Retrieval analysis of Harris-Galante I and II acetabular liners in situ for more than 10 years

Influence of Accelerated Aging on the Wear Behavior of Cross-Linked Polyethylene Liners—A Hip Simulator Study

Sequential cross-linked and annealed ultra-high-molecular-weight polyethylene (SX-PE) is known as a low-wear articulating partner, especially for total hip endoprostheses. Aging of polymeric materials, irrespective of if induced by shelf or in vivo life, can degrade their tribological and mechanical properties. However, changes in wear behavior of aged SX-PE liners have not been not quantified so far. An accelerated aging procedure, to simulate shelf and in vivo aging, was performed on thin SX-PE liners after five million load cycles using a simulator (“worn-aged”) as well as on new SX-PE liners (“new-aged”). A subsequent hip simulator test was performed with both thin SX-PE liner sets in combination with large-diameter ceramic femoral head, representing a combination known as advantageous for treatment after revision because of dislocation. Oxidation indices were measured on the liners after each step of the procedure. SX-PE liners after accelerated aging show bedding-in phases during simulator test, which was a characteristic only known from clinical investigations. Hence, the wear rates of the “new-aged” ((1.71 ± 0.49) mg/million cycles) and of the “worn-aged” ((9.32 ± 0.09) mg/million cycles) SX-PE were increased in the first period compared to new unaged SX-PE liners. Subsequently, the wear rates decreased for “new-aged” and “worn-aged” inserts to (0.44 ± 0.48) mg/million cycles and (2.72 ± 0.05) mg/million cycles, respectively. In conclusion, the results show promising effects of accelerated aging on SX-PE liners in simulator testing and for potential long-term use in clinical applications.

Average 22-Year Results of Total Hip Arthroplasty Using Harris-Galante Prosthesis in Patients under 50 Years

Background

The Harris-Galante (HG) prosthesis is a first-generation, cementless total hip arthroplasty (THA) prosthesis. Considering the recent increase in the demand for THA in young patients and their life expectancy, a study with a follow-up duration of longer than 20 years in a young population is needed. Therefore, we evaluated the long-term clinical and radiographic results after cementless THA using the HG prosthesis in patients younger than 50 years.

Methods

A total of 61 THAs performed using the HG with a minimum follow-up of 10 years were included. There were 38 men and 11 women with an average age of 46 years and the mean follow-up duration was 22 years. Clinical evaluation included modified Harris Hip Score (HHS) and radiographic analysis consisted of cup inclination, anteversion angle, component stability, osteolysis, liner wear rate, wear-through, liner dissociation, and heterotopic ossification. Complications included recurrent dislocation, periprosthetic femoral fracture, and periprosthetic joint infection. Survivorship analysis included cup and stem revision for aseptic loosening, as well as any revision.

Results

The HHS improved from 46.5 preoperatively to 81.8 postoperatively (p < 0.001). The average linear wear rate was 0.36 mm/yr. A total of 34 hips (56%) were revised: stem revision in 10 (16.4%), cup revision in 9 (14.8%), exchange limited to bearing surface in 8 (13.1%), and revision of all components in 7 (11.5%). Estimated survivorship at 34 years postoperatively was 90.9% for cup revision for aseptic loosening, 80.5% for stem revision for aseptic loosening, and 22.1% for any revision.

Conclusions

THA using the HG prosthesis showed satisfactory estimated survivorship of the acetabular and femoral components at 34 years postoperatively with good clinical outcomes. Bearing-related problems, such as osteolysis and liner dissociation, accounted for 56% of revision operations and were concerns in patients younger than 50 years.

Dissociation of Acetabular Polyethylene Liners With a Morse Taper Design

BACKGROUND

Polyethylene liner dissociation is an uncommon complication of hip replacement. Dissociation has been associated with particular acetabular component designs. This study reviewed acetabular liner dissociations in a specific modular cup with a Morse taper locking mechanism that has not been previously reported.

METHODS

The senior author performed 655 primary total hip arthroplasties with one particular design of acetabular component using Class A polyethylene liners and metal head articulation. Cases with revision surgery performed for acetabular liner dissociation were reviewed.

