Marathon and Enduron Polyethylene at Long-Term Follow-up

A Prospective, Randomized Clinical Study Comparing Marathon Polyethylene and Enduron Polyethylene Acetabular Liners Used in Total Hip Arthroplasty at Long-Term Follow-up

The purpose of the study is to determine whether crosslinked Marathon and standard Enduron polyethylene liners show differences in survivorship due to wear-related revisions at minimum 14-year follow-up and every 5 years after.

Several institutions have reported very low wear rates with crosslinked polyethylene based on early and midterm clinical data. However, since revisions associated with osteolysis typically occur after 10-year follow-up, the greatest benefits of the reduced wear associated with crosslinked polyethylene are expected to be reflected in lower revision rates for wear-related complications at long-term follow-up. While crosslinking has proven to substantially reduce polyethylene wear during the first decade in vivo, characterizing the long-term clinical performance of Marathon polyethylene remains important because crosslinking is accompanied by a reduction in the ultimate tensile strength, fatigue strength, and elongation to failure of ultra high molecular weight polyethylene. As a consequence, concerns have been expressed about the potential for the liner fracture, in vivo polyethylene oxidation or accelerated wear at long-term follow-up, the effects of femoral head roughening over time and the bioreactivity of crosslinked polyethylene debris particles. Ultimately, the best way to address these concerns is in the context of well-controlled, long-term clinical outcome studies. This study will evaluate outcome at a minimum of 14-years after surgery among the same group of patients whose outcome was previously reported at 10-year follow-up. As part of our efforts to follow patients throughout their lives to obtain long-term outcome data, we will continue to obtain routine follow-up every 5 years from the date of the patient's primary total hip arthroplasty for the duration of the patient's life or until revision of the polyethylene liner (estimated to be 25 years). Because we anticipate that the reduced incidence of wear and osteolysis will result in a lower incidence of revision surgery among the patients randomized to Marathon liners, implant revision for reasons related to wear will be our primary outcome measure at long-term follow-up.

The crosslinked Marathon polyethylene liners used for the primary total hip replacements in this study were treated with 5 Mrad (50 kGy) of gamma irradiation to induce crosslinking and then heated above the melting temperature (150 degrees Celsius) to eliminate free radicals. This manufacturing process was designed to improve the polyethylene's resistance to wear through increased crosslinking and eliminate free radicals that render it susceptible to oxidative degradation. These liners were machined and terminally sterilized with gas plasma, a noncrosslinking chemical surface treatment. These liners did not have had free radicals at the time of implantation and did not incorporate antioxidants.

The standard, noncrosslinked Enduron polyethylene liners used for the primary total hip replacements in this study were manufactured from the same polyethylene resin as the crosslinked Marathon liners but never irradiated. Like the Marathon components, these liners were machined and terminally sterilized with gas plasma, a noncrosslinking chemical surface treatment. Based on the manufacturing methods, these liners would not have had free radicals at the time of implantation and did not incorporate antioxidants.

At 15-year follow-up and every 5 years after from the date of the patient's primary total hip arthroplasty for the duration of the patient's life or until revision of the polyethylene liner (estimated to be 25 years)

A single reviewer, blinded to the type of polyethylene liner, evaluated femoral head penetration among all hips using serial anteroposterior pelvic radiographs. Two-dimensional head penetration was determined for each follow-up radiograph using Hip Suite Analysis version 8.0 with elliptical correction, a validated, computer-assisted technique. A linear wear rate was evaluated for each hip that had a minimum of three follow-up radiographs using a least-squares linear regression to calculate the slope of the best-fit line for the wear vector magnitude versus time in situ data. The slope from this regression represented the steady-state linear wear rate. The steady-state linear wear rate data from all hips in a group was used to compute a mean polyethylene wear value.

At minimum 14-year radiographic follow-up and every 5 years after from the date of the patient's primary total hip arthroplasty for the duration of the patient's life or until revision of the polyethylene liner (estimated to be 25 years)

The incidence of clinically important osteolysis is based on the number of unrevised THAs (total hip arthroplasties) with at least 1.5 square centimeters of pelvic and/or femoral osteolysis. Osteolysis was defined as an area of localized loss of trabecular bone or cortical erosion that was not apparent on the pre-operative or immediate postoperative radiograph. To obtain lesion sizes, the defects were outlined on the anteroposterior pelvic and lateral radiographs. The area of the osteolysis was measured using Martell's Hip Analysis Suite software. Lesions were considered clinically important if the total area of osteolysis around a hip replacement was at least 1.5 square centimeters on either the AP or lateral view.

At minimum 14-year radiographic follow-up and every 5 years after from the date of the patient's primary total hip arthroplasty for the duration of the patient's life or until revision of the polyethylene liner (estimated to be 25 years)

Patients Who Answered "Yes" to the Question, "Are You Satisfied With the Results of Your Hip Operation?"

Patient satisfaction was quantified by asking participants to respond "yes" or "no" to the question, "Are you satisfied with the results of your hip operation?" Because some patients had both of their hips included in the study, these patients responded to the question, "Are you satisfied with the results of your hip operation?" for their right and left hips. As a consequence, the "Units Analyzed" is reported as hips while the "Number of Participants Analyzed" reflects the number of patients.

At minimum 14-year follow-up and every 5 years after from the date of the patient's primary total hip arthroplasty for the duration of the patient's life or until revision of the polyethylene liner (estimated to be 25 years)

The Harris Hip Score measures outcome after hip replacement and is based on a scale from 0 (worst) to 100 (best). The score includes assessments of pain, functional ability, deformity and range of motion.

At minimum 14-year follow-up and every 5 years after from the date of the patient's primary total hip arthroplasty for the duration of the patient's life or until revision of the polyethylene liner (estimated to be 25 years)

Inclusion Criteria: (from original study) Elective total hip replacement patient (from 10-year follow-up) Consented to the original study. Received a Duraloc 100 cup with either a crosslinked Marathon or standard Enduron liner. Received an AML/Solution or a Prodigy stem with 28mm cobalt chrome femoral head. Exclusion Criteria: (from original study) None (from 10-year follow-up) Patient did not receive device as specified in inclusion criteria. Patient refused to consent to continued follow-up.

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