Triage methodology for the evaluation of implant-bone interfaces

615

Triage methodology for the evaluation of implant-bone interfaces Jo& Ricardo Lenzi Mariohi”, William Dias Belangero+ and Antonio Celso Fonseca de ArrudaS ‘Technological Center, State University of Campinas, Caixa Postal 6737, BR 13081-970 Campinas SP, Brazil; ‘Department of Orthopaedics, faculty of Medical Sciences, State University of Campinas, 8R 73087-970 Campinas SP, Brazil; tfaculty of Mechanical Engineering, State University of Campinas, BR 13087-970 Campinas SP, Brazil Stainless

steel

in order

plugs

to develop

of implant-bone scarce.

After

radiographed preliminary

coated

interfaces. a maximum using

precise

thickness

Received

This approach follow-up

determination bone

28 April 1993; accepted

The introduction of an implant in a living tissue elicits an interfacial response which depends on a large number of variables, like material biocompatibility, shape, size, surface of the implant, kind of tissue bed (osseous or soft tissue), condition of the tissue, surgical technique, mechanical interaction between and implant and host tissue’. The understanding of the interfacial tissue response is essential to the research of new implant materials. To achieve it, it is necessary to investigate the interface at various levels of resolution’. Because of this multiplicity of influencing variables, the complete tissue response analysis demands the study of the interface at different perspectives (morphological, analytical, biomechanical) with the consequent application of several methods of investigation. A morphological study of the interface embraces radiological and histological investigations to provide information basically expressed in the form of images. The conventional orthopaedic X-ray technique, which allows the qualitative assessment of the tissue density, is the oldest and usually the first choice to study the implant-tissue interface”. However, because of its poor sensitivity and resolution, this technique is not always reliable for such study4-“. Consequently, the microradiographic technique was developed, as described by Jowsey et c11.~Others eventually employed mammographic’ and MRI techniques”. Measuring the optical density of the film, which is inversely proportional to

Correspondence to Dr J.R. Lenzi Mariolani. (’ 1994 Butterworth-Heinemann Ltd 0142.9612/94/15615-06

high

resolution

Analysis

radiographic

formed

in areas

where

containing (which

fluorescence

into canine for deeper research

plugs

femora analysis

funds

are

were

allowed

a good

spectrometry

of the microradiographs

around

imaging,

inserted

specimens

techniques

by X-ray

Microdensitometry

of the tissue

4 November

meaningful

of 52 wk, bone segments

techniques,

implant,

of appropriate

is especially

period

by the implants.

A1203, Ti02 and Nb205 were

identification

and microradiography.

of the materials

Interface,

of rapid

conventional

evaluation)

release

Keywords:

with and without

a methodology

indicated

allowed

a

the implants.

microdensitometry,

X-ray

fluorescence

1993

the tissue density, leads to an improved analysis of the radiographs’,“. The histological investigation can be carried out by optical or electron microscopy. The latter presents better resolution, but the interpretation of its results can be difficult due to artefacts introduced during specimen preparation’“. The aim of analytical study is the evaluation of particles and ions released by the implant. Among several available analytical techniques, X-ray fluorescence spectrometry is one which is easily applicable, since it requires no special specimen preparation. However, it does not give information about the material’s distribution around the implant bed, once the specimen is analysed as a whole. There are many other analytical techniques which have been used to study the implant-bone interface, such as electron microprobe analysisll-l”, Auger electron spectroscopy”.‘2, photoelectron spectroscopy’z, infrared reflection spectroscopy14, energy-dispersive X-ray analysis”. I’, atomic absorption spectrophotometry’“, neutron activation analysis’” and X-rav diffraction”‘. Biomechanical study- usually consists of pulling out the implant from the osseous bed to obtain the loaddisplacement curve and the values of ultimate strength, energy to failure and stiffness of the interface. The investigation of the interface from all these perspectives is expensive and time consuming. For this reason a triage methodology was elaborated, which should allow a rapid and simple preliminary evaluation of the interface in order to identify specimens worthy of further study, so that the use of more sophisticated methods can be reduced17. Biomaterials

1994,

Vol. 15 No. 8

616

Triage of bone-implant interfaces: J.R.L. Mario/ad et at.

