Squeaking is a rare complication of hard-on-hard hip bearings. Occasionally the noise is troublesome enough to warrant revision surgery. The purpose of this study is to contribute to the understanding of the mechanism(s) underlying squeaking. We analyzed 10 alumina ceramic-on-ceramic bearings from squeaking hips collected at revision surgery. The reason for revision was given as squeaking (6 cases) or squeaking and pain (4 cases). Six of the 10 patients were male, average patient age was 48. Bearings were retrieved after an average of 23 months in service (11 to 61 months). There were 4 different designs of acetabular component from 2 different manufacturers. Nine have an elevated metal rim which is proud of the ceramic and one does not. Two bearings were 36mm in diameter, 6 were 32mm and 2 were 28mm. All 10 bearings showed evidence of edge loading wear. Mean dimensions of the wear patch were 37mm by 12mm on the acetabular component and 32mm by 13mm on the femoral heads. Wear dimension was not related to bearing diameter. Seven of the 10 implants also had evidence of impingement of the femoral neck against the elevated metallic rim or the ceramic insert or both. There was no chipping or fracture of any of the ceramic components. Squeaking is a recently recognized complication of hard on hard bearing surface. This retrieval study is the first of its kind, to our knowledge attempting to unravel the mechanism of this undesirable complication. Although impingement seems to be present in majority of cases, the latter does not seem to be necessary. Edge loading wear was the common factor in all cases and this may prove to be a critical mechanism

Squeaking of ceramic-on-ceramic (CoC) hips is a clinical phenomenon that is concerning with regard to the long term performance of these joint devices. Investigations into the cause of the squeaking have focused on patient factors and demographics, surgical placement, and other non-ceramic components in the devices. The current study tests latest-generation CoC devices to measure the vibration modes and frequencies of the components individually as well as assembled in the complete surgical construct. Audio data from clinical cases of squeaking hips were analysed to determine the frequencies present. Retrieved CoC hips (n = 7) and never-implanted CoC bearing couples (n = 3) were tested in the laboratory for squeaking under loaded articulation. Bovine serum was introduced into the CoC articulation and dried to promote stick-slip motion at the articulation. Squeaking sounds from the in vitro tests were recorded for audio analysis. Low mass, high frequency-response ceramic shear piezoelectric accelerometers (PCB Piezotronics) were adhered to the hip components along multiple axes to measure vibrations during testing. Clinical audio shows that squeaking occurs at fundamental frequencies in the range of 1 to 3 kHz, with harmonics above the fundamental frequency. Retrieved CoC bearing couples squeaked at fundamental frequencies from 1.5 kHz to 3.8 kHz. Fourier Transform analysis of the audio closely matched the concurrent output from the accelerometers mounted directly on the ceramic components. This held true even in the absence of metal components in the system. With metal components included in the test construct (acetabular shell, acetabular cup, femoral stem), those components also vibrated at the same frequencies as the ceramic bearing couples, indicating that the CoC articulation is the source of the vibrations, with metal components conducting and emanating the sound. The never-implanted bearing couples were made to squeak and vibrated at fundamental frequencies ranging from 1 kHz to 8 kHz. Squeaking from CoC hips can be reproduced in the lab using components from clinical retrievals. Instrumentation of the explanted hips confirms that the vibration frequencies of the ceramic components themselves match the audible squeaking. The squeaking of ceramic components mounted with soft polymers and with no metal contact at any point indicates that the ceramic components themselves are the source of the clinical squeaking. The measured vibration of ceramic components in the audible range is an observation not predicted by modeling studies reported in the literature to date

INTRODUCTION. Squeaking after total hip replacement has been reported in up to 10% of patients. Some authors proposed that sound emissions from squeaking hips result from resonance of one or other or both of the metal parts and not the bearing surfaces. There is no reported in vitro study about the squeaking frequencies under lubricated regime. The goal of the study was to reproduce the squeaking in vitro under lubricated conditions, and to compare the in vitro frequencies to in vivo frequencies determined in a group of squeaking patients. The frequencies may help determining the responsible part of the noise. METHODS. Four patients, who underwent THR with a Ceramic-on-Ceramic THR (Trident(r), Stryker(r)) presented a squeaking noise. The noise was recorded and analysed with acoustic software (FMaster(r)). In-vitro 3 alumina ceramic (Biolox Forte Ceramtec(r)) 32 mm diameter (Ceramconcept(r)) components were tested using a PROSIM(r) hip friction simulator. The cup was positioned with a 75° abduction angle in order to achieve edge loading conditions. The backing and the cup liner were cut with a diamond saw, in order to avoid neck-head impingement and dislocation in case of high cup abduction angles (Figure1). The head was articulated ± 10° at 1 Hz with a load of 2.5kN for a duration of 300 cycles. The motion was along the edge. Tests were conducted under lubricated conditions with 25% bovine serum without and with the addition of a 3. rd. body alumina ceramic particle (200 μm thickness and 2 mm length). Before hand, engineering blue was used in order to analyze the contact area and to determine whether edge loading was achieved. RESULTS. Edge loading was obtained. In-vitro, no squeaking occurred under edge loading conditions. However, with the addition of an alumina ceramic 3. rd. body particle in the contact region squeaking was obtained at the beginning of the tests and stopped after ∼20 seconds (dominant frequency 2.6 kHz). In-vivo, recordings had a dominant frequency ranging between 2.2 and 2.4 kHz. DISCUSSION. For the first time, squeaking was reproduced in vitro under lubricated conditions. In-vitro noises followed edge loading and 3. rd. body particles and despite, the severe conditions, squeaking was intermittent and difficult to reproduce. However, squeaking is probably more difficult to reproduce because the cup was cut and the head was fixed in the simulator, preventing vibration to occur. Squeaking noises of a similar frequency were recorded in-vitro and in-vivo. The lower frequency of squeaking recorded in-vivo, demonstrates a potential damping effect of the soft tissues. Therefore, the squeaking in the patients was probably related to the bearing surfaces and modified lubrication conditions that may be due to edge loading. Varnum et al reported recently (3) that all the revised squeaking patients had a neck-cup impingement with metal 3. rd. body particles. These metallic wear particles may generate squeaking as shown in vitro. However, a larger cohort of squeaking patients is needed to confirm these results

