Influence of polyethylene and femoral head surface quality on wear: a retrieval study

May the surface roughness of the retrieved femoral head influence the wear behavior of the polyethylene liner?

This study was aimed at determining the surface degradation occurred on retrieved ceramic and metallic heads, as well as the influence of the head surface quality on the wear of the polyethylene counterface. To this purpose, 14 ceramic and 14 metallic femoral heads retrieved at revision surgery were examined. Scanning electron microscopic analysis provided visual evidence that some metallic heads presented crescent wear more often than the ceramic ones; the former showed a higher volumetric loss (as determined by Coordinate Measuring Machine) than the latter, but less negative Rsk values. This apparent lack of correlation between volumetric loss (i.e., wear factor) and roughness data may be explained by considering that they are two temporally variant parameters. No significant differences were observed between the Ra values of the two sets of femoral heads. The cups articulating against metal heads were characterized by higher mean wear volumes than those articulating against alumina although this difference was not statistically significant; metal heads displayed significantly higher mean wear volumes than alumina heads. The micro-Raman analysis of the cup articulated against the most worn alumina femoral head showed an orthorhombic into monoclinic phase transformation that was not observed in the cups coupled to metal heads. The obtained results showed that the surface finishing of the femoral head (in terms of Rsk values) determined the morphological changes experienced by the ultra-high-molecular-weight polyethylene crystalline phase at the molecular level. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1374-1385, 2016.

Wear testing of total hip replacements under severe conditions

Controlled wear testing of total hip replacements in hip joint simulators is a well-established and powerful method, giving an extensive prediction of the long-term clinical performance. To understand the wear behavior of a bearing and its limits under in vivo conditions, testing scenarios should be designed as physiologically as possible. Currently, the ISO standard protocol 14242 is the most common preclinical testing procedure for total hip replacements, based on a simplified gait cycle for normal walking conditions. However, in recent years, wear patterns have increasingly been observed on retrievals that cannot be replicated by the current standard. The purpose of this study is to review the severe testing conditions that enable the generation of clinically relevant wear rates and phenomena. These conditions include changes in loading and activity, third-body wear, surface topography, edge wear and the role of aging of the bearing materials.

Manufacturing conditioned roughness and wear of biomedical oxide ceramics for all-ceramic knee implants

BACKGROUND

Ceramic materials are used in a growing proportion of hip joint prostheses due to their wear resistance and biocompatibility properties. However, ceramics have not been applied successfully in total knee joint endoprostheses to date. One reason for this is that with strict surface quality requirements, there are significant challenges with regard to machining. High-toughness bioceramics can only be machined by grinding and polishing processes. The aim of this study was to develop an automated process chain for the manufacturing of an all-ceramic knee implant.

METHODS

A five-axis machining process was developed for all-ceramic implant components. These components were used in an investigation of the influence of surface conformity on wear behavior under simplified knee joint motion.

RESULTS

The implant components showed considerably reduced wear compared to conventional material combinations. Contact area resulting from a variety of component surface shapes, with a variety of levels of surface conformity, greatly influenced wear rate.

CONCLUSIONS

It is possible to realize an all-ceramic knee endoprosthesis device, with a precise and affordable manufacturing process. The shape accuracy of the component surfaces, as specified by the design and achieved during the manufacturing process, has a substantial influence on the wear behavior of the prosthesis. This result, if corroborated by results with a greater sample size, is likely to influence the design parameters of such devices.

Radiographic and retrieval wear analyses of the first generation highly cross-linked polyethylene cup against a ceramic femoral head

In this study, the in vivo wear of highly cross-linked polyethylene (CLPE) cups against alumina ceramic femoral heads was evaluated by radiographic and retrieval analysis. The radiographic wear of six ethylene oxide gas-sterilized (i.e., non-cross-linked) conventional polyethylene (PE) cups with the mean follow-up of 20.9 years and 60 CLPE cups with the mean follow-up of 7.4 years was measured. The retrieved 16 PE cups with clinical use for mean 21.5 years and 10 CLPE cups with clinical use for mean 2.9 years was evaluated as a retrieval analysis. In the radiographic analysis, the linear wear of CLPE cups was significantly lower (99% reduction) compared to conventional polyethylene cups. The results of retrieval analyses for both cups were similar to those of radiographic analyses. Even when third-body wear occurred during clinical use, no surface damage was observed on the surface of ceramic femoral heads. The surface is not sensitive to third-body wear, and hence, the ceramic femoral head has a great advantage in terms of the wear of CLPE under third-body wear conditions. In conclusion, CLPE cups used with alumina ceramic femoral heads in total hip arthroplasty should have favorable wear resistance in several in vivo situations.

