Relevant anatomy (muscles)
The anterior and peroneal muscle compartments are approached via an anterolateral incision: the superficial and deep posterior compartments are approached through a separate medial incision.
A good knowledge of the disposition of the four compartments and the muscles within them is essential to safe decompression.
It is important to protect subcutaneous nerves, particularly the common peroneal where it crosses the fibula proximally.
Relevant anatomy (neurovascular structures)
The principle superficial neurovascular structures at risk in these approaches are, medially, the great saphenous vein and its accompanying nerve, and laterally, the superficial peroneal nerve. The superficial peroneal nerve branches from the common peroneal nerve near the neck of the fibula and passes between the peroneus longus and brevis muscles, supplying motor branches to these muscles. The superficial branch then continues onto the dorsum of the foot to supply sensory fibers to the skin there.
The main deep neurovascular bundle at risk is the posterior tibial, as it lies on the posterior aspect of the tibialis posterior and flexor digitorum longus muscles, and medial to the belly of flexor hallucis longus. Remember this is more superficial at the medial ankle.
The two posterior compartments are approached through a single longitudinal incision in the lower leg, two centimeters behind the palpable posteromedial edge of the tibia.
After reaching the fascia, undermine anteriorly to the posterior tibial margin, in order to avoid the saphenous vein and nerve. The deep posterior compartment here is superficial and readily accessible.
The fascia of the deep posterior compartment is carefully opened distally and proximally, under the belly of the soleus muscle, paying special attention to the posterior tibial neurovascular bundle.
Through the same incision, the fascia of the superficial posterior compartment is opened widely, two centimeters posterior and parallel to the incision in the fascia of the deep compartment.
The anterior and lateral compartments are approached through a single longitudinal incision on the outer aspect of the leg, two centimeters anterior to the fibular shaft and long enough to expose the whole length of the compartments. The incision lies approximately over the anterior intermuscular septum that divides the anterior and lateral compartments and allows easy access to both.
A small incision is made in the fascia of the anterior compartment, midway between the septum and the tibial crest. The fascia is opened proximally and distally, respecting any visible superficial nerve.
The lateral compartment fasciotomy is in line with the fibular shaft. Directing the scissors towards the lateral malleolus helps avoid the superficial peroneal nerve as it exits from the fascia in the distal third of the leg near the septum and courses anteriorly. Look for this nerve, which may be branched, and protect it.