RESULTS

Seven of 655 patients with this cup underwent revision surgery for a dissociated liner. Liner dissociation occurred at a mean of 73 months postoperatively. Patients presented with new-onset hip pain or squeaking, 4 of which developed symptoms acutely. Two patients treated with polyethylene liner exchange into the same cup required a second revision surgery for recurrent dissociation.

CONCLUSION

Polyethylene liner dissociation is an infrequent but possible complication associated with modular acetabular components using a Morse taper locking. Providers should be vigilant with long-term follow-up of patients with this acetabular system for patient complaints of catching or squeaking. Patients treated for liner dissociation should not have a new liner placed into the same acetabular shell given the risk for further dissociation.

Efficacy of vitamin E for mechanical damage and oxidation of polyethylene rim by stem neck impingement

BACKGROUND

The aim of this study is to determine the influence of crosslinking and addition of 0.3 wt% vitamin E in a polyethylene rim on its mechanical damage and oxidation caused by impingement.

METHODS

Six ultrahigh-molecular weight polyethylene samples were studied (control; crosslinked; vitamin-E containing; crosslinked and vitamin-E containing; aged control; and aged crosslinked and vitamin-E containing). Crosslinking was attained by irradiation with a 300 kGy electron beam; vitamin E incorporation was at 0.3 wt%; and aging was performed through forced oxidation for 14 days. Resistance to impingement was evaluated by stereoscopic observations, three-dimensional measurements, and oxidation measurements by Fourier transform infrared spectroscopy.

FINDINGS

Rim breakage (delamination and fracture) due to impingement was observed only for the aged control specimen. In contrast, crosslinked specimens containing vitamin E showed no failure of the rim after aging. The addition of vitamin E to polyethylene suppressed its oxidation and reduced the oxidation caused by crosslinking or impingement. The impingement resistance of the control sample deteriorated upon oxidation, whereas that of vitamin E-containing crosslinked polyethylene remained high due to the antioxidant property of vitamin E.

INTERPRETATION

Vitamin E-containing polyethylene showed a reduced risk of wear/breakage of polyethylene rims by impingement.

Are Radiographic and Direct Measures of Acetabular Polyethylene Wear Comparable?

BACKGROUND

All polyethylene acetabular liners wear over time, and numerous methods for calculating linear wear rates exist. The objective of this study was to compare 2-dimensional wear rates between direct, micrometer measurements and the computerized, edge-detection method using Hip Analysis Suite (HAS) 8.0.4.3.

METHODS

Two groups of retrieved acetabular liners from Harris-Galante Prosthesis I and Harris-Galante Prosthesis II implants in situ for more than 10 years were evaluated. Group 1 (n = 18) contained liners with both early postoperative (<6 months) and prerevision radiographs taken within 1 month of explantation. Group 2 (n = 55) included liners with only prerevision X-rays (ie, 1 radiograph for wear assessment). Average and maximum direct linear wear was calculated from thicknesses measured at 6 consistent, well-separated locations (3 in the worn and 3 in the unworn regions) using a calibrated, digital micrometer. HAS 8.0.4.3 was used to calculate 2-dimensional wear from anteroposterior pelvic radiographs.

RESULTS

Aggregate wear rates calculated by HAS were higher than those calculated by the average of direct measurements for group 1 (P = .020) and group 2 (P < .001). However, comparing the maximum direct micrometer measurements to HAS showed no difference for either group 1 (P = .351) or group 2 (P = .451). Linear regression analysis showed a strong correlation between HAS and both average and maximum direct wear measures for both groups, though the coefficient for the direct maximum measurement comparisons were closer to one, indicating a better one-to-one correspondence between HAS and direct maximum wear.

CONCLUSION

To our knowledge, this is the first study to compare and validate 2-dimensional wear rates in polyethylene acetabular liners between direct measurements from retrieved components and a radiographic computer-assisted technique (as opposed to comparison against a phantom component). Wear rates determined by direct measurements from retrievals were consistent with computer-assisted 2-dimensional methods when comparing maximum wear measurements. In addition, a single prerevision radiograph appears to be sufficient to assess 2-dimensional in vivo wear.

