A comparative animal study showed that, after implantation in skull defects in guinea pigs, porous high-density polyethylene (PHDPE) was substantially better anchored in the bone than Proplast, and had greater stability of form and structure. In Proplast, ingrowth of fibrous tissue caused partial structural dilatation and fragmentation, which could limit its suitability for use in reconstructive surgery

Berghaus, Alexander

Handrock, M.

Mulch, G.

English

Universität München: Elektronischen Publikationen

Arch Otorhinolaryngol (1984) 240:115-123 
Archives of 
Oto-Rhino-Laryngology 
9 Springer-Verlag 1984 
Porous Polyethylene and Proplast: 
Their Behavior in a Bony Implant Bed* 
Alexander  Berghaus 1, Gfinther Mulch 2, and Michael Handrock 1 
1 HNO-Klinik und Poliklinik (Leiter: Prof. Dr. D. Zfihlke), Klinikum Steglitz 
der Freien Universitfit Berlin, Hindenburgdamm 30, D-1000 Berlin 45 
2 HNO-Klinik und Poliklinik (Leiter: Prof. Dr. E. R. Kastenbauer), Klinikum Charlottenburg 
der Freien Universitfit Berlin, Spandauer Damm 130, D-1000 Berlin 19 
Summary. A comparative animal study showed that, after implantation in 
skull defects in guinea pigs, porous high-density polyethylene (PHDPE)  was 
substantially better  anchored in the bone than Proplast, and had greater 
stability of form and structure. In Proplast, ingrowth of fibrous tissue caused 
partial structural dilatation and fragmentation, which could limit its 
suitability for use in reconstructive surgery. 
Key words: P H D P E  - Proplast - Bone - Animal experiment 
The requirements of implants and grafts in reconstructive surgery include: 
adequate availability, problem-free sterilization, good formability, and form 
stability, good tissue tolerance and a low level of resorption. In addition, stable 
anchorage is necessary especially for bony implant beds. 
So far, no available material - not even autogenous bone or cartilage - has 
fulfilled all these requirements at  o n e  t ime .  Experimental  and clinical 
investigations in this field indicate that, in principle, various porous synthetic 
materials are suitable for cartilaginous and osseous structures [1, 2, 5, 6, 10, 13, 
18]. Porous polyethylene has been used for reconstruction of cartilaginous 
structures [1, 2, 14-16] ,  but should also be suitable for bony structures, 
especially in light of the fact that ingrowth of bone into the pores of this material 
has been described repeatedly [6, 9 -12 ,  19-21].  
In the present study, we chose to do a comparison with Proplast, which is 
also a recently developed porous material commercially available for use in 
reconstructive surgery. 
* Presented in part at the 54th Annual Meeting of the Deutsche Gesellschaft ffir Hals-Nasen-Oh- 
ren-Heilkunde, Kopf- und Halschirurgie, Travemfinde, 1983 
Translated from the German by Randall A. Condra 
Offprint requests to: Alexander Berghaus, MD (address see above) 
116 A. Berghaus et al. 
The primary purpose of the comparative animal experiments was to gain 
information about the stability of form and structure of the two materials after 
implantation in a bony bed in the skull. 
Materials and Methods 
Porous Polyethylene 
Porous high-density polyethylene (PHDPE; Ruhrchemie AG, Oberhausen, FRG) is a sintered 
synthetic which is more elastic than the rather brittle ceramics and is more chemically resistant than 
porous metals. For the sintering process, a powder is used which is made from low-pressure 
polyethylenes with a relatively broad fusion range. This makes it possible to produce plates and tubes 
as well as pieces with special profiles and shapes, which can then be sawed, drilled, milled, cut, 
stamped, etc. and also fused or further re-formed thermoplastically. Density is about 0.6 g/cm 3 and 
porosity 40% [4]. Pore size ranges between 40 and 150 lxm, but can be 200 ~m and more. 
In principle, sterilization in the autoclave is possible. However, because thermoplastic 
deformation begins at about 110 ~ C, we preferred to use gamma or gas sterilization. 
Proplust 
Proplast I consists of Teflon fluorocarbon polymer and carbon fibers, which give it a grey color 
(Fig. 1). Proplast II, which is now available as well, contains aluminium fibers instead of carbon 
fibers and is white. Porosity is 70% - 9 0 %  and pore size is between 100 and 400 ~m (manufacturer's 
data). The material is easily compressible (which can close the pores); it can be cut easily and is 
somewhat more brittle than porous polyethylene. The manufacturer (Vitek Inc., Houston, Texas) 
