The gluteus maximus muscle is then retracted superiorly and hinged medially to expose the sciatic nerve as it exits beneath the piriformis muscle and leaves the pelvis. The sciatic nerve is identified by carrying the incision distally and following the nerve proximally. Many variations occur in the sciatic nerve's relationship to the piriformis muscle: the piriformis muscle occasionally passes between the two divisions of the nerve, but most commonly the nerve courses below this muscle. The inferior gluteal artery should be identified and protected because it contributes to the blood supply of the sciatic nerve. In the posterior thigh, the sciatic nerve is easily exposed with a vertical incision. In the midthigh, the biceps femoris muscle passes over the nerve. The integrity of this muscle should be preserved. In the distal aspect of the thigh, the biceps femoris muscle is retracted laterally. More proximally, the biceps muscle is retracted medially. The posterior femoral cutaneous nerve is maintained by medial biceps femoris muscle retraction, thus leading to no additional sensory loss. Once the sciatic nerve is dissected, an attempt to divide its two major branches, the common peroneal and tibial nerves is undertaken. This facilitates repair by allowing for two separate anastomoses. In many cases, only one part of the nerve requires repair, while the other simply requires a careful neurolysis. By using the techniques of intraoperative nerve action potential recording, intraoperative decision-making is facilitated. The more distal aspect of the sciatic nerve in the thigh is easily exposed through a curvilinear incision over the popliteal fossa. The common peroneal and tibial branches are readily identified between the biceps femoris muscle laterally and the semitendinosus and semimembranosus muscles medially. By dissecting under the biceps femoris muscle and working proximally, the nerve can be completely freed from surrounding tissue. The femur in this region is directly below the nerve and can be readily palpated.
In the distal leg, the common peroneal and tibial nerves have already divided. The common peroneal nerve hugs the border of the biceps femoris muscle as it descends on the fascial attachments next to the fibula. The nerve then passes around to the lateral aspect of the proximal fibula. The common peroneal nerve is palpable just below the prominence of the fibular head. It passes below the extensor digitorum longus and the peroneus muscles. The superficial branch maintains a lateral course and innervates the cutaneous aspect of the dorsum of the foot.The deep peroneal nerve is the more important branch. It innervates the extensors of the toes. The tibial nerve descends through the midportion of the popliteal fossa between the heads of the gastrocnemius muscle into the back of the leg. Two important cutaneous branches are found at the point of bifurcation of the sciatic nerve into distinct entities of the common peroneal nerve and the tibial nerve. The lateral cutaneous sural nerve arises from the common peroneal nerve, and the medial cutaneous sural nerve arises from the tibial nerve. Often these two branches will rejoin as the common sural nerve. If these branches are observed to be intact during the exposure of this region, they should be preserved.
Exposure of the common peroneal nerve in the popliteal fossa is accomplished with a curvilinear incision. In this manner, the incision does not directly cross the region of the popliteal fossa. The nerve's course, once the subcutaneous tissue is penetrated and flaps are raised, is easily identified on the medial and inferior aspect of the biceps femoris muscle. It then passes lateral to the lateral head of the gastrocnemius muscle. Once beneath the fibular head, a small recurrent articular branch is observed. It then divides into its two major branches: (1) the deep peroneal nerve supplies the tibialis anterior muscle and the extensors of the toes; (2) the superficial peroneal nerve provides two small branches to the peroneus longus and brevis muscles and is responsible for sensation on the dorsum of the foot. The most common location for peroneal nerve injury is just below the fibular head and below the large attachment for the biceps femoris muscle. Beneath the fibular head, there is a groove under which the common peroneal nerve passes. It is in this groove that the nerve is commonly injured. The injury may be as trivial as a minor blow, may be caused by squatting for a prolonged period of time, or may be a result of cast compression. The common peroneal nerve is very vulnerable to injury as it passes over (around) the fibular head.
