Should We Use the Largest Femoral Head With the Smallest Acetabular Component in Primary Total Hip Arthroplasty?

BACKGROUND

There has been an increasing use of larger femoral head sizes to mitigate dislocation risk after total hip arthroplasty. Manufacturers have created thinner, highly cross-linked polyethylene (HXLPE) liners to maximize effective head size. We investigated whether there was a survivorship penalty if the largest head was chosen at the smallest compatible acetabular component size, and as a secondary aim, we analyzed whether there was a decreased dislocation risk.

METHODS

We reviewed 1,860 posterior approach primary total hip arthroplasties with HXLPE from 2005 to 2021. Subjects were divided into three groups based on acetabular component transition points at which a larger femoral head could be used: group 1 was 28-mm (N = 18) versus 32-mm (N = 89) heads, group 2 was 32-mm (N = 383) versus 36-mm (N = 429) heads, and group 3 was 36-mm (N = 806) versus 40-mm (N = 135) heads. The mean age was 66 years, 75% were women, and the mean body mass index was 30. There were 48% that had ceramic heads, and 52% had metal heads. The mean follow-up was 7 years.

RESULTS

There were two liner dissociations (0.1%) and no liner fractures. The 10-year survivorships free of dislocation, revision, and reoperation were 95, 95, and 93%, respectively. The 5-year survivorship free of dislocation for group 1 was 94% for 28-mm and 99% for 32-mm heads; for group 2, 96% for 32-mm and 99% for 36-mm heads; and for group 3, 96% for 36-mm and 95% for 40-mm heads. Cox regression demonstrated no difference in reoperation or revision rates between head sizes in any group.

CONCLUSIONS

When using HXLPE liners, pairing the largest femoral head with the smallest compatible cup for 32-mm, 36-mm, and 40-mm heads did not increase risk for liner-related complications, revisions, or reoperations. There was no difference in dislocation risk when using the larger femoral head at transitional cup sizes, though this study was under-powered to detect this difference.

LEVEL OF EVIDENCE: III, retrospective comparative cohort study.