Abstract
Purpose:
Differences in the sizes of femoral and tibial components between females and males, between osteoarthritis (OA) and rheumatoid arthritis (RA), and between measured bone resection and the gap control technique during TKA were assessed.
Method:
500 PS-TKAswith the Stryker NRG system in 408 cases were assessed. There were 83 male knees and 417 female knees, and 472 OA knees and 28 RA knees. This study was performed in Japan, and almost all OA knees had varus deformities. In each case, the sizes of the femoral and tibial components were measured on radiographs. The measured sizes represented those of the measured bone resection. TKA was performed by the gap control technique using a tensor/balancer with 30 inch-pounds expansion strength, and the sizes of the femoral and tibial components (used size) were recorded.
Results:
The measured size was the same for the femoral and tibial components in 80.6% of females. The measured size of the tibial component was larger than the femoral size in 42.2% and the same in 53.0% of males. The used size of the femoral component was larger than the measured size in 43.6%, and it was the same in 43.6% of all cases. The used size of the tibial component was smaller than the measured size in 42.2%, and it was the same as the measured size in 53.4% of OA cases. The used size of the tibial component was the same as the measured size in 75.0% of RA cases. The used size of the femoral component was larger than the used size of the tibial component in 65.6% of all cases. These results showed that: the tibial condyle is larger than the femoral condyle in males; a larger size of the femoral component than the tibial component was used in the gap control technique; the used size of the tibial component was the same as the measured size in RA knees; and the used size of the tibial component was smaller than the measured size in OA knees.
Discussion:
During PS-TKA, the PCL is resected and the flexion gap is enlarged when the tensor/balancer is applied. Therefore, the size of the femoral component is larger with the gap control technique than with measured bone resection. In varus knees in Japan, the proximal articular surface shifts medially from the central line of the tibial shaft. Therefore, when the tibial component is set based on the central line of the tibial shaft, the medial condyle edge is not covered by the tibial component and is resected. A smaller size of the tibial component is used with this method. On the other hand, RA knees have no varus deformity, and the size of the femoral component was the same for the gap control technique and measured bone resection. The sizes of the femoral and tibial components in PS-TKA differ between the sexes, between OA and RA, and between measured bone resection and the gap control technique.
