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Orthopaedic Proceedings
Vol. 106-B, Issue SUPP_5 | Pages 27 - 27
23 Apr 2024
Howard A Harwood P Benton A Merrel C Culmer P Bolton W Stewart T
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Introduction

Ilizarov fixators are reliant on tensioned fine wires for stability. The tension in the wires is generated using specific tensioning devices. Loss of wire tension over time may lead of loss a stability and complications. A series of in vitro experiments were undertaken to explore wire tensioner accuracy, the impact of fixation bolt torque and initial tension on loss of tension in ilizarov constructs under static and dynamic loads.

Materials & Methods

Medical grade materials were applied to a synthetic bone analogue using surgical instruments in all experiments. Bolt torque was fixed at 6, 10 or 14 Nm using a torque limiting wrench. Wire tension was assessed using a strain measurement bridge. Wires were tensioned to 90, 110 and 130kg as measured by a commercial dynamometric tensioner. Static and dynamic testing was undertaken using an instron testing machine. Cyclical loads from 50–750N were applied for 5000 cycles.


Orthopaedic Proceedings
Vol. 105-B, Issue SUPP_16 | Pages 17 - 17
17 Nov 2023
Naeem H Maroy R Lineham B Stewart T Harwood P Howard A
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Abstract

OBJECTIVES

To determine if force measured using a strain gauge in circular external fixation frames is different for 1) different simulated stages of bone healing, and for 2) fractures clinically deemed either united or un-united.

METHODS

In a laboratory study, 3 similar Ilizarov frame constructs were assembled using a Perspex bone analogue. Constructs were tested in 10 different clinical situations simulating different stages of bone healing including with the bone analogue intact, with 1,3 and 50mm gaps, and with 6 materials of varying stiffness's within the 50mm gap. A Bluetooth strain gauge was inserted across the simulated fracture focus, replacing one of the 4 threaded rods used to construct the frame. Constructs were loaded to 700N using an Instron testing machine and maximum force during loading was measured by the strain gauge. Testing was repeated with the strain gauge replacing each of the 4 threaded rods in turn, with measurements being repeated 3 times, across all 3 frame constructs for all 10 simulated clinical situations (n=360). Force measurements between the situations were compared using a Kruskal-Wallis test (KW) and a post-hoc Steel test was used for multiple comparison against control (intact bone model). Additionally, a pilot study has been initiated to assess clinical efficacy of the strain gauge measurement in patients with circular frames. The strain gauge replaced the anterior rod across the fracture focus for each patient. Patients were asked to step on a weighing scale with their affected limb, and maximum weight transfer through the limb and maximal force measured in the frame were recorded. This was repeated 3 times and a mean ratio of force to weight through affected limb was calculated for each patient. The clinical situation at each measurement was designated as united or un-united by one of the senior authors for analysis. Force measurements between the situations were compared using a Wilcoxon-Mann-Whitney test.


There is a strong association between the presence of a calcar collar on a cementless stem and a reduced risk of revision surgery for periprosthetic fracture of the femur (PFF). A medial calcar collar may act to reduce relative movement between the implant and femur during PFF, through calcar-collar contact (CCC). The aims were:

Estimate the effect of CCC on periprosthetic fracture mechanics.

Estimate the effect of initial calcar-collar separation on the likelihood of CCC.

Three groups of six composite femurs were implanted with a fully coated collared cementless femoral stem. Neck resection differed between groups (group 1 = no additional resection, group 2 = 3mm additional resection, group 3 = 6mm additional resection). PFF were simulated using a previously published technique. Fracture torque and rotational displacement were measured and torsional stiffness and rotational work prior to fracture were estimated. Results between trials where CCC did and did not occur where compared using Mann-Whitney U tests. Logistic regression estimated the odds (OR) of failing with 95% confidence interval (CI) to achieve CCC for a given initial separation.