Squeaking in hip arthroplasty is now well-documented but hitherto poorly understood. In this paper, we report data progressively accumulated from a series of studies undertaken by our group to investigate the mechanisms of noise production associated with ceramic-on-ceramic bearings. We reviewed demographic and radiographic data comparing squeaking with silent hips. Edge loading of the acetabular components was investigated on retrieved bearings and with finite element analysis. The squeaking sound itself was further investigated through acoustic analysis. Squeaking occurs in younger, heavier, and taller patients. We found a higher incidence of acetabular component malposition in squeaking hips and edge loading appears to be a causative factor. Finite element analysis revealed a stiffness mismatch between the shell and liner which may allow the shell to oscillate producing an audible squeak. Acoustic and modal analysis show that squeaking is due to a forced vibration and that the natural frequencies of the ceramic components are above the audible range, suggesting that resonance occurs in the metallic, not the ceramic parts. This phenomenon is related to patient factors, surgical factors, and implant factors, which may produce sound by a combination of edge loading of the ceramic and forced vibration of the acetabular shell and/or the femoral stem

Introduction: Squeaking after total hip replacement has been reported in up to 10% of patients. Some authors proposed that sound emissions from squeaking hips result from resonance of one or other or both of the metal parts and not the bearing surfaces. There is no reported in vitro study about the squeaking frequencies under lubricated regime. The goal of the study was to reproduce the squeaking in vitro under lubricated conditions, and to compare the in vitro frequencies to in vivo frequencies determined in a group of squeaking patients. The frequencies may help determining the responsible part of the noise. Methods: Four patients, who underwent THR with a Ceramic-on-Ceramic THR (Trident. ®. , Stryker. ®. ) presented a squeaking noise. The noise was recorded and analysed with acoustic software (FMaster. ®. ). In-vitro 3 alumina ceramic (Biolox Forte Ceramtec. ®. ) 32 mm diameter (Ceramconcept. ®. ) components were tested using a PROSIM. ®. hip friction simulator. The cup was positioned with a 75° abduction angle in order to achieve edge loading conditions. The backing and the cup liner were cut with a diamond saw, in order to avoid neck-head impingement and dislocation in case of high cup abduction angles. The head was articulated ± 10° at 1 Hz with a load of 2.5kN for a duration of 300 cycles. The motion was along the edge. Tests were conducted under lubricated conditions with 25% bovine serum without and with the addition of a 3rd body alumina ceramic particle (200 μm thickness and 2 mm length). Results: Edge loading was obtained incompletely. In-vitro, no squeaking occurred under edge loading conditions. However, with the addition of an alumina ceramic 3rd body particle in the contact region, squeaking was obtained at the beginning of the tests and stopped after ~20 seconds (dominant frequency 2.6 kHz). In-vivo, recordings had a dominant frequency ranging between 2.2 and 2.4 kHz. Discussion: For the first time, squeaking was reproduced in vitro under lubricated conditions. In-vitro noises followed edge loading and 3rd body particles and despite, the severe conditions, squeaking was intermittent and difficult to reproduce. However, squeaking is probably more difficult to reproduce because the cup was cut and the head was fixed in the simulator, preventing vibration to occur. Squeaking noises of a similar frequency were recorded in-vitro and in-vivo. The lower frequency of squeaking recorded in-vivo, demonstrates a potential damping effect of the soft tissues. Therefore, the squeaking in the patients was probably related to the bearing surfaces and modified lubrication conditions that may be due to edge loading. The determined values of frequencies may help to analyze the squeaking patients in order to determine the mechanism generating the sound

