Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
BIOMAT., MED. DEV., ART. ORG., 3(2), 233-243 (1975)
Effect of Electrical Stimulation on the Tensile Strength of the Porous Implant and Bone Interface
J. B. PARK, Ph.D.
Bioengineering Faculty and G. H. KENNER, Ph.D.
Department of Veterinary Biological Structure, Ceramic Engineering, and Bioengineering Faculty University of Illinois a t Urbana- Champaign Urbana, Illinois 61801
ABSTRACT The effect of electrical stimulation upon the direct tensile strength of the interfacial union between porous calcium aluminate implants (100 to 200 cc diameter pores) and bone was studied in the femurs of rabbits. After about 4 weeks of implantation the tensile strength of the electrically stimulated specimens was approximately two times that of the nonstimulated ones. This indicates that electrical stimulation increased the rate of new bone formation under the experimental conditions. 233 Copyright 0 1975 by Marcel Dekker, Inc. All Rights Reserved. Neither this work nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage and retrieval system, without permission in writing from the publisher.
234
PARK AND KENNER
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
I.
INTRODUCTION
The fixation of foreign materials to bone is a major problem in orthopedic implant work [ 1, 21. Recently a number of methods of overcoming this difficulty have been studied. These include a system of mechanical interlocking developed by having bone grow into porous materials [ 3-61. This helps to spread the load over a large area, thereby minimizing the s t r e s s concentrations and facilitating a continuous viable connection between the implant and tissue. The discovery of piezoelectricity in bone and tendon [ 7-91 opened the possibility of using electrical stimulation to control the osteogenic and osteoclastic mechanisms of bone. To date, electrical stimulation has been used in experimental animals to accelerate healing rates following fracture and to retard the development of disuse osteoporosis [ 10-141, Clinical evaluations in human patients have been investigated [ 15, 161. Among all the investigations reported there a r e no quantitative analyses of tissue growth during the electrical stimulation process, although there are some qualitative kinetic studies [ 131. Also, there are no reported studies regarding the interfacial strength of the electrically stimulated bone ingrowth into porous implants. The present study was designed to measure directly the tensile strength of the porous ceramic-bone union following electrical stimulation with those obtained from control animals. 11.
EXPERIMENTAL PROCEDURES
Porous calcium aluminate cylinders, 1/4 in. long by 1/8 in. diam, were prepared using the method employed previously in our laboratory [ 171. Pore size ranged from 100 to 200 ,u diam. A hole -0.025 in. in diameter was drilled through the center along the longitudinal axis to allow passage of an electrode. For electrical stimulation, a mercury battery (1.4 V, Mallory Duracell RM-675) was used as a constant current source. The battery was connected with Teflon-coated copper wire and a 0.18 MS2 resistor in s e r i e s [ 181. 0.020 in. diameter Pt-Rh (13%) wire was used as electrodes. The power pack was coated with medical grade elastomer (MDX-4-4210, Dow Corning Co.) and cured at room temperature (1 day) and 60' C subsequently (1day). This was done three times to ensure leak-proof coating. The potential drop between electrodes was The control power -0.65 V. in vitro. The current in vivo was -7
a.
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
POROUS IMPLANT AND BONE INTERFACE
235
pack was the same except one wire was not connected to one of the poles of the battery. The ceramic implant was heat sterilized (200"C, 2 hr) and the power pack was sterilized in a 0.1% Roccal solution (room temperature, 4 hr). The ceramic implant with negative electrode was inserted in the midshaft of a right femur of a white New Zealand rabbit (8 to 10 weeks old) and the other electrode was placed in a hole drilled about 1 cm proximad (Fig. 1). The wires were bent near the implant sites and run proximad
FIG. 1. Radiograph after implantation.
PARK AND KENNER
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
236
along the femur and brought subcutaneous near the third trochanter. The muscles were then sutured together to hold the wires in place. The power pack was placed subcutaneously overlying the Biceps femoris muscle. Fifty milligrams of tetracycline (Achromycin, Lederle Laboratories) was injected following surgery. Radiographs were taken within 1 week following implantation to check the position of the implant. Several leads broke during the course of the experiment. These samples were used as partial controls since once broken, current was absent. Following necropsy, 1.5 cm long by 0.25 cm wide tensile specimens with implant in the middle were prepared using a GillingsBronwill Thin Sectioning Machine (Will Corp., Rochester, New York). The thickness of the specimens corresponded to the natural thickness of the bone (usually about the same as the width). For the actual tensile testing a special set-up similar to that used by Hoffman e t al. was used [ 193. The specimen was mounted on a pair of serrated grips and stressed to fracture in 0.15 M saline solution a t 37" C. Microradiographs were prepared u&g the techniques of Jowsey et al. [ 201 and Klawitter and Hulbert [ 31. 111.