The most frequent operation on the common peroneal nerve in this area is a release of the distal fascia over the nerve with an accompanying external neurolysis. A curvilinear incision is used for the exposure of the nerve, beginning in the popliteal fossa. It is curved downward on the lateral aspect of the thigh. A cutaneous flap is raised. An external neurolysis may then be performed distally to where it branches into its deep and superficial components. The common peroneal nerve is essential for dorsiflexion of the foot. While foot drop can be treated with a cock-up splint and brace, aggressive attempts at the restoration of nerve function is desirable in younger patients. A more distal exposure is needed for anastomotic repair of the common peroneal nerve. The knee joint can be flexed to as much as 70°- 80° in order to obtain a relaxed nerve. The leg is casted for 3 weeks in this position. The cast is then removed and a splint applied so that the leg is not overextended for the next 2-3 weeks. Physical therapy is used in order to obtain full mobility of the knee. On rare occasion, the deep peroneal nerve can be injured focally. This nerve is located on the lateral border of the fibula and adjacent to the extensor digitorum longus muscle. At this point the anterior compartment of the leg is vulnerable to pressure and compression. A syndrome of anterior tibial compartment compression is characterized by severe pain, swelling, and discoloration over the anterior aspect of the leg and over the foot with strenuous activity. Weakness of foot dorsiflexion may be present. The treatment of this condition it to enlarge the osseous fascial compartment where the nerve is entrapped along with the artery. Following decompression, the patient should be relieved of the symptoms of the so-called "shin splints".
The incision for this exposure is over the palpable tibialis anterior muscle. The dissection is carried distally between the tibialis anterior and the extensor hallucis longus muscles. Once the deep peroneal nerve is exposed, the anterior tibial artery and vein are visualized. By simply separating the strong fascial planes in this area, a neurolysis can be achieved.
The tibial nerve lies directly in the midline of the popliteal fossa. It courses between the two heads of the gastrocnemius muscle to lie between the flexor digitorum longus and the flexor hallucis longus muscles. Just distal to the knee posteriorly, the tibial nerve divides into many branches. These include two branches to the gastrocnemius muscle and branches to the popliteus muscle and the plantar flexors of the foot. Further distally, the branches to the flexor digitorum longus and hallucis longus muscles become apparent. The deep aspect of the tibial nerve continues distally. Near the ankle, it may be entrapped in a similar manner to median nerve entrapment in the carpal tunnel syndrome.
The approach to the tibial nerve in the popliteal fossa is best made through a Z-plasty type of exposure. Further distally, an incision along the medial border of the gastrocnemius muscle can be used for exposure of the tibial nerve in the dorsal midline. Once the incision is carried through the fascia, the medial border of the gastrocnemius muscle can be retracted to expose the popliteus and soleus muscles. It is necessary to dissect through some of the fibers of the soleus muscle to visualize the medial aspect of the transverse intermuscular septum. Once this fascial layer is opened vertically, the tibial nerve is easily exposed directly behind the tibia. Following its exposure, distal dissection of the tibial nerve is carried out with ease.
At the level of the ankle, the tibial nerve can be entrapped in the "tarsal tunne1." The nerve is simply exposed around the medial malleolus through the thick fascial planes which support the ankle. The strong flexor retinaculum on the medial aspect of the ankle needs to be opened in order to fully decompress the nerve in this area. Rarely is it necessary to take down the muscular attachments of the gastrocnemius muscle in order to obtain exposure of the nerve in the popliteal fossa and in the more medial aspect of the leg itself. The tibial nerve, as it leaves the popliteal fossa, passes under a tendinous arch of the soleus muscle. This should be opened. The nerve then descends beneath the transverse intermuscular septum where it overlies the tibialis posterior muscle proceeding toward the medial malleolus. The distal aspect of the tibial nerve can be entrapped under the retinaculum beneath the medial malleolus.
There are many anatomical variations of peripheral nerves of the lower extremity. Only by studying a variety of textbooks, both old and new, can the patient's particular problems often be appreciated. This allows for the best possible patient care. It is important to notice that the sural and the saphenous nerves can bridge the gap between three-four levels of anastamosis, eliminating during that the need for two donors in the surgical treatment of paraplegia below D8. It is important to mention that the targeted nerves, must be long, minimally branching and cause no harm to the patient after harvest.