~
A new rat model of free muscle flap transfer is presented. Microvascular transplantation of the cutaneous maximus muscle flap is performed at the groin site, with anastomosis of the axillary vessels to the appropriate femoral vessels. This muscle flap has many useful attributes for experimental manipulation. It has a high success rate following transplantation, the anatomy is consistent, the dissection is straightforward, the length of pedicle is relatively long (10 mm), the vessels for repair are of sufficient size (1.0-1.35 mm diameter), and the microsurgical procedure can be performed in a relatively short period. The donor site deficit causes minimal impairment to animal mobility, and no evidence of limb ischemia is noted after ligation of the axillary vessels. The cutaneous area adjacent to the muscle is perfused by muscular perforators supplied by the flap pedicle; thus a skin island may be used to monitor the flap or to create a composite myocutaneous transfer. The cutaneous maximus muscle has mixed muscle types and anatomic dimensions similar to those of the latissimus dorsi muscle, and it provides ample tissue for pharmacological and biochemical studies, yet it presents easier dissection and microanastomoses than the latissimus flap, with more potential for versatility in application. The advantages of this muscle flap make it a very useful experimental model for flap transfer research. o 1992Wdey-Liss, inc. MICROSURGERY 13206-213
1992
FREE FLAP TRANSFER OF THE CUTANEOUS MAXIMUS MUSCLE IN THE RAT: COMPARISON TO THE LATISSIMUS DORSI MUSCLE FLAP XIAOLU LI, M.D., BRIAN C. COOLEY, SUZANN M. GRUEL, ZHONG YE, M.D., and JOHN S. GOULD, M.D.
Successful experimental transfer of the free muscle flap widens and thins into an aponeurosis as it approaches the using microsurgical techniques was first reported by Tamai linea alba.’ Its peculiar fan-like appearance arises from et al.’ Since then, several free muscle transfer models have nerves radiating throughout the whole muscle region, and been identified and developed in the rat, such as the rectus movement of the skin of the trunk is its main function. abdominis,2 the latissimus dorsi and serratus a n t e r i ~ r , ~ - ~ and the gracilis.6-7 These experimental flaps were based MATERIAL AND METHODS Male Sprague-Dawley rats weighing 250-300 g were anatomically on muscle flaps that were developed cliniused throughout the study. The NIH guidelines for the care cally. The present study was designed to investigate the and use of laboratory animals were followed throughout. usefulness of the rat cutaneous maximus (CM) muscle, as Each rat received intraperitoneal pentobarbital for anestheeither a muscle or a myocutaneous flap. sia (50 mg/kg body weight), with supplemental doses given The rat cutaneous maximus muscle,* also referred to as as necessary. the cutaneous trunci muscle,’ is a thin sheet-like muscle Initially, two rats were used to study the anatomy of the covering the lateral thoracic and abdominal wall from the CM muscle, skin, and vasculature. Following anesthetic shoulder to the root of the tail (Fig. 1). The muscle is overdose, blue latex was injected through the aorta to the thickest at its dorsal origin near the axilla and gradually flap vasculature, and flaps were dissected bilaterally. Two additional rats were used to gain familiarity with the CM muscle, eight rats were used for transplantation of the CM, From the Department of Orthopaedic Surgery (X.L., B.C.C., S.M.G., J.S.G.) and another eight rats were used for the transplantation of and Division of Plastic and Reconstructive Surgery (Z.Y.), Medical College of the latissimus dorsi (LD) muscle, as previously de~cribed.~ Wisconsin, Milwaukee, WI. Another four rats were used for transfer of the CM muscle This paper was presented at the 8th Annual Meeting of the Society of Microtogether with a skin paddle as a myocutaneous flap. surgical Specialists, Milwaukee, WI, September 14, 1991. Address reprint requests to Brian C. Cooley, at the Department of Orthopaedic Surgery, Medical College of Wkconsin, 8700 W. Wisconsin Avenue, Milwaukee, WI 53226. Received for publication October 30, 1991. 0 1992 Wiley-Liss, Inc.
