Increased femoral head size reduces the rate of dislocation after total hip arthroplasty (THA). With the introduction of highly crosslinked polyethylene (HXLPE) liners in THA there has been a trend towards using larger size femoral heads in relatively smaller cup sizes, theoretically increasing the risk of liner fracture, wear, or aseptic loosening. Short to medium follow-up studies have not demonstrated a negative effect of using thinner HXLPE liners. However, there is concern that these thinner liners may prematurely fail in the long-term, especially in those with thinner liners. The aim of this study was to evaluate the long-term survival and revision rates of HXLPE liners in primary THA, as well as the effect of liner thickness on these outcomes. We hypothesized that there would be no significant differences between the different liner thicknesses.

We performed a retrospective database analysis from a single center of all primary total hip replacements using HXLPE liners from 2010 and earlier, including all femoral head sizes. All procedures were performed by fellowship trained arthroplasty surgeons. Patient characteristics, implant details including liner thickness, death, and revisions (all causes) were recorded. Patients were grouped for analysis for each millimeter of PE thickness (e.g. 4.0-4.9mm, 5.0-5.9mm). Kaplan-Meier survival estimates were estimated with all-cause and aseptic revisions as the endpoints.

A total of 2354 patients (2584 hips) were included (mean age 64.3 years, min-max 19-96). Mean BMI was 29.0 and 47.6% was female. Mean follow-up was 13.2 years (range 11.0-18.8). Liner thickness varied from 4.9 to 12.7 mm. Seven patients had a liner thickness <5.0mm and 859 had a liner thickness of <6.0mm. Head sizes were 28mm (n=85, 3.3%), 32mm (n=1214, 47.0%), 36mm (n=1176, 45.5%), and 40mm (n=109, 4.2%), and 98.4% were metal heads. There were 101 revisions, and in 78 of these cases the liner was revised. Reason for revision was instability/dislocation (n=34), pseudotumor/aseptic lymphocyte-dominant vasculitis associated lesion (n=18), fracture (n=17), early loosening (n=11), infection (n=7), aseptic loosening (n=4), and other (n=10). When grouped by liner thickness, there were no significant differences between the groups when looking at all-cause revision (p=0.112) or aseptic revision (p=0.116).

In our cohort, there were no significant differences in all-cause or aseptic revisions between any of the liner thickness groups at long-term follow-up. Our results indicate that using thinner HXPE liners to maximize femoral head size in THA does not lead to increased complications or liner failures at medium to long term follow-up. As such, orthopedic surgeons can consider the use of larger heads at the cost of liner thickness a safe practice to reduce the risk of dislocation after THA when using HXLPE liners.

With the introduction of highly crosslinked polyethylene (HXLPE) in total hip arthroplasty (THA), orthopaedic surgeons have moved towards using larger femoral heads at the cost of thinner liners to decrease the risk of instability. Several short and mid-term studies have shown minimal liner wear with the use HXLPE liners, but the safety of using thinner HXPLE liners to maximize femoral head size remains uncertain and concerns that this may lead to premature failure exist. Our objective was to analyze the outcomes for primary THA done with HXLPE liners in patients who have a 36-mm head or larger and a cup of 52-mm or smaller, with a minimum of 10-year follow-up. Additionally, linear and volumetric wear rates of the HXLPE were evaluated in those with a minimum of seven-year follow-up. We hypothesized that there would be minimal wear and good clinical outcome.

Between 2000 and 2010, we retrospectively identified 55 patients that underwent a primary THA performed in a high-volume single tertiary referral center using HXLPE liners with 36-mm or larger heads in cups with an outer diameter of or 52-mm or smaller. Patient characteristics, implant details including liner thickness, death, complications, and all cause revisions were recorded. Patients that had a minimum radiographic follow-up of seven years were assessed radiographically for linear and volumetric wear. Wear was calculated using ROMAN, a validated open-source software by two independent researchers on anteroposterior X-rays of the pelvis.

A total of 55 patients were identified and included, with a mean age of 74.8 (range 38.67 - 95.9) years and a mean BMI of 28.98 (range 18.87 - 63-68). Fifty-one (94.4%) of patients were female. Twenty-six (47.7%) patients died during the follow-up period. Three patients were revised, none for liner wear, fracture or dissociation. Twenty-two patients had a radiographic follow-up of minimum seven years (mean 9.9 years, min-max 7.5 –13.7) and were included in the long-term radiographic analysis. Liner thickness was 5.5 mm at 45 degrees in all cases but one, who had a liner thickness of 4.7mm, and all patients had a cobalt-chrome head. Cup sizes were 52mm (n=15, 68%) and 50mm (n=7, 32%). Mean linear liner wear was 0.0470 mm/year (range 0 - 0.2628 mm) and mean volumetric wear was 127.69 mm3/year (range 0 - 721.23 mm3/year).

Using HXLPE liners with 36-mm heads or bigger in 52-mm cups or smaller is safe, with low rates of linear and volumetric wear in the mid to long-term follow-up. Patients did not require revision surgery for liner complications, including liner fracture, dissociation, or wear. Our results suggest that the advantages of using larger heads should outweigh the potential risks of using thin HXLPE liners.