Sciatic Nerve variation: case report

Introduction The Sciatic Nerve(SN) is the largest nerve in the human body. It arises from the Sacral Plexus, formed from the ventral and dorsal branches of the ventral rami of L4 to S3 spinal nerves. It exits the pelvic cavity passing through the Greater Sciatic Foramen, below the Piriformis Muscle(PM), between the Ischial Tuberosity and the Greater Trochanter of the Femur. On its course, the SN gives lateral branches, which are responsible for the movement and sensitivity of the posterior part of the lower limb. The terminal bifurcation, the Common Fibular Nerve(CFN) and the Tibial Nerve(TN), can occur at different height, from the Sacral Plexus to the lower part of the Popliteal Region, most common. Background Since the beginning of the XX century, many anatomical variations have been reported by several authors such as Cruveilhier, Testut and Le Double. The most comprehensive approach is the Beaton and Anson's classification, which consists of 6 types of relations of the SN with the PM in the pelvic cavity, Type 1: Undivided nerve below undivided PM; Type 2: Divisions of the nerve between and below undivided muscle; Type 3: Divisions above and below undivided muscle; Type 4: Undivided nerve between heads; Type 5: Divisions between and above heads; Type 6: Undivided nerve above undivided muscle. It has served as a reference for medical doctors to characterize their cases. A different interpretation suggests the variations of the height as a result of a low formation of the nerve, rather than a high terminal division. Several cases of SN variations were reported according to the height of the division. In one of them, the SN was dividing just at the upper border of the Quadratus Femoris Muscle in the Gluteal Region, as in our specimen. Results In our case, the lower limb of a Brazilian male cadaver with no evidence of previous pathologic disorders, traumatic condition or surgical intervention, was dissected, which the gluteus maximus and the medium were sectioned vertically, parallel to the Sacrum, and reflected, to obtain a clear view of the SN. SN was coursing down for 7,93cm (from the lower border of the Greater Sciatic Foramen). It divides into CFN and TN below the border of PM, at the caudal border of the Quadratus Femoris Muscle. We characterized this variation as a high division. Three palpable points were used to localize the division. We present the distance from the bifurcation to each point (Figs. 1A, 1B, 1C): I.Iliac Crest, 17,3cm; II. Greater Trochanter, 6,7cm; III. Ischial Tuberosity, 3cm. Therefore, the anatomical relationship between the SN and the PM was recorded and classified according to the Beaton and Anson classification as type I. Discussion and Conclusion The knowledge of the variation of the SN, its location and course is fundamental in daily medical practice of Neurology, Orthopedics, Rehabilitation, Sports Medicine, Surgery and Anesthesiology. These studies have critical importance due to common pathologies such as Piriformis Syndrome, defective block anesthesia and any kind of therapeutic intervention of the area. Great knowledge is required for optimal clinical outcomes. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .