Ultra-low wear rates for rigid-on-rigid bearings in total hip replacements

Concomitant evolution of wear and squeaking in dual-severity, lubricated wear testing of ceramic-on-ceramic hip prostheses

Ceramic-on-ceramic (CoC) hip bearings were tested in short-term wear tests with a systematically varied contact force. Continuous vibration and intermittent surface roughness measurements were obtained to elucidate potential causes of in vivo hip joint squeaking. The three-phase test comprised alternating cycles of edge loading (EL) and concentric articulation (CA), always using ample serum lubricant. A 50,000-cycle wear trial in which the contact force during CA was distant from the head's wear patch yielded no squeaking and practically no liner roughening. In 10-cycle trials of an edge-worn head coupled with a pristine liner, the contact force was varied in magnitude and point of application; immediate, recurrent squeaking occurred only when the contact force exceeded a critical threshold value and was centered upon the head's wear patch. In a 27,000-cycle wear trial with the contact force applied near the margin of the head's wear patch, recurrent squeaking emerged progressively as the liner's inner surface was roughened via its articulation with the worn portion of the head. The results reveal key conditions that yield recurrent squeaking in vitro in various scenarios without resorting to implausible dry conditions. A fundamental theory explains that hip squeaking is induced by myriad stress waves emanating from asperity collisions; yet, the root cause is edge loading.

Metal-on-metal total hip arthroplasty: causes and high incidence of early failure

Early failures of metal-on-metal total hip arthroplasty (THA) occur due to aseptic loosening, metal hypersensitivity reactions, pseudotumor formation, and component seizing. The purpose of this study was to investigate the timing, common modes of failure, clinical outcomes, and incidence of metal-on-metal THA revisions. A review was performed of 80 patients who underwent revision of a failed metal-on-metal THA for any reason. The most common reason for metal-on-metal failure was aseptic acetabular loosening, with a rate of 56.25% (45/80 patients). Early failure of metal-on-metal THAs was noted, with 78% of these revisions being performed within 2 years of the index operation and 92.5% within 3 years. Furthermore, 13% of patients experienced significant localized soft tissue reactions. Mean preoperative Harris Hip Score was 42.35 ± 14.24 and mean postoperative Harris Hip Score was 66.5 ± 23.2 (range, 9.55-95.4), with an average follow-up of 438 ± 492 days (range, 40-2141), or 1.2 years.It is imperative that clinicians be cognizant of the fact that the proposed advantages of metal-on-metal THA are not without potential detrimental sequelae. This article proposes an algorithm to aid in diagnosing the etiology of a painful metal-on-metal THA, as well as 2 classification schemes regarding metal-on-metal THA complications to help direct treatment.

Causes of failure of ceramic-on-ceramic and metal-on-metal hip arthroplasties

BACKGROUND

Few large series of hard bearing surfaces have reported on reasons for early failure. A number of unique mechanisms of failure, including fracture, squeaking, and adverse tissue reactions, have been reported with these hard bearing surfaces. However, the incidence varies among the published studies.

QUESTIONS/PURPOSES

To confirm the incidences, we identified the etiologies of early failures of hard-on-hard bearing surfaces for ceramic-on-ceramic and metal-on-metal THAs.

METHODS

We retrospectively reviewed records of 2907 THAs with hard-on-hard bearing surfaces implanted between 1996 and 2009; 1697 (58%) had ceramic-on-ceramic and 1210 (42%) had metal-on-metal bearing surfaces. We recorded bearing-related complications and compared them to nonspecific reasons for revision THA. The minimum followup of the ceramic-on-ceramic and metal-on-metal cohorts was 6 months (mean, 48 months; range, 6-97 months) and 24 months (mean, 60 months; range, 24-178 months), respectively.

RESULTS

The overall revision rate for ceramic-on-ceramic THA was 2.2% (38 of 1697), with aseptic loosening accounting for 55% of revisions (femur or acetabulum). The bearing accounted for 13% of the revisions in the ceramic-on-ceramic THA cohort. The overall metal-on-metal revision rate was 5.4% (65 of 1210), 17 involving adverse tissue reactions related to the metal-on-metal bearing surface (17 of 1210, 1.4% of cases; 17 of 65, 26% of revisions).

CONCLUSIONS

Twenty-six percent of the revisions from metal-on-metal and 13% of ceramic-on ceramic were bearing related. The overall short- to medium-term revision rate was 2.2% and 5.4% for ceramic-on-ceramic and metal-on-metal, respectively. The most common etiology of failure was loosening of the femoral or acetabular components.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of level of evidence.

Cushion bearings versus large diameter head metal-on-metal bearings in total hip arthroplasty: a short-term metal ion study

INTRODUCTION

Metal-on-metal total hip arthroplasty (MOM THA) has the advantage of replicating the femoral head size, but the postoperative elevation of serum metal ion levels is a cause for concern. Metal-on-polycarbonate-urethane is a new cushion bearing featuring a large diameter metal head coupled with a polycarbonate-urethane liner.

AIM

The aim of this study was to assess and compare serum cobalt (Co) and chromium (Cr) levels in a group of 15 patients treated with a cushion bearing THA system (Group A) and a group of 15 patients treated with a MOM THA system (Group B) at short-term. At a mean follow-up of 27.3 months (18-35 months), in Group A the median Cr and Co serum levels were significantly lower than in Group B, measuring 0.24 μg/L (0.1-2.1 μg/L) and 0.6 μg/L (0.29-2.3 μg/L) compared to 1.3 μg/L (0.1-9 μg/L, p < 0.001) and 2.9 μg/L (0.85-13.8 μg/L, p < 0.001) respectively.

RESULTS

All patients demonstrated an excellent clinical result, as shown by the Harris and Oxford hip scores. The cushion bearing THA studied in this paper showed clinical outcomes similar to the MOM THA bearing, with the advantage of no significant metal ion elevation in the serum.

CONCLUSION

These findings warrant the continued clinical study of compliant bearing options.

