J. BIOMEI). MATER. RES.
VOL. 9, PP. 303-313 (1975)
MP,5N: A Corrosion Resistant, High Strength Alloy for Orthopedic Surgical Impants: Bio-Assay Results FELIX ESCALAS, JORGE GALAKTE, WILLIAM ROSTOKER, and PHILIP S. COOGAN, Rush Presbyterian, St. Luke's Medical Center, 1753 West Congress Parkway, Chicago, Illinois 60612
Summary A cobalt based alloy, MP,,N, with excellent mechanical properties has been recently introduced as a material for surgical orthopedic implants. A study was made of local and systemic host response to this material in two differentmammal species. The implantation time ranged from one to 12 months. The result of this study indicated: MPa5N produces a degree of local tissue response comparable to that of 316L stainless steel. No systemic side effects were observed during the implantation times included in this study.
INTRODUCTION Corrosion resistant cobalt, based alloys have been successfully used for many years in the manufacture of orthopedic surgical implants. Their mechanical properties and their corrosion resistance has accounted for their widespread acceptance. The purpose of this study is to present the bio-assay of a cobalt based alloy, MP3JV2 (Trademark of the Standard Pressed Steel Company), recently introduced in ciinical practice. The nominal composition of this material is 35% Ni, 35% Co, 20% Cr and 1Oyo Mo. This alloy is characterized by very high tensile strength, in the level of 260,000 psi when work strengthened, with good ductility, toughness and corrosion resistance in vitro. These characteristics make MP3,N an excellent material for permanent implants, such as total hip prostheses, where long standing cyclic stresses are the rule. 303 @ 1975 by John Wiley di Sons, Inc.
ESCALAS ET AL.
304
Literature Review Although the material is in clinical use in Europe, under the trade name Protasul 10, 110 reported data is available in the literature as to its biological acceptance. Zierold3 gave the first description of local tissue reaction to a cobalt based alloy. He described the bone reaction to Stellite (Co-Cr-Mo), in dogs, 6 weeks after implantation, as a moderate swelling of the bone around the implant with no discoloration or changes in the periosteum. He noticed the presence of a lining membrane, described as a dense, narrow rim of connective tissue. Recent studies reproduced the same results, placing cobalt based alloys among the best biologically tolerated meta1s.l~~Emneus and Stenram6 compared tissue reactions induced around Vitallium rods, with stainless steel ;less reaction was demonstrated mound Vitallium. Cohen,6 working with metallic particles showed appreciable tissue reaction around Vitallium and warned of the relative inertness of so-called corrosion resistant metals; however, in his work he described Vitallium as being more inert in tissues than stainless steel. This concept was supported by Ferguson' who stressed the importance of minimal ion migration rate in living tissues for Vitallium and stainless steel. Experimental data from I,aing* correlated ion migration with fibrous r e a d o n around the implants and showed this effect t o be minimal around Co-Cr-Mo, Co-Cr-Ni and Co-Cr-Xi-Mo in experimental animal implantation. Seltzerg reproduced these results adding additional data obtained from electron microscopy study of the tissues around Vitallium implants and evidencing minimal surface corrosion. A bio-assay of porous Vitallium has been done in rats by Cameron,lO and he described the material as being very well tolerated and producing minimal encapsulating fibrous tissue. Reports of local tissue tolerance of cobalt-chromium alloys in humans show in general a n acceptable correlation with experimental data.I1-l3 I n uitro studies have been done using tissue culture tech~iique'~ and show moderate inhibition of growth rates for cobalt based alloys. In general, results from these techniques are regarded as controversiaL1 Idiosyncratic toxicity of cobalt alloy iniplants has been described in humans in several i n s t a ~ i c e s . ~ No ~ J ~other systemic 'J
ALLOY FOR SURGICAL IMPLANTS
hlP,N:
305
or generalized side effects have been reported either in humans or in animal experimentation. Long term effect of exposure to cobalt based alloys and implant materials in general has aroused a general interest, especially concerning possible carcinogenesis. Sarcoma induction around subcutaneous Vitallium discs;18J9 Chromium and chromates, cobalt powder, oxide and sulphide,20~*1 has been described experimentally. Nickel has local carcinogenic effect by direct, inhalation in humans and by inhalation in experimental animals.** When nickel is implanted in soft, tissues i t produces tumors in rodents and other species.23 Particulate Co-Cr-Mo has also produced tumors experimentally in soft tissues in the rat.24 One questionable case of a tumor arising around a cobalt-chromium alloy has bern described in humans.25
MATERIALS AND METHODS Materials. The test samples were cut from standard comercial rod supplied by Latrobe Steel Company. The dimensions of the iinplants are described as follows: Animal-Implant
-
Dog-Soft tissue Dog-Bone Rabbit-Soft tissue Rabbit-Bone
Long
Diameter
__
1 in. (25 mm)
% in. (12.6 mm) % in (12.6 mm) in. (6.3 mm)
in (9.5 mm)
W in. (3.2 mm) W in. (3.2 mm) % in (1.6 mm)
The surface of the implants was prepared following the ASTM recommendation. * 6 316L (Joslyn Stainless Steel; Div. of Joslyn Mfg., Fort Wayne, Indiana), control implants of the same shape and dimensions as described for the test samples were used. The samples were then heat sterilized. The composition of the materials used is described in Table I. Animals. Adult, male mongrel dogs, kveighing approximately 60 lbs., and adult male New Zealand albino rabbits, weighing 5 to 6 lbs. were used for the experiment. A total of 16 rabbits and two dogs were used. The animals were fed a standard diet and water ad libitum. Activity was not restricted.