offers prefabricated implants, among other things for augmentation in the areas of the chin, the 
cheekbone and the bridge of the nose. 
Fig. 1. Proplast I. Carbon fiber fragments embedded relatively loosely in synthetic ground substance. 
Scanning electron microscope, approx, x 200 
Porous Polyethylene and Proplast 117 
Furthermore, for reconstruction of the auditory ossicle chain, one can purchase alloplastic 
ossicles comparable to those made of porous polyethylene which are already on the market 
(manufacturer: Richards, Memphis, Tennessee). Comparisons of the two materials for use in the 
replacement of auditory ossicles can be found elsewhere [e.g., 7, 8, 17]. Proplast can be sterilized i n  
an autoclave. 
The animals used in the tests were guinea pigs weighing 300-600 g. 
Under general anesthesia, predefined defects were milled into the calotte (diameter: 7 ram) and 
lower jaw (5 x 2 • 2 ram). In addition, the periosteum was lifted from the nasal dorsum. The defects 
were filled with synthetic implants of exactly corresponding size (calotte: 7 mm diameter, 1 mm 
thick; lower jaw: 5 • 2 • 2 mm). A 9 x 3 x 1 mm subperiosteal implant was placed on the nasal 
dorsum (Fig. 2). After a maximum observation period of 6 months, the implants and implant beds 
were embedded in methacrylate and stained according to Giemsa. 
Evaluations were made for 55 porous polyethylene and 55 Proplast implants. 
Quantitative determination of bone ingrowth into porous polyethylene is impaired by a number 
of difficulties [10]. We restricted ourselves to a determination of the percentage of ossification, 
because the main concern of this study was the stability of form and structure of the 
implants. 
The second of three histological sections through the center of the implant served as the basis for 
evaluation of the degree of ossification of the pores. We recorded whether the pores recognizable in 
the histological section were 25%, 50%, 75%, or more than 75% filled with newly formed 
bone. 
Results 
It became clear that porous polyethylene stimulated new formation of bone 
substantially better  than Proplast. With Proplast, even after 6 months, there was 
no case of more than 25% of the pore volume being filled with bone. However,  
with Porous polyethylene, between 50% and 75% ossification was already 
visible in five of 14 implants after only i month. After  3 months, ossification was 
already above 50% in 14 of 19 implants, of which seven were over 75%. 
However ,  there was no further improvement in this situation after 6 months (8 of 
18 implants over 50%, of which 5 were over 75%). 
B 
C 
Fig. 2. Selected implant beds on the guinea pig skull. A, circular defect in the center of the calotte 
extending to the dura; B, subperiosteal pocket without bone defect; C, block-shaped bone defect in 
the lower jaw 
118 A. Berghaus et al. 
Fig. 3. Surface of porous high-density polyethylene (PHDPE) cut with electric saw. The pores are 
dosed. Scanning electron microscope, approx, x 200 
Fig. 4. Surface of PHDPE cut manually with a sharp knife. Open pores. Scanning electron 
microscope, approx, x 200 
Bone  ingrowth was more  marked  f rom the nar row side of  the implant ,  an 
observat ion which was also m a d e  by H a n d r o c k  [9]. Examining  the surface of  the 
implants  with a scanning electron microscope  provided  an explanat ion for  this 
fact: the fast ro ta ry  saws used to cut  the implants to size deve loped  high 
tempera tures ,  which caused the pores  on the surface to fuse (Fig. 3). Therefore ,  
Porous Polyethylene and Proplast 119 
Fig. 5. PHDPE 6 months after implantation in the calotte of the guinea pig. Complete bony 
interpenetration of the pore system. Giemsa 
Fig. 6. Proplast 6 months after implantation in the calotte of the guinea pig. No incorporation of 
bone; formation of cystic cavities; deformation of the synthetic material. The edges appear "frayed". 
Giemsa 
in growth of tissue was no longer possible there, in contrast to the narrow sides of 
the implants, which had been cut manually. This permits the conclusion that 
ossification is more marked when fusion of pores on the surface of such implants 
is avoided by shaping them with sharp knives only instead of using fast rotary 
milling equipment (Fig. 4). However ,  even under the conditions of this study, 
some porous polyethylene implants showed ingrowth of bony tissue through 
their entire breadth (Fig. 5). 
In contrast, with Proplast I, there was usually no newly formed bone,  but 
only unspecific granulation tissue, and this tended to form cystic cavities in larger 
pores (Fig. 6). This should not be confused with the vessels which were 
occasionally recognizable in the ossified pores of PHDPE.  Spector et al. [21] 
120 A. Berghaus et al. 
Fig. 7. PHDPE 3 months after implantation on the bridge of the nose in guinea pigs. Sinking below 
the original surface level (marked line); encasement by newly formed bone (b). No penetration into 
the nasal cavity. Implant retains its form. Giemsa 
attributed the low degree of bone ingrowth in Proplast to too narrow 
interconnections between the pores. 
However ,  besides ossification of the pores, another mechanism observed in 
both synthetic materials was important for anchorage of the implants in the 
implant bed: in the implants in the calotte and lower jaw as well as the 
subperiosteal grafts onto the bridge of the nose, the implant was surrounded by 
tongue-shaped areas of bone tissue advancing along the surface of the graft. This 
process was much more marked in polyethylene than in Proplast. The contact 
between the newly formed bone lamellae and the implant surface was in part 
very close and immediate. On the other hand, there was occasionally a layer of 
fine connective tissue between the synthetic material and the bone. The 
enclosure described was especially marked on the surfaces of the calotte implant 
facing the outer skin and dura, respectively, as well as in the blocks implanted 
under the periosteum of the bridge of the nose. Furthermore,  these last implants 
were regularly found to sink about 0.5 mm below the surface of the nasal bone 
(Fig. 7). However,  none of these grafts penetrated the main nasal cavity or 
perforated the outer skin. In combination with the described formation of a 
surrounding wall of bone, we interpret this as a marked tendency of the bony 
implant bed to integrate the synthetic material. 
Assessment of  Form Stability 
PHDPE. Except for slight bending in the longitudinal axis of the implants, the 
material retained its predetermined form macroscopically and histologically. 
With only a few exceptions, the corners and edges of the blocks were neither 
deformed nor rounded; signs of resorption were not observed (Fig. 8). Form and 
s t ructure  were even retained in the implants which sank into the nasal bone 
(Fig. 7). 
Porous Polyethylene and Proplast 121 
Fig. 8. PHDPE 3 months after implantation in the calotte. Bony encasement of the edge without loss 
of form. Close contact of the surfaces (i = implant; b = bone). Giemsa 
Fig. 9. Proplast 3 months after implantation in the calotte: structural deterioration of the synthetic 
material (i, implant). The material appears in bone marrow cavities (x). Giemsa 
Proplast L The carbon fiber fragments are embedded  relatively loosely in the 
synthetic ground substance of the Teflon f luorocarbon polymer  (Fig. 1). As we 
have also demonstra ted  for Proplast  I I  with aluminum fibers [2], histological 
examination shows that the material  loses varying amounts of its fibers. These 
fibers are then dispersed along the periphery,  but are either embedded  there 
without irritation or t ransported further. This situation leads to a loosening of 
the structure of the entire implant,  which is reflected in deformation and 
fragmentat ion.  Thus, we have observed substantial deformation in almost all 
Proplast  implants. Beyond that,  surface scratches are an almost regular finding. 
Fur thermore ,  ingrowing tissue causes splitting of the edges, which then appear  
frayed (Fig. 6). For Proplast,  the clearest expression of material  degradation is 
122 A. Berghaus et al. 
the appearance of fragments of the synthetic material in neighboring bone 
marrow cavities (Fig. 9). 
The behavior described confirms the impression existing before implantation 
that the material was somewhat brittle. The present study could not answer the 
questions about possible undesirable effects resulting from the long-term 
presence of dispersed particles of synthetic material and carbon fiber. 
Two calotte implants were rejected after 3 months. Two purulent infections 
were observed. 
Discussion 
The greater stability of porous polyethylene compared to Proplast was 
confirmed 6 months after implantation: the polyethylene implants retained their 
form almost completely, while Proplast was destabilized by the host tissue, 
partially fragmented, and deformed. 
When predefined, artificially created defects are filled with either of the two 
synthetics, the bony implant bed reacts in two ways: with ingrowth of newly 