CM Muscle Transfer
After placing the rat on its dorsal surface and securing the front limbs in an outstretched position, a midlateral
Cutaneous Maximus Muscle Flap
a
b
-
spinotrapez ius
'T' aeriatus
anterior
utaneous maxlmus
C Figure 1. Position of the cutaneous maximus muscle in the rat. a: lateral view. b: Dorsal view. c: Lateral view relative to nearby supetficial muscles.
209
210
Li et al.
as well as the pedicle length and vessel diameters at the level of their transection. Each CM flap was transplanted to the right groin of the animal from which it was harvested. The femoral vessels served as the recipient vessels. All microvascular anastomoses were performed end-to-end using 10-0 nylon suture. Upon completion of both anastomoses, blood flow was reestablished and patency was assessed. A gas-permeable silicone membrane was fashioned into a pocket and placed around the muscle flap to prevent local diffusion of nutrients from the recipient bed. lo Heparinized saline (20 units/ ml) was used as the irrigating solution, and topical lidocaine (2%) was used to relieve vasospasm. The groin wound was closed, covering the silicone pocket. The animals were resuscitated and were returned to animal housing. LD Muscle Transfer As described by de la Pena et al.,4 harvesting the LD flap was achieved by elevating the LD and skeletonizing the thoracodorsal pedicle to the axillary vessels, ligating the pedicle, dividing the nerve and removing the flap. The same measurements as for the CM were taken at the time of transfer. Microvascular anastomosis to the inferior epigastric vessels was performed end-to-end using 11-0 nylon suture. A gas-permeable silicone membrane was also used to isolate the muscle. The groin wound was closed. The animals were allowed to recover and were returned to animal housing. Three CM and three LD flaps were harvested and autografted to the left groin site, with neither revascularization nor silicone pockets, to serve as avascular controls. CM Myocutaneous Flap Transfer Figure 2. Operative position and skin incision for isolation of the cutaneous maximum muscle.
thoracic skin incision (Fig. 2) was made to the operative side. The pectoralis major and minor muscle were transected, beginning just caudal to the appearance of the external jugular vein and continuing through the muscles (Fig. 3), exposing the axillary vasculature and cutaneous muscles. The connective tissue was separated between the chest wall and the CM muscle, retracting and securing the CM laterally (Fig. 4). The LD was dissected away from the CM. Fatty tissue on the CM was dissected away as much as possible. The axillary vasculature was skeletonized; the vessels supplying the LD and forelimb were ligated, isolating all flow to the CM. The muscle was then elevated following ligation of the vessels proximally. The nerves were severed, and the CM was removed (Fig. 5). The pectoralis major and minor were reunited and the donor site was closed with 5-0 nylon suture. At the time of transfer, measurements were taken of the dimensions of each muscle
An oval skin island (2 X 1.5 cm) was outlined just under the right axilla. An S-shaped incision was made from a midlateral thoracic point through the axilla to the skin island (Fig. 6). The skin surrounding the island was dissected from the CM muscle. The pectoralis major and minor were again cut in the middle. The composite flap was elevated and transferred similar to the CM. Following anastomosis to the femoral vessels, the wound was closed by suturing the skin island to the groin skin; the muscle portion was not placed in a silicone pocket. Postoperative Evaluation
After a reperfusion period of either 3 or 14 days, each rat underwent walking-track analysis to assess possible disability to forelimb function. The color of the skin in the operated limb was compared to that of the contralateral limb. Each rat was then reanesthetized, and the free muscle or myocutaneous flap was examined under the operating microscope to assess gross viability and vessel patency. Each flap was then carefully dissected free, removed from the recipient, and extracted from the silicone pocket. The
Cutaneous Maximus Muscle Flap
211
I
Figure 3. Level for transection of the pectoralis minor and major muscles.
animals were then killed by intracardiac pentobarbital overdose injection. Each harvested muscle was split in half lengthwise, along the axis from the proximal location of the pedicle to the distal extreme. One-half was immediately fixed in 10% buffered formalin and subsequently processed for histologic evaluation with standard hematoxylin and eosin (H & E) staining. The remaining one-half of each muscle was briefly washed with saline. Four biopsies (-10 pg each) were excised from the central aspect of the longitudinally cut surface, taken from four equidistant points. Each biopsy was subjected to quantitative histochemical analysis; it was immediately placed into a test tube containing 0.2% nitroblue tetrazolium chloride (NBT) in 0.1 M phosphate buffer, pH 7.4, with subsequent observation at X 16 until the first appearance of blue stain in the muscle was noted. l 1 Nonoperated specimens from the contralateral CM and LD were used for normal control muscle.
Figure 4. Axillaty vasculature (at?eries) relative to the cutaneous maximus (CM) and latissimus dorsi (LD) muscles aRer transection of the pectoralis minor (PMI) and pectoralis major (PMA) muscles, and separation from the chest wall. ct, Cervical trunk; sc,subclavian; a, axillaty; b, brachial; It, lateral thoracic; ss, subscapular; td, thoracodorsal. Correspondingveins are omitted for clarity; thejugular vein corresponds to the cervical trunk.
are found arising from the LT, unlike the thoracodorsal vessels, which have many branches. The LD muscle receives one such branch, while the distal thoracodorsal vessels supply the spinotrapezius, skin, and multilocular adipose tissue. Motor innervation to the CM is supplied by the medial anterior thoracic nerve and may be harvested with the muscle. The CM muscle originates at the lesser tubercle of the humerus and the surface of the pectoralis, then radiates posteriorly over the dorsal, lateral, and ventral surface of trunk. Skin movement (twitching) is its main function. Perfusion of the overlying cutaneous region arises solely from muscle perforators, allowing the flap to be modified easily into a myocutaneous flap. RESULTS Anatomical data collected from CM and LD flaps are All 20 rats survived dissection and flap transfer. The shown for comparison in Table 1. The CM flaps had diaverage times per transplant procedure were 1.2 hrs for the mensions and muscle weights similar to those of the LD free muscle and 1.45 hrs for the myocutaneous flap. The flaps but provided longer vascular pedicles and larger vessel diameters, which offered technically simpler microvascular ischemic times for all flaps were under 60 mins. The lateral thoracic (LT) artery and accompanying vein transfers. All of the CM muscle and myocutaneous flaps, and supply axial circulation to the CM.' The LT vessels originate from the rat axillary vessels and are located superficial seven of eight LD flaps were viable with patent pedicle to the thoracodorsal vessels. In general, no small branches vessels when inspected at 3 days or 2 weeks postopera-
212
Li et al.
Figure 5. Cutaneous maximus free muscle flap immediately following harvest. Ruler in centimeters.
Table 1. Comparison of Anatomic Parameters: Cutaneous
Maximus vs. Latissimus Dorsi. Cutaneous maximus (n = 8 )
Weight range (9) Dimensions (cm) Pedicle length (mm) (mean) Diameter of artery (mm) (mean) Diameter of vein (rnm)
0.75-1.05 3.0 x 2.0 10 1 1.2-1.5
Lattissimus dorsi (n = 8) 0.83-1.01 2.0 X 1.5 9 0.5 0.6-0.7
tively. One LD flap at 3 days was completely - inspected necrotic; the epigastric vessels were observed to have-severe vasospasm, with thrombus filling the vessel lumen proximally, but both anastomoses remained patent. The NBT staining time in all viable flaps was under 2 min, comparable to that for normal nonischemic muscle. l 1 All CM and LD muscles transferred without anastomosis resulted in complete necrosis; the NBT time was greater than 10 min in all cases. Histologic evaluation of all viable muscle flaps revealed normal muscle fibers, with minimal cellular infiltration due to the transplantation procedure. No evidence of limping or other motor deficits was seen with walking-track analysis, even after resection of both the CM and LD muscles. No complications related to limb ischemia were noted in the affected upper extremity following ligation of the axillary vessels.