ESCALAS ET AL.
306
__
TABLE I Compobitiort of MP3$Nand 316L Stainless Steel ~~
____.
_ _ - ~ ____
Element
Percent
~~
JIPXbN
316L Stainless Steel
Carbon Nickel Molybdenum Chromium Cobalt Carbon Silicon Manganese Nickel Chromium Molybdenum Sulphur Phosphorus Iron
__ 0.25 max. 33.00-37.00 9.00- 10.50 19.00-21.00 Balance
.__
Check Analysis yo Under % Over Minimum Maximum -
0.30 0.15 0.25
.01 0.30 0.15 0.25
-
-
0.20 0.50 11.00 16.50 2.25
Balance
0.03 1.00 2.00 14.00 18.50 3.00 0.03 0.04 Ba 1ance
Surgical technique. Intravenous Nembutal was used for the rabbits and methothane inhalation anesthesia for the dogs. Standard aseptic surgical technique was used. Soft tissue samples were implanted in the paravertebral muscle, through a posterior midline incision. The femora were approached by means of a lateral incision and after drilling a small hole in the lateral cortex, the cylindrical samples were introduced in the bone. The implants were handled with teflon coated forceps. Tissue preparation. Following sacrifice by Nembutal overdose, the soft tissue implants were retrieved “en bloc” with the surrounding tissue and fixed in 10% buffered formalin. After 48 hr the implants were extracted taking care to preserve the fibrous tissue lining. Subsequently, the blocks were embedded in paraffin and sectioned in 6 p thick slices with a Jung microtomr. The plane of a section was perpendicular to the axis of the implant. The sections were stained with hemotoxilin-eosin and Mallory stain and mounted in standard microscopy slides. The femora containing the implants were fixed in buffered formalin for 48 hr and contact x-ray pictures taken to localize the implants
h I P J 4 : ALLOY FOR SURGICAL IJIPLANTS
307
and study the bone in contact with the metals. The bones were sectioned in blocks, containing one implant and decalcified in Cal-Ex solution. (Fisher Scientific Co., Fairlawn, N.J.) The metallic rods were then removed from the decalcified blocks which were subsequently sectioned and processed for light microscopy, as described above. The liver, lung, kidney and spleen of all the animals were fixed in formalin, immediately after sacrifice. These organs were then sectioned and representative samples from each one processed for histopathological study.
Methods of Evaluation 1. Macroscopic Tissue Response: The tissues surrounding the implant were checked for abnormal proliferation, gross necrosis and/ or color changes. 2. X-ray Evaluation: Contact x-ray pictures used to localize the cylinders in the bone were carefully studied to determine if any radiological signs of osteolysis, osteoporosis or bone proliferation were present near the implants. 3. Microscopic Tissue Response: I n the soft tissues three histological structures surrounding the implant were studied. (a) The fibrous membrane-the thickness of this structure was measured using a “Zeiss” measuring eyepiece at four different points and the average values calculated.* The cellular pattern in the membrane was recorded as well, as the presence of opaque bodies in the inner lining. (b) The thickness of the zone of loose connective tissue around the membrane was also measured. The cellular type, the presence of giant cells, blood vessels and polymorphonuclear cells was recorded. (c) The muscle around the implant n a s screened for signs of degeneration and/or abnormal cellular infiltrates. The evaluation of implanted bone inciuded: (a) Measurement of the lining fibrous membranes; (b) a record of osteolysis, osteoporosis and over-abundant osteoid seams around the implant; and ( c ) a rough estimate of the amount of cellularity in the bone in contact with the implant.
