Tribology and total hip joint replacement: Current concepts in mechanical simulation

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Medical Engineering & Physics 30 (2008) 1305–1317

Review

Tribology and total hip joint replacement: Current conceptsin mechanical simulation

S. Affatato a,∗, M. Spinelli a,b, M. Zavalloni a, C. Mazzega-Fabbro a,c, M. Viceconti a

a Laboratorio di Tecnologia Medica, Istituti Ortopedici Rizzoli, Bologna, Italyb DMTI, Università di Firenze, Firenze, Italyc DMRN, Università di Trieste, Trieste, Italy

Received 28 February 2008; received in revised form 16 July 2008; accepted 18 July 2008

Abstract

Interest in the rheology and effects of interacting surfaces is as ancient as man. This subject can be represented by a recently coined word:tribology. This term is derived from the Greek word “tribos” and means the “science of rubbing”. Friction, lubrication, and wear mechanismin the common English language means the precise field of interest of tribology.

Wear of total hip prosthesis is a significant clinical problem that involves, nowadays, a too high a number of patients. In order to acquirefurther knowledge on the tribological phenomena that involve hip prosthesis wear tests are conducted on employed materials to extend lifetimeof orthopaedic implants.

The most basic type of test device is the material wear machine, however, a more advanced one may more accurately reproduce someof the in vivo conditions. Typically, these apparatus are called simulators, and, while there is no absolute definition of a joint simulator,its description as a mechanical rig used to test a joint replacement, under conditions approximating those occurring in the human body, isacceptable. Simulator tests, moreover, can be used to conduct accelerated protocols that replicate/simulate particularly extreme conditions,thus establishing the limits of performance for the material. Simulators vary in their level of sophistication and the international literaturereveals many interpretations of the design of machines used for joint replacement testing.

This paper aims to review the current state of the art of the hip joint simulators worldwide. This is specified through a schematic overviewby describing, in particular, constructive solutions adopted to reproduce in vivo conditions.

An exhaustive commentary on the evolution and actually existing simulation standards is proposed by the authors. The need of a sharedprotocol among research laboratories all over the world could lead to a consensus conference.© 2008 Published by Elsevier Ltd on behalf of IPEM.

Keywords: Hip simulator studies; Hip implants; Wear evaluation; Machines for wear tests; Simulator review

Contents

1. History of tribology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13062. Classification of wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13063. Wear and total hip replacement (THR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13074. Hip joint wear simulator machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13085. Hip simulators in the world: state of the art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1309

5.1. Position of the head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13105.2. DOF reproduced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13105.3. Load profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13125.4. Lubricant and applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1312

∗ Corresponding author. Tel.: +39 0516366864; fax: +39 0516366863.E-mail address: [email protected] (S. Affatato).

1350-4533/$ – see front matter © 2008 Published by Elsevier Ltd on behalf of IPEM.doi:10.1016/j.medengphy.2008.07.006


1306 S. Affatato et al. / Medical Engineering & Physics 30 (2008) 1305–1317

6. International guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13137. Comparison across hip joint simulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13138. Conclusions and future directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1314

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1314References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1314

1. History of tribology

The word tribology was first used in a landmark reportby Jost as referenced by Bhushan [1]. The etymology hasto be referred to the Greek term tribos meaning rubbing, sothat literally this would signify “the science of rubbing” [2].The equivalent ordinary English language is “friction andwear”. The Oxford dictionary defines tribology as the sci-ence and technology of interacting surfaces in relative motionand of related subjects and practices [3]. Tribology as a sci-ence succeeds in applying effective analysis to problems ofgreat economic significance for social communities, that is,reliability, maintenance, and wear of technical equipment,ranging from spacecraft to medical devices [4–8]. Interestin the essential parts of tribology is older than recordedhistory [9]. It is well-known that drills made during thePalaeolithic period for drilling holes or producing fire werefitted with bearings made from antlers or bones, and potters’wheels or stones for grinding cereals, had preferable require-ment for some form of bearings [10]. Traces of low-frictionmechanical devices for load support and transmission can bedated about A.D. 40 and localized in Lake Nimi near Rome.Records show the use of wheels from 3500 B.C., whichillustrates our ancestors’ practice with reducing friction intranslation motion while the moving of large stone buildingblocks and monuments required the knowledge of frictionaldevices and lubricants, such as water-lubricated sleds [11].The use of a sledge to transport a heavy statue by Egyptiansin 1880 B.C. is referenced by Bhushan [1].

An ancient observation that gave a good description ofwear phenomena was made by Lucretius in De rerum natura,I (95–55 B.C.) [12]: “. . . a ring is worn thin next to the fingerwith continual rubbing. Dripping water hollows a stone, acurved ploughshare, iron though it is, dwindles imperceptiblyin the furrow. We see the cobblestones of the highway wornbe the feet of many wayfarers. The bronze statues by the citygates show their right hands worn thin by the touch of alltravellers who have greeted them in passing. We see that allthese are being diminished since they are worn away. But toperceive what particles drop off at any particular time is apower grudged us by our ungenerous sense of sight.”

During the centuries of Roman domination, military engi-neers gained profound experience by continual improvementin designing both war machineries and methods of fortifi-cation, by means of tribological principles [9]. It was therenaissance engineer–artist Leonardo da Vinci (1452–1519),famous through the history for his genius in military con-struction as well as for his painting and sculpture, which firstmethodically appreciated friction [13–15]. Da Vinci deduced

the laws governing the motion of a rectangular block slidingover a flat surface [13,14]. He introduced, for the first time,the concept of coefficient of friction as the ratio of the frictionforce to normal load. His work had no historical influence,however, because his notebooks remained unpublished forhundreds years [16].

Friction laws gained light again in 1699 when Amontonsobserved and described dry sliding between two flat surfaces[17]. What he pointed out can be described by two simpleprinciples:

1. the friction force that resists sliding at an interface isdirectly proportional to the normal load;

2. the amount of friction force does not depend on the appar-ent area of contact.

The French physicist Coulomb verified these practicalobservations [18] and added a third law stating the indepen-dence of friction force from velocity, once motion starts. Hewas also the first who made a clear distinction between staticfriction and kinetic friction.

It was Hooke that, at the end of 18th century, suggested toemploy the combination of steel shafts and bell-metal bushesinstead of wood shod with iron for wheel bearings. Furtherdevelopments were associated with the growth of industri-alization in the latter part of the eighteenth century. Earlydevelopments in the oil industry started in Scotland, Canada,and the United States in the 1850s [18,19]. Scientific under-standing of lubricated bearing operations was not achieveduntil the end of the nineteenth century. Indeed, the begin-ning of our understanding of the principle of hydrodynamiclubrication was made possible by the experimental studiesof Tower [20], by the theoretical interpretations of Reynolds[21], and related work by Petroff [22]. Since then develop-ments in hydrodynamic bearing, theory and practice wereextremely rapid in meeting the demand for reliable bearingsin new machinery [23]. Wear is a much newer subject thanfriction and bearing development, and it was initiated on alargely empirical basis. Scientific studies of wear developedlittle until the mid-twentieth century [24]. Since the beginningof the twentieth century, knowledge in all areas of tribologyhas expanded tremendously [25–29], for the enormous indus-trial growth leading to demand for a better understanding oftribology.

2. Classification of wear

Wear mechanism can have a variegate nature, so it isimportant to distinguish its fundamental features, the changes


S. Affatato et al. / Medical Engineering & Physics 30 (2008) 1305–1317 1307

in the appearance (the morphological characteristics) of thebearing surfaces, which are referred to as surfaces damageand the conditions under which the prosthesis was function-ing when the wear occurred, which have been termed as wearmodes [38,39].

