14.2.1 Introduction to the Medial and Lateral Gastrocnemius Flap

Over the past half century, many would say that the gastrocnemius (Fig. 14‑2) and soleus muscles have been the “dynamic duo” (Fig. 14‑3) when considering coverage of the lower leg. ¹ In actuality, the medial and lateral heads of the gastrocnemius muscle alone have been a “dynamic duo” and deserve their appellation as lower leg “workhorse” flaps. ^{2 ,​ 3} Long before this achievement, Stark ⁴ had recognized the value of the pedicled gastrocnemius muscle for treatment of infected compound fractures, but only after similar repetitive reports by Barfod and Pers ⁵ as well as Ger and Efron ⁶ were surgeons convinced of their efficacy. McCraw et al ⁷ defined their reliable musculocutaneous territory, and believed as such were more versatile since reach was significantly extended. The gastrocnemius muscle has even been used in cross-leg fashion as a regional flap. ^{7 ,​ 8} With the acquisition of microsurgical capabilities, this muscle soon proved useful under special circumstances as a free flap donor site for the more distal lower limb. ^{9 ,​ 10} Neurovascular anastomoses have even permitted dynamic transfers for forearm function restoration. ^{9 ,​ 11} Indeed, similarly an innervated pedicled gastrocnemius muscle flap has been attempted as an even simpler way to correct foot drop. ³

The medial head of the gastrocnemius (MHG) muscle, since usually larger and longer (Fig. 14‑4), ^{1 ,​ 12 ,​ 13 ,​ 14} has traditionally been selected to correct problems of the distal thigh, region of the patella and knee joint, and proximal third of the leg itself (Fig. 14‑5). ^{1 ,​ 15} The less often used lateral head of the gastrocnemius (LHG) muscle still is important and a better choice for lateral knee or defects around the proximal fibula (Fig. 14‑6). ^{3 ,​ 16} The gastrocnemius muscle as a whole not only assists plantar flexion of the foot but also is a knee flexor and stabilizer. ^{17 ,​ 18} Yet the soleus muscle is a more powerful agonist with regard to ankle movement; so, many patients even after transfer of both gastrocnemius heads can ambulate normally, suggesting that either or both heads are expendable. ² However, Daigeler et al ⁷ in an extensive review of their experience found that patients had some restrictions in basic activities like walking upstairs, standing, or jumping on tiptoes, and especially running—even if only a single head had been used as a flap.

14.2.2 Attributes and Detriments

14.2.3 Anatomical Considerations

Literally the “belly of the calf,” the gastrocnemius muscle is the most superficial muscle of the posterior compartment of the leg. ¹³ There are two distinct heads, each with a discreet neurovascular supply. The medial head originates from the popliteal surface of the femur just superior to the medial condyle, whereas the lateral head arises from the lateral epicondyle of the femur. ^{3 ,​ 18} The proximal portion of each head forms the borders of the lower triangle of the popliteal fossa. ³ Distal to this, the two heads are fused together at a midline raphe that can be indistinguishable if not for the presence of the medial sural cutaneous nerve and accompanying branch of the lesser saphenous vein that traverse a groove between the two. ¹⁸ The muscle fibers of each head again become distinct when they insert on the posterior aspect of its aponeurosis (Fig. 14‑4) that joins its counterpart from the soleus muscle to form the triceps surae (Fig. 14‑3). This conjoined aponeurosis becomes the Achilles tendon that ultimately inserts on the calcaneus. Most consider the medial head to be the larger and longer of the two, ^{1 ,​ 12 ,​ 13 ,​ 14} although Andejeklov et al ¹⁹ in a recent anatomical study of fresh cadavers suggest that there is really no significant difference between them.

