Highly Cross-Linked Polyethylene Reduces Wear and Revision Rates in Total Hip Arthroplasty: A 10-Year Double-Blinded Randomized Controlled Trial.

BACKGROUND: Highly cross-linked polyethylene (XLPE) was developed to address the problem of wear and osteolysis associated with metal-on-conventional ultra-high molecular weight polyethylene (UHMWPE) bearing surfaces. The purpose of this study was to compare in vivo wear rates and clinical and radiographic outcomes between XLPE and UHMWPE in a prospective double-blinded randomized controlled trial with a minimum of 10 years of follow-up. METHODS: We randomized 122 patients to receive either a conventional UHMWPE liner (Enduron; DePuy) or an XLPE liner (Marathon; DePuy). Ninety-one patients were assessed clinically and radiographically at a minimum of 10 years (range, 10.08 to 12.17 years). Oxford Hip Scores and Short Form-12 Health Survey scores were collected. The radiographs were analyzed for osteolysis and for 2-dimensional (2-D), 3-dimensional (3-D), and volumetric wear using validated software. RESULTS: All 122 patients were accounted for at the 10-year follow-up evaluation. Twelve patients had undergone revision surgery, 21 patients had died (1 of whom had previously undergone revision surgery), and 2 patients were unable to return for follow-up, leaving 91 patients available for clinical and radiographic evaluation. At a minimum of 10 years, 3-D wear rates were significantly lower (p < 0.001) in the XLPE group (mean, 0.03 mm/yr) than in the conventional UHMWPE group (mean, 0.27 mm/yr). The prevalence of osteolysis was also significantly lower in the XLPE group (38% versus 8%, p < 0.005), as was the revision rate (14.6% versus 1.9%, p = 0.012), with 10 of the 12 revisions being in the Enduron group. There was no significant difference between the clinical scores of the 2 groups. CONCLUSIONS: XLPE liners have significantly reduced wear and are associated with a greater implant survival rate at 10 years compared with conventional UHMWPE liners. LEVEL OF EVIDENCE: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Do joint registries report true rates of hip dislocation?

BACKGROUND: Despite advances in primary THA, dislocation remains a common complication. In New Zealand (NZ), dislocations are reported to the National Joint Registry (NJR) only when prosthetic components are revised in the treatment of a dislocation. Closed reductions of dislocated hips are not recorded by the NJR. QUESTIONS/PURPOSES: We compared the true dislocation rate for patients receiving primary THA in the Wellington region with the rate reported by the NZ NJR for the same group of patients. METHODS: The NZ NJR identified 570 patients undergoing primary THA from January 1, 2008, to December 31, 2009, with addresses in the Wellington region. The mean age was 67.5 years (range, 27-96 years). The minimum followup was 2 years (mean, 3 years; range, 2-4 years). RESULTS: Six patients required revision of at least one component for dislocation. There was 100% agreement between the hospital database and the NJR. Using the NJR criteria of revision of any component as an end point, the dislocation rate in the Wellington region after primary THA was 1.05%. The hospital database identified a further eight patients who presented with a dislocation of their primary THA and underwent a closed reduction. These patients were not recorded by the NJR. The true rate of all dislocations, which includes closed reductions, was 2.46%. CONCLUSIONS: This article documents the discrepancy between the NZ NJR reported rate of revision for dislocation and the true rate of dislocation in primary THA. We recommend documentation of all dislocations by NJR in their database to allow more accurate comparisons between centers and research outcomes. LEVEL OF EVIDENCE: Level IV, clinical research study. See Guidelines for Authors for a complete description of levels of evidence.

Highly crosslinked polyethylene reduces wear in total hip arthroplasty at 5 years.

BACKGROUND: Although hip arthroplasty reliably relieves pain and improves function, problems have arisen with wear and osteolysis. Highly crosslinked polyethylene has been developed to address this problem although at present there is limited clinical evidence it does so longer term. QUESTIONS/PURPOSES: We compared the in vivo wear of standard versus highly crosslinked polyethylene (HXLP) in primary total hip arthroplasty at a minimum of 5-year followup. METHODS: We enrolled 122 patients in a prospective, double-blinded, randomized trial and followed them annually to assess their progress. Annual radiographs were analyzed using previously validated edge detection software to assess for two-dimensional, three-dimensional, and volumetric wear. The mean follow up was 5.5 years (range, 4.1 to 7 years). RESULTS: The two-dimensional wear measurements for HXLP showed lower wear compared to the conventional group (0.05 mm/year versus 0.26 mm/year, respectively). Three-dimensional and volumetric wear were similarly lower in the HXLP group. CONCLUSIONS: Highly crosslinked polyethylene undergoes substantially less wear than conventional polyethylene at medium term. The effect of hip arthroplasty longevity will need to be assessed with longer-term studies, but this may lead to a decreased need for revision as a result of less wear and osteolysis.

A double-blind, prospective, randomized controlled trial comparing highly cross-linked and conventional polyethylene in primary total hip arthroplasty.

