Purpose: Combining biomaterials with non-cemented cups is a new approach to acetabular construction in patients with bone stock loss after failure of conventional techniques. We evaluated our early results and attempted to ascertain limitations.
Material and methods: Between January 1, 1996 and December 31, 2000, we changed 229 cups. The reconstruction combined biomaterials with a non-cemented cup for 48 patients (mean age 57 years, age range 29–84). Mean retrospective follow-up was 37 months (7–67) with two patients lost to follow-up early.
Two types of cups coated with hydroxyapatite were used depending on the acetabular potential for retaining the implant: 26 ATLAS press-fit cups (four screwed) and 22 Cerafit cups with Surfix anchor screws. Bony defects were filled with grains of macroporous calcium phosphate ceramic, alone or in combination with an autol-ogous bone graft (five patients) and/or an iliac bone marrow graft (24 patients). The Harris and modified PMA clinical scores were used for assessment. According to the Antonio classification, preoperative bone loss was grade II in 18, grade III in 27, grade IV in 3. We attempted to determine the percent of bone support under the cup before reconstruction. The centre of the prosthesis rotation and the interfaces with the biomate-rials were checked regularly.
Results: At short-term, this technique provided a clear functional improvement (Harris improved from 53.7 to 81.3 points). The bone-biomaterial interface did not show any lucent lines and tended to become homogeneous (31 cases). Seven patients (15.2%) developed millimetric lucent lines around stable implants. We had nine failures (19.6%) and performed four surgical revisions (8.7%) for major inclination of the cup in three and recurrent dislocation in one. There were also five patients with an asymptomatic implant migration. Excepting one case, the cup inclinations occurred when the bony support was less than 50% of the acetabulum while only one migration was noted with less than 50% bony support (p=0.02).
Discussion: At short-term this technique, which is easy to perform and less costly and safer than allografting, provides similar results. We observed a continuous construct between the receiver bone and the macroporous biomaterial in all cases. Mechanically, the cup was stable when the bony support was healthy and involved more than 50% of the acetabulum. Other reconstruction strategies should be considered in other cases.