MATERIALS

AND METHODS

Fifty stainless steel plugs ASTM F-138/82 Grade B coated with and without porous A1203, TiOz and Nbz05 were inserted into the femoral diaphysis and metaphysis of seven mongrel dogs. Plugs with a diameter of 5.Omm were inserted in the femora without clearance. Forty-six useful specimens were obtained on killing (Table 1). After killing, bone segments containing the plugs were radiographed using a conventional orthopaedic X-ray technique with a Siemens Heliophos 4B X-ray tube (polyenergeti~ spectrum produced by a W-target filtered by Al) with the following exposure data: 56 kV, 40 mA, exposure time of 0.25 s and distance film-focus of 600 mm. Subsequently, the segments were radiographed using a high resolution technique (mammographic technique) with a Siemens MAMMOMAT X-ray tube (monoenergetic spectrum produced by an MO-target and filtered by MO, focal spot of 0.6 x 0.6mm). The exposure data were: 39 kV, 250mA, exposure time of 2.0 s and distance film-focus of 400 mm. Next, the segments were fixed by immersion in formaldehyde, dehydrated in a graded sequence of ethanol and acetone solutions and embedded with acrylic resin. The plugs obviously loose were removed before the embedding. Slices 0.4 mm thick were cut off from each sample using a diamond cutting disc and polished using a conventional metallographi~ technique. The implants still remaining in the samples were removed before the microradiographs were taken. The microradiographs of the slices were obtained in an Xray diffractometer (Rigaku RU-200; monoenergetic spectrum produced by a Cu-target and filtered by Ni, focal spot of 0.5 x lO.Omm). The exposure data were: 25 kV, 20 mA, exposure time of 1.0 s and distance filmfocus of 450 mm. The optical densities of the microradiographs were then measured in a microphotometer (Rigaku MP 3). Each microradiograph was scanned in two directions (cranial-caudal and proximal-distal) under the following operation conditions: field slit of 2.0 x 5.0mm, scan slit of 0.05 x l.Omm, scan speed of l.Omm/min and chart speed of 2O.Omm/min (resulting in a density profile magnification of 20 times related to the actual microradiograph). The limits of the tissue formed around the implants were identified by the density profiles and the tissue thickness was measured. In order to evaluate the reliability of the Table 1 Bone type

Cortical

Trabecular

Distribution of specimens Plug coating

‘mammographic’ images of the interface, the apparent thickness of the tissue formed around the implants was measured on the mammographic films by light transmission in a universal measuring microscope (Carl Zeiss UMM). Eighteen specimens (with follow-up periods of 18 and 52 wk) were also analysed by X-ray fluorescence spectrometry in order to investigate the release of Fe, Ni, Cr, MO, Al, Ti and Nb by the implants. This analysis was semi-quantitative. The value 100 was arbitrarily attributed to the highest difference between the measured counting rate and the background level of each element. The other values were calculated proportionally to the maximal one.

RESULTS AND DISCUSSION After the animals were killed it was noticed that 27 implants were loosened. Observation of the conventional radiographs allowed no conclusion about the type of tissue formed around the implants. These images were reliable only when a severe resorption was present. This technique was shown to be inappropriate for the evaluation of the interface, as long as the mammographic technique produced sharper images and allowed a good preliminary evaluation. Cases of bone resorption which could not be realized by the conventional radiographs were discerned with the respective m~mographs. This is seen by comparing Figures 2 and 2. In Figure I, a radiopaque zone can be observed around the implant on the right, which suggests the occurrence of bone growth. The corresponding mammographic image (Figure z), however, shows a lightly radiolucent zone around the implant, revealing the interposition of a soft tissue layer between implant and bone. The better image resolution of the mammographic technique is due to its low-energy, almost monoenergetic X-ray beam, which maximizes the contrast among materials with similar attenuation coefficients (similar densities), as long as conventional radiography with its polyenergetic beam minimizes the contrast and eliminates details. The same results can be produced by any X-ray equipment with a low-energy, monoenergetic beam source. So, the use of a mammograph is not mandatory to achieve higher resolution radiographs. The interpretation of the mammographic image, however, is not always unequivocal. Figure 3 shows an

according to bone type, plug coating and follow-up period Follow-up (wk) 3d

4

8

10

12

18

52

TiOP

1 1

-

Nb205 none

-

1 1

1 1 -

1 1 2 2

1 1 -

1 1 1 1

1 2 1 1

AVJ3

TiOz

1 1

-

NbzOs none

-

1 1

1 1 -

1 1 2 2

1 1 -

1 1 1 1

1 2 1 1

Ah203

Biomaterials 1994, Vol. 15 No. 8

Triage

of bone-implant

Figure 1

interfaces:

J.R.L. Mariohi

Conventional radiograph of plugs implanted in the diaphysis. From coated with Ti02 and A1203, respectively.

et al.

a femur with two left to right: plugs Follow-up: 10 wk.