Where CCC occurred fracture torque was greater (47.33 [41.03 to 50.45] Nm versus 38.26 [33.70 to 43.60] Nm, p= 0.05) and torsional stiffness was greater (151.38 [123.04 to 160.42] rad.Nm−1 versus 96.86 [84.65 to 112.98] rad.Nm−1, p <0.01).

CCC was occurred in all cases in group one, 50% in group two and 0% in group three. OR of failure to obtain CCC increased 3.8 fold (95% CI 1.6 to 30.2, p <0.05) for each millimetre of separation.

Resistance to fracture and construct stiffness increased when a the collar made contact with the calcar prior to fracture and the chances of contact decrease with increasing initial separation at the time of implantation. Surgeons should aim to achieve a calcar-collar distance of less than 1mm following implantation to ensure CCC and to reduce the risk of fracture


Abstract

Objective

To compare the periprosthetic fracture mechanics between a collared and collarless fully coated cementless femoral stem in a composite femur.

Methods

Two groups of six composite femurs (‘Osteoporotic femur’, SawBones, WA USA) were implanted with either a collared (collared group) or collarless (collarless group) cementless femoral stem which was otherwise identical by a single experienced surgeon. Periprosthetic fractures of the femur were simulated using a previously published technique. High speed video recording was used to identify fracture mechanism. Fracture torque and angular displacement were measured and rotational work and system stiffness were estimated for each trial. Results were compared between collared and collarless group and the comparison was evaluated against previously published work using fresh frozen femurs and the same protocol.


Orthopaedic Proceedings
Vol. 103-B, Issue SUPP_2 | Pages 19 - 19
1 Mar 2021
Lamb J Coltart O Adekanmbi I Stewart T Pandit H
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Abstract

Objective

To estimate the effect of calcar collar contact on periprosthetic fracture mechanics using a collared fully coated cementless femoral stem.

Methods

Three groups of six composite femurs were implanted with a fully coated collared cementless femoral stem. Neck resection was increased between groups (group 1 = normal, group 2 = 3mm additional, group 3 = 6mm additional), to simulate failure to obtain calcar collar contact. Periprosthetic fractures of the femur were simulated using a previously published technique. Fracture torque and rotational displacement were measured and torsional stiffness and rotational work prior to fracture were estimated. High speed video recording identified if collar to calcar contact (CCC) occurred. Results between trials where calcar contact did and did not occur where compared using Mann-Whitney U tests.


Orthopaedic Proceedings
Vol. 103-B, Issue SUPP_2 | Pages 41 - 41
1 Mar 2021
Lamb J Coltart O Adekanmbi I Stewart T Pandit H
Full Access

Abstract

Objective

To estimate the effect of calcar collar separation on the likelihood of calcar collar contact during in vitro periprosthetic fracture.

Methods

Three groups of six composite femurs were implanted with a collared cementless femoral stem. Neck resection was increased between groups (group 1 = normal, group 2 = 3mm additional, group 3 = 6mm additional), to simulate failure to obtain calcar collar contact. Prior to each trial, the distances between anterior (ACC) and posterior (PCC) collar and the calcar were measured. Periprosthetic fractures of the femur were simulated using a previously published technique. High speed video recording identified when collar to calcar contact (CCC) occurred. The ACC and PCC were compared between trials where the CCC was and was not achieved. Regression estimated the odds of failing to achieve CCC for a given ACC or PCC.


Orthopaedic Proceedings
Vol. 100-B, Issue SUPP_3 | Pages 89 - 89
1 Apr 2018
Salhab M Kimpson P Freeman J Stewart T Stone M
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Background

Acute pain following total knee replacements (TKRs) is associated with higher peri-operative opiate requirements and their side effects, longer hospital stay and lower patient satisfaction (Petersen 2014). It may also be associated with higher rates of chronic pain at 1 and 5 years (Beswick 2012). We present a novel technique using combination of Local Infiltration Anaesthesia (LIA) with PainKwell infusion system (Bupivacaine 0.5 @ 4mls and 6mls/hr) to improve pain management following TKRs.

Methods

Between October 2015 and March 2016. 110 patients undergoing primary TKR were prospectively studied. All patients studied had spinal anaesthesia (SA) with diamorphine. Demographics between the two groups were similar.