formed bone into the implant (PHDPE) and with encasement or encapsulation. 
However, only with PHDPE does this lead to adequate bony anchorage and 
stabilization in the predetermined form. With Proplast, the procedure is 
accompanied by deformation of the implant. In our opinion, this limits the 
suitability of Proplast for reconstructive facial surgery. With both synthetics, 
subperiosteal implantation on the bridge of the nose leads to "wandering" in the 
direction of the nasal cavity. This observation can be interpreted as a tendency of 
the bone to incorporate the material, because there is no penetration of the main 
nasal cavity, and the implant becomes anchored in the bone by simultaneous 
bone ingrowth and encasement. Thus, especially the form-stable PHDPE could 
be suitable for correction, e.g., of a saddle nose, in spite of the tendency to sink 
below the bone surface. 
Both of the synthetic materials examined can be viewed as relatively safe 
from the danger of infection. 
Based on the present study, porous polyethylene was selected for clinical use 
in correcting defects of the facial skull. In two patients with defects of the 
forehead and eye socket, the results were subjectively and objectively 
satisfactory after 1.5 and 2 years, respectively [3]. 
Acknowledgements. We thank the Institute of Pathology, Klinikum Steglitz, Free University of 
Berlin (Provisional Director: Prof. U. Gross) for assisting in the evaluation of the histological 
preparations. 
References 
1. Berghaus A, Axhausen M, Handrock M (1982) Zur Verwendbarkeit von Kunststoffen bei der 
Rekonstruktion der Ohrmuschel. Arch Otorhinolaryngol 235 : 622-625 
2. Berghaus A, Axhausen M, Handrock M (1983) Por6se Kunststoffe ftir die Ohrmuschelplastik. 
Laryngol Rhinol Otol 62:320-327 
Porous Polyethylene and Proplast 123 
3. Berghaus A, Mulch G, Handrock M (1983) Zur Verwendbarkeit von porOsem Poty~thylen fiir 
die Korrektur von Schfideldefekten. Arch Otorhinolaryngol (in press) 
4. Berzen J, Braun G, Spengler H (1976) Por6ses Poly~ithylen. Chem Tech 5:351-353 
5. Brown BL, Neel HB III, Kern EB (1979) Implants of Supramid, Proplast, Plasti-Pore, and 
Silastic. Arch Otolaryngol 105:605-609 
6. Cestero HJ Jr, Salyer KE, Toranto IR (1975) Bone growth into porous carbon, polyethylene, 
and polypropylene prostheses. J Biomed Mater Res 9 : 1 - 7  
7. Chtiden HG (1978) Ober den Wiederautbau der Geh6rkn6chelchenkette mit Hilfe einer 
Kunststoffprothese (Shea-TORP). HNO 26:57-59 
8. Fisch U (1978) Zur Rekonstruktion der Geh6rkn6chelchenkette. HNO 26:53-56 
9. Handrock Ch (1979) Tierexperimentelle Untersuchungen tiber die Verwendbarkeit eines neuen 
por6sen Polyfithylens im Mittelohr. Inaugural Dissertation, Berlin 
10. Klawitter JJ, Bagwell JG, Weinstein AM, Sauer BW (1976) An evaluation of bone growth into 
porous high density polyethylene. J Biomed Mater Res 10:311-323 
11. Kozinn SC, Hedley A, Kim W, Urist M (1982) Observations on bone ingrowth into bone 
morphogenetic protein impregnated porous polyethylene implants. Orthop Trans 6:273 
12. Mayer RD, Moyle DD, Sauer BW (1983) Fracture of porous polyethylene-bone composite. 
J Biomed Mater Res 17:59-70 
13. Neel HB III (1983) Implants of Gore-Tex. Arch Otolaryngol 109:427-433 
14. Sauer BW (1976) Correction of faulty ear carriage in the dog with porous polyethylene implants. 
Vet Med Small Anita Clin 71 : 1071-1075 
15. Sauer BW, Lade RB (1982) Porous high density polyethylene-autogenous tissue tracheal 
prosthesis. Trans Am Soc Artif Intern Organs 28:369-373 
16. Senechal G, Mamelle G, Rodriguez J, Senechal B (1981) Reflexions sur la reconstruction du 
pavilion de l'oreille. Ann Oto-Laryngol (Paris) 98:367-370 
17. Shea JJ (1977) Ober die Verwendung yon Proplast- und Plastipore-Implantaten bei der 
Tympanoplastik. HNO 25 : 96-98 
18. Skinner HB, Sbaekelford JF, Lin HJ, Cutler AD (1979) Tensile strength of bone (bone/porous 
polyethylene) interface. Biomater Med Devices Artif Organs 7:133-140 
19. Spector M, Flemming WR, Sauer BW (1975) Early tissue infiltrate in porous polyethylene 
implants into bone: a scanning electron microscope study. J Biomed Mater Res 
9 : 537-542 
20. Spector M, Flemming WR, Kreutner A (1976) Bone growth into porous high-density 
polyethylene. J Biomed Mater Res 10:595-603 
21. Spector M, Harmon SL, Kreutner A (1979) Characteristics of tissue growth into proplast and 
porous polyethylene implants in bone. J Biomed Mater Res 13 : 677-692 
Received February 14, 1984/Accepted March 10, 1984 


