Should HXLPE Be Considered the Gold Standard for THA? (AAOS 2014)
Since its development, ultra-high molecular weight polyethylene (UHMWPE) has been the primary bearing option for total hip arthroplasty (THA). However, highly cross-linked polyethylene (HXLPE), which was introduced in the 1990s, has generally demonstrated superior wear properties to UHMWPE in clinical and laboratory studies.
“At our institution, we have been using HXLPE implants since 1999,” said John Mutu-Grigg, MD, a clinical fellow at the London Health Sciences Centre in London, Ontario, Canada. “We undertook this study to review our results with the use of first generation HXLPE implants.” Yesterday, Dr. Mutu-Grigg presented the results of “A Decade of Experience with Highly Cross-Linked Polyethylene in Total Hip Replacements: A Review of 1,484 Cases.”
To investigate the issue, Dr. Mutu-Grigg and his colleagues conducted a retrospective review of a prospective database on all cases of HXLPE liners carried out at a single institution between 1999 and 2007. They used validated clinical outcome scores, including the SF-12, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and the Harris Hip Scores (HHS) to assess pre- and post-operative function in 1,484 THA patients, and compared their findings against data from other published studies covering both HXLPE and UHMWPE liners. All cases had a minimum 5-year follow-up, and 418 cases (28 percent) were followed for a minimum of 10 years.
“Revision for any reason was determined as our end point,” explained Dr. Mutu-Grigg. “We then reviewed each revision case to determine the cause of revision and to specifically assess if failure could be attributed to the use of HXLPE.”
Dr. Mutu-Grigg noted that during the study period, HXLPE from four different manufacturers was used, with the breakdown as follows:
- Type A—57 patients (3.8 percent of total)
- Type B—97 patients (6.5 percent)
- Type C—321 patients (21.6 percent)
- Type D—1,009 patients (68 percent)
The authors note that although the exact method of cross-linking polyethylene differs between manufacturers, the basic principles are common to all. Irradiated resin cleaves the polymer chains and leads to increased cross-linking of the polymer. The new material is heat treated either by annealing (below its melting point) or by remelting to remove free radicals. The final product is sterilized and packaged.
The research team found that patients who received the implants showed significant improvement in all outcome measures. Average WOMAC scores improved from 40.5 at preoperative baseline to 75.3 at latest follow-up, while SF-12 physical scores changed from 28.4 to 40.3. Similarly, the mean Harris Hip Score was 44.0 at baseline and 89.5 at most recent follow-up.
Overall, there were 56 revision surgeries (3.8 percent). Of those, 17 were associated with instability, 16 with infection, 11 with aseptic loosening, 7 with periprosthetic failure, and 5 were linked with various other causes. Of the 11 cases of aseptic loosening, all occurred early in the study period and were linked with either surgical error or cement fracture and subsidence. There were no cases of liner fracture or liner wear linked to reoperation.
Although the researchers did not assess all patients for osteolysis using computed tomography (which they identified as a shortcoming of the study), they note that isolated osteolysis is known to occur in the presence of excellent clinical function.
“We found that our complication rates were similar to other published results. Based on our findings, we argue that the use of HXLPE is both safe and effective,” said Dr. Mutu-Grigg. “It should be considered the gold standard bearing surface in modern total joint replacement.”
Dr. Mutu-Grigg’s coauthors include Richard W. McCalden, MD; Douglas Naudie, MD, FRCSC; James P. McAuley, MD; and Steven J. MacDonald, MD.
Details of the authors’ disclosure as submitted to the Orthopaedic Disclosure Program can be found in the Final Program; the most current disclosure information may be accessed electronically atwww.aaos.org/disclosure
2014 Annual Meeting News
Tuesday through Friday, March 11 – 14, 2014.
http://www.aaos.org/news/acadnews/2014/AAOS11_3_12.asp