* The microscopic evaluation data reported in Table 111, represents an average of the values assigned or measured to the histology sections of 4 test and 2 control samples in each of two rabbits, for every follow-up time, and 8 test and 4 control samples in one dog for every follow-up time.
ESCALAS E T AL.
308
These different parameters were arbitrarily graded from 0 to +3 with the exception of the thickness measurements which were recorded in microns.
EXPERIMENTS AND RESULTS I n the soft tissue experiment each rabbit received 6 implants in the paravertebral muscles, 3 on each side. Each one of the rabbits used to test implants in bone, received a total of 6 implants, 3 in each femur. Two of the implants for every animal were 316L control samples and the remainder test samples. Two dogs were used for the experiment, each implanted with a group of 12 femoral implants. Four samples in each group were 316L controls. The number of animals and sacrifice period is indicated in Table I. Macroscopic evaluation of soft tissue and bone showed minimal reaction. No tumors were present in the animals sacrificed. TABLE I1 Bio-Assay Protocol for R.IP,aN Implants Rabbit Soft tissue
Rabbit Femura
Time (in Months)
Number of Animals
1 2 3 12
2 2 2 2
12
2 2 2b 2
6 12
1 1
6 12
1 1
1
2
3 Canine Soft tissue Canine Femur"
* A specimen of bone surrounding one implant from each animal was sent for electron microprobe analysis, to determine the metallic ion migration in the tissue. b All specimens from one animal, were sent for electron probe analysis.
hlP3bN: ALLOY F01t SURGICAL IllPLANTS
309
Fig. 1. Low-power microphotography of the living fibrous membrane arouiid a MP,,N implant in rabbit soft tissue, 6 months after implantation. The membrane is regular and minimal cellularit,y is present; a loose connective tissue layer appears underneath.
On histological examination the lining membranes from rabbit samples (Fig. 1) showed moderatcl crllularity with abundant macrophages during the first months and regrrssc,d to a hwcr cellular type with more mature fibrocytcs by the 12th month. Vascularity was an incidental finding in thc initial months. N o “forcign body particles” were seen in the specimens. Inflammatory response in the loose connective tissue around the membrane and muscle was moderate in the first and second month after implantation and became minimal later with very few histocytes and absence of giant cells and polymorphonuclears. The reaction pattern given by the control samples was essentially the same, except for a thicker lining membrane during the initial months. I n canine soft tissue, a t 6 months, very thick fibrous membranes and moderate proliferative reaction in the surrounding tissue was present. No abnormal cells or acute inflammatory cellular patterns were observed. The fibrous membranes around the control coupons
310
ESCALAS ET AL.
were thicker than those around the test coupons. Twelve months after surgery a general regression in the membrane thickness and a decreased cellularity was present around the test and control samples. I n the rabbit femora sections, the membrane was extremely fine and fragile and was destroyed in many cases when removing the implant. No osteolysis or abnormal bone proliferation was present as revealed by the x-ray study of the bones and confirmed by the microscopic study of the sections. Bone growth was apparent around the implant appearing as a thin rim of woven bone. Test and control coupons elicited the same response in the bone. The test samples in canine femora elicited a somewhat more fibrotic reaction with well developed lining membranes averaging 18 p for the 12 month specimens. Bone growth was present around the implants forming an involucrum of woven and lamellar bone with abundant osteocytes (Pig. 2 ) . The control coupons presented basically the same picture except for a slightly thickclr fibrous membrane.
Fig. 2 . Low-power microphotography (x100) of the bone around a klP,,N implant in a dog, 6 months after implantation. A thin layer of woven bone appears in contact with the implant. Cellularity and structure of the remaining bone is entirely normal.
MPabN : ALLOY FOlb SURGICAL IhlPLANTS
311
The x-ray study of the canine femora showed moderate bone proliferation, occupying the medullary canal and slight cortical thickening a t the level of the implants. No definite differences were observed between test, and control samples. The results obtained are summarized in Table 111. TABLE I11 Local Tissue Response X-ray Evaluation
Microscopic Evaluation Average MemMacroscopic brane E,valuation Thickness Animal and Tissue (Fibrosis) (pm) T
C
Rabbit, bone 1 mo. 2 mo. 3 mo. 12 mo.
0 +1
0 0 +1 +1
Canine, bone 6 mo. 12 mo.