One possible general wear classification scheme is dividedinto two main categories: single-phase and multiphase wear[40]. In single-phase wear a solid, liquid or gas moving rela-tive to a sliding surface causes material to be removed fromwearing surfaces. In addition to this, multiphase wear hasa carrier for a second phase (particles, asperities, etc.) thatactually produces the wear. A wear mechanism is the fun-damental microscopic process by which material is removedfrom a surface [41]. There is no organised catalogue contain-ing an exact description of the state of the stress or chemicalconditions imposed on materials subjected to wear. How-ever, wear mechanisms are often classified into some broadtypes: Abrasive, Adhesive, Fatigue, Fretting, Erosive, Corro-sive [12,41–47]:

• Abrasive wear: is due to hard particles or hard protuber-ances that are forced to move against and along a solidsurface. Wear is so defined as damage to a solid surface thatgenerally involves progressive loss of material and is dueto relative motion between that surface and a contactingsubstance or substances.

• Adhesive wear: is generated by the sliding of one solidsurface along another surface. Adhesive wear is as ambigu-ously defined as could be sliding wear, though the two arenot strictly synonymous. Adhesive wear occurs when theasperities on mutually opposing surfaces become fusedtogether and are then subsequently ruptured because oftheir relative motion.

• Fatigue wear: exists in macroscopic and microscopicform. The macroscopic form can occur in non-conformingmachine elements in the form of pitting or rolling contactfatigue. The main forms of this type of wear are so severeas to lead to failure. Fatigue wear on a microscopic scaleis similar to that described above except that it is associ-ated with individual asperity contacts rather than with thesingle large region.

• Fretting wear: fretting is the small amplitude oscillatorymovement that may occur between contacting surfaces,which are usually nominally at rest. The movement is usu-ally the result of an external vibration, but in many casesit is a consequence of the cyclic stress to which one of thecontact members is subjected causing another and usuallymore damaging aspect of fretting.

• Erosive wear: is caused by particles that impinge on acomponent surface or edge and remove material from thatsurface due to momentum effects. This type of wear isespecially noticed in components with high velocity flowssuch as servo and proportional valves. Particles repeatedlystriking the surface may also cause denting and eventualfatigue of the surface.

• Corrosive wear: occurs as a result of a chemical reaction ona wearing surface; the most common form of corrosion isoxidation; corrosion products, usually oxides, have shearstrengths different from those of the metal wearing surfacesfrom which they derived. The oxides tend to flake away,resulting in the pitting of working surfaces. Ball and rollerbearings depend on extremely smooth surfaces to reducefrictional effects; corrosive pitting is especially detrimentalto these bearings.

3. Wear and total hip replacement (THR)

The problems associated with prosthetic failure andrevision surgery still constitute the main clinical problemrelated to total hip replacement (THR) [30]. The preva-lence of primary and revision total hip and knee arthroplastyincreased steadily between 1990 and 2002 [31]. The eco-nomic consequences of these demands on hospitals areburdensome [32,33]. Since total joint replacement has beenapplied to younger and more active patients current lim-itations are related to the rapid wear of the components[48].

The need to solve or reduce wear problems is ofprimary importance. Tribology research leads to greaterimplant efficiency, better performance, fewer breakdowns,and significant savings. The purpose of research in tri-bology is, reasonably, the minimization and eliminationof losses resulting from friction and wear at all lev-els of technology where the rubbing of surfaces isinvolved.

During the wear process, worn material is expelled fromthe contact between two surfaces in the form of debris. Thewear products of hip implants can cause adverse tissue reac-tions leading to massive bone loss around the implant andconsequently loosening of the fixation [35–37]. Such asep-tic loosening requires a revision surgery, where the failedprosthesis is replaced with a new one; this process is stillcomplicated, expensive, and dangerous.

There is no doubt that the biomaterials used play animportant role, and as consequence in vitro tests for suchmaterials are of great importance. Currently, the knowl-edge of laboratory wear rate is an important aspect in thepre-clinical validation of prostheses. Wear tests are con-ducted on materials and designs are used in prosthetichip implants to obtain quality control and acquire fur-ther knowledge about the tribological processes in jointprostheses.

The objective of wear evaluation is to determine the wearrate and its dependence on the test conditions (i.e. load, rangeof motion, lubricant and temperature).

To obtain realistic results, a wear test can be performedto reproduce in vivo working conditions. The degree of reli-ability of these tests depends on the accuracy in recreating,in vitro, the conditions of a prosthetic implant in the humanbody.



4. Hip joint wear simulator machines

Wear resistance of surfaces is not an intrinsic materialproperty but depends on system variables such as operatingconditions, type of counterface, environment, etc. [49]. Ide-ally, each new orthopaedic material should be characterizedfor evaluating its wear properties in a device intended to simu-late the tribological conditions encountered in the human hipjoint and so “eliminate” undesirable variation in materialsproperties that could affect the wear process. To character-ize these specific materials, a wide variety of machines weredeveloped. In the 1960s, the American Society for Lubrica-tion Engineers listed more than 200 types of wear tests andequipment in use [6]. More recently, the use of multi-axialwear machines was implemented to give a better simulationof the type of motion found in vivo and to be of particularvalue in the study of biomaterials wear [50,51].

Generally, two categories of laboratory wear test equip-ments are employed:

• Wear screening devices (quick tests) that provide informa-tion exclusively on the intrinsic features of the materialsstudied (Fig. 1). They are quick; do not accurately rep-resent the specimen geometry of the biomaterials usedthat can influence the lubrication or the contact stress,

thus reproducing approximately the same wear mecha-nisms that occur with a given pair of materials in vivo,but using simplified specimens rather than actual pros-thetic joints. They are inadequate in predicting wear ratesin the implanted joints as they overlook their distinguishingmorphological aspects [52–54].

• Wear joint devices in which real prostheses are tested inan environment that simulates physiological conditions.These machines are “so-called” hip joint wear simulators(Fig. 2) and represent complex, dynamic test conditions.Hip joint simulators predict some aspects of clinical per-formance of the materials tested reproduction in vivo wearpatterns [50,55–59].

Since hip joint simulators wear tests are a prerequisitefor new design and materials combinations prior to their usein the patients, in this review our attention will focus on anextensive variety of hip joint mechanical devices worldwide.

What does simulator mean?

“A hip joint wear simulator is any device, which, under appro-priate test conditions, causes a prosthesis to wear in a mannersubstantially equivalent to that which it would experience intypical clinical use in a patient. In order to accomplish this, ahip joint wear simulator will typically apply a set of motions

Fig. 1. Some of the most popular wear screening devices; they are used to give information exclusively on the intrinsic features of the materials studied.



Fig. 2. Two sections representative of the hip joint wear simulators: (a)Anatomical and (b) the inverted position. These machines simulate physio-logical conditions and represent complex dynamic situation of analysis.

and loads and a lubricant that, in combination, create tribo-logical conditions comparable, but not necessarily identical,to those occurring in vivo [60]”.

These machines vary in their level of sophistication:various references in the literature demonstrate many inter-pretations of the design of equipment used for jointreplacement testing [61,62]. During the last quarter of the pre-vious century, simulators existing in the whole world couldcertainly have been counted on the fingers of two handsand probably only one [63], whereas now laboratories ofalmost all major orthopaedic companies and several univer-sity departments bristle with them [57]. Table 1 shows a briefsummary of these first developed machines.

