This retrospective case series study was approved by the Institutional Review Board of Seoul National University Hospital (IRB No. H-1703-054-837). Informed consent was waived. Between September 1995 and August 2012, isolated liner exchange with curettage and bone graft for osteolysis was performed in 37 consecutive cases (36 patients). Two patients (three hips) were excluded because of inadequate follow-up, and the remaining 34 patients (34 hips) were included in the final analysis. There were 20 men and 14 women with an average age of 49 years (range, 21 to 81 years) at the time of index surgery that was performed 3 to 21 years (mean, 10.1 years) after the previous surgery. This procedure was indicated for severe wear of the polyethylene liner or marked periprosthetic osteolysis despite the well-fixed acetabular metal shell. The acetabular metal shell was considered to be well fixed when the patient could bear weight without pain or discomfort and some portion of the bone ingrowth area remained intact on plain radiographs and computed tomography (CT) images.

The initial diagnosis was osteonecrosis of the femoral head in 15 cases, infection sequelae in 10, fused hip in five and miscellaneous in four. The index surgery was the first revision in 28 cases, second in five cases, and third in one case. Surgery was performed in the lateral decubitus position through a transtrochanteric approach in 18 cases, posterolateral approach in 12, and anterolateral approach in four. After removal of the worn polyethylene liner and screws, the stability of the metal shell was confirmed by forceful manipulation.

The osteolytic area was curetted out using curved curettes through screw holes and so was the cortical defect at the outer margin of the metal shell. In two cases, an additional cortical window was made for thorough curettage. The curetted cavity was filled with autogenous and allogenic cancellous chip bone grafts in the first three cases and only with allogenic bone grafts in the remaining cases. The replacement liner was made of conventional polyethylene in 26 cases and highly cross-linked polyethylene in eight cases. In three cases, the liner was cemented in the metal shell because a compatible liner could not be used.

After surgery, all patients were instructed to maintain the hip abduction position with limited flexion and walk with crutches without weight bearing for the first 6 weeks like after complete cup revision. Patients were evaluated clinically and radiographically at postoperative 6 weeks, 3 months, 9 months, and then annually. The follow-up period was 8.3 years on average (range, 5 to 20.2 years). Polyethylene liner wear was measured by the method of Scheier and Sandel19) on anteroposterior radiographs taken preoperatively and at the latest follow-up.

After a minimum follow-up of 5 years (range, 5 to 20.2 years), re-revision surgery was necessary in 10 cases (29.4%): eight for wear and osteolysis at 55 to 101 months after liner exchange (mean, 77 months) (Fig. 1) and two for acetabular loosening at 1 and 1.5 years after liner exchange (Fig. 2). Re-revision surgery included all component revision (four cases), cup revision (four cases), and liner exchange (two cases). In all re-revision cases, a conventional polyethylene liner was used. There was no failure in the cases in which a highly cross-linked polyethylene liner was used.

Postoperative complications included greater trochanter nonunion in two cases, sciatic nerve palsy in one case, and heterotopic ossification in one case. One trochanteric nonunion was treated by open reduction and internal fixation and the other one was treated conservatively. Sciatic nerve palsy recovered gradually but not completely. There were no cases of dislocation. The average polyethylene wear rate was 0.28 mm per year before the index surgery. The wear rate of the replaced conventional polyethylene was 0.20 mm per year and that of the replaced highly cross-linked polyethylene was 0.02 mm per year on average.

In this study, re-revision was necessary in 10 out of 34 cases (29.4%). This re-revision rate is higher than those reported previously.16) However, we believe that this result is satisfactory because most re-revisions (eight cases) were performed because of wear and osteolysis again; even if revision of all acetabular components had been performed in these cases, re-revision would have been necessary.

There were two cases of loosening of the metal shell early after liner exchange. Early failure indicates that the preoperative evaluation on the stability of the metal shell was incorrect or inadequate. Mehin et al.20) recommended isolated polyethylene liner exchange when less than 50% of the circumference of the metal shell was affected by osteolysis on plain radiographs. However, evaluation on plain radiographs is not always clear and is known to underestimate the amount of osteolysis.21) Even on CT images, there are frequently limitations because of scattering. At present, a metal artifact reduction algorithm for orthopedic implants is used to analyze on CT scans. With the use of this algorithm, objective criteria for the evaluation of stability of the metal shell might be established.

Most studies reported a higher dislocation rate after isolated polyethylene liner exchange than after complete acetabular component revision, and dislocation was the most frequent cause of reoperation.2223) In contrast to previous reports, there were no cases complicated by dislocation in this study, possibly owing to a strict postoperative care regimen.

A limitation of this study is the retrospective evaluation of the relatively small number of cases. However, this study demonstrated a definite difference in the results between the use of conventional polyethylene and highly cross-linked polyethylene. Curettage and bone grafting through screw holes are time-consuming and tedious. Some studies reported the same results without bone grafting.571324) Nevertheless, it is believed that bone grafting should be done for a future revision surgery. By using CT scanning, Egawa et al.25) found that a bone graft site was filled by about 50%. For this reason, they emphasized the necessity of developing proper tools for the bone graft procedure. In our cases, conventional curettes bent in various ways were used to make curettage easier (Fig. 3). For bone grafting, instruments named trumpets introduced by Chiang et al.2) would be helpful.

In conclusion, the results of this study suggest that isolated acetabular liner exchange is a reasonable option for wear and osteolysis when the metal shell is well fixed. More promising long-term results are expected with the use of highly crosslinked polyethylene liners than liners made of conventional polyethylene.