Introduction: The goal of the study was to compare the squeaking frequencies of Ceramic-on-Ceramic THR in-vitro and in-vivo among patients who underwent THR. Method: Four patients, who underwent THR with a Ceramic-on-Ceramic THR (Trident. ®. , Stryker. ®. ) presented a squeaking noise. The noise was recorded and analysed with acoustic software (FMaster. ®. ). In-vitro 2 alumina ceramic (Biolox Forte Ceramtec. ®. ) 32 mm diameter (Ceramconcept. ®. ) components were tested using a PROSIM. ®. hip friction simulator. The cup was positioned with a 70° abduction angle in order to achieve edge loading conditions and the head was articulated ± 10° at 1 Hz with a load of 2.5kN for a duration of 300 cycles. Tests were conducted under lubricated conditions with 25% bovine serum and with the addition of a 3rd body alumina ceramic particle (200 μm thickness and 2 mm length). Results: In-vivo, recordings had a dominant frequency ranging between 2.2 and 2.4 kHz. In-vitro no squeaking occurred under edge loading conditions. However, with the addition of an alumina ceramic 3rd body particle in the contact region squeaking was obtained at the beginning of the tests and stopped after ~20 seconds (dominant frequency 2.6 kHz). Discussion and Conclusion: Squeaking noises of a similar frequency were recorded in-vitro and in-vivo. In-vitro noises followed edge loading and 3rd body particles and despite, the severe conditions, squeaking was intermittent and difficult to reproduce. The lower frequency of squeaking recorded in-vivo, demonstrates a potential damping effect of the soft tissues. No damage was observed on the components, however, the test duration was very short. Squeaking may be related to third body particles that could be generated by wear or impingement between the femoral neck and the metal back. Cup design seems to be of particular importance in noisy hip, leading to a high variability of squeaking rate according to the implants

Introduction: Squeaking is reported ceramic-on-ceramic hip bearings in association with acetabular component malposition – particularly too much or too little anteversion. Acoustic analysis of squeaking hips with modular ceramic-titanium acetabular components suggests that there may be dynamic uncoupling of the ceramic insert from the titanium shell with edge loading of the ceramic. The aim of this study was to investigate edge loading of a modular ceramic-titanium acetabular component during gait at different positions of anteversion using the finite element (FE) method. Methods: An intact and reconstructed 3D FE model of a human pelvis was generated using PATRAN. Bone properties extracted from the CT data were applied using FORTRAN subroutines. A generic acetabular titanium shell and ceramic liner were modelled and placed in the pelvis in two different positions: ideal anteversion and 18 degree excess anteversion. The contact conditions simulated a fully osseointegrated acetabular shell and a matched taper junction with a friction coefficient of 0.2. We ran FE analysis with ABAQUS software to determine the stress distribution and surface separation of shell and liner at toe-off. Results: The separation distance between the ceramic liner and the acetabular shell for the anteverted component (40mm) was an order of magnitude greater than that for the ideally positioned component (4mm). There was “tilting” of the ceramic liner out of the acetabular shell in both cases. Discussion: Based on clinical observations, the toe-of phase of gait is a common position for squeaking to occur. Clinical retrievals also show evidence of edge loading wear and contralateral taper interface separation with the “tilting” of the liner out of the acetabular shell. It is envisaged that the “tilting” of the liner in the acetabular shell may allow forced vibrations associated with the squeaking phenomena, possibly in combination with edge loading

Aluminia ceramic on ceramic (COC) bearing surfaces have been used for 35 years in total hip arthroplasty (THA). Studies report 85% survival at a minimum follow-up of 18.5 years. Nonetheless, an audible noise is a finding associated with COC bearings with incidence rates of 2–10%. This study aims to determine the prevalence of noise and evaluate its effect on patients. All patients who had a COC THA from August 2003 to December 2010 were contacted and asked to complete a standardised questionnaire. This asked about the presence and characteristics of a noise and if associated with activities, pain and whether this phenomenon should be mentioned preoperatively. Four consultant surgeons performed 282 consecutive primary COC THAs in 258 patients. (Male=122, Female=136 mean age 68.5; age range 28–88). In all cases, the same brand of ceramic acetabular component and stems were implanted. 11.0% had a noise, of which 5.5% had a squeak. Pain was experienced in 38.7% of patients in hips that made a noise. There was no trauma and one dislocation in this group. In this study, 85% of noises occur during weight-bearing although no patients have reduced daily activities as a result of the noises. Of all the patients, 55.0% stated they would have preferred to have known about a noisy hip possibility before consenting but none would have refused consent. Squeaking has not been a problem here despite the prevalence being higher than most in the literature. The authors recommend that squeaking should be discussed preoperatively. A checklist for Orthopaedic Trainees is being drafted to enable trainees to counsel patients appropriately, allowing patients a better opportunity to give informed consent

