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A pig model for investigation of muscle and myocutaneous flaps
Britbh Journal qf Plastic Surgery (1985) 3&X,364368 c~ 1985 The Trustees of British Association of Plastic Surgeons
A pig model for investigation of muscle and myocutaneous flaps P. G. MILLICAN
and M. D. POOLE
Department of Plastic Surgery, Radcliffe Infirmary, Oxford, and the University of Oxford
Summary.-An experimental model in the pig is described which readily enables studies to be made on musculocutaneous and muscle flaps. The model allows easy, reliable control over the pedicle blood supply at any time in the postoperative period.
together with teres major into the humerus. Trapezius abuts its cephalodorsal border, with the serratus ventralis muscle running deep to the cephalad portion of latissimus dorsi. The principal arterial supply is the thoracodorsal artery, which is a branch of the subscapular artery which comes off the subclavian artery. The common trunk bifurcates quite early. Two venae comitantes are present, as well as the adjacent thoracodorsal nerve. The neurovascular leash clings to the deep surface of the latissimus dorsi, bifurcating mid way along the muscle. The caudal part of the muscle is supplied by two perforators from the underlying intercostal vessels. A constant branch from the thoracodorsal vessel to teres major is present along the cephalic border of latissimus dorsi. The midpoint of a line drawn between olecranon and caudal apex of scapula, marks the position of the muscle at that level. Skin raised in association with latissimus dorsi must be raised caudal to this point, as the muscle passes deep to the long head of triceps more cephalad, to gain the humerus (Fig. 1). On its way to the humerus the latissimus dorsi curls on itself, the vascular leash coming in just caudal to the beginning of its tendinous change. There is no other vascular supply to the latissimus dorsi muscle at this proximal level. The pedicle is superficial to the fascial layer deep to latissimus dorsi and appears under the ventral border of teres major. Small branches may be given off to serratus fibres.
Together with increased understanding of the macroscopic anatomy of musculocutaneous flaps and definition of further vascular territories, has come a proliferation of studies of microcirculation. Animal studies have increasingly used the pig as a valid comparative animal to man because of the lack of contribution of the panniculus carnosus to the blood supply of the skin of the pig. (Milton 1967, 1972; Prather et al., 1979; Daniel, 1973, 1982; Young, 1982). The pig has been used extensively for investigation of skin flaps either axial or random in type (Patterson, 1968; Milton, 1972; Myers and Cherry, 1971). The omnipotential skin flap (Daniel, 1982) is unfortunately not a musculocutaneous flap. Free flaps have been used (Black et al., 1978) as well as musculocutaneous flaps to include the rectus abdominis, gracilis, intercostal or latissimus dorsi muscles. The purpose of this report is to describe a technique for using the latissimus dorsi flap (as a musculocutaneous island or muscle flap) on which the vascular pedicle may be ligated, clamped, or controlled proximally and at a distance from the flap and overlying skin. Thus, various parameters (blood flow., ~02, pH, temperature, skin expansion etc.) may be assessed without violation of the flank of the pig to gain access to the muscle pedicle. Anatomy
The anatomy of the latissimus dorsi in the pig is similar to man, except that the muscle takes origin only from the last four ribs but one, compared with the lower six thoracic vertebrae, lumbar fascia, and ilium in the human (Getty, 1975). If the origin from the ribs is divided, the latissimus dorsi can be totally isolated except for its tendinous insertion
Operative technique
The latissimus dorsi can be raised as an island musculocutaneous or muscle flap without necrosis, 364
A PIG MODEL FOR INVESTIGATION
OF MUSCLE AND ~YOCUTANEOUS
FLAPS
34.5
Caudal Apex of Scapula Trapetius
I
Abdominal
Lat. Dorsi
Oblique
Triceps Lateral Head Triceps
Long Head
Fig. 1 Figure I-Muscular
anatomy of
pig flank.