\ I
Figure 6. Skin incision for isolation of the cutaneous maximus myocutaneous flap.
stant. The histochemical evaluation offers a quantitative marker for muscle viability,” since the CM muscle has a significant composition from type I muscle fibers.I3 The CM muscle provides tissue mass (as does the LD muscle) sufficient to perform enzymatic and other biochemical assays on a single flap. The CM flap, however, presents an easier, straightforward dissection and shorter overall time for the procedure. Since perfusion of the overlying cutaneous portion arises from CM muscle perforators, a myocutaneous flap is readily created using the same basic model. Based on these findings, we believe that microvascular transfer of the CM muscle presents an easier, faster, and DISCUSSION more versatile model than the LD flap. In reviewing the literature, we found that the CM musThis study demonstrates that microvascular transplantation of the CM muscle in rats can be reliably performed. All cle was mentioned by Tilgner et aL3 in their report of the rat flaps were found to be viable 3 days and 2 weeks after LD myocutaneous flap. However, their flap included two transplantation, with patent pedicles and well-perfused muscles, the LD and CM muscles. From our study and muscle and skin. The anatomy of these flaps is fairly con- investigation of the rat anatomy,* the LD muscle is sepa-
Cutaneous Maximus Muscle Flap
rated from the skin by the CM muscle and cannot be used alone for creating a myocutaneous flap. The muscle perforators to the cutaneous area arise from the CM muscle, therefore, the dependence of this myocutaneous flap on the CM leads us to call this model a cutaneous maximus myocutaneous flap. The LD muscle is not required for a successful transfer in this model. REFERENCES 1. Tamai S , Komatsu S , Sakamoto H, Sano S , Sasauchi N, Hori Y,
Tatsumi Y, Okuda H: Free muscle transplants in dogs with microsurgical neurovascular anastomoses. Plasr Reconstr Surg 46:219-225, 1970. 2. Tilgner A, Hemberger U Myokutane lappenmodelle an der ratte: Anatomie, histologie und praparations tecknik des myokutanen rectus abdominis-lappens. Z Versuchstierkd 29:231-237, 1987. 3. Tilgner A, Herrberger U, Oswald P Myocutanwus flap models in the rat: Anatomy, histology and operative technique of the latissimus dorsi myocutaneous flap. Z Versuchstierkd 31:225-232, 1988. 4. de la Pena JA, Lineaweaver W, Buncke HJ: Microvascular transfer of
5.
6. 7. 8. 9. 10. 11.
12. 13.
213
latissimus dorsi and serratus anterior muscles in rats. Microsurgery 918-20, 1988. Briones R, Lineaweaver W, Newlin L, Whitney TM, Buncke HJ: Single pedicle microvascular transfers of the serratus anterior and latissimus dorsi muscle in rats. Microsurgery 10:269-273, 1989. Dautel G, Braga da Silva J, Merle M:Pedicle or free flap transfer of gracilis muscle in rats. J Reconstr Microsurg 7:23-25, 1991. Yim KK, Lineaweaver WC, Siko PP, Buncke HJ: Microvascular transfer of anterior and posterior gracilis muscles in rats. Microsurgery 12:262-267, 1991. Greene EC: Anatomy of the Rat. New York, (The American Philosophical Society) Hafner Publishing Company, 1963. Hebel R, Stromberg MW: Anatomy of the Laboratory Rut. Baltimore, Williams and Wilkins Co., 1976. Nishikawa H, Manek S, Green CJ: The oblique rat groin flap. Br J Plust Surg 44:295-298, 1991. Chachques JC, Fabiani JN,Perier P, Swanson J, Dreyfus G, Carpentier A: Reversibility of muscular ischemia: A histochemical quantification by NBT test. Angiology 36:493-498, 1985. Seidler E New nitroblue tetrazoliurn salt and their use in histochemistry. Histochem J 12:619-630, 1980. Wheater PR, Burkitt HG, Daniel VG: Functional Histology: A Text and Colour Atlas, ed II New York, Churchill Livingstone, 1987, p 87.