Comparison of surgical outcomes and implant wear between ceramic-ceramic and ceramic-polyethylene articulations in total hip arthroplasty

The results of a prospective multicenter trial comparing 357 hips randomized to total hip arthroplasty with either ceramic-ceramic or ceramic-polyethylene couplings are presented. No statistically significant difference in clinical outcomes scores between the ceramic-ceramic and ceramic-polyethylene groups was observed at any time interval. The mean linear rate was statistically lower (P < .001) in the ceramic-ceramic group (30.5 μm/year) when compared with the ceramic-polyethylene group (218.2 μm/year). The rates of ceramic implant fracture (2.6%) and audible component-related noise (3.1%) were statistically higher in the ceramic-ceramic group when compared with the ceramic-polyethylene group (P < .05). Lastly, there was no statistically significant difference in the dislocation or revision rate between the groups at the time of last clinical follow-up.

Metal-on-metal vs metal-on-improved polyethylene bearings in total hip arthroplasty

Major weaknesses of total hip arthroplasty (THA) in the 20th century were polyethylene wear and dislocation. Efforts to improve THA took several directions including improvement of polyethylene and use of metal-on-metal (MoM) articulations. Metal-on-metal articulations showed excellent early results, but concerns mount over hypersensitivity and increasing failure. This study compares our experience with MoM and metal-on-improved polyethylene (MoIP) bearings in primary THA. We identified 1362 patients undergoing 1589 MoM THA and 693 patients undergoing 779 MoIP THA (all compression molded and sterilized in argon). Overall, more MoM than MoIP cups have been revised (4.0% vs 2.2%; P = .0241). Revision incidence for infection was similar; higher with MoM for loosening (P = .0020), metal complication (P = .0017), and combined aseptic causes (P = .0067); and higher for dislocation in MoIP (P = .0246). Metal-on-improved polyethylene devices had superior results compared with MoM in this study. Furthermore, 5 MoIP revisions were liner exchanges, a conservative option not available with MoM.

Microseparation and Stripe Wear in Alumina-On-Alumina Hip Implants

The combination of materials that still has highest wear resistance for total hip replacement is ceramic-on-ceramic. However, brittleness is a major concern for ceramics: in vivo and in vitro studies on ceramic hip prostheses correlate microseparation with hip noise, ceramic wear, or ceramic liner damage. Ceramic microseparation can lead to edge load, ceramic head wear, and squeaking.

The aim of this in vitro study was to investigate whether different angles of inclination influence the wear pattern of alumina-on-alumina hip joints with micro-separation during the swing phase. We also evaluated the wear rate obtained from this in vitro investigation with retrieval specimens obtained at 13 years' mean follow-up.

The study was performed using a 12-station hip joint wear simulator (Shore Western, Monrovia, CA, USA) under bovine calf serum used as lubricant. Wear was evaluated by the gravimetric method and the test length was set at two million cycles.

After two million cycles, a volumetric loss of 0.11 ±0.03 mm3 and 0.12 ±0.06 mm3 was observed, respectively, for 23° and 63° angles of inclination. In particular, the results obtained in this work revealed an increase of about 12-fold compared to previous results without microseparation conditions. No significant differences were observed between the two different inclinations on the wear patterns of the acetabular cups with a level of significance of α = 0.5. The location and general shape of the stripes wear were similar for the retrieved and simulator balls.

Clinical experience of revision of metal on metal hip arthroplasty for aseptic lymphocyte dominated vasculitis associated lesions (ALVAL)

There has been growing concern regarding the systemic and local effects of metal ions released from metal-on-metal hip resurfacings and total hip replacements, including the development of aseptic lymphocyte dominated vasculitis associated lesions (ALVAL). We describe our experience of treating 13 patients with failed metal on metal bearing hip prostheses secondary to this condition. Hip revision occurred at mean of 45 months following primary surgery. Groin pain was present in all patients. Other common features included large bursal swelling and mechanical symptoms. 3 patients developed their symptoms immediately postoperatively. The mean time to presentation was 21 months. Radiographic abnormalities noted included 3 patients with cup loosening and 2 patients with neck thinning. The mean cup inclination was 52 degrees. Surgical findings included bursal swellings and creamy brown fluid. Osteolysis was rarely seen. 12 revisions were achieved with primary implants and all patients had immediate symptomatic improvement. One patient was left with a pseudoarthrosis due to extensive soft tissue destruction. Diagnosis of ALVAL was confirmed histologically. The diagnosis of ALVAL should be considered in patients with unexplained pain from a metal on metal bearing hip arthroplasty. Surgical findings are typical and symptoms tend to resolve reliably following conversion to an alternative bearing surface.

Wear and surface analysis of 38 mm ceramic-on-metal total hip replacements under standard and severe wear testing conditions

The purpose of this study was to compare the wear of zirconia-toughened alumina (ZTA) and alumina femoral heads tested against as-cast CoCrMo alloy acetabular cups under both standard and severe wear conditions. A new severe test, which included medio-lateral displacement of the head and rim impact upon relocation, was developed. This resulted in an area of metal transfer and an area of increased wear on the superior-anterior segment of the head that were thought to be due to dislocation and rim impact respectively. While the wear of all ceramic heads was immeasurable using the gravimetric method, the wear rates for the metallic cups from each test were readily calculated. An average steady state wear rate of 0.023 ± 0.005 mm3/106 cycles was found for the cups articulating against ZTA under standard wear conditions. A similar result had previously been obtained for the wear of cups articulated against alumina heads of the same size (within the same laboratory). Under severe wear conditions an increase in the metallic cup steady state wear rate was found with the ZTA and alumina tests giving 0.623 ± 0.252 and 1.35 ± 0.154 mm3/106 cycles respectively. Wear of the ceramic heads was detected using atomic force microscopy which showed, under severe wear conditions, a decrease in polishing marks and occasional grain removal. The surfaces of the ZTA heads tested under standard conditions were virtually unchanged from the unworn samples. Friction tests showed low friction factors for all components, pre and post wear.

