- Email: [email protected]
Heterologous collagen matrix sponge: histologic and clinical response to its implantation in third-degree burn injuries
BritW Jouma~ofPlasticSwgery(1992), 45,117-122
Heterologous collagen matrix sponge: histologic and clinical response to its implantation in third-degree bum injuries A. C. Abram0 and J.C. Viola Division of Plastic and Reconstructive
Surgery, General Hospital of Benejichcia
Portuguesa, Silo Paulo, Brazil
SUMMARY. Heterologous collagen matrix sponge has been used to prepare third-degree burn wounds for autologous skin graft. The porosity and the multiple connections among the interstices of the sponge enable ready ingrowth of endothelial and inflammatory cells. Heterologous collagen matrix sponge also increased the rate of formation of granulation tissue in bum wounds.
saline and loose skin removed. The bum wound was covered with moist white cotton cloth and a conventional dry absorptive dressing was applied. At day 3 postbum the burn necrotic tissue was excised and dressed as aforementioned. At day 6 postbum the remaining bum necrosis was excised and the bum wound was biopsied. At this time both heterologous collagen matrix sponge and white cotton cloth were placed symmetrically, one on each side of the same patient in each group. Biopsies were taken at the time of every dressing change with intervals of 3 days, each one constituting an individual time of observation, until wound granulation tissue appeared clinically, indicating the wound was ready for autologous skin grafting. Heterologous collagen matrix sponge was compared with white cotton cloth, employed as a control, in its effect to stimulate capillaries, fibroblasts, macrophages and polymorphonuclears on bum wounds. Histological count was made by Weibel’s method, employing a KlOX Zeiss oculon Integrationplatte I, having 25 points arranged in five symmetrical lines, each one with five geometrically allocated points. A 40X Zeiss objective was employed for capillaries and for fibroblasts, macrophages and polymorphonuclears a 100X Zeiss objective was used. It was analysed forty fields per lamina by means of the horizontal reading. At the same time, macroscopic evaluation of the bum wounds with both materials was performed by measuring the time in days until the wound granulation tissue was suitable to receive autologous skin graft.
To cover surfaces where skin is lost, skin substitutes can be employed (Tavis et al., 1978) as temporary dressings to be placed on the wound and left until healed, or as a semipermanent dressing, remaining attached to the wound or changed at regular intervals to prepare it for grafting (Bartlett, 1981). Comparative studies of several skin substitutes revealed that collagen is more suitable than other materials (Norton and Chvapil, 1981). Adherence is the most important of these properties. Porosity of the material has great relevance in the mechanism of adhesion. The adhesion of collagen is equivalent to that presented by normal skin (Tavis et al., 1976; Alsbjom, 1984). Collagen has been prepared in several physical forms, but sponges are more efficient dressings than others in third-degree burn wounds (Chvapil et al., 1973). This paper reports histologic and clinical behaviour of heterologous collagen matrix sponge (HCMS) as a semipermanent biological dressings in third-degree burn wounds (Abramo, 1990) and its comparison with standard white cotton cloth (WCC) dressings.
Materials and methods Heterologous collagen matrix sponge used in this particular study is polymerised native collagen or type I collagen in the form of a sponge, prepared from deer’s skin (Hut et al., 1981). The pore size of the sponge varies from 80 to 1500 u in diameter with an average size of 500 u. The thickness of the sponge is 1.5 mm and the surface is 23 x 28 cm. The collagen sponge was sterilised in a dry state using ethylene oxide. White cotton cloth is employed in the form of a mesh cloth. The mesh aperture varies from 0.4 to 0.5 mm with 0.5 mm thick cloth measuring 10 x 20 cm. The white cotton cloth was sterilised by autoclaving. Third-degree thermal bum injuries were separated into three groups for observation. Group I were injuries of the upper limbs, group II injuries of the lower limbs and group III injuries of the thoracic wall. On the injury day the bum surfaces were cleaned with