This is a clear indication not only of the value of suchdevices, but also of the international recognition that careful

laboratory evaluation of new products should precede clinicaltrials. The introduction of this engineering approach itselfrepresented significant progress at the end of the 20th century[54].

Joint simulator tests have been developed to replicate thebiomechanics of human joints in controlled conditions [64].Some simulators are developed in order to be used as weartest machines and to measure as well friction between thejoint bodies [51,54,65–67].

The motions and loading cycles usually represent steadywalking conditions, although in future an agreed daily cycleof motions and loads may need to be specified for lab-oratory evaluations. It is also essential that the mode oflubrication encountered in vivo should be well replicated ifsatisfactory prediction of in vivo wear rates is to be made.At this purpose, coordinate measuring machines (CMM)have been applied in orthopaedic fields, which enable toacquire changes in the overall geometry of surfaces to berecorded with considerable accuracy. It should be noted,however, that such measurements yield the total, morpho-logical changes in geometry, involving both wear and creep[54].

It should also be recognised that the information to repro-duce such conditions may either not be available or, beaccessible, without a high level of accuracy.

5. Hip simulators in the world: state of the art

Considering that all new materials have to be tested beforeclinical trials, hip joint simulators play an important role inthe pre-clinical validation phase. These machines can also beused as research tools allowing experiments to be conductedin a controlled environment, where variables such as sur-face roughness and scratching could change and the effectsmeasured.

The following section analyses the main simulator modelsand their recent applications.

Simulators currently in use differ from each other in manyparameters: number of stations, loading, Degree of Freedom(DOF), ball-cup relative position, temperature-controlled testfluid baths for each hip joint assembly. Moreover, single-station control is still a commonly applied design solution: itcould enable single specimen removal without test interrup-tion.

Table 2 proposes a summary of worldwide hip joint sim-ulators based on an extensive international literature. Inparticular, a schematic description of constructive solutionsadopted by different authors to reproduce in vivo conditionsmay be found out.

We also have to remember that in vivo wear of hip jointshugely varies from patient to patient, even in the case ofidentical prostheses. This happens because wear is influencedby numerous factors such as patient activity, weight, bonequality and surgeon’s experience [59], which, in general, isdifficult to reproduce and control.



Table 1Historical hip joint simulator description (few and dispersed data for available simulators before 1989)

Simulator’s name DOF and load details Lubricant used Notes

Sulzer [105] (Switzerland) DOF: FE Water Single channel inLoad: 300–3500 N Saline Inverted positionFrequency: 60–200 c/min Serum

MIT [106–109] (USA) DOF: FE Saline Two channelsLoad: Paul curve (3115 N) Serum Non-inverted positionFrequency: 30 c/min Synovial fluid Friction study

Veronate buffer

Stanmore Mark I [110,111] (England) DOF: NS Dry Single channelLoad: 700 N Saline NS positionFrequency: NS Plasma Friction study

Stanmore Mark II [112] (UK) DOF: FE, AA and IO Dry NS positionLoad: 1400 N Saline Friction studyFrequency: NS Plasma

MMED [63] (USA) DOF: BRM Bovine blood serum Ten channelsLoad: Paul curve (2448 N) Non-inverted positionFrequency: NS

Leeds Hip-I [113] (UK) DOF: FE and IO NS Single channel in Non-inverted positionLoad: Paul curve (3000 N)Frequency: NS

Leeds Hip-II [74] (UK) DOF: FE, AA and IO NS Three channels inLoad: 0–3000 N Non-inverted positionFrequency: 0.5–2 Hz

Cornell [114] (USA) DOF: AA Synovial fluid Single channel inLoad: 1500–2000 N Non-inverted positionFrequency: NS

NS: not specified; FE: flex-extension; AA: ab-adduction; IO: in–out rotation; DOF: degree of freedom; BMR: biaxial rocking motion; Inverted: the positionwhere the cup is located below the head with respect to a horizontal plane; Non-inverted: the position where the cup is located above the head with respect toa horizontal plane; Anatomical: the position where the cup is located above the head in the position of about 45 degrees abduction (inclination) and also 20degrees flexion (anteversion) [ISO 14242-Part 1].

Multiple stations devices certainly provide greater flexibil-ity, capacity, and the ability to perform multivariate analyseswith greater confidence within a single test [68].

Basic differences still exist in selected simulators regard-ing the mounting position, DOF reproduced, load profilesand lubricant used; a brief discussion is presented in thefollowing.

5.1. Position of the head

The upside-down simulator, which provides an invertedposition of the prosthesis compared with the physiologicalanatomical one, has the advantage of a better lubrication. Infact, the articulation would be prone to drying out due to airbubbles, which gather in the contact area during the test. Theonly metallic parts, which the lubricant is in contact with, arethose of the prosthesis.

In this way, third body particles tend to be drawn into thecup by gravity; if we consider that any third-body particlesthat are in the joint fluid have a high probability of circulatingbetween the bearing surfaces multiple times, this invertedposition may be a ‘closer representation’ of the situation invivo. Here, the small amount of joint fluid volume would

promote high probability of multiple time debris circulationbetween the bearing surfaces.

Lubrication related to the mounting configuration of headand cup might result in a temperature distribution differentfrom the in vivo situation. A higher maximum temperaturehas been reported in the upright position [69]. This suggeststhat the inverted position helps an appropriate circulation ofthe lubricant between the bearing surfaces, thus contributingto prevent overheating. Moreover, it has to be considered thatthe higher the maximum temperature is, the faster proteinsprecipitation takes place, thus resulting in the formation ofadherent layers constituting a protective film between the balland the cup; this can produce the least wear of the testedmaterial [69].

5.2. DOF reproduced

A hip joint simulator should be capable of generating theangular range of movements of the femoral component mim-ing the natural human motion and loading by adapting theDOF in kinematic motion. The great variety of hip simu-lators reproduce various DOF. In particular, a single-axiship simulator mimics flexion/extension movement [70,71].



Table 2Modern hip joint simulator description (from 1990 to 2007)

Simulator’s name DOF Load data Lubricant used Notes

HUT-I [115,73] Custom-Made machine Finland FE: ±30◦ Type: hydraulic Distilled water Single channels inProfile: double peak Non-inverted positionLmax: 5000 N Temperature control

(37 ± 1 ◦C)Frequency: 0.4–2.2 Hz

HUT-II [116,138] Custom-Made machine Finland FE: ±30◦ Type: pneumatic Distilled water,Bovine serum

Five channels

Profile: on/off Inverted positionLmax: 3500 N Temperature control

(37 ± 1 ◦C)Frequency: 1.08 Hz

HUT-III [73,78] Custom-Made machine Finland AA: range 12◦ Type: pneumatic Distilled water, Single channelFE: range 46◦ Profile: on/off Bovine serum Inverted positionIO: range 12◦ Lmax: 3500 N Temperature control

(37 ± 1 ◦C)Frequency: 1.18 Hz

MTS-BIONIX [117,118] Commercial machine USA BRM: ±22.5◦ Type: hydraulic Balancedalpha-calf serum

12 channels

Profile: physiologic Non-inverted positionLmax: 2450 N Temperature controlLmin: 50 NFrequency: 1 Hz

Shore western [55,119–122] Commercial machine USA BRM: ±22.5◦ Type: hydraulic Calf serum 12 channelsProfile: sinusoidal Bovine serum Inverted positionLmax: 2450 NLmin: 150 NFrequency: 1.1 Hz

Shore western [120,123,124] Commercial machine USA BRM: ±22.5◦ Type: hydraulic Calf serum Nine channelsProfile: Paul Bovine serum Non-inverted positionLmax: 2450 NLmin: 150 NFrequency: 1 Hz

AMTI [50,125] Commercial machine USA AA: ±8.5◦ Type: hydraulic Bovine serum 12 channelsFE: ±23◦ Profile: Paul Non-inverted positionIO: ±10◦ Lmax: 2450 N Temperature

monitoringLmin: 150 NFrequency: 2 Hz

BRM [126,127] Custom-Made machine Finland BRM: ±22.5◦ Type: spring Calf serum Three channelsProfile: static Non-inverted positionLmax: 1000 N Temperature

monitoringFrequency: 1 Hz

HUT-4 [59,128] AA: ±6◦ Type: pneumatic Calf serum 12 channelsCustom-Made machine Finland Currently commerciallyavailable from Phoenix Tribology Ltd.