Thirty years of experience with alumina-on-alumina bearings in total hip arthroplasty

Alumina-on-alumina bearings in total hip arthroplasty have been developed in an attempt to minimise debris and the occurrence of osteolytic lesions. The outstanding tribological properties of this bearing system are explained by low surface roughness, high hardness for major scratch resistance, and high wettability. Since the 1970s, technological improvements in the manufacturing process of alumina components together with a better understanding of Morse taper technology have provided a surgical grade material with high density, high purity and small grains. Published studies on the outcome of total hip arthroplasty performed with this new generation of implants showed high survivorship especially in young and active patients, with survival rates free of revision of 90.8% to 97.4% at ten years. However, concern remains over ceramic liner fracture and squeaking, which has been noted recently with increasing prevalence. This review will discuss the current knowledge on the use of alumina-on-alumina bearings.

Characterization of protein degradation in serum-based lubricants during simulation wear testing of metal-on-metal hip prostheses

A size exclusion high performance liquid chromatography (SEC-HPLC) method has been developed which is capable of separation and quantitation of bovine serum albumin (BSA) and bovine serum globulin (BSG) components of serum-based lubricant (SBL) solutions. This allowed characterization of the stability profiles of these proteins when acting as lubricants during hip wear simulation, and identification of wear-specific mechanisms of degradation. Using cobalt-chromium metal-on-metal (MOM) hip joints, it was observed that BSA remained stable for up to 3 days (215K cycles) of wear testing after which the protein degraded in a fairly linear fashion. BSG on the other hand, began to degrade immediately and in a linear fashion with a rate constant of 5% per day. Loss of both proteins occurred via the formation of high molecular weight aggregates which precipitated out of solution. No fragmentation of the polypeptide backbone of either protein was observed. Data obtained suggest that protein degradation was not due to microbial contamination, denaturation at the air-water interface, or frictional heating of articulating joint surfaces in these studies. We conclude that the primary source of protein degradation during MOM simulation testing occurs via high shear rates experienced by SBL solutions at articulating surfaces, possibly coupled with metal-protein interactions occurring as new and reactive metal surfaces are generated during wear testing. The development of this analytical methodology will allow new studies to clarify the role of SBL solutions in wear simulation studies and the interactions and lubricating properties of serum proteins with prosthetic surfaces other than MOM.

Risk of complication and revision total hip arthroplasty among Medicare patients with different bearing surfaces

BACKGROUND

To address the long-term problems of bearing surface wear and osteolysis associated with conventional metal-polyethylene (M-PE) total hip arthroplasty (THA), metal-metal (M-M), and ceramic-ceramic (C-C) bearings have been introduced. These bearing surfaces are associated with unique risks and benefits and higher costs. However the relative risks of these three bearings in an older population is unknown.

QUESTIONS/PURPOSES

We compared the short-term risk of complication and revision THA among Medicare patients having a primary THA with metal-polyethylene (M-PE), metal-metal (M-M), and ceramic-ceramic (C-C) bearings.

METHODS

We used the 2005 to 2007 100% Medicare inpatient claim files to perform a matched cohort analysis in three separate cohorts of THA patients (M-PE, M-M, and C-C) who were matched by age, gender, and US census region. Multivariate Cox proportional-hazards models were constructed to compare complication and revision THA risk among cohorts, adjusting for medical comorbidities, race, socioeconomic status, and hospital factors.

RESULTS

After adjusting for patient and hospital factors, M-M bearings were associated with a higher risk of periprosthetic joint infection (hazard ratio, 3.03; confidence interval, 1.02-9.09) when compared with C-C bearings (0.59% versus 0.32%, respectively). There were no other differences among bearing cohorts in the adjusted risk of revision THA or any other complication.

CONCLUSIONS

The risk of short-term complication (including dislocation) and revision THA were similar among appropriately matched Medicare THA patients regardless of bearing surface. Hard-on-hard THA bearings are of questionable value in Medicare patients, given the higher cost associated with their use and uncertain long-term benefits in older patients.

LEVEL OF EVIDENCE

Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Metal-on-metal total hip arthroplasty

The effects of elevated levels of metal ions in patients who have undergone metal-on-metal total hip arthroplasty are not fully understood. The effects of femoral head size on serum metal-ion levels have been the subject of conflicting reports, and further investigation is needed to evaluate the impact of acetabular and femoral component alignment. The conduct of clinical trials of metal-on-metal total hip arthroplasties has been inadequate as few investigators have used a randomized controlled design to compare metal-on-metal bearings with other bearing surfaces. Additional clinical research needs to include appropriate validated patient-reported outcome measures, activity monitoring, and health economics.

Changes in whole blood metal ion levels following resurfacing: serial measurements in a multi-centre study

Seventy-seven patients implanted with unilateral resurfacing prosthesis were recruited from four centres. Serial whole blood samples were collected and ion levels were analysed. In most cases, the ion levels stabilized by 3 months. The 24 month median ion levels were 1.49ug/l for chromium and cobalt. In approximately 50% of patients the increase in chromium and cobalt level was less than 1ug/l. There were 6 patients with abnormally high metal ion levels. Of these 4 were significant outliers, had high ion levels that became apparent between 12 and 24 months after implantation, and had a high cup abduction angle. Not all patients with high cup abduction angles demonstrated high levels. There were differences in ion levels between the four centres that correlated with variation in acetabular component placement. Variability in ion levels was seen with the same prosthesis, underscoring the importance of surgical technique, longitudinal analysis, and multi-centre trials.

The effect of stem design on the prevalence of squeaking following ceramic-on-ceramic bearing total hip arthroplasty

BACKGROUND

The ceramic-on-ceramic bearing for total hip arthroplasty has an extremely low wear rate and demonstrates minimal inflammatory response in comparison with other bearing choices. However, acoustic emissions such as squeaking and clicking are being reported as annoying complications related to its use. The cause or causes of this phenomenon have not been determined. The purpose of the present study was to evaluate the possibility that design aspects of the femoral component may be a contributing factor to the etiology of squeaking associated with the ceramic-on-ceramic bearing total hip arthroplasty.