Results The study was performed on 16 patients with thermal injury. Only corporal surfaces with third-degree bum injuries were analysed. Twenty bum wounds were observed in each group. Table 1 summarises indications and outcomes. After time 0, biopsies were taken at intervals of 3 days on bum wounds with both collagen sponge and cotton cloth (Table 2). 117
118
British Journal of Plastic Surgery
Table 1 Autologous skin graJt** Gp II
GPI Age/sex
44/M 9lW 32/M 34/w 36/M 11/M 29/M 27/M 34/w 37/M 26/M 25/M 8/W 12/w 36/W 42/M
R
%’
16 19 31 25 41 20 39 13 46 16 25 30 32 14 19 14
-
Materials
L
R
-
9
15
6
9 9 18
21 18 9
6 18 9 6 15
15 6 24 15 27
6
18
12 9 18 15 6 9 12 6 18
Gp III L
R
18
-
27 21 9 6 9 21 24 18 9
6 21 9 9 15 9 6 21 9 9 -
Gp II
GPI L 18 9 21 21 24 6 12 9 18 24 -
R
L
-
-
Gp III
R HCMS
WCC
HCMS -
HCMS HCMS WCC
WCC WCC HCMS -
HCMS WCC HCMS HCMS HCMS
WCC HCMS WCC WCC WCC -
HCMS
WCC -
L
R
L
WCC -
-
-
HCMS WCC HCMS HCMS HCMS WCC -
WCC HCMS WCC WCC WCC HCMS -
HCMS WCC
WCC HCMS -
HCMS
WCC -
HCMS
WCC -
WCC
HCMS HCMS
WCC
WCC WCC HCMS
HCMS HCMS WCC
HCMS -
WCC -
HCMS HCMS
WCC WCC
WCC
HCMS
(*) third-degree burn surface area (**) days for autologous skin graft after time 0 WCC: White cotton cloth HCMS : heterologous collagen matrix sponge
Table 2
Average of biopsies taken at intervals of 3 days Group I
Number
of biopsies
Group II
HCMS
WCC
HCMS
WCC
HCMS
WCC
2, 7
6, 3
299
672
299
6, 3
Histologic findings The data presented in Figures 4,5 and 6 were obtained
from the biopsies at each time of the observation from time 0 until transplantation of autologous skin graft. Statistical tests such as Wilcoxon’s test, Friedman’s variance analysis and multiple comparisons test were applied. Figures 4 and 5 show an increase of capillaries and fibroblasts from time 0 with both materials. However, the amount of capillaries (pCO.01) and fibroblasts (p < 0.05) was significantly higher in burn wounds dressed with the collagen sponge (Fig. 1). After time 6, decrease of fibroblasts was observed, but only with burn wounds dressed with collagen sponge. Figure 6 shows that macrophages and polymorphonuclears were equal with either collagen sponge or cotton cloth. At time 3, the amount of macrophages and polymorphonuclears was more than time 0 with both materials, but significantly higher (p ~0.05) in Table 3 Effect of the materials grafting. *
Macroscopic observations
Dressings were soaked with saline for relatively atraumatic removal from the wound at the time of every dressing. Granulation tissue was judged ready to receive autologous skin grafts when the wounds presented a red colour and moderate bleeding at every dressing change. Burn wounds dressed with collagen sponge received autologous skin grafts at a mean of 8.4 days, while those dressed with cotton cloth were autografted at a mean of 18.7 days. The time to autologous skin grafting was significantly shorter (p < 0.05) in burn wounds dressed with the collagen sponge.
Group II
tissue for
Group III
HCMS
WCC
HCMS
WCC
HCMS
WCC
8,l
18,9
8,7
18,9
894
18,3
(P
burn wounds dressed with collagen sponge (Fig. 2). At time 6, macrophages and polymorphonuclears were lower in burn wounds dressed with collagen sponge.
in days average to prepare granulation
Group I
Mean days to grafting after time 0
Group III
were in each group.
(PCO.05)
(PCO.05)
Heterologous
Collagen
Matrix Sponge : Response
in Third-Degree
Burns
119
Fig. 1
Fig. 2 Figure l-Extensive capillary ingrowth in bum wounds for both materials, with significant preponderance of it in bum wound dressed with heterologous collagen matrix sponge (B). Fipre 2-Macrophages and polymorphonuclears are higher in bum wounds dressed with heterologous collagen matrix sponge (B).