FE: ±23◦ Profile: double peak Anatomical positionLmax: 2000 NLmin: 400 NFrequency: 1 Hz

MARK I [129,130] Custom-Made machine UK FE: ±25◦ Type: pneumatic Calf serum Five channelsIO: +8◦ to −20◦ Profile: Paul Non-inverted position

Lmax: 2000 NFrequency: 1 Hz

Mark II [131] Custom-Made machine UK FE: +30◦ to −15◦ Type: pneumatic Calf serum Five channelsIO: +8◦ to −20◦ Profile: square wave Non-inverted position

Lmax: 2000 NFrequency: NS



Table 2 (Continued )

Simulator’s name DOF Load data Lubricant used Notes

PA II [132] Custom-Made machine UK FE: +30◦ to −15◦ Type: NS Profile: Paul Lmax:3000 N Frequency: 1 Hz

Calf serum Six channels

IO: ±10◦ Non-inverted position

Prosim [56] Commercial machine UK FE: +30◦ to −15◦ Type: pneumatic Calf serum 10 channelsIO: ±10◦ Profile: Paul Non-inverted position

Lmax: 2780 NFrequency: 1 Hz

Matco-Ew08mmed [133] (Custom-Made machine;USA)

BRM: ±22.5◦ Type: hydraulic Calf serum 16 channelsProfile: Paul Bovine serum Inverted positionLmax: 2100 NFrequency: 1.13 Hz

Endolab [134–136] Commercial machine Germany AA: +7◦ to −4◦ Type: hydraulics Bovine serum Six channelsFE: +25◦ to −18◦ Profile: Paul Non-inverted positionIO: +2◦ to −11◦ Lmax: 3000 N

Frequency: 1 Hz

Fime II [137] Custom-Made machine Mexico AA: ±23◦ Dynamic load system Bovine serum NS channelsFE: ±23◦ Different load patterns

reproducibleNon-inverted position

IO: ±7.5◦ Frequency: 1.4 Hz

NS: not specified; FE: flex-extension; AA: ab-adduction; IO: in–out rotation; DOF: degree of freedom; BMR: biaxial rocking motion; Lmax: Maximum load;Lmin: Minimum load; Inverted: the position where the cup is located below the head with respect to a horizontal plane; Non-inverted: the position where thecup is located above the head with respect to a horizontal plane; Anatomical: the position where the cup is located above the head in the position of about 45degrees abduction (inclination) and also 20 degrees flexion (anteversion) [ISO 14242-Part 1].

A two-axis simulator reproduces flexion/extension move-ment and abduction/adduction motion or flexion/extensionand inward/outward rotation [68,72], while a three-axis sim-ulator attempts to include full performance criteria suchas flexion/extension, abduction/adduction movements andinward/outward rotation [50,73,74].

However, the more complex the test system becomes, themore difficult it may be to justify multiple test channels (dueto cost) and the harder it will be to keep the machine operableand its operating specifications consistent (due to complexity)[51].

5.3. Load profile

In a hip simulator the force control system should be capa-ble of replicating a simplified gait cycle (physiologic profile)according to the ISO 14242 [75]. Although force transmissionaccuracy is a basic requirement for every hip joint simulator,when the system is used to assess the wear of articulating sur-faces, other requirements should be taken into account, sincewear is also related to other parameters (i.e. sliding distance,velocity, acceleration, etc.) [76].

Many studies take into account different load profiles fortheir laboratory tests to investigate substantial differences infinal results [77,78]. The first simulators were characterizedby sinusoidal load profiles, with variable peak loads, evenif the real forces between the ball and the cup were known[79]. In the same way a number of studies focus on the effectsinduced on the wear results by the application of a static loadobtained by averaging more complex load profiles obtainedfrom gait analyses [72,78].

A broad debate, however, is still open about weathersimplistic load profiles can reproduce physiological wearpatterns and weight loss, thus reducing mechanical sophisti-cation and managing competences.

5.4. Lubricant and applications

A hip simulator should be able to maintain the contactsurface immersed in the fluid test medium (bovine serum,saline, water, etc.) and enclosed in a flexible plastic bag inorder to reduce fluid evaporation and oxygen-related changesto the serum or other components as recommended by theinternational standard [75,80,81]. Moreover, there shouldbe a temperature control system so to maintain the tem-perature of the fluid test medium at 37 ± 2 ◦C. A widediscussion is ongoing within the scientific community aboutthe possibility of using different lubricants such as distilledwater, bovine serum or synthetic ones, though providing thesame wear behaviour [37]. The main problem with lubricat-ing conditions is the increase in precipitated proteins and,as a consequence, lubrication regime [37,82]. The gradualincrease in proteins, related even to temperature augmenta-tion, would cause a gradual drop in wear rate because of anun-physiological protection effect against wear. It is not stillclear what proteins are denaturing and providing the bound-ary lubrication, i.e. albumin, globulin, or others [57,83].Generally, water, saline, gelatine solutions, and other sim-ilar fluids do not produce relevant clinical wear rates or weardebris [34,57,84,85]. Protein degradation masks true wearrates, so care should be taken with regard to protein concen-tration and ratios, temperature and volume of the lubrication



serum [57,82,84]. In other words, in an attempt to idealis-tically simulate the ‘correct’ temperature one likely reducesthe validity of the simulation; in such a case it is best to run atroom temperature and have a large, open lubricant chamber sothat there is always sufficiently soluble protein present and sothat the evaporation further helps in preventing overheating.

6. International guidelines

The continuous research to improve wear resistant mate-rials for hip prostheses leaves open the debate about the needto adopt a common approach for wear testing of total hip jointprosthesis. A quick glance at Table 2 presented in the follow-ing section shows the “jungle” of hip implants simulators, inparticular in the first decades of their use.

In 1989, the International Organizations for Standard-ization (ISO) drafted an international procedure to obtaincomparable results between laboratories. With the intro-duction of these guidelines [86] the important aspectscontrol-related for wear test, in case of using biomaterials,were outlined (polymer, metal, ceramic or composite mate-rials).

In 1996 the American Society for Testing and Materi-als (ASTM) introduced “The standard guide for gravimetricwear assessment of prosthetic Hip-Designs in SimulatorDevices” [80] to implement the standard basic wear-screening tests, such as pin on-disk [52] or ring-on-disc [87].

Since 2000 the ISO recommendations specified the meth-ods of wear assessment and the kinematics to apply inorder to conduct a consistent wear test [75,81]. The inno-vation of this international standard, with respect to the

previous recommendation, is reported in the first part. Inparticular, the normative identifies three degrees of freedom(abduction/adduction, inward/outward rotation, and flex-ion/extension) and axial load obtained from gait analysis. Theaim of this normative is to specify the kinematics between thearticular components relatively to the relative angular move-ments, the pattern of the applied force, frequency and durationof testing, sample configuration and test environment.