Porous polyethylene and proplast

Open Access LMU

Arch Otorhinolaryngol (1984) 240:115-123 Archives of Oto-Rhino-Laryngology 9 Springer-Verlag 1984 Porous Polyethylene and Proplast: Their Behavior in a Bony Implant Bed* Alexander Berghaus 1, Gfinther Mulch 2, and Michael Handrock 1 1 HNO-Klinik und Poliklinik (Leiter: Prof. Dr. D. Zfihlke), Klinikum Steglitz der Freien Universitfit Berlin, Hindenburgdamm 30, D-1000 Berlin 45 2 HNO-Klinik und Poliklinik (Leiter: Prof. Dr. E. R. Kastenbauer), Klinikum Charlottenburg der Freien Universitfit Berlin, Spandauer Damm 130, D-1000 Berlin 19 Summary. A comparative animal study showed that, after implantation in skull defects in guinea pigs, porous high-density polyethylene (PHDPE) was substantially better anchored in the bone than Proplast, and had greater stability of form and structure. In Proplast, ingrowth of fibrous tissue caused partial structural dilatation and fragmentation, which could limit its suitability for use in reconstructive surgery. Key words: PHDPE - Proplast - Bone - Animal experiment The requirements of implants and grafts in reconstructive surgery include: adequate availability, problem-free sterilization, good formability, and form stability, good tissue tolerance and a low level of resorption. In addition, stable anchorage is necessary especially for bony implant beds. So far, no available material - not even autogenous bone or cartilage - has fulfilled all these requirements at one  t ime. Experimental and clinical investigations in this field indicate that, in principle, various porous synthetic materials are suitable for cartilaginous and osseous structures [1, 2, 5, 6, 10, 13, 18]. Porous polyethylene has been used for reconstruction of cartilaginous structures [1, 2, 14-16], but should also be suitable for bony structures, especially in light of the fact that ingrowth of bone into the pores of this material has been described repeatedly [6, 9-12,  19-21]. In the present study, we chose to do a comparison with Proplast, which is also a recently developed porous material commercially available for use in reconstructive surgery. * Presented in part at the 54th Annual Meeting of th  Deutsche Gesellschaft ffir Hals-Nasen-Oh- ren-Heilkunde, Kopf- und Halschirurgie, Travemfinde, 1983 Translated from the German by Randall A. Condra Offprint requests to: Alexander Berghaus, MD (address see above) 116 A. Berghaus et al. The primary purpose of the comparative animal experiments was to gain information about the stability of form and structure of the two materials after implantation i a bony bed in the skull. Materials and Methods Porous Polyethylene Porous high-density polyethylene (PHDPE; Ruhrchemie AG, Oberhausen, FRG) is a sintered synthetic which is more elastic than the rather brittle ceramics and is more chemically resistant than porous metals. For the sintering process, a powder is used which is made from low-pressure polyethylenes with a relatively broad fusion range. This makes it possible to produce plates and tubes as well as pieces with special profiles and shapes, which can then be sawed, drilled, milled, cut, stamped, etc. and also fused or further e-formed thermoplastically. Density is about 0.6 g/cm 3 and porosity 40% [4]. Pore size ranges between 40 and 150 lxm, but can be 200 ~m and more. In principle, sterilization in the autoclave is possible. However, because thermoplastic deformation begins at about 110 ~ C, we preferred to use gamma or gas sterilization. Proplust Proplast I consists of Teflon fluorocarbon polymer and carbon fibers, which give it a grey color (Fig. 1). Proplast II, which is now available as well, contains aluminium fibers instead of carbon fibers and is white. Porosity is 70% -90% and pore size is between 100 and 400 ~m (manufacturer's data). The material is easily compressible (which can close the pores); it can be cut easily and is somewhat more brittle than porous polyethylene. The manufacturer (Vitek Inc., Houston, Texas) offers prefabricated implants, among other things for augmentation i  the areas of the chin, the cheekbone and the bridge of the nose. Fig. 1. Proplast I. Carbon fiber fragments embedded relatively loosely in synthetic ground substance. Scanning electron microscope, approx, x 200 Porous Polyethylene and Proplast 117 Furthermore, for reconstruction f the auditory ossicle chain, one can purchase alloplastic ossicles comparable to those made of porous polyethylene which are already on the market (manufacturer: Richards, Memphis, Tennessee). Comparisons of the two materials for use in the replacement of auditory ossicles can be found elsewhere [ .g., 7, 8, 17]. Proplast can be sterilized in  an autoclave. The animals used in the tests were guinea pigs weighing 300-600 g. Under general anesthesia, predefined defects were milled into the calotte (diameter: 7 ram) and lower jaw (5 x 2 • 2 ram). In addition, the periosteum was lifted from the nasal dorsum. The defects were filled with synthetic implants of exactly corresponding size (calotte: 7 mm diameter, 1mm thick; lower jaw: 5 • 2 • 2 mm). A 9 x 3 x 1 mm subperiosteal implant wasplaced on the nasal dorsum (Fig. 2). After a maximum observation period of 6 months, the implants and implant beds were embedded in methacrylate and stained according to Giemsa. Evaluations were made for 55 porous polyethylene and 55 Proplast implants. Quantitative determination f bone ingrowth into porous polyethylene is impaired by a number of difficulties [10]. We restricted ourselves to a determination f the percentage of ossification, because the main concern of this study was the stability of form and structure of the implants. The second of three histological sections through the c nter of the implant served as the basis for evaluation