What Factors Are Associated With Stem Breakage in Distal Femoral Endoprosthetic Replacements Undertaken for Primary Bone Tumors?

Abstract

Background: The advantages of distal femoral replacement prostheses for reconstructions after tumors are well known; one such implant, the Global Modular Replacement System (GMRS), has been widely used since 2003. Although implant breakage has been reported, the frequency of this event has varied across different studies.

Questions/purposes: (1) What percentage of patients who underwent distal femur resection and replacement using the GMRS for primary bone tumors at one center experienced stem breakage? (2) At what timepoints did these breakages occur, and what factors were common among the stems that broke?

Methods: We performed a retrospective study of all patients who underwent distal femur resection and replacement using the GMRS for a diagnosis of primary bone sarcoma by the Queensland Bone and Soft-tissue Tumor service from 2003 to 2020 who had a minimum of 2 years of follow-up. Standard follow-up for primary bone sarcoma involves radiographic imaging of the femur at 6 weeks and 3 months postoperatively and yearly thereafter. From a chart review, we identified patients with femoral stem breakage. Patient and implant details were recorded and analyzed. A total of 116 patients had undergone a distal femoral replacement with the GMRS prosthesis for primary bone sarcoma; however, 6.9% (eight of 116 patients) died before completing the 2-year follow-up period and were excluded. Of the remaining 108 patients, 15% (16 patients) had died at the time of this review; however, given that they completed the 2-year follow-up period and did not experience stem breakage, they were included. Furthermore, 15% (16 patients) were considered lost to follow-up and excluded because they have not been seen in the past 5 years but were not known to have died or experienced stem breakage. This left 92 patients for analysis.

Results: Stem breakages were identified in 5.4% (five of 92) of patients. All stem breakages occurred in stem diameters 11 mm or less with a porous body construct; the percentage of patients with breakage in this group was 16% (five of 31). All patients with stem fracture demonstrated minimal ongrowth to the porous coated body. The median time to stem fracture was 10 years (range 2 to 12 years); however, two of the five stems broke within 3 years.

Conclusion: We recommend the use of a larger-diameter GMRS cemented stem (> 11 mm), and either the line-to-line cementing method or an uncemented stem from an alternative company should be considered in order to achieve this larger stem in smaller canals. If a stem less than 12 mm in diameter must be used or there is evidence of minimal ongrowth, then close follow-up and prompt investigation of new symptoms should occur.

Level of evidence: Level IV, therapeutic study.