Reconstruction of soft tissue defects of the lower limb using the free serratus anterior flap

Abstract

Objective:  To present the application and clinical results of soft tissue reconstruction of the lower limb with the free serratus anterior muscle flap.

Methods:  Twenty Chinese adult cadavers were studied to determine detailed anatomical information about the serratus anterior muscle flap. From 1997 to 2007, 82 patients with soft tissue defects of the lower limbs were treated with free serratus anterior muscle flaps and skin grafts. There were 24 females and 58 males, aged from 22 to 63 years (mean 34). The patients were followed up for an average of 30 months (range, 8 months–5 years).

Results:  All flaps survived except for one, in which necrosis occurred. Six patients developed partial necroses of the muscle flap or skin graft. Five of them healed with debridement or wound care, and one healed with a repeat skin graft. There was no notable donor site morbidity. Dysfunction of the shoulder was not found in any of the patients.

Conclusion:  The serratus anterior muscle flap is a good option for the treatment of soft tissue defects of the lower limb. This muscle flap has many advantages owing to its anatomical features.

Introduction

The reconstruction of soft tissue defects of the foot, ankle and lower leg is challenging, especially where there is infection associated with bone. There are three options for reconstructing soft tissue: local flaps, pedicled flaps and microsurgical free flaps. Unfortunately, local flaps can not be used to cover defects in the regions mentioned above as there is insufficient tissue redundancy available. Some rotated pedicled flaps can be useful, such as the sural artery flap, or the distally based sural neurocutaneous flap which have been more widely used in the past decade. However, pedicled flaps are not always available after injuries of these regions because the rotational axes are usually damaged ¹ . Therefore these flaps are of limited use.

Microsurgery has revolutionized reconstructive options, because it allows for coverage of soft tissue defects when local viable tissue is unavailable, inadequate, or would result in too great a functional loss. Furthermore, it eliminates functional limitation caused by scar contraction around the joint. Free flaps have been used extensively for areas of the foot, ankle and lower leg. The free serratus anterior muscle flap was first reported in 1982 ² . Since then, this flap has been widely used for reconstructing soft tissue defects of the chest wall, face and distal extremities ³ , ⁴ , ⁵ . However, few articles have documented the application of this flap. Free serratus anterior muscle flap transfer surgery to the lower limb has been performed in our department since 1997, and over 80 cases have now been managed in this way. The purpose of this article is to present the application and clinical results of soft tissue reconstruction and treatment of osteomyelitis with free serratus anterior muscle flap to the lower limb.

Materials and methods

Anatomical study

The serratus anterior muscle is located on the lateral thoracic wall. It is a quadrilateral flat muscle. It originates from the first to eighth (or ninth) ribs, and inserts onto the medial border and inferior angle of the scapula. This muscle is multidigitate, and can be classified into three parts; namely, the upper (one or two slips), middle (3–5 slips) and lower portions (the remaining slips). The muscle slips of the upper and middle portion lie almost transversely and attach to the vertebral border of the scapula. The lower portion inserts onto the inferior angle of the scapula in a radiate pattern. The serratus anterior muscle has a dual blood supply, with the upper part supplied by the lateral thoracic artery and the middle and lower by the terminal branches of the thoracodorsal artery. This muscle is innervated by the long thoracic nerve ⁶ , ⁷ , ⁸ .

In order to obtain detailed anatomical information about this muscle so as to decrease donor site morbidity (iatrogenic nerve damage), we carried out a study on the applied anatomy of this muscle on 20 Chinese adult cadavers (40 sides). We found that the anatomy of the main trunk of the thoracodorsal vessels and the long thoracic nerve is constant and reliable. The bundle of blood vessels and nerve lies in the middle and posterior thirds of the lower serratus anterior slips. The lower part of the muscle slips inserts onto the lower angle of the scapula, and occupies only 21% of the total length of muscle insertion. The lower part of the serratus anterior muscle has an independent blood supply and innervation. The lowest 4–5 slips of the muscle can be obtained without influencing the main functions of the shoulder ⁹ .

Patients

Between 1997 and 2007, free serratus anterior muscle flap transfers were used in 82 patients. There were 58 males and 24 females ranging from 22 to 63 years old (mean 34 years). The sizes of flaps varied from 4.4 cm × 6.2 cm to 11.0 cm × 13.0 cm. The primary diagnoses were soft tissue defect after trauma, soft tissue and bone defect after trauma, soft tissue infection, and soft tissue infection combined with osteomyelitis. One case was treated with a free latissimus dorsi and serratus anterior muscle combined flap. Another case was treated with a free serratus anterior and rib myo‐osseous composite flap.