Discussion The structure of the collagen sponge framework is a decisive factor for rapid tissue permeation. The porosity of around 80 u and larger, and the multiple connections in the interstices of the sponge, are important to allow cell migration into the framework (Chvapil ef al., 1969) and may be the reason for the fast permeation of fibroblasts, macrophages, polymorphonuclears and capillaries on bum wounds dressed with collagen sponge. The degree of adhesion of collagen sponge is important for cellular permeation also. This adhesion appeared to reduce local infection with subsequently increased take of the grafts, as observed in bum wounds dressed withcollagen sponge. Heterologous collagen matrix sponge also allowed ingrowth of endothelial cells and fibroblasts, providing a highly vascularised connective tissue. The rate of
wound preparation in burn wounds treated with collagen sponge was significantly shorter than for those dressed with cotton cloth. Bum wounds with restored circulatory function appear to provide a wound apparently free from infection (Wolf et al., 1980). This may be due to the presence of large numbers of polymorphonuclears and macrophages. In the present study circulatory function was achieved earlier in bum wounds dressed with collagen sponge. The results of this study suggest some advantages to heterologous collagen matrix sponge in preparing third-degree bum wounds for autologous skin grafting, in comparison with cotton mesh dressing. Acknowledgement We are grateful for the statistical assistance and useful suggestions of Yara Juliano and Neil F. Novo, from the Division of Biostatistics at Escola Paulista de Medicina.
British Journal of Plastic Surgery
120
Fig. 3 Figure >(A) Bum wound (group III) at injury day. (B) Arrow indicates the site of the biopsy after second escharectomy (time 0 of the observation). (C) Bum wound dressed with heterologous collagen matrix sponge. (D, E) Biopsies taken at time 3 and time 6 when autologous skin graft was performed. (F) at 90 days post autograft.
Heterologous
Matrix Sponge : Response
Collagen
in Third-Degree
121
Burns
FIB
DBLASTS
125 124
-.
,.”
117 107
/
96
l
//
75 74
COHAGLGII --__COTTON CLOTH
BIOPSIES 9
3
0
9
3
0’
0
/ ,’
65
0
0
----
COLLAGh COTTON
CLOTH
Fig. 5
Fig. 4
‘OLYMORPHOS .
OPHAGES
-w . \
II
Ii ----
.R’
3
6
-2. .
B IOPS IES Y
CGlLAGEW GGTTON CLOTH Fig. 6
Figsue &Capillaries (average number) in bum wounds at each time of observation for the three groups. Figure S-Fibroblasts number) in bum wounds at each time of observation for the three groups. FIgme bMacrophages and polymorphonuclears number) at each time of observation for the three groups.
References Abramo, A.C. (1990). Tese apresentada ao curso de Ws-Graduacb da Es&a Paulista de Medicina, area de concentracb em Cirurgia Plbtica Reparadora, para obtencgo do titulo de Doutor. AlsI@-t~, B. (1984). In search of a skin substitute. Scandinavian Journal of Plastic Surgery, 18, 121. J%artlett, R. H. (1981). Skin substitutes. Journalof Trauma, 21,731.
Chvnpll, M., HoIusa, R., KIlnsent, K. and StoII, M. (1969). Some clinical and biological characteristics of a new collagen-polymer
(average (average
compound material. Journal of Biomedical Materials Research, 3, 315.
ChvapII, M., ~nthaI, R. L. and Van WinkIe, W. (1973). Medical and surgical applications of collagen. In Hall, D. A. and Jackson, D. S. (Eds). International Review of Connective Tissue Research. Vo16. London, Academic Press, p. 1. Hut, A., Herbage, D. and Ronvienx, R. (198 1). Le collagen ; structure, extraction et proprietes cicatrizantes et antihemorragiques. Revue del’A.D.P.H.S.O., 1,53.
122 Norton, L. and Chvapil, M. (1981). Comparison of newer synthetic and biological wound dressings. Journalof Trauma, 21,463. Tavis, M. J., Thornton, J. W., Hamey, J. H., Woodroof, E. A. and Bartlett, R. H. (1976). Graft adherence to de-epithelialized surfaces. Annals of Surgery, 184,594. Tavis, M. J., Thornton, J., Danet, R. and Bartlett, R. (1978). Current status of skin substitutes. Surgical Clinics of North America, 58, 1233.
Wolf, D. L., Capozzi, A. and Pemisi, V. R. (1980). Evaluation of biological dressings. Annals of Plastic Surgery, 5, 186.
British Journal of Plastic Sureerv
The Authors A. C. Abramo, MD, Staff Member J. C. Viola, MD, Staff Member Division of Plastic and Reconstructive Surgery, General Hospital of BeneficCncia Portuguesa, Sb Paulo, Brazil. Requests for reprints to Dr A. C. Abramo. Paper received 1 November 1990. Accepted 3 September 1991 after revision.