+1 +I
0 ()
T
C 5
Membrane Cellularity T
C
T
C
+1
+1
+1
+1
-
- b -
Inflammatory Response
-
-
-
0 0
0 0
-a
-a
10
10
+2+2 +2 $2
+1 +1
15 18
20 25
+2 +2
+2 +2
+1 0
0
Rabbit, soft tissue 1 mo. +1 +1 2 mo. +1 3 mo. 12 mo. +1
+1 +1 +1 +1
12 16 13 1s
27 23 23 20
+2 +2 4-2 +I
+3 +2 +1 +1
+2 +l 4-1 +1
+2 +1 +1 +1
Canine, soft tissue 6 mo. +1 +1 12 mo.
+1 +1
80 120 25 23
+2 +1
+3 +1
+2 +1
+2 +1
0
T = Test Implant. C
=
Control Implant.
* Unsatisfactory specimens for membrane thickness measurement. b
No histology available.
Bone Proliferation T 0 0 0 0
f l +1
C 0 0 0 0
+I +l
312
ESCALAS E T AL.
DISCUSSION The macroscopic, radiological and histological studies indicate that MP,,N is a t least as well tolerated as the controls in the 12 months interval in which this study was conducted. Systemic toxicity was not present in this series and histopathological post-mortem examination of the organs failed to reveal any side effect. As MP,,N is not a suitable material for wearing parts in joint pro~theses,~7 bio-assay of local tissue response to particles was not considered relevant in this study. In conclusion, the material appears to be well suited as a skeletal implant from a biocompatibility viewpoint. This investigation was supported by Research Grant No. AM-16485 from the Ilepartment of Health, Education, and Welfare, Public Health Service, The National Institutes of Health. The authors thank Mr. R. Urban for his technical collaboration in this study.
References 1. Proceedings of the Society for Metallic Surgical Implants. May 22, 1970. J . Bone Joint Surg., 53B,314 (1971). 2. Multiphase MP35N, Technical Data. Latrobe Steel Company, Latrobe, Pennsylvania. 3. A. A. Zierold, Arch. Surg., 9, 365 (1924). 4. C. S. Venable, W. G. Stuck, and A. Beach, Ann. Surg., 917 (1932). 5. H. Emneus and U. Stenram, Acta. Orthop. Scand., 29,315 (1960). 6. J. Cohen and G. Hammond, J . Bone Joint Surg., 41A, 524 (1959). 7. A. B. Ferguson, J . Bone Joint Surg., 42A, 77 (1960). 8. P. G. Laing, A. B. Ferguson, and E. S. Hodge, J . Biomed. Muter. Res,, 1,315 ( 1967). 9. S. Seltzer, D. B. Green, R.De LaGuardia, and J. Maggio, Oral Surg., M e d . and Path., 35(6), 828 (1973). 10. H. U. Cameron, It. M. Pilliar, and I. Macnab, J . Biomed. Mater. Res., 8,283 (1974). 11. C. S. Venable and W. G. Stuck, Ann. Surg., 114, 309 (1941). 12. H. Emneus and U. Stenram, Acta. Orthop. Scand., 36, 115 (1965). 13. P. G. Laing, Orthop. Clin. North Am., 4(2), 249 (1973). 14. A. M. Pappas, J . Bone Joint Surg., 50A, 535 (1968). 15. It. J. Hegyeli, J . Biomed. Muter. Res. (Symposium),1, 1 (1971). 16. P. P. Symeonides, J . Alterg. Clin. Immunol., 51, 251 (1973). 17. D. L. Brendlinger, J . Am. Dent. Assoc., 81,392 (1970). 18. B. S. Oppenheimer, E. T. Oppenheimer, I. Danishefsky, and A. P. Stout, Cancer Res., 16, 439 (1956).
MPQSN:ALLOY FOIl SURGICAL IhlPLANTS
3 13
D. F. Mitchell, J . Dent. Res., 38, 715 (1959). F. W. Sunderman, Jr; Food, Cosmet. Tozicol., 9, 105 (1971). J. C. Heath, M. Webb, and Nl. Caffrey, Brit. J. Cancer, 23, 1.53 (1969). F . W. Sunderman, Jr., Dis. Chest, 5L, 527 (1968). W. C. Hueper, J . Null. Cancer Znst., 16, 55 (1955). S. A. V. Swanson, M. A. R. Freeman, and J. C. Heath, J. Bone Joint Surg., 55B,4 (1973). 25. Ariel and Jacobs (1964) in, Ott, G., Experimentelle Medizin, Pathologie Und Klinik., 32, 1 (1970). 26. ASTM, Standard recommended practice for experimental testing for biological compatibility of metals for surgial implants. ASTM designation, Committee F-4 on Surgical Implant Materials, October, 1971. 27. J . 0. Galante and W. Rostoker, in The H i p , Proceedings of the first open scientific meeting of the Hip Society, 67-78, 1973.
19. 20. 21. 22. 23. 24.
