UNCEMENTED CONICAL FEMORAL STEM FIXATION IN TUMOR PROSTHESIS FOR TOTAL KNEE REPLACEMENT

Siebernrock KA, Ballmer FT, Schöll E (Orthopaedic Surgery, University of Berne, Switzerland)

Introduction: The principle of femoral stem fixation in revision total hip arthroplasty introduced by Wagner was adapted to the femoral component in total knee replacement for bone tumors. Femoral fixation was obtained by an uncemented conical titanium alloy stem with a coarse surface and eight sharp longitudinal ribs. Primary stability is achieved by the longitudinal ribs cutting into the cortical bone and secondary stability has been evidenced by osseous ongrowth on the ribs. First experiences with this concept of stem fixation implanted minimally 5 years ago in patients with distal femoral tumors are reported and illustrated.

Patients and Methods: Uncemented femoral fixation was achieved by a long conical stem which was connected to the original femoral component of a semiconstrained GSB total knee revision prosthesis (Sulzer Inc., Wintherthur, CH) by a standard 12/14 mm cone. The tibial component was cemented in the usual manner. This type of prosthesis was used within a 3-year period in 3 female and 3 male patients with a mean age of 36 years (range 7—75 years). Distal femoral tumors included high-grade central osteosarcoma in 4 cases, recurrent paraosseal osteosarcoma and dedifferentiated chondrosarcoma each in 1 patient. Two patients died within 1 year after surgery due to lung metastases.

Results: The 4 surviving patients had a mean follow-up of 6.8 years (6 -8 years) without evidence of tumor disease. Bone remodeling and a continuous solid bone-implant interface was observed in all cases without clinical or radiographic signs of femoral stem loosening until present follow-up. Complications included rotational instability of the cone attachment in 2 patients which required surgical correction. During the same surgery a loose cemented tibial compent was revised in one of these patients.

Conclusions: Uncemented conical femoral stem fixation adapted to a total knee prosthesis for reconstructive surgery after distal femoral tumors has maintained clinical and radiographic stability after a mean follow-up of nearly 7 years. This concept of femoral anchorage adapted from revision surgery of THA seems promising and will be continuously used in our department. The cone system between the conical stem and the femoral prosthetic component has been modified in the meantime.