Introduction. Squeaking is a potential problem of all hard on hard bearings yet it has been less frequently reported in metal-on-metal hips. We compared a cohort of 11 squeaking metal-on-metal hip resurfacings to individually matched controls, assessing cup inclination and anteversion between the groups to look for any differences. Methods. We retrospectively reviewed the patient records of 332 patients (387 hip resurfacings) who underwent hip resurfacing between December 1999 and Dec 2012. 11 hips in 11 patients were reported to squeak postoperatively. Each of these patients, except one, were matched by age, sex, BMI and implant to 3 controls. The final patient only had one control due to his high BMI. The latest post-operative radiographs of the squeaking group and controls were analysed using EBRA (Einzel-Bild-Roentgen-Analysis, University of Innsbruck, Austria) software to evaluate cup inclination and anteversion. Results. Post- operative audible squeaking occurred in 11 out of 387 hips (2.84%). The mean follow up of the squeaking group was 88.6 months (19–131 months). The mean time to squeak was 11.3 months (3–22 months). 8 (73%) patients were male, 10 (91%) patients had a Birmingham hip resurfacing and 9 (82%) patients had an operation on the left hip. The mean inclination angle of the cups in the squeaking group was 48.4° (43.9°–55.4°) compared to 50° (37.8° −63°) in the control group. The mean anteversion of the cups in the squeaking group was 17.1°(6.3°–25.7°) compared to 14.6° (4.3° −33.5°) in the control group. There was no statistically significant difference between the cases and their controls for cup inclination (p = 0.36) or cup anteversion (p = 0.31). The mean head size in the squeaking group was smaller at 49.3 mm (46 mm-54 mm), compared to 51.4 mm (48 mm-54 mm) in the control group (p = 0.026). The mean cup size in the squeaking group was also smaller at 56.5 mm (54 mm-62 mm), compared to 57.9 mm (48 mm-60 mm) in the control group (p = 0.007). Overall, 4 (40%) male patients in the squeaking group had a head size less than 50 mm, compared to 0 (0%) in the control group. 3 (27%) patients with squeaking resurfacings underwent revision surgery. 1 (9%) at 72 month for a pseudotumour, 1 (9%) at 114 months for persistant squeaking and 1 (9%) at 117 months for a subtrochanteric fracture after a fall. Conclusions. No difference was found between the radiographic inclination or anteversion of squeaking metal-on-metal hip resurfacing cups compared to a control group. Male patients with squeaking hips were noted to have smaller head and cup sizes than their controls

Background: Squeaking in hip arthroplasty is a phenomenon that was described decades ago, but has only been brought back to attention recently. It occurs predominantly in ceramic on ceramic bearings, and has a reported incidence from less than 1% to 21%. The cause and the implication of squeaking are still unknown and many factors have been suggested to contribute. This study has looked into the patient factors to investigate if any clinical features are associated with an increased risk of squeaking. Methods: All primary total hip arthroplasties with ceramic on ceramic bearing that were performed at our unit were reviewed and all squeaking hips presented are included in the study. Patient demographics and clinical outcome data were analysed and compared with matched controls from the silent hips. Results: Between 1997 and 2008, 3375 primary hip arthroplasties in 3182 patients with ceramic on ceramic bearing were performed in our unit. Seventy one hips (2.1%) presented with squeaking on direct questioning and self reporting. Those patients were found to be taller, heavier and younger. They also have a significantly higher post-operative range of hip motion and higher Harris hip score when compared to matched controls. There was no difference in the satisfaction score. Only 4 patients (5.6%) presented with pain as well as squeaking, and 2 (2.8%) resulted in revision surgery for problematic squeaking. Conclusions: We present the largest series of squeaking primary hip arthroplasties with ceramic on ceramic bearing to date. A number of patient factors were found to be associated with squeaking. The taller, heavier and younger patients with more flexible and functional hips were at a higher risk, presumably because these patients put greater mechanical demands on their hips. Majority of the patients with squeaking are pain free and there is only a small risk of requiring revision surgery

Explanations for “bearing” noise in ceramic-on-ceramic hips (COC) included stripe-wear formation and loss of lubrication leading to higher friction. However clinical and retrieval studies have clearly documented stripe wear in patients that did not have squeaking. Seldom highlighted has been the risk of metal-on-metal or metal-on-ceramic impingement present in total hip arthroplasty (THA) with metal and ceramic cup designs. The limitation in THA positioning studies has been (i) reliance on 2-dimensional radiographic images and (ii) patients lying supine on the examination table, thus not imaged in squeaking positions. We collected eleven squeaking COC cases for an EOS 3D-imaging functional study. Hip positions were documented in each patient's functional ‘squeaking’ posture using standard and 3-D EOS images for sitting, rising from a chair, hip extension in striding, and single-legged stance. EOS imaging documented for the 1st time that postural dysfunctions with potential impingements were demonstrable for each squeaking case. The 1st major insight in this study came from a female patient who complained of squeaking while walking in flat-soled shoes (Figs. 1a, b). She found that when wearing high-heeled shoes her hip stopped squeaking (Figs. 1c, d). Her lateral EOS view in standing position with heeled shoes revealed that the femoral stem had approximately 3o less hyper-extension compared to flat shoes (Figs. 1b, d, arrows #1,3). The three-dimensional ‘sky-view’ EOS reconstruction of pelvis and femurs (Fig. 2) showed that her femur was also more internally rotated when she wore heels. These subtle shifts in position changed her COC hip from one of squeaking to non-squeaking. A squeaking male patient observed similar postural effects while walking up his boat ramp but not going down the ramp. In both cases, the squeaking was a consequence of cup impinging on a metal femoral neck. Thus the primary cause of squeaking appeared to be hip impingement, i.e. repetitive subluxations that patients generally were not aware of. Another case is representative of situations due to atypical and subtle cup/stem mal-adjustments (Fig. 3); frontal pelvic-tilt, thoracolumbar scoliosis, with 1cm of femur lengthening and a significant increase of offset are observed. Also evident was the femoral-neck retroversion in both standing and sitting. Squeaking occurred when modification of the functional neck orientation occured in one-legged stance (Fig. 3c) or when climbing a stair (Fig. 3d). It was apparent in our EOS studies that patient functionality controlled whether squeaking occurred or not. Thus the new data indicated COC squeaking was a three-fold consequence of component positioning, spine and pelvic adaptions, and variations in patient posture. One limitation here is that our conclusions are based on a small sample of patients and may not be applicable to all. A consequence of such repetitive impingement can be cup rim damage and neck-notching, with release of metal debris. It is well documented that retrieved ceramic bearings are frequently stained black. Thus hip squeaking may likely result from (i) impingement and secondarily (ii) due to ingress of metal particles, and then (iii) producing a failure of lubrication. To view tables/figures, please contact authors directly