METHODS

We retrospectively reviewed 266 consecutive patients (304 hips) who had undergone total hip arthroplasty with use of ceramic-on-ceramic bearings. The first 131 consecutive patients (152 hips) (Group 1) received a hydroxyapatite-coated stem composed of titanium-aluminum-vanadium alloy with a C-taper neck geometry and robust midsection with an anteroposterior diameter of 13 mm. The second 135 consecutive patients (152 hips) (Group 2) also received a hydroxyapatite-coated stem, but in that group the stem was composed of titanium-molybdenum-zirconium-iron alloy, with a V-40 neck geometry and a midsection with an anteroposterior thickness of only 10 mm. All 304 hips received the same cup, composed of titanium-aluminum-vanadium alloy. Demographic characteristics, such as age, sex, height, weight, and body mass index, were similar in both groups. Data regarding the presence of squeaking were obtained prospectively. Patients who were seen for clinical follow-up either expressed the squeaking phenomenon themselves or were asked about it by the physician. Patients who were not seen at a recent clinical follow-up visit were contacted by telephone and were asked specifically about squeaking that might be associated with the hip replacement. Only patients with confirmed squeaking noise were included in the present study. Postoperative radiographs, the Short Form-36 health survey, the Harris hip score, and office or telephone interviews of the patient were used to determine the overall outcome of the procedure.

RESULTS

The prevalence of squeaking was seven times higher for patients who received the titanium-molybdenum-zirconium-iron-alloy stem (twenty-seven patients, twenty-eight hips [18.4%]) than in those who received the titanium-aluminum-vanadium-alloy stem (three patients, four hips [2.6%]); this difference was significant (p < 0.0001).

CONCLUSIONS

Our study suggests that different stem alloys, stem geometries, or neck geometries can have an impact on the frequency of squeaking following a ceramic-on-ceramic total hip arthroplasty.

Is ceramic-on-ceramic squeaking phenomenon reproducible in vitro? A long-term simulator study under severe conditions

Clinical and in vitro studies on ceramic hip prostheses correlate cup implant position with hip noise, ceramic wear, or ceramic liner damage. A ceramic cup malposition could lead to edge load, ceramic head wear, and squeaking. A noise of a ceramic hip could also be correlate with implant instability and liner damage. Aim of this study was to investigate the long-term wear behavior of 12 commercial alumina-on-alumina bearings under severe conditions: different angles of inclination (23 degrees, 45 degrees, and 63 degrees) and the addition of third body particles (titanium and alumina powder) to address the effective role of cup position and ceramic particles on wear and hip noise. The study was performed using a 12-stations hip joint wear simulator (Shore Western, Monrovia) under bovine calf serum used as lubricant. Wear was evaluated by gravimetric method and the piezo-spectroscopic technique was used to evaluate the residual stress of the ceramic components and correlate this to the weight loss. After eight million cycles, we found that the inclination of the cup (63 degrees in this study) was the most disadvantaged and it was correlated with a hip noise. Gravimetric measurements showed higher wear than the other configurations and these results were in agreement with the Photoluminescence investigation. In particular, the results obtained in this work revealed a residual stress state greater not only with respect to the other angles of inclination but also to two retrieved alumina acetabular cups with a 10 years follow-up.

A review of the biologic effects of spine implant debris: Fact from fiction

BACKGROUND

Biologic-reactivity to implant-debris is the primary determinant of long-term clinical performance. The following reviews: 1) the physical aspects of spinal-implant debris and 2) the local and systemic biologic responses to implant debris.

METHODS

Methods included are: 1) gravimetric wear analysis; 2) SEM and LALLS; 3) metal-ion analysis; 4) ELISA, toxicity testing, patch testing; and 5) metal-lymphocyte transformation testing (metal-LTT).

RESULTS

Wear and corrosion of spine-implants produce particles and ions. Particles (0.01-1000 μm) are generally submicron ( <1 µm). Wear rates of metal-on-polymer and metal-on-metal disc arthroplasties are approximately 2-20 and 1 mm(3)/yr, respectively. Metal-on-metal total disc replacement components have significant increases in circulating metal (less than 10-fold that of controls at 4 ppb-Co and 3 ppb-Cr or ng/mL). Debris reactivity is local and systemic. Local inflammation is caused primarily by ingestion of debris by local macrophages, which produce pro-inflammatory cytokines TNFα, IL-1β, IL-6, and PGE2. Systemic responses associated with implant-debris have been limited to hypersensitivity reactions. Elevated amounts of in the liver, spleen, etc of patients with failed TJA have not been associated with remote toxicological or carcinogenic pathology to date. Implant debris are differentially bioreactive. Greater numbers are pro-inflammatory; the smaller-sized debris are more bioreactive by virtue of their greater numbers (dose) for a given amount of implant mass loss (one 100-μm-diameter particle is equivalent in mass to 1 million 1-μm-diameter particles). Elongated particles are pro-inflammatory (ie, aspect ratio of greater than 3). Metal particles are more proinflammatory than polymers, ceteris paribus.

CONCLUSION

Spinal arthroplasty designs have been in use for more than 20 years internationally; therefore, concerns about neuropathology, toxicity, and carcinogenicity are mitigated. Debris-induced inflammation still depends on the individual and the type of debris. The consequence of debris-induced inflammation is continued; vigilance by physicians is recommended monitoring of spinal implants using physical exams and testing of metal content and bioreactivity, as is planning for the likelihood of revision in younger individuals.

Seating of ceramic liners in the uncemented trident acetabular shell: is there really a problem?

Concerns have been raised regarding the risk of incomplete seating of metal-backed ceramic liners in the Trident acetabular system. This prompted us to audit our series of primary and revision THAs. We retrospectively reviewed 68 patients (78 arthroplasties, 55 of which were primary and 23 revisions) using the Trident acetabular system between 2003 and 2007. Anteroposterior and lateral radiographs were reviewed independently by two specialist registrars and one consultant surgeon to look for incomplete seating. Six liners were seated incompletely, representing 8% overall. All unseated liners were in the primary group, representing 10% risk in this group, compared with 0% risk in the revision group. The incidence of malseating in our primary arthroplasty group was similar to the published incidence (16.4%). We encountered no problems in patients having a revision. We suspect shell deformation contributes to malseating of the metal-backed ceramic liners. To reduce the rate of malseating, we now underream by 0.8 mm rather than the usual 1.8 mm, particularly if the bone is sclerotic.

LEVEL OF EVIDENCE

Level IV, case series. See the Guidelines for Authors for a complete description of levels of evidence.

