PRIMARY RECONSTRUCTIONS OF THE LOWER LIMB WITH MODULAR PROSTHESES: AN ANALYSIS OF IMPLANT SURVIVAL COMPARING CEMENTED VERSUS UNCEMENTED STEMS.

Abstract

Purpose was to evaluate the incidence of complication in lower limb reconstructions with modular prostheses comparing cemented versus uncemented stems in two different orthopedic tumor Centers.

Methods: retrospective analysis of implant survival, complications and functional results assessed according to MSTS system of the Rizzoli and Moffitt series of modular megaprosthesis in lower limb.

From 2002 and 2007, 238 modular prostheses of same design with a rotating hinge knee, were implanted in the lower limb as primary reconstruction in these two Centers. In 130 cases the prosthesis was implanted with cemented stems and in 108 cases with uncemented stems. Sites included: 120 distal femur, 61 proximal femur, 46 proximal tibia, 10 total femur and in 1 case both distal femur and proximal tibia. Histologic diagnoses included: 89 osteosarcoma, 13 Ewing sarcoma, 21 chondrosarcoma, 19 sarcoma, 55 metastasis, 17 TGC, 7 MFH, 11 other diagnoses and 6 non oncologic cases.

Major prostheses-related complications were analysed and functional results according to Muscolo Skeletal Tumor Society system, at a mean follow up of 2.03 yrs. Also a statistical evaluation with Kaplan Meier curves, a comparative statistical analysis with Wilcoxon test and multivariate Cox regression analysis were performed.

Results: Outcome in 223 evaluated oncologic pts, showed: 121 pts continuously disease free, 26 NED after treatment of relapse, 54 AWD, 16 DWD. Margins were wide in 94.3% (214/227 pts) of evaluated pts. Complications causing implants failure were: infections in 20/238 (8.41%), aseptic loosening in 7/238 (2.95%). No breakages of prosthetic components were observed.

Infections occurred at mean time of 1.3 yrs, sites included: 9 distal femurs, 4 proximal femurs, 5 proximal tibias, 2 total femurs. Aseptic loosening occurred at mean time of 2.3 yrs, sites included: 3 proximal tibias, 2 distal femurs, 2 proximal femurs. Rate of aseptic loosening was higher for cemented stems 5/130 (3.85%) vs uncemented 2/108 (1.85%). This difference is not statistically significant. Infection rate was 10% (13/130) for cemented stems and 6.5% (7/108) for uncemented stems. This difference is statistically significant at comparison of survival curves logrank test. Average MSTS function score was 83.5%. Multivariate Cox regression analysis showed that the significant factor favourable reluted with lower incidence of complications was the use of uncemented stems.

Conclusions: lower limb modular prostheses with both cemented and uncemented stems gave good results and a low complication rate. Better results were observed with uncemented stems and statistically confirmed, but this needs to be further investigate in a future study at long term.