While alumina ceramic-ceramic THA has been performed in the US for more than 12 years, the phenomenon of frequent, clinically reproducible squeaking is relatively new. The current study investigates the influence of implant design on the incidence of squeaking. We reviewed implant information on 1275 consecutive revision THAs performed from 10/2002 through 10/2007 to identify any patients who had complained of squeaking or grinding. We also identified, 2778 consecutive primary ceramicceramic THA. Of these, we reviewed the clinical records of 1,039 patients (37%) to date. Any patient complaint of squeaking or grinding at the time of an office visit or by phone interview was recorded. Hips were divided into group 1: flush mounted ceramic liner; group 2a: recessed ceramic liner mated with a stem made of TiAlV and using a 12/14 neck taper; and group 2b: recessed ceramic liner mated with a stem made of a beta titanium alloy comprised of 12% molybdenum, 6% Zirconium, and 2% Iron and using a neck taper smaller than a 12/14 taper. Of the revision THAs, 5 hips (0.4%) were in patients who had complained of squeaking or grinding. All 5 hips had a recessed, metal-backed ceramic liner and evidence of metallosis. In primary THAs, Group 2b had statistically significantly (p=0.04) more squeaking (7.6%) than group 2a (3.2%) which had statistically significantly (p=0.002) more squeaking than group 1 (0.6%). Squeaking following ceramic-ceramic THA is associated with use of a recessed metal-backed ceramic liner in combination with a femoral component made of a betatitanium alloy and using a relatively small head-neck taper. Since all revised hips in our study had metallosis, it is possible that metal debris is adversely affecting the bearing and that the elevated metal rim combined with a small head neck taper and the beta-titanium alloy contribute to this problem. Use of bearings with a flush-mounted ceramic liner mated with femoral components made of TiAlV and using a 12/14 taper appears to be prudent

Large diameter metal-on-metal (MOM) bearings are becoming increasingly popular for young, active patients. Clearance is a particularly important consideration for designing MOM implants, considering historical experience of equatorial contact and high frictional torque. Lubrication theory predicts increasing the clearance will result in diminished lubrication, resulting in increased friction and wear. Clinical cases of transient squeaking in patients with resurfacing bearings have been noted in recent years, with some reporting an incidence of up to 10% between 6 months and 2 years post-implantation. This study aimed to investigate the impact of increasing clearance on the lubrication, friction and squeaking of a large diameter metal-on-metal resurfacing bearing through frictional studies. Clinical-grade MOM implants of 55mm diameter and 100μm diametric clearance, and custom-made, 55mm bearings with diametric clearances of approximately 50μm and 200μm (DePuy International Ltd) were tested in a friction simulator. Components were inverted with a flexion-extension of ±25o applied to the head and lubricated with 25% and 100% newborn bovine serum. A peak load of 2kN, with swing-phase loads of 25N, 100N and 300N were applied. Sound data was recorded during each friction test using a MP3 recorder and pre-amplifier. A microphone was set up at a distance of 50mm from the implant, and data recorded over a minimum of 10 seconds where sound was generated. Sound data was assessed through narrow band analysis on Frequency Master software (Cirrus Research, UK). Lubrication was assessed by directly measuring the separation between the head and cup during the test cycle by ultrasonic methods (Tribosonics, UK). An ultrasound sensor was bonded to the back of the cup and reflection measurements were taken during the friction tests with a sampling rate of 100Hz. Using equations which related reflection coefficient to lubricant properties and thickness, values for the film thickness were calculated. The surface replacement with the largest clearance yielded the highest friction factor for each test condition. The difference between the large clearance bearing and the smaller clearance samples was statistically significant in 25% bovine serum, the more clinically relevant lubricant (ANOVA, p< 0.05). The 50μm clearance group yielded similar results to the 100μm clearance bearing, although a slight increase in friction was observed. Squeaking occurred during every test in the large clearance group. There was a reduced incidence of squeaking in the smaller clearances, with the lowest incidence observed in the 100μm clearance group. The smallest separation of the head and cup was observed within the large clearance bearings. The best lubrication condition measured ultrasonically was observed within the 100μm clearance bearing. There appeared to be good correlation between friction, lubrication and the incidence of squeaking. This study suggests a large diametric clearance results in reduced lubrication, increased friction and an increased incidence of squeaking. However, there is a minimum diametric clearance that can be tolerated, as clearance must accommodate the manufacturing tolerance