Group 1. SA plus LIA plus traditional multimodal analgesia. 32 patients.

Group 2. SA plus LIA plus PainKwell for 48 hours rate 4mls. 38 patients

Group 3. SA plus LIA plus PainKwell for 48 hours rate 6mls. 40 patients


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_9 | Pages 57 - 57
1 May 2017
Salhab M Macdonald D Kimpson P Freeman J Stewart T Stone M
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Background

Hip arthroplasties are associated with high postoperative pain scores. In some reports, moderate to severe pain was 58% on the first day postoperatively in total hip replacements (THRs). Several techniques are currently used at our institution to tackle acute pain following THRs. These include: 1) Spinal anaesthetic (SA) with Diamorphine only; 2) General anaesthetic (GA) only; 3) SA with local infiltration anaesthetic mixture 1 (LIA1,). Mixture 1 consisted of ropivacaine, adrenaline, and ketorolac; 4) SA with LIA mixture 2 (LIA2). Mixture 2 consisted of bupivacaine and adrenaline; 5) SA with LIA1 and PainKwell pump system. In this study we report on the techniques of acute pain control following THR at our regional centre for elective primary THRs.

Methods

Between June 2011 and July 2014, 173 consecutive patients undergoing primary THR using the posterior approach were prospectively followed up. Group 1. GA only. 31 patients, Group 2. SA only. 37 patients, Group 3. SA plus LIA1 only. 38 patients, Group 4. SA plus LIA2 only, 34 patients, Group 5. SA plus LIA1 plus PainKwell Pump System for 48 hours. 33 patients.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_9 | Pages 98 - 98
1 May 2017
Salhab M Kimpson P Freeman J Stewart T Stone M
Full Access

Background

Pain control following knee replacement (TKR) surgery is often poor. Moderate to severe pain is often reported in the first 48 hours following surgery requiring opiate analgesia. The Local Infiltration Anaesthetic (LIA) technique has been described as a method to reduce post operative pain. In this study we report on our experience using LIA in addition to the PainKwell system (Peak Medical) of continuous infusion intra-articularly, of 0.25% bupivacaine at 4–5 mls/hour for 48 hours post surgery. The PainKwell catheter is placed in the knee joint during surgery.

Methods

Between the June 2012 and Sep 2012, 62 patients undergoing primary TKR were prospectively followed up. All patients studied had spinal anaesthesia (SA) with diamorphine. Group 1. GA. No LIA and no PainKwell. 20 patients. Group 2. SA plus LIA plus PainKwell for 48 hours post operatively with catheter placed anteriorly under the patella. 21 patients. Group 3. SA plus LIA plus PainKwell for 48 hours post operatively with catheter placed posteriorly in the knee joint. 21 patients.


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_1 | Pages 17 - 17
1 Jan 2013
Whitwell G Brockett C Young S Stone M Stewart T
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Introduction

During broach preparation and implant insertion of the proximal femur the surgeon may be able to use audible pitch changes to judge broaching adequacy and implant position. The aim of this study was to analyse the sound produced and explain the sound spectra using acoustic physics.

Methods

A highly sensitive microphone was used to digitally record the sound made during femoral preparation and definitive implant insertion in 9 patients undergoing total hip arthroplasty. The sound data was analysed using a fast Fournier transformation spectrum analyser. The highest 4 peak spectral amplitudes of the first broach, the last strike of the final broach and the definitive implant were recorded. The sound spectra produced by striking the implant introducer in isolation were analysed in a similar manner.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXIX | Pages 65 - 65
1 Jul 2012
Dahabreh Z Stewart T Stone M
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Purpose of the Study

This study aims at investigating the effect of application time of bone cement on the cement-bone interface strength in two types of commercially available bone cements, Cement-A and Cement-B.

