Pedicled medial sural perforator flap for the reconstruction of knee defects

Abstract

Soft tissue defects exposing the patellar tendon or bone are common in patients who have experienced trauma or implant infection. The purpose of this article is to present our experience of six patients who underwent reconstruction of soft tissue defects of the knee using a pedicled medial sural perforator flap. Between November 2013 and November 2015, six patients who presented with a soft tissue defect overlying the knee were admitted to our hospital. After adequate debridement or wide excision of the tumour, these patients underwent pedicled medial sural perforator flap placement to resurface the complex soft tissue defects and to provide a gliding surface for the exposed patellar tendon. The patients' age, comorbidity, aetiology, defect size and location, flap size, perforator numbers and lengths, outcome and follow‐up period were reviewed. The six medial sural perforator flaps survived completely, and the wounds healed satisfactorily over a mean follow‐up of 21·5 months (range, 6–51 months). Donor sites were closed primarily or covered with a split‐thickness skin graft. The medial sural perforator flap is a reliable flap for coverage of defects overlying the knee. The thin and pliable flap, long pedicle length and less donor site mobility benefit patients. Thus, the medial sural perforator flap may be a valuable alternative for defect reconstructions overlying the knee, which produces satisfactory results both functionally and cosmetically.

Introduction

Soft tissue defects overlying the knee are often the result of trauma involving patellar tendon rupture, malignancy requiring a wide excision or implant infection. These defects represent a challenge to surgeons when encountered in reconstruction surgery. This is especially relevant when insufficient soft tissue coverage following total knee arthroplasty jeopardises prosthesis retention and may lead to significant complications 1 in patients who have undergone trauma requiring tendon repair, which can further compromise an already poorly vascularised bed. Skin grafts often fail because of poor vascularity or an exposed patellar tendon, bone or implant. Reconstructive options include the use of local fasciocutaneous, muscle and free flaps 1. Although there are many different methods of surgical treatment of knee defects, the optimal treatment remains controversial. The pedicled medial sural perforator flap provides sufficient tissue for coverage of small to moderate defects and constant vascularity, which helps to restore the original thin, pliable and tough skin properties, and acceptable donor‐site morbidity. In this report, we present our experience with six patients who were treated successfully, without complications, using the pedicled medial sural perforator flap for coverage of soft tissue defects of the knee.

Materials and methods

Between November 2013 and November 2015, six pedicled medial sural perforator flaps were used to resurface soft tissue defects overlying the knee. One patient was a woman and the other five were men; their mean age was 59 years (range, 36–87 years). The patients were followed up for 6–51 months (mean, 21·5 months). The most common medical comorbidity was diabetes mellitus (three patients, 50%), followed by hypertensive cardiovascular disease (two patients, 33%), peripheral arterial vascular disease (one patient, 16·7%), coronary artery disease (one patient, 16·7%) and atrial fibrillation (one patient, 16·7%). The defects were caused by postoperative implant infection of the knee (n = 4), malignancy (n = 1) or a post‐traumatic defect of the knee (n = 1). After admission, debridement and wound care were performed to clean the wound base for subsequent reconstruction. All of the wounds had skin and soft tissue defects, involving tendon, bone or implant exposure that could not be closed primarily or healed by secondary intention. The size of the defects for reconstruction ranged from 15 to 135 cm² (mean, 66·88 cm²). The characteristics of the patients' age, sex, comorbidities, defect location and size, flap size, perforator numbers and lengths, outcome and follow‐up period were reviewed and recorded (Table 1).

Table 1.

Characteristics of the patients, wounds, operations and follow‐up

Patient	Sex/Age (year)	Comorbidity	Aetiology	Location (knee, portion)	Size of defect (cm2)	Flap size (cm2)	Perforator number	Pedicle length (cm2)	Donor site	Outcome	Follow‐up period (months)
1	Male/36	None	Trauma, plate exposure	Left, lower	7 × 6	15 × 9	2	5	STSG	Good	51
2	Male/48	DM, PVD	Infection, plate exposure	Left, lower	5 × 3	9 × 4	1	5	STSG	Good	6
3	Male/61	None	Infection, plate exposure	Left, lower	6·5 × 4·5	9 × 7	1	5	STSG	Good	12
4	Male/79	DM, CAD, HCVD	Infection, TKR exposure	Left, anterior	15 × 8	15 × 12	1	10	STSG	Good	31
5	Male/87	DM, AF, HCVD	Infection, TKR exposure	Right, anterior	10 × 6	18 × 6	1	6	Primary closure	Good	23
6	Female/43	None	Maligancy, tendon exposure	Right, lateral	15 × 9	17 × 9	2	12	STSG	Good	6

AF, atrial fibrillation; CAD, coronary artery disease; DM, diabetes mellitus; HCVD, hypertensive cardiovascular disease; PVD, peripheral arterial vascular disease; STSG, split‐thickness skin graft; TKR, total knee replacement.