In particular, the ISO 14242 parts 1 and 2 suggest to per-form a hip wear test using an axial load having a doublepeak profile with a peak intensity of 3000 N [79]. Moreover,the flexion/extension angular movement is a simple sinusoidbetween 25◦ and –18◦, while the abduction/adduction is asinusoid between 7◦ and –4◦, and the inward/outward rotationwork in a range between 2◦ and –10◦.

7. Comparison across hip joint simulators

Joint simulator tests have been developed to simulatethe biomechanics of human joints in controlled conditions.Results from simulator testing can provide confirmation ofthe material’s performance for a given geometric designunder a variety of operating conditions. Different simula-tor designs provide different wear results for the differentbearings as shown in Fig. 3.

As a consequence, Fig. 3 emphasizes that it is not pos-sible to compare the wear behaviour obtained with differentsimulator rigs even when testing the same prostheses. At themoment, in fact, not every ones follow ISO standards and theones who do, introduce slight variations to them accordingto internal protocols. This result in high data dispersion even

Fig. 3. Volumetric wear data, plotted for different bearings, of all treated hip joint simulators.



with a narrow assortment of commercially available materi-als, for such medical devices (i.e. UHMWPE, CoCr alloys,alumina, etc.).

This fact addressed many investigators towards moreobjective wear indicator such as the relative wear rate. If thetest conditions are appropriate, then the same types of wearmechanisms will be generated and the relative wear rates (i.e.,the percent reductions) exhibited by a new material will becomparable among different simulators and between the labtests and subsequent clinical performance [139].

On the other hand the “comparison” presented in Fig. 3is not exhaustive due to the high number of uncontrolledvariables related both to mechanical simulation factors, mate-rials tested (i.e. metals, polyethylene or ceramic) and bearingdimensions. In clinical situations, the wear can be traced, forexample, radiologically but these measurements are ofteninaccurate and insensitive to small changes [54]. That isthe reason why it was impossible to compare, in the samepicture, the in vitro vs. in vivo mean wear rates. Someresults, derived from in vivo studies, report, for example,a linear mean wear rate ranging between 0.003 mm/year(ceramic-on-ceramic bearing) and 0.15 mm/year (metal-on-UHMWPE bearing); the wear performance of the otherbearings (ceramic-on-UHMWPE and metal-on-metal) isknown to be about 0.06 mm/year and 0.004 mm/year respec-tively [88–99]. These results are not linkable with the meanvolumetric wear rate obtained from the in vitro results dueto the different wear estimation techniques (i.e. gravimet-ric, geometrical, volumetric, image processing, etc.) and alsonon-homogeneity in the dimension of the tested specimens.

It was stressed that several factors affect in vivo wear withrespect to the more restrictive and controlled laboratory con-ditions [100] so that a correlation between in vitro vs. in vivodata remain a challenge.

8. Conclusions and future directions

Research and development in wear-resistant materialscontinues to be a high priority. Clinical research, designed toevaluate carefully the performance of new materials intendedto reduce wear, is essential to ascertain their efficacy andprevent the possibility of unexpected failure [101].

Given the large number of implanted devices, long-termsurveillance of relevant populations will also be valuable inunderstanding the nature and severity of potential systemiceffects. Furthermore, long-term follow-up studies throughregional or national registries would be of great value inascertaining the performance of implant systems [102–104].

Continuous development of simulators is needed to repli-cate in vivo behaviour as closely as possible.

Wear and simulator testing are complicated tasks becauseof the lack of understanding of the basic wear mechanismsunder a variety of operating conditions. Controlled wear test-ing should not only be routinely done to qualify a material,but also to elucidate wear mechanisms. Until now, con-

fidence in the interpretation of wear testing data derivesfrom the successful correlation of bench test wear surfaceswith retrieved implant surfaces in terms of surface textureand wear debris size and shape. One of the critical issuesin wear and joint simulator testing is how to extrapolateshort-term testing results to long-term projections. Theserequire a solid understanding of the relationship betweenmaterial structures, properties, and wear mechanisms. Acarefully designed parametric study is needed to examinesystematically the influence of speed, loading cycles, andmotion directions on a material’s behaviour and the resultingwear phenomena. Material selection and component designare important factors in the performance and durability oftotal joint replacement. The roles of wear testing and jointsimulation studies are often unclear, however, in terms ofdiscriminating the effect of materials and design on per-formance. Controlled bench wear testing should be used todevelop an understanding of wear mechanisms and the influ-ence of environmental, design, and material parameters onwear behaviour. By replicating the specific conditions occur-ring in a hip joint, simulator testing can then be used to testspecific design and material combinations. The elements ofa wear system include the contact surfaces, lubricant, load,articulating surfaces speed and relative position, motions,surface roughness, and temperature. The general conditionsat the contact interface may not control wear as much asthe specific load conditions at the asperities on the contactsurfaces.

To use the same simulation parameters is a shared needamong the laboratories all over the world; this could be appre-ciated with a round-robin-test or a consensus conference inorder to define a common protocol for total hip arthroplasty invitro simulation. Future developments in this direction couldbe useful to carry out remarkable discussions on comparableresults.

Acknowledgments

The authors wish to thank Keith Smith for his linguisticsupport and Luigi Lena for the illustrations.

References

[1] Bhushan B. Definition and history of tribology. In: Principles andapplications of tribology. 1st ed. New York: John Wiley & Sons; 1999.p. 1–3.

[2] Petterson A. High-performance base fluid for environmentallyadapted lubricants. Tribol Int 2007;40:638–45.

[3] Oxford, D. Tribology; 2008, http://www.askoxford.com/concise oed/tribology?view=uk.

[4] Batchelor AW, Stachowiak GW. Tribology in materials processing. JMater Process Technol 1995;48:503–15.

[5] Cole GS, Sherman AM. Lightweight materials for automotive appli-cations. Mater Character 1995;35:3–9.

[6] Katz A, Redlich M, Rapoport L, Wagner HD, Tenne R. Self-lubricating coatings containing fullerene-like WS2 nanoparticles for



orthodontic wires and other possible medical applications. Tribol Lett2006;21(2):135–9.

[7] Taylor CM. Automobile engine tribology—design considerations forefficiency and durability. Wear 1999;221:1–8.

[8] Tichy JA, Meyer DM. Review of solid mechanics in tribology. Int JSolids Struct 2000;37:391–400.

[9] Dowson D. History of tribology. London: Professional EngineeringPublishing; 1998. p. 1–7 [chapter 1].

[10] Davidson CSC. Bearings since the stone age. Engineering1957;183:2–5.

[11] Bhushan B. Introduction to tribology. Wiley; 2002. p. 752.[12] Archard JF. Wear theory and mechanism. In: Peterson MB, Winer

WO, editors. Wear control handbook. New York: ASME; 1980. p.35–80.

[13] Thompson BS. Environmentally-sensitive design: Leonardo WASright! Materials and Design 1999;20:23–30.

[14] Lenard JG. Flat Rolling — A General Discussion. Primer on FlatRolling 2007:17–35.

[15] Gao J, Luedtke WD, Gourdon D, Ruths M, Israelachvili JN, LandmanU, et al. Amontons’ Law: From the Molecular to the MacroscopicScale. J Phys Chem B 2004;108(11):3410–85.


[17] Amontons G. De la Résistance Causée e dans les Machines. Mémoiresde l’Académie Royale 1699:257–82.

[18] Coulomb CA. The orie des Machines Simples, en ayant regard auFrottement de leurs Parties, et a la Roideur des Cordages. Mem MathPhys 1785;X:161–342.


