Comparing Conventional and Highly Cross-Linked Poly in Younger THA Patients

    Dr. Jeffrey Stambough comments on a study from Washington University, presented at the AAOS meeting in New Orleans, that evaluated polyethylene wear rates, revision rates, and patient-reported outcomes in total hip arthroplasty patients under age 50.

    How well do polyethylene bearing surfaces perform in total hip arthroplasty (THA) patients under age 50, and is there a difference in survivorship between conventional polyethylene (CPE) and highly cross-linked polyethylene (HXPLE) bearings?

    Investigators at Washington University in St. Louis, Missouri, sought to answer those questions by retrospectively reviewing outcomes in 201 consecutive patients age 16 to 50 who had undergone THA at their institution between 1996 and 2004.

    Their findings were presented at the 2018 Annual Meeting of the American Academy of Orthopaedic Surgeons in New Orleans.

    Evaluating Wear Rates

    Although implant survivorship is generally good in patients under age 50, the need for revision THA due to wearing of the polyethylene bearing surface is a real concern. In this study, the investigators evaluated linear and volumetric wear rates, component survivorship, and functional outcomes in 2 patient groups:

    • Group 1: CPE liners with cementless acetabular components, cobalt-chrome (CoCr) femoral head
    • Group 2: HXLPE liners in cementless acetabular components, CoCr femoral head

    They used software to calculate polyethylene wear. They also documented patient-reported UCLA Activity, SF-12, and modified Harris Hip scores.In this cohort, HXLPE bearings were found to perform better than CPE bearings, with 10 times less linear wear and 7.5 times less volumetric wear in patients with HXLPE bearings. Radiographic wear analysis showed:

    • Median true linear wear rate of 0.1 mm/yr (SD 0.11) in Group 1 compared with 0.016 mm/yr (SD 0.05) in Group 2
    • Median true volumetric wear rate of 44.59 mm3/yr (SD 43.9) in Group 1 compared with 5.77 mm3/yr (SD 23.83) in Group 2

    Patients with CPE bearings were more likely to undergo wear-related revision procedures than patients with HXLPE bearings, with 8 revisions in Group 1 (7.1%) and zero in Group 2 (P<0.001). These revisions were done an average of 14 years from the primary procedure. Overall, 17 patients in Group 1 underwent a revision procedure, compared with 2 patients in Group 2, both for deep infection.Patient-reported outcomes improved in both groups.The investigators were not surprised by their findings on wear rates, based on what is known about wear rates in older patients. “We hypothesized that younger patients would show increased wear and less survivorship due to wear-related revisions at the 15-year time point,” said lead author Jeffrey B. Stambough, MD.

    “We were surprised, however, by the timing of the revisions, with the majority occurring after 12 years. That signified to us that these patients, who live longer than older patients, will need close follow-up in the future.”

    Comparable Findings

    Wear and revision rates in this study’s younger patients were comparable to those found in other studies with younger and older patients. Devane et al [1] found a CPE linear wear of 0.27 mm/yr and a 14.6% wear-related revision rate at a minimum 10-year follow-up in a cohort of 122 patients who had received either a CPE liner or an HXLPE liner. Waddell et al [2] reported that 4 of 28 patients (14%) with CPE liners were revised for wear. The average linear wear rate in the CPE group was 0.092 mm/yr at an average 15-year follow-up. 

    In a cohort of 226 patients who had 236 primary THAs, Hopper et al [3] found a 12% wear-related revision rate at 15 years after surgery for those with CPE liners, with a mean linear wear of 0.17 mm/yr. Other reports with follow-up between 10 and 13 years found similar wear rates of 0.11 mm/yr to 0.13 mm/yr and radiographic evidence of osteolysis in 25% to 60% of patients with CPE liners. [4,5]

    “Conventional poly wear is a big issue for older patients,” Dr. Stambough said, “and from our findings, it will be an increasingly important issue for younger patients as well.”