Materials and methods

Cement-A and Cement-B were applied to cancellous bone specimens at two different times; 2 and 4 minutes (min). The bone specimens were formulated from bovine bone. Specimens were loaded to failure and the force at which the cement-bone interface failed was recorded. The shear strength of the cement-bone interface was calculated by dividing the force at failure by the cross-sectional surface area of the cement-bone interface.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXIX | Pages 7 - 7
1 Jul 2012
Walshaw T Karuppiah S Stewart T
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Introduction

A common complication whilst harvesting the hamstring tendon in ACL reconstruction is injury to the infra-patellar branch of the saphenous nerve (IPBSN), resulting in altered sensation to the anterior and lateral aspects of the knee and leg.

Aim

The aim of this study was to understand the course of IPBSN in relation to tendon harvest in ACL reconstruction.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXV | Pages 55 - 55
1 Jun 2012
El-Hadi S Stewart T Jin Z Fisher J
Full Access

Background

High cup abduction angles generate increased contact stresses, higher wear rates and increased revision rates. However, there is no reported study about the influence of cup abduction on stresses under head lateralisation conditions for ceramic-on-Ceramic THA.

Material and method

A finite elements model of a ceramic-on-ceramic THA was developed in order to predict the contact area and the contact pressure, first under an ideal regime and then under lateralised conditions. A 32 mm head diameter with a 30 microns radial clearance was used. The cup was positioned with a 0°anteversion angle and the abduction angle was varied from 45° to 90°. The medial-lateral lateralisation was varied from 0 to 500 microns. A load of 2500 N was applied through the head center.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXV | Pages 56 - 56
1 Jun 2012
El-Hadi S Stewart T Jin Z Fisher J
Full Access

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 3rd 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.


Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_IV | Pages 533 - 534
1 Nov 2011
Sariali E Stewart T Jin Z Fisher J
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Purpose of the study: Implantation of the acetabular socket with high inclination generates increased contract stress, wear and revision rate for total hip arthroplasty (THA). Study of ceramic-on-ceramic THA explants has revealed a high wear rate in bands, suggesting a microseparation effect generating edge loading. There have not been any studies examining the influence of the cup inclination on the contact pressures in ceramic-on-ceramic THA exposed to microseparation between the head and the cup.

Material and methods: A finite elements model of a ceramic-on-ceramic hip prosthesis was developed with ABAQUS in order to predict the surface contact and the distribution of the contract pressures, first during ideal centred function then under conditions of microseparation. A 32mm head and a radial clearance head (30μm) were used. The cup was positioned in zero anteversion and 45, 65, 70, and 90° anteversion. Progressive microseparation (0 to 500 μm) was imposed. A 2500N loading force was applied to the centre of the head.

Results: For 45° inclination, edge loading appeared for mediolateral separation greater than 30 μm and became complete for 60 μm separation. When edge loading appeared, the contact surface was elliptic. The length of the lesser axis converged towards 0.96mm; the greater axis towards 8.15mm, respectively in the anteroposterior and mediolateral directions. For inclinations of 45°, the contact pressure was 66 Mpa for the centred force. As the mediolateral separation increased, the maximal contact pressure increased, converging towards an asymptotic value of 205 MPa. Increasing the inclination angle of the cup generated an increase in the maximal contact pressure. However, this increase in contact pressure generated by the increasing inclination angle was negligible if the microseparation increased.

Discussion: Cup inclination and mediolateral laxity increase stress forces of ceramic-on-ceramic THA and should be avoided. However, the influence of the cup inclination becomes negligible beyond a separation value of 240 μm, the stress forces already having reached their asymptotic value.


Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_IV | Pages 534 - 534
1 Nov 2011
Sariali E Stewart T Jin Z Fisher J
Full Access

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.


Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_IV | Pages 415 - 415
1 Nov 2011
Zeng P Rainforth W Inkson B Stewart T
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Retrieved alumina-on-alumina hip joints frequently exhibit a localised region of high wear, commonly called ‘stripe wear’. This ‘stripe wear’ can be replicated in vitro by the introduction of micro-separation, where the joint contact shifts laterally reproducing edge loading during the simulated walking cycle. While the origin of stripe wear is clearly associated with the micro-scale impact resulting from micro-separation, the wear processes leading to its formation and the wear mechanisms elsewhere on the joint are not so well understood. The purpose of this study was to compare the surface microstructure of in vivo and in vitro alumina hip prostheses, and investigate the origins of the damage accumulation mechanisms that lead to prosthetic failure.