Preoperative management

Aggressive debridement was performed to ensure a clean wound. Any internal fixation devices were removed at the same time if they existed on infected bone. Any exudation from the deep tissue of the wound was cultured to guide the use of antibiotics. Patients with diabetes and vesicular (vascular) diseases were excluded. All patients were educated to give up smoking. Angiography was performed in the lower extremity to evaluate the distribution of arteries. If there was infection associated with bone, radiographs were taken to determine the extent of the infection.

Surgical technique

All patients were placed in a lateral position with 50° obliquity and operated on under general anesthesia. A simultaneous two‐team approach was used. One team harvested the flap, while the other prepared the recipient site.

The incision for the donor site was in the subaxillary region, along the anterior border of the latissimus dorsi. This incision was about 10 cm long and just above the projection of the middle portion of the serratus anterior muscle. It was smaller than what has been described in previous literature ¹ , ¹⁰ . Because the skin border of the incision was lifted when elevating the muscle, this incision was long enough. The vessel pedicle, which is usually covered with fatty tissue, was identified at the surface of the middle and lower portions of the serratus anterior muscle,. The lowest 3–5 slips were harvested according to the requirements of the recipient area. In our series the size of the flap varied from 6.5 cm × 9 cm to 11.5 cm × 14.5 cm. Once the vascular pedicle had been isolated, the branch to the latissimus dorsi could be tied and dissection extended into the axilla to gain a long vascular pedicle if needed. When a relatively short pedicle was all that was needed, the blood supply to the latissimus dorsi could be left intact. In our series, long pedicles were obtained in 28 patients. A combined flap (the serratus anterior muscle combined with the ribs and/or the latissimus dorsi) could be obtained if required owing to the rich vascularity of this region. The remaining muscle was carefully treated by electric coagulation and sutured together. Vacuum drainage was placed.

Debridement of the recipient area was thoroughly performed. The artery of the free muscle flap was anastomosed to the anterior tibial, posterior tibial or dorsalis pedis artery according to the preoperative angiography result. The vein of the flap was anastomosed to the accompanying vein or the saphenous vein. If osteomyelitis was present, the sequestra were removed, and the cavity filled with the muscle flap. The muscle flap was tailored as required and sutured to the neighboring tissue beneath the border of the wound. Drainage was placed beneath the muscle flap. Finally, a skin graft was performed on the flap, which had several holes pricked in it to improve drainage. A hole was made in the dressing to enable observation of the vascularity of the flap ¹ .

Postoperative management

Intravenous antibiotics were administered based on culture sensitivities. Low molecular dextran, salvia miltiorrhiza and anisodamine hydrobromide were used to improve the microcirculation. The dosage of these medications was slowly decreased. Any medications that could contract blood vessels were avoided. The potentially compromising elements of cold, pain and nicotine were avoided with special care. Drainage was removed after 24–48 h. The vitality of the muscle flap could be evaluated by direct observation through the hole in the dressing. The flap appeared red when the blood supply was normal, while it turned pale when the artery was obstructed and became purple if there was venous congestion. Another way to assess this was to palpate the pulse of the vessel in the flap pedicle at the anastomosis region.

Results

Follow‐up ranged from 8 months to 5 years (mean 30 months). All flaps survived except in one case, one of a 63‐year‐old male, the oldest patient in our series. He had previously undergone an unsuccessful attempt to repair a massive soft tissue defect of the heel with a sural neurofasciocutaneous flap. Our attempt at a free serratus anterior muscle flap transplantation also failed. In addition, the skin graft on the muscle flap necrosed in one case, this healed with a repeat skin transplantation. Part of the muscle flap necrosed in three cases. In one of them it appeared that most of the muscle flap had been destroyed; the remaining healthy tissue was just a layer of musculomembrane containing blood vessel reticula. All three cases achieved good results after debridement. Another three cases developed partial skin graft necroses which healed after wound care. All other flaps survived completely. All donor sites healed uneventfully. No dysfunction of the shoulder has been found in any of the patients. Illustrative examples are shown in 1, 2, 3, 4, 5, 6.

Figure 1.