[20] Tower B. First report on friction experiments. Proc Inst Mech Eng1884;34(a):632–59.

[21] Reynolds OO. On the theory of lubrication and its applicationto Mr. Beauchamp Tower’s experiments. Phil Trans R Soc Lond1886;177:157–234.

[22] Petroff NP. Friction in machines and the effects of the lubricant. EngJ 1883;71:228–79.

[23] Bhushan B. Principles of tribology. Washington, DC: LLC; 2001.[24] Stachowiak GW, Batchelor AW. Introduction. In: Engineering tribol-

ogy. London: Butterworth Heinemann; 2002. p. 1–8 [chapter 1].[25] Holm R. Electrical contacts. In: Bowden FP, Tabor D, editors. The

friction and lubrication of solids, Part II. New York: Springer-Verlag;1946.

[26] Tabor D, Winterton RHS. The direct measurement of normal andretarded van der Waals forces. Proc R Soc Lond 1969;A312:435–50.

[27] Bhushan B. Mechanics and reliability of flexible magnetic media.New York: Springer-Verlag; 1992. p. 664.

[28] Bhushan B. Tribology and mechanics of magnetic storage devices.2nd ed. New York: Springer; 1996. p. 1160.

[29] Bhushan B, Gupta BK. Handbook of Tribology: Materials Coatingsand Surface Treatments. Malabar, FL: Krieger Publishing; 1997. p.1785.

[30] NIH. Total hip replacement; 1994. http://consensus.nih.gov/1994/1994HipReplacement098html.htm.

[31] Kurtz S, Mowat F, Ong K, Chan N, Lau E, Halpern M. Preva-lence of primary and revision total hip and knee arthroplasty inthe United States from 1990 through 2002. J Bone Jt Surg [Am]2005;87:1487–97.

[32] Straffelini G. Attrito ed usura dei materiali. Trento (Italy): ASSIM;2000. p. 152.

[33] Kurtz SM, Ong KL, Schmier J, Mowat F, Saleh K, Dybvik E, et al.Future Clinical and economic impact of revision total hip and knee. JBone Jt Surg [Am] 2007;89:144–51.

[34] O’Connor DT, Choi MG, Kwon SY, Sung K-LP. New insight into themechanism of hip prosthesis loosening: effect of titanium debris sizeon osteoblast function. J Orthop Res 2004;22:229–36.

[35] McGee MA, Howie DW, Costi K, Haynes DR, Wildenauer CI, PearcyMJ, et al. Implant retrieval studies of the wear and loosening ofprosthetic joints: a review. Wear 2000;241:158–65.

[36] Yan Y, Neville A, Dowson D. Tribo-corrosion properties of cobalt-based medical implant alloys in simulated biological environments.Wear 2007;263(7–12):1105–11.

[37] Brown SS, Clarke IC. A review of lubricant conditions for wearsimulation in artificial hip joint replacements. Tribol Trans 2006;49:72–8.

[38] McKellop HA, Campbell P, Park S-H, Schmalzried TP, Grigoris P,Amstutz HC, et al. The origin of submicron polyethylene wear debrisin total hip arthroplasty. Clin Orthop Relat Res 1995;311:3–20.

[39] Czichos H, Klaffke D, Santner E, Woydt M. Advances in tribology:the materials point of view. Wear 1995;190:155–61.

[40] Peterson MB. Clasification of wear process. In: Peterson MB, WinerWO, editors. Wear control handbook. New York: ASME; 1980. p.9–15.

[41] Scherge M, Shakhvorostov D, Pöhlmann K. Fundamental wear mech-anism of metals. Wear 2003:395–400.

[42] Schmalzried TP, Callaghan JJ. Current concepts review—wear in totalhip and knee replacements. J Bone Jt Surg [Am] 1999;81:115–36.

[43] Jones SMG, Pinder IM, Moran CG, Malcolm AJ. Polyethylene wearin uncemented knee replacements. J Bone Jt Surg [Br] 1992;74-B1:18–22.

[44] Lombardi AVJ, Mallory TH, Vaughn BK, Drouillard P. Aseptic loos-ening in total hip arthroplasty secondary to osteolysis induced bywear debris from titanium-alloy modular femoral heads. J Bone JtSurg [Am] 1989;71-A:1337–42.

[45] Black J. The future of polyethylene. J Bone Jt Surg [Br] 1978;60-B3:303–6.

[46] Callaghan JJ, Pedersen DR, Olejniczak JP, Goetz DD, Johnston RC.Radiographic measurement of wear in 5 cohorts of patients observedfor 5 to 22 years. Clin Orthop Relat Res 1995;317:14–8.

[47] Peterson MB. Classification of wear process. In: Peterson MB, WinerWO, editors. Wear control handbook. 1980. p. 9–16.

[48] Wright T, Goodman S. Implant wear: the future of total joint replace-ment. Rosemont, IL, USA: AAOS; 1995.

[49] Ravikiran A. Wear quantification. J Tribol 2000:650–6.[50] Bragdon CR, O’Connor DO, Lowenstein JD, Jasty M, Syniuta WD.

The importance of multidirectional motion on the wear of polyethy-lene. Proc Inst Mech Eng [H] 1996;210(3):157–65.

[51] Wang A, Stark C, Dumbleton JH. Mechanistic and morphologi-cal origins of ultra-high molecular weight polyethylene wear debrisin total joint replacement prostheses. Proc Inst Mech Eng [H]1996;210(3):141–55.

[52] ASTM F732-00. Standard Test Method for Wear Testing of PolymericMaterials used in Total Joint Prostheses. West Conshohocken, PA:ASTM; 2006.

[53] ASTM G133-95. Standard Test Method for Linearly ReciprocatingBall-on-Flat Sliding Wear. Annual book of ASTM standards, vol.03.02. West Conshohocken, PA: 2002, pp 558–565.

[54] Dowson D. New joints for the millennium: wear control in totalreplacements hip joints. Proc Inst Mech Eng [H] 2001;215:335–58.

[55] Affatato S, Leardini W, Jedenmalm A, Ruggeri O, Toni A. Largerdiameter bearings reduce wear in metal-on-metal hip implants. ClinOrthop Relat Res 2007;456:153–8.

[56] Barbour PS, Stone MH, Fisher J. A hip joint simulator study using newand physiologically scratched femoral heads with ultra-high molec-ular weight polyethylene acetabular cups. Proc Inst Mech Eng [H]2000;214(6):569–76.

[57] Clarke IC, Chan FW, Essner A, Good V, Kaddick C, Lappalainen R,et al. Multi-laboratory simulator studies on effects of serum proteinson PTFE cup wear. Wear 2001;250(1–12):188–98.

[58] Goldsmith AA, Dowson D, Isaac GH, Lancaster JG. A comparativejoint simulator study of the wear of metal-on-metal and alternativematerial combinations in hip replacements. Proc Inst Mech Eng [H]2000;214(1):39–47.



[59] Saikko V. A 12-station anatomic hip joint simulator. Proc Inst MechEng [H] 2005;219(6):437–48.

[60] ASTM-WK451. New method for wear assessment of prosthetic hipdesigns in simulator devices. West Conshohocken, PA: ASTM Inter-national; 2008. www.astm.org.

[61] Dumbleton JH. The evaluation of prostheses on joint simulators.In: Dumbleton JH, editor. Tribology of natural and artificial joints.Amsterdam: Elsevier; 1981. p. 258–322.