Purpose of the study: Ceramic-on-ceramic THA explants exhibit a higher wear rate than that predicted by classical simulators. This appears to be related to edge loading, which could perhaps be reproducible in vitro by creating a microseparation between the two components. The purpose of this study was to evaluate this coefficient of friction for ceramic-on-ceramic THA with edge loading. This should enable prediction of wear in the event of microseparation. Material and methods: Three 32mm alumina inserts (Biolox Forte Ceramtec. ®. ) were tested on a friction simulatior (Prosim. ®. ). The cup was positioned vertically (75° inclination) to reproduce edge loading. The metal-back and the acetabular insert were sectioned to avoid impingement between the neck and cup. Contact was imposed along the border of the cup, then perpendicularly to it. The tests were performed under lubrication conditions (25% bovine serum). In order to simulate severe contact pressures, the tests were also conducted with a third body inserted between the head and the edge of the cup. To obtain reference values of the centred regimen, tests were first run with identical components positioned horizontally. Results: Edge loading was achieved for cups inclined at 75°. The coefficient of friction was 0.02±0.001 under centred conditions. For edge loading conditions, the coefficient of friction was significantly increased, to a mean 0.09±0.00 for movement along the acetabular border and 0.034±0.001 for movement perpendicular to the border. Squeaking occurred for 15 s when the third body was introduced, corresponding to a coefficient of friction 15-fold higher (0.32±0.003) than under ideal conditions. Discussion: For the first time, the coefficient of friction of edge loading was determined under conditions of lubrication. The friction coefficient of ceramic-on-ceramic THA was greater for a very vertical cup, but remained (0.1) equivalent to the metal-on-metal coefficient under optimal conditions. When a third body was introduced, transient squeaking occurred with a very high coefficient of friction. Conclusion: Implantation of cups with a high abduction angle induces edge loading and an increased coefficient of friction, and should be avoided