Received August 5, 1974
VOL. 9, PP. 303-313 (1975)
MP,5N: A Corrosion Resistant, High Strength Alloy for Orthopedic Surgical Impants: Bio-Assay Results FELIX ESCALAS, JORGE GALAKTE, WILLIAM ROSTOKER, and PHILIP S. COOGAN, Rush Presbyterian, St. Luke's Medical Center, 1753 West Congress Parkway, Chicago, Illinois 60612
Summary A cobalt based alloy, MP,,N, with excellent mechanical properties has been recently introduced as a material for surgical orthopedic implants. A study was made of local and systemic host response to this material in two differentmammal species. The implantation time ranged from one to 12 months. The result of this study indicated: MPa5N produces a degree of local tissue response comparable to that of 316L stainless steel. No systemic side effects were observed during the implantation times included in this study.
INTRODUCTION Corrosion resistant cobalt, based alloys have been successfully used for many years in the manufacture of orthopedic surgical implants. Their mechanical properties and their corrosion resistance has accounted for their widespread acceptance. The purpose of this study is to present the bio-assay of a cobalt based alloy, MP3JV2 (Trademark of the Standard Pressed Steel Company), recently introduced in ciinical practice. The nominal composition of this material is 35% Ni, 35% Co, 20% Cr and 1Oyo Mo. This alloy is characterized by very high tensile strength, in the level of 260,000 psi when work strengthened, with good ductility, toughness and corrosion resistance in vitro. These characteristics make MP3,N an excellent material for permanent implants, such as total hip prostheses, where long standing cyclic stresses are the rule. 303 @ 1975 by John Wiley di Sons, Inc.
ESCALAS ET AL.
304
Literature Review Although the material is in clinical use in Europe, under the trade name Protasul 10, 110 reported data is available in the literature as to its biological acceptance. Zierold3 gave the first description of local tissue reaction to a cobalt based alloy. He described the bone reaction to Stellite (Co-Cr-Mo), in dogs, 6 weeks after implantation, as a moderate swelling of the bone around the implant with no discoloration or changes in the periosteum. He noticed the presence of a lining membrane, described as a dense, narrow rim of connective tissue. Recent studies reproduced the same results, placing cobalt based alloys among the best biologically tolerated meta1s.l~~Emneus and Stenram6 compared tissue reactions induced around Vitallium rods, with stainless steel ;less reaction was demonstrated mound Vitallium. Cohen,6 working with metallic particles showed appreciable tissue reaction around Vitallium and warned of the relative inertness of so-called corrosion resistant metals; however, in his work he described Vitallium as being more inert in tissues than stainless steel. This concept was supported by Ferguson' who stressed the importance of minimal ion migration rate in living tissues for Vitallium and stainless steel. Experimental data from I,aing* correlated ion migration with fibrous r e a d o n around the implants and showed this effect t o be minimal around Co-Cr-Mo, Co-Cr-Ni and Co-Cr-Xi-Mo in experimental animal implantation. Seltzerg reproduced these results adding additional data obtained from electron microscopy study of the tissues around Vitallium implants and evidencing minimal surface corrosion. A bio-assay of porous Vitallium has been done in rats by Cameron,lO and he described the material as being very well tolerated and producing minimal encapsulating fibrous tissue. Reports of local tissue tolerance of cobalt-chromium alloys in humans show in general a n acceptable correlation with experimental data.I1-l3 I n uitro studies have been done using tissue culture tech~iique'~ and show moderate inhibition of growth rates for cobalt based alloys. In general, results from these techniques are regarded as controversiaL1 Idiosyncratic toxicity of cobalt alloy iniplants has been described in humans in several i n s t a ~ i c e s . ~ No ~ J ~other systemic 'J
ALLOY FOR SURGICAL IMPLANTS
hlP,N:
305
or generalized side effects have been reported either in humans or in animal experimentation. Long term effect of exposure to cobalt based alloys and implant materials in general has aroused a general interest, especially concerning possible carcinogenesis. Sarcoma induction around subcutaneous Vitallium discs;18J9 Chromium and chromates, cobalt powder, oxide and sulphide,20~*1 has been described experimentally. Nickel has local carcinogenic effect by direct, inhalation in humans and by inhalation in experimental animals.** When nickel is implanted in soft, tissues i t produces tumors in rodents and other species.23 Particulate Co-Cr-Mo has also produced tumors experimentally in soft tissues in the rat.24 One questionable case of a tumor arising around a cobalt-chromium alloy has bern described in humans.25
MATERIALS AND METHODS Materials. The test samples were cut from standard comercial rod supplied by Latrobe Steel Company. The dimensions of the iinplants are described as follows: Animal-Implant
-
Dog-Soft tissue Dog-Bone Rabbit-Soft tissue Rabbit-Bone
Long
Diameter
__
1 in. (25 mm)
% in. (12.6 mm) % in (12.6 mm) in. (6.3 mm)
in (9.5 mm)
W in. (3.2 mm) W in. (3.2 mm) % in (1.6 mm)
The surface of the implants was prepared following the ASTM recommendation. * 6 316L (Joslyn Stainless Steel; Div. of Joslyn Mfg., Fort Wayne, Indiana), control implants of the same shape and dimensions as described for the test samples were used. The samples were then heat sterilized. The composition of the materials used is described in Table I. Animals. Adult, male mongrel dogs, kveighing approximately 60 lbs., and adult male New Zealand albino rabbits, weighing 5 to 6 lbs. were used for the experiment. A total of 16 rabbits and two dogs were used. The animals were fed a standard diet and water ad libitum. Activity was not restricted.
