13.1 Introduction

The correction of any wound involving the lower extremity requires repair of disrupted parts, while a defect will always require the restoration of missing components. ² Traditionally, the method to accomplish either of these objectives adhered to the reconstructive ladder, beginning in the basement with the simplicity of a secondary closure, then stepwise in a sequential fashion proceeding upward with increasing complexity through skin grafts and dermal matrices until reaching the available assortments of flaps. ^{2 ,​ 3} Levin expanded his orthoplastic ladder to also include the appropriate steps for management of bone injury or gaps. ⁴ Gottlieb and Krieger ⁵ challenged this conventional approach with their reconstructive “elevator” that allowed them to jump at will to whatever level they considered the best solution not only for the immediate problem but also for the long term. The reconstructive matrix may be the best model of all as it emphasizes all aspects of the critical preoperative decision-making analysis necessary to provide the best overall result ⁶ ; that will be unique in the lower limb, as this must assure not only bony stability and adequate soft-tissue coverage but also, most importantly, the maintenance of function and mobility. ⁷ Closer inspection of this matrix reveals a three-dimensional structure with its axes corresponding to the technological capabilities available at the given institution, which may somewhat correspond to the rungs of the reconstructive ladder, patient surgical risk factors such as comorbidities, and the complexity of the problem that needs to be solved (Fig. 13‑2). ⁶ A simultaneous assessment of how all of these parameters interconnect will be essential for each individual patient to permit formulation of their optimal reconstructive strategy. ⁸ Thus, if a vascularized flap is indicated, the exact choice will never be the same for every patient, as the product of all these parameters will have an infinite variability necessitating that the final selection always be individualized so that the best outcome can be anticipated.

Rausky et al ⁹ believed that the goals of lower limb reconstruction must include timely intervention to better ensure function preservation, creation of no impediment in the use of shoe wear, and the provision ultimately of a reasonable appearance, while causing minimal donor site morbidity. A properly selected flap may be the only alternative that is possible to fulfill all these prerequisites. The possible options for bone deficits will be better discussed in Chapter 23. Soft-tissue requirements are the more common need anyway in this region, and hereafter the most practical or workhorse flaps will be emphasized (Fig. 13‑3), recognizing that a “laundry list” of all available flaps would be an impossibility and that notable satisfactory exceptions exist that may rely instead on a surgeon’s familiarity and particular preferences. ¹⁰

Comparable rates of primary fracture and skin healing, time to ambulation, and thus limb salvage are similar regardless of whether a muscle or fasciocutaneous flap is used. ^{11 ,​ 12} The latter includes the genre of perforator flaps, which many consider provide a superior aesthetic result, the potential for later elevation to allow secondary procedures as a better option than a muscle flap, and, since no muscle is included, minimize function loss at the donor site (Table 12‑1). The adoption of this concept of perforator flaps has rapidly seen an increase in the use of local or so-called freestyle ^{13 ,​ 14} flaps throughout the lower extremity in lieu of free flaps, perhaps a consequence of the fact that the latter may be riskier, especially in patients with multiple comorbidities, and certainly require a greater allocation of resources and time as well as technical expertise that may not be universal. However, even a small defect may still be better resurfaced with a microsurgical tissue transfer if adjacent tissues have been damaged and perforators are unavailable or unreliable ¹⁵ ; and it certainly will always be a solution for all zones of the lower extremity even if some might think that choice inappropriate (Fig. 13‑4).

13.2 Selection According to the Recipient Site

Formerly, the lower extremity was divided into regional zones (Fig. 13‑4) where the flap choice would be either a pedicled flap available from that zone or a free flap. ¹⁶ Mathes and Nahai ¹⁷ in their original book on muscle flaps listed some 22 available muscles in the lower limb as possible local flaps, but most were too diminutive or had an unreliable pattern of circulation. Those still commonly in use include the vastus lateralis or tensor fascia lata ¹⁸ muscle for the trochanteric area; gracilis and rectus femoris ¹⁹ for the groin, or occasionally also the sartorius, ⁸ but its vascular supply may be unreliable; gastrocnemius for the knee and proximal third of the leg; and soleus for the middle third (see Chapter 14; Table 13‑2). The rectus abdominis muscle, although a distant flap, can still reach the upper thigh and groin, but at the potential price of causing abdominal wall incompetence. ²⁰ A paradigm shift has recently evolved for the utilization of local cutaneous flaps instead throughout the lower limb, whether based on perforators or not (Fig. 13‑5). ²¹ These have included propeller, peninsular, island, or advancement flaps including keystone flaps (see Chapter 15). Many would consider the distal-based sural flap, which many prefer for more acral defects as a substitute for a free flap, to be a peninsular flap or even a propeller flap, depending on the method of elevation. ^{22 ,​ 23}