[62] Ahmed AM, Burke DL, Yu A. In-vitro measurement of static pres-sure distribution in synovial joints—Part II: retropatellar surface. JBiomech Eng Trans ASME 1983;105:226–36.

[63] Clarke IC. Wear of artificial joint materials IV. Eng Med1981;10(4):189–98.

[64] Hsu SM. What is the role of wear testing and joint simulator stud-ies in discriminating among materials and designs? AAOS; 2001. p.147–55.

[65] Brockett C, Williams S, Jin Z, Isaac G, Fisher J. Friction of totalhip replacements with different bearings and loading conditions. JBiomed Mater Res Part B: Appl Biomater 2007;81B:508–15.

[66] Barbour PSM, Stone MH, Fisher J. A hip joint simulator study usingsimplified loading and motion cycles generatine physiological wearpaths and rates. Proc Inst Mech Eng [H] 1999;213:455–67.

[67] Lu Z, McKellop H. Frictional heating of bearing materials tested in ahip joint wear simulator. Proc Inst Mech Eng [H] 1997;211(1):101–8.

[68] Goldsmith AA, Dowson D. Development of a ten-station, multi-axiship joint simulator. Proc Inst Mech Eng [H] 1999;213(4):311–6.

[69] Lu Z, McKellop H, Liao P, Benya P. Potential thermal artifacts in hipjoint wear simulators. J Biomed Mater Res 1999;48(4):458–64.

[70] Beutler H, Lehmann M. Wear behaviour of medical engineering mate-rials. Wear 1975;33:337–50.

[71] Dumbleton JH, Miller DA, Miller EH. A simulator for load bearingjoints. Wear 1972;20:165–74.

[72] Saikko V, Calonius O. Slide track analysis of the relative motionbetween femoral head and acetabular cup in walking and in hip sim-ulators. J Biomech 2002;35(4):455–64.

[73] Saikko VO. A three-axis hip joint simulator for wear and fric-tion studies on total hip prostheses. Proc Inst Mech Eng [H]1996;210(3):175–85.

[74] Dowson D, Jobbins B. Design and development of a versatile hip jointsimulator and a preliminary assessment of wear and creep in Charnleytotal replacement hip joints. Eng Med 1988;17(3):111–7.

[75] ISO-14242/1. Implants for surgery––Wear of total hip jointprostheses––Part 1: Loading and displacement parameters for wear-testing machines and corresponding environmental conditions fortests; 2002.

[76] Viceconti M, Cavallotti G, Andrisano AO, Toni A. Discussion on thedesign of a hip joint simulator. Med Eng Phys 1996;18:234–40.

[77] Schwenke T, Schneider E, Wimmer MA. Load profile, fluid compo-sition influence the soak behaviour of UHMWPE implants. J ASTMInt 2006;3(8):5–10.

[78] Saikko V, Ahlroos T. Type of motion and lubricant in wear sim-ulation of polyethylene acetabular cup. Proc Inst Mech Eng [H]1999;213(4):301–10.

[79] Paul JP. Forces transmitted by joints in the human body. Lubricationand wear in living and artificial human joints. Proc Inst Mech Eng1966;3J(8):181.

[80] ASTM-F1714. Standard Guide for Gravimetric Wear Assessment ofProsthetic Hip-Designs in Simulator Devices. West Conshohocken,PA: ASTM International; 2008. www.astm.org.

[81] ISO-14242/2. Implants for surgery—Wear of total hip joint prosthe-ses. Part 2: Method of measurement; 2000.

[82] Saikko V. Effect of lubricant protein concentration on the wear ofultra-high molecular weight polyethylene sliding against a CoCrcounterface. Trans ASME 2003;125:638–42.

[83] Wang A, Essner A, Schmidig G. The effects of lubricant compositionon in vitro wear testing of polymeric acetabular components. J BiomedMater Res B Appl Biomater 2004;68(1):45–52.

[84] Heubergera MP, Widmera MR, Zobeley E, Glockshuber R, SpenceraND. Protein-mediated boundary lubrication in arthroplasty. Bioma-terials 2005;26:1165–73.

[85] Calonius O, Saikko V. Analysis of polyethylene particles pro-duced in different wear conditions in vitro. Clin Orthop Relat Res2002;399:219–30.

[86] ISO/TR-9325. Implants for surgery—Partial and total hip joint pros-theses. Recommendations for simulators for evaluation of hip jointprostheses; 1989.

[87] ISO-6474. Implants for surgery—Ceramic materials based on highpurity alumina; 1994.

[88] McKellop H, Park SH, Chiesa R, Doorn P, Lu B, Normand P, et al. Invivo wear of three types of metal on metal hip prostheses during twodecades of use. Clin Orthop Relat Res 1996;329(suppl):S128–40.

[89] Wroblewski BM, Siney PD, Dowson D, Collins SN. Prospective clin-ical and joint simulator studies of a new total hip arthroplasty usingalumina ceramic heads and cross-linked polyethylene cups. J BoneJoint Surg Br 1996;78(2):280–5.

[90] Silva M, Heisel C, Schmalzried TP. Metal-on-metal total hip replace-ment. Clin Orthop Relat Res 2005;430:53–61.

[91] Kothari M, Bartel DL, Booker JF. Surface geometry of retrievedMcKee-Farrar total hip replacements. Clin Orthop Relat Res1996;329:S141–7.

[92] Schmidt M, Weber H, Schön R. Cobalt chromium molybdenummetal combination for modular hip prostheses. Clin Orthop Relat Res1996;329:S35–47.

[93] Willert HG, Buchhorn GH, Göbel D, Köster G, Schaffner S, SchenkR, et al. Wear behavior and histopathology of classic cementedmetal on metal hip endoprostheses. Clin Orthop Relat Res 1996;329:S160–86.

[94] Clarke IC, Gustafson A. Clinical and hip simulator comparisonsof ceramic-on-polyethylene and metal-on-polyethylene wear. ClinOrthop Relat Res 2000;379:34–40.

[95] Schüller HM, Marti RK. Ten-year socket wear in 66 hip arthroplasties.Ceramic versus metal heads. Acta Orthop Scand 1990;61(3):240–3.

[96] Zichner LP, Willert HG. Comparison of alumina-polyethyleneand metal-polyethylene in clinical trials. Clin Orthop Relat Res1992;282:86–94.

[97] Wroblewski BM, Siney PD, Fleming PA. Low-friction arthroplastyof the hip using alumina ceramic and cross-linked polyethylene. Aten-year follow-up report. J Bone Jt Surg Br 1999;81:54–5.

[98] Skinner HB. Ceramic bearing surfaces. Clin Orthop Relat Res1999;369:83–91.

[99] Boehler M, Knahr K, Plenk HJ, Walter A, Salzer M, Schreiber V.Long-term results of uncemented alumina acetabular implants. J BoneJt Surg Br 1994;76(1):53–9.

[100] Saikko V, Calonius O, Keranen J. Effect of counterface roughnesson the wear of conventional and crosslinked ultrahigh molecularweight polyethylene studied with a multi-directional motion pin-on-disk device. J Biomed Mater Res 2001;57:506–12.

[101] Essner A, Schmidig G, Wang A. The clinical relevance of hipjoint simulator testing: In vitro and in vivo comparisons. Wear2005;259:882–6.

[102] Garellick G, Malchau H, Herberts P. Survival of total hip replace-ments: A comparison of a randomized trial and a registry. Clin Orthop2000;375:157–67.

[103] Stea S, Bordini B, De Clerico M, Petropulacos K, Toni A. First hiparthroplasty register in Italy: 55000 cases and 7 year follow-up. IntOrthop 2007. Epub ahead of print.

