Surface Damage Is Not Reduced With Highly Crosslinked Polyethylene Tibial Inserts at Short-term

Abstract

Background Highly crosslinked ultrahigh-molecularweight polyethylene (XLPE) has been shown to reduce wear in hip arthroplasty, but the advantages over conventional polyethylene (PE) in total knee arthroplasty (TKA), if any, remain unclear. Questions/purposes Do differences exist in (1) surface damage as measured by damage score and percent area affected; and (2) extent and location of dimensional changes between XLPE and conventional PE observed on retrieved TKA tibial inserts?Methods In this study of components retrieved at the time of revision surgery, we matched 44 XLPE to 44 conventional PE inserts from four manufacturers; the matching approach considered implant design (exact match), insert size (exact match), and length of implantation (matched ± 6 months). Surface damage on the articular surfaces was subjectively graded and digitally mapped to determine the percent damaged area of each damage mode. Three-dimensional changes that had occurred as a result of implantation were determined by comparing laser scans of the retrieved inserts with size-matched pristine inserts. Results The differences of damage scores and percent damaged areas between the matched XLPE and conventional PE inserts were not large enough to be clinically significant with low corresponding levels of statistical significance (scores: 42 ± 13; 95% confidence interval [CI], 38-46 versus 45 ± 13; 95% CI, 41-49; p = 0.4; percent areas: 54% ± 38%; 95% CI, 44%-64% versus 54% ± 32%; 95% CI, 42%-65%; p = 0.9). However, XLPE inserts showed greater articular surface dimensional changes with high significance (root mean square of the distance: 0.16 ± 0.06 mm; 95% CI, 0.13-0.18 mm versus 0.14 ± 0.05 mm; 95% CI, 0.11-0.16 mm; p = 0.03). Within the same design, deviation patterns were consistent between the two materials; however, as expected, the location of the dimensional changes differed among designs: the negative deviations on the plateaus were centrally located in Zimmer PS inserts, were located on the perimeter in Smith & Nephew PS inserts, and were across the entire surface in DePuy PS inserts.

Less Midterm Damage and Oxidation Are Seen in Retrieved Highly Crosslinked Ultrahigh-Molecular-Weight Polyethylene Tibial Inserts than in Direct Compression Molded Polyethylene Inserts

“…Peak oxidation index greater than 1 leads to variability in mechanical properties. XLPE highly crosslinked ultrahigh-molecular-weight polyethylene, compPE compression-molded polyethylene previously reported; however, the same trend was found as in the shorter-term retrieved inserts-namely, the largest reduction in crosslink density occurred at the loaded surface region [15]. Decreased crosslink density with implantation time has been postulated to be caused either by mechanical means with tensile stresses near the surface reaching sufficient magnitudes to break crosslinks between the polyethylene chains or by chemical means through the absorption of lipids into the polyethylene, which could also be greater in highly stressed regions of the material [18].…”

“…Furthermore, concern exists that XLPE may be associated with increased oxidation, reduced mechanical strength, decreased yield strength, and decreased toughness. These drawbacks are of particular concern in posterior-stabilized designs, given the risk of fracture of the polyethylene tibial post [4,8,12,14,15,17].…”

Crosslink Density Is Reduced and Oxidation Is Increased in Retrieved Highly Crosslinked Polyethylene TKA Tibial Inserts

“…The regions on which they were present were manually replicated onto the digital images using Photoshop CS2 software (Adobe Systems, San Jose, CA, USA) to quantify the area of damage for each mode on both medial and lateral plateaus. This damage mapping technique has been described in more detail elsewhere [10,24]. Burnishing was the most prevalent damage mode on the PE articular surface and was considered the in vivo-loaded contact area with the surface of the metallic femoral component while the insert had been implanted in the patient.…”

“…In contrast, clinical reports with mid-term followup such as those from the Kaiser Implant Registry [18] demonstrated no benefits or differences in revision surgery rates between TKAs with crosslinked PE versus conventional polyethylene inserts [19,20,28]. In a recent shortterm implant retrieval study comparing retrieved crosslinked PE and conventional polyethylene TKA inserts, Liu et al found no difference in polyethylene surface damage between the two materials [24]. However, surface damage does not preclude the possibility that a difference in wear and creep might still exist [34].…”

Comparison of two different on-shelf femoral stems for Crowe type IV developmental dysplasia of the hip

“…10 These findings might explain the difficulties encountered by surgeons. A modified 3D comparison method developed in a previous prosthetic evaluation study by our group 31 was applied for comparisons between the femoral stems and the medullary canal models. Advantages of such a method are the ability to obtain quantitative results and use color maps during visualization.…”