Comparison of surface characteristics of retrieved cobalt-chromium femoral heads with and without ion implantation

Nitrogen ion implantation of CoCr is reported to produce increased surface hardness and a lower friction surface. Femoral heads with and without ion implantation retrieved from 1997 to 2003 were evaluated for surface roughness (average surface roughness [Ra], mean peak height [Rpm], and maximum distance from peak to valley [Rmax]), nanohardness, and the ion-treated layer thickness. The difference in average Rmax (P = .033) and average Rpm (P = .008) was statistically significant, but there was no correlation between the average or maximum roughness parameters (average surface roughness, Rmax, and Rpm) and time in vivo (P > .05). Overall, nanohardness was greater for the low-friction ion-treated heads (P < .001); and it decreased with increasing time in vivo (P = .01). Ion treatment produces an increased surface hardness, but the advantage of this increased hardness appears to dissipate over time in vivo.

Alumina-on-Polyethylene Bearing Surfaces in Total Hip Arthroplasty

The long-term durability of polyethylene lining total hip arthroplasty (THA) mainly depends on periprosthetic osteolysis due to wear particles, especially in young active patients. In hip simulator study, reports revealed significant wear reduction of the alumina ceramic-on-polyethylene articulation of THA compared with metal-on-polyethylene bearing surfaces. However, medium to long-term clinical studies of THA using the alumina ceramic-on-polyethylene are few and the reported wear rate of this articulation is variable. We reviewed the advantages and disadvantages of ceramicon- polyethylene articulation in THA, hip simulator study and retrieval study for polyethylene wear, in vivo clinical results of THA using alumina ceramic-on-polyethylene bearing surfaces in the literature, and new trial alumina ceramic-onhighly cross linked polyethylene bearing surfaces.

In vivo femoral head damage and its effect on polyethylene wear

The purposes of this study were to determine the spectrum of femoral head damage in patients undergoing revision total hip arthroplasty and to determine the impact of that damage on polyethylene wear. One hundred eight consecutive modular metal femoral heads were retrieved at revision surgery. The mean roughness (Ra) value was 0.18 +/- 0.18 microm. The roughest femoral heads (mean Ra, 0.56 microm) were from retrievals correlated with mode 2 wear (recurrent dislocation and complete wear through of the polyethylene liner). Five million cycles of wear tests were performed using retrieved femoral heads against both new conventional and highly cross-linked polyethylene. The mean wear rate of conventional polyethylene was 15.9 +/- 4.3 mg and that of highly cross-linked polyethylene was 0.04 +/- 0.14 mg per 1 million cycles (P < .001). Highly cross-linked polyethylene was more resistant to wear than conventional polyethylene, even when mated against roughened femoral heads.

Complete polyethylene wear-through and secondary breakage of the expansion cup in a ceramic-polyethylene total hip

INTRODUCTION

Catastrophic polyethylene failure is an uncommon complication of ceramic-on-polyethylene total hip arthroplasty (THA) because of the favourable tribological characteristics of these implants. We present a case of a 50-year-old woman who formerly underwent bilateral ceramic-on-polyethylene THA with expansion acetabular cups and eleven years later presented with unilateral THA dislocation, secondary to catastrophic polyethylene failure and metal shell fracture.

CASE PRESENTATION

The patient came to our hospital for worsening pain in her left hip and an acute incapacity to bear weight on her left lower limb. Twelve and eleven years earlier she had undergone bilateral ceramic-on-polyethylene THA with acetabular expansion components of identical size on both sides. Radiographically, the left femoral head appeared superiorly dislocated and severe polyethylene wear was detected. The inclination angles of the left and right cups were 60° and 44°, respectively. The patient underwent left acetabular revision, and complete polyethylene wear-through with fracture of a cranial lobe of the expansion metal shell was noted at surgery. One large osteolytic lesion in the roof of the acetabulum and diffuse periarticular metallosis were also present. These findings required the use of a Burch–Schneider reinforcement cage. Two years later the patient is functioning well and has full autonomy in her activities of daily living.

