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PDF Total Hip Arthroplasty: Wear Behaviour of Different Articulations

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The characteristic surfaces seen in the three-dimensional topographic images of Figure 4 are a result of the manufacturing methods of each polyethylene design. The repeating peak and valley topography in Figure 4 is indicative of the machining marks, which occur during the machining portion of liner formation. The compression molded topographic image in comparison lacks the large surface wave ranges and is flatter owing to the forming process.

The micron-level surface differences between each polyethylene cause a higher surface roughness average Ra in the machined polyethylene. The representative images show an Ra of 1. Despite the SEM and surface profile findings noted, the gross inspection of each retrieval specimen showed no visible signs of delamination, pitting, scratches, or cracking. In summary, the implant design using GUR bar stock, sterilized in ETO, with final articular surface geometry machined had significantly more linear wear and radiographic osteolysis.

The implant using GUR stock powder, compression-molded into final surface geometry without machining, and sterilized in inert gamma irradiation showed significantly less radiographic measured wear and osteolysis. It is beyond the scope of this paper to conjecture which of the differing elements is responsible for the greater linear wear rate in one implant versus the other. PE wear rates have been shown to predict osteolysis, implant longevity, and revision surgery, and it is routine practice to monitor all implants for wear and signs of failure.

Most current THA implants are using highly cross-linked PE because of more favorable reported wear rates. However, there are a large number of hip arthroplasty implants using conventional PE that were implanted before highly cross-linked PE was available. Cross-linked PE has also been slow to move into wide-scale implementation on a global scale due to its high cost and low availability outside of the United States.

Thus, understanding the fundamental core materials and the manufacturing process for conventional PE implants and having comparative clinical reviews as described here suggest that it may be prudent to monitor some implants more closely than others for polyethylene wear-related signs of problems. Advances in Orthopedics. Indexed in Web of Science.

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Table of Contents Alerts. Thomas B. DesJardins 3. Abstract Multiple factors have been identified as contributing to polyethylene wear and debris generation of the acetabular lining. Introduction Ultra high molecular weight polyethylene UHMWPE is currently the most widely used polymer for joint replacement prosthesis. Materials and Methods Institutional Review Board approval was granted for this study.

Table 1: Patient demographical information for the different manufactured polyethylene groups with different material pairings. Table 2: Comparison of the characteristics of the acetabular polyethylene. Figure 1: a The machined polyethylene acetabular cup retrieved at 5. A photomicrograph of the nonarticulating surface of the retrieved conventional UHMWPE machined liner b 40x and c 95x backscattered Topographical mode. Figure 2: a The retrieved compression-molded polyethylene acetabular cup retrieved at 7. A photomicrograph of the non-articulating surface of the retrieved UHMWPE compression molded b 40x and c 95x backscattered topographical mode.

Table 3: Incidence and polyethylene wear rates for both groups of material pairings used in this study. Table 4: Clinical results for hip scores and pain for both groups material pairings used in this study. Table 5: Radiographic findings for each acetabular liner articulating against Same CoCr bearing counterface. Table 6: Radiographic results for each acetabular liner articulating against different femoral head material. There is focal stem osteolysis and calcar erosion arrow.

There were no significant signs of osteolysis. Table 7: Reported clinical complications for the seventy-seven THR considered in this study. Figure 4: a Nonarticulating surface profile for machined polyethylene. The machining marks are represented by the peaks and valleys illustrated by the color scale. References W. Garcia-Cimbrelo and L. Eskelinen, V. Remes, I. Helenius, P. Pulkkinen, J. Nevalainen, and P. Faris, M. Ritter, A. Pierce, K. Davis, and G. Meding, M. Keaton, and K. View at Google Scholar I. Nakahara, N. Nakamura, T. Nishii, H. Miki, T. Sakai, and N.

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McKellop, F. Shen, B. Lu, P. Campbell, and R. Sutula, J. Collier, K. This may be explained by the practice of using Al 2 O 3 heads in younger more active patients. While there was not a difference in average age or range, there was a tendency for more males in the compression molded Al 2 O 3 head group. There was a trend towards younger males in the Al 2 O 3 head group compared to either group machined or compression molded with CoCr. This was not statistically different Table 1. The final variable of interest that could significantly affect polyethylene wear is the manufacturing technique.

Advances in Orthopedics

There are various types of fabrication methods that can be employed in the fabrication of polyethylene orthopedic implants. Most of the acetabular liners used today are machined from extruded bar stock or compression-molded directly from the polyethylene powder resin [ 4 ]. Machined polyethylene liners are made by first producing a polyethylene bar stock from the resin, followed by the machining process, which cuts the bar stock to a very precise size and geometry through the use of a lathe. The polyethylene bar stocks themselves are produced through a process known as ram extrusion where the polyethylene resin is simultaneously heated and pressurized within an evacuated chamber.