ESCALAS ET AL.
306
__
TABLE I Compobitiort of MP3$Nand 316L Stainless Steel ~~
____.
_ _ - ~ ____
Element
Percent
~~
JIPXbN
316L Stainless Steel
Carbon Nickel Molybdenum Chromium Cobalt Carbon Silicon Manganese Nickel Chromium Molybdenum Sulphur Phosphorus Iron
__ 0.25 max. 33.00-37.00 9.00- 10.50 19.00-21.00 Balance
.__
Check Analysis yo Under % Over Minimum Maximum -
0.30 0.15 0.25
.01 0.30 0.15 0.25
-
-
0.20 0.50 11.00 16.50 2.25
Balance
0.03 1.00 2.00 14.00 18.50 3.00 0.03 0.04 Ba 1ance
Surgical technique. Intravenous Nembutal was used for the rabbits and methothane inhalation anesthesia for the dogs. Standard aseptic surgical technique was used. Soft tissue samples were implanted in the paravertebral muscle, through a posterior midline incision. The femora were approached by means of a lateral incision and after drilling a small hole in the lateral cortex, the cylindrical samples were introduced in the bone. The implants were handled with teflon coated forceps. Tissue preparation. Following sacrifice by Nembutal overdose, the soft tissue implants were retrieved “en bloc” with the surrounding tissue and fixed in 10% buffered formalin. After 48 hr the implants were extracted taking care to preserve the fibrous tissue lining. Subsequently, the blocks were embedded in paraffin and sectioned in 6 p thick slices with a Jung microtomr. The plane of a section was perpendicular to the axis of the implant. The sections were stained with hemotoxilin-eosin and Mallory stain and mounted in standard microscopy slides. The femora containing the implants were fixed in buffered formalin for 48 hr and contact x-ray pictures taken to localize the implants
h I P J 4 : ALLOY FOR SURGICAL IJIPLANTS
307
and study the bone in contact with the metals. The bones were sectioned in blocks, containing one implant and decalcified in Cal-Ex solution. (Fisher Scientific Co., Fairlawn, N.J.) The metallic rods were then removed from the decalcified blocks which were subsequently sectioned and processed for light microscopy, as described above. The liver, lung, kidney and spleen of all the animals were fixed in formalin, immediately after sacrifice. These organs were then sectioned and representative samples from each one processed for histopathological study.
Methods of Evaluation 1. Macroscopic Tissue Response: The tissues surrounding the implant were checked for abnormal proliferation, gross necrosis and/ or color changes. 2. X-ray Evaluation: Contact x-ray pictures used to localize the cylinders in the bone were carefully studied to determine if any radiological signs of osteolysis, osteoporosis or bone proliferation were present near the implants. 3. Microscopic Tissue Response: I n the soft tissues three histological structures surrounding the implant were studied. (a) The fibrous membrane-the thickness of this structure was measured using a “Zeiss” measuring eyepiece at four different points and the average values calculated.* The cellular pattern in the membrane was recorded as well, as the presence of opaque bodies in the inner lining. (b) The thickness of the zone of loose connective tissue around the membrane was also measured. The cellular type, the presence of giant cells, blood vessels and polymorphonuclear cells was recorded. (c) The muscle around the implant n a s screened for signs of degeneration and/or abnormal cellular infiltrates. The evaluation of implanted bone inciuded: (a) Measurement of the lining fibrous membranes; (b) a record of osteolysis, osteoporosis and over-abundant osteoid seams around the implant; and ( c ) a rough estimate of the amount of cellularity in the bone in contact with the implant.