Tribological and surface analysis of 38mm alumina–as-cast Co–Cr–Mo total hip arthroplasties

There is currently much discussion over the use of ceramic femoral components against metal acetabular cups, for use in total hip arthroplasty. The current study investigates six hot isostatically pressed alumina femoral heads of 38 mm diameter articulating against six as-cast Co—Cr—Mo metallic acetabular cups. Standard walking-cycle simulator wear testing was carried out to 5×106 cycles using the Durham Mark II hip wear simulator, and wear was determined gravimetrically. In addition, surface topography, using a non-contacting profilometer, an atomic force microscope, and an optical microscope, was monitored throughout the wear test. The wear of the ceramic heads was found to be undetectable using the current gravimetric method; however, a change in the surface topography was seen, as grain removal on the pole was observed through atomic force microscopy analysis. A biphasic wear pattern was found for the metallic cups, with low wear rates of 1.04 ± 0.293 mm3/106 cycles (mean, ±95 per cent confidence interval) and 0.0209 ± 0.004 mm3/106 cycles (mean, ±95 per cent confidence interval) for running-in and steady state wear phases respectively. Frictional measurement revealed that the joints were tending towards full fluid-film lubrication in parts of the walking cycle. The results show that the combination of hot isostatically pressed alumina and as-cast Co—Cr—Mo is a promising alternative for total hip arthroplasties.

Surface engineering: a low wearing solution for metal-on-metal hip surface replacements

Increased patient blood and serum levels of Co and Cr and dissemination of metal wear particles throughout organs and tissues are the primary concerns with metal-on-metal surface replacements. Surface engineering, providing a ceramic bearing surface on a metal substrate, could provide a solution. This study investigated thick (>10 microm) arc evaporation plasma vapor deposition chromium nitride (CrN) coated surface replacements in terms of wear, ion levels, and wear particles in a 10 million cycle hip simulator study, compared to a contemporary metal-on-metal surface replacement. The ion levels were measured by inductively coupled plasma mass spectroscopy. The wear particles were imaged by field emission gun scanning electron microscopy. The CrN-coated bearings had 80% lower wear than the MoM controls. The Cr and Co ion levels in the lubricant of the CrN bearings were 73 and 98% lower than in the MoM controls. The wear particles produced were in the nanometer size range and round to oval in morphology. The CrN coating could provide a reduction in the wear and ion release of MoM surface replacements, thereby reducing the perceived risks to the patient associated with these prostheses.

The epidemiology of bearing surface usage in total hip arthroplasty in the United States

BACKGROUND

Hard-on-hard bearings offer the potential to improve the survivorship of total hip arthroplasty implants. However, the specific indications for the use of these advanced technologies remain controversial. The purpose of this study was to characterize the epidemiology of bearing surface utilization in total hip arthroplasty in the United States with respect to patient, hospital, geographic, and payer characteristics.

METHODS

The Nationwide Inpatient Sample database was used to analyze bearing type and demographic characteristics associated with 112,095 primary total hip arthroplasties performed in the United States between October 1, 2005, and December 31, 2006. The prevalence of each type of total hip arthroplasty bearing was calculated for population subgroups as a function of age, sex, census region, payer class, and hospital type.

RESULTS

The most commonly reported bearing was metal-on-polyethylene (51%) followed by metal-on-metal (35%) and ceramic-on-ceramic (14%). Metal-on-polyethylene bearings were most commonly reported in female Medicare patients who were sixty-five to seventy-four years old, while metal-on-metal and ceramic-on-ceramic bearings were most commonly reported in privately insured male patients who were less than sixty-five years old. Thirty-three percent of patients over sixty-five years old had a hard-on-hard bearing reported. There was substantial regional variation in bearing usage; the highest prevalence of metal-on-polyethylene bearings was reported in the Northeast and at nonteaching hospitals, and the highest prevalence of metal-on-metal bearings was reported in the South and at teaching hospitals.

CONCLUSIONS

The usage of total hip arthroplasty bearings varies considerably by patient characteristics, hospital type, and geographic location throughout the United States. Despite uncertain advantages in older patients, hard-on-hard bearings are commonly used in patients over the age of sixty-five years. Further study is necessary to define the appropriate indications for these advanced technologies in total hip arthroplasty.

Incidence of ceramic liner malseating in Trident acetabular shell

The low wear rates associated with ceramic hip articulations have made them a popular bearing for younger patients. Although few complications have been observed, one report revealed several instances of incomplete seating of the ceramic liner in the metallic shell. We performed a cohort study of consecutive THAs using a ceramic-ceramic bearing. Radiographic analysis showed 50 (7.2%) of the group of 694 hips had evidence of incomplete seating of the liner in the metallic shell. Although we observed no adverse effects at 6 to 12 weeks, we encourage surgeons to carefully assess liner placement in the metal shell at the time of surgery to avoid this unintended consequence and to assess placement at the time of followup so patients can be properly followed when incomplete seating is identified.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Fabrication and testing of silicon nitride bearings in total hip arthroplasty: winner of the 2007 "HAP" PAUL Award

Total hip arthroplasty (THA) bearings were fabricated from silicon nitride (Si(3)N(4)) powder. Mechanical testing showed that Si(3)N(4) had improved fracture toughness and fracture strength over modern alumina (Al(2)O(3)) ceramic. When tested with Si(3)N(4) cups in a hip simulator, both cobalt-chromium (CoCr) and Si(3)N(4) femoral heads produced low wear rates that were comparable to Al(2)O(3)-Al(2)O(3) bearings in THA. This study offers experimental support for a novel metal-ceramic THA bearing couple that combines the reliability of CoCr femoral heads with the wear advantages of ceramic surfaces.

In vitro assessment of serum-saline ratios for fluid simulator testing of highly modular spinal implants with articulating surfaces

BACKGROUND

The increasing complexity of articulating spinal implants prohibits the use of serum-supplemented simulator fluid testing because multicomponent interfaces retain residual protein and preclude gravimetric measurement. Our original hypothesis was that simulator testing of a posterior dynamic stabilization implant that has metal-on-metal articulating bearings will not produce dramatically different wear debris when tested using pure saline versus testing in saline supplemented with 20% serum.