As the solid polyethylene forms, it is extruded through an open extrusion port within the chamber [ 22 ]. Because the extrusion process is noncontinuous, inconsistencies can be found within the solid polyethylene bar stock. These zones of polyethylene inconsistencies, or what Bankston et al. The alternate process of compression molding is a single-step process where the polyethylene resin is molded directly into the predetermined size and geometry of the acetabular insert. In addition to the maldistribution of solid-phase polyethylene within the ram extruded bar stock, surface characteristics and topography may have a significant role in polyethylene oxidation.

In the machined polyethylene insert, machine marks from the lathe creates numerous micron size grooves and shreds on the bearing surface, which are not found on the surface of the compression molded polyethylene insert. This was confirmed in the current study as shown in Figure 4. Bankston et al. The characteristic surfaces seen in the three-dimensional topographic images of Figure 4 are a result of the manufacturing methods of each polyethylene design. The repeating peak and valley topography in Figure 4 is indicative of the machining marks, which occur during the machining portion of liner formation.

The compression molded topographic image in comparison lacks the large surface wave ranges and is flatter owing to the forming process. The micron-level surface differences between each polyethylene cause a higher surface roughness average Ra in the machined polyethylene. The representative images show an Ra of 1. Despite the SEM and surface profile findings noted, the gross inspection of each retrieval specimen showed no visible signs of delamination, pitting, scratches, or cracking. In summary, the implant design using GUR bar stock, sterilized in ETO, with final articular surface geometry machined had significantly more linear wear and radiographic osteolysis.

The implant using GUR stock powder, compression-molded into final surface geometry without machining, and sterilized in inert gamma irradiation showed significantly less radiographic measured wear and osteolysis. It is beyond the scope of this paper to conjecture which of the differing elements is responsible for the greater linear wear rate in one implant versus the other.

PE wear rates have been shown to predict osteolysis, implant longevity, and revision surgery, and it is routine practice to monitor all implants for wear and signs of failure. Most current THA implants are using highly cross-linked PE because of more favorable reported wear rates. However, there are a large number of hip arthroplasty implants using conventional PE that were implanted before highly cross-linked PE was available.

Cross-linked PE has also been slow to move into wide-scale implementation on a global scale due to its high cost and low availability outside of the United States. Thus, understanding the fundamental core materials and the manufacturing process for conventional PE implants and having comparative clinical reviews as described here suggest that it may be prudent to monitor some implants more closely than others for polyethylene wear-related signs of problems.

Advances in Orthopedics.

Wear Performance of Ceramic-On-Metal Hip Bearings

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Special Issues Menu. Subscribe to Table of Contents Alerts. Table of Contents Alerts. Thomas B. DesJardins 3. Abstract Multiple factors have been identified as contributing to polyethylene wear and debris generation of the acetabular lining. Introduction Ultra high molecular weight polyethylene UHMWPE is currently the most widely used polymer for joint replacement prosthesis. Materials and Methods Institutional Review Board approval was granted for this study. Table 1: Patient demographical information for the different manufactured polyethylene groups with different material pairings.

Table 2: Comparison of the characteristics of the acetabular polyethylene. Figure 1: a The machined polyethylene acetabular cup retrieved at 5. A photomicrograph of the nonarticulating surface of the retrieved conventional UHMWPE machined liner b 40x and c 95x backscattered Topographical mode. Figure 2: a The retrieved compression-molded polyethylene acetabular cup retrieved at 7. A photomicrograph of the non-articulating surface of the retrieved UHMWPE compression molded b 40x and c 95x backscattered topographical mode.

Table 3: Incidence and polyethylene wear rates for both groups of material pairings used in this study. Table 4: Clinical results for hip scores and pain for both groups material pairings used in this study. Table 5: Radiographic findings for each acetabular liner articulating against Same CoCr bearing counterface. Table 6: Radiographic results for each acetabular liner articulating against different femoral head material. There is focal stem osteolysis and calcar erosion arrow. There were no significant signs of osteolysis.

Total Hip Arthroplasty

Table 7: Reported clinical complications for the seventy-seven THR considered in this study. Figure 4: a Nonarticulating surface profile for machined polyethylene. The machining marks are represented by the peaks and valleys illustrated by the color scale. References W.

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Garcia-Cimbrelo and L. Eskelinen, V. Remes, I. Helenius, P. Pulkkinen, J. Nevalainen, and P. Faris, M. EFORT decided that, given the wide interest in these discussions, publication of the presentations would be warmly welcomed by all fellow professionals who were unable to attend. This book is the result. It provides detailed information on currently used articulating materials and their wear performance. Clinical outcomes are discussed, and important new frontiers are carefully considered. The book will be of interest both to novices who want to learn more about the field and to experienced orthopaedic surgeons wishing to keep abreast of the latest developments.

Karl Knahr completed his medical studies at the University of Vienna in and subsequently trained as an orthopaedic surgeon at the Orthopaedic University Clinic of Vienna. He is currently a member of the editorial boards of International Orthopaedics and the Archives of Orthopaedic and Trauma Surgery and previously served as an editorial board member for the Journal of Arthroplasty.

Professor Knahr has published widely on the subjects of tribology and hip arthroplasty.