[104] Servizio Sanitario Regionale, E.-R. R.I.P.O.2007, https://ripo.cineca.it/.

[105] Semlitsch M, Lehmann M, Weber H, Doerre E, Willert HG. Newprospects for a prolonged functional life-span of artificial hip jointsby using the material combination polyethylene/aluminium oxideceramin/metal. J Biomed Mater Res 1977;11(4):537–52.

[106] Linn FC. Lubrication of animal joints I. The arthrotripsometer. J BoneJoint Surg Am 1967;49(6):1079–98.



[107] Rose RM, Nusbaum HJ, Schneider H, Ries M, Paul I, Crugnola A, etal. On the true wear rate of ultra high-molecular-weight polyethylenein the total hip prosthesis. J Bone Joint Surg Am 1980;62(4):537–49.

[108] Simon SR, Paul IL, Rose RM, Radin EL. “Stiction-friction” of totalhip prostheses and its relationship to loosening. J Bone Joint Surg Am1975;57(2):226–30.

[109] Weightman BO, Paul IL, Rose RM, Simon SR, Radin EL. Acomparative study of total hip replacement prostheses. J Biomech1973;6(3):299–311.

[110] Duff-Barclay I, Spillman DT. Total human hip joint prostheses—alaboratory study of friction and wear. Proc Inst Mech Eng1967;181(3J):8–15.

[111] Scales JT, Kelly P, Goddard D. Friction torque studies of total jointreplacements. The use of a simulator. Ann Rheum Dis 1969;28(5Suppl):30–5.

[112] Scales JT, Mech CI, Wright KW. Experimental methods for the assess-ment of wear of materials potentially useful for endoprostheses. ActaOrthop Belg 1975;41(Suppl 1 (1)):160–8.

[113] Dowson D, Walker PS, Longfield MD, Wright V. A joint simulatingmachine for load-bearing joints. Med Biol Eng 1970;8(1):37–43.

[114] Walker PS, Gold BL. The tribology (friction, lubrication and wear)of all-metal artificial hip joints. Wear 1971;17:285–99.

[115] Saikko V. A simulator study of friction in total replacement hip joints.Proc Inst Mech Eng [H] 1992;206(4):201–11.

[116] Saikko VO. Wear of the polyethylene acetabular cup. The effect ofhead material, head diameter, and cup thickness studied with a hipsimulator. Acta Orthop Scand 1995;66(6):501–6.

[117] Essner A, Sutton K, Wang A. Hip simulator wear comparison of metal-on-metal, ceramic-on-ceramic and crosslinked UHMWPE bearings.Wear 2005;259(7):992–5.

[118] Wang A, Polineni VK, Stark C, Dumbleton JH. Effect of femoralhead surface roughness on the wear of ultrahigh molecular weightpolyethylene acetabular cups. J Arthroplasty 1998;13(6):615–20.

[119] Affatato S, Torrecillas R, Taddei P, Rocchi M, Fagnano C, CiapettiG, et al. Advanced nanocomposite materials for orthopaedic appli-cations. I: A long-term in vitro wear study of zirconia-toughenedalumina. J Biomed Mater Res B Appl Biomater 2005.

[120] Oonishi H, Clarke IC, Good V, Amino H, Ueno M. Alumina hipjoints characterized by run-in wear and steady-state wear to 14million cycles in hip-simulator model. J Biomed Mater Res A2004;70(4):523–32.

[121] Affatato S, Frigo M, Toni A. An in vitro investigation of Diamond-Like Carbon as a femoral head coating. J Biomed Mater Res (ApplBiomater) 2000;53:221–6.

[122] Affatato S, Goldoni M, Testoni M, Toni A. Mixed oxides prostheticceramic ball heads. Part 3: effect of the ZrO2 fraction on the wear ofceramic on ceramic hip joint prostheses. A long-term in vitro study.Biomaterials 2001;22:717–23.

[123] Clarke IC, Good V, Williams P, Schroeder D, Anissian L, Stark A,et al. Ultra-low wear rates for rigid-on-rigid bearings in total hipreplacements. Proc Inst Mech Eng [H] 2000;214(4):331–47.

[124] Mizoue T, Yamamoto K, Masaoka T, Imakiire A, Akagi M, ClarkeIC. Validation of acetabular cup wear volume based on direct andtwo-dimensional measurements: hip simulator analysis. J Orthop Sci2003;8(4):491–9.

[125] Ramamurti BS, Estok DM, Jasty M, Harris WH. Analysis of the kine-matics of different hip simulators used to study wear of candidatematerials for the articulation of total hip arthroplasties. J Orthop Res1998;16(3):365–9.

[126] Saikko V, Ahlroos T, Calonius O, Keranen J. Wear simulation of totalhip prostheses with polyethylene against CoCr, alumina and diamond-like carbon. Biomaterials 2001;22(12):1507–14.

[127] Saikko V, Calonius O, Keranen J. Wear of conventional and cross-linked ultra-high-molecular-weight polyethylene acetabular cupsagainst polished and roughened CoCr femoral heads in a biaxial hipsimulator. J Biomed Mater Res 2002;63(6):848–53.

[128] Saikko V. A hip wear simulator with 100 test stations. Proc Inst MechEng [H] 2005;219(5):309–18.

[129] Smith SL, Ash HE, Unsworth A. A tribological study of UHMWPEacetabular cups and polyurethane compliant layer acetabular cups. JBiomed Mater Res 2000;53(6):710–6.

[130] Smith SL, Burgess IC, Unsworth A. Evaluation of a hip joint simula-tor. Proc Inst Mech Eng [H] 1999;213(6):469–73.

[131] Smith SL, Unsworth A. A five-station hip joint simulator. Proc InstMech Eng [H] 2001;215(1):61–4.

[132] Barbour PS, Stone MH, Fisher J. A hip joint simulator studyusing simplified loading and motion cycles generating physiolog-ical wear paths and rates. Proc Inst Mech Eng [H] 1999;213(6):455–67.

[133] McKellop HA, Shen FW, Campbell P, Ota T. Effect of molecularweight, calcium stearate, and sterilization methods on the wear ofultra high molecular weight polyethylene acetabular cups in a hipjoint simulator. J Orthop Res 1999;17(3):329–39.

[134] Oberbach T, Gien W, Kaddick C. Third-body-wear as a risk factor injoint endoprosthetics. Key Eng Mater 2005;284–286:995–8.

[135] Oberbach T, Begand S, Glien W, Kaddick C. Investigation of ageddispersion ceramics by means of hip simulator. Key Eng Mater2008;361–363:771–4.

[136] Kaddick C, Wimmer MA. Hip simulator wear testing according tothe newly introduced standard ISO 14242. Proc Inst Mech Eng [H]2001;215:429–42.

[137] Ortega-Sáenz JA, Hernández-Rodríguez MAL, Pérez-Unzueta A,Mercado-Solis R. Development of a hip wear simulation rig includingmicro-separation. Wear 2007;263:1527–32.

[138] Saikko V, Paavolainen P, Kleimola M, Slätis P. A five-stationhip joint simulator for wear rate studies. J Eng Med 1992;206:195–200.

[139] Engh Jr CA, Stepniewski AS, Ginn SD, Beykirch SE, Sychterz-Terefenko CJ, Hopper Jr RH, et al. A randomized prospectiveevaluation of outcomes after total hip arthroplasty using cross-linked marathon and non-cross-linked Enduron polyethylene liners. JArthroplasty 2006;21(6 suppl 2):17–25.

Tribology and total hip joint replacement: Current concepts in mechanical simulation

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