R E S U L T S AND D I S C U S S I O N
The results of the experiment are summarized in Table 1 and Figs. 2-4. Figure 2 shows some of the stress-strain behavior, while Fig, 3 illustrates the maximum fracture s t r e s s v s duration of implantation. Substantially greater force and energy were required to pull apart specimens from electrically stimulated animals than those from controls. From this result one can conclude that the electrical stimulation in vivo definitely increased the strength of the interface between the porous implant and bone. The values for the strength of the interface given in Table 1 are much smaller than reported values of the "push-out" tests [ 4-6, 21-24], This is because during surgery it is impossible to achieve perfect alignment of the implant relative to the bone. In case of push-out tests, such misalignment causes impingements which increase the force required for shearing the interface, During uniaxial tension tests, such misalignment causes no impingement effects on the interfacial strength. It is interesting to note that the fracture strength of the
Duration of implant (days)
17 26 27 39 41 43 44 56
Sample
1
2
3
4
5
6
?
8
3.5
103 116 50
0.60 0.32
0.66
2.0
3.5
4.5
3.8
5.7
3.1
5.0
Fracture strain (%)
117
332
240
207
73
Fracture stress (psi)
0.53
0.06
0.26
0.31
0.62
Potential after excision (V)
Control
Partial control
Control
Partial controla
I
Broken in the implant
-
-
Note
aPartial control: the wires broke in early stage of the experiment as shown by x-rays.
No.
TABLE 1. Summary of Results
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
4
W
N
H
b n
2!m
m
8
H
?z
2
PARKAND KENNER
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
23 8
300
4 (stimulated: sedays)
[
I
h
%
3 200
Y
v) v)
w
[1:
Iv,
I00
"0
2
4
6
8 1 0
STRAIN (%) FIG. 2. Stress-strain curves of electrically stimulated and control samples.
electrically stimulated interface is roughly proportional to the amount of potential used in vivo as shown in Fig. 4. This tends to support the above-mentioned conclusion on the increased osteogenic activity by electrical stimulation-the more stimulation, the higher activity for a given constant electrical current. This results in stronger bone-implant interface. Figure 5 shows a microradiograph of one of the electrically stimulated samples. A s can be seen, extensive ingrowth of
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
POROUS IMPLANT AND BONE INTERFACE
239
IMPLANT PERIOD(days1 FIG. 3. Maximum fracture s t r e s s vs duration of implantation.
mineralized bone (black-dotted white) into the pores of the ceramic (white) occurred. IV.
CONCLUSION
In vivo electrical stimulation substantially increased the tensile strength of the interface between porous ceramic and bone when compared to the controls.
PARK AND KENNER
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
240
POTENTIAL AT SACRIFICE (volt) FIG. 4. Maximum fracture s t r e s s v s potential at sacrifice. ACKNOWLEDGMENTS The tensile testing was done at the Materials Research Laboratory at' the University of Illinois with the help of Professor W. S. Williams. The authors a r e very grateful for the many suggestions given by Professor S. D. Brown throughout this work. Partial support was provided by the Bioengineering Faculty and the Department of Veterinary Biological Structure of the University of Illinois at Urbana-Champaign, Urbana, Illinois 6 1801.
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
POROUS IMPLANT AND BONE INTERFACE
FIG. 5. Microradiograph of an electrically stimulated sample. White area is ceramic, black region represents soft tissues, while gray mottled area i-s bone (115X).
241
PARK AND KENNER
242 REFERENCES
[ 11 C. 0.Bechtol, Metals and Engineering in Bone and Joint Surgery, Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
Williams and Wilkins. Baltimore, 1959.
[ 21 E. Korostoff (ed.), Re'search in Dental and Medical Materials, Plenum, New York, 1969.