A new rat model of free muscle flap transfer is presented. Microvascular transplantation of the cutaneous maximus muscle flap is performed at the groin site, with anastomosis of the axillary vessels to the appropriate femoral vessels. This muscle flap has many useful attributes for experimental manipulation. It has a high success rate following transplantation, the anatomy is consistent, the dissection is straightforward, the length of pedicle is relatively long (10 mm), the vessels for repair are of sufficient size (1.0-1.35 mm diameter), and the microsurgical procedure can be performed in a relatively short period. The donor site deficit causes minimal impairment to animal mobility, and no evidence of limb ischemia is noted after ligation of the axillary vessels. The cutaneous area adjacent to the muscle is perfused by muscular perforators supplied by the flap pedicle; thus a skin island may be used to monitor the flap or to create a composite myocutaneous transfer. The cutaneous maximus muscle has mixed muscle types and anatomic dimensions similar to those of the latissimus dorsi muscle, and it provides ample tissue for pharmacological and biochemical studies, yet it presents easier dissection and microanastomoses than the latissimus flap, with more potential for versatility in application. The advantages of this muscle flap make it a very useful experimental model for flap transfer research. o 1992Wdey-Liss, inc. MICROSURGERY 13206-213
1992
FREE FLAP TRANSFER OF THE CUTANEOUS MAXIMUS MUSCLE IN THE RAT: COMPARISON TO THE LATISSIMUS DORSI MUSCLE FLAP XIAOLU LI, M.D., BRIAN C. COOLEY, SUZANN M. GRUEL, ZHONG YE, M.D., and JOHN S. GOULD, M.D.
Successful experimental transfer of the free muscle flap widens and thins into an aponeurosis as it approaches the using microsurgical techniques was first reported by Tamai linea alba.’ Its peculiar fan-like appearance arises from et al.’ Since then, several free muscle transfer models have nerves radiating throughout the whole muscle region, and been identified and developed in the rat, such as the rectus movement of the skin of the trunk is its main function. abdominis,2 the latissimus dorsi and serratus a n t e r i ~ r , ~ - ~ and the gracilis.6-7 These experimental flaps were based MATERIAL AND METHODS Male Sprague-Dawley rats weighing 250-300 g were anatomically on muscle flaps that were developed cliniused throughout the study. The NIH guidelines for the care cally. The present study was designed to investigate the and use of laboratory animals were followed throughout. usefulness of the rat cutaneous maximus (CM) muscle, as Each rat received intraperitoneal pentobarbital for anestheeither a muscle or a myocutaneous flap. sia (50 mg/kg body weight), with supplemental doses given The rat cutaneous maximus muscle,* also referred to as as necessary. the cutaneous trunci muscle,’ is a thin sheet-like muscle Initially, two rats were used to study the anatomy of the covering the lateral thoracic and abdominal wall from the CM muscle, skin, and vasculature. Following anesthetic shoulder to the root of the tail (Fig. 1). The muscle is overdose, blue latex was injected through the aorta to the thickest at its dorsal origin near the axilla and gradually flap vasculature, and flaps were dissected bilaterally. Two additional rats were used to gain familiarity with the CM muscle, eight rats were used for transplantation of the CM, From the Department of Orthopaedic Surgery (X.L., B.C.C., S.M.G., J.S.G.) and another eight rats were used for the transplantation of and Division of Plastic and Reconstructive Surgery (Z.Y.), Medical College of the latissimus dorsi (LD) muscle, as previously de~cribed.~ Wisconsin, Milwaukee, WI. Another four rats were used for transfer of the CM muscle This paper was presented at the 8th Annual Meeting of the Society of Microtogether with a skin paddle as a myocutaneous flap. surgical Specialists, Milwaukee, WI, September 14, 1991. Address reprint requests to Brian C. Cooley, at the Department of Orthopaedic Surgery, Medical College of Wkconsin, 8700 W. Wisconsin Avenue, Milwaukee, WI 53226. Received for publication October 30, 1991. 0 1992 Wiley-Liss, Inc.