    The findings reported at the AAOS meeting, he said, “highlight the need for close clinical follow-up and surveillance of this younger, more active cohort of patients with longer life expectancy than the typical joint replacement cohort,” Dr. Stambough said.

    “Six of the 10 patients in our cohort were revised for lysis-related reasons between 15 and 18 years after the index procedure. Thus, it is critically important for surgeons to know about these patients and scrutinize their radiographs closely at yearly intervals to look for potential problems, such as osteolytic trochanteric fractures, wear-related instability events, or late component loosening from excessive osteolysis.”

    He noted that although CPE bearings have fallen out of favor, “it is important for surgeons to be aware that this bearing was commonly used in the late 1990s and early 2000s. Bearing-related problems from CPE should remain high in the differential when currently working up a painful or failed THA when the index procedure was done during that time period.”

    Dr. Stambough said that in his practice, he and his colleagues have been contacting patients who received a CPE bearing surface and have not been seen by their surgeons recently, encouraging them to make an appointment for clinical and radiographic follow-up. 

    “We want to make sure that a lesser surgery – ie, liner exchange – could be done sooner to avoid a full revision if a complication, such as fracture or component loosening from ongoing poly wear, were to occur,” he said.

    “We also stress the importance of continued 1- to 2-year surveillance for patients who were followed for 15 years already, depending on their symptoms and amount of lysis already found on radiographs.”

    Is There an Ideal Bearing Surface?

    Based on the study’s findings, Dr. Stambough and his colleagues concluded that surgeons can be assured that HXLPE bearings are effective in primary THA patients under age 50 for at least 15 years after surgery.

    But is HXLPE the ideal bearing surface for these younger patients? Does an ideal bearing even exist, or is it still to be developed? Dr. Stambough said ceramic-on-HXLPE and ceramic-on-ceramic are both good options for younger patients, noting that “I, and others, would argue that ceramic heads on HXLPE liners is the current best options for these patients.”

    In a study using the Humana dataset, Bedard et al [6] found that use of ceramic-HXLPE bearings has increased by more than 40% since 2007, with more than 50% of all THA patients now receiving ceramic-HXLPE bearings. Cash and Khanduja [7] claimed that ceramic heads on HXLPE liners is the preferred option for young THA recipients due to concerns about ceramic fractures with hard-on-hard bearings and difficulty seating the ceramic liner.

    “Our own unpublished internal data are also finding that linear wear rates are consistently remaining around 0.01 mm/yr at 9 to 10 years after surgery in young patients with ceramic-HXLPE bearing couples,” Dr. Stambough said.

    The question of whether an ideal surface exists now is difficult to answer. “In a perfect world, the ideal bearing surface couple would produce infinitesimal or no wear particles, unlimited strength against fatigue fracture and propagation, and complete oxidation resistance,” Dr. Stambough said.

    “Achieving this balance has historically called for trade-offs, so the search continues.”


    Stambough JB, Pashos G, Egan JT, Maloney WJ, Martell JM, Clohisy JC. Where Are We at 15 Years? Highly Cross-Linked versus Conventional Polyethylene Wear in Total Hip Arthroplasty in Patients <50 Years (Paper 854). Presented at the 2018 Annual Meeting of the American Academy of Orthopaedic Surgeons, March 6-10, 2018, New Orleans, Louisiana.


    Dr. Stambough, Ms. Pashos, and Mr. Egan have no disclosures relevant to this study. Dr. Maloney has disclosed that he has stock or stock options in Bristol-Myers Squibb, Flexion Therapeutics, Johnson & Johnson, Medtronic, Norvartis, Pfizer, and Total Joint Orthopedics and that he receives royalties from Stryker and Zimmer Biomet. Dr. Martell has disclosed that he is a paid consultant for Zimmer Biomet and StelKast Inc. and that he receives royalties for a patent from the University of Chicago. Dr. Clohisy has disclosed that he is a paid consultant for Microport Orthopedics and Zimmer Biomet and that he receives research support from Zimmer Biomet.


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