The soleus muscle, one of the components of the superficial posterior compartment of the leg, was used initially as a local flap, as described by Ger and later, by Mathes and Nahai. Since then, multiple surgical modalities have been described that have approached this flap in different ways and used it for different purposes, as both a local and a free flap. Its use requires precise anatomic knowledge to gain the utmost benefit from its versatility. It deserves to be more extensively used due to its wide coverage potential and minimal negative effects at the donor site. The soleus muscle is often harvested as part of the fibula flap (see Ch. 52 ).
Flap Anatomy (see Figs 50.1 , Figs 50.2 , Figs 50.4 , Figs 13.3 , Figs 13.6 , Figs 13.9 , Figs 13.10 , Figs 13.11 , Figs 13.19 )
The soleus muscle is a large, broad, and rather long muscle located at the posterior aspect of the leg. It is a bipenniform muscle consisting of a lateral and a medial head. The lateral head originates from the fibula head and body and the medial head originates from the medial side of the middle third of the tibia. The lateral and medial soleus muscles are separated in the midline by a septum, which is present in the distal part of the muscle. The two muscle heads join together to form the dorsolateral and dorsomedial component of the Achilles tendon. This tendon, which is formed by the soleus and gastrocnemius muscles, inserts on the calcaneum tuberosity ( Fig. 51.5 ).
The anatomic findings presented in this chapter are based on a study by Caix, in an article by Baudet and colleagues published in 1982. This study was performed on 22 fresh cadavers.
We will use the following terms to describe the soleus muscle in this chapter:
Soleus muscle (implying the entire muscle)
Medial head of the soleus muscle
Lateral head of the soleus muscle.
Arterial Supply of the Flap ( Figs 51.2–51.4 and Fig 13.3 , Fig 13.6 , Fig 13.9 )
The Lateral Soleus
The vasculo-nervous (neurovascular) pedicles to the lateral soleus muscle are usually found at three levels, providing what we term the “upper, middle, and inferior pedicles” of the lateral soleus muscle. These three pedicles are mainly derived from collateral branches of the peroneal vessels and, in some cases, the inferior pedicle is derived from the posterior tibial artery. The middle pedicle provides the main blood supply to the muscle and is made up of two (76%); or three (24%) branches.
branch from the popliteal artery (“upper pedicle”)
Length: 2.3 cm (range 1.2–5 cm)
Diameter: 1.3 mm (range 0.5–2 mm)
This branch is part of what is considered the “upper pedicle”; it is constant and is accompanied by venae comitantes. It penetrates the muscle 2.2 cm below the fibula head. One nerve branch emerging from the medial popliteal nerve joins this arterial branch.
branch from the tibioperoneal artery or peroneal artery (upper branch of the “middle pedicle”)
Length: 1.4 cm (range 0.5–3.5 cm)
Diameter: 1.9 mm (range 1–3 mm)
This branch is part of what is considered the “upper branch” of the “middle pedicle.” In 45% of cases, this branch comes from the peroneotibial artery and in 55% of cases, from the peroneal artery. The distance of origin of this branch from the anterior tibial artery is 3.3 cm. The point of penetration into the muscle is 7.5 cm from the head of the fibula.
branch from the peroneal artery (lower branch of the “middle pedicle”)
Length: 1.6 cm (range 0.3–4.0 cm)
Diameter: 1.73 mm (range 0.5–3.5 cm)
This is termed the “lower branch” of the “middle pedicle.” It is always derived from the peroneal artery. The distance of origin of this branch from the anterior tibial artery is 5.68 cm and the point of penetration into the muscle is 9.9 cm from the head of the fibula. This lower branch is absent in 9% of the population (two out of 22 in our study). In 13.6% of cases (three out of 22 in our study) a third branch of the middle pedicle was present.
branch from the peroneal artery (50%) or from the posterior tibial artery (50%) (“inferior pedicle”)
Length: 2.4 cm (range 1.2–3.5 cm)
Diameter: 1.1 mm (range 0.5–2 mm)
This branch is considered part of the “inferior pedicle” of the flap and is an accessory pedicle. In half of the cases it originates from the peroneal artery and in the other half from the posterior tibial artery. The distance of origin from the anterior tibial artery is 11.5 cm and the point of penetration into the muscle is 10.7 cm. The inferior pedicle is absent in 18% of cases.
The Medial Soleus
The medial soleus is supplied by several pedicles emerging from the peroneotibial and posterior tibial vessels ( Fig. 51.6C ).
upper pedicle, division of the upper branch supplying the lateral soleus
middle pedicle, most often three branches emerging from the posterior tibial artery
inferior pedicle common with the lateral soleus supply
perforating vessels from both gastrocnemius muscles emerging from the perifibular peroneal artery arcade
intramuscular cross-anastomoses between the lateral and medial soleus
These branches were elucidated from our anatomic study and they are very important in clinical application since the whole soleus can be harvested on a single branch from the peroneal pedicle and used as a regional or even free flap transfer. Two clinical cases will be presented in further detail, below.