Long-term retrospective study on the placement of the cementless acetabular cup and clinical outcomes in patients undergoing femoral head autografting for hip dysplasia and total hip arthroplasty

BACKGROUND

Placement of acetabular cup in the dysplastic hip is a challenging procedure. Using bulk femoral head autograft to increase the bony coverage of the cup is one of the techniques, which have been described. The impact of cup position on cup and autograft survival is a controversial issue. We aimed to determine whether the position of cementless acetabular cup used in conjunction with femoral head autograft in dysplastic hips affected the autograft-host incorporation with its final radiographic appearance and the cup survivorship into the second decade.

METHODS

Thirty-eight dysplastic hips with varying Crowe types in 31 patients (30 women and one man) were included. The mean age was 47 years (range, 29-64 years) and the mean follow-up was 20.3 years (range, 14.8-25.9 years). The initial postoperative and final radiographs were evaluated. The survival rate of the cups was analysed using Kaplan-Meier statistics and the log-rank test. Multivariate analysis was used to evaluate the effect of variables (Crowe type, radiographic initial host bone coverage over the cup and position of the cup) on survivorship.

RESULTS

The acetabular cups were positioned anatomical in 27/38 hips according to Ranawat measurement technique. Trabecular bridging at graft-host interface was seen in all cases at an average 22.1 months. Neither acetabular cup position nor initial host bone coverage over acetabular cup less than 50% had any significant effect on either cup survival or final radiographic appearance of the graft. The 20-year cup survival rate without aseptic revision was 66% (95 CI, 52%-84%). No revision was performed due to graft resorption.

CONCLUSION

Twenty-year survival rate of the cementless cup combination with femoral head autograft showed no significant differences whether it was placed at high or anatomic hip centre. The final radiographic appearance of the autograft was not affected from either the cup location or the initial radiographic horizontal host bone coverage.

Total hip arthroplasty with step-cut subtrochanteric femoral shortening osteotomy in high riding hip dislocated patients with previous femoral osteotomy

BACKGROUND

To evaluate the long-term clinical and radiological outcomes of cementless total hip arthroplasty (THA) in high riding hip dislocated patients with previous proximal femoral osteotomy.

METHODS

Twenty-one consecutive patients with a mean age forty-two years were treated with cementless THA Step-cut subtrochanteric femoral osteotomy was performed in all twenty-eight hips. Metal on polyethylene (MoP) and ceramic on ceramic (CoC) bearings were used in two different consecutive time periods. The mean follow-up time was twelve years. Harris hip score, limb length discrepancy, complications, union status of the osteotomy, survivorship of constructs were the criteria for evaluation.

RESULTS

The mean Harris hip score improved from 39.5 to 88.7 points. The mean limb length discrepancy in unilateral cases decreased from 54.5 mm to 12.3 mm. The mean amount of femoral shortening was 37 mm. The mean union time was 3.5 months and there were no delayed union and non-union. There were three cup and two femoral revisions due to osteolysis in patients who had MoP. There was only one femoral revision in patients who had CoC. The Kaplan Meier survivorship with an end point of any revision of the stem and the acetabular component was 94% (95% CI, 75%-98%) and 92% (95% CI, 74%-99%) at ten years respectively.

CONCLUSIONS

Total hip arthroplasty with subtrochanteric step-cut femoral shortening is a successful technique to improve the hip functions and reconstruct limb length discrepancy in young patients with proximal femoral deformities.

Supramacroparticulate PE in 6 different joint endoprostheses localisations: An indicator for PE damage?

