The leg has several characteristics that make it unique. Humans are bipedal, thus full weight bearing in the erect position is on the two lower extremities. The full force of the weight of the body is transmitted through the legs. The muscles of the leg provide ankle function with plantarflexion, dorsiflexion, eversion, and inversion. Additional leg muscle functions include toe flexion, knee extension, and knee flexion. If the ankle were fused, the functional needs of the leg muscles are greatly unnecessary. Therefore, significant muscle loss of the leg can be tolerated with maintenance of bipedal ambulation. Consequently, muscle loss of the leg is not a contraindication to reconstruction and salvage.

The hydrostatic pressures imposed on the leg increase the incidence of edema, deep venous thrombosis, and venous stasis problems. These problems are rare in the upper extremity, but common in the lower extremity. The lower extremity is also much more commonly afflicted with atherosclerosis than the upper extremity. Therefore, both venous and arterial problems are more common in the lower extremity and must be considered when developing a reconstructive plan.

The anteromedial portion of the tibia is covered by the skin and subcutaneous fat only. This relatively unprotected anatomy leads to many instances of bone exposure, which require specialized soft-tissue coverage.

Because the full force of the body is transmitted to the feet, sensibility on the plantar aspect of the foot is necessary for normal ambulation. Normal sensibility is required for tactile sensation, position sensation, and protection of the vulnerable pressure-bearing portion of the body. Loss of the tibial nerve, with loss of sensibility on the plantar aspect of the foot, is a relative contraindication for lower extremity salvage. However, many patients with peripheral neuropathy are able to ambulate. They must remain cognizant of the potential problems; motivated patients can reasonably enjoy normal ambulation without soft-tissue breakdown. Thus, in selected patients, loss of sensation of the plantar aspect of the foot may not be an absolute contraindication for lower extremity salvage.

The bones of the leg are the tibia and the fibula. The tibia provides 85% of the weight-bearing capacity of the leg, whereas the fibula serves as a structure for muscle and fascial attachments and as a significant structural portion of the ankle joint.

The tibia is the second longest bone in the body. It articulates with the femur at the knee joint on two condyles and joins the fibula to articulate with the talus to form the ankle joint. It articulates with the fibula proximally at the tibiofibular joint and distally at the tibiofibular syndesmosis. The tibia is connected to the fibula in its midportion with the interosseous membrane. It is a classic long bone with a diaphyseal shaft with a thick cortical bone surrounding a marrow cavity. The tibia is wide proximally where it articulates with the femur and narrows to the shaft. The diaphyseal portion is usually described as three surfaces: medial, lateral, and posterior. The medial border is subcutaneous, and thus most prone to exposure during injury. The lateral surface is one of the origins of the tibialis anterior muscle and is protected by the anterior compartment muscles. The posterior surface is well protected by the soleus and gastrocnemius muscles.

The fibula is the smaller bone of the leg. It originates slightly posterior and distal to the tibia and it articulates with the posterolateral tibia. The shaft of the fibula serves as the origin of many of the muscles of the leg. Distally, it articulates with the talus and forms the lateral malleolus. Because the fibula is not weight bearing and is in a relatively protected position, it is of less concern in trauma, except when the lateral malleolus is involved. Only the proximal and distal portions of the fibula are required, and because of an independent blood supply from the peroneal artery, the central portion of fibula is an excellent source of vascularized long bone and can be sacrificed readily.

The anatomy of the leg is best understood by dividing it into its four muscle compartments: anterior, lateral, posterior, and deep posterior. The deep fascia of the leg forms discrete areas or compartments (Table 94.1 and Figure 94.1).

The anterior compartment is comprised of four muscles: the tibialis anterior, the extensor hallucis longus, the extensor digitorum longus, and the peroneus tertius. All four muscles dorsiflex the foot, but the primary dorsiflexor is the tibialis anterior, which also inverts the foot. The extensor hallucis longus primarily extends the great toe; further contraction causes foot dorsiflexion. The extensor digitorum longus extends the phalanges of the lateral four toes and dorsiflexes the foot. The peroneus tertius dorsiflexes and everts the foot. All four muscles are innervated by the deep peroneal nerve, and their blood supply is from muscular branches of the anterior tibial artery.

