Cementless fixation of hip prostheses in dogs.

Fixation of smooth cementless femoral prostheses was studied in 16 dogs which were killed 2, 3 and 4 months after operation. Rotational stability, examined by hand, was good in 9 cases and all stable prostheses could be extracted. Five out of 6 dogs, who did not bear weight after the operation, had a stable prosthesis compared with 4 out of 10 who walked early. Histology showed close bone apposition in 4, tight fibrous encapsulation in 4 and lack of tissue apposition in 8 which were loose. Bone remodelling in radiographs reflected the histological appearances; narrow radiolucent spaces were associated with dense well organised fibrous tissue, and wide radiolucent spaces with loose connective tissue. Prostheses with stems which fill the femoral canal should improve the fixation of smooth cementless prostheses.