Definitive soft tissue management

10. Definitive soft tissue management

The overall aim of soft tissue management is to provide stable wound coverage with an acceptable appearance and minimal donor site morbidity. Choice of the type of soft tissue coverage is dependent on the extent and location of the open tibial injury and patient factors such as age and co-morbidities. In circumstances such as type I, type II and even type IIIa open fractures, primary closure is often appropriate if the size of the wound and skin defect is localised (Kamath et al., 2012).

In type IIIb and IIIc fractures with large wounds with appreciable skin defects and exposed bone and tendon, more complex techniques are often necessary. These may include local or microvascular free flap reconstruction (Kamath et al., 2012; Boyce & Shokrollahi, 2006).

However, the principles of soft tissue management remain the same: thorough wound debridement, control of wound infection by appropriate antibiotic treatment and coverage with healthy donor tissues harvested from outside the zone of injury. In high-energy tibial fractures, definitive soft tissue reconstruction should ideally be undertaken within 72 hours of the original injury and within a maximum of 7 days after the original injury to reduce the risk of osteomyelitis and fracture non-union (Ong & Levin, 2010).

10.1. Local flaps

A flap is a unit of tissue that can be transferred to cover a wound while maintaining its own vascular supply (Boyce & Shokrollahi, 2006). Flaps can be classified in several different ways. One way is to categorise them according to their circulation: they can be random pattern (no directional blood supply, common in the face) or axial, including fasciocutaneous and musculocutaneous flaps. The latter are particularly useful for covering defects in the proximal two-thirds of the lower limb.

10.2. Local muscle flaps

Muscle flaps can be classified according to their blood supply. Five different types were classified by Mathes and Nahai (Mathes & Nahai, 1981). Type I flaps are supplied by a single vascular pedicle such as the gastrocnemius. The soleus is classified as type II because it has one dominant pedicle and minor pedicles. Both these muscles are found in the superficial posterior compartment of the leg. The gastrocnemius, and less commonly the soleus, can be used for local flap reconstruction in complex open tibial fractures because of their good blood supply.

The gastrocnemius muscle has two heads (medial and lateral) arising from the medial femoral condyle and lateral femoral condyle, respectively. As the blood supply to this muscle is derived from the sural vessels above the knee, either head can theoretically be used to cover small defects of the knee and proximal tibia. In practice, the medial gastrocnemius muscle is most commonly used to cover defects in proximal third tibial fractures because it is larger and longer than the lateral head (Kamath et al., 2012). The functional deficit on locomotion of losing one head of the gastrocnemius muscle is minimal.

The soleus muscle is located deep to the gastrocnemius muscle, and only half of the muscle (hemi-soleus) is usually harvested as a muscle flap in order to preserve muscle function (Hyodo et al., 2004). It is easily and readily available and transposes well over large defects along the middle third of the tibia. Because of the arc of rotation, muscle flaps considerably larger than the defect are required in order to provide adequate coverage. Neither the gastrocnemius nor the soleus muscle flap is generally considered appropriate for the distal third of the leg.

A small defect over the middle tibia may rarely benefit from a turnover flap of the tibialis anterior muscle. Due to its segmental and less reliable blood supply (type IV), the tibialis anterior muscle should be split longitudinally, leaving an intact tendon. Furthermore, this muscle is extremely important in dorsiflexion of the foot and is thus less preferable to other local muscle flaps.

The major problem with using local muscle flaps is that in extensive open wound injuries such as Gustilo IIIb and IIIc, the donor muscles are often severely injured and thus not available for transfer.

10.3. Fasciocutaneous flaps

Fasciocutaneous flaps are based on vessels running in close association with or within the fascia. They are commonly derived from the limbs and were categorised by Cormack and Lamberty into four types (A–D) according to the pattern of their blood supply (Cormack & Lamberty, 1984). Fasciocutaneous flap options in the lower limb include the saphenous flap and the medial or lateral distal fasciocutaneous flap. The most commonly used flap is a distal medial fasciocutaneous flap.