Surgical procedure

The operative technique for flap harvesting has been described previously 2, 3. Briefly, after general anaesthesia, the patient is placed in a supine position. The hip joint is maintained in a posture of abduction and slight external rotation, and the knee joint in flexion. This permits the convenience of flap harvesting from the medial aspect of the upper calf and allows further knee reconstruction in the same position. In these patients, the operation was facilitated under pneumatic tourniquet control, without limb exsanguination and under loupe magnification. To mark the perforator, a line is drawn from the medial malleolus to the midpoint of the popliteal fossa posteriorly. A handheld Doppler is then moved along this line to identify any perforators. In general, the number of cutaneous perforators of the medial sural artery varies from one to five, and there are usually two major perforators. The most sizeable myocutaneous perforators are located within the upper one fifth to one third of the lower leg 4. The size of the flap is determined by the knee defect to be repaired, and the perforator is placed on the centre of the skin paddle.

The medial border of the flap is elevated to confirm the locations and sizes of the perforators. When one or two sizeable perforators are identified, the opposite border is then incised and the flap elevated. The pedicle is freed from the medial head of the gastrocnemius muscle using retrograde intramuscular dissection. After the appropriate length of the vascular pedicle of the flap is reached, the residual lateral portion of the flap is elevated from the muscle, and the sural nerve and lesser saphenous vein are preserved. The medial sural artery of the major branch, measuring 1–2 mm in diameter, is usually accompanied by two venae comitantes.

After excellent blood flow to the flap is confirmed on tourniquet release, the flap is transferred to the knee defect. The donor‐site defect can be closed directly when the skin elasticity is sufficient and the width of the skin flap is <6 cm 5. A large donor‐site defect must be covered with a split‐thickness skin graft. Postoperatively, the affected knees in these patients were immobilised with a short‐leg splint for 2 weeks, after which passive and active mobilisations were started carefully.

Results

Six flaps survived completely, and no further operations were needed to achieve defect coverage. Four flaps had one medial sural perforator, and two flaps had two perforators. The flap size ranged from 9 × 4 cm (36 cm²) to 15 × 12 cm (180 cm²). The length of the pedicle ranged from 5 to 12 cm, which was sufficient to reach the defect without tension (Figure 1). One donor site was closed primarily and five received split‐thickness skin graft coverage. All patients had an uneventful postoperative course. The flaps were raised safely and showed excellent functional and cosmetic results over a mean follow‐up of 21·5 months (range, 6–51 months). The surgical outcomes are listed in Table 1. No patient needed additional flaps for defect reconstruction or a secondary debulking procedure. In our series, no complications or patient discomfort were observed, and no patient complained of muscle weakness. Contraction of the gastrocnemius muscle could be seen through the skin or skin graft postoperatively in all patients. No disturbances of knee mobility and strength were observed.

Figure 1.

The flaps can be transposed to all aspects of a knee defect. The numbers represent the case numbers in our series.

Case presentation

Case 5

An 87‐year‐old man with type 2 diabetes mellitus, atrial fibrillation and hypertensive cardiovascular disease had received a right total knee replacement for treatment of traumatic arthritis 2 months before admission. The wound became infected and developed necrosis of the overlying tissue and prosthesis exposure. Broad‐spectrum antibiotics were prescribed initially and were changed after a specific organism was isolated from the wound culture. The wound was evaluated every day, and additional debridement was performed if residual necrotic tissue was present. The defect measured 10 × 6 cm after the last debridement. Seven days after the last debridement, a pedicled medial sural perforator flap, measuring 18 × 6 cm with one perforator, was designed and transposed to the defect area to cover the exposed prosthesis (Figure 2), and the donor site was closed primarily (Figure 3). The patient's subsequent recovery was uneventful, and the defect healed completely. Two months after the reconstruction, the patient was ambulatory without complications.

Figure 2.

(A) Preoperative appearance of an infected prosthesis causing an exposed wound on the right knee. (B, C) The 18 × 6‐cm pedicled medial sural perforator flap was raised based on one myocutaneous perforator (black arrow). (D) The appearance of the flap immediately after surgery.

Figure 3.

The donor‐site defect can be closed directly if the width of the skin flap is <6 cm.

Case 6

A 43‐year‐old woman presented with a malignant fibrous histiocytoma of the right knee. After wide excision, a 17 × 9 cm right pedicle medial sural perforator flap was designed based on two myocutaneous perforators and was elevated from the right calf. The 12‐cm vascular pedicle was dissected towards its origin at the popliteal artery, and the flap was transposed to the defect without tension. The donor site was covered with a split‐thickness skin graft. After the reconstructive surgery, the knee defect was well covered, and the flap showed good cosmetic outcome at the postoperative 6‐month follow‐up (Figure 4).

Figure 4.

(A) A 43‐year‐old woman exhibited sarcoma on the lateral aspect of the right knee. After wide excision, the defect measured 15 × 9 cm or 135 cm². (B) A pedicled medial sural perforator flap was designed and elevated. (C) The thin and pliable flap was transposed to the knee defect. (D) At the 6‐month follow‐up, the patient was satisfied with the knee motion and appearance.