In the histopathological particle algorithm polyethylene (PE) particles with maximum lengths of more than 100μm - called PE supramacroparticles - are identified exclusively for knee joint and hip prostheses. However, a definitive characterisation, detection in all joint localisations and a causal clarification of the pathogenesis are lacking. In this study a total of 175 SLIM (synovial-like interface membrane) cases with PE supramacroparticles of knee joint prostheses (n=89), hip joint prostheses (n=44), ankle joint prostheses (n=36) and prostheses in three localisations of the upper extremities (n=6) were systematically investigated. The arithmetic mean of the particle length varied greatly within the prosthesis types. This had a significant positive correlation with the prosthesis lifetime and negative correlation with the date of implantation. It can be concluded that both the lifetime and the time of implantation have an influence on the particle length. The prostheses with supramacroparticulate damage moreover showed a clearly reduced survival rate compared with other data published on the prosthesis lifetime. The material wear therefore could not be attributed solely to the usual fatigue factors. Since loosening of the prostheses, decentring of the PE components or damage to the PE inlay existed in all cases, mechanical dysloading seems to be the most probable cause of PE supramacroparticle genesis. Due to the striking length and for demarcation from PE macroparticles, the term supramacroparticulate PE is proposed for a length of more than 100μm. In the extended histopathological particle algorithm supramacroparticulate PE has been included in the macroparticles category and should be taken into account and interpreted causally in histopathological diagnostics of joint prosthesis failure.

A review of outcomes and modes of presentation following liner dissociation from Harris-Galante uncemented acetabular components

PURPOSE

Dissociation of the polyethylene liner is a known failure mechanism of the Harris Galante I and II uncemented acetabular components. The outcomes of revision surgery for this indication and the influence of time to diagnosis are not well described.

METHODS

We report a series of 29 cases revised due to this failure mechanism. The median time from primary to revision surgery was 13 years.

RESULTS

At a median of 4 years follow-up, the mean OHS was 34 (range 6-48) but results were poorer (mean 29; range 6-45) when the diagnosis and revision was delayed compared to when it was not (mean 39; range 20-48). A large proportion of our patients (n = 14) presented with sudden onset of symptoms with or without trauma. Osteolysis was common in this series but the cup was well fixed in 20/29 cases. There was macroscopic damage to the shell in all cases.

CONCLUSIONS

In our experience, prompt revision of liner dissociation optimises outcomes in this group of patients and radiology reporting alone is not sufficient to identify these cases.

Backside Wear Analysis of Retrieved Acetabular Liners with a Press-Fit Locking Mechanism in Comparison to Wear Simulation In Vitro

Backside wear due to micromotion and poor conformity between the liner and its titanium alloy shell may contribute to the high rates of retroacetabular osteolysis and consequent aseptic loosening. The purpose of our study was to understand the wear process on the backside of polyethylene liners from two acetabular cup systems, whose locking mechanism is based on a press-fit cone in combination with a rough titanium conical inner surface on the fixation area. A direct comparison between in vitro wear simulator tests (equivalent to 3 years of use) and retrieved liners (average 13.1 months in situ) was done in order to evaluate the backside wear characteristics and behavior of these systems. Similar wear scores between in vitro tested and retrieved liners were observed. The results showed that this locking mechanism did not significantly produce wear marks at the backside of the polyethylene liners due to micromotion. In all the analyzed liners, the most common wear modes observed were small scratches at the cranial fixation zone directly below the rough titanium inner surface of the shell. It was concluded that most of the wear marks were produced during the insertion and removal of the liner, rather than during its time in situ.

Failure of Polyethylene Inlays in Cementless Total Hip Arthroplasty: A Retrieval Analysis

A retrieval analysis has been performed on 50 polyethylene inlays of cementless screw ring implants (Mecring, Mecron, Berlin, Germany) to investigate the failure mechanism of this specific open cup hip arthroplasty design that has shown a high clinical failure rate. Design-specific damage modes like rim creep, collar fatigue, and backside wear were assessed. Furthermore, the inlays were measured using a CMM to determine deformation. In 90% backside wear was observed and collar fatigue occurred in 68% of the cases. Rim creep was present in 38% of the polyethylene inlays. In 90% of the cases the cup opening diameter was 32.1 mm or less and 46% had a diameter less than 32 mm. It seems that creep and deformation of the polyethylene leads to a reduced diameter at the cup opening and consequently decreased clearance. To avoid this type of failure, polyethylene inlays should be supported at the back by the cup to reduce the risk of ongoing creep deformation.

