[Intra- and postoperative fractures of the femur in total knee arthroplasty: risk factors in 32 cases].

PURPOSE OF THE STUDY: We reviewed fractures of the distal femur occurring during or after total knee arthroplasty in order to identify risk factors.

MATERIAL AND METHODS: Twelve intraoperative fractures occurred between 1990 and 2000 among 617 total knee arthroplasties performed during this period. The circumstances of these fractures were noted in comparison with other prosthetic implants. Twenty other fractures of the distal femur occurred in 20 patients who had had a total knee arthroplasty during the same time period. Mean patient age at surgery was 72 years (range 69-77). In addition to demographic data, we noted risk factors: bone demineralization related to general condition, rheumatoid arthritis or corticosteroid therapy, trochlear notch prior to the trochlear cut, bone resorption under the femoral implant, repeated knee surgery, abnormal stress on the distal femur due to hip disease, periprosthetic osteolysis without loosening related to polyethylene debris or metallosis, loosening, type of prosthesis, loss of bone stock because of the femoral implant, life of prosthesis.

RESULTS: Intraoperative fractures usually occurred in specific circumstances: use of a posterior stabilized prosthesis, probably with insufficient preparation and position of the stabilization element, probably excessive impaction in osteoporotic bone (rheumatoid arthritis), difficult exposure (arthroplasty after prior osteotomy), fracture starting from the separator passing over the posterior aspect of the tibia and reaching the intercondylar notch. Independently of these intercondylar fractures, supracondylar or diaphyseal fractures were essentially observed for revision prostheses using a femoral stem. Postoperative fractures were observed in patients who had prior surgery of the distal femur (revision of femoral osteotomy, fracture of the distal femur, arthrodesis), in patients with significant loss of bone stock (posterior stabilized prosthesis), or poor bone quality (rheumatoid arthritis), and in elderly patients with neurological impairment and frequent falls. The trochlear notch did not appear to be sufficient to be the only cause of fracture but was nevertheless an element frequently associated with other risk factors.

DISCUSSION AND CONCLUSION: This study shows that fracture of the distal femur occurs in certain preferential circumstances. Considering these elements, a certain number of preventive measures can be discussed for technical modifications or choice of implants.