Anatomical ceramic arthroplasty (AN.C.A.): preliminary experience with a new cementless prosthesis

The study reports the results obtained in 100 hips operated with a new cementless arthroplasty (AN.C.A.) characterized by the anatomical shape of a stem coated with Al2O3 and by a spherical acetabulum in ceramic-titanium, stabilized to the acetabulum first by screwing of the titanium ring and then by bony ingrowth in the cupola covered with porous ceramic. The patients were followed-up after an average of 17.4 months (+/- 8 SD). The patients were clinically evaluated using on the Merle d'Aubigné system, with the following average values +/- SD: pain 5.51 +/- 1, walking 5.01 +/- 1.1, and range of motion 5.38 +/- 0.9. The radiographic stabilization of the prosthesis (considering the worst results of the acetabulum and/or of the stem) was bony (BS) in 83% of the case and fibrous (FS) in 11%; 6 cases (5 acetabulums and 1 stem) showed signs of radiographic instability. Of these, 2 were submitted to further surgery to substitute the acetabulum. Two other patients were also submitted to a second operation: 1 involved substitution of the fractured ceramic head, and the other involved substitution of the stem in a patient with progressive coxalgia and no radiographic signs of loosening. The method of radiographic evaluation was significantly correlated with pain (p = 0.0001) and with walking (p = 0.0095). Instead, there were no significant correlations between stabilization of the prosthesis and precision of the femoral fit (press-fit) of the stem, age, evaluation of preoperative mineralization of the bone, and length of the stem. 8% of the cases presented important radiographic signs of stress-shielding; while 16% presented hypertrophy of the femoral cortex. These radiographic findings were not correlated to clinical ones.