of the degree of ossification of the pores. We recorded whether the pores recognizable in the histological section were 25%, 50%, 75%, or more than 75% filled with newly formed bone. Results It became clear that porous polyethylene stimulated new formation of bone substantially better than Proplast. With Proplast, even after 6 months, there was no case of more than 25% of the pore volume being filled with bone. However, with Porous polyethylene, between 50% and 75% ossification was already visible in five of 14 implants after only i month. After 3 months, ossification was already above 50% in 14 of 19 implants, of which seven were over 75%. However, there was no further improvement in this situation after 6 months (8 of 18 implants over 50%, of which 5 were over 75%). B C Fig. 2. Selected implant beds on the guinea pig skull. A, circular defect in the center of the calotte extending to the dura; B, subperiosteal pocket without bone defect; C, block-shaped bone defect in the lower jaw 118 A. Berghaus et al. Fig. 3. Surface ofporous high-density polyethylene (PHDPE) cut with electric saw. The pores are dosed. Scanning electron microscope, approx, x 200 Fig. 4. Surface of PHDPE cut manually with a sharp knife. Op n pores. Scanning electron microscope, approx, x 200Bone ingrowth was more marked from the narrow side of the implant, an observation which was also made by Handrock [9]. Examining the surface of the implants with a scanning electron microscope provided an explanation for this fact: the fast rotary saws used to cut the implants to size developed high temperatures, which caused the pores on the surface to fuse (Fig. 3). Therefore,  Porous Polyethylene a d Proplast 119 Fig. 5. PHDPE 6 months after implantation in the calotte of the guinea pig. Complete bony interpenetration of the pore system. Giemsa Fig. 6. Proplast 6 months after implantation in the calotte of the guinea pig. No incorporation fbone; formation of cystic avities; deformation f the synthetic material. The edges appear "frayed". Giemsa in growth of tissue was no longer possible there, in contrast to the narrow sides of the implants, which had been cut manually. This permits the conclusion that ossification is more marked when fusion of pores on the surface of such implants is avoided by shaping them with sharp knives only instead of using fast rotary milling equipment (Fig. 4). However, even under the conditions of this study, some porous polyethylene implants showed ingrowth of bony tissue through their entire breadth (Fig. 5). In contrast, with Proplast I, there was usually no newly formed bone, but only unspecific granulation tissue, and this tended to form cystic cavities in larger pores (Fig. 6). This should not be confused with the vessels which were occasionally recognizable in the ossified pores of PHDPE.  Spector et al. [21] 120 A. Berghaus et al. Fig. 7. PHDPE 3 months after implantation on the bridge of the nos  in guinea pigs. Sinking below the original surface level (marked line); encasement by newly formed bone (b). No penetration into the nasal cavity. Implant retains its form. Giemsa attributed the low degree of bone ingrowth in Proplast to too narrow interconnections between the pores. However, besides ossification of the pores, another mechanism observed in both synthetic materials was important for anchorage of the implants in the implant bed: in the implants in the calotte and lower jaw as well as the subperiosteal grafts onto the bridge of the nose, the implant was surrounded by tongue-shaped areas of bone tissue advancing along the surface of the graft. This process was much more marked in polyethylene than in Proplast. The contact between the newly formed bone lamellae and the implant surface was in part very close and immediate. On the other hand, there was occasionally a layer of fine connective tissue between the synthetic material and the bone. The enclosure described was especially marked on the surfaces of the calotte implant facing the outer skin and dura, respectively, as well as in the blocks implanted under the periosteum of the bridge of the nose. Furthermore, these last implants were regularly found to sink about 0.5 mm below the surface of the nasal bone (Fig. 7). However, none of these grafts penetrated the main nasal cavity or perforated the outer skin. In combination with the described formation of a surrounding wall of bone, we interpret his as a marked tendency of the bony implant bed to integrate the synthetic material. Assessment of Form Stability PHDPE. Except for slight bending in the longitudinal axis of the implants, the material retained its predetermined form macroscopically and histologically. With only a few exceptions, the corners and edges of the blocks were neither deformed nor rounded; signs of resorption were not observed (Fig. 8). Form and structure were even retained in the implants which sank into the nasal bone (Fig. 7). Porous Polyethylene and Proplast 121 Fig. 8. PHDPE 3 months after implantation in the calotte. Bony encasement of the edg  without loss of form. Close contact of the surfaces (i = implant; b = bone). Giemsa Fig. 9. Proplast 3 months after implantation in the calotte: structural deterioration of the synthetic material (i, implant). The material appears in bone marrow cavities (x).Giemsa Proplast L The carbon fiber fragments are embedded relatively loosely in the synthetic ground substance of the Teflon fluorocarbon polymer (Fig. 1). As we have also demonstrated for Proplast I I  with aluminum fibers [2], histological examination shows that the material loses varying amounts of its fibers. These fibers are then dispersed along the periphery, but are either embedded there without irritation or transported further. This situation leads to a