The arterial supply to each head of the gastrocnemius muscle always arises from the posterior surface of the popliteal artery just above the knee joint, but may bifurcate from a single common vessel or have double pedicles. ⁹ Most often, however, there is a distinct solitary branch to each head, making each a type I muscle as defined by Mathes and Nahai. ²⁰ The caliber of these arteries at their takeoff is about 2 to 3 mm, and potential pedicle length is 2 to 5 cm. ^{18 ,​ 21} Soon after entering the hilum of each muscle, each source vessel bifurcates into two or more branches that run longitudinally throughout the length of the muscle, ¹⁸ and is the basis for safely splitting the muscle. ²² Communicating branches between the heads through the more distal fusion of the muscles will provide sufficient circulation such that one head can survive on that supplied by the other. ^{23 ,​ 24} Major musculocutaneous perforators from the longitudinal branches typically are found in the more proximal half of the muscle. ²⁵ Numerous venae comitantes accompany the arteries until eventually emptying into the popliteal vein. ^{18 ,​ 21}

Motor innervation of the gastrocnemius muscle is by a distinct branch from the medial popliteal nerve that accompanies the dominant vascular pedicle into the hilum of each head. ¹⁸ According to Taylor et al, ²⁶ this is a type III mode of innervation, since having multiple branches from the same nerve trunk to the gastrocnemius muscle as a whole, but an argument could be made that each head if considered individually would have a solitary unbranched nerve entering that muscle, and thus be a type I muscle. Especially when assessing the use of the LHG, it must be understood that the common peroneal nerve will be found near the head and neck of the fibula superficial to that muscle and deep to the biceps femoris. ¹²

14.2.4 Anatomical Variants and Potential Pitfalls

14.2.5 Flap Design

The defect requiring reconstruction will dictate the flap design, beginning with which head should be selected. Except in the obese individual, having the patient preoperatively stand on their tiptoes with the ankle joint maximally plantar flexed usually allows visualization of the outline of each head as they insert into the triceps surae. The muscle chosen will usually be the longer and that most likely to reach the defect.

Donor site morbidity is limited if only muscle is taken as the flap, but composite, chimeric, or other variations are possible; an overview on these anatomical variants has already been given in the preceding section. Both muscle heads and their vascular sources are readily approached using a stocking seam incision that is marked to crisscross the popliteal crease before continuing vertically distally along the midportion of the calf up to the triceps surae. ³⁴ This is easiest with the patient in the prone position, but most parapatellar and proximal third leg defects are more amenable to having the patient in the supine position, which also simplifies the administration of anesthesia and nursing staff preparation. Depending on the margins of the defect (Fig. 14‑5), a curvilinear line starting at the knee joint and continued longitudinally to the level of the triceps surae about 2 cm posterior to the medial posterior border of the tibia will, in this position, most readily allow access to the medial head. The lateral head will require a similar line drawn (Fig. 14‑6), but instead 2 cm posterior to the lateral border of the fibula.

14.2.6 Flap Harvest

Proper markings for harvesting the gastrocnemius as a muscle flap will depend on the location of the defect, patient position on the operating table, and which head will be utilized, as described in the preceding section on flap design. In the majority of cases, the patient can be in the supine or lateral decubitus position to allow independent elevation of either head only, which will minimize donor site functional morbidity. Use of a mid-thigh tourniquet with the leg exsanguinated will provide the clearest assessment of anatomical details.

14.2.7 Postoperative Care Protocols

Usually a suction drain left to collapse the void created by removal of either head of the gastrocnemius is a reasonable routine. Especially if the origins remain intact, or the muscle has been transposed across the knee joint, a posterior splint with the knee extended is essential until healing appears satisfactory, to prevent inadvertent knee joint flexion or hyperextension causing flap dehiscence. Care should be taken to also keep the ankle joint in a neutral position to prevent a subsequent equinus deformity of the foot.

14.2.8 Conclusion

The gastrocnemius muscle has two heads with distinct neurovascular pedicles that allow either or both to be used as a flap for reliable coverage of the distal thigh, knee, or proximal-third leg regions. Although considered expendable, there can sometimes be a considerable functional deficit left afterward, preventing common exercise activities. Design and harvest of either head as a flap is straightforward, as the muscle has a superficial location in the calf with a fairly reliable anatomy. Use as a musculocutaneous flap has virtually been abandoned primarily because of aesthetic concerns at the donor site and recipient site contour irregularities. Although possible to use as a regional or free flap donor site, the greatest efficacy in using the gastrocnemius muscle remains as a local pedicled flap.

