No difference in in vivo polyethylene wear particles between oxidized zirconium and cobalt-chromium femoral component in total knee arthroplasty

Oxidized Zirconium Components Maintain a Smooth Articular Surface Except Following Hip Dislocation

BACKGROUND

Oxidized zirconium (OxZr) offers theoretical advantages in total hip and knee arthroplasty (THA and TKA, respectively) relative to other biomaterials by combining the tribological benefits of ceramics with the fracture toughness of metals. Yet, some studies have found that OxZr does not improve outcomes or wear rates relative to traditional bearing materials such as cobalt-chromium (CoCr). Separately, effacement of the thin ceramic surface layer has been reported for OxZr components, though the prevalence and sequelae are unclear.

METHODS

To elucidate the in vivo behavior of OxZr implants, the articular surfaces of 94 retrieved THA and TKA femoral components (43 OxZr TKA, 21 OxZr THA, 30 CoCr THA) were analyzed using optical microscopy, non-contact profilometry, and scanning electron microscopy.

RESULTS

We found that OxZr components maintain a smooth articular surface except following hip dislocation. Three of four OxZr femoral heads revised following dislocation exhibited severe damage to the articular surface, including macroscopic regions of ceramic-layer effacement and exposure of the underlying metal substrate; these components were 23-32 times rougher than pristine OxZr controls. When revised for dislocation, OxZr femoral heads were substantially rougher than CoCr femoral heads (median S_a = 0.431 v. 0.020 μm, P = .03). In contrast, CoCr femoral heads exhibited low overall roughness values regardless of whether they dislocated (median S_a = 0.020 v. 0.008 μm, P = .09, CoCr dislocators v. non-dislocators).

CONCLUSIONS

Effacement of the ceramic surface layer and substantial articular surface roughening is not atypical following dislocation of OxZr femoral heads, making OxZr much less tolerant than CoCr to hip dislocation.

Vitamin E-infused highly cross-linked polyethylene did not reduce the number of in vivo wear particles in total knee arthroplasty

AIMS

Vitamin E-infused highly cross-linked polyethylene (E1) has recently been introduced in total knee arthroplasty (TKA). An in vitro wear simulator study showed that E1 reduced polyethylene wear. However there is no published information regarding in vivo wear. Previous reports suggest that newly introduced materials which reduce in vitro polyethylene wear do not necessarily reduce in vivo polyethylene wear. To assist in the evaluation of the newly introduced material before widespread use, we established an in vivo polyethylene wear particle analysis for TKA. The aim of this study was to compare in vivo polyethylene wear particle generation between E1 and conventional polyethylene (ArCom) in TKA.

METHODS

A total of 34 knees undergoing TKA (17 each with ArCom or E1) were investigated. Except for the polyethylene insert material, the prostheses used for both groups were identical. Synovial fluid was obtained at a mean of 3.4 years (SD 1.3) postoperatively. The in vivo polyethylene wear particles were isolated from the synovial fluid using a previously validated method and examined by scanning electron microscopy.

RESULTS

The total number of polyethylene wear particles obtained from the knees with E1 (mean 6.9, SD 4.0 × 10⁷ counts/knee) was greater than that obtained from those with ArCom (mean 2.2, SD 2.6 × 10⁷ counts/knee) (p = 0.001). The particle size (equivalent circle of diameter) from the knees with E1 was smaller (mean 0.5 μm, SD 0.1) than that of knees with ArCom (mean 1.5, SD 0.3 μm) (p = 0.001). The aspect ratio of particles from the knees with E1 (mean 1.3, SD 0.1) was smaller than that with ArCom (mean 1.4, SD 0.1) (p < 0.001 ).

CONCLUSION

This is the first report of in vivo wear particle analysis of E1. E1 polyethylene did not reduce the number of in vivo polyethylene wear particles compared with ArCom in early clinical stage. Further careful follow-up of newly introduced E1 for TKA should be carried out. Cite this article: Bone Joint J 2020;102-B(11):1527-1534.

The 2018 Mark Coventry, MD Award: Does a Ceramic Bearing Improve Pain, Function, Wear, or Survivorship of TKA in Patients Younger Than 55 Years of Age? A Randomized Trial

BACKGROUND

Methods to reduce the revision rate of total knee prostheses because of wear-related issues are important to examine, particularly because younger patients have a disproportionately high risk of revision.