[ 31 J. J. Klawitter and S. F. Hulbert, "Application of Porous Ceramics for the Attachment of Load Bearing Internal Orthopedic Applications," J. Biomed. Mater. Res. Symp., 2(1), 161 (1971). 141 J. L. Nilles and M. Lapitsky, "Biomechanical Investigations of Bone-Porous Carbon and Porous Metal Interfaces," _ lkd.,_4, 63 (1973). [ 51 R. A. Lueck, J. Galante, W. Rostoker, and R. D. Ray, "Development of an Open Pore Metallic Implant to Permit Attachment to Bone," Surg. Forum, 20, 456 (1969). [6] J. G. Bagwell, J. J. KlawTter, B. W. Sauer, and A. M. Weinstein, "An Evaluation of Bone Growth into Porous Polyethylene," Presented at the 6th Annual Biomaterials Symposium, Session 1, Clemson University, South Carolina, April 1974. [ 71 E. Fukada, Wn the Piezoelectric Effect of Bone," J. Phys. SOC. Japan, - 12, 1159 (1956). [ 81 M. Shamos and L. Lavine, "Piezoelectric Effect in Bone," Nature, 197, 81 (1963). ~[ 9 ] R. 0.Becker, C. A. L. Bassett, and C. H. Backman, "The Bioelectric Factors Controlling Bone Structure," in Bone Biodynamics (H. M. Frost, ed.), Little Brown, Boston, 1964, p. 209. [ 101 L. S. Lavine, "Electrical Enhancement of Bone Healing," Science, 175, 1118 (1972). ~[ 111 R. 0.Becker and D. G. Murray, "The Electrical Control System Regulating Fracture Healing in Amphibians," Clin. Orthop., 73, 169 (1970). [ 121 A. L. Bassett, "Biophysical Principles Affecting Bone Structure," in The Biochemistry and Physiology of Bone, 2nd ed., Vol. I11 (G. H. Bourne, ed.) Academic, New York, 1971, p. 1. [ 131 Z. B. Friedenberg, L. M. Zemsky, R. P. Pollis, and C. T. Brighton, "The Response of Non-Traumatized Bone to Direct Current," Presented at the New York Academy of Science Meeting, New York, 1973. [ 141 E. Gabrielson, G. H. Kenner, W. S. Williams, A. E. Marshall, and J. E. Lovell, Effects of Electrical Stimulation on Bone Losses Caused by Limb Immobilization, University of Illinois a t Urbana-Champaign, 1973.
243
POROUS IMPLANT AND BONE INTERFACE
[ 151 R. 0.Becker, "Augmentation of Regenerative Healing in Man, A Possible Alternative to Prosthetic Implantation," Clin. Orthop.,
83, 255 (1972). Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
[ 161 % B. Friedenberg, M. C. Harlow, and C. T. Brighton, "Healing of Non-Union of the Medial Malleolus by Means of Direct Current: A Case Report," J. Trauma, 11, 883 (1971). [ 171 G. D. Schnittgrund, G. H. Kenner, and S. D. Brown, "In vivo and in vitro Changes in Strength of Orthopedic Calcium Aluminates," J. Biomed. Mater. Res. Symp., 4, 435 (1973). [ 181 L. S. Lavine and I. Lustrin, "Experimental Model for Studying the Effect of Electric Current on Bone in vivo," _ Nature, _ _ -224, ~
1112 (1969). [ 191 A. S. Hoffman, J. B. Park, and J. Abrahamson, "Sequential Enzymolysis of Ligament and Resultant Stress-Strain Behavior," Biomat., Med. Dev., Art. Org., 1(3), 453 (1973). [ 201 J. Jowsey, T. J. Kelly, L. R i g g c A. M. Bianco, D. A. Scholz, and J. G . Cohen, "Quantitative Microradiographic Studies of Normal and Osteoporotic Bone," J. Bone Joint Surg., 47A, 785
(1965). [ 211 S. F. Hulbert, F. W. Cooke, J. J. Klawitter, R. B. Leonard, B. W. Sauer, and D. D. Moyle, "Attachment of Prosthesis to the Musculo-Skeletal System by Tissue Ingrowth and Mechanical Locking,'' J. Biomed. Mater. Res. Symp., 4, 1 (1973). [ 221 H. Hahn and W. Palich, "Preliminary Evaluations of Porous Metal Surfaced Titanium for Orthopedic Implants,'' J. Biomed. Mater. Res.,?, 571 (1970). [ 231 C. L. Stanitski and V. Mooney, "Osseous Attachment to Vitreous Carbon," J. Biomed. Mater. Res. Symp., 4, 97 (1973). [ 241 P. Predecki, B. A. Auslaender, J. E. Stephan, VT L. Mooney, and C. Stanitski, "Attachment of Bone to Threaded Implants by Ingrowth and Mechanical Interlocking," J. Biomed. Mater. Res.. 6. 401 (1972). Received by editor June 11, 1974
BIOMAT., MED. DEV., ART. ORG., 3(2), 233-243 (1975)
Effect of Electrical Stimulation on the Tensile Strength of the Porous Implant and Bone Interface
J. B. PARK, Ph.D.
Bioengineering Faculty and G. H. KENNER, Ph.D.