Squeaking in ceramic on ceramic bearing total hip arthroplasty is well documented but its aetiology is poorly understood. In this study we have undertaken an acoustic analysis of the squeaking sound recorded from 31 ceramic on ceramic bearing hips. The frequencies of these sounds were compared with in vitro acoustic analysis of the component parts of the total hip implant. Analysis of the sounds produced by squeaking hip replacements and comparison of the frequencies of these sounds with the natural frequency of the component parts of the hip replacements indicates that the squeaking sound is due to a friction driven forced vibration resulting in resonance of one or both of the metal components of the implant. Finite element analysis of edge loading of the prostheses shows that there is a stiffness incompatibility between the acetabular shell and the liner. The shell tends to deform, uncoupling the shell-liner taper system. As a result the liner tends to tilt out of the acetabular shell and slide against the acetabular shell adjacent to the applied load. The amount of sliding varied from 4–40μm. In vitro acoustic and finite element analysis of the component parts of a total hip replacement compared with in vivo acoustic analysis of squeaking hips indicate that either the acetabular shell or the femoral stem can act as an “oscillator’ in a forced vibration system and thus emit a squeak. Introduction: Squeaking has long been recognized as a complication in hip arthroplasty. It was first reported in the Judet acrylic hemiarthroplasty. 1. It was the squeak of a Judet prosthesis that led John Charnley to investigate friction and lubrication of normal and artificial joints which ultimately led to the concept of low friction arthroplasty. Ceramic on ceramic bearings were pioneered by Boutin in France during the 1970’s, but experienced unacceptably high fracture rates. Charnley demonstrated in vitro squeaking when he tested one of Boutin’s ceramic-on-ceramic bearings in his pendulum friction comparator. 2. Squeaking has also been reported in other hard on hard bearings, and can also occur after polyethylene bearing surface failure resulting in articulation between metal on metal or ceramic on metal surfaces. 3–6. Recently, squeaking has been increasingly reported in modern ceramic-on-ceramic bearings in hip arthroplasty. However, although well-documented, the aetiology of squeaking in ceramic on ceramic bearings is still poorly understood. The incidence ranges from under 1% to 10%. 7–10. It has been reported in mismatched ceramic couples,11and after ceramic liner fracture. 12,13. An increased risk of squeaking has been demonstrated with acetabular component malposition, as well as in younger, heavier and taller patients. 9. However, it may also occur in properly matched ceramic bearings with ideal acetabular component position and in the absence of neck to rim impingement. 7–9. In rare cases, the squeak is not tolerated by the patient and has prompted a revision. Under ideal conditions hard-on-hard bearings are assumed to be operating under conditions of fluid film lubrication with very low friction. 14,15. However, if fluid film lubrication breaks down leading to dry sliding contact there will be a dramatic increase in friction. If this increased friction provides more energy to the system than it can dissipate, instabilities may develop in the form of friction induced vibrations and sound radiation. 16. Friction induced vibrations are a special case of forced vibration, where the frequency of the resulting vibration is determined by the natural frequency of the component parts. Running a moistened finger around the rim of a wine glass is an example of this. [Appendix]. The hypothesis of this study is that the squeaking sound that occurs in ceramic on ceramic hip replacement is the result of a forced vibration. This forced vibration can be broken down into a driving force and a resultant dynamic response. 17. The driving force is a frictional driving force and occurs when there is a loss of fluid film lubrication resulting in a high friction force. 14,15,18. The dynamic response is a vibration of a part of the device (the oscillator) at a frequency that is influenced by the natural frequency of the part. 16. By analyzing the frequencies of the sound produced by squeaking hip replacements and comparing them to the natural frequency of the component parts of a hip replacement this study aims to determine which part produces the sound. Materials and methods: In vitro determination of the natural frequencies of implant components Modal analysis has suggested that resonance of the ceramic components would occur only at frequencies above the human audible range and that resonance of the metal parts would occur at frequencies within the human audible range. Furthermore, that resonance of the combined ceramic insert and titanium shell would not be within the human audible range. To test this hypothesis we performed a simple acoustic analysis. The natural frequency of hip replacement components was determined experimentally using an impulse-excitation method (Grindo-sonic). Components were placed on a soft foam mat in a quiet environment and struck with a wooden mallet. The sound emitted from the component was recorded on a personal computer with an external microphone with a frequency response which ranges from 50Hz to 18,000Hz (Beyerdynamic MCE87, Heilbronn, Ger-many). The computer has an integrated sound card with a frequency response from 20Hz to 24kHz (SoundMAX integrated digital audio chip, Analogue Devices Inc, Norwood, M.A.) and we used a codec with a frequency response from 20Hz to 20kHz (Audio Codec ’97, Intel, Santa Clara, CA). Sound files were captured as 16 bit mono files at a sample rate of 48000Hz using acoustic analysis software (Adobe Audition 1.5, Adobe Systems Incorporated, San Jose, California, USA). We performed fast Fourier transform (FFT) of the sound using FFT size 1024 with a Blackmann-Harris window to detect the frequency components of the emitted sound. (Fast Fourier transform is an accepted and efficient algorithm which enables construction of a frequency spectrum of digitized sound). We tested the following components: modular ceramic/titanium acetabular components, which included testing the titanium shell and the respective ceramic inserts both assembled according to the manufacturer’s instructions and unassembled; titanium femoral stems and ceramic femoral heads both assembled and unassembled. A range of sizes of each component was tested according to availability from our retrieval collection. In vivo acoustic analysis: Sound recordings were collected from 31 patients. Nineteen recordings were made at our institution: 16 of these were video and audio recordings and 3 were audio only recordings. Video recording was with a digital video camera recorder (Sony DCR-DVD101E Sony Electronics, San Diego, CA, USA) with the same external microphone used in the in vitro analysis. For 3 patients who could not reproduce the sound in the office we lent them a digital sound recorder for them to take home and record the sound when it occurred (Sony ICD-MX20, Sony Electronics, San Diego, CA, USA). This device has a In vivo acoustic frequency range from 60Hz to 13,500Hz. The remainder of the recordings were video and audio recordings made by surgeons at three other institutions on digital video camera recorders. Sound files were captured and analyzed by the same method used in the in vitro analysis. Each recording was previewed in the spectral view mode which allows easy visual identification of the squeak in the sound recording. In addition all sound recordings were played, listening for the squeak. Once a squeak was identified a fast Fourier transform (FFT) was performed. We used FFT size 1024 with a Blackmann-Harris window which allowed us to easily pick out the major frequency components. All prominent frequency components were recorded at the beginning of the squeak and at several time points during the squeak if there was any change. A range was recorded for the fundamental frequency component. We were able to determine the frequency range of the recording device used by observing the frequency range of the background noise on the recording. We found that if a squeak was audible on the recording we had no difficulty determining its frequency regardless of the quality of the device used to make the recording or the amount of background noise. The mean age of the patients was 54 years (23 to 79 years), mean height was 171cm (152 to 186cm) and mean weight was 79kg (52 to 111kg). There were 17 female and 14 male patients. There were nineteen ABGII stem and ABGII cup combinations, 10 accolade stem and trident cup, 1 Exeter stem and trident cup and 1 Osteonics Securfit stem with an Osteonics cup. Ethics committee approval was obtained for this project from our institution and from the referring institutions and informed consent was gained from the patients. Finite element analysis of edge loading: Edge-loading wear which may provide a mechanism for failure of fluid film lubrication and may therefore play a role in squeaking. To evaluate edge loading further we conducted finite-element analysis (FEA). 9. Computed tomography (CT) scans of an intact pelvis were obtained from visual human data set (VHD, NLM, Bethesda, Maryland). Slices were taken at 1mm thick with no inter-slice distance through the entire pelvis. The CT files were then read into a contour extraction program and saved into an IGES file format which was imported into PATRAN (MSC Software, Los Angeles, CA) to develop the pelvic geometry. The pelvis was meshed with 10 noded modified tetrahedral elements. The model was reconstructed with a 54mm titanium alloy generic acetabular shell and a 28mm alumina ceramic liner. The acetabular shell and ceramic liner were meshed using 8 noded hexahedral elements. The shell-liner modular taper junction incorporated an 18° angle. The implant contact conditions (Lagrangian multiplier) allowed the liner and shell to slide with a friction coefficient of 0.9. Tied contact conditions were applied between the generic acetabular shell and the bone representing bone ongrowth. Bone material properties were extracted from the CT files by taking the Hounsfield value and the coordinates and mapping to the element in the model allowing us to calculate the Young’s modulus for each element . 19. Material properties for the shell and liner were based on published values. 20. for titanium alloy and alumina ceramic