leaving it attached solely by its narrow tendinous insertion and vascular pedicle. Indeed quite a large area of skin beyond the limits of the muscle must be raised in order to cause skin necrosis. Method (I) Mark the mid-point of the line drawn between the olecranon and the caudal apex of the scapula. Mark a further point at the junction of the upper third and lower two-thirds of the spine of the pig. The line joining these two points marks the direction of the muscle midline. (2) Mark out the area of skin desired (Fig. 2). (3) Incise the cephalic border of the skin marking, through fat and panniculus down to muscle. The cephalic border of latissimus dorsi is found, mobilised and the adjacent teres major identified. The branch from the thoracodorsal artery to teres major should not be ligated until the flap is raised, and the parent vessel identified from below. (4) Incise the remaining borders of the flap down to muscle until the latissimus dorsi is outlined. The deep surface is easily mobilised by blunt dissection, though the two intercostal per-
forators and surrounding fascia may need sharp division (Fig. 3). (5) When the caudal origin is divided, the muscle and overlying skin are mobilised forward, and the thoracodorsal vessels seen. The small branches to teres (and serratus) are divided, and the muscle completely mobilised to its tendinous insertion (Fig. 4). (6) At this level a plane is dissected between the latissimus muscle and the neurovascular leash. A silastic catheter or infant feeding tube is passed between the two (Fig. 5). The two ends are passed through a small stab incision in the axilla and sutured together. Traction on the catheter will completely occlude the thoracodorsal vessels and circulation to the musculocutaneous flap. Upon release, blood flow will be restored. This can be verified (as well as the vascular isolation of the flap) with the intravenous injection of disulphine blue. Upon release, blood flow quickly returns as shown by return of dye (Figs. 6A-C), suggesting minimal spasm. The catheter ends are buried superficially under the stab incision and are easily retrieved at subsequent investigations.
366
BRITISH JOURNAL OF PLASTIC SURGERY
Fig. 2 Figure 2-Surface
points and rhomboid flap outlined. (Head of pig is to the left.)
Sixteen latissimus dorsi muscle or musculocutaneous island flaps were raised in 8 pigs using this method. Weekly traction on the silastic catheter over the next month, temporarily occluding circulation to the flap as shown by dye studies, failed to induce necrosis of the flaps. The nerve can be divided if necessary. Access is poor for resuturing the thoracodorsal vessels as a free flap, because the pedicle origin and muscle insertion is deep to the scapula. The latissimus dorsi musculocutaneous flap is quite easily dissected with minimal blood loss, and the anatomy is quite similar to that of the human. It is safe. Indeed, quite a large area of skin has to be raised for any cutaneous necrosis to occur. The operative site can be protected post-operatively by adapted garments. As the muscle is paired, a control is available. If necessary, axial skin flaps ^^- l__ __:_-A ^_ CL_ L..*C^^,._ A-,, ,,,..,,,..
Figure 3-Musculocutaneous Fig. 3
flap dissected free.
A PIG MODEL FOR INVESTIGATION OF MUSCLE AND MYOCUTANEOUS FLAPS
Fig. 4 Figure
&Flap
lifted anteriorly
to demonstrate
the blood
supply
on the deep surface.
Fig. 5 Figure 5--(A
and B) Silastic catheter
around
thoracodorsal
leash, proximal
to supplying
Lat. dorsi.
367
368
BRITISH JOURNAL OF PLASTIC SURGERY
Fig. 6 Figure 6-(A-C) Return of dye to temporarily occluded flap after release of catheter.
References Black, M. J., Chait, L., O’Brien, B., Sykes, P., Sharzo, L. (1978). How soon may the axial vessels of a surviving free flap be safely ligated: a study in pigs. British Journal of Plastic Surgery, 31, 295. Daniel, R. K. (1973). The free transfer of skin flaps by microvascular anastomoses. Plastic and Reconstructive Surgery, 52, 16. Daniel, R. K. (1982). The omnipotential pig buttock flap. Plastic and Reconstructive Surgery, IO, 11. Getty, R. (1975). The anatomy of the domestic animals. 5th
edition. Philadelphia. Saunders. Milton, S. H. (1967). The survival of experimental pedicled skin
flaps, Thesis, Kilner Library, Oxford. Milton, S. H. (1972). Experimental studies on island flaps. II. Ischaemia and delay. Plastic and Reconstructive Surgery, 49, 444. Myers, M. B., Cherry,
G. (1971). Differences in the delay phenomenon in the rabbit, rat, and pig. Plastic and Reconstructive Surgery, 41, 73. Patterson, T. J. S. (1968). The survival of skin flaps in the pig. British Journal of Plastic Surgery, 21, 113.
A., Blackburn, J., WilIIams, T., LYM, J. (1979). Evaluation of tests for predicting the viability of axial pattern skin flaps in the pig. Plastic and Reconstructive Surgery, 63,
Prather,
250.
Young, C. M. A. (1982). The revascularization of pedicle skin flaps in pigs: A functional and morphologic study. Plastic and Reconstructive Surgery, 70,455.
The Authors P. G. Milliean, FRCS, FRACS, Overseas Fellow, Department of Plastic Surgery, Radcliffe Infirmary, Oxford. M. D. Poole, FRCS, FRACS, Consultant, Department of Plastic Surgery, Radcliffe Infirmary, Oxford. Requests for reprints to: Mr M. D. Poole, Plastic Surgery Department, Radcliffe Infirmary, Oxford, OX2 6HE. This work was supported by a grant from the Medical Research Fund, University of Oxford.