Department of Veterinary Biological Structure, Ceramic Engineering, and Bioengineering Faculty University of Illinois a t Urbana- Champaign Urbana, Illinois 61801
ABSTRACT The effect of electrical stimulation upon the direct tensile strength of the interfacial union between porous calcium aluminate implants (100 to 200 cc diameter pores) and bone was studied in the femurs of rabbits. After about 4 weeks of implantation the tensile strength of the electrically stimulated specimens was approximately two times that of the nonstimulated ones. This indicates that electrical stimulation increased the rate of new bone formation under the experimental conditions. 233 Copyright 0 1975 by Marcel Dekker, Inc. All Rights Reserved. Neither this work nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage and retrieval system, without permission in writing from the publisher.
234
PARK AND KENNER
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
I.
INTRODUCTION
The fixation of foreign materials to bone is a major problem in orthopedic implant work [ 1, 21. Recently a number of methods of overcoming this difficulty have been studied. These include a system of mechanical interlocking developed by having bone grow into porous materials [ 3-61. This helps to spread the load over a large area, thereby minimizing the s t r e s s concentrations and facilitating a continuous viable connection between the implant and tissue. The discovery of piezoelectricity in bone and tendon [ 7-91 opened the possibility of using electrical stimulation to control the osteogenic and osteoclastic mechanisms of bone. To date, electrical stimulation has been used in experimental animals to accelerate healing rates following fracture and to retard the development of disuse osteoporosis [ 10-141, Clinical evaluations in human patients have been investigated [ 15, 161. Among all the investigations reported there a r e no quantitative analyses of tissue growth during the electrical stimulation process, although there are some qualitative kinetic studies [ 131. Also, there are no reported studies regarding the interfacial strength of the electrically stimulated bone ingrowth into porous implants. The present study was designed to measure directly the tensile strength of the porous ceramic-bone union following electrical stimulation with those obtained from control animals. 11.
EXPERIMENTAL PROCEDURES
Porous calcium aluminate cylinders, 1/4 in. long by 1/8 in. diam, were prepared using the method employed previously in our laboratory [ 171. Pore size ranged from 100 to 200 ,u diam. A hole -0.025 in. in diameter was drilled through the center along the longitudinal axis to allow passage of an electrode. For electrical stimulation, a mercury battery (1.4 V, Mallory Duracell RM-675) was used as a constant current source. The battery was connected with Teflon-coated copper wire and a 0.18 MS2 resistor in s e r i e s [ 181. 0.020 in. diameter Pt-Rh (13%) wire was used as electrodes. The power pack was coated with medical grade elastomer (MDX-4-4210, Dow Corning Co.) and cured at room temperature (1 day) and 60' C subsequently (1day). This was done three times to ensure leak-proof coating. The potential drop between electrodes was The control power -0.65 V. in vitro. The current in vivo was -7
a.
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
POROUS IMPLANT AND BONE INTERFACE
235
pack was the same except one wire was not connected to one of the poles of the battery. The ceramic implant was heat sterilized (200"C, 2 hr) and the power pack was sterilized in a 0.1% Roccal solution (room temperature, 4 hr). The ceramic implant with negative electrode was inserted in the midshaft of a right femur of a white New Zealand rabbit (8 to 10 weeks old) and the other electrode was placed in a hole drilled about 1 cm proximad (Fig. 1). The wires were bent near the implant sites and run proximad
FIG. 1. Radiograph after implantation.
PARK AND KENNER
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
236
along the femur and brought subcutaneous near the third trochanter. The muscles were then sutured together to hold the wires in place. The power pack was placed subcutaneously overlying the Biceps femoris muscle. Fifty milligrams of tetracycline (Achromycin, Lederle Laboratories) was injected following surgery. Radiographs were taken within 1 week following implantation to check the position of the implant. Several leads broke during the course of the experiment. These samples were used as partial controls since once broken, current was absent. Following necropsy, 1.5 cm long by 0.25 cm wide tensile specimens with implant in the middle were prepared using a GillingsBronwill Thin Sectioning Machine (Will Corp., Rochester, New York). The thickness of the specimens corresponded to the natural thickness of the bone (usually about the same as the width). For the actual tensile testing a special set-up similar to that used by Hoffman e t al. was used [ 193. The specimen was mounted on a pair of serrated grips and stressed to fracture in 0.15 M saline solution a t 37" C. Microradiographs were prepared u&g the techniques of Jowsey et al. [ 201 and Klawitter and Hulbert [ 31. 111.