Squeaking ceramics bearing surfaces have been recently recognised as a problem in total hip arthroplasty. The position of the acetabular cup has been alluded to as a potential cause of the squeaking, along with particular combinations of primary stems and acetabular cups. This study has used the finite element method to investigate the propensity of a new large diameter preassembled ceramic acetabular cup to squeaking due to malpositioning. A verified three-dimensional FE model of a cadaveric human pelvis was developed which had been CT scanned, and the geometry reconstructed; this was to be used to determine the behaviour of large diameter acetabular cup system with a thin delta ceramic liner in the acetabulum. The model was generated using ABAQUS CAE pre-processing software. The bone model incorporated both the geometry and the materials properties of the bone throughout based on the CT scan. Finite element analysis and bone material assignment was performed using ABAQUS software and a FORTRAN user subroutine. The loading applied simulated edge loading for rising from a chair, heel-strike, toe off and stumbling. All results of the analysis were used to determine if the liner separated from the shell and if the liner was toggling out of the shell. The results were also examined to see if there was a propensity for the liner to demobilise and vibrate causing a squeaking sound under the prescribed loading regime. This study indicates that there is a reduction in contact area between the ceramic liner and titanium shell if a patient happens to trip or stumble. However, since the contact between the liner and the shell is not completely lost the propensity for it to squeak is highly unlikely

Introduction

One of the most common complications of ceramic on ceramic hip replacement is squeaking. The association of Accolade stem and Trident acetabular system has been reported to have squeaking incidence of up to 35,6%. There is doubt if this phenomenon occurs due to: the stem titanium alloy, the V40 femoral neck, the recessed liner of the trident cup or even the mal-seating of the trident insert on the cup.

Audible squeaking following ceramic-on-ceramic total hip arthroplasty (THA) is a rare but troublesome problem. We retrospectively reviewed records of 1002 patients where a ceramic-on-ceramic THA had been done during the study period. Fifteen patients complained of squeaking, at any time following their arthroplasty. Fourteen of these 15 patients were evaluated clinically and radiologically. The demographics of these patients were compared to that of all the other patients who did not have squeaking following ceramic-on-ceramic THA. The radiographic data was compared to a control group matched for age, sex, body mass index (BMI), primary diagnosis, type of implant, date of surgery and length of follow-up.

There were 12 males and 2 females of a mean age of 44.5 years (range, 25–65 years). These 14 patients were found to have significantly higher BMI of 25.98 kg/m2 (range, 21.6–32.3 kg/m2) as compared to the other patients who had ceramic-on-ceramic THA (mean, 23.61 kg/m2; range, 15.8 –30.3 kg/m2) (p=0.005). The lateral opening angle was found to be significantly lower (mean, 34°; range 29°–40°) in these patients than the matched control group (mean, 38°; range 30°–41°) (p=0.016). Mean acetabular anteversion was 22° (range 9°–37°), which was not significantly different to that of the matched controls (mean 23°; range 2°–33°) (p=.957). Limb length shortening of more than 5mm was observed in 12 of the 14 (85.7%) patients as compared to only 4 of 14 (28.6%) patients in the matched control group. Two patients had intermittent squeaking while the other 12 had continuous squeaking. Flexion and sitting cross legged were identified as the movements which most commonly (11 of 12) resulted in squeaking. Mean Harris hip score (HHS) improved from 44 (range, 19–66) to 94 (range, 88–100) and most patients (13 of 14) were satisfied with the outcome of the surgery.

Thus the incidence of squeaking was found to be low (1.5%, 15 of 1002) in our series. We identified high BMI, decreased lateral opening angle and limb length shortening as factors associated with occurrence of squeaking. Proper patient selection, implant placement, and avoidance of limb length discrepancy are likely to further reduce the incidence of this complication of ceramic-on-ceramic THA.

Introduction

Increasing numbers and incidence rates of noisy (squeaking, scratching or clicking) ceramic-on-ceramic (CoC) total hip arthroplasties (THA) are being reported. The etiology seems to always involve stripe wear producing a stick-slip effect in the bearing which excites vibrations. As stripe wear is also found in silent CoC bearings, a theory has been developed that the vibrations become audible only via amplification through the vibrating stem. This was supported by showing that the excitation frequency and the resonance frequency of the plain stem are similar [1]. However, stem resonance in-vivo would be influenced by the periprosthetic bone damping and transmitting stem vibrations. Thus, if stem resonance is conditional for noisy COC hips, these should show periprosthetic bone different to silent hips.

This study compares stem fit&fill and periprosthetic bone between noisy and silent CoC hips.

Introduction

Acetabular cup orientation has been shown to be a factor in edge-loading of a ceramic-on-ceramic THR bearing. Currently all recommended guidelines for cup orientation are defined from static measurements with the patient positioned supine. The objectives of this study are to investigate functional cup orientation and the incidence of edge-loading in ceramic hips using commercially available, dynamic musculoskeletal modelling software that simulates each patient performing activities associated with edge-loading.