A pig model for investigation of muscle and myocutaneous flaps P. G. MILLICAN
and M. D. POOLE
Department of Plastic Surgery, Radcliffe Infirmary, Oxford, and the University of Oxford
Summary.-An experimental model in the pig is described which readily enables studies to be made on musculocutaneous and muscle flaps. The model allows easy, reliable control over the pedicle blood supply at any time in the postoperative period.
together with teres major into the humerus. Trapezius abuts its cephalodorsal border, with the serratus ventralis muscle running deep to the cephalad portion of latissimus dorsi. The principal arterial supply is the thoracodorsal artery, which is a branch of the subscapular artery which comes off the subclavian artery. The common trunk bifurcates quite early. Two venae comitantes are present, as well as the adjacent thoracodorsal nerve. The neurovascular leash clings to the deep surface of the latissimus dorsi, bifurcating mid way along the muscle. The caudal part of the muscle is supplied by two perforators from the underlying intercostal vessels. A constant branch from the thoracodorsal vessel to teres major is present along the cephalic border of latissimus dorsi. The midpoint of a line drawn between olecranon and caudal apex of scapula, marks the position of the muscle at that level. Skin raised in association with latissimus dorsi must be raised caudal to this point, as the muscle passes deep to the long head of triceps more cephalad, to gain the humerus (Fig. 1). On its way to the humerus the latissimus dorsi curls on itself, the vascular leash coming in just caudal to the beginning of its tendinous change. There is no other vascular supply to the latissimus dorsi muscle at this proximal level. The pedicle is superficial to the fascial layer deep to latissimus dorsi and appears under the ventral border of teres major. Small branches may be given off to serratus fibres.
Together with increased understanding of the macroscopic anatomy of musculocutaneous flaps and definition of further vascular territories, has come a proliferation of studies of microcirculation. Animal studies have increasingly used the pig as a valid comparative animal to man because of the lack of contribution of the panniculus carnosus to the blood supply of the skin of the pig. (Milton 1967, 1972; Prather et al., 1979; Daniel, 1973, 1982; Young, 1982). The pig has been used extensively for investigation of skin flaps either axial or random in type (Patterson, 1968; Milton, 1972; Myers and Cherry, 1971). The omnipotential skin flap (Daniel, 1982) is unfortunately not a musculocutaneous flap. Free flaps have been used (Black et al., 1978) as well as musculocutaneous flaps to include the rectus abdominis, gracilis, intercostal or latissimus dorsi muscles. The purpose of this report is to describe a technique for using the latissimus dorsi flap (as a musculocutaneous island or muscle flap) on which the vascular pedicle may be ligated, clamped, or controlled proximally and at a distance from the flap and overlying skin. Thus, various parameters (blood flow., ~02, pH, temperature, skin expansion etc.) may be assessed without violation of the flank of the pig to gain access to the muscle pedicle. Anatomy
The anatomy of the latissimus dorsi in the pig is similar to man, except that the muscle takes origin only from the last four ribs but one, compared with the lower six thoracic vertebrae, lumbar fascia, and ilium in the human (Getty, 1975). If the origin from the ribs is divided, the latissimus dorsi can be totally isolated except for its tendinous insertion
Operative technique
The latissimus dorsi can be raised as an island musculocutaneous or muscle flap without necrosis, 364
A PIG MODEL FOR INVESTIGATION
OF MUSCLE AND ~YOCUTANEOUS
FLAPS
34.5
Caudal Apex of Scapula Trapetius
I
Abdominal
Lat. Dorsi
Oblique
Triceps Lateral Head Triceps
Long Head
Fig. 1 Figure I-Muscular
anatomy of
pig flank.
