5.1 Methods for Repairing Skin and Soft Tissue Defects in the Mid and Forefoot
High-energy injuries around the ankle often result in extensive skin and soft tissue defects in the foot and ankle region, frequently accompanied by exposure of bone and tendon tissues. These injuries lead to refractory infections and persistent non-healing wounds, complicating clinical treatment 3, 4. Traditional treatment methods, such as wound dressing changes and grafting exposed bone, pose significant challenges, are time-consuming, and do not facilitate secondary tendon transfer or ankle joint functional reconstruction. Exposed tendons and bone surfaces hinder the survival of skin grafts due to their poor durability and infection resistance, often resulting in surgical failure. Extensive soft tissue defects in the foot and ankle, sometimes accompanied by severe infection, adherent scars to the bone, and underlying dead space, further limit the use of skin stretchers. Given the complexity of these wounds and the limitations of conventional techniques, flap transplantation remains the preferred method for treating complex soft tissue defects in the foot and ankle. Cross-leg flap transplantation necessitates prolonged immobilization of the patient, has a limited repair scope, and requires a secondary surgery to sever the pedicle, increasing patient discomfort. Although free flap transplantation yields positive outcomes, it demands advanced microsurgical skills, prolongs operative time due to vascular anastomosis, and elevates the risk of postoperative vascular crises, thereby increasing failure rates. Additionally, poor vascular compatibility at the recipient site further limits its clinical application. Consequently, the island flap with a reverse sural artery perforator pedicle has emerged and is widely used for clinical repair of foot and ankle skin and soft tissue defects 5-7. However, for larger defects or those near the distal end, a single blood supply flap often fails to completely cover the wound or leads to flap edge necrosis postoperatively. Therefore, this study aims to design a wide-pedicle double-blood-supply flap on the medial side of the lower leg, incorporating the supra-malleolar perforator of the posterior tibial artery and the saphenous neurotrophic vessels. This approach expands the flap's harvestable area and enables one-stage repair of skin and soft tissue defects in the foot and ankle, extending even to the midfoot and forefoot regions.
5.2 Anatomical Basis of the Medial-Side Double-Blood-Supply Flap of the Lower Leg
There are 2-4 perforating branches of the posterior tibial artery located 5-12 cm above the tip of the medial malleolus, typically two branches. The most common branch is situated 6-8 cm above the medial malleolus, with a diameter of 0.5-1.6 mm. It primarily supplies blood to the skin on the medial side of the lower leg 8-10, with its perforating branches positioned at a horizontal distance of 0.5-3.0 cm from the saphenous nerve 11. The farthest branch is located 2.5-3.5 cm above the most prominent point of the medial malleolus, accompanied by 1-2 veins, which eventually converge into the posterior tibial artery and its accompanying veins 12-14.
The saphenous nerve nutrient vascular skin flap was first reported by Masquelet 15 in 1992 for repairing soft tissue defects in the lower third of the calf and foot-ankle. This flap is widely used in clinical practice due to its large cutting area, good compression resistance, and wear resistance, without sacrificing important blood vessels and nerves 16. The procedure is straightforward and does not require special microsurgical techniques. After transfer to the recipient site, it offers an aesthetically pleasing appearance and can restore sensory function by matching with the sensory nerves in the donor site. The position of the saphenous nerve is constant, and its nutrient vessels are distributed in stages from multiple sources 17, 18, including the saphenous artery originating from the descending genicular artery and the longitudinal vascular network formed along the saphenous nerve 16, 19. In the lower third of the calf, several anastomotic branches of the posterior tibial artery accompany the saphenous nerve in both anterior and posterior directions. These anastomotic branches connect with the peripheral and intrinsic vascular systems of the saphenous nerve, forming a multi-source, chain-like network of saphenous nerves and blood vessels 20, 21.
Numerous studies have found that the medial malleolus perforating branch of the posterior tibial artery forms an anastomotic arch around the saphenous nerve, with its vascular chain repeatedly anastomosing and communicating to create a three-dimensional and multi-dimensional blood supply system 20-22. This constitutes the anatomical basis for the double-blood-supply flap of the medial malleolus perforating branch of the posterior tibial artery and the saphenous nerve nutrient vessel.
5.3 Characteristics of the Retrograde Double-Blood-Supply Flap of the Medial Side of the Lower Leg
- The main blood vessels of the posterior tibial artery are preserved, ensuring that the blood supply to the foot is not compromised. The dual blood supply sources from the posterior tibial artery perforating branch and the saphenous nerve nutrient vessels are retained, expanding the blood supply range of the posterior tibial artery perforating branch. This approach allows the skin flap to be elevated to a higher plane, ensuring adequate blood circulation and enabling the repair of large wounds in the lower leg and foot-ankle circumference 20, 23.