METHODS

This hypothesis was tested using simulator testing of 12 dynamic stabilization spinal implants, 6 in 100% saline and 6 in 20%-serum saline. Gravimetric and particle analysis were performed after every million cycles up to 10 million cycles, with flexion of 11.3°/extension of 5.6° coupled with axial rotation of ± 4°.

RESULTS

The mean gravimetric weight loss was approximately 200 mg over 10 million cycles for the implants tested in 100% saline, while the mean weight loss for those tested in 20%-serum saline was below the method detection limits (< 10 mg over 10 million cycles). For the 100%-saline and 20%-serum simulator fluids, the average particle size over the course of 0 to 10 million cycles remained relatively constant at 0.2 µm-dia (saline) and 3.2 µm-dia (20%-serum saline). Testing in 100% saline generated > 1000-fold more particles, compared to testing in 20% serum-supplemented saline. Energy-dispersive X-ray (EDAX) analyses of particles demonstrated that the 100% saline debris was composed of Co-Cr-P-O (Cr-Co metal oxides), and for the 20%-serum saline debris only bulk metal Co-Cr was detected.

CONCLUSION

Our initial hypothesis was not supported. There were significant differences in gravimetric wear, average size, and type of wear debris that were mechanistically attributable to the type of simulator fluid used. The over-protective effect of serum proteins appears to underscore the importance of using both saline and serum when establishing upper and lower bounds of predictive implant debris generation modeling, where saline represents a worst-case scenario and as little as 20% serum masks all weight loss completely in highly modular articulating implants.

CLINICAL RELEVANCE

Clinical Relevance = 5 (Oxford Centre for Evidence-based Medicine Levels of Evidence). Study findings are limited to a greater understanding of the science associated with predictive wear testing of articulating spinal implants.

Design considerations and life prediction of metal-on-metal bearings: the effect of clearance

BACKGROUND

Clinical observations suggest that metal-on-metal arthroplasties that have been implanted for more than twenty years do fail. It is proposed that there are not two, but three distinct phases of wear life for any metal-on-metal implant system: bedding-in, steady state, and end point. In this study, we asked two questions: can we explain late failure due to wear, and will there be a late failure mechanism due to a change in the frictional torque?

METHODS

In order to characterize wear failure, an analysis was made of five retrieved metal-on-metal couples that were mapped with use of a roundness machine. A geometrical model was developed on the basis of these observations, and wear at the end point was calculated. The literature on first-generation metal-on-metal implants retrieved for aseptic loosening was reviewed to assess the agreement with the retrieval findings as well as the wear model.

RESULTS

A wear patch of an appreciable and constant size could be measured in all five retrieved couples. The end point of revision was observed to occur when the wear progression reached a contact area corresponding to approximately 75% of the projected diameter of the ball. The wear volume was calculated from the geometry. The available literature describing the wear characteristics of retrieved bearings after successful clinical use showed good agreement with the calculated wear model.

CONCLUSIONS

During the implant life of long-term successful metal-on-metal devices, a wear patch develops, as evident from retrieved failed devices. Failure often occurs through loosening, and the observed wear patch is similar in size for devices measured by us and for those described in the literature. We hypothesized that failure by loosening occurs through the accumulation of wear, which eventually leads to high friction within the bearing and increased torsional forces across the joint and its fixation.

Characterization of the running-in period in total hip resurfacing arthroplasty: an in vivo and in vitro metal ion analysis

BACKGROUND

Metal-on-metal total hip resurfacing arthroplasty is increasingly being performed in young and active patients. Preclinical in vitro testing of implants is usually performed with use of hip simulators, and the serum metal ion concentration is determined for the purpose of monitoring the patients. The goal of this study was to characterize the early running-in period in vivo and in vitro by characterizing metal ion levels.

METHODS

A well-functioning total hip resurfacing prosthesis was implanted in fifteen consecutive patients, and the serum metal ion concentrations in these patients were then determined preoperatively and at intervals during the first postoperative year (at one, six, twelve, twenty-four, and fifty-two weeks). The number of walking cycles was measured with use of a computerized accelerometer in order to compare walking cycles to hip simulator cycles. In vitro, five similar components were investigated for 3 million cycles with use of a hip simulator. Serum samples were obtained at different time points, and wear was measured by quantifying wear particles and ions in the samples. All patient and simulation serum samples were analyzed with use of inductively coupled plasma-mass spectrometry. One simulator implant was investigated with use of scanning electron microscopy.

RESULTS

The serum chromium and cobalt levels of the patients continuously increased during the first six months and showed an insignificant decrease thereafter. The molybdenum concentration was unchanged compared with preoperative values. In contrast, the simulator measurements showed a different wear pattern with a high-wear running-in period and a low-wear steady-state phase. The running-in period was delayed by 300,000 cycles and lasted up to 1 million cycles. Scanning electron microscopic analysis showed a carbon-rich protein film predominantly in the early phases of simulation. Scratches were detected originating from pits filled with aluminum oxide and silicon oxide and from pulled-out carbides that were causing third-body wear.

CONCLUSIONS

The simulator study allowed an exact characterization of the running-in period and showed a delayed onset of running-in wear. In contrast, the clinical data showed a slow increase in measured ion concentrations. These different wear patterns are probably due to the effects of distribution, accumulation, and excretion of particles and ions in vivo.

Wear of an experimental metal-on-metal artificial disc for the lumbar spine

STUDY DESIGN

In vitro wear simulation.

OBJECTIVE

To determine the type and amount of wear produced by experimental metal-on-metal artificial discs for the lumbar spine. To minimize the amount of wear by changing the carbon content, clearance, and presence of a keel and notch.

SUMMARY OF BACKGROUND DATA

In contrast to the extensive number of hip joint replacement simulator studies examining the effects of individual design variables on wear, existing artificial lumbar disc wear publications have measured wear using only the final version of each product. That is, the effects of individual variables such as material, diameter, or clearance on wear of artificial discs are not known, even though the importance of such variables has been established in artificial hip wear studies.

METHODS

Experimental metal-on-metal artificial discs for the lumbar spine were tested in a 3-station, biaxial spine wear simulator designed and constructed by the investigators. Two versions of the implants were manufactured with differences in carbon content, clearance, and the presence of a keel. Additionally, implants were tested with or without a surgical notch.