Discussion

Adequate coverage of the knee region is often challenging for plastic and orthopaedic surgeons. After adequate debridement of infected tissue or wide resection for a soft tissue sarcoma, the knee vascular web may be damaged and perforator flaps based on a local pedicle are not reliable. In addition, raising a local flap near a wound with a previous infection or malignant area is risky. Reconstructive options for defects of the knee include myocutaneous flaps arising from the sartorius, gastrocnemius or femoral biceps, reverse anterolateral thigh island flaps, superior lateral genicular flaps and free latissimus dorsi myocutaneous flaps 6, 7.

A myocutaneous flap is thick and has a limited arc of rotation for knee reconstruction if the knee defect is shallow, and it often requires aggressive primary thinning and multi‐staged defatting procedures to improve the appearance. Harvesting one of the major muscles in the ipsilateral extremity to repair the defect can be a contraindication between soft tissue coverage and functional reconstruction. For reconstruction of the knee using a free flap, the recipient vessels are usually deep‐seated and microvascular anastomosis can be difficult, especially if the defect is in the anterior knee 7. The disadvantages also include donor‐site morbidity, increased operation time, use of a major leg vessel and the need for microsurgical expertise 8.

The pedicled medial sural artery perforator flap is another good alternative for reconstruction of soft tissue defects of the knee. In 2001, Cavadas et al. 3 reported on the anatomy and clinical applications of the medial sural artery perforator flap for 10 cadaver dissections and 6 clinical cases. The medial sural artery supplies the medial gastrocnemius muscle and sends perforating branches to the skin. The medial sural artery has a mean of 2·2 perforators, which measure 9–18 cm from the popliteal crease 3. The flap is now used widely in reconstructive surgical procedures, especially as a free flap for reconstruction of the head and neck, hand, and lower limbs 2, 4, 5, 9, 10. Although not used extensively, it is has been used successfully as a pedicled flap for reconstruction of defects in the lower leg 11.

The advantages of the medial sural artery perforator flap are its very thin and pliable nature and its consistent anatomy and straightforward intramuscular course, which make its use easy. Intramuscular dissection of the perforator produced a longer pedicle compared with a conventional gastrocnemius myocutaneous flap. The thin flap does not need a longer pedicle, and the flap has easier access to the defect and can be harvested away from the infected area. Although exposing the pedicle of the medial sural artery perforator flap involves a long intramuscular dissection, which often requires division of numerous small branches and can make the dissection tedious, the course of the vessel is relatively superficial within the muscle 12. Standard retractors allow good visualisation of the entire dissection. In our experience, the average time of harvesting the flap is about 70 minutes. In this series, we used the medial sural artery perforator flap with a 12‐cm pedicle length for a lateral knee defect without tension in 1 patient, and the flap survived well.

The medial sural perforator flap can provide soft tissue coverage without functional loss of the donor muscle by saving the gastrocnemius muscle, its motor nerve, deep fascia, lesser saphenous vein, and sural nerve. The maximum size possible for the medial sural artery perforator flap is unknown. However, the largest flap in our series was 15 × 12 cm with one perforator. We did not observe any flap necrosis in these patients. All of the defects were reconstructed successfully using the pedicle medial sural artery perforator flap.

The main disadvantage of this perforator flap is that it leaves a visible scar at the donor site on the posterior leg. Lin et al. 5 reported that donor sites measuring 6 cm could be closed directly. If a skin graft is used to close the donor site, the scar is more conspicuous. The cosmetic aspects should also be considered when selecting patients.

A review of the English literature about pedicled medial sural perforator flaps for knee defects showed that Umemoto et al. 11 performed the flap in the upper third of the lower leg and low portion of the knee in four patients. Kim et al. 13 reported on their use of a medial sural perforator island flap for the reconstruction of postburn knee flexion contractures to cover the defect in the posterior knee in 12 patients. However, we found no reports indicating that the pedicled medial sural perforator flap is sufficient for coverage of knee defects. In our series, the pedicled medial sural perforator flap covered the lower portion of the knee in three patients, anterior portion of the knee in two patients and lateral portion of the knee in one patient; all had sufficient pedicle length and no tension.

Although the present series is small, our experience suggests that the pedicled medial sural artery perforator flap may be a sufficient and useful flap for knee reconstruction. We prefer the pedicled medial sural perforator flap for reconstruction of knee defects because of its long vascular pedicle, wide arc of reach, thin and pliable characteristics and satisfactory aesthetic outcome, without causing any functional defects in the donor area and areas proximal to the knee defect.

Conclusion

The medial sural perforator flap provides an anatomically simple and clinically reliable solution to events such as trauma, excision of a tumour, infection involving exposed bone, tendon, joint or an artificial joint that must be covered with vascularised soft tissue. Pedicled medial sural artery perforator flap transfer is appropriate for knee defect reconstruction and has acceptable functional and aesthetic outcomes in selected cases.