QUESTIONS/PURPOSES

(1) Are long-term Knee Society knee and function scores better in younger patients with an oxidized zirconium (OxZr) TKA compared with those with a cobalt-chrome (CoCr) TKA? (2) Are there differences in radiographic signs of loosening or CT findings of osteolysis between OxZr TKAs and CoCr TKAs? (3) Are there fewer polyethylene wear particles in the OxZr TKA than CoCr TKA? (4) Do the groups differ in terms of survivorship free from revision surgery at 13 years?

METHODS

From April 2003 to January 2007, we enrolled 110 patients younger than 55 years of age in this randomized, double-blind, prospective trial. Each patient served as his or her own control and each received an OxZr femoral component in one knee and a CoCr femoral component in the other. The minimum followup was 10 years (mean, 13 years; range, 10-14 years); two died and nine were lost to followup before that time, leaving 99 patients (198 knees) for analysis. There were 28 men and 71 women with a mean age of 53 ± 6 years (range, 40-55 years). We obtained Knee Society knee scores for each knee, but Knee Society function scores, WOMAC scores, and UCLA activity scores were obtained for each patient preoperatively and at each followup. Additionally, we performed radiographic examination preoperatively and at each followup. At a minimum of 10 years (mean, 13 years) followup, we obtained CT scans in all patients. Polyethylene wear particles in the synovial fluid were analyzed at the final followup using thermogravimetric methods and scanning electron microscopy. Survivorship was ascertained using the Kaplan-Meier calculator. A sample size calculation determined that to detect a difference in the Knee Society knee score of 5 points, assuming a SD of 5 points, with an α = 0.05 and β = 0.80, a total of 90 patients would be needed in each group.

RESULTS

At the most recent followup, the mean Knee Society knee scores (92 versus 93 points; p = 0.857), function scores (85 versus 85 points; p = 1.000), WOMAC scores (23 versus 23 points; p = 1.000), UCLA activity scores (6.5 versus 6.5 points; p = 1.000), and range of knee motion (125° versus 127°; p = 0.365) were not different between the two groups. There was no radiographic evidence of loosening and no osteolysis visible on CT scan in either group. The weight of polyethylene wear particles produced at the bearing surface was 0.046 ± 0.010 g in 1 g of synovial fluid in patients with an OxZr femoral component and 0.0448 ± 0.0108 g in patients with a CoCr femoral component (p = 0.583). Kaplan-Meier survivorship free from revision was 97% for the OxZr group (95% confidence interval [CI], 93-100) and 98% for the CoCr group (95% CI, 93-100) at 13 years after surgery (p = 0.918).

CONCLUSIONS

Given the absence of demonstrated superiority of either the CoCr implant or the OxZr implant, we recommend that surgeons and healthcare systems can reasonably choose the less expensive device for routine use, unless there is some compelling reason in an individual patient to choose one over the other (such as severe, documented metal sensitivity).

LEVEL OF EVIDENCE

Level I, therapeutic study.

Sequentially annealed highly cross-linked polyethylene reduced in vivo wear particle generation in total knee arthroplasty

INTRODUCTION

Sequentially annealed highly cross-linked polyethylene (HXLPE) was recently introduced to reduce the wear in total knee arthroplasty (TKA). However, an in vivo advantage of sequentially annealed HXLPE on wear particle generation is still controversial. The purpose of this study is to compare the characteristics of in vivo wear particles between sequentially annealed HXLPE and conventional polyethylene after TKA.

MATERIALS AND METHODS

Synovial fluid was obtained from the eight knees with sequentially annealed HXLPE and from eight knees with conventional polyethylene 12 months after the operation. Polyethylene particles were isolated and examined using a scanning electron microscope and image analyzer.

RESULTS

Total number of wear particles in each knee was 2.1 ± 1.0 × 10⁷ with sequentially annealed HXLPE (mean ± standard deviation) and 4.9 ± 3.6 × 10⁷ with conventional polyethylene ( p = 0.036). Particle size (equivalent circle diameter) was 1.01 ± 0.26 μm with sequentially annealed HXLPE and 1.02 ± 0.20 μm with conventional polyethylene ( p = 0.674). Aspect ratio was 1.33 ± 0.04 with sequentially annealed HXLPE and 1.39 ± 0.10 with conventional polyethylene ( p = 0.462).

