A new model of rat muscle free flap transfer is presented. The flap is based on a long pedicle originating from the femoral vessels and continuing down to the distal saphenous margin at the ankle. The distal portion of the semiten- dinosus muscle is harvested along with the saphenous artery and great sa- phenous vein. A larger muscle flap may be harvested by including the distal portions of the posterior and anterior gracilis muscles. The flap can be trans- ferred to remote sites on the animal, with a vascular pedicle of up to 3 cm in length. The diameters of the vessels repaired are of standard microsurgical size. This model has distinct advantages of simplicity, speed of dissection, high success rate after microvascular transfer, and versatility in placement of the muscle mass (due to the long pedicle).

MICROSURGERY 13:338-339 1992 o 1992 wiley-Liss. inc.

THIGH ADDUCTOR FLAP: AN EXPERIMENTAL MODEL FOR FREE FLAP TRANSFER IN THE RAT

BASEM KOUDSI, M.D., and ROGER K. KHOURI, M.D.

T h e rat is an extremely useful species for experimental studies in the field of reconstructive microsurgery. The small size, hardiness, and resistance to infection make it very cost effective for large experimental series. Increasing numbers of surgical models that mimic clinical procedures have been developed in the rat. Recently, several models of muscle free flaps have been described,'-' with applications to important problems in reconstructive rnicros~rgery.~.~ In this report, another model of rat muscle free flap is pre- sented. Several advantages of this new model over existing ones are described.

MATERIALS AND METHODS The model is based on the saphenous vessels that supply

the distal portion of the thigh adductors. A skin incision is made on the medial surface of the rat hindleg, from the ankle to the groin above the inguinal ligament. Beginning just above the ankle, the saphenous artery and great saphe- nous vein are dissected, starting where these vessels divide into two or three branches. The distal ends are doubly li- gated, with division between the ligatures. The pedicle is then raised in a proximal direction, taking the underlying muscle bed with the vessels, thus not isolating these vessels from the surrounding tissue. The distal segment of the semi- tendinosus is included with the pedicle; creating a generous muscular cuff around and inferior to the pedicle. A larger block of muscle may be used by including the posterior and

From the Division of Plastic Surgery, Washington University School of Medi- cine, St. Louis, MO.

Address reprint requests to Roger Khouri. M.D., Division of Plastic Surgery, Washington University School of Medicine, One Barnes Hospital Plaza, St. Louis, MO 631 10.

Received for publication August 11, 1992.

0 1992 Wiley-Liss. Inc.

anterior gracilis muscles. The tendinous insertions of the muscles are sharply divided from the tibia just below the knee. Branches from the saphenous vessels to these muscles are preserved (Fig. 1). The muscle cuff can be enlarged by dividing across the muscles further proximally, taking up to half the muscle length (Fig. 2). The saphenous vessels join the femoral vessels in a branching cluster; all other branches are doubly ligated and transected between the ligatures, leaving all femoral flow to the saphenous pedicle. The fem- oral vessels may be dissected back to the inguinal ligament, ligated, and cut distally, creating the free flap now ready for transfer.

We performed 25 saphenous pedicle muscle flap trans- fers to the neck, in Sprague-Dawley rats weighing -200 g. The NIH Guide for the Care and Use of Laboratory Animals was followed throughout. After anaesthesia induction with pentobarbital (40 mg/kg body weight), the femoral artery was anastomosed to the common carotid artery, and the femoral vein to the ipsilateral jugular vein, using standard end-to-end microvascular technique with 10-0 nylon suture. Ten of the flaps were placed in the wound lateral to the sternomastoideus. Another ten flaps were swung on their pedicles to the lower dorsal surface of the head, to cover a 10-mm-diameter experimental skull defect. For an addi- tional five flaps, a skin and skull defect were created, and a full-thickness skin graft (1.5 X 2 cm) was harvested from the groin simultaneously and placed over the muscle flap covering the skull defect. Flaps were evaluated grossly and for signs of vascular patency 3 days postoperatively.

RESULTS All 25 flaps survived, with well-perfused muscle clearly

in evidence. The anastomoses remained patent for all 50 repairs (25 artery and vein pairs). The skin graft overlying five of the flaps appeared to be taking, with maintenance of

Figure 1. Photomicrograph showing course of saphenous vessels from the femoral vessels down to the ankle. Arrowheads indicate saphenous vascular bundle; ST. semitendinosus muscle; G, gracilis muscle.

Figure 2. The flap has been raised, still in place, taking large por- tions of the semitendinosus. posterior, and anterior gracilis muscles.

a soft, supple texture. The donor site suffered minimal def- icits; rats continued to ambulate on both legs during the 3-day recovery period. There was no sign of limb ischemia or functional compromise other than minor changes in gait

Rat Thigh Adductor Muscle Flap 339

(subjective evaluation); this may have been due in part to leg alteration created by the skin wound.

DISCUSSION The model presented in this report offers added versa-

tility for investigations that require a rat muscle free flap model. A long vascular leash, up to 3 cm in length in a normal adult rat, provides placement of a vascularized mus- cle at a considerable distance from the anastomotic repair site. The vessel diameters used in the anastomoses are suf- ficiently large (0.8-1.6 mm in diameter) to permit easy repair by a moderately skilled microsurgeon. The flap dis- section is simple, rapidly performed, and easily learned. The donor site morbidity is negligible, owing to the excel- lent collateral circulation of the rat leg. Finally, in our hands, the results are excellent, even with transplantation to a remote anatomic site.

We recommend use of this muscle flap for models re- quiring speed in dissection and high reliability of flap sur- vival as well as a long pedicle for flexibility and flap place- ment. Other rat muscle flap models are more difficult to dissect and have less than 100% success when trans- ferred.'-' Our model may be very useful particularly in research involving flap prefabrication, since the isolated muscle is spatially well separated from the anastomotic re- pair site following transfer of the flap.

REFERENCES 1. de la Pena JA, Lineaweaver W, Buncke HI: Microvascular transfer of

latissimus dorsi and serratus anterior muscles in rats. Microsurgery

2. Briones R, Lineaweaver W, Newlin L, Whitney TM, Bunke HJ: Single pedicle microvascular transfers of the serratus anterior and latissimus dorsi muscle in rats. Microsurgery 10269-273, 1989.

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Dautel G, da Silva JB, Merle M: Pedicle or free flap transfer of gracilis muscle in rats. J Reconsrr Microsurg 7:23-25, 1991. Tilgner A, Herrberger U, Oswald P: Myocutaneous flap models in the rat: anatomy, histology and operative technique of the latissimus dorsi myocutaneous flap. Z Versuchstierskd 31:225-232, 1988. Li XL, Cooley BC, Ye 2, Gruel SM, Gould JS: Free flap transfer of the cutaneous maximus muscle in the rat: Comparison to the latissimus dorsi muscle flap. Microsurgery 13:208-213, 1992. Li XL, Cooley BC, Gould JS: Effect of age upon ischemia-reperfusion injury in rat muscle free flaps. J Surg Res (in press). Li XL, Cooley BC, Gould JS: Brief ex vivo perfusion with anticoag- ulated blood decreases ischemialreperfusion injury in rat muscle flaps. Submitted for publication.