The sciatic nerve, the largest branch of lumbosacral plexus is composed of ventral and dorsal divisions of ventral rami of L4 to S3 spinal nerves. The sciatic nerve is formed when the large dorsal component of the sacral plexus (common fibular nerve) and the ventral component (tibial nerve) move downward close together [1, 6, and 7] and hence the common peroneal and tibial components can separate from each other at various levels from their origin [1, 6, and 7]. Various studies are available in the literatures regarding sciatic nerve variations. The present study shows five lower limbs (9 %) with two terminal branches of sciatic nerve emerging below the Piriformis muscle directly and descends separately throughout their course and in one lower limb (2 %) the common peroneal nerve emerges above the Piriformis muscle and the tibial nerve emerges below Piriformis. In a study by Shewale et al., 2 % of the specimens showed the common peroneal and the tibial nerve emerge separately below the Piriformis muscle. The tibial nerve was in the rootlet stage [17]. 15–30 % of the sciatic nerve variations in relation to Piriformis muscle are reported in the previous studies [25]. Beaton and Anson have classified the relationship of sciatic nerve to the Piriformis muscle in 120 specimens in 1937 and 240 specimens in 1948 into six types [14, 26]. Their classification is as follows:
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Type 1: Undivided nerve below undivided muscle.
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Type 2: Divisions of nerve between and below undivided muscle.
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Type 3: Divisions above and below undivided muscle.
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Type 4: Undivided nerve between heads.
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Type 5: Divisions between and above heads.
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Type 6: Undivided nerve above undivided muscle.
In our study, according to Beaton and Anson’s classification of the relation of sciatic nerve variation to Piriformis muscle, 75 % (42 specimens) belongs to type I, 9 % (5 specimens) belongs to type II and 2 % (1 specimens) belongs to type III category. Specimens of type 4, type 5 and type 6 category of Beaton and Anson’s classification are not found in our study. A rare variation of common peroneal nerve passing under the Piriformis and tibial nerve passing under the superior gemellus has been reported by Babinski [5]. This variable is not found in the present study. Various studies have been reported about the high division of the sciatic nerve in the gluteal region. Shewale et al. [17], has reported 11 % of sciatic nerve division in the gluteal region. In study by Anbumani et al. [29], nine regions (18 %) of fifty lower limbs showed variations in the sciatic nerve, of which five regions (10 %) showed a variation of the sciatic nerve in relation to Piriformis muscle. Such cases were also reported by Shashtrakar et al. [30] in their study, where the existence of high SN division in 48 % of the cases. In some gluteal regions, the TN and CPN passed through infrapiriformis portion of the greater sciatic foramen with different sheaths (20 %) and other gluteal regions with high division shows the exit of TN and CPN through different routes. Similarly, Prakash et al. [22], has also reported 16.3 % sciatic nerve division in the gluteal region. Guvencer et al. [19], has also reported that 48 % of sciatic nerve divides in the gluteal region. Moore et al. [23], has been reported that common peroneal nerve passing through the Piriformis and the tibial nerve passing below Piriformis is at 12 % of specimens. Similarly, Chiba [24], has reported that common peroneal nerve passing through the Piriformis is in 34 % of cases in 514 extremities. These above mentioned findings are in line with our study which shows high division of the sciatic nerve found in 11 % of specimens. Previous anatomical studies have demonstrated 15 % variation in the relationship between the Piriformis and sciatic nerve [25].
Trifurcation of the sciatic nerve is rarely cited in the literatures. The sciatic nerve trifurcation were revealed in three lower limbs (5 %) in this present study. In this case, the sciatic nerve terminated in the middle of the popliteal fossa by giving three branches on the right side of the male lower limb (tibial nerve, common peroneal nerve and an unusual trunk). The unusual trunk divides into the lateral cutaneous nerve of the calf and peroneal communicating nerve and in one female lower limb, trifurcation of sciatic nerve into tibial, superficial and deep peroneal nerves were observed on the left side at the superior angle of popliteal fossa. This finding is supported by Nyak [2], who showed trifurcation of sciatic nerve into tibial, common peroneal and abnormal trunk in the middle of popliteal fossa and in a case report by Sharadkumar Pralhad Sawant [11] who reported bilateral trifurcation of the sciatic nerve in the middle of the popliteal fossa into tibial, superficial peroneal and deep peroneal nerves. Moreover, our study showed five lower limbs (9 %) had three branches: tibial, common peroneal and sural nerves. In this case, the sural nerve on three lower limbs originated directly from common peroneal nerve on the left side and the other two lower limbs originated directly from the tibial nerve on the left and right side. Our finding is similar to that of Tanvi et al. [12], who reported that the variant formation of sural nerve was found in the left leg of the 50-year-old male cadaver. In this case, the medial sural cutaneous nerve and the lateral sural cutaneous nerve, after respectively deriving from the tibial and common fibular nerve, were noticed to continue their course without any formation of a unique nerve trunk on the posterior side of left leg.
In this present study,
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The Sciatic nerve variations are found in 25 % of lower.
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11 % of sciatic nerve variations are related to Piriformis.
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75 % of type 1, 11 % of type 2 and 2 % of type 3 variations of the sciatic nerve in relation to Piriformis muscle are observed according to Beaton and Anson’s classification.
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The higher divisions of the sciatic nerve in the gluteal region immediately below the Piriformis muscle are in five lower limbs.
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Common peroneal component emerges above the Piriformis muscle and tibial component arises below the Piriformis muscle in one lower limb.
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Trifurcation of sciatic nerve into tibial nerve, common peroneal nerve and an unusual trunk in two lower limbs.
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Trifurcation of sciatic nerve into tibial, superficial and deep peroneal nerves in one lower limb.
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Formation of Sural nerve only from Tibial nerve in two lower limbs.
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Formation of Sural nerve only from common peroneal nerve in three lower limbs.
Clinical significance
The variation of sciatic nerve division at different level of the body is challenging for diagnostic and therapeutic procedure in many clinical and surgical cases. Quick recognition of sciatic nerve variation makes surgical approaches more precise and effective. The anatomical variations in the level of division of the sciatic nerve require knowledge in nerve grafting for the most common surgical procedure in the popliteal region. It follows that describing the usual and the variant anatomical relationship of the sciatic nerve in the popliteal region. Its distribution is associated with different structures and blood vessels which are important to conduct a safe operation and good outcome [3, 5].
Data on the prospective variation in the anatomy of the sciatic nerve and sural nerve help surgeons in avoiding unnecessary complications. Knowledge of the unusual variety of sciatic nerve an in the present case enables the surgeon to find and preserve the nerve during fasciotomy, neurolysis, neuroma resection, or bony and soft tissue reconstruction. Surgical, Diagnosis (biopsy and nerve conduction velocity studies) and therapeutic interventions (nerve grafting) can be problematic due to the confuse on the origin of the may confuse the origin of the nerves and associated structures. Describing the origin, distribution and variation of the sciatic nerve in the lower extremities is potentially helpful for surgeons, radiologists and anatomists. Knowing the usual bifurcation anatomy as well as the possible variations of the sciatic nerve and its branches helps the radiologist and the surgeons to interpret correctly what they see and encounter in the work-up and treatment of patients with sciatica and other nerve problems. This knowledge is likely to result in more accurate, expeditious and effective diagnosis and treatment of diseases related to nerve problems with consequent reduction in paralysis of the extremities and disabilities. Therefore, the accomplishment of this study contributes to the subject of sciatic nerve variation, by confirming the previous studies and emphasizing the need of a profound anatomical knowledge and good clinical outcomes.