Radiographic assessment of distal femur cemented stems in tumor endoprostheses

Distal femoral endoprosthesis (DFE) has become the optimal method of reconstruction in the skeletally mature patients treated for malignant bone tumor. Albeit literature has reported wide range of aseptic loosening in cemented components (6-32%), few authors showed that cement was not detrimental to long-term success of primary distal femoral implants possibly relating to cementing technique.

A series of consecutive of DFE (MRS and GMRS, Styker Orthopaedics, Mahwah, NJ) was retrospectively reviewed for evidence of loosening on plain radiographs. All prostheses had the standard straight 127-mm stem and a cemented polyethylene tibial component. Cementing technique involved reaming line to line to the selected stem size and cementing without pressurization. Radiographs were assessed by two independent blinded reviewers and scored for radiolucent zones (>1 mm) and graded as not loose, possibly, probable and definite loose. Furthermore, the final reamer/stem diameters, length of resection, tumor type, adjuvant treatment modalities, bushing exchange/revision surgery and infection rate were recorded.

There were 70 patients and none were lost to follow-up. The average radiographic follow-up was 7.2 years (58% had f/u >5 years). Examiner A found 89% of femoral components to be "Not Loose" and 11% (n = 6) "Possibly Loose". Examiner B found 96% of femoral components to be "Not Loose" and 4% (n = 2) to be "Possibly Loose". No components scored as probably or definitely loose. Two DFE stems were reported as "Possibly Loose" by both reviewers. No femoral stem required revisions for either loosening, femur fracture or metal failure. Although infection was frequent, there was no septic loosening.

Despite our study limitations, no radiographic evidence of loosening was found. Cementing distal femur prosthesis with a tight canal fit and with a thin and inconsistent cement mantle appears to be a viable option at short and medium term.