Heterologous collagen matrix sponge: histologic and clinical response to its implantation in third-degree bum injuries A. C. Abram0 and J.C. Viola Division of Plastic and Reconstructive
Surgery, General Hospital of Benejichcia
Portuguesa, Silo Paulo, Brazil
SUMMARY. Heterologous collagen matrix sponge has been used to prepare third-degree burn wounds for autologous skin graft. The porosity and the multiple connections among the interstices of the sponge enable ready ingrowth of endothelial and inflammatory cells. Heterologous collagen matrix sponge also increased the rate of formation of granulation tissue in bum wounds.
saline and loose skin removed. The bum wound was covered with moist white cotton cloth and a conventional dry absorptive dressing was applied. At day 3 postbum the burn necrotic tissue was excised and dressed as aforementioned. At day 6 postbum the remaining bum necrosis was excised and the bum wound was biopsied. At this time both heterologous collagen matrix sponge and white cotton cloth were placed symmetrically, one on each side of the same patient in each group. Biopsies were taken at the time of every dressing change with intervals of 3 days, each one constituting an individual time of observation, until wound granulation tissue appeared clinically, indicating the wound was ready for autologous skin grafting. Heterologous collagen matrix sponge was compared with white cotton cloth, employed as a control, in its effect to stimulate capillaries, fibroblasts, macrophages and polymorphonuclears on bum wounds. Histological count was made by Weibel’s method, employing a KlOX Zeiss oculon Integrationplatte I, having 25 points arranged in five symmetrical lines, each one with five geometrically allocated points. A 40X Zeiss objective was employed for capillaries and for fibroblasts, macrophages and polymorphonuclears a 100X Zeiss objective was used. It was analysed forty fields per lamina by means of the horizontal reading. At the same time, macroscopic evaluation of the bum wounds with both materials was performed by measuring the time in days until the wound granulation tissue was suitable to receive autologous skin graft.
To cover surfaces where skin is lost, skin substitutes can be employed (Tavis et al., 1978) as temporary dressings to be placed on the wound and left until healed, or as a semipermanent dressing, remaining attached to the wound or changed at regular intervals to prepare it for grafting (Bartlett, 1981). Comparative studies of several skin substitutes revealed that collagen is more suitable than other materials (Norton and Chvapil, 1981). Adherence is the most important of these properties. Porosity of the material has great relevance in the mechanism of adhesion. The adhesion of collagen is equivalent to that presented by normal skin (Tavis et al., 1976; Alsbjom, 1984). Collagen has been prepared in several physical forms, but sponges are more efficient dressings than others in third-degree burn wounds (Chvapil et al., 1973). This paper reports histologic and clinical behaviour of heterologous collagen matrix sponge (HCMS) as a semipermanent biological dressings in third-degree burn wounds (Abramo, 1990) and its comparison with standard white cotton cloth (WCC) dressings.
Materials and methods Heterologous collagen matrix sponge used in this particular study is polymerised native collagen or type I collagen in the form of a sponge, prepared from deer’s skin (Hut et al., 1981). The pore size of the sponge varies from 80 to 1500 u in diameter with an average size of 500 u. The thickness of the sponge is 1.5 mm and the surface is 23 x 28 cm. The collagen sponge was sterilised in a dry state using ethylene oxide. White cotton cloth is employed in the form of a mesh cloth. The mesh aperture varies from 0.4 to 0.5 mm with 0.5 mm thick cloth measuring 10 x 20 cm. The white cotton cloth was sterilised by autoclaving. Third-degree thermal bum injuries were separated into three groups for observation. Group I were injuries of the upper limbs, group II injuries of the lower limbs and group III injuries of the thoracic wall. On the injury day the bum surfaces were cleaned with