R E S U L T S AND D I S C U S S I O N
The results of the experiment are summarized in Table 1 and Figs. 2-4. Figure 2 shows some of the stress-strain behavior, while Fig, 3 illustrates the maximum fracture s t r e s s v s duration of implantation. Substantially greater force and energy were required to pull apart specimens from electrically stimulated animals than those from controls. From this result one can conclude that the electrical stimulation in vivo definitely increased the strength of the interface between the porous implant and bone. The values for the strength of the interface given in Table 1 are much smaller than reported values of the "push-out" tests [ 4-6, 21-24], This is because during surgery it is impossible to achieve perfect alignment of the implant relative to the bone. In case of push-out tests, such misalignment causes impingements which increase the force required for shearing the interface, During uniaxial tension tests, such misalignment causes no impingement effects on the interfacial strength. It is interesting to note that the fracture strength of the
Duration of implant (days)
17 26 27 39 41 43 44 56
Sample
1
2
3
4
5
6
?
8
3.5
103 116 50
0.60 0.32
0.66
2.0
3.5
4.5
3.8
5.7
3.1
5.0
Fracture strain (%)
117
332
240
207
73
Fracture stress (psi)
0.53
0.06
0.26
0.31
0.62
Potential after excision (V)
Control
Partial control
Control
Partial controla
I
Broken in the implant
-
-
Note
aPartial control: the wires broke in early stage of the experiment as shown by x-rays.
No.
TABLE 1. Summary of Results
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
4
W
N
H
b n
2!m
m
8
H
?z
2
PARKAND KENNER
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
23 8
300
4 (stimulated: sedays)
[
I
h
%
3 200
Y
v) v)
w
[1:
Iv,
I00
"0
2
4
6
8 1 0
STRAIN (%) FIG. 2. Stress-strain curves of electrically stimulated and control samples.
electrically stimulated interface is roughly proportional to the amount of potential used in vivo as shown in Fig. 4. This tends to support the above-mentioned conclusion on the increased osteogenic activity by electrical stimulation-the more stimulation, the higher activity for a given constant electrical current. This results in stronger bone-implant interface. Figure 5 shows a microradiograph of one of the electrically stimulated samples. A s can be seen, extensive ingrowth of
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
POROUS IMPLANT AND BONE INTERFACE
239
IMPLANT PERIOD(days1 FIG. 3. Maximum fracture s t r e s s vs duration of implantation.
mineralized bone (black-dotted white) into the pores of the ceramic (white) occurred. IV.
CONCLUSION
In vivo electrical stimulation substantially increased the tensile strength of the interface between porous ceramic and bone when compared to the controls.
PARK AND KENNER
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
240
POTENTIAL AT SACRIFICE (volt) FIG. 4. Maximum fracture s t r e s s v s potential at sacrifice. ACKNOWLEDGMENTS The tensile testing was done at the Materials Research Laboratory at' the University of Illinois with the help of Professor W. S. Williams. The authors a r e very grateful for the many suggestions given by Professor S. D. Brown throughout this work. Partial support was provided by the Bioengineering Faculty and the Department of Veterinary Biological Structure of the University of Illinois at Urbana-Champaign, Urbana, Illinois 6 1801.
Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
POROUS IMPLANT AND BONE INTERFACE
FIG. 5. Microradiograph of an electrically stimulated sample. White area is ceramic, black region represents soft tissues, while gray mottled area i-s bone (115X).
241
PARK AND KENNER
242 REFERENCES
[ 11 C. 0.Bechtol, Metals and Engineering in Bone and Joint Surgery, Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
Williams and Wilkins. Baltimore, 1959.
[ 21 E. Korostoff (ed.), Re'search in Dental and Medical Materials, Plenum, New York, 1969.