14.3.1 Introduction to the Gracilis Local Muscle Flap

The history of muscle and musculocutaneous flaps has been marked by numerous yet sporadic precedents. The gracilis muscle as a flap has been no exception (Fig. 14.7). Pickrell et al ¹ used this as an option for recreating a rectal sphincter. Notably, the rebirth of the entire genre of muscle flaps in the 1970s and 1980s followed quickly after Orticochea ² showed that large skin peninsular flaps could be safely raised without the need for any delay maneuvers. The trick was to include muscle underneath during the skin flap elevation, which he did by keeping the gracilis muscle attached to form a composite flap that then provided staged coverage of an ankle. ² Orticochea claimed that perforators from the muscle allowed better perfusion to sustain a larger skin flap, although he used that word without a true understanding of their anatomical course. ²

The gracilis muscle has truly become a “workhorse flap” found to solve all conceivable problems within the “skin and its contents,” the realm of the true reconstructive surgeon. As a local flap, it can provide coverage for the genitalia, ³ perineum, ^{1 ,​ 4} pubis, ⁵ groin, ^{6 ,​ 7} ischium, ⁵ and sometimes if distal based even for the knee. ⁸ The muscle functions as a thigh adductor, knee and hip flexor, and medial hip rotator, ⁹ but only a minimal deficit is noted if absent, so it is considered expendable. ¹⁰ Potential donor site morbidity is minimal, and scarring on the medial thigh usually can be well hidden. ^{10 ,​ 11 ,​ 12} These characteristics demand that complete knowledge of this donor site be mastered by all who could potentially use it!

14.3.2 Attributes and Detriments

14.3.3 Anatomical Considerations

The gracilis muscle is found in the more posterior aspect of the medial thigh. It is the most superficial of the muscles of the adductor compartment, extending longitudinally for some 30 cm from its aponeurotic origin at the symphysis pubis and pubic arch to where its tendon inserts as part of the pes anserinus on the medial tibial condyle, found inferior to that of sartorius and above semitendinosus. ^{5 ,​ 9} The width of the muscle may be up to about 7 cm at the level of the major vascular hilum, ⁶ then tapers distally toward its long tendon, forming overall a somewhat triangular shape (Fig. 14‑8).

The dominant vascular supply to the gracilis muscle is most commonly considered to be the medial circumflex femoral artery (MCFA), ⁵ although others state it may be the adductor branch or even the first profunda perforator, ^{6 ,​ 8} but in essence always ultimately arising from the profunda femoris. ^{6 ,​ 13} The MCFA then courses medially between the adductor longus and magnus muscles before entering the anterolateral undersurface of the gracilis at a point about 10 cm (range: 5–14 cm ⁶ ) inferior to the pubic tubercle. ¹⁴ The artery caliber varies from 1.5 to 3 mm, ⁸ and venae comitantes that are larger are always present. The potential pedicle length is about 7 cm. ⁸ As with most muscles, minor pedicles may be found near the origin and insertion. For example, Tremp et al ¹⁵ describe a more proximal pedicle that was a deep branch of the MCFA. Cavadas et al ⁸ found a mean 2.2 distal secondary pedicles that arose from the superficial femoral or descending genicular arteries, with the most proximal of these commonly near the midportion of the muscle. Since circulation to the entire muscle is routinely satisfactory via just its dominant pedicle in spite of these minor pedicles, this would be considered a type II muscle using the classification of Mathes and Nahai. ¹⁶

Motor innervation of the gracilis muscle is via the anterior branch of the obturator nerve. ⁹ That takes an oblique course between the adductor longus and magnus muscles before entering the gracilis muscle just superior to its dominant vascular hilum.

After entry into the muscle, the nerve splits into branches allowing segmental functional muscle transfers, making this a type I muscle according to the mode of innervation following the schema of Taylor et al. ¹⁷