Venous Drainage of the Flap
venae comitantes running along the arterial branches
The venae comitantes all drain into the peroneal, postero-tibial and finally, the popliteal veins. There are some cross-anastomoses with the superficial subcutaneous vein. Each main pedicle and collateral branches have two venae comitantes, their diameter being larger than that of the adjacent artery. They drain finally into the popliteal vein but there are some cross-anastomoses with the superficial subcutaneous vein. Including a skin paddle with the muscle flap can help to solve the venous drainage by anastomosing one or several veins (main trunk or collateral branches from the long saphenous vein or short saphenous vein).
Flap Innervation ( Figs 51.1, 51.5 and 51.6 and see Fig 13.9 , Fig 13.10 , Fig 13.11 , Fig 13.19 )
Lateral Soleus Muscle
branches from the medial popliteal and tibial nerves:
An upper branch which originates from the medial popliteal nerve, ranging from 0.5 mm to 2 mm
Two middle branches emerging from the tibial nerve
An inferior branch which is not constant.
Medial Soleus Muscle
Three branches from the posterior tibial nerve; usually there are three nerve branches.
If a skin paddle is included in the flap and a sensory branch supplying the skin (e.g., branches of the sural nerve) can be included and anastomosed with the recipient site ( Figure 13.19 ).
The soleus flap is harvested as a muscle flap. It can include fascia overlying the muscle, tendons such as part of the Achilles tendon, bone by including the fibula based on branches from the peroneal artery which supply the fibula and lateral soleus muscle, and skin by including the lateral skin overlying the fibula.
If necessary, a skin paddle can be harvested with the medial head of soleus. It is supplied by musculocutaneous perforators.
Bipenniform morphology with independent neurovascular pedicles supplying the medial and lateral soleus, allowing for separate transfer of each muscle.
Constant blood supply.
Minimal functional and cosmetic donor site morbidity since the soleus muscle contributes to a minor degree to the motion of the ankle in conjunction with the lateral and medial gastrocnemius. The gastrocnemius muscles, flexor hallucis longus, flexor digitorum longus, and tibialis posterior compensate for the loss of the soleus muscle.
The muscle can reach the distal third of the leg when transposed based on the distal blood supply.
It can be used as a functional muscle.
The complexity of vascular and nervous supply requires a thorough anatomic knowledge in order to achieve muscle dissection and inclusion of as many vessels as possible during the transfer.
The distally-based medial soleus muscle flap, which is useful for coverage of distal third defects of the leg, may not have a reliable inferior pedicle to support the flap and, also, may not be reliable in smokers.
A routine preoperative work-up is performed for all patients undergoing general anesthesia (the most comfortable for the patient). A preoperative consultation by the anesthesiologist is mandatory. According to the past medical history of the patient, further studies are performed if necessary.
In elderly patients, who may present with vascular risks or post-traumatic injury, an echo Doppler of the lower limb vessels and, if needed, an angiogram are recommended at the donor and recipient sites. Preoperative examination depends upon age of the patient, cardiovascular background, and vascular damage of the recipient site vessels by a previous injury. Doppler and an angiogram are recommended in a large percentage of patients.
Anatomic Landmarks ( Fig. 51.7 )
Lateral approach ( Fig. 51.10A ): the posterolateral edge of the fibula.
Medial approach ( Fig. 51.8A ): the posteromedial aspect of the tibia.
General Thoughts About Flap Design
The design depends upon whether the whole soleus, the lateral, or the medial soleus is to be harvested, and on the need for inclusion of adjacent components (i.e., fibula bone and/or a skin paddle).
A skin paddle can be included with the soleus or lateral soleus muscle. Musculocutaneous perforators supply the skin in the upper third of the lateral aspect of the leg while a larger skin island can be harvested based on both musculocutaneous perforating vessels and septocutaneous branches from the peroneal artery.
The distal extent and size of the soleus muscle are variable. Occasionally, if the muscle reaches the malleoli and its size is large enough at that position, the muscle can be transposed, based proximally, to cover distal third leg defects. This decision can be made preoperatively using magnetic resonance imaging (MRI) or clinical examination, or during intraoperative exploration. The size and location of the defect are major factors in the success of this type of transposition.
In cases where a distally-based hemi-soleus is planned for coverage of a distal leg defect, the exposure is the same as that for dissection of the posterior tibial vessels as recipient vessels for a free flap; therefore, if it is felt that the distally-based flap is not reliable, the same exposure is used to dissect the posterior tibial vessels and a free flap is performed.
If fibula bone is included in a composite flap, it is important to preserve the head of the fibula with the adjacent superior peroneotibial joint, as well as the common peroneal nerve and to stay away from the inferior peroneotibial joint, in order to avoid ankle instability.
The most common location for defects is proximally in the upper two-thirds of the leg. In this case, a proximally-based medial soleus flap is indicated or even the whole soleus if the defect is wider (up to 13 cm).
If the defect is in the lower third of the leg, a distally-based soleus can be harvested, provided that the medial soleus is supplied by an inferior pedicle. This point will be discussed later in the chapter.