potentialities of wear measurement in total knee arthroplasty

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Alexei Katashev, Yuri Dekhtyar, Janis Spigulis (Eds.): NBC 2008, Proceedings 20, pp. 390–392, 2008

www.springerlink.com © Springer-Verlag Berlin Heidelberg 2008

Potentialities of Wear Measurement in Total Knee Arthroplasty

M. Pochmon1, T. Rössler 2, J. Gallo3, M. Hrabovský1, D. Mandát1 and V. Havránek 1

1 Joint Lab. of Optics of the Palacky Univ. and the Inst. of Physics of the Acad. of Sciences of the Czech Rep., Olomouc, Czech Republic2 Palacky Univ./ Fac. of Natural Sciences, Dept. of Experimental Physics, Olomouc, Czech Republic

3 University Hospital, Palacky Univ./Fac. of Medicine and Dentistry, Department of Orthopedics, Olomouc, Czech Republic

Abstract — The contribution describes two optical and one

contact measuring method used to measure the wear of poly-

ethylene insert of knee implants. These implants are under

stress in patient body and therefore they suffer from wear. The

purpose of these measurements is the creation of sensor in-

tended to measure a statistic file of damaged implants and

compare this file with way of life and other parameters of

patients, who used them.

Keywords — Total endoprothesis, phase-shifting profilome-

try, 3D laser scan profilometry, contact surface measurement.

I. I NTRODUCTION

Total knee arthroplasty is the best method to heal the ar-thritis of knee joint [1]. Today, in most cases are used implants with polyethylene insert, which suffer from wear.The size of this wear depends on the patient’s age, sex,activity, weight, way of life, etc. By measuring of enough

amounts of used knee implants, it is possible to create astatistic file of these implants and classify each wear ac-

cording to specific patient.The wear is depended upon the shape of polyethylene in-

sert, too. There are several manufactures, that produce these

insert, and each of these producer has its own shape of kneeimplant insert that differ a little from another ones. Another purpose of wear measurement is to discover, which shape ismore resistant to wear.

In this paper, three 3D measuring methods are described.One contact method and two optical methods, 3D laser scan profilometry and phase-shifting profilometry. In conclusion,the advantages and disadvantages of these methods will bediscussed and one of them will be chosen for building sen-sor, which will serve to measure the file of weared implants.

Every method measures the surface of used implant in-sert, and the result is then subtracted from the reference

unused implant insert. This way, the wear is achieved.

II. K NEE IMPLANT

The knee implant is created of polyethylene insert, that is

connected to shin-bone (see fig.1) and metal part connectedto thigh-bone. At fig.2 it is possible to see polyethylene

insert from other manufactures. The shape difference be-tween them can be well seen.

The wear of polyethylene insert has two origins, loss ofmaterial because of using and little fragments and grooves,

made by extraneous objects and by material defect. Thesesmall defects are very small compared to wear caused by

attrition of metal and polyethylene parts.

Fig. 1 The polyethylene insert of knee implant.

Fig. 2 The polyethylene insert of knee implant – other producer.



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III. CONTACT MEASURING METHOD

This method is based on scanning of the surface of meas-

ured object by contact sensing head [2]. For measurement,the Talysurf from Tyler-Hobson was used. Resolution of themeasurement was approximately 50 m. The implant insert

is put under the sensing head and it is scanning insert’ssurface in premeditate determined plains. The more plainsare defined, the more time measurement takes. The speed ofthe sensing head is about 2 mm per second. Results of the

contact measurements are shown at fig.3 and fig.4.

IV. 3D LASER SCAN PROFILOMETRY

This 3D optical non-coherence method is based on pro-

jecting of linear laser stripe on the measured object [3]. Thisstripe is deformed by the surface of the object and savedinto computer by CCD camera. Because the calibration ofthe deformations of laser line is done, the height variationthrough the laser line can be computed. The whole surfaceis measured, when the laser line is shifted over whole meas-

ured area in defined steps (for examples 1 mm). The area between two nearby lines is approximated. The resolution

of this method is about 100 m. The deformed linear laserstripe is shown in fig.5, the result of measurement is shownin fig.6.

V. PHASE-SHIFTING PROFILOMETRY

This optical 3D non-coherence method is based onevaluating of change of phase of sinusoidal pattern. These

patterns are projected on the reference plain and measuredobject, each one shifted from another. If there are used N patterns, each pattern is shifted by 2/N and all of them aresaved into computer by CCD camera. After computingalgorithm, which gives a change of phase in whole meas-ured area, it is possible to compute height variation in each pixel of CCD chip and whole profile of measured object is

achieved. The resolution of that method is about 100 m.For the result, it is necessary to take at least 4 snapshots of

Fig. 3 The result of contact polyethylene insert measurement.

Fig. 4 The result of contact polyethylene insert measurement – other

visualization.

Fig. 5 The linear laser stripe deformed by measured surface.

Fig. 6 The result of measurement using 3D laser scan profilometry.



392 M. Pochmon, T. Rössler, J. Gallo, M. Hrabovský, D. Mandát and V. Havránek

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patterns on measured object and 4 snapshots of patterns onreference plain. The sinusoidal pattern is shown in fig.7 and

in fig.8 is shown the result of knee insert measurement.

VI. CONCLUSIONS

It is obviously, that contact method is the most accuratemethod for measuring of knee implant inserts. On the other

side, one measurement takes too much time – about hours.And for this kind of application, its superior resolution isnot necessary.

3D laser scan profilometry has sufficient resolution, butit is time-consuming measurement. The width of knee insert

is about 7,5 cm, it means 75 position changes and 75 snap-shots during one measurement with 1 mm step.

For this kind of surface, the most proper measuringmethod is phase-shifting profilometry. It has sufficient reso-lution, its projected optical structure covers whole measuredarea and it takes only 4 snapshots of measured object. The

measurement can be done during few seconds and is enoughaccurate for its purpose.

Another step will be construction of measuring sensorand creation of large statistic file of knee implant inserts.This will lead to improve insert’s shape, quality of its mate-rial, and its lifetime.

ACKNOWLEDGMENT

These results of the project 1M06002 was supported by

The Ministry of Education of the Czech Republic.These results of the project OC168 was supported by The

Ministry of Education of the Czech Republic.

R EFERENCES

1. Gallo J, Havránek V, echová I, Zapletalová J (2006) Wear measure-

ment of retrieved polyethylene ABG 1 cups by universal measuringmicroscope and x-ray methods. Biomed Pap Med Fac Univ Palacky

Olomouc Czech Repub 150(2):231-236.

2. Havránek V, Gallo J (2007) measurement of the polyethylene liner

wear of the extracted total knee substitute. Fine mechanics and optics52(11-12):316-320.

3. Mandát D, Rössler T, Hrabovský M, Gallo J (2006) Optical topog-raphical methods in medical practice. Acta mechanica Slovaca

10(1):327-332.

Author: Pochmon MichalInstitute: Joint Lab. of Optics of the Palacky Univ. and the Inst. of

Physics of the Acad. of Sciences of the Czech Rep.

Street: T . 17 listopadu 50aCity: Olomouc

Country: Czech republic

Email: [email protected]

Fig. 7 Sinusoidal pattern projected on the knee implant insert.

Fig. 8 Result of phase-shifting profilometry.

potentialities of wear measurement in total knee arthroplasty

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