Primary bone tumors of the femur are commonly reconstructed using an endoprosthesis. Different modes of implant failure have been described, including structural failure; although uncommon, this may be an under-reported complication. The purpose of this study is to examine the rates and risk factors for implant fracture of the Kotz Modular Femoral Tibial Reconstruction system (KMFTR).
Two hundred twenty-one patients (95 women and 126 men) who underwent a KMFTR reconstruction were reviewed. Twenty-seven patients (12%) sustained a prosthetic fracture. The mean time to fracture was 7 years postoperatively. The fractured component most commonly involved the distal femur (n = 21) and a screw hole in the stem (n = 12). In patients with stem fractures (n = 21), the mean intramedullary stem diameter was 12 mm and the mean extramedullary component length was 18 cm.
Compared to patients who did not fracture, those with a prosthetic fracture had a significantly smaller stem diameter (12 vs 14 mm, P = .001) and a significantly longer extramedullary component length (18 vs 15 cm, P = .04). There was no difference between the preoperative and postoperative Toronto Extremity Salvage Scores (P = .98), Musculoskeletal Tumor Society 87 (P = .78), or Musculoskeletal Tumor Society 93 (P = 1.0) ratings for patients with or without a prosthetic fracture.
This study shows that fracture is an under-reported complication associated with the KMFTR stem. We identified an endoprosthetic component fracture rate of 12%. Patients with smaller stem diameter and longer resection lengths were more likely to sustain a stem fracture. Subsequent revision provides a durable means of reconstruction, with no significant loss of patient function.