CM Muscle Transfer
After placing the rat on its dorsal surface and securing the front limbs in an outstretched position, a midlateral
Cutaneous Maximus Muscle Flap
a
b
-
spinotrapez ius
'T' aeriatus
anterior
utaneous maxlmus
C Figure 1. Position of the cutaneous maximus muscle in the rat. a: lateral view. b: Dorsal view. c: Lateral view relative to nearby supetficial muscles.
209
210
Li et al.
as well as the pedicle length and vessel diameters at the level of their transection. Each CM flap was transplanted to the right groin of the animal from which it was harvested. The femoral vessels served as the recipient vessels. All microvascular anastomoses were performed end-to-end using 10-0 nylon suture. Upon completion of both anastomoses, blood flow was reestablished and patency was assessed. A gas-permeable silicone membrane was fashioned into a pocket and placed around the muscle flap to prevent local diffusion of nutrients from the recipient bed. lo Heparinized saline (20 units/ ml) was used as the irrigating solution, and topical lidocaine (2%) was used to relieve vasospasm. The groin wound was closed, covering the silicone pocket. The animals were resuscitated and were returned to animal housing. LD Muscle Transfer As described by de la Pena et al.,4 harvesting the LD flap was achieved by elevating the LD and skeletonizing the thoracodorsal pedicle to the axillary vessels, ligating the pedicle, dividing the nerve and removing the flap. The same measurements as for the CM were taken at the time of transfer. Microvascular anastomosis to the inferior epigastric vessels was performed end-to-end using 11-0 nylon suture. A gas-permeable silicone membrane was also used to isolate the muscle. The groin wound was closed. The animals were allowed to recover and were returned to animal housing. Three CM and three LD flaps were harvested and autografted to the left groin site, with neither revascularization nor silicone pockets, to serve as avascular controls. CM Myocutaneous Flap Transfer Figure 2. Operative position and skin incision for isolation of the cutaneous maximum muscle.
thoracic skin incision (Fig. 2) was made to the operative side. The pectoralis major and minor muscle were transected, beginning just caudal to the appearance of the external jugular vein and continuing through the muscles (Fig. 3), exposing the axillary vasculature and cutaneous muscles. The connective tissue was separated between the chest wall and the CM muscle, retracting and securing the CM laterally (Fig. 4). The LD was dissected away from the CM. Fatty tissue on the CM was dissected away as much as possible. The axillary vasculature was skeletonized; the vessels supplying the LD and forelimb were ligated, isolating all flow to the CM. The muscle was then elevated following ligation of the vessels proximally. The nerves were severed, and the CM was removed (Fig. 5). The pectoralis major and minor were reunited and the donor site was closed with 5-0 nylon suture. At the time of transfer, measurements were taken of the dimensions of each muscle
An oval skin island (2 X 1.5 cm) was outlined just under the right axilla. An S-shaped incision was made from a midlateral thoracic point through the axilla to the skin island (Fig. 6). The skin surrounding the island was dissected from the CM muscle. The pectoralis major and minor were again cut in the middle. The composite flap was elevated and transferred similar to the CM. Following anastomosis to the femoral vessels, the wound was closed by suturing the skin island to the groin skin; the muscle portion was not placed in a silicone pocket. Postoperative Evaluation
After a reperfusion period of either 3 or 14 days, each rat underwent walking-track analysis to assess possible disability to forelimb function. The color of the skin in the operated limb was compared to that of the contralateral limb. Each rat was then reanesthetized, and the free muscle or myocutaneous flap was examined under the operating microscope to assess gross viability and vessel patency. Each flap was then carefully dissected free, removed from the recipient, and extracted from the silicone pocket. The
Cutaneous Maximus Muscle Flap
211
I
Figure 3. Level for transection of the pectoralis minor and major muscles.