Results The study was performed on 16 patients with thermal injury. Only corporal surfaces with third-degree bum injuries were analysed. Twenty bum wounds were observed in each group. Table 1 summarises indications and outcomes. After time 0, biopsies were taken at intervals of 3 days on bum wounds with both collagen sponge and cotton cloth (Table 2). 117
118
British Journal of Plastic Surgery
Table 1 Autologous skin graJt** Gp II
GPI Age/sex
44/M 9lW 32/M 34/w 36/M 11/M 29/M 27/M 34/w 37/M 26/M 25/M 8/W 12/w 36/W 42/M
R
%’
16 19 31 25 41 20 39 13 46 16 25 30 32 14 19 14
-
Materials
L
R
-
9
15
6
9 9 18
21 18 9
6 18 9 6 15
15 6 24 15 27
6
18
12 9 18 15 6 9 12 6 18
Gp III L
R
18
-
27 21 9 6 9 21 24 18 9
6 21 9 9 15 9 6 21 9 9 -
Gp II
GPI L 18 9 21 21 24 6 12 9 18 24 -
R
L
-
-
Gp III
R HCMS
WCC
HCMS -
HCMS HCMS WCC
WCC WCC HCMS -
HCMS WCC HCMS HCMS HCMS
WCC HCMS WCC WCC WCC -
HCMS
WCC -
L
R
L
WCC -
-
-
HCMS WCC HCMS HCMS HCMS WCC -
WCC HCMS WCC WCC WCC HCMS -
HCMS WCC
WCC HCMS -
HCMS
WCC -
HCMS
WCC -
WCC
HCMS HCMS
WCC
WCC WCC HCMS
HCMS HCMS WCC
HCMS -
WCC -
HCMS HCMS
WCC WCC
WCC
HCMS
(*) third-degree burn surface area (**) days for autologous skin graft after time 0 WCC: White cotton cloth HCMS : heterologous collagen matrix sponge
Table 2
Average of biopsies taken at intervals of 3 days Group I
Number
of biopsies
Group II
HCMS
WCC
HCMS
WCC
HCMS
WCC
2, 7
6, 3
299
672
299
6, 3
Histologic findings The data presented in Figures 4,5 and 6 were obtained
from the biopsies at each time of the observation from time 0 until transplantation of autologous skin graft. Statistical tests such as Wilcoxon’s test, Friedman’s variance analysis and multiple comparisons test were applied. Figures 4 and 5 show an increase of capillaries and fibroblasts from time 0 with both materials. However, the amount of capillaries (pCO.01) and fibroblasts (p < 0.05) was significantly higher in burn wounds dressed with the collagen sponge (Fig. 1). After time 6, decrease of fibroblasts was observed, but only with burn wounds dressed with collagen sponge. Figure 6 shows that macrophages and polymorphonuclears were equal with either collagen sponge or cotton cloth. At time 3, the amount of macrophages and polymorphonuclears was more than time 0 with both materials, but significantly higher (p ~0.05) in Table 3 Effect of the materials grafting. *
Macroscopic observations
Dressings were soaked with saline for relatively atraumatic removal from the wound at the time of every dressing. Granulation tissue was judged ready to receive autologous skin grafts when the wounds presented a red colour and moderate bleeding at every dressing change. Burn wounds dressed with collagen sponge received autologous skin grafts at a mean of 8.4 days, while those dressed with cotton cloth were autografted at a mean of 18.7 days. The time to autologous skin grafting was significantly shorter (p < 0.05) in burn wounds dressed with the collagen sponge.
Group II
tissue for
Group III
HCMS
WCC
HCMS
WCC
HCMS
WCC
8,l
18,9
8,7
18,9
894
18,3
(P
burn wounds dressed with collagen sponge (Fig. 2). At time 6, macrophages and polymorphonuclears were lower in burn wounds dressed with collagen sponge.
in days average to prepare granulation
Group I
Mean days to grafting after time 0
Group III
were in each group.
(PCO.05)
(PCO.05)
Heterologous
Collagen
Matrix Sponge : Response
in Third-Degree
Burns
119
Fig. 1
Fig. 2 Figure l-Extensive capillary ingrowth in bum wounds for both materials, with significant preponderance of it in bum wound dressed with heterologous collagen matrix sponge (B). Fipre 2-Macrophages and polymorphonuclears are higher in bum wounds dressed with heterologous collagen matrix sponge (B).
