KNEE RECONTRUCTION WITH MODULAR PROSTHESIS AFTER RESECTION OF BONE TUMORS: FUNCTIONAL OUTCOME AND COMPLICATIONS AT A LONG TERM FOLLOW UP

Abstract

Purpose of this paper was to review the Rizzoli experience in prosthetic reconstruction of the knee after resection of bone tumors with special attention to major complications and functional outcome.

Material: 669 knee modular uncemented prostheses were implanted between 1983 and 2006 after resection of the distal femur, total femur or proximal tibia. These prostheses include 126 first generation Kotz prosthesis (KMFTR) and 543 second generation HMRS prostheses.

Methods: All patients are followed periodically in the clinic. Data for this study was obtained from clinical charts; imaging studies were reviewed with special attention to prosthesis related major complications requiring revision surgery. Revision for polyethylene wear was considered a minor complications, since it does not imply change of main prosthetic components, thus failure of the implant. Functional results were assessed according to the MSTS system.

Since abrupt data could be misleading due to the oncologic population and related deaths (although 2/3 of the patients were cured or long survivors), to censore the implant unrelated events a statistical analysis of the implant survival was performed and Kaplan-Meyer curves of implant survival were studied.

Results: In the 126 KMFTR group major complications included infection 13%, breakage of the stems 12%, aseptic loosening 8.7%, while revision for polyethylene wear rated 45%.

In 543 HMRS prostheses major complications were infection 8%, stem breakage 2%, aseptic loosening 4%, while revision for polyethylene wear components rated 7.4%.

Techniques of revisions were analyzed, as well as the outcome of revised cases, which showed that about 2/3 of the patients treated for major complications do well, although the risk for further complications is significantly incresed in revised implants.

Functional results were evaluated according to the MSTS system: in KMFTR prostheses were good or excellent in 80% of the patients, while in HMRS were good or excellent in 90% of the patients.

Discussion: The reduction of major complication rate with the newer designs of the modular prosthesis was statistically significant and this seems to confirm that newer materials and a modified stem design positively affected the implant survival. Also the wear of polyethylene component was dramatically decreased in the newer prosthetic design. Functional results were satisfactory in most of the patients that did not experience major complications, with a trend to improvement in the newer design. Revision surgery is technically demanding and sometimes newer ‘hybrid’ techniques are suggested, implying the use of bone allografts.

Appropriate timing of revisions is crucial. An early treatment of complications can improve the final outcome.