This is most reliably based on the posterior tibial artery perforator arising approximately 10 cm above the medial malleolus, which is why the correct placement of fasciotomy incisions, when required, is paramount (see section 6). Saphenous flaps are useful for covering small defects around the proximal tibia in low-energy tibial fractures where the vasculature has not been compromised by the zone of injury or by degloving. The length of the flap can extend down the leg as far as the 15-cm perforator arising from the posterior tibial artery. Fasciocutaneous flaps are insufficient to cover large defects requiring well-vascularised soft tissue coverage. In this case, the donor site will usually require a split-thickness skin graft.

10.4. Microvascular free flap reconstruction

A free flap is a unit of tissue harvested with its blood supply from a distant site in the body. It is completely detached from the source vessels and subsequently anastomosed to recipient vessels close to the defect using microsurgical techniques.

Microvascular free flap reconstruction has an important role in the management of high-energy lower limb trauma with associated bone, soft tissue and muscle loss as a result of its ability to provide versatile healthy tissue that can fill dead space and provide additional vascularity to the wound. Free flaps are particularly useful in the management of fractures involving the distal third of the tibia, ankle and foot, where local reconstructive options are limited.

In all cases, thorough debridement of contaminated or devascularised tissue from the site of injury is mandatory prior to free flap reconstruction. Investigations such as computed tomography angiography and plain angiography afford the analysis of distal arterial blood flow, thus allowing appropriate pre-operative planning. Microvascular free flap reconstruction should take place in a specialist centre on a scheduled daytime theatre list by plastic surgeons experienced in microsurgical techniques.

The most common free flaps selected for reconstruction of the lower limb include the anterolateral thigh flap, often used as a chimeric flap with the vastus lateralis muscle which provides a rich blood supply to the fracture site (see below); the free radial forearm flap; and the latissimus dorsi and gracilis muscle free flaps. The rectus abdominis free flap is now less frequently used for reconstruction of the lower limb.

Recipient vessels must be carefully selected from outside the zone of injury to prevent post-operative thrombosis and end-to-side anastomosis should be performed where possible to preserve circulation to the distal limb.

Microvascular flap tissue transfer in the management of open tibial fractures was traditionally reserved for circumstances in which local or regional flap reconstruction was not feasible owing to the technically demanding nature of the surgery, longer operative time, greater medical complication rates, longer hospital stay and high incidence of flap loss (Kamath et al., 2012).

However, evidence now suggests that in experienced hands in specialised centres there are actually fewer complications with free flaps than with fasciocutaneous flaps and that patients previously thought to be inappropriate candidates for microvascular transfer, such as elderly patients and those with diabetes or peripheral vascular disease, are in fact most prone to complications following local flaps. No randomised clinical studies have compared the use of local fasciocutaneous flaps and free flaps. However, available experimental evidence from animal models favours muscle flap coverage for open tibial shaft fractures to promote more rapid bony healing when compared with fasciocutaneous flaps, which may be best reserved for coverage of metaphyseal fractures, particularly at the ankle.

The division between local fasciocutaneous flap and free muscle transfer has become increasingly blurred with the growing use of the anterolateral thigh flap, which can be raised as a chimeric flap to include a portion of vastus lateralis muscle. This is a particularly attractive option for the reconstruction of complex lower limb soft tissue defects because it not only provides well-vascularised healthy muscle from outside the zone of injury with a skin paddle, but has the added benefit of avoiding an unsightly skin grafted donor site that is typically associated with the local fasciocutaneous flap (Ong & Levin, 2010). Table 8.1 summarises some of the common options for soft tissue reconstruction by zone of tibial injury (proximal, middle and distal thirds of the lower limb) (Park et al., 2009).

Table 8.1. Local or distant flap recommendations based on zone of injury and type of soft tissue defect.

SSG = split skin grafting.