RESULTS

The wear rates of the experimental metal-on-metal lumbar discs in the current study ranged from 6.2 to 15.8 mm3/million cycles. However, changing the carbon content of the ball from low to high, decreasing the initial clearance, and eliminating the anteroposterior keel reduced the wear rate from 12.4 to 7.6 mm3/million cycles. Furthermore, removing the surgical notch reduced the wear rate from 7.6 to 6.2 mm3/million cycles. The surface damage was generally consistent with low lubrication and varying degrees of abrasive and fatigue wear, with impingement of nonbearing surfaces observed at 1.5 million cycles for the longer-term test.

CONCLUSION

Although the implants tested in the current study were experimental, the results suggest that metal-on-metal lumbar discs have the potential to produce wear of this magnitude and mechanism in vivo. Therefore, careful consideration of individual design variables, including those considered in the current study, is necessary to avoid production of excessive wear in artificial lumbar discs.

The 2007 Otto Aufranc Award. Ceramic-on-metal hip arthroplasties: a comparative in vitro and in vivo study

The performance of novel ceramic-on-metal bearing couples has been compared with metal-on-metal and ceramic-on-ceramic bearing couples in laboratory and short-term clinical studies. Laboratory studies compared ceramic-on-metal with metal-on-metal and ceramic-on-ceramic bearings with diameters of 28 and 36 mm under standard conditions and under adverse conditions with head loading on the rim of the cup. Clinical studies compared metal ion levels in ceramic-on-metal with metal-on-metal, ceramic-on-ceramic, and ceramic-on-polyethylene bearings in a randomized prospective study. In the laboratory studies, friction, wear, and ion levels were lower in ceramic-on-metal bearings compared with metal-on-metal, with results similar to ceramic-on-ceramic couples. Under adverse conditions and rim loading, all bearings showed increased wear with lower wear and absence of stripe wear in ceramic-on-metal compared with metal-on-metal bearings. Short-term studies in 31 patients at 6 months revealed lower metal ion levels (cobalt and chromium) in those with ceramic-on-metal compared with metal-on-metal bearings.

Incomplete seating of the liner with the Trident acetabular system: a cause for concern?

We reviewed the initial post-operative radiographs of the Trident acetabulum and identified a problem with seating of the metal-backed ceramic liner. We identified 117 hips in 113 patients who had undergone primary total hip replacement using the Trident shell with a metal-backed alumina liner. Of these, 19 (16.4%) were noted to have incomplete seating of the liner, as judged by plain anteroposterior and lateral radiographs. One case of complete liner dissociation necessitating early revision was not included in the prevalence figures. One mis-seated liner was revised in the early post-operative period and two that were initially incompletely seated were found on follow-up radiographs to have become correctly seated. There may be technical issues with regard to the implanting of this prosthesis of which surgeons should be aware. However, there is the distinct possibility that the Trident shell deforms upon implantation, thereby preventing complete seating of the liner.

The wear properties of CFR-PEEK-OPTIMA articulating against ceramic assessed on a multidirectional pin-on-plate machine

In an attempt to prolong the lives of rubbing implantable devices, several 'new' materials have been examined to determine their suitability as joint couplings. Tests were performed on a multidirectional pin-on-plate machine to determine the wear of both pitch and PAN (polyacrylonitrile)-based carbon fibre reinforced-polyetheretherketone (CFR-PEEK-OPTIMA) pins articulating against both BioLox Delta and BioLox Forte plates (ceramic materials). Both reciprocation and rotational motion were applied to the samples. The tests were conducted using 24.5 per cent bovine serum as the lubricant (protein concentration 15 g/l). Although all four material combinations gave similar low wear with no statistically significant difference (p > 0.25), the lowest average total wear of these pin-on-plate tests was provided by CFR-PEEK-OPTIMA pitch pins versus BioLox Forte plates. This was much lower than the wear produced by conventional joint materials (metal-on-polyethylene) and metal-on-metal combinations when tested on the pin-on-plate machine. This therefore indicates optimism that these PEEK-OPTIMA-based material combinations may perform well in joint applications.

Friction of total hip replacements with different bearings and loading conditions

Metal-on-ultra-high molecular weight polyethylene (UHMWPE) total hip replacements have been the most popular and clinically successful implants to date. However, it is well documented that the wear debris from these prostheses contributes to osteolysis and ultimate failure of the prosthesis, hence alternative materials have been sought. A range of 28 mm diameter bearings were investigated using a hip friction simulator, including conventional material combinations such as metal-on-UHWMPE, ceramic-on-ceramic (CoC), and metal-on-metal (MoM), as well as novel ceramic-on-metal (CoM) pairings. Studies were performed under different swing-phase load and lubricant conditions. The friction factors were lowest in the ceramic bearings, with the CoC bearing having the lowest friction factor in all conditions. CoM bearings also had low friction factors compared with MoM, and the trends were similar to CoC bearings for all test conditions. Increasing swing phase load was shown to cause an increase in friction factor in all tests. Increased serum concentration resulted in increased friction factor in all material combinations, except MoM, where increased serum concentration produced a significant reduction in friction factor.

Die Bedeutung der Gleitpaarung beim jüngeren Endoprothesenpatienten

The success and long-term survival rates of modern joint arthroplasty leads to a high patient satisfaction and, together with its technical improvements, has broadened the indications to an increasingly younger population. Limitations to the established systems are the long-term survival rates, which are mainly influenced by wear of the articulating parts and the resulting problems. Beside "classic" long-stemmed cemented shafts articulating with metal against polyethylene, short-stemmed or cup designs with a hard-hard self pairing are increasingly used in total hip arthroplasty. This paper reflects the current state of the art in joint arthroplasty for younger patients with the focus on wear couples and discusses future perspectives. Special interest is focused on the advantages and disadvantages of ceramic bearings, problems with allergies to implant components and the design of endoprostheses with regard to avoidance of impingement.