animals were then killed by intracardiac pentobarbital overdose injection. Each harvested muscle was split in half lengthwise, along the axis from the proximal location of the pedicle to the distal extreme. One-half was immediately fixed in 10% buffered formalin and subsequently processed for histologic evaluation with standard hematoxylin and eosin (H & E) staining. The remaining one-half of each muscle was briefly washed with saline. Four biopsies (-10 pg each) were excised from the central aspect of the longitudinally cut surface, taken from four equidistant points. Each biopsy was subjected to quantitative histochemical analysis; it was immediately placed into a test tube containing 0.2% nitroblue tetrazolium chloride (NBT) in 0.1 M phosphate buffer, pH 7.4, with subsequent observation at X 16 until the first appearance of blue stain in the muscle was noted. l 1 Nonoperated specimens from the contralateral CM and LD were used for normal control muscle.
Figure 4. Axillaty vasculature (at?eries) relative to the cutaneous maximus (CM) and latissimus dorsi (LD) muscles aRer transection of the pectoralis minor (PMI) and pectoralis major (PMA) muscles, and separation from the chest wall. ct, Cervical trunk; sc,subclavian; a, axillaty; b, brachial; It, lateral thoracic; ss, subscapular; td, thoracodorsal. Correspondingveins are omitted for clarity; thejugular vein corresponds to the cervical trunk.
are found arising from the LT, unlike the thoracodorsal vessels, which have many branches. The LD muscle receives one such branch, while the distal thoracodorsal vessels supply the spinotrapezius, skin, and multilocular adipose tissue. Motor innervation to the CM is supplied by the medial anterior thoracic nerve and may be harvested with the muscle. The CM muscle originates at the lesser tubercle of the humerus and the surface of the pectoralis, then radiates posteriorly over the dorsal, lateral, and ventral surface of trunk. Skin movement (twitching) is its main function. Perfusion of the overlying cutaneous region arises solely from muscle perforators, allowing the flap to be modified easily into a myocutaneous flap. RESULTS Anatomical data collected from CM and LD flaps are All 20 rats survived dissection and flap transfer. The shown for comparison in Table 1. The CM flaps had diaverage times per transplant procedure were 1.2 hrs for the mensions and muscle weights similar to those of the LD free muscle and 1.45 hrs for the myocutaneous flap. The flaps but provided longer vascular pedicles and larger vessel diameters, which offered technically simpler microvascular ischemic times for all flaps were under 60 mins. The lateral thoracic (LT) artery and accompanying vein transfers. All of the CM muscle and myocutaneous flaps, and supply axial circulation to the CM.' The LT vessels originate from the rat axillary vessels and are located superficial seven of eight LD flaps were viable with patent pedicle to the thoracodorsal vessels. In general, no small branches vessels when inspected at 3 days or 2 weeks postopera-
212
Li et al.
Figure 5. Cutaneous maximus free muscle flap immediately following harvest. Ruler in centimeters.
Table 1. Comparison of Anatomic Parameters: Cutaneous
Maximus vs. Latissimus Dorsi. Cutaneous maximus (n = 8 )
Weight range (9) Dimensions (cm) Pedicle length (mm) (mean) Diameter of artery (mm) (mean) Diameter of vein (rnm)
0.75-1.05 3.0 x 2.0 10 1 1.2-1.5
Lattissimus dorsi (n = 8) 0.83-1.01 2.0 X 1.5 9 0.5 0.6-0.7
tively. One LD flap at 3 days was completely - inspected necrotic; the epigastric vessels were observed to have-severe vasospasm, with thrombus filling the vessel lumen proximally, but both anastomoses remained patent. The NBT staining time in all viable flaps was under 2 min, comparable to that for normal nonischemic muscle. l 1 All CM and LD muscles transferred without anastomosis resulted in complete necrosis; the NBT time was greater than 10 min in all cases. Histologic evaluation of all viable muscle flaps revealed normal muscle fibers, with minimal cellular infiltration due to the transplantation procedure. No evidence of limping or other motor deficits was seen with walking-track analysis, even after resection of both the CM and LD muscles. No complications related to limb ischemia were noted in the affected upper extremity following ligation of the axillary vessels.
