Increased polyethylene wear associated with lateralized THA liners, study finds

Three hips implanted with a neutral liner and six implanted with a lateralized liner showed some osteolysis, but none required revision.

Implanting lateralized acetabular liners during total hip arthroplasty can result in an increased rate of polyethylene wear compared to neutral liners, a retrospective study found. However, both lateralized and neutral liners performed equally well in terms of stability and radiographic loosening, the study authors noted.

W. Vincent Burke, MD, and colleagues at the Anderson Orthopaedic Research Institute in Alexandria, Va., compared polyethylene wear rates between patients implanted with either a standard, neutral liner or a lateralized liner, which had a 4-mm thicker polyethylene apex.

The lateralized liner group included 56 hips in 56 patients treated at a mean age of 62.7 years. The neutral liner group included 39 hips in 39 patients at a mean age of 68.9 years.

Follow-up averaged 6.8 years for the lateralized liner group and 7.5 years for the neutral liner group. All patients had at least 5 years of radiographic follow-up, the authors noted.

In all cases, surgeons implanted a Duraloc 100 acetabular cup (DePuy, a Johnson & Johnson Company) without screw fixation. Also, all cases received uncemented, porus-coated femoral components and 28-mm cobalt-chrome femoral heads, according to the study, published in the Journal of Arthroplasty.

"Initial comparison of wear rates revealed that the neutral liners wore less rapidly than the lateralized liners. The initial statistics, however, also indicated that the neutral liners were implanted in a significantly older group of patients," the authors said.

To control for the differences in age, as well as other factors, such as liner shelf life, the researchers performed a multivariate regression analysis, which confirmed that the lateralized liners had a significantly higher polyethylene wear rate. These liners had a polyethylene wear rate 0.04 mm/year higher than the neutral liners (P=.028).

According to the study, the multivariate analysis also found that age, gender and liner shelf life all significantly influenced the rate of polyethylene wear, as follows:

male gender increased wear by 0.04 mm/year (P=.021);
each 10-year increase in age at time of surgery decreased wear by 0.03 mm/year (P=.001); and
each additional year of shelf life increased wear by 0.03 mm/year (P=.005).

Radiographic analyses found no cases of loosening or component migration, the authors said.

Radiolucent lines were found around three of the 39 cups (7.7%) in the neutral liner group and around nine of the 56 cups (16.1%) in the lateralized liner group. However, none were complete radiolucencies or progressive, according to the study.

Three hips in the neutral liner group and six hips in the lateralized liner group showed evidence of osteolysis. But, "At the time of this analysis, no cup in either study group was revised for any reason," the authors said.

Logistic regression analysis also found no significant difference in dislocation rates between groups, they noted.

"We believe the potential for increased stability and longevity provided by increased polyethylene thickness justifies the use of lateralized acetabular inserts in some instances. However, continued analysis of these components beyond 7.1 years after arthroplasty is necessary to determine whether the increase in polyethylene wear ... leads to a significant increase in osteolysis," the authors said.

For more information:
Burke WV, Orishimo KF, McAuley JP, Engh CA. Midterm radiographic comparison of cementless acetabular shells containing lateralized and nonlateralized liners. J Arthroplasty. 2006;21:1099-1104.