The in vivo alumina hip prosthesis was Biolox (Ceram-Tec, AG, Plochingen, Gemany) implanted for 11 years [1]. The in vitro alumina hip prosthesis was Biolox-forte (CeramTec, AG, Plochingen, Gemany), which had been tested in a hip joint simulator under micro-separation at Leeds University using the procedures given in [2]. The worn surfaces of the alumina hip prostheses were investigated using a Scanning Electron Microscopy (SEM). Similar worn surfaces were seen for both in vivo and in vitro samples. Focused ion beam (FIB) microscopy was used to determine the sub-surface damage across the stripe wear. Samples were subsequently removed for Transmission Electron Microscopy (TEM). Sub-surface damage was found to be limited to a few μm beneath the surface; ~ 2μm for in vivo samples and ~1μm for in vitro samples. The transition from mild wear to more severe (stripe) wear was entirely triggered by intergranular fracture. The first stages of fracture lead to the liberation of surface grains which act as 3rd body abrasives. The TEM showed that abrasive grooves are associated with extensive surface dislocation activity, which leads to further grain boundary fracture.

This allows the cycle to be repeated and accelerated, thus yielding the stripe wear region.

The conclusions are: 1. In vitro hip simulation with micro-separation can produce similar microstructure to in vivo alumina hip prostheses; 2. To extend the life of the joint through the avoidance of severe wear, material and design solutions can be investigated using ceramic materials that have an increased surface inter-granular fracture toughness and component designs with reduced contact stress under edge loading.


Orthopaedic Proceedings
Vol. 92-B, Issue SUPP_IV | Pages 529 - 529
1 Oct 2010
Sariali E Fisher J Jin Z Stewart T
Full Access

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.


Orthopaedic Proceedings
Vol. 92-B, Issue SUPP_I | Pages 103 - 104
1 Mar 2010
Sariali* E Stewart* T Jin* Z Fisher* J
Full Access

Introduction: The use of hard-on-hard hip prostheses has highlighted specific problems like the “stripe-wear” and the squeaking. Many authors have related these phenomena to a micro-separation between the cup and the head. The goal of the study was to model the hip kinematics under micro-separation regime in order to develop a computational simulator for total hip prosthesis including a joint laxity, and to use it to perform a sound analysis.

Method: A three-dimensional model of the Leeds II hip simulator was developed on ADAMS® software. A spring was used to introduce a controlled micro-separation (less than 500 microns) during the swing phase of the walking cycle. The increase of the load during the stance phase induced a relocation of the head in the cup. Values of the medial-lateral separation predicted from the model were compared to experimental data measured using a LVDT of less than 5 microns precision. Theoretical wear path predicted from the model was compared to the literature data. The frequencies of the vibratory phenomena were determined, using the Fourier transformation.

Results: There was an excellent correlation between the theoretical prediction and the experimental measurement of the medial-lateral separation during the walking cycle (0.92). Edge-loading contact occurred during 57% of the cycle according to the model and 47% according to the experimental data. Velocity and acceleration were increased during the relocation phase in a chaotic manner, leading to vibration. The contact force according to the model had also a chaotic variation during the micro-separation phase, suggesting a chattering movement. Fourier transformation showed many frequencies in the audible area.

Discussion: A three-dimensional computational model of the kinematics of the hip after total replacement was developed and validated with an excellent precision under microseparation. It highlighted possible explanations for the squeaking that may occur during either relocation phase or edge loading.


Orthopaedic Proceedings
Vol. 92-B, Issue SUPP_I | Pages 139 - 139
1 Mar 2010
Sariali* E Stewart* T Jin* Z Fisher* J
Full Access

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.