How Does Wear Rate Compare in Well-functioning Total Hip and Knee Replacements? A Postmortem Polyethylene Liner Study

BACKGROUND

The longevity of total hip (THR) and knee replacements (TKR) that used historical bearing materials of gamma-in-air sterilized UHMWPE was affected more by osteolysis in THRs than in TKRs, although osteolysis remains a concern in TKRs. Therefore, the study of polyethylene wear is still of interest for the knee, particularly because few studies have investigated volumetric material loss in tibial knee inserts. For this study, a unique collection of autopsy-retrieved TKR and THR components that were well-functioning at the time of retrieval was used to compare volumetric wear differences between hip and knee polyethylene components made from identical material.

QUESTIONS/PURPOSES

The following questions were addressed: (1) How much did the hip liners wear and what wear patterns did they exhibit? (2) How much did the knee inserts wear and what wear patterns did they exhibit? (3) What is the ratio between TKR and THR wear after controlling for implantation time and patient age?

METHODS

We compared 23 THR components (Harris-Galante [HG] and HG II) and 20 TKR components (Miller-Galante [MG II]) that were retrieved postmortem. The components were made from the same polyethylene formulation and with similar manufacturing and sterilization (gamma-in-air) processes. Twenty-one patients (12 males, nine females) had THRs and 16 (four males, 12 females) had TKRs. Patients who had TKRs had an older (p = 0.001) average age than patients who had THRs (age, 75 years; SD, 10, versus 66 years; SD, 12, respectively). Only well-functioning components were included in this study. Therefore, implants retrieved postmortem from physically active patients and implanted for at least 2 years were considered. In addition, only normally wearing TKR components were considered, ie, those with fatigue wear (delamination) were excluded. The wear volume of each component was measured using metrology. For the tibial inserts an autonomous mathematic reconstruction method was used for quantification.

RESULTS

The acetabular liners of the THR group had a wear rate of 38 mm(3) per year (95% CI, 29-47 mm(3)/year). Excluding patients with low-activity, the wear rate was 47 mm(3) per year (95% CI, 37-56 mm(3)/year). The wear rate of normally wearing tibial inserts was 17 mm(3) per year (95% CI, -6 to 40 mm(3)/year). After controlling for the relevant confounding variable of age, we found a TKR/THR wear rate ratio of 0.5 (95% CI, 0.29-0.77) at 70 years of age with a slightly increasing difference with increasing age.

CONCLUSIONS

Excluding delamination, TKRs exhibited lower articular wear rates than THRs for historical polyethylene in these two unique cohorts of postmortem retrievals.

CLINICAL RELEVANCE

The lower TKR wear rate is in line with the lower incidence of osteolysis in TKRs compared with THRs.

Thin-Walled Cross-Linked Acetabular Liners Need Not Exhibit Reduced Locking Strength

Use of larger diameter femoral heads has emerged as a promising strategy to reduce the risk of dislocation after total hip arthroplasty, but thinning the walls of cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) acetabular liners to accommodate these larger heads may compromise the locking mechanism of the liner. The purpose of this study was to test the mechanical integrity of the locking mechanism in cross-linked and re-melted UHMWPE acetabular components with reduced wall thickness. The locking mechanism of cross-linked (100 kGy/re-melted) acetabular liners in sizes 50/28, 50/36, and 52/36 mm of 1 design was evaluated by lever-out tests and torsion tests. Torsion tests were performed at 2 angles to isolate the liner's locking tabs independent of the contribution of its central post. Lever-out testing demonstrated nominally reduced failure strength in 50/36-mm liners (13.3 N · m) compared with 50/28-mm liners (12.3 N · m; P=.0502), whereas the lever-out strength of 52/36-mm liners was 12.2±0.94 N · m. Failure torques were similar between 50/28- and 50/36-mm liners at 45° and 90°, but the failure torque of size 52/36-mm liners was significantly higher at each angle. The use of larger diameter femoral heads does not compromise the locking mechanism of thinned MicroSeal (Signal Medical Corp, Marysville, Michigan) acetabular liners. Use of a cross-linked UHMWPE acetabular liner, with a locking mechanism that is not compromised when the liner is thinned to a thickness of at least 2.86 mm, appears to be a biomechanically sound construct when articulated with large diameter femoral heads.

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.