (average, 99 months). The knee score of the Hospital for Special Surgery (the HSS knee score) was used for clinical evaluation.

Clinical results by the HSS knee score showed that 2 joints were judged as “good”, 13 as “fair”, and 3 as “poor” before surgery. After surgery 13 joints were improved to “excellent”, 3 to “good”, and 2 to “fair”. The two joints with fair results had revision surgery. In all, 16 joints had satisfactory results. With radiological evaluation, the average preoperative alignment on standing was 14.9o of valgus angulation and corrected to 6.9 o of valgus. Although radiolucent lines under the tibial component were not found, a radiolucent line was observed and extended to loosening in one femoral component. This patient was successfully revised to another type of UKA 3 years after the index surgery. In the medial compartment, we found slight deterioration of osteoarthritic change in 5 joints. Of these, one patient, needed medial UKA.

Lateral UKA is a reliable and successful option compared with other procedures in a patient with low level of physical activity, because the long-term results tend to last and loosening of the tibial components has not been observed as commonly as in medial UKA. However, deterioration of the medial compartment may occur. The alignment after surgery must be in slight valgus for a satisfactory long-term result.