617

Figure 3 jmplanted

Mammographic image of plug coated in trabecular bone. Follow-up: 18 wk.

with

Nb205

size of the microradiographs) and the semi-quantitative assessment of bone growth. The density profile presented in Figure # shows a minor density of the tissue at the interface. In this case it was clear on the microradiograph that there was a soft tissue layer between implant and bone. However, this was not always the case. In this work there was a specimen in which the presence of a soft tissue layer at the interface

Figure 2 implanted 10wk.

Mammographic image of plug coated with A&O3 in cortical bone (shown in Figure 7). Follow-up:

example of dubious interpretation. By means of this image only, it cannot be confirmed whether the trabeculae were growing around the implant or if they were placed in other planes out of the interface. Since mammography produces a two-dimensional image of a solid body, it does not represent the exact reproduction of the interface at one plane. In order to achieve this, it was necessary to cut off slices of the specimens and take microradiographs of them. The use of tomography was impossible in this work because of the artefacts produced by the metallic implant cores. The microradio~raphs allowed a clear radiographic view of the tissue formed around the implants at a plane and eliminated any doubt over the mammographic images. That can be observed in Figure 4 (microradiograph corresponding to the specimen presented in Figure 3). This microradiograph shows no trabecular bone growing around the implant, but a soft tissue layer interposed between implant and bone. The microradiographs also allowed the evaluation of their optical densities (microdensitometry). This made possible the precise measurement of the thickness of the tissue formed at the interface (because of the magnified density profiles in proportion to the actual

Figure 4

Microradiograph of trabecular bone slice which contained the plug coated with Nb205 presented in figure 3 and the corresponding density profile. The microradiograph is inverted, i.e. the radiopaque zones appear dark here and the radiolucent ones appear clear. This was done to allow better visualization of the interface. 1, Trabecular bone; 2, soft tissue formed round the implant; 3, implant bed. had

Biomaterials

1994, Vol.

15 No. 8

Triage of bone-implant

618

could not be detected by examining the microradiograph. It was only detected by the co~espond~ng density profile, because the resolution of a photometer is better than that of the human eye. The comparison between the thickness of the tissues formed around the interfaces measured by the mammographic images and those obtained from the density profiles exhibited a satisfactory correlation, The co~elation coefficient between the two groups (for follow-up periods of 18 and 52 wk; Table 2) was 0.76. Theoretically, it should be 1.00, since both groups of data were originated from the same specimens. The value 0.76 is due to the limitation of the human eye in the interpretation of a radiographic

fable 2

Thickness

Follow up

of the tissue formed

Bone type

18wk

at the interface

Plug coating

A1203

Cortical

TiOz Nb&.L none A1203

Trabecular

TiOg NW35

none 52 wk

A1203

Cortical

TiO, TiOp NbzO, none A1203

Trabacuiar

TiOz Ti& NbzG none Column

A: values

tion coefficient

obtained

between

from

the density

profiles

A and B = 0.76. Values

(width

interfaces:

~ario/a~i

J.R.L.

image. In fact, although the mammographi~ images have been measured in a microscope, it was not always easy to recognize the limits of the newly formed tissue. These results, together with those observed in Figures 2-4, point out that the mammographic technique (or any other high resolution technique) is suitable only for a preliminary assessment of the interface. It is reliable only when the tissue response is not good. However, further investigation is then recommended when a good tissue response is observed. The results of the X-ray fluorescence spectrometry analysis (Table 3) showed the release of iron and nickel by the majority of the implants, as long as