Highly cross-linked polyethylene was developed to reduce articular bearing wear in total hip arthroplasty. In vitro studies have shown reduced wear in comparison with conventional polyethylene. A double-blind, prospective, randomized trial was performed comparing highly cross-linked and conventional polyethylene in 119 patients. The primary outcome variables were linear, 3-dimensional, and volumetric wear as determined by analysis of digitized radiographs using validated wear measurement software. Linear, 3-dimensional, and volumetric wear rates were significantly less in the highly cross-linked polyethylene group between 6 months and 4 years postoperatively (P < .05). The data presented here show that highly cross-linked polyethylene reduces short-term polyethylene wear. The intermediate and long-term clinical results of highly cross-linked polyethylene remain unknown pending further follow-up.

Femoral revision with a fluted, tapered, modular stem seventy patients followed for a mean of 3.9 years.

Fluted tapered revision femoral stems have been used successfully in Europe. Modularity makes these implants more versatile, but outcomes of modular designs have not been reported. We report a retrospective review of 70 such stems with a mean follow-up of 47 months. Combined metaphyseal/diaphyseal bone loss was present preoperatively in 36 (51%) of 70 hips. Three hips (4.3%) were re-revised or in need of re-revision, and worst-case survival was 87%. The mean postoperative patient-assessed Oxford Hip Score was 21.1. Restoration of proximal bone was noted in 56%. Complications included mean subsidence of 9.9 mm, dislocation in 7 (10%) of 70 hips, and fracture or cortical perforation in 17 (24.2%) of 70. These results are equivalent to, or better than, reported results of other types of cementless revision femoral stems.

Does pelvic osteolysis occur with a nonmodular uncemented acetabular component?

We present a radiographic follow-up of an uncemented, nonmodular, pure titanium-backed acetabular component at 6 to 12 years postimplantation. Between 1990 and 1992, 130 primary total hip arthroplasties were carried out by 1 surgeon using this implant, in association with both cemented and uncemented femoral components. There were 19 deaths, 5 revisions, and 19 hips lost to follow-up, leaving 87 hips available for review at a mean of 9.6 years. Two revisions were for infection, whereas 3 well-fixed cups were changed at the time of revision of a loose femoral component to allow downsizing to a 28-mm head. No cup has been revised for aseptic loosening. There was no radiographic evidence of periacetabular osteolysis or loosening of any of the cups, even in a subgroup of 31 patients who were 60 years or younger at the time of implantation.

Proximal femoral osteotomy for the treatment of hip arthritis in young adults.

BACKGROUND: The outcome of proximal femoral osteotomy for hip arthritis in young adults performed at the Wellington Hospital (Wellington, New Zealand) was reviewed. METHODS: Seventeen patients underwent 21 proximal femoral osteotomies for the treatment of hip arthritis at Wellington Hospital between 1992 and 1999. Thirteen patients (17 hips) were contacted and were able to complete a questionnaire form specific for hip pain and function. RESULTS: There was a response rate of 76.5% (13 out of a possible 17 patients undergoing proximal femoral osteotomy) at a mean 3 years 4 months postoperatively. Of these, one patient has had a total hip joint replacement and one patient is currently on the waiting list for a total hip joint replacement. Three other patients (three hips) report moderate or severe hip pain. The remaining eight patients (12 hips) report having mild or no hip pain. Questionnaire results show a postoperative decrease in hip pain in most patients. Hip function as assessed by the questionnaire was essentially unchanged. CONCLUSIONS: Proximal femoral osteotomy is a satisfactory option for young patients with degenerative hip arthritis. The operation is only likely to be useful in the treatment of pain.

Chemical eluates from ultra-high molecular weight polyethylene and fibroblast proliferation.

Although polyethylene wear particles have been implicated in osteolysis and implant loosening, this study is the first to test whether chemical eluates extracted from ultra-high molecular weight polyethylene (UHMWPE) could also be involved in this process. Eluates were prepared from UHMWPE bar stock and examined for their effects on (3)H-thymidine incorporation by human foreskin fibroblasts grown in 96-well culture plates. Low concentrations of eluates stimulated (3)H-thymidine uptake; whereas, high concentrations inhibited uptake in a dose-dependent manner. Maximum inhibition of proliferation for eluates (87+/-0.03% inhibition, n = 45 paired wells) was greater than that observed for particles (54+/-0.07% inhibition, n = 45 paired wells). Ethylene oxide sterilization of UHMWPE reduced (3)H-thymidine uptake at low eluate concentrations relative to sterilization by gamma-irradiation. It was concluded that leachable eluates from UHMWPE implantse contribute to the osteolytic process at the bone-implant interface.

Polyethylene particles from a hip simulator cause (45)Ca release from cultured bone.

Periprosthetic osteolysis is a dominant factor in the success or failure of total hip prostheses. Polyethylene wear debris has been implicated in the process of bone resorption and subsequent implant loosening. The present study is the first to examine the effect of ultra high molecular weight polyethylene (UHMWPE) wear debris produced by a hip simulator on calvarial bone resorption in vitro. (45)Ca release was measured in cultured mouse calvarial bone samples. Although short-term exposure to UHMWPE particles (2 h) decreased (45)Ca release, longer-term exposure for 1-2 days increased release in a dose-dependent manner. After one-day exposure to 7.5 x 10(6) particles per mL, 18% more (45)Ca was released from cultured calvarial bone than from control samples. It was concluded that UHMWPE wear particles either directly or indirectly stimulated osteoclasts to activate bone resorption. Polyethylene wear debris contributes to the osteolytic process at the bone-implant interface.