* The microscopic evaluation data reported in Table 111, represents an average of the values assigned or measured to the histology sections of 4 test and 2 control samples in each of two rabbits, for every follow-up time, and 8 test and 4 control samples in one dog for every follow-up time.
ESCALAS E T AL.
308
These different parameters were arbitrarily graded from 0 to +3 with the exception of the thickness measurements which were recorded in microns.
EXPERIMENTS AND RESULTS I n the soft tissue experiment each rabbit received 6 implants in the paravertebral muscles, 3 on each side. Each one of the rabbits used to test implants in bone, received a total of 6 implants, 3 in each femur. Two of the implants for every animal were 316L control samples and the remainder test samples. Two dogs were used for the experiment, each implanted with a group of 12 femoral implants. Four samples in each group were 316L controls. The number of animals and sacrifice period is indicated in Table I. Macroscopic evaluation of soft tissue and bone showed minimal reaction. No tumors were present in the animals sacrificed. TABLE I1 Bio-Assay Protocol for R.IP,aN Implants Rabbit Soft tissue
Rabbit Femura
Time (in Months)
Number of Animals
1 2 3 12
2 2 2 2
12
2 2 2b 2
6 12
1 1
6 12
1 1
1
2
3 Canine Soft tissue Canine Femur"
* A specimen of bone surrounding one implant from each animal was sent for electron microprobe analysis, to determine the metallic ion migration in the tissue. b All specimens from one animal, were sent for electron probe analysis.
hlP3bN: ALLOY F01t SURGICAL IllPLANTS
309
Fig. 1. Low-power microphotography of the living fibrous membrane arouiid a MP,,N implant in rabbit soft tissue, 6 months after implantation. The membrane is regular and minimal cellularit,y is present; a loose connective tissue layer appears underneath.
On histological examination the lining membranes from rabbit samples (Fig. 1) showed moderatcl crllularity with abundant macrophages during the first months and regrrssc,d to a hwcr cellular type with more mature fibrocytcs by the 12th month. Vascularity was an incidental finding in thc initial months. N o “forcign body particles” were seen in the specimens. Inflammatory response in the loose connective tissue around the membrane and muscle was moderate in the first and second month after implantation and became minimal later with very few histocytes and absence of giant cells and polymorphonuclears. The reaction pattern given by the control samples was essentially the same, except for a thicker lining membrane during the initial months. I n canine soft tissue, a t 6 months, very thick fibrous membranes and moderate proliferative reaction in the surrounding tissue was present. No abnormal cells or acute inflammatory cellular patterns were observed. The fibrous membranes around the control coupons
310
ESCALAS ET AL.
were thicker than those around the test coupons. Twelve months after surgery a general regression in the membrane thickness and a decreased cellularity was present around the test and control samples. I n the rabbit femora sections, the membrane was extremely fine and fragile and was destroyed in many cases when removing the implant. No osteolysis or abnormal bone proliferation was present as revealed by the x-ray study of the bones and confirmed by the microscopic study of the sections. Bone growth was apparent around the implant appearing as a thin rim of woven bone. Test and control coupons elicited the same response in the bone. The test samples in canine femora elicited a somewhat more fibrotic reaction with well developed lining membranes averaging 18 p for the 12 month specimens. Bone growth was present around the implants forming an involucrum of woven and lamellar bone with abundant osteocytes (Pig. 2 ) . The control coupons presented basically the same picture except for a slightly thickclr fibrous membrane.
Fig. 2 . Low-power microphotography (x100) of the bone around a klP,,N implant in a dog, 6 months after implantation. A thin layer of woven bone appears in contact with the implant. Cellularity and structure of the remaining bone is entirely normal.
MPabN : ALLOY FOlb SURGICAL IhlPLANTS
311
The x-ray study of the canine femora showed moderate bone proliferation, occupying the medullary canal and slight cortical thickening a t the level of the implants. No definite differences were observed between test, and control samples. The results obtained are summarized in Table 111. TABLE I11 Local Tissue Response X-ray Evaluation
Microscopic Evaluation Average MemMacroscopic brane E,valuation Thickness Animal and Tissue (Fibrosis) (pm) T
C
Rabbit, bone 1 mo. 2 mo. 3 mo. 12 mo.
0 +1
0 0 +1 +1
Canine, bone 6 mo. 12 mo.
+1 +I
0 ()
T
C 5
Membrane Cellularity T
C
T
C
+1
+1
+1
+1
-
- b -
Inflammatory Response
-
-
-
0 0
0 0
-a
-a
10
10
+2+2 +2 $2
+1 +1
15 18
20 25
+2 +2
+2 +2
+1 0
0
Rabbit, soft tissue 1 mo. +1 +1 2 mo. +1 3 mo. 12 mo. +1
+1 +1 +1 +1
12 16 13 1s
27 23 23 20
+2 +2 4-2 +I
+3 +2 +1 +1
+2 +l 4-1 +1
+2 +1 +1 +1
Canine, soft tissue 6 mo. +1 +1 12 mo.