CONCLUSION

The correct inclination of the acetabular component is necessary to prevent accelerated polyethylene wear in THA, even though favourable articular bearing surfaces have been used (e.g., ceramic-on-polyethylene coupling). Should the cup appear well fixed and fairly oriented on follow-up radiographies, the early detection of severe polyethylene wear may permit a revision of only the femoral head and acetabular liner.

Effect of head surface roughness and sterilization on wear of UHMWPE acetabular cups

The impact of femoral head surface roughness on wear of gamma-irradiation sterilized (3 MRad in nitrogen, crosslinked) and nonsterilized (not crosslinked) UHMWPE acetabular cups has been evaluated. Gravimetric wear testing was performed in a hip joint simulator for 2 x 10(6) cycles. CoCrMo heads were used with different surface roughness (R(a) = 15 nm and R(a) = 400 nm). The surface roughness after wear test was unchanged for the roughened heads, whereas the initially smooth heads showed a few scratches. The roughened heads increased the wear of the acetabular cups 2-fold. The gamma-irradiated cups tested against rough heads underwent the highest wear. The absorption of water was highest for the gamma-irradiated cups (0.0204% compared to 0.0031% after 85 days). Raman spectroscopy showed small but significant crystallinity changes in the wear zone, where the gamma-irradiated cups with the most extensive abrasion increased in crystallinity, whereas the nonsterilized cups underwent a crystallinity decrease.

[Should monobloc cemented stems be systematically revised during revision total hip arthroplasty? A prospective evaluation]

PURPOSE OF THE STUDY

The main reason for revision of Charnley type total hip arthroplasty is socket loosening related to high polyethylene wear and periacetabular osteolysis. In these situations, the monobloc cemented stem is frequently not loosened and it is not clear whether the femoral component can be retained during the revision procedure. The aim of this study was to evaluate surface and sphericity damage to the femoral head of a prospective and consecutive series of revision total hip arthroplasties during which the cemented monobloc femoral component has been systematically revised.

MATERIALS AND METHODS

We performed 22 revisions of both components of Charnley type cemented total hip arthroplasties. In all cases, the 22.2 mm head of the monobloc femoral component was made of 316 L stainless steel. The international standard for such femoral heads includes an average surface roughness (Ra) of 0.05 microm, a total roughness (Rt) value of 0.5 microm and a sphericity of +/-5 microm. The mean age of the patients at the time of the index arthroplasty was 51.3 years. The average time to revision was 14.8 years (seven to 25 years). The reasons for revision included isolated socket loosening (12), extensive periacetabular osteolysis without socket loosening (two), recurrent dislocation associated with socket loosening (one), sepsis without implant loosening (one), loosening of both components (one), and isolated loosening of the femoral component (five). Hence, 15 of the 22 (68.2%) femoral components could theoretically have been retained. The surface roughness of the femoral heads was evaluated using a contact-type profilometer. For each head, the apex and two zones, either macroscopically scratched or with loss of the mirror finish, were analyzed. Moreover, the sphericity of the heads was measured using a spherometer.

RESULTS

The stem explanted after recurrent dislocation was analyzed separately as the femoral head had major scratches. The mean Ra and Rt of the series at the apex was 0.029 and 0.876 microm, respectively. The mean Ra and Rt of the series for the macroscopically damaged areas was 0.05 microm and 1.540 microm, respectively. The mean sphericity of the series was 7.2 microm. Hence among the 22 explanted stems, 10 femoral heads (45.4%) had Ra or Rt apex and 18 (81.8%) Ra or Rt scratched area values beyond ISO standards, respectively. Sphericity was greater than +/-5mm for 13 of the 22 femoral heads (59.1%). With the numbers available, the age at the time of the index arthroplasty, the BMI, the time and the reason for revision were not significantly associated with the degree of femoral head damage for both roughness and sphericity parameters.

DISCUSSION

Retaining the femoral component during revision of the total hip arthroplasty including a monobloc femoral component is theoretically an interesting alternative. However, femoral head surface damage occurring in vivo would have lead us to retain severely scratched heads in over 80% of the hips, and heads with abnormal roughness and sphericity values in over 90% of the hips. Bases upon our results, we recommend systematically revising the femoral component during revision THA including a monobloc stem, irrespective of the reason for revision.

