[Treatment of fractures of the distal femur on total knee arthroplasty].

PURPOSE OF THE STUDY: Fractures of the distal femur near a total knee arthroplasty are usually observed in patients aged over 70 years victims of low-energy trauma. The rate of complications is high: in the literature 25-75 %, even when treated by experienced surgeons. The purpose of this study was to detail therapeutic modalities used for the treatment of these fractures with their advantages and disadvantages and to determine the morbidity of complications which do occur.

MATERIAL AND METHODS: Twenty distal fracture of the femur were treated between 1990 and 2000 in twenty patients who had a total knee arthroplasty. Mean patient age at surgery was 72 years (range 69-77). The fracture was a short oblique fracture in four, transversal in five, long and spiral in four and comminuted in the others. In four fractures, the preoperative radiographic analysis suggested concomitant loosening. Therapeutic modalities included suspension traction for two, femorotibial external fixation for two. Retrograde nailing was possible in two patients. Fixation with a screw plate or a blade plate was used for nine fractures. The prosthesis was revised systematically if loosening was observed. This was done in three cases with preservation of the tibial piece and in two cases, changing the complete prosthesis, using a long femoral stem in all.

RESULTS: Mean follow-up was two to ten years. Immediate weight bearing was possible for four of the five patients for whom only the femoral piece was changed with a long stem. For the others, weight bearing was deferred until fracture healing was obtained after a mean five months (range 4-42). Bone healing required one, or two, revisions in three patients. Three patients died within one year of their fracture of the distal femur. There were no cases of infection or late healing. At last follow-up, the knee and function score regressed after treatment of the fracture. The two scores dropped 20 points compared with the pre-operative score (78 +/- 15 to 56 +/- 19 for the knee score and 72 +/- 16 to 54 +/- 18 for the function score). The knee score fell because of difficulty going up and down stairs and use of crutches. Treatments which stiffened the knee were traction suspension and external fixation. Loss of joint motion was about the same with or without prosthesis revision. The tibiofemoral angle measured before the fractures (postoperative goniometry) then after fracture healing or after changing the femoral prosthesis, showed an alignment of 183 degrees before the fracture and 178 degrees after healing or revision of the femoral piece. Three patients experienced another fracture of the same femur after healing of the initial fracture or after changing the knee prosthesis.

DISCUSSION: Fracture of the distal femur on a total knee prosthesis is a serious complications because of the mortality and the difficulty in achieving functional recovery after treatment. Therapeutic difficulties involve the type of skin incision, the position of the screws in relation to the femoral component, the possible need for bone graft, and finally the requirement to change the femoral piece with a centro-medullary stem.