Abstract
Back ground
In 1970's, condylar type knee prosthese with anatomic design appeared, however, joint flexion was not satisfactory. Y/S II total knee arthroplasty (TKA) was developed to obtain deep flexion together with bilateral ligament balance in 1980. The articular surface of the tibial component was flattened to permit femoral shift posteriorily during knee flexion. Medial and lateral soft tissue release was determined by a unique ligament tensor both at flexion and extension. A metal tray was embedded in polyethylene, which had a shape of glasses frame. Though the usage of Y/SII TKA was finished in 1984, we here studied its long term surgical results using the Kaplan-Meyer method.
Study design
From 1988 to 1991, 122 knees were replaced by Y/SII TKA in 81 patients with rheumatoid arthritis (RA). Among them, 24 joints in 12 patients were examined directly. The average age of follow-up was 19.5 years. The survival rate was investigated according to medical records.
Results
The HSS knee score was 53.6 prior to the operation and 76.8 at the final observation. The average flexion was improved from 110.7degrees to 124.0 degrees after the operation, and was 115.8 degrees at the follow up. Radiological analysis showed no distinct clear zone around the femoral and tibial components. There was no breakage of components or polyethylene wear that cause a metal contact. The survival rate was 99% at 4 years and 97% at 19 years after the operation. Three prostheses were removed due to loosening in 2 and infection in 1.
Discussion
While modern knee prostheses are designed to get deep flexion and long-term durability, the purposes of TKA in the earlier era were pain relief, stability and correction of deformity. Y/SII TKA was developed in such period, and obtained fairly deep flexion probably by its design and soft tissue release using the special instrument. Another result was that Y/SII TKA had long durability with a high rate of survival. One of the reasons was considered as the structure of femoral component. The metal tray with a shape of glasses frame conducts mechanical load anatomically to the bone and prevent from metal contact when polyethylene wears. The number of the size of component was only 3 and was fewer compared to current-generation prostheses. While this requires some technique when an operator inserts Y/SII prostheses, only a few instruments are needed during operation. Conclusively, we showed the good long term results of Y/SII TKA developed in relatively early era of knee prostheses.
