3. Discussion
Researchers have reported many variations of the sciatic nerve and the relationship between this nerve and the piriformis muscle. Ignoring these variations can cause irreparable damages to patients. SU Rao et al. reported that sciatic nerve in 16% (8 limbs of 50 dissected lower limbs) of cases bifurcates at a higher level (in the gluteal region after emerging below the piriformis [7 limbs] or at lower one-third of the back of the thigh [1 limb]). Other studies reported this type of variation 13.7% (
Gabrielli, Olave, Mandiola & Rodrigues, 1997), 4% (
Ugrenović et al., 2005), 20.9% (
Pokorný, Jahoda, Veigl, Pinskerová & Sosna, 2006), 16.3% (
Prakash et al., 2010), 48% (
Güvençer, Iyem, Akyer, Tetik & Naderi 2009), 20.1% (
Ogeng’o, El-Busaidy, Mwika, Khanbhai & Munguti, 2011), 8% (
Adibatti & Sangeetha, 2014),18% (
Anbumani et al., 2015), and 31.66% (
Budhiraja et al., 2016). In Bryan Jason Bergsteedt study, 170 South African cadavers (340 lower limbs) were dissected to assess anatomical variations in relation to the piriformis and sciatic nerve bifurcation among the South African population. She reported that in 21.4% of cases, sciatic nerve bifurcation has not occurred in the popliteal fossa (
Bergsteedt, 2019). These studies show that this type of variation ranges from 4% to 48%, suggesting that race can play a unique role in anatomic variations.
Another anatomic variation in the more clinically important region is the relationship of the sciatic nerve with the piriformis muscle. Beaton and Anson classified six variants regarding the anatomical relationship between these two structures: type 1, an undivided sciatic nerve below the piriformis muscle (normal course); type 2, a divided sciatic nerve passing through and below the piriformis muscle; type 3, a divided nerve passing above and below an undivided muscle; type 4, an undivided sciatic nerve passing through the piriformis muscle; type 5, a divided nerve passing through and above the muscle heads; and finally type 6, the undivided sciatic nerve passes above the piriformis muscle (
Beaton & Anson, 1938). The right and left sides of the present case can be considered as subgroups of types 1 and 6, respectively. Types 1, 2, and 3 have been reported frequently in literature. The other types are rarer (less than 1% of the populations studied) (
Tomaszewski et al., 2016). Types 5 and 6 were only hypothesized and not seen in Beaton and Anson’s study sample.
In the present case, the high division of the sciatic nerve was observed both in the right and left sides. Besides, on the right side, there was a thick inferior gluteal nerve medial to terminal branches of sciatic nerves that its diameter was nearly equal to the tibial and common peroneal nerve. However, the injury of the inferior gluteal nerve is rare but often happens as a complication of posterior approach in hip replacement. Indeed, such a thick inferior gluteal nerve increases the risk of nerve injury during such procedures.
On the left side, tibial and common peroneal nerves have emerged above the piriformis muscle. We know that intramuscular injection is an essential procedure for administering a variety of medications (
Ramtahal, Ramlakhan & Singh, 2006), and unfortunately, injury to the sciatic nerve is a worldwide problem resulting from a misplaced intramuscular injection in the gluteal region (
Mishra & Stringer, 2010). In the present case that the emerging point of the sciatic nerve parts in the gluteal region is nearer to the safe area of muscular injection, the risk of nerve injury increases noticeably, and such variations are very important clinically. On the other hand, local injection to piriformis is used to manage piriformis syndrome (
Benzon, Katz, Benzon & Iqbal, 2003). If such a variation exists in a candidate for this treatment, the risk of nerve damage is very high.
The other variation in the left side was the vertical route of the common fibular nerve (It did not cross the head and neck of the fibula and reached the lateral aspect of the leg nearly 5 cm below the fibular head). Although such a route reduces the nerve injuries due to proximity of head and neck of fibula, it increases the risk of its cutting in upper leg surgeries.
Although some of these variations, like division of sciatic nerve in the pelvis, are more common, and some are relatively rare, a collection of these variations in a single cadaver is unique and has not been reported ever.
4. Conclusion
Medical students, as future physicians and nurses, learn in gross anatomy classes a general description of the human body, and soon, they will diagnose and treat all patients based on this knowledge. It is often overlooked that anatomy is a description of most people’s bodies and not all of them. In the case of the gluteal region, what students learn about the sciatic nerve and its relation with piriformis muscle may be quite different from what they will experience in the clinic and operating room. Anatomical variations of the sciatic nerve, at least partly, contribute to some injuries to the gluteal region by the medical team. So having up-to-date knowledge of anatomical variations of the region is necessary to reduce this type of injury.
This case report indicates that peripheral nerve distribution patterns may be different to a great extent from what students learn as normal anatomy of the human body. This concept can promote the vision of our future physicians, nurses, and other medical team members in selecting better diagnostic and therapeutic procedures for patients. Finally, medical progress needs more accurate knowledge of the human body variations to improve diagnosis and therapeutic management (
Khanday, 2019).
Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of Sabzevar University of Medical Sciences (Code: IR.MEDSAB.REC.1399.038).
Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.
Authors' contributions
Both authors equally contributed to preparing this article.
Conflict of interest
The authors declared no conflict of interest.
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