obtained

by two different

methods

Position

of the measured

layer

Distal A

6

Cranial A

%

Caudai A

%

* * 0.30 0.10 065 0.05 0.40 0.22

0.51 0.43 0.27 0.07 0.78 0.13 0.33 0.08

0.35 * 0.30 0.00 0.50 0.45 0.30 0.24

0.44 0.36 0.16 0.08 0.58 0.53 0.25 0.00

1.45 0.90 0.55 0.55 0.00 1.08 1 .oo 1.35 1.75 0.65

0.00 0.00 0.00 0.32 0.00 1.66 0.50 0.63 1.49 0.87

0.45 1.00 0.50 0.55 0.00 1.08 0.60 2.90 0.56 0.25

0.00 0.00 0.00 0.42 0.00 1.31 0.37 3.13 1.62 0.52

Proximal A

%

0.25 2.27 0.68 0.00 0.45 0.60 0.38 0.25

0.36 0.23 0.27 0.07 0.68 0.80 0.29 0.21

0.90 0.70 0.54 0.19

0.48 0.58 0.24 0.08 0.57 0.50 0.50 0.14

1.75 1.45 1.00 0.90 0.00 1.08 0.56 3.75 2.60 0.90

0.69 0.64 0.57 0.58 0.00 1.72 0.70 4.12 2.79 0.51

1.95 t.20 0.85 0.50 0.00 1.08 1.10 2.35 1.20 0.10

0.89 0.38 1.01 0.83 0.00 2.32 0.89 3.53 1.37 0.42

of the zone 2 in figure

0.50 1.55 z::

4). Column

B: values

obtained

direct

from

the mammographic

images.

in miliimetres.

*Not measured.

Table 3 Follow

Relative up

concentration

Bone type

of elements Plug coating

released

by the implants

Relative Ni

18wk

Cortical

TiOa Nb.zG none Trabecular

A1203

TiOs NbzG none 52 wk

Cortical

Trabecular

A1203

TiOs TiOz Nb&z none ‘No statlsticat

significance

relative

to the background.

iNot measured.

Biomateriais

1994, Vol. 15 No. 8

Al

86+ 1 74 f i 100it

89 rir 2 31 f 1 29zt 1 50f3

18fO 18&O 18f 1 12fO

9514 65f2 46 f 2 6Ort3

403

TiO, TiO, NbiG none

concentration

38 zt 0 47 i 0 24 Z+I0

Al203

17zto 18fO 43+1 12fO 611

et af.

t

obtained i- sd.

spectrom~try

analysis

(n = 4)

Ti

-

by X-ray fluorescence

11 f2 99 f 2

56f3 33 f 4 -

-

Nb

Fe

lOOf -

88 f 73il 1010 22i 33 * 42 i lOOi43*1

-

-

-

loo*4 75f2 41+2 t

-

x

t

-

-

62i7 73f4

43 i

2

1 1 1

1

20-+4 45il 82fl 42 + 2 45f4 -

MO

Cr

100 rir 17 67 i 4 66zJzl9 *

-

* * -

-

Correla-

Triage of bone-implant

interfaces:

J.R.L. Mariolani et al.

619

molybdenum was found in few specimens and chromium in none. Aluminium and titanium were found in all specimens which contained implants coated with aluminium oxide and titanium oxide, respectively, but niobium was found only in one specimen which had contained niobium oxide. This method of analysis offered only semi-quantitative results and the fact that an element was not found does not necessarily mean that it was not present in the specimen. Its concentration could be under the limit of detection of the equipment. $

CONCLUSIONS

Take microradiographs of the specimens

Based on the results of the experimental study, we suggest the following methodology (summarized in Figure 5):

(1) After

the killing of the animals, take with mammagraphic images or radiographs another technique of high resolution of the implant-bone specimens. (2) Reject the specimens which show evidence of bone resorption. (31 Cut off slices of the remaining specimens and take microradiographs of them. (4) Measure the optical density of the microradiographs which have not shown evidence of bone resorption and estimate the bone regeneration quantitatively. (5) Use X-ray fluorescence spectrometry analysis for a preliminary evaluation of the release of materials by the implants. If after this sequence the interface shows good quality, investigate it by means of other sophisticated and more expensive methods.

f Measure of the

No

the optical density microradiographs

of the release of material by the

Yes

ACKNOWLEDGEMENTS The authors are grateful to Professor Iris CL. Torriani for the kind use of the Laboratory of Crystallography, Unicamp and for technical assistance, to Dr Aurea A.A. Cairo for the kind use of the mammograph of the CAISM, Unicamp, and to Ana C. Morais and Gomes S. Alvin of the NMCE, IJnicamp for their assistance with the surgical procedures.

j]