loosening of the structure of the entire implant, which is reflected in deformation and fragmentation. Thus, we have observed substantial deformation in almost all Proplast implants. Beyond that, surface scratches are an lmost regular finding. Furthermore, ingrowing tissue causes splitting of the edges, which then appear frayed (Fig. 6). For Proplast, the clearest expression of material degradation is122 A. Berghaus et al. the appearance of fragments of the synthetic material in neighboring bone marrow cavities (Fig. 9). The behavior described confirms the impression existing before implantation that the material was somewhat brittle. The present study could not answer the questions about possible undesirable ffects resulting from the long-term presence of dispersed particles of synthetic material and carbon fiber. Two calotte implants were rejected after 3 months. Two purulent infections were observed. Discussion The greater stability of porous polyethylene compared to Proplast was confirmed 6months after implantation: the polyethylene implants retained their form almost completely, while Proplast was destabilized by the host tissue, partially fragmented, and deformed. When predefined, artificially created efects are filled with either of the two synthetics, the bony implant bed reacts in two ways: with ingrowth of newly formed bone into the implant (PHDPE) and with encasement or encapsulation. However, only with PHDPE does this lead to adequate bony anchorage and stabilization in the predetermined form. With Proplast, the procedure is accompanied by deformation of the implant. In our opinion, this limits the suitability of Proplast for reconstructive facial surgery. With both synthetics, subperiosteal implantation on the bridge of the nose leads to "wandering" in the direction of the nasal cavity. This observation can be interpreted as a tendency of the bone to incorporate the material, because there is no penetration f the main nasal cavity, and the implant becomes anchored in the bone by simultaneous bone ingrowth and encasement. Thus, especially the form-stable PHDPE could be suitable for correction, e.g., of a saddle nose, in spite of the tendency to sink below the bone surface. Both of the synthetic materials examined can be viewed as relatively safe from the danger of infection. Based on the present study, porous polyethylene was selected for clinical use in correcting defects of the facial skull. In two patients with defects of the forehead and eye socket, the results were subjectively and objectively satisfactory after 1.5 and 2 years, respectively [3].Acknowledgements. We thank the Institute of Pathology, Klinikum Steglitz, Free University of Berlin (Provisional Director: Prof. U. Gross) for assisting in the evaluation of the histological preparations. References 1. Berghaus A, Axhausen M, Handrock M (1982) Zur Verwendbarkeit von Kunststoffen bei der Rekonstruktion der Ohrmuschel. Arch Otorhinolaryngol 235 : 622-625 2. Berghaus A, Axhausen M, Handrock M (1983) Por6se Kunststoffe ftir die Ohrmuschelplastik. Laryngol Rhinol Otol 62:320-327 Porous Polyethylene and Proplast 123 3. Berghaus A, Mulch G, Handrock M (1983) Zur Verwendbarkeit von porOsem Poty~thylen fiir die Korrektur von Schfideldefekten. Arch Otorhinolaryngol (in press) 4. Berzen J, Braun G, Spengler H (1976) Por6ses Poly~ithylen. Chem Tech 5:351-353 5. Brown BL, Neel HB III, Kern EB (1979) Implants of Supramid, Proplast, Plasti-Pore, and Silastic. Arch Otolaryngol 105:605-609 6. Cestero HJ Jr, Salyer KE, Toranto IR (1975) Bone growth into porous carbon, polyethylene, and polypropylene prostheses. J Biomed Mater Res 9 :1 -7  7. Chtiden HG (1978) Ober den Wiederautbau der Geh6rkn6chelchenkette mit Hilfe einer Kunststoffprothese (Shea-TORP). HNO 26:57-59 8. Fisch U (1978) Zur Rekonstruktion der Geh6rkn6chelchenkette. HNO 26:53-56 9. Handrock Ch (1979) Tierexperimentelle Untersuchungen tiber die Verwendbarkeit eines neuen por6sen Polyfithylens im Mittelohr. Inaugural Dissertation, Berlin 10. Klawitter JJ, Bagwell JG, Weinstein AM, Sauer BW (1976) An evaluation of bone growth into porous high density polyethylene. J Biomed Mater Res 10:311-323 11. Kozinn SC, Hedley A, Kim W, Urist M (1982) Observations on bone ingrowth into bone morphogenetic protein impregnated porous polyethylene implants. Orthop Trans 6:273 12. Mayer RD, Moyle DD, Sauer BW (1983) Fracture of porous polyethylene-bone composite. J Biomed Mater Res 17:59-70 13. Neel HB III (1983) Implants of Gore-Tex. Arch Otolaryngol 109:427-433 14. Sauer BW (1976) Correction of faulty ear carriage in the dog with porous polyethylene implants. Vet Med Small Anita Clin 71 : 1071-1075 15. Sauer BW, Lade RB (1982) Porous high density polyethylene-autogenous tissue tracheal prosthesis. Trans Am Soc Artif Intern Organs 28:369-373 16. Senechal G, Mamelle G, Rodriguez J, Senechal B (1981) Reflexions ur la reconstruction du pavilion de l'oreille. Ann Oto-Laryngol (Paris) 98:367-370 17. Shea JJ (1977) Ober die Verwendung yon Proplast- und Plastipore-Implantaten bei der Tympanoplastik. HNO 25 : 96-98 18. Skinner HB, Sbaekelford JF, Lin HJ, Cutler AD (1979) Tensile strength of bone (bone/porous polyethylene) interface. Biomater Med Devices Artif Organs 7:133-140 19. Spector M, Flemming WR, Sauer BW (1975) Early tissue infiltrate in porous polyethylene implants into bone: a scanning electron microscope study. J Biomed Mater Res 9 : 537-542 20. Spector M, Flemming WR, Kreutner A (1976) Bone growth into porous high-density polyethylene. J Biomed Mater Res 10:595-603 21. Spector M, Harmon SL, Kreutner A (1979) Characteristics of tissue growth into proplast and porous polyethylene implants in bone. J Biomed Mater Res 13 : 677-692 Received February 14, 1984/Accepted March 10, 1984 