Larger diameter bearings reduce wear in metal-on-metal hip implants

Metal-on-metal hip arthroplasty has the longest clinical history of all total arthroplasties. We asked whether large diameter femoral heads would result in less wear than those with small diameters. We also asked if there is a threshold diameter that ensures good wear behavior. We tested three batches of cast high-carbon cobalt-chromium-molybdenum hip implants (28 mm, 36 mm, and 54 mm diameters) in a hip simulator for 5 million cycles. We used bovine serum as lubricant and weighed the samples at regular intervals during testing. The 28-mm configuration had almost twice the wear of the 54-mm configuration, but we observed no difference between the 36-mm and the 54-mm configurations. The similarity in the wear performances of the larger configurations supports the presence of a threshold diameter that ensures good wear behavior.

Laboratory studies on the tribology of hard bearing hip prostheses: Ceramic on ceramic and metal on metal

Total hip replacements offer relief to a great many patients every year around the world. With an expected service life of around 25 years on most devices, and with younger and younger patients undergoing this surgery, it is of great importance to understand the mechanisms of their function. Tribological testing of both conventional and hard bearing joint combinations have been conducted in many centres throughout the world, and, after being initially abandoned owing to premature failures, hard bearing combinations have been revisited as viable options for joint replacements. Improved design, manufacturing procedures, and material compositions have led to improved performance over first-generation designs in both metal-on-metal and ceramic-on-ceramic hip prostheses. This paper offers a review of the work conducted in an attempt to highlight the most important factors affecting joint performance and tribology of hard bearing combinations. The tribological performance of these joints is superior to that of conventional metal- or ceramic-on-polymer designs.

Engineering aspect of alumina on alumina hip prosthesis

Alumina on the alumina sliding system in a total hip replacement is recognized as a breakthrough in orthopaedic surgery. Advantages and problems with this material are explained and discussed in the light of 36 years of clinical application. Laboratory data as well as clinical ones are summarized.

Meniscal wear at a three-component total ankle prosthesis by a knee joint simulator

Despite the fundamental value of wear simulation studies to assess wear resistance of total joint replacements, neither specialised simulators nor established external conditions are available for the human ankle joint. The aim of the present study was to verify the suitability of a knee wear simulator to assess wear rates in ankle prostheses, and to report preliminary this rate for a novel three-component total ankle replacement design. Four intact 'small' size specimens of the Box ankle were analysed in a four-station knee wear simulator. Special component-to-actuator holders were manufactured and starting spatial alignment of the three-components was sought. Consistent load and motion cycles representing conditions at the ankle joint replaced exactly with the prosthesis design under analysis were taken from a corresponding mechanical model of the stance phase of walking. The weight loss for the three specimens, after two million cycles, was 32.68, 14.78, and 62.28mg which correspond to a linear penetration of 0.018, 0.008, and 0.034mm per million-cycle, respectively for the specimens #1, #2, and #3. The knee wear simulator was able to reproduce load-motion patterns typical of a replaced ankle. Motion of the meniscal bearing in between the tibial and talar components was smooth, this component remaining in place and in complete congruence with the metal components throughout the test.

Serum aluminium and cobalt levels after ceramic-on-ceramic and metal-on-metal total hip replacement

In a randomised study, 28 patients with a mean age of 62.2 years (32 to 81) with osteoarthritis or avascular necrosis of the hip received either a ceramic-on-ceramic or a metal-on-metal total hip replacement. Apart from the liners the acetabular and femoral components were made of Ti-Al-Nb alloy. The serum aluminium and cobalt levels were measured before, and at one year after surgery. The 15 patients in the ceramic-on-ceramic group had a median pre-operative aluminium level of 1.3 microg/l (0.25 to 8.4) and a cobalt level below the detection limit. At one year the aluminium level was 1.1 microg/l (0.25 to 2.3) and the cobalt level was 0.4 microg/l (0.15 to 0.7). The 13 patients in the metal-on-metal group had a median pre-operative aluminium level of 1.9 microg/l (0.25 to 4.4) and a cobalt level below the detection limit. At one year the median aluminium level was 0.9 microg/l (0.25 to 3.9) whereas the cobalt level was 1.4 microg/l (0.5 to 10.5). This increase in the cobalt level at one year was significant (p < 0.001). Our findings indicate that ceramic-on-ceramic bearings do not cause elevated levels of serum aluminium in the first post-operative year.

Ergebnisse zementfreier Hüftendoprothetik

Hip arthroplasty is performed nowadays according to the needs of the patients irrespective of their age. Tapered rectangular stems for cementless fixation are chosen in most cases in central Europe. They provide primary stability by press-fit implantation into a precisely rasped osseous bed and secondary stability by bone ingrowth into the highly biocompatible titanium alloy with a microrough surface. The 10-year survival of such devices is 92%. Typical radiographic patterns include cortical atrophy and radiolucent lines in Gruen zones 1 and 7. They are due to stress shielding with these distally fixed implants. The number one reason for revision is polyethylene wear and subsequent osteolysis. Metal-on-metal and ceramic-on-ceramic bearings show less wear but osteolysis continues to be a problem.

Finite Element Analysis of the Long-Term Fixation Strength of Cemented Ceramic Cups

Clinical studies have shown that adequate fixation of ceramic cups using bone cement is difficult to achieve. As the cement-ceramic bond strength is low, a satisfactory fixation strength requires a cup design that allows mechanical interlocking, although such a design will probably promote cement cracking and therefore cup loosening in the long term. An investigation has been carried out to establish whether a cemented ceramic cup can be designed in such a way that both a satisfactory initial fixation strength is obtained and cement cracking is reduced to levels found around PE cups functioning well in vivo. By means of finite element analysis, the fatigue loading of three geometrically different cemented acetabular cups, with ceramic and PE material properties, has been simulated, and the severity of the crack patterns produced in the cement has been analysed. Furthermore, the fixation strength has been analysed by simulating a pull-out test prior to and after fatigue testing. All ceramic cups produced much larger amounts of cement damage during fatigue testing than any PE cup, caused by stress concentrations in the cement that were attributable to the high stiffness of the ceramic. Even a completely smooth ceramic cup produced more damage than a sharp-grooved PE cup. Owing to the excessive cement cracking, the fixation strength of the ceramic cups dropped after fatigue loading. It is concluded that cemented ceramic cups have an increased risk of long-term mechanical failure by comparison with PE cups, and that a ceramic cup design that combines sufficient fixation strength with low cement failure may be difficult to achieve.