A better way to evaluate lower limb soft-tissue requirements has been proselytized by Lachica ²⁴ who has introduced an “expanded zone concept” (Fig. 13‑6). Again, because of the advent of perforator flaps, the traditional zone idea has become too restrictive as it lacked specificity with regard to wound size and complexity as well as type of tissue loss. ²⁴ The “expanded lower extremity zones” are not restricted by arbitrary boundaries, and are differentiated according to soft-tissue anatomical and functional requirements throughout this region, which in turn determines appropriate flap selection (Table 12. 3). ²⁴ Areas densely surrounded by muscle such as the thigh and calf have no functional restrictions, and, although a skin graft or muscle flap would suffice, a thin perforator flap would give a superior aesthetic result, ^{20 ,​ 24} replacing “like with like.” ²⁵ Most of the rest of the leg also requires soft-tissue replacement only, and that usually best as a perforator flap (Table 12.3). Any flap in the knee area must allow unrestricted motion and the patella, since pressure bearing, must also have a more durable, resilient coverage. ^{24 ,​ 26} Following the subunit principle for foot and ankle soft-tissue restoration, ^{27 ,​ 28} all areas are similar in that a thin flap is mandatory to allow proper fit of shoes, while the plantar heel and forefoot differ in that any flap must be durable as these will be subjected constantly to weight bearing and the strains of ambulation. ²⁴

If for any reason a local flap is not available, a free flap may be the next option. Restricting the donor site to the same extremity if possible will minimize the overall scarring and burden on the rest of the body. The anterolateral thigh flap has become the “ideal” soft-tissue free flap to fulfill these requirements ²⁹ (Table 12‑1), as this donor site can be prefabricated, ³⁰ can undergo thinning to the proper contour, ³¹ can have gigantic dimensions or split into multiple smaller flaps, ³² has a long and reliable vascular pedicle, and can even be used in combination with other adjacent tissue components such as fascia lata or muscle if desired. ³³ The medial sural artery perforator free flap is another option specifically for smaller defects, as it also has a potentially long pedicle to reach any available recipient vessels to thereby avoid use of vein grafts, with still moderately large caliber vessels. ³⁴ The radial forearm flap similarly has a long pedicle, and may be the only thin cutaneous flap in the obese patient encountered most often in the western hemisphere, albeit sometimes this can create significant donor site compromise. ^{20 ,​ 23 ,​ 35} As an alternative for the morbidly obese, muscle flaps may still be preferable for proper contour and logistical reasons, with the “workhorse” flaps being the latissimus dorsi (LD) for large defects or the gracilis for smaller ones (Table 13‑2). Other cutaneous flaps from the dorsal thoracic fascia such as the circumflex scapular artery perforator flaps (also known as the scapular ³⁶ or parascapular flaps ³⁷ ) or the thoracodorsal artery perforator (TDAP) flap may be just as versatile as the LD muscle, but the former offer function preservation if important. Note also that many prefer the TDAP flap over the scapular or parascapular flap, as the vascular pedicle is easier to dissect and can be longer (see Chapter 16).

If three-dimensional fill is required or more extensive soft-tissue coverage is necessary, multiple flap combinations incorporating diverse tissue types may instead be the proper choice. ³⁸ The chimeric flap that has multiple adjoining flaps connected only by a common source vessel would be the best example, as each component can be independently inset wherever needed. ³⁹ This option can also relieve the risk of tension on insetting of a solitary flap, or cover an exposed microanastomosis. ⁴⁰ Another advantage of chimeric flaps is that only a single recipient site is needed for microanastomoses to the combination’s solitary source pedicle, often essential in the dysvascular or traumatized patient. Hong et al ⁴¹ have used a chimeric muscle and perforator flap for treating osteomyelitis, with the muscle filling the void after bony debridement, and the perforator flap then completing skin closure. The subscapular ⁴⁰ and lateral circumflex femoral systems ⁴² are the most versatile donor sites for chimeric flaps. In addition, any perforator flap that is supplied by a musculocutaneous perforator, since that muscle after the latter’s dissection remains relatively intact, could include in a relatively straightforward way as a chimeric muscle–perforator flap!