An evaluation of bone growth into porous high density polyethylene.

Bone growth into porous carbon, polyethylene, and polypropylene prostheses.

Correction of faulty ear carriage in the dog with porous polyethylene implants.

Early tissue infiltrate in porous polyethylene implants into bone: a scanning electron microscope study.

Fracture of porous polyethylene-bone composite.

Implants of Gore-Tex.

Kreutner A

Ober die Verwendung yon Proplast- und Plastipore-Implantaten bei der Tympanoplastik.

Observations on bone ingrowth into bone morphogenetic protein impregnated porous polyethylene implants.

Porous high density polyethylene-autogenous tissue tracheal prosthesis.

Reflexions sur la reconstruction du pavilion de l'oreille. Ann Oto-Laryngol

Tensile strength of bone (bone/porous polyethylene) interface.

Tierexperimentelle Untersuchungen tiber die Verwendbarkeit eines neuen por6sen Polyfithylens im Mittelohr. Inaugural Dissertation,

Zur Verwendbarkeit von Kunststoffen bei der Rekonstruktion der Ohrmuschel.

Zur Verwendbarkeit von porOsem Poty~thylen fiir die Korrektur von Schfideldefekten. Arch Otorhinolaryngol

https://epub.ub.uni-muenchen.de/6207/1/Berghaus_Alexander_6207.pdf

Porous polyethylene and proplast

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