\ I
Figure 6. Skin incision for isolation of the cutaneous maximus myocutaneous flap.
stant. The histochemical evaluation offers a quantitative marker for muscle viability,” since the CM muscle has a significant composition from type I muscle fibers.I3 The CM muscle provides tissue mass (as does the LD muscle) sufficient to perform enzymatic and other biochemical assays on a single flap. The CM flap, however, presents an easier, straightforward dissection and shorter overall time for the procedure. Since perfusion of the overlying cutaneous portion arises from CM muscle perforators, a myocutaneous flap is readily created using the same basic model. Based on these findings, we believe that microvascular transfer of the CM muscle presents an easier, faster, and DISCUSSION more versatile model than the LD flap. In reviewing the literature, we found that the CM musThis study demonstrates that microvascular transplantation of the CM muscle in rats can be reliably performed. All cle was mentioned by Tilgner et aL3 in their report of the rat flaps were found to be viable 3 days and 2 weeks after LD myocutaneous flap. However, their flap included two transplantation, with patent pedicles and well-perfused muscles, the LD and CM muscles. From our study and muscle and skin. The anatomy of these flaps is fairly con- investigation of the rat anatomy,* the LD muscle is sepa-
Cutaneous Maximus Muscle Flap
rated from the skin by the CM muscle and cannot be used alone for creating a myocutaneous flap. The muscle perforators to the cutaneous area arise from the CM muscle, therefore, the dependence of this myocutaneous flap on the CM leads us to call this model a cutaneous maximus myocutaneous flap. The LD muscle is not required for a successful transfer in this model. REFERENCES 1. Tamai S , Komatsu S , Sakamoto H, Sano S , Sasauchi N, Hori Y,
Tatsumi Y, Okuda H: Free muscle transplants in dogs with microsurgical neurovascular anastomoses. Plasr Reconstr Surg 46:219-225, 1970. 2. Tilgner A, Hemberger U Myokutane lappenmodelle an der ratte: Anatomie, histologie und praparations tecknik des myokutanen rectus abdominis-lappens. Z Versuchstierkd 29:231-237, 1987. 3. Tilgner A, Herrberger U, Oswald P Myocutanwus flap models in the rat: Anatomy, histology and operative technique of the latissimus dorsi myocutaneous flap. Z Versuchstierkd 31:225-232, 1988. 4. de la Pena JA, Lineaweaver W, Buncke HJ: Microvascular transfer of
5.
6. 7. 8. 9. 10. 11.
12. 13.
213
latissimus dorsi and serratus anterior muscles in rats. Microsurgery 918-20, 1988. Briones R, Lineaweaver W, Newlin L, Whitney TM, Buncke HJ: Single pedicle microvascular transfers of the serratus anterior and latissimus dorsi muscle in rats. Microsurgery 10:269-273, 1989. Dautel G, Braga da Silva J, Merle M:Pedicle or free flap transfer of gracilis muscle in rats. J Reconstr Microsurg 7:23-25, 1991. Yim KK, Lineaweaver WC, Siko PP, Buncke HJ: Microvascular transfer of anterior and posterior gracilis muscles in rats. Microsurgery 12:262-267, 1991. Greene EC: Anatomy of the Rat. New York, (The American Philosophical Society) Hafner Publishing Company, 1963. Hebel R, Stromberg MW: Anatomy of the Laboratory Rut. Baltimore, Williams and Wilkins Co., 1976. Nishikawa H, Manek S, Green CJ: The oblique rat groin flap. Br J Plust Surg 44:295-298, 1991. Chachques JC, Fabiani JN,Perier P, Swanson J, Dreyfus G, Carpentier A: Reversibility of muscular ischemia: A histochemical quantification by NBT test. Angiology 36:493-498, 1985. Seidler E New nitroblue tetrazoliurn salt and their use in histochemistry. Histochem J 12:619-630, 1980. Wheater PR, Burkitt HG, Daniel VG: Functional Histology: A Text and Colour Atlas, ed II New York, Churchill Livingstone, 1987, p 87.
