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Gastrocnemius Flap


Figure 50.1
Gastrocnemius Flap.

Introduction

The gastrocnemius flap is one of the most useful flaps. Described very early, it has been proven to be easy to raise and very reliable. Typically, it can be used by non-specialized reconstructive surgeons, since its field of application concerns the area of the knee and upper part of the leg, which is frequently involved in injury and is an area in which prosthetic surgery is frequently performed. As is the latissimus dorsi flap for the upper limb, the gastrocnemius is the mainstay of the armamentarium of flaps that can be used for lower extremity reconstructions and should be known by surgeons in orthopedic and plastic surgery. Although the musculocutaneous flap has significant potential as a functional muscle transplant to restore elbow flexion, the main indication is the use of the medial head as a proximally based pedicled muscle flap for reconstructing defects around the knee. With the increasing number of knee prostheses and the existing risk of skin disunion or infection, especially in the elderly, the medial gastrocnemius flap is the “cornerstone” of the strategy for dealing with problem cases of prosthetic knee replacement.

Flap Anatomy ( Figure 50.1 and see Ch. 13 and Fig 13.3 , Fig 13.6 , Fig 13.9 , Fig 13.10 , Fig 13.11 , Fig 13.19 )

The gastrocnemius muscle has two heads: medial and lateral. The medial head originates on the posterior surface of the femur superior to the medial condyle and posterior to the insertion of the adductor magnus muscle. The lateral head originates in the lateral epicondyle of the femur. Both insert into a long common muscle aponeurosis that forms the Achilles tendon with the aponeurosis of the soleus.

  • The proximal part of the muscle forms the lower triangle of the popliteal fossa, the upper triangle being formed by the diverging hamstring muscles.

  • The muscle bellies extend from the popliteal fossa to the mid- to distal third of the leg.

  • The plantaris muscle and tendon lie between the medial gastrocnemius and the soleus muscle and can be used to clearly identify the plane of separation.

  • The medial and lateral head run side by side and are separated by a fibrous septum.

  • The gastrocnemius muscles contribute to plantar flexion of the foot through their pull on the Achilles tendon. These muscles also contribute to knee flexion.

Arterial Supply of the Flap ( Figs 50.1 and Fig 13.3 , Fig 13.6 , Fig 13.9 )

The vascular supply is type I in the Mathes and Nahai classification, and each head, lateral or medial, can be mobilized individually on its own neurovascular pedicle. One muscle head can survive totally based on the vascular communications between the two muscle bellies. The dominant vessel in most patients is the medial sural artery.

Medial Gastrocnemius Muscle

Dominant:

medial sural artery

  • Length: 5.1 cm (range 1.6–9.5 cm)

  • Diameter: 2.5 mm (range 1.8–4 mm)

Minor:

branches from the lateral sural artery

These branches have variable length and diameter. They are located in the distal half of the muscle and communicate between the two muscle heads.

Minor:

branch from the posterior tibial artery

The branches have variable length and diameter. The distal part of the medial head receives a vascular pedicle from a musculocutaneous artery issuing from the tibialis posterior artery at the midleg. This pedicle gives off a direct skin branch and a muscular branch that divides into two small branches, one for the soleus and the other for the distal part of the medial aspect of the medial head. Not infrequently, this branch is well developed and permits the raising of an inferiorly based portion or the entire muscle based only on this pedicle. It provides an elegant solution to cover the middle or the distal third of the leg.

Lateral Gastrocnemius Muscle

Dominant:

lateral sural artery

  • Length: 4.8 cm (range 1.8–9 cm)

  • Diameter: 2.2 mm (range 1.2–3.7 mm)

Minor:

branches from the medial sural artery

These branches have variable length and diameter. They are located in the distal half of the muscle.

Venous Drainage of the Flap

All arteries to these flaps are accompanied by venae comitantes.

Primary:

venae comitantes of the medial and lateral sural artery

Two venae comitantes are found with each artery. The diameter of the veins is approximately 3.5 mm (range 3–4 mm).

Secondary:

superficial veins such as the lesser saphenous vein ( Fig. 13.19 )

This vein can be included with the flap to augment drainage or to serve as primary drainage of the flap. This is particularly useful when a large skin island is included with the flap.

Flap Innervation (see Fig. 50.1 and Fig 13.9 , Fig 13.10 , Fig 13.11 , Fig 13.19 )

Motor:

medial and lateral sural motor nerves that come off the tibial nerve

These nerves are approximately 4–5 cm in length and enter the muscle on its deep proximal surface with the sural vascular pedicle. As the gastrocnemius is a rapid-contraction muscle, it is preferable to cut the nerve when raising a pedicled flap to avoid muscle contraction on the donor site.

Sensory:

skin overlying the medial gastrocnemius muscle

Posterior femoral cutaneous nerve and saphenous nerve (L3–L4) innervate this area. The saphenous nerve follows the course of the greater saphenous vein and can be found near the medial side of the gastrocnemius muscle.

Sensory:

skin overlying the lateral gastrocnemius muscle

The sural nerve (S1–S2) supplies the skin in this part of the calf and the nerve can be found running along the lesser saphenous vein. The nerve runs in a subfascial plane and pierces the fascia in the posterior calf to travel more superficially and supply the skin.

Flap Components

The gastrocnemius flaps are harvested as muscle flaps. They can include the overlying fascia and skin. A strip of tendon can be included with the flap. The flap can be harvested as a chimeric flap with the skin island and muscle harvested based on the same common pedicle.

Advantages

  • Muscle dissection is rapid in case of a proximally based pedicled flap.

  • The external diameter and length of the pedicle are suitable for microsurgical transplantation.

  • Contour deformity following the use of one head is acceptable.

  • When only one head is raised, functional loss is negligible, compared with the benefit of the procedure.

  • The medial or the lateral head can be transposed distally by extending the pedicle length. However, this technique is no longer so popular after the recent description of fasciocutaneous flaps for covering the distal leg.

  • The length of the distal tendon, the length of excision of the body muscle, and the strength of contraction make functional transfer an interesting possibility.

Disadvantages

  • In case of a free transfer, the prone position is more suitable for dissecting the pedicle but makes transplantation to an anterior recipient site more difficult.

  • The posterior incision is not desirable in females.

  • The elevation of a pedicled flap in supine position can be difficult in case of stiffness in hip or knee.

  • The donor site following the transplantation of an extended musculocutaneous flap is not cosmetically acceptable.

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