The lateral compartment is comprised of the peroneus longus and peroneus brevis muscles. Both muscles plantarflex and evert the foot. They are both innervated by the peroneal nerve. The vascular supply of the peroneus longus is the muscular branches of the anterior tibial and peroneal arteries. The vascular supply of the peroneus brevis is muscular branches from the peroneal artery.

The superficial posterior compartment is comprised of the gastrocnemius, soleus, plantaris, and popliteus muscles. They are all innervated by the tibial nerve. The gastrocnemius muscle plantarflexes the foot and flexes the knee. Its blood supply
is from sural branches of the popliteal artery. The soleus muscle plantarflexes the foot and is supplied by the muscular branches of the posterior tibial, peroneal, and sural branches of the popliteal artery. The plantaris muscle plantarflexes the foot and is supplied by the sural branches of the popliteal. The popliteus flexes the knee and rotates the tibia and is supplied by genicular branches of the popliteal.

The deep posterior compartment is comprised of the flexor hallucis longus, flexor digitorum longus, and tibialis posterior muscles. They are all innervated by the tibial nerve. The flexor hallucis longus flexes the great toe and aids in plantarflexion of the foot. It is supplied by muscular branches of the peroneal artery. The flexor digitorum longus flexes the phalanges of the lateral four toes and aids in plantarflexion of the foot. It is supplied by the branches of the posterior tibial artery. The tibialis posterior plantarflexes and inverts the foot. It is supplied by muscular branches from the peroneal artery.

Compartment syndrome is an increase in interstitial fluid pressure within an osseofascial compartment of sufficient magnitude to cause a compromise of the microcirculation, leading to myoneural necrosis. Any crush injury to a closed compartment may lead to compartment syndrome. The literature indicates an incidence of compartment syndrome of 6% to 9% in open tibial fractures. It is important to realize that a laceration with an open fracture may not provide adequate decompression to prevent compartment syndrome.

The cardinal signs of compartment syndrome are pain disproportionate to the injury, pain on passive flexion or extension, and palpably swollen or tense compartments. Loss of pulses is a late sign and the presence of pulses does not rule out compartment syndrome. The definitive diagnosis is made by measuring the compartment pressure.

Various methods have been used to measure the intercompartmental pressure, including slit catheters and saline injection techniques. Although commercially produced units are available, an 18G needle flushed with saline and connected to a transducer is usually adequate. The threshold for fasciotomy is controversial. Some surgeons consider a pressure >30 mm Hg in any compartment as an indication for fasciotomy. Allen et al. considered fasciotomy when the compartment pressure was >40 mm Hg for 6 hours or was >50 mm Hg for any length of time.11 Four-compartment fasciotomy should be performed when there is any index of suspicion of compartment syndrome, as the morbidity of a fasciotomy is far less than the morbidity of ischemic necrosis of the lower extremity secondary to an untreated compartment syndrome.

Classification of open tibial fractures in relation to fracture pattern and soft-tissue injury is useful in describing injuries and prognosis. The most commonly quoted classification for open fractures is that of Gustilo (Table 94.2).

A grade IIIA injury is an open fracture with soft-tissue damage. Because it is classified as having adequate soft-tissue coverage of the fracture, it rarely requires complex plastic surgical procedures. These injuries are usually treated with local wound care, debridements, skin grafts, or simple local flaps. A grade IIIB injury involves an open fracture with periosteal stripping and bone exposure. A grade IIIC injury is an open
fracture associated with an arterial injury requiring repair. Although this is the most commonly quoted classification, it remains woefully inadequate to describe the injury or to evaluate the prognosis of an open tibial fracture for which the plastic surgeon is involved. An open tibial fracture with 3 cm of periosteal stripping and exposed bone (Figure 94.2A) is not the same as an open tibial fracture with an 8-cm bone gap, 12 cm of exposed bone, and necrosis of 16 cm in all four-compartment muscles (Figure 94.2B), though they would be both classified as grade IIIB injuries. Similarly, the phrase “arterial injury requiring repair” in the classification of a grade IIIC injury is ambiguous. Some surgeons may believe it is necessary to repair a second vessel in a one-vessel leg, whereas others believe that a single vessel is an adequate blood supply to the foot. In the first case, the injury would be classified as grade IIIC; in the second case, as grade IIIB. The classification does not tale nerve injury into consideration, which is crucial in the assessment of prognosis.