[Oblong implants for revision total hip arthroplasty].

PURPOSE OF THE STUDY

A prerequisite for the successful implantation of an acetabular component in a defective bone tissue is, in addition to providing sufficient primary fixation of the implant, reconstruction of the acetabular bone bed. To achieve this, one of the options involves the use of an oblong implant. Data published on this topic are sparse and therefore the aim of this study was to gain a deeper insight into this issue. In addition, we wanted to compare the results achieved with the oblong component with those obtained using its original model.

MATERIAL

One group comprised 111 patients with 133 sides who underwent acetabular revision for aseptic loosening or extraction of an infected acetabular component with subsequent implantation of an oblong cup (Langs-Ovale Revisionspfanne [L.O.R.], Allopro, Switzerland). The average age of this group at the time of surgery was 62.2 (range, 31-83) years, and average follow-up was 9.7 (range, 0.6-13.9) years. The other group consisted of 134 patients with 152 sides who for the same indications as the L.O.R. group received a Walter Oval cup (Medin Orthopaedics, Czech Republic). The average age at the time of surgery was 64.6 (22-86) years, and average follow-up was 7.3 (range, 1.1-9.8) years. The proportion and nature of defects and underlying clinical diagnoses in the two groups were statistically comparable. The patients requiring replacement or removal of the acetabular component were not included in clinical evaluation, but their data were used for survival analysis. The clinical evaluation included: in the L.O.R. group, 115 hip joints at an average follow-up of 10.8 (range, 4.5-13.9) years and, in the Walter Oval group, 144 hip joints at an average follow-up of 7.5 (range, 2.3-9.8) years. The data of patients who died during ;the study (L.O.R., 7 Walter Oval, 11) were included in the clinical evaluation as of the date of the final follow-up.

METHODS

The results for each group were evaluated using the Kaplan-Meier survival analysis, with a simple survival curve and a"worst case" survival curve. The statistical difference between the curves was calculated by the Gehan-Wilcoxon test. Survival tables were constructed for 12 or 8 years. A comparison of the initial and the final Harris hip score (HHS) was made using the t-test. Radiographs were inspected for the signs of implant migration, the presence of translucent lines surrounding the implant and screws and screw breaks. The results were evaluated by the Chi-square and Fisher's exact tests, with the level of significance set at 0.05.

RESULTS

In the I.O.R. group, 18 implants (13.5%) were reimplanted or removed in the Walter Oval group it was eight cups (5.3%). Aseptic loosening was the cause of reimplantation in 8.3% and 3.9% of the hips in the L.O.R. and Walter Oval groups, respectively. Deep infection required revision surgery in 5.3% of the L.O.R hips, and in 1.3% of the Walter Oval hips. The Walter Oval group showed a longer implant survival, but this was not confirmed by the "worst case" analysis. The final HHS markedly improved in comparison with the initial one in both groups. No radiographic difference between the groups was found.

DISCUSSION

The comparison of our results with those of other methods used in the indications described here provides evidence in favour of oblong implants. The major advantage, as well as the condition of success, is the anchoring of an oblong cup in the patient's own load-bearing bone.

CONCLUSIONS

Acetabular defects in the range of Paprosky types IIB to IIIA are indicated for the use of oblong implants in a basic position. The Arbond hydroxyapatite coating providing an osteoactive surface for the oblong cup described significantly improves the survival of this implant in comparison with the original model.