Catastrophic failure of a modular revision total hip polyethylene insert

Early catastrophic failure of a modular polyethylene component is a potential problem after revision total hip arthroplasty. We describe an unusual case of polyethylene failure that occurred within 18 months of implantation in which no obvious technical error or mechanical failure was identified. The acetabular polyethylene insert was prepared with gas plasma sterilization, and the shelf life was 4 months. Radiographic evaluation used generalized Hough transforms to assess the cup articulation. We identified cup penetration of 2.8 mm before revision and catastrophic destruction of the polyethylene liner at the time of revision. Possible factors implicated for failure included a thin polyethylene liner, increased hip separation, femoral head mismatch, and the high activity level of a younger patient. We believe that this case report highlights the need for future investigations of these subtle factors.

Three-dimensional laser micrometry characterization of surface wear in total hip arthroplasty

Even after decades of clinical use, our ability to quantify wear across total hip replacement implant surfaces is largely limited to single value measurements. The influence of patient factors on wear remains enigmatic. This pilot study for the development of three-dimensional laser micrometry (3DLM) introduces an easy, accurate means of 'mapping' and quantifying material removal. A three-dimensional laser micrometer was constructed using a laser micrometer having an accuracy of 0.5 microm. A 3D surface map is triangulated from a point cloud consisting of approximately 140,000 individual points. Comparison to a reference sphere determines radial wear over the entire surface. 3DLM was able to map and quantify fine scale surface features. Even for zirconia on relatively soft ultra-high molecular weight polyethylene, this technique maps the contributions of localized wear at the macroscopic level. The 0.5 microm (or greater) accuracy of these lasers allows us to image surfaces with a high degree of confidence. This analysis lends itself well to automation, and we anticipate that this advance will prove valuable in establishing that each head and cup combination emerging from a given clinical environment has unique wear patterns as observed in this trial data set.

The predictive Power of Surface Profile Parameters on the Amount of Wear Measured In Vitro on Metal-On-Polyethylene Artificial Hip Joints

Various studies report a weak correlation between the average surface roughness Ra of metallic ballheads and the observed wear rate of the polyethylene cups coupled to them. The aim of this study is to verify, with controlled in vitro experiments, whether other parameters such as the total roughness Rt, and the skewness Rsk are better predictors of the polyethylene wear when the metallic heads present a surface conditioning that varies substantially from specimen to specimen, as is usually the case with retrieved specimens. Twelve CoCrMo (cobalt-chromium-molybdenum) ballheads were intentionally damaged in order to reproduce a wide spectrum of surface conditioning and were then subjected to the standard wear test against polyethylene cups, using a hip joint wear simulator. After 2 × 106 cycles the weight lost by the cups was assessed with a gravimetric procedure, and the surface roughness of the metallic ballheads was qualified in terms of Ra, Rt, and Rsk. The various parameters were correlated to the weight loss using a linear regression analysis. The skewness Rsk showed a coefficient linear regression R2 = 0.80, while the average roughness Ra, used in most previous studies, presented an R2 = 0.56. It was concluded that when specimens with substantially different surface conditioning are compared, as in retrievals analysis, it is also important to report the skewness Rsk so that qualify the surface roughness of the specimens can be qualified.

Analysis of survivorship after total hip arthroplasty using a ceramic head

To determine the clinical efficacy of an alumina ceramic head, 119 cemented total hip arthroplasties in 97 patients using an alumina head coupled with ethylene oxide gas sterilized polyethylene were reviewed. Eighty-two patients (101 hips) with greater than 10 years followup were evaluated clinically and radiographically (range, 10-17.6 years), and 97 patients (119 hips) were evaluated for survivorship analysis (range, 0.6-17.6 years). The average functional hip scores according to Merle d'Aubigné and Postel improved from 8.6 preoperatively to 15.0 at the final followup, and 57 patients (64 hips) had no pain. The average polyethylene wear rate was 0.15 mm/year (range, 0.04-0.34 mm/year). Patients with polyethylene wear greater than 3 mm showed significantly higher rates of acetabular loosening. Fifteen-year survival rates (with 95% confidence intervals) with radiographic evidence of aseptic loosening as the end point were 46.8% +/- 13.4% in acetabular components and 91.9% +/- 6.6% in femoral components. Fifteen-year survival rates of hip arthroplasties with revision because of aseptic loosening as the end point were 75.3% +/- 10.2% and 97.9% +/- 3.0%, respectively. Results of the current study suggest that using an alumina head instead of a metal head may not be beneficial when coupled with ethylene oxide gas sterilized polyethylene.