VERTICAL EXTENT OF CEMENT CORRELATES WITH A RADIOLUCENCY AROUND IMPLANTS FIXED WITH A HYBRID TECHNIQUE IN REVISION TOTAL KNEE ARTHROPLASTY

Purpose Although the use of stems in revision total knee arthroplasty (RTKA) enhances survival by improving the stability of implant, questions as to the optimal fixation method as well as the vertical extent of the cement, remain unanswered. This study aimed 1) to determine the correlation between the vertical extent of cement and implant loosening; and 2) to determine the minimum cementing extent for a stable implant in revision TKA with a hybrid technique. Materials and Methods We retrospectively analyzed 109 stemmed RTKAs with average follow-up of 63 months. In each case, a single varus-valgus constrained implant was used and fixed with a hybrid technique. During surgery, stem was partially covered with cement beyond stem-implant junction. Stability of implant was evaluated according to the modified Knee Society Radiographic Scoring System. Cementing extent was defined as length from implant base to the end of the radiopaque line around the stem. The correlation between the vertical cementing extent and implant stability was analyzed, and the minimal vertical cementing extent for a stable implant was evaluated with a scatter plot. Results The vertical cementing extent was longer in stable implants (femur: P =.002, tibia: P =.007) and the correlation between the vertical cementing extent and implant stability was significant (femur: P P =.001). Logistic regression analysis found that the risk of loosening was 8.7 times higher if the cementing extent was less than 40mm (tibia=16.1 times). The minimal vertical cementing extent for a stable implant in femur was estimated to be 65mm for middle stem (40% of total implant length) and 50mm for long stem (25% of total implant length). For tibia, it was 55mm for middle stem (45% of total implant length) and 40mm for long stem (25% of total implant length). Conclusion We confirmed that a negative correlation exists between the radiolucent line and the cementing extent in stemmed revision TKA with a hybrid fixation technique. We could expect a durable implant in revision TKA with a minimal vertical cementing extents and it was 65mm for the femur and 55mm for the tibia. Level of Evidence IV, Cases series