Causes of stem breakage in prostheses for malignant bone and soft tissue tumors

Purpose To clarify the causes of breakage in knee prostheses for patients after wide excision of malignant bone and soft tissue tumors. Materials and methods Wide excision of malignant bone and soft tissue tumors in 25 patients was carried out between 1987 and 1994. The follow-up period ranged from 8 to 12 years. Stem breakage occurred in 6 cases. We investigated the prosthetic type, stem diameter, site of breakage, duration from first operation and revision procedure. Results The model affected was The Kozt Modular Femur and Tibia Reconstruction System in 4 cases, Howmedica Modular resection system in 1 case and Physio Hinge Total Knee System in 1 case. The stem diameter was 10 mm in 5 cases and 11 mm in 1 case. The breakage occurred around the stem base. The period between the initial surgery and breakage ranged from 1 to 9 years (mean period, 5.2 years). Revision was performed in all patients. Discussion and Conclusion The following were considered as causal factors: a narrow stem, bone resorption at the stem base, and a lack of corner radius. In order to prevent breakage, it is important to improve the implant model, to employ a larger stem, and to perform a bone graft at the stem base.