[ 31 J. J. Klawitter and S. F. Hulbert, "Application of Porous Ceramics for the Attachment of Load Bearing Internal Orthopedic Applications," J. Biomed. Mater. Res. Symp., 2(1), 161 (1971). 141 J. L. Nilles and M. Lapitsky, "Biomechanical Investigations of Bone-Porous Carbon and Porous Metal Interfaces," _ lkd.,_4, 63 (1973). [ 51 R. A. Lueck, J. Galante, W. Rostoker, and R. D. Ray, "Development of an Open Pore Metallic Implant to Permit Attachment to Bone," Surg. Forum, 20, 456 (1969). [6] J. G. Bagwell, J. J. KlawTter, B. W. Sauer, and A. M. Weinstein, "An Evaluation of Bone Growth into Porous Polyethylene," Presented at the 6th Annual Biomaterials Symposium, Session 1, Clemson University, South Carolina, April 1974. [ 71 E. Fukada, Wn the Piezoelectric Effect of Bone," J. Phys. SOC. Japan, - 12, 1159 (1956). [ 81 M. Shamos and L. Lavine, "Piezoelectric Effect in Bone," Nature, 197, 81 (1963). ~[ 9 ] R. 0.Becker, C. A. L. Bassett, and C. H. Backman, "The Bioelectric Factors Controlling Bone Structure," in Bone Biodynamics (H. M. Frost, ed.), Little Brown, Boston, 1964, p. 209. [ 101 L. S. Lavine, "Electrical Enhancement of Bone Healing," Science, 175, 1118 (1972). ~[ 111 R. 0.Becker and D. G. Murray, "The Electrical Control System Regulating Fracture Healing in Amphibians," Clin. Orthop., 73, 169 (1970). [ 121 A. L. Bassett, "Biophysical Principles Affecting Bone Structure," in The Biochemistry and Physiology of Bone, 2nd ed., Vol. I11 (G. H. Bourne, ed.) Academic, New York, 1971, p. 1. [ 131 Z. B. Friedenberg, L. M. Zemsky, R. P. Pollis, and C. T. Brighton, "The Response of Non-Traumatized Bone to Direct Current," Presented at the New York Academy of Science Meeting, New York, 1973. [ 141 E. Gabrielson, G. H. Kenner, W. S. Williams, A. E. Marshall, and J. E. Lovell, Effects of Electrical Stimulation on Bone Losses Caused by Limb Immobilization, University of Illinois a t Urbana-Champaign, 1973.
243
POROUS IMPLANT AND BONE INTERFACE
[ 151 R. 0.Becker, "Augmentation of Regenerative Healing in Man, A Possible Alternative to Prosthetic Implantation," Clin. Orthop.,
83, 255 (1972). Artif Cells Blood Substit Immobil Biotechnol Downloaded from informahealthcare.com by ThULB Jena on 11/12/14 For personal use only.
[ 161 % B. Friedenberg, M. C. Harlow, and C. T. Brighton, "Healing of Non-Union of the Medial Malleolus by Means of Direct Current: A Case Report," J. Trauma, 11, 883 (1971). [ 171 G. D. Schnittgrund, G. H. Kenner, and S. D. Brown, "In vivo and in vitro Changes in Strength of Orthopedic Calcium Aluminates," J. Biomed. Mater. Res. Symp., 4, 435 (1973). [ 181 L. S. Lavine and I. Lustrin, "Experimental Model for Studying the Effect of Electric Current on Bone in vivo," _ Nature, _ _ -224, ~
1112 (1969). [ 191 A. S. Hoffman, J. B. Park, and J. Abrahamson, "Sequential Enzymolysis of Ligament and Resultant Stress-Strain Behavior," Biomat., Med. Dev., Art. Org., 1(3), 453 (1973). [ 201 J. Jowsey, T. J. Kelly, L. R i g g c A. M. Bianco, D. A. Scholz, and J. G . Cohen, "Quantitative Microradiographic Studies of Normal and Osteoporotic Bone," J. Bone Joint Surg., 47A, 785
(1965). [ 211 S. F. Hulbert, F. W. Cooke, J. J. Klawitter, R. B. Leonard, B. W. Sauer, and D. D. Moyle, "Attachment of Prosthesis to the Musculo-Skeletal System by Tissue Ingrowth and Mechanical Locking,'' J. Biomed. Mater. Res. Symp., 4, 1 (1973). [ 221 H. Hahn and W. Palich, "Preliminary Evaluations of Porous Metal Surfaced Titanium for Orthopedic Implants,'' J. Biomed. Mater. Res.,?, 571 (1970). [ 231 C. L. Stanitski and V. Mooney, "Osseous Attachment to Vitreous Carbon," J. Biomed. Mater. Res. Symp., 4, 97 (1973). [ 241 P. Predecki, B. A. Auslaender, J. E. Stephan, VT L. Mooney, and C. Stanitski, "Attachment of Bone to Threaded Implants by Ingrowth and Mechanical Interlocking," J. Biomed. Mater. Res.. 6. 401 (1972). Received by editor June 11, 1974
