Cement Mantle Thickness at the Bone Cement Interface in Total Knee Arthroplasty: Comparison of PS150 RP and LPS-Flex Knee Implants

PURPOSE: To analyze the thickness of cement mantle at the bone cement interface in knees with closed and open box designs in total knee arthroplasty (TKA). MATERIALS AND METHODS: Eighty cases of TKA were performed from October 2013 to March 2014. The average age of the patients was 68.4 years. All patients were women and they were divided into two groups: group I with a closed box implant (PS150 RP, n=40) and group II with an open box implant (LPS-Flex, n=40). We measured the cement mantle thickness at the bone cement interface from the distal femur and proximal tibia. If the thickness was >1 mm, it was considered an outlier. RESULTS: The mean cement mantle thickness at the interface was 1.4 mm in the distal femur and 0.8 mm in the proximal tibia. The value exceed 1 mm in 40 cases (50%) in the distal femur and in 6 cases (7.5%) in the proximal tibia (p<0.001). The mean cement mantle thickness measured in the distal femur was 1.7 mm in group I and 1.0 mm in group II. The value exceed 1 mm in 32 cases (80%) in group I and in 8 cases (20%) in group II (p<0.000). CONCLUSIONS: The cement mantle at the interface was thicker in the knees with the closed box implant than those with the open box implant in TKA, especially in the distal femoral area. A thick cement mantle at the interface should be avoided because it affects the gap balance. In case of using a closed box implant in TKA, cementing should be performed with extra care.