- This skin flap contains a composite pedicle consisting of deep fascia, subcutaneous tissue, superficial veins, cutaneous nerves, and nutrient vessels. It has a shallow depth and is easy to operate. The flap can be designed to be longer and larger, and its rotation is flexible, which avoids pedicle swelling and maintains aesthetics.
- By moving the rotation point of the distal pedicle downwards, the length of the skin flap can be increased, allowing the repair of wounds that extend as far as the metatarsophalangeal joint 24.
- This skin flap can include a portion of the medial head of the gastrocnemius muscle, retained to form a composite tissue flap. This provides strong anti-infection capabilities and ensures effective coverage and filling of infected wounds, tendons, bone exposure, or bone marrow cavities.
- This flap is an axial flap, with the long axis of the flap aligned with the axis of the blood vessel, which promotes flap survival. The blood supply to this flap is reliable, combining the advantages of the perforator flap and the cutaneous nerve nutrient flap. Furthermore, the integrity of the cutaneous nerve nutrient vessels is preserved, and the flap benefits from the greater saphenous vein-saphenous nerve nutrient vessel network at the pedicle. This results in a more reliable blood supply without the need for vascular anastomosis, leading to a higher success rate.
5.4 Design and Harvesting of the Retrograde Double-Blood-Supply Flap of the Medial Side of the Lower Leg
To repair distal foot wounds and prevent wound necrosis, many scholars have adjusted the rotation point in an attempt to maximize the exposure of the medial malleolus perforating branch of the posterior tibial artery and reduce soft tissue traction. However, the results are often limited. Therefore, we utilize the extensive vascular communication network between the medial malleolus perforating branch of the posterior tibial artery and the saphenous nerve, incorporating the nutrient branches of the saphenous nerve to achieve double blood supply. This approach extends the cutting range and increases the area of the flap, thereby enabling the repair of skin and soft tissue defects in the foot, ankle, and even the forefoot.
The retrograde wide pedicle dual-blood supply flaps, located on the medial side of the lower leg, includes the medial malleolus perforating branch of the posterior tibial artery and the nutrient vessels of the saphenous nerve. The flap is based on an axis from the midpoint of the line connecting the Achilles tendon and the medial malleolus to the posterior edge of the tibial medial condyle, extending up to the level of the popliteal fossa or the lower edge of the patella, with a minimum distance of 3-5 cm above the medial malleolus 25. The flap does not exceed the tibial crest anteriorly or the posterior midline of the lower leg. Various designs of skin flaps that include skin bridges can be created according to the size and shape of the wound. When cutting the skin flap in reverse under the deep fascia, the integrity of the periosteum is maintained. The flap pedicle width is 4-5 cm, and its length is approximately 2 cm longer than the distance from the rotation point to the distal end of the wound to prevent swelling and contraction of the skin flap, which could complicate wound suturing.
5.5 Precautions for Harvesting a Retrograde dual-blood supply flaps from the Medial Side of the Lower Leg
- The risk of perforator injury is a critical preoperative consideration. Therefore, routine preoperative Doppler ultrasonography is performed to locate the perforating branches above the medial malleolus of the posterior tibial artery, ensuring their patency and marking their positions.
- Patients with avulsion injuries may not be suitable candidates for this flap treatment.
- The pedicle of the flap is incised and dissected in the subdermal plane with a sharp blade to avoid the formation of "cat ear" deformities after transposition.
- Intraoperatively, the great saphenous vein at both the distal and proximal ends of the flap is ligated to prevent superficial venous reflux and subsequent flap edema. Alternatively, the proximal stump of the great saphenous vein within the flap can be anastomosed to the superficial veins around the ankle, creating an additional venous outflow system to reduce the risk of venous congestion.
- During flap harvesting, the size of the donor area is designed to slightly exceed the wound size by 1-2 cm, and dissection is performed under the deep fascia to better preserve the vascular network supplying the cutaneous nerves. Simultaneously, the deep fascial vascular network augments the flap's blood supply, promoting flap survival.
- After flap elevation, if the wound is small, a tunnel can be created for transposition; if the wound is large, a "tennis racket" transposition can be performed.
- Meticulous hemostasis is achieved intraoperatively, and a half-tube drain is placed to prevent hematoma formation beneath the flap and at the pedicle.
- Postoperatively, warmth is maintained, smoking is avoided, and the lower limb is elevated to prevent vascular complications.
- In the event of postoperative venous congestion, early decompression through small incisions along the flap margins should be performed to improve flap survival rates.