[Oblong acetabular cup, type TC, for revision total hip arthroplasty]

Revision total hip arthroplasty is a demanding surgical procedure. It involves a massive loss of acetabular bone stock associated with primary implant removal, and a complicated revision cup fixation in the highly damaged surrounding bone. The authors describe the use of a novel oblong acetabular cup, type TC (Trč-Cingr), for replacement of a loose acetabular component. The aim of the study is to present this novel implant with evaluation of the first clinical results and to report on the authors' experience with revision arthroplasty assessed at 24 to 62 months of follow-up.

The TC cup was used in revision total hip arthroplasty in 40 patients treated between February 2004 and June 2007. Aseptic loosening of a cemented cup was an indication for surgery in the majority of patients. The first 10 treated patients were supervised, according to the strict rules of good clinical practice, by the State Institute for Drug Control. A total of 31 patients were evaluated. There were 20 women and 11 men with an average age of 68 years (range, 41 to 81 years) at the time of primary implantation.

At the end of 2009, 31 patients were evaluated at a follow-up of 24 to 62 months (average, 44.8 months) after revision surgery. The patients' age, gender, body mass index, physical activity, diagnosis for indication, implant size and intra- and post-operative complications were recorded. The development of secondary implant stability was assessed on X-ray films taken at 3, 6, and 12 months and then at 1 year after surgery. Attention was paid to implant and screw positions and potential implant migration and signs of osteolysis around the cup and screws. An objective assessment of the results was obtained by comparing the pre- and post-operative values of the Harris hip score (HHS).

A femoral component was replaced together with a revision cup in 20 patients. The average HHS value increased from 41.86 points pre-operatively to 82.70 points post-operatively. The results were recorded as excellent in six, very good in 17, satisfactory in six and poor in two patients. The radiographic findings showed good bone-implant integration in 26 patients and radiolucent lines . 1mm in width in DeLee zone 3 in three patients. In one overweight patient, discontinuity of two proximally inserted screws, but no detectable implant migration, was recorded. There was only one case of proximal migration of the TC cup, with osteolysis detected around all screws (Paprosky type 3B defect).

The acetabular cup is the most frequently re-implanted component in our country. This is due to a high proportion of total hip arthroplasties with the previous frequent use of a cemented POLDI prosthesis whose neck in a valgus position probably played its role in increased wear of the cup. Acetabular bone defects are usually extensive and the operative tactics are based on the Paprosky classification. Type 3A and 3B defects, exceptionally also type 2C defects, are most serious and acetabular cup replacement is most difficult. The oval-shaped uncemented TC cup was developed with the objective to reconstruct defects on the bottom of the acetabulum, with stable and firm primary fixation of the implant secured in bone with implant augmentation screws and additional fixation screws. Good primary fixation with bone grafting to fill defects and spaces between implant ribs should facilitate bone remodelling in the close vicinity of the cup. A minimum of 24 months after revision cup implantation is regarded as sufficient for an objective evaluation of hip function and radiographic evidence of good bone-implant integration.

The results show good applicability of the oval-shaped implant which is easy to implant, maintains good primary fixation and allows for good bone remodelling in its vicinity.