leaving it attached solely by its narrow tendinous insertion and vascular pedicle. Indeed quite a large area of skin beyond the limits of the muscle must be raised in order to cause skin necrosis. Method (I) Mark the mid-point of the line drawn between the olecranon and the caudal apex of the scapula. Mark a further point at the junction of the upper third and lower two-thirds of the spine of the pig. The line joining these two points marks the direction of the muscle midline. (2) Mark out the area of skin desired (Fig. 2). (3) Incise the cephalic border of the skin marking, through fat and panniculus down to muscle. The cephalic border of latissimus dorsi is found, mobilised and the adjacent teres major identified. The branch from the thoracodorsal artery to teres major should not be ligated until the flap is raised, and the parent vessel identified from below. (4) Incise the remaining borders of the flap down to muscle until the latissimus dorsi is outlined. The deep surface is easily mobilised by blunt dissection, though the two intercostal per-
forators and surrounding fascia may need sharp division (Fig. 3). (5) When the caudal origin is divided, the muscle and overlying skin are mobilised forward, and the thoracodorsal vessels seen. The small branches to teres (and serratus) are divided, and the muscle completely mobilised to its tendinous insertion (Fig. 4). (6) At this level a plane is dissected between the latissimus muscle and the neurovascular leash. A silastic catheter or infant feeding tube is passed between the two (Fig. 5). The two ends are passed through a small stab incision in the axilla and sutured together. Traction on the catheter will completely occlude the thoracodorsal vessels and circulation to the musculocutaneous flap. Upon release, blood flow will be restored. This can be verified (as well as the vascular isolation of the flap) with the intravenous injection of disulphine blue. Upon release, blood flow quickly returns as shown by return of dye (Figs. 6A-C), suggesting minimal spasm. The catheter ends are buried superficially under the stab incision and are easily retrieved at subsequent investigations.
366
BRITISH JOURNAL OF PLASTIC SURGERY
Fig. 2 Figure 2-Surface
points and rhomboid flap outlined. (Head of pig is to the left.)
Sixteen latissimus dorsi muscle or musculocutaneous island flaps were raised in 8 pigs using this method. Weekly traction on the silastic catheter over the next month, temporarily occluding circulation to the flap as shown by dye studies, failed to induce necrosis of the flaps. The nerve can be divided if necessary. Access is poor for resuturing the thoracodorsal vessels as a free flap, because the pedicle origin and muscle insertion is deep to the scapula. The latissimus dorsi musculocutaneous flap is quite easily dissected with minimal blood loss, and the anatomy is quite similar to that of the human. It is safe. Indeed, quite a large area of skin has to be raised for any cutaneous necrosis to occur. The operative site can be protected post-operatively by adapted garments. As the muscle is paired, a control is available. If necessary, axial skin flaps ^^- l__ __:_-A ^_ CL_ L..*C^^,._ A-,, ,,,..,,,..
Figure 3-Musculocutaneous Fig. 3
flap dissected free.
A PIG MODEL FOR INVESTIGATION OF MUSCLE AND MYOCUTANEOUS FLAPS
Fig. 4 Figure
&Flap
lifted anteriorly
to demonstrate
the blood
supply
on the deep surface.
Fig. 5 Figure 5--(A
and B) Silastic catheter
around
thoracodorsal
leash, proximal
to supplying
Lat. dorsi.
367
368
BRITISH JOURNAL OF PLASTIC SURGERY
Fig. 6 Figure 6-(A-C) Return of dye to temporarily occluded flap after release of catheter.
References Black, M. J., Chait, L., O’Brien, B., Sykes, P., Sharzo, L. (1978). How soon may the axial vessels of a surviving free flap be safely ligated: a study in pigs. British Journal of Plastic Surgery, 31, 295. Daniel, R. K. (1973). The free transfer of skin flaps by microvascular anastomoses. Plastic and Reconstructive Surgery, 52, 16. Daniel, R. K. (1982). The omnipotential pig buttock flap. Plastic and Reconstructive Surgery, IO, 11. Getty, R. (1975). The anatomy of the domestic animals. 5th
edition. Philadelphia. Saunders. Milton, S. H. (1967). The survival of experimental pedicled skin
flaps, Thesis, Kilner Library, Oxford. Milton, S. H. (1972). Experimental studies on island flaps. II. Ischaemia and delay. Plastic and Reconstructive Surgery, 49, 444. Myers, M. B., Cherry,
G. (1971). Differences in the delay phenomenon in the rabbit, rat, and pig. Plastic and Reconstructive Surgery, 41, 73. Patterson, T. J. S. (1968). The survival of skin flaps in the pig. British Journal of Plastic Surgery, 21, 113.
A., Blackburn, J., WilIIams, T., LYM, J. (1979). Evaluation of tests for predicting the viability of axial pattern skin flaps in the pig. Plastic and Reconstructive Surgery, 63,
Prather,
250.
Young, C. M. A. (1982). The revascularization of pedicle skin flaps in pigs: A functional and morphologic study. Plastic and Reconstructive Surgery, 70,455.
The Authors P. G. Milliean, FRCS, FRACS, Overseas Fellow, Department of Plastic Surgery, Radcliffe Infirmary, Oxford. M. D. Poole, FRCS, FRACS, Consultant, Department of Plastic Surgery, Radcliffe Infirmary, Oxford. Requests for reprints to: Mr M. D. Poole, Plastic Surgery Department, Radcliffe Infirmary, Oxford, OX2 6HE. This work was supported by a grant from the Medical Research Fund, University of Oxford.