L

Indication of bone regeneration microdensitometry?

by

RJZFERENCES 1

Albrektsson T, Brdnemark P-I, Hansson H-A, LindstrGm

J. Osseointegrated titanium implants. Acta Stand 1981;52:155-170. 2 3

Orfhop

Albrektsson T, Albrektsson B. Bone-implant interface characteristics. Acta Orfhop Stand 1987; 58:715-717. Puech B, Cameli M, Chancrin JL, Pierre C, Dufour M, Elizagaray A. Biointegration of massive bone allografts: imaging and histological studies in cat. ~io~at~r~als

Figure 5

1990;11:75-78. 4

5

Bobyn JD, Pilfiar RM, Cameron HU. Weatherly GC. Osteogenic phenomena across endosteal bone-implant spaces with porous surfaced intramedullary implants. Acfa Orthop Stand 1981;52:145-153. Heck DA, Nakajima I, Kelli PJ, Chao Y. The effect of

6

Flow chart of the presented

triage methodology.

load alteration on the biological and biomechanical performance of a titanium fiber-metal segmental prosthesis. JBone Joint Surg 1986;88A(l):118-126, Mjiiberg B, Selvik G, Hansson LI, Rosenqvist R, ijnnerfglt R. Mechanical loosening of total hip prostheses: a new radiographic and Roentgen stereophotogrammetric study. Actu Orthop Stand 1987; 58: 445. Biomaterials 1994, Vol. 15 No. 8

Triage of bone-implant interfaces: J&L.

620 7

8

9

10

11

12

Jowsey J, Kelli PJ, Riggs BL, Bianco AJ Jr, Scholz DA, Gershon-Cohen J. Quantitative microradiographic studies of normal and osteoporotic bone. 1 Bone Joint Surg 1965; 47A(4): 785-806. Linder L, Strid K-G. Radiographic comparison of currently used metallic implant materials. Acfa Ofthop Stand 1987; 58: 456. Kalebo P, Jacobsson M. Recurrent bone regeneration in titanium implants. Experimental model for determining the healing capacity of bone using quantitative microradiography. Biomateriols 1988; 9: 295-301. McNamara A, Williams DF. Scanning electron microscopy of the metal-tissue interface: I. Fixation methods and interpretation of results. Biomateriuls 1982; 3: 165-176. Ducheyne P. Bioglass coatings and bioglass composites as implant materials. J Biomed Mater Res 1985; 19: 273-291. Muster D, Humbert P, Mosser A. Surface physics

13

14 15

16

17

~ario/anj

et af.

methods and in vitro bone-biomaterial interface control. Biomaterials 1990; 11:57-62. Pernot F, Baldet P, Bonnel F, Rabischong P. In viva corrosion of sodium silicate glasses. 1 Biomed Mater Res 1985; 19:293-301. Hench LL, Ethridge EC. Bjomaterja~s: An l~te~ac~al Approach. New York: Academic Press, 1982: 385. Chignier E, Guidollet J, Dureau G et cd. Characterization of the tissue proliferated at the blood interface of carbon/ceramic composites. ] Biomed Mater Res 1987; 21: 1415-1433. Mervyn Evans E, Freeman MAR, Miller AJ, VernonRoberts B. Metal sensitivity as a cause of bone necrosis and loosening of the prosthesis in total joint replacement. 1 Bone Joint Surg 1974; 56B(4):626-642. Mariolani JRL. Metodologia para avalia@o da interface biomaterialkecido Bsseo: estudo tebrico e experimental. MSc Thesis, State University of Campinas, 1991: 105.

Wuhan International Symposium on Biomat~rials and Fine Polymers October 18=22nd, 1994 Wuhan University, Wuhan, China Themajor topics of the stasis

will be:

Hemocompatible polymers. Polymers for controlled drug release systems. Polymeric drugs. Soft and hard tissue materials, i.e. skiu, suture, bone, joints, contact lenses and dental materials. Biomedical membranes for separation and transport purposes. Polymers for enzyme and cell ~ob~on. Biosensors. Polymeric adsorbeuts. Fine polymers. For further information please contact: Professor Ren-Xi Zhuo, Chairman of the Symposium, Department of C~erni~~, Wuhan 430072, China. Tel: +fJ6 027 7822 712 or Fax: +86 027 7812661. Biomaterials 1994, Vol. 15 No. 8