+1 +1
80 120 25 23
+2 +1
+3 +1
+2 +1
+2 +1
0
T = Test Implant. C
=
Control Implant.
* Unsatisfactory specimens for membrane thickness measurement. b
No histology available.
Bone Proliferation T 0 0 0 0
f l +1
C 0 0 0 0
+I +l
312
ESCALAS E T AL.
DISCUSSION The macroscopic, radiological and histological studies indicate that MP,,N is a t least as well tolerated as the controls in the 12 months interval in which this study was conducted. Systemic toxicity was not present in this series and histopathological post-mortem examination of the organs failed to reveal any side effect. As MP,,N is not a suitable material for wearing parts in joint pro~theses,~7 bio-assay of local tissue response to particles was not considered relevant in this study. In conclusion, the material appears to be well suited as a skeletal implant from a biocompatibility viewpoint. This investigation was supported by Research Grant No. AM-16485 from the Ilepartment of Health, Education, and Welfare, Public Health Service, The National Institutes of Health. The authors thank Mr. R. Urban for his technical collaboration in this study.
References 1. Proceedings of the Society for Metallic Surgical Implants. May 22, 1970. J . Bone Joint Surg., 53B,314 (1971). 2. Multiphase MP35N, Technical Data. Latrobe Steel Company, Latrobe, Pennsylvania. 3. A. A. Zierold, Arch. Surg., 9, 365 (1924). 4. C. S. Venable, W. G. Stuck, and A. Beach, Ann. Surg., 917 (1932). 5. H. Emneus and U. Stenram, Acta. Orthop. Scand., 29,315 (1960). 6. J. Cohen and G. Hammond, J . Bone Joint Surg., 41A, 524 (1959). 7. A. B. Ferguson, J . Bone Joint Surg., 42A, 77 (1960). 8. P. G. Laing, A. B. Ferguson, and E. S. Hodge, J . Biomed. Muter. Res,, 1,315 ( 1967). 9. S. Seltzer, D. B. Green, R.De LaGuardia, and J. Maggio, Oral Surg., M e d . and Path., 35(6), 828 (1973). 10. H. U. Cameron, It. M. Pilliar, and I. Macnab, J . Biomed. Mater. Res., 8,283 (1974). 11. C. S. Venable and W. G. Stuck, Ann. Surg., 114, 309 (1941). 12. H. Emneus and U. Stenram, Acta. Orthop. Scand., 36, 115 (1965). 13. P. G. Laing, Orthop. Clin. North Am., 4(2), 249 (1973). 14. A. M. Pappas, J . Bone Joint Surg., 50A, 535 (1968). 15. It. J. Hegyeli, J . Biomed. Muter. Res. (Symposium),1, 1 (1971). 16. P. P. Symeonides, J . Alterg. Clin. Immunol., 51, 251 (1973). 17. D. L. Brendlinger, J . Am. Dent. Assoc., 81,392 (1970). 18. B. S. Oppenheimer, E. T. Oppenheimer, I. Danishefsky, and A. P. Stout, Cancer Res., 16, 439 (1956).
MPQSN:ALLOY FOIl SURGICAL IhlPLANTS
3 13
D. F. Mitchell, J . Dent. Res., 38, 715 (1959). F. W. Sunderman, Jr; Food, Cosmet. Tozicol., 9, 105 (1971). J. C. Heath, M. Webb, and Nl. Caffrey, Brit. J. Cancer, 23, 1.53 (1969). F . W. Sunderman, Jr., Dis. Chest, 5L, 527 (1968). W. C. Hueper, J . Null. Cancer Znst., 16, 55 (1955). S. A. V. Swanson, M. A. R. Freeman, and J. C. Heath, J. Bone Joint Surg., 55B,4 (1973). 25. Ariel and Jacobs (1964) in, Ott, G., Experimentelle Medizin, Pathologie Und Klinik., 32, 1 (1970). 26. ASTM, Standard recommended practice for experimental testing for biological compatibility of metals for surgial implants. ASTM designation, Committee F-4 on Surgical Implant Materials, October, 1971. 27. J . 0. Galante and W. Rostoker, in The H i p , Proceedings of the first open scientific meeting of the Hip Society, 67-78, 1973.
19. 20. 21. 22. 23. 24.
Received August 5, 1974