Discussion The structure of the collagen sponge framework is a decisive factor for rapid tissue permeation. The porosity of around 80 u and larger, and the multiple connections in the interstices of the sponge, are important to allow cell migration into the framework (Chvapil ef al., 1969) and may be the reason for the fast permeation of fibroblasts, macrophages, polymorphonuclears and capillaries on bum wounds dressed with collagen sponge. The degree of adhesion of collagen sponge is important for cellular permeation also. This adhesion appeared to reduce local infection with subsequently increased take of the grafts, as observed in bum wounds dressed withcollagen sponge. Heterologous collagen matrix sponge also allowed ingrowth of endothelial cells and fibroblasts, providing a highly vascularised connective tissue. The rate of
wound preparation in burn wounds treated with collagen sponge was significantly shorter than for those dressed with cotton cloth. Bum wounds with restored circulatory function appear to provide a wound apparently free from infection (Wolf et al., 1980). This may be due to the presence of large numbers of polymorphonuclears and macrophages. In the present study circulatory function was achieved earlier in bum wounds dressed with collagen sponge. The results of this study suggest some advantages to heterologous collagen matrix sponge in preparing third-degree bum wounds for autologous skin grafting, in comparison with cotton mesh dressing. Acknowledgement We are grateful for the statistical assistance and useful suggestions of Yara Juliano and Neil F. Novo, from the Division of Biostatistics at Escola Paulista de Medicina.
British Journal of Plastic Surgery
120
Fig. 3 Figure >(A) Bum wound (group III) at injury day. (B) Arrow indicates the site of the biopsy after second escharectomy (time 0 of the observation). (C) Bum wound dressed with heterologous collagen matrix sponge. (D, E) Biopsies taken at time 3 and time 6 when autologous skin graft was performed. (F) at 90 days post autograft.
Heterologous
Matrix Sponge : Response
Collagen
in Third-Degree
121
Burns
FIB
DBLASTS
125 124
-.
,.”
117 107
/
96
l
//
75 74
COHAGLGII --__COTTON CLOTH
BIOPSIES 9
3
0
9
3
0’
0
/ ,’
65
0
0
----
COLLAGh COTTON
CLOTH
Fig. 5
Fig. 4
‘OLYMORPHOS .
OPHAGES
-w . \
II
Ii ----
.R’
3
6
-2. .
B IOPS IES Y
CGlLAGEW GGTTON CLOTH Fig. 6
Figsue &Capillaries (average number) in bum wounds at each time of observation for the three groups. Figure S-Fibroblasts number) in bum wounds at each time of observation for the three groups. FIgme bMacrophages and polymorphonuclears number) at each time of observation for the three groups.
References Abramo, A.C. (1990). Tese apresentada ao curso de Ws-Graduacb da Es&a Paulista de Medicina, area de concentracb em Cirurgia Plbtica Reparadora, para obtencgo do titulo de Doutor. AlsI@-t~, B. (1984). In search of a skin substitute. Scandinavian Journal of Plastic Surgery, 18, 121. J%artlett, R. H. (1981). Skin substitutes. Journalof Trauma, 21,731.
Chvnpll, M., HoIusa, R., KIlnsent, K. and StoII, M. (1969). Some clinical and biological characteristics of a new collagen-polymer
(average (average
compound material. Journal of Biomedical Materials Research, 3, 315.
ChvapII, M., ~nthaI, R. L. and Van WinkIe, W. (1973). Medical and surgical applications of collagen. In Hall, D. A. and Jackson, D. S. (Eds). International Review of Connective Tissue Research. Vo16. London, Academic Press, p. 1. Hut, A., Herbage, D. and Ronvienx, R. (198 1). Le collagen ; structure, extraction et proprietes cicatrizantes et antihemorragiques. Revue del’A.D.P.H.S.O., 1,53.
122 Norton, L. and Chvapil, M. (1981). Comparison of newer synthetic and biological wound dressings. Journalof Trauma, 21,463. Tavis, M. J., Thornton, J. W., Hamey, J. H., Woodroof, E. A. and Bartlett, R. H. (1976). Graft adherence to de-epithelialized surfaces. Annals of Surgery, 184,594. Tavis, M. J., Thornton, J., Danet, R. and Bartlett, R. (1978). Current status of skin substitutes. Surgical Clinics of North America, 58, 1233.
Wolf, D. L., Capozzi, A. and Pemisi, V. R. (1980). Evaluation of biological dressings. Annals of Plastic Surgery, 5, 186.
British Journal of Plastic Sureerv
The Authors A. C. Abramo, MD, Staff Member J. C. Viola, MD, Staff Member Division of Plastic and Reconstructive Surgery, General Hospital of BeneficCncia Portuguesa, Sb Paulo, Brazil. Requests for reprints to Dr A. C. Abramo. Paper received 1 November 1990. Accepted 3 September 1991 after revision.