Case 1: (a, b, c) A 41‐year‐old male who suffered a crush injury of the right lower leg, resulting in an open comminuted fracture combined with Gustilo IIIB severe soft tissue damage. Pedicled flaps carried a high risk because the blood supply and soft tissue conditions around the wound were bad. (d) After external fixation, the soft tissue problem was solved successfully with a free serratus anterior muscle flap transplantation and meshed skin graft.

Figure 2.

Case 2: (a) A 33‐year‐old male, infection after internal fixation with a plate for calcaneal fracture. Bone and cartilage were exposed at the time of admission. The plate and dead bone were removed and a free serratus anterior muscle flap transplanted to eliminate the bone cavity. Calcaneal osteomyelitis was cured without recurrence. (b) The postoperative appearance was excellent.

Figure 3.

Case 3: (a) A 47‐year‐old male with an unstable scar with a fistula under the heel after trauma. (b) Angiography showed that the foot was supplied by only one main artery. Pedicled flaps were impossible. (c, d) A free serratus anterior muscle flap was a good substitute. This muscle flap has the advantages of high stability and low shearing force.

Figure 4.

Case 4: (a) A patient in whom the second to fifth toes are absent, and the head of the metatarsals exposed, after injury. (b, c) A free serratus anterior muscle flap not only solved the problem of coverage with a good contour, but also preserved the head of the metatarsals to facilitate a better gait.

Figure 5.

Case 5: (a) A 22‐year‐old male with severe osteomyelitis of the tibial shaft. There was a large bone defect after debridement. (b) A free serratus anterior and rib myo‐osseous composite flap transplantation was performed. (c) The appearance and (d, e) the X‐ray films of the leg after surgery.

Figure 6.

Case 6: (a, b, c) A patient with a severe crush injury which involved the lower leg, ankle and foot. Massive soft tissue has been lost, and bones and tendons are exposed. (d) This case was treated with a free latissimus dorsi muscle and serratus anterior muscle combined flap. (e, f) This combined flap avoided fat and clumsiness of the foot and ankle region. (g) X‐ray films just after surgery and (h) 6 months after surgery.

Discussion

The choice of reconstructive flaps

Soft tissue defects of various causes involving the foot, ankle and lower leg are common problems in practice and are difficult to handle. Because there is little soft tissue in this area, there is a high risk of exposure of bone and tendon after injury, leading to an unstable scar, which is difficult to treat. Due to insufficiency of the blood supply, the wound can become worse in this region leading to a more serious situation: osteomyelitis. The means of reconstruction include various local and pedicled flaps as well as microsurgical free flaps.

Currently, two kinds of flaps are used for massive soft tissue defects of the foot and ankle region: one is the distally based lower leg flap with reverse transposition, such as the distally based sural fasciocutaneous flap, and the other is the microsurgical free flap.

Local and pedicled flaps were first used to reconstruct the foot and ankle in the late 1960s. In the interim many such flaps have been developed, such as the sural artery flap, neurocutaneous flaps and the medial plantar cutaneous flap. These flaps have the advantages of being easy to harvest and not requiring vascular anastomosis. However, there are also disadvantages. There is insufficient tissue redundancy to allow local flaps to cover a defect of the lower limb. Accordingly, a local flap is rarely recommended as a solution, unless the defect is very small. Because of limitations in the length of the pedicle, some areas of the foot are difficult to cover with a pedicled flap. The blood supply and condition of the soft tissue near the wound are usually not good when the injury has been severe. The influence of the function and appearance of the donor site can not be ignored if the pedicled flap is not small. If by any chance the attempt fails, further treatment will be even more difficult.

Owing to the rapid development of microsurgery from the late 1970s, the free flap has become one of the most important methods of reconstruction. As to the region of the foot, ankle and lower leg, the free cutaneous or musculocutaneous flap is not the most suitable, due to its fat and clumsy features. Special footwear is likely to become necessary. A muscle flap with skin graft has the advantages of a low profile and high stability. More importantly, muscle flaps have good vascularity, which is helpful in the treatment of infection and has a positive effect on bone healing. So a muscle flap with skin graft is the preferred choice when filling wounds with osteomyelitis at their base. Yazar et al. ¹¹ have indicated that grossly tridimensional defects need free muscle flaps because they can conform better to such complex defects. Anthony et al. ¹² have demonstrated that debridement and immediate muscle flap coverage provide effective, single‐stage treatment for wounds complicated by chronic osteomyelitis, and allow antibiotics to be restricted to short‐term use. Furthermore, muscle flaps covered with skin grafts provide durable coverage, while allowing subsequent ancillary procedures such as bone grafts to be performed under the flaps. Lin et al. ¹³ have reported that free tissue transfer in pediatric patients is a viable and reliable option. Skin/musculocutaneous flaps and skin‐grafted muscle flaps both had equal survival rates.

In this series of 82 cases, the free serratus anterior muscle flap necrosed completely in only one patient. The reason for failure may have been the low quality of the blood vessels; because this patient was 63 years old. Another reason may have been that a pedicled flap had previously been performed in this patient in an attempt to repair a massive soft tissue defect at the heel, but had failed. The blood supply around the heel had been damaged. In this series all other serratus anterior muscle flaps survived and there was no recurrence of bone and soft tissue infection.

The advantages of the free serratus anterior muscle flap

Muscle flaps are usually preferred for reconstruction of the region of the foot, ankle and lower leg, and muscles used include the gracilis, rectus abdominis, latissimus dorsi and serratus anterior. The gracilis muscle is an optimum muscle, but its pedicle is short. The rectus abdominis muscle has a slightly longer pedicle and is larger and flatter, but the appearance of the donor site after muscle harvesting is not attractive, and there is a risk of herniation in the abdominal wall. The latissimus dorsi flap is too bulky for the foot and ankle region.

The serratus anterior muscle flap has a lot of advantages. This muscle is large in area, with flat and slim muscle bellies. It is multidigitated in shape and can easily be contoured, so that further breakdown and revision can be avoided. Our anatomical studies showed that this muscle flap has a long pedicle with a constant anatomical position. The approach to, and harvest of, the flap is easy, and the incision is concealed. The diameter of the blood vessels of the pedicle is similar to those at the foot and ankle, so vascular anastomosis is not much of a problem. Therefore it provides an optimum solution for soft tissue repair and reconstruction in this region. The features of its lower profile make it a perfect material for repairing a defect that lies at the distal extremity and has nerve, tendon and bone exposed. In our series, all flaps transplanted to the foot and ankle region looked good. The patients could wear normal shoes without special adjustments. Owing to the rich vascularity of this muscle and the tissues around it, the serratus anterior muscle flap can be elevated as a combined flap with the latissimus dorsi and/or the ribs. Such a combined flap can be used to treat complex massive bone and soft tissue defects. In our series two patients treated with serratus anterior muscle combined flaps had successful outcomes.

Pitfalls and cautions

Microsurgery techniques have developed quickly and spread widely in our country. The anastomosis technique has not been a limiting factor. However, attention should be paid to some aspects of this procedure to avoid complications ¹⁴ . Hematoma and seroma can be early complications. Once the muscle flap has been harvested, hemostasis should be performed carefully; and the remaining muscle slips should be sutured together to close the cavity. A vacuum drainage is placed and removed 24–48 h later, depending on the amount of drainage. Two patients in our series developed a hematoma, which was solved by compression. ‘Winged scapula’ is a more severe complication, to which more attention should be paid ¹⁵ . The serratus anterior muscles act to prevent the scapula from moving backward. When the long thoracic nerve is damaged, the serratus anterior muscle is paralyzed; this can lead to ‘winged scapula’. According to our anatomical studies, the lowest 4–5 slips of the muscle can be removed without influencing its main functions ⁹ . However, the ramuli of the long thoracic nerve, which innervate the upper portion of the serratus anterior muscle, must be left intact during operation. One case in our series was diagnosed as having a mild ‘winged scapula’, but there was no limitation of shoulder function. The reason might be that the level of flap elevation was higher than the upper border of the flap. Six patients developed partial necroses of the muscle flap or skin graft but these healed with debridement or wound care. It is important to diagnose such necroses early, so the muscle flap must be carefully observed.

Summary

In conclusion, the serratus anterior muscle has many advantages owing to its anatomical features. The procedure is safe and effective. Donor site morbidity is rare. This muscle flap seems to be an optimum option for lower limb defects where local and pedicled flaps are difficult or impossible to perform. The features of its lower profile make the serratus anterior muscle flap a perfect material for repairing defects in the distal extremity and, owing to its plentiful blood flow, this flap is especially suitable for reconstructing defects of the lower limb with underlying bone pathology.