CONCLUSIONS

The sequentially annealed HXLPE reduced the in vivo polyethylene wear particles by 58% compared with conventional polyethylene without the significant change of particle size and shape.

Comparison of in vivo polyethylene wear particles between mobile- and fixed-bearing TKA in the same patients

PURPOSE

Polyethylene wear particle generation is one of the most important factors that affects the mid- to long-term results of total knee arthroplasties (TKA). Mobile-bearing total knee prostheses were developed to reduce polyethylene wear generation. However, whether mobile-bearing prostheses actually generate fewer polyethylene wear particles than fixed-bearing prostheses remains controversial. The aim of this study was to compare, within individual patients, the in vivo polyethylene wear particles created by a newly introduced mobile-bearing prosthesis in one knee and a conventional fixed-bearing prosthesis in other knee.

METHODS

Eighteen patients receiving bilateral TKAs to treat osteoarthritis were included. The synovial fluid was obtained from 36 knees at an average of 3.5 years after the operation. The in vivo polyethylene wear particles were isolated from the synovial fluid using a previously validated method and examined using a scanning electron microscope and an image analyser.

RESULTS

The size and shape of the polyethylene wear particles from the mobile-bearing prostheses were similar to those from the conventional fixed-bearing prostheses. Although the number of wear particles from the mobile-bearing prosthesis (1.63 × 10⁷ counts/knee) appeared smaller than that from the fixed-bearing prosthesis (2.16 × 10⁷ counts/knee), the difference was not statistically significant.

CONCLUSIONS

The current in vivo study shows that no statistically significant differences were found between the polyethylene wear particles generated by a newly introduced mobile-bearing PS prosthesis and a conventional fixed-bearing PS prosthesis during the early clinical stage after implantation.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

Twelve-Year Outcomes of an Oxinium Total Knee Replacement Compared with the Same Cobalt-Chromium Design: An Analysis of 17,577 Prostheses from the Australian Orthopaedic Association National Joint Replacement Registry

BACKGROUND

Oxidized zirconium (Oxinium) was introduced as an alternative bearing surface to cobalt-chromium (CoCr) in an attempt to reduce polyethylene wear and decrease aseptic mechanical failure of total knee replacements. While noncomparative reports have been described as promising, we were aware of no short or long-term clinical studies showing the superiority of Oxinium on polyethylene as a bearing surface. Using data from a comprehensive national joint replacement registry, we compared the long-term outcomes after cruciate-retaining total knee arthroplasty (TKA) with an Oxinium femoral component and those with the same prosthetic design but with a CoCr femoral component.

METHODS

The cohorts consisted of 17,577 cemented Genesis-II cruciate-retaining total knee replacements using non-cross-linked polyethylene, which included 11,608 with CoCr femoral components and 5,969 with Oxinium femoral components. The cumulative percent revision and hazard ratio (HR) for revision risk were estimated for the cemented Genesis-II Oxinium and CoCr cruciate-retaining TKAs performed in Australia from September 1, 1999, to December 31, 2013. In addition, the revision diagnoses and the effects of age and patellar resurfacing were examined.

RESULTS

No difference in the HR for revision risk was found between the Oxinium and CoCr cohorts for any age category for all causes of revision (HR = 0.92 [95% confidence interval (CI), 0.92 to 1.29]; p = 0.329), loosening or lysis, or aseptic causes, except for loosening or lysis in the group of patients who were ≥75 years old (p = 0.033). In these patients, TKA with Oxinium femoral components had a higher rate of revision. Younger patients preferentially received Oxinium femoral components. The revision risk was not affected by patellar resurfacing or nonresurfacing. At 12 years, the cumulative percent revision was 4.8% (95% CI, 4.2% to 5.4%) for the CoCr Genesis-II prosthesis compared with 7.7% (95% CI, 6.2% to 9.5%) for the Oxinium Genesis-II prosthesis.

CONCLUSIONS

In this cohort study involving the same prosthetic design, Oxinium femoral components did not reduce revision rates for all causes, loosening or lysis, or when infection as a cause of revision was removed compared with the same CoCr femoral component across all age groups including patients who were <55 years old. The cumulative percent revision was greater for the Oxinium components than for the CoCr components.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.