The SN has great individual anatomical variability [15]. The SN formation patterns and the SN location may vary. Therefore, the possibility of anatomical variations should be considered in both clinical and surgical areas [8].
We found Type 4 in most of the lower limbs evaluated. Previous studies performed on fetuses corroborate this, as exemplified by Büyükmumcu et al. and Ulcay et al. [4, 29], which show a high prevalence of this anatomical pattern. Studies in adults have ratified this information and set Type 4 as the classic pattern [1, 5, 6, 14, 17, 23, 31]. Thus, we hypothesize that Type 4 is present in the fetal population and remains stable until adulthood. Furthermore, the studies conducted on fetal and adult people are studies of Asian ethnicity; thus, there is an Asian influence on the cadaver sample studied. Only one study [21]—with an adult population, European ethnicity, and anatomical assessment by ultrasound—showed a lower frequency of Type 4.
In the current study, Type 1 was the second most frequent pattern, as in all previous studies analyzed with fetal populations [7, 28]. However, Type 1 had a lower prevalence in the adult population, according to Olave et al. [18] and Popieluszko et al. [21], but had a high prevalence in the studies by Mestdagh et al. [15], Nieto et al. [16], and Sekiya et al. [25]. Thus, LSCN may likely present branching like FCB, with a higher prevalence in fetal samples.
Type 6 was reported in all previous articles in both fetal and adult populations. This pattern was found in seven studies with Asian samples [10, 12, 14, 17, 24, 26, 31] and five studies with Eurasian ethnicity, all from Turkey [1, 2, 4, 7, 29]. However, only three European studies showed Type 6 [15, 21, 28]. Type 6 may be present in the Asian, European, and South American (Brazilian) populations.
Bilateral symmetry of the SN formation pattern was highly prevalent in prior studies [5, 7, 10, 26, 29]. This agrees with our results, which showed high symmetry between the patterns of nerve formation. However, Mahakkanukrauh et al. revealed high bilateral asymmetry in their study [14]. This variation, compared to the higher prevalence of symmetry in the other articles, may be associated with the Asian geographical subgroup or the studied sample number of this single article with high asymmetry. Thus, the existence of the bilateral asymmetrical distribution requires researchers to evaluate both lower limbs in future anatomical studies [21].
Many studies have described variations in SN anatomy, focusing mainly on the SN location for surgical procedures [1, 3, 11, 18, 19, 22]. However, in the clinical area, this nerve is widely used for diagnostic, such as in nerve conduction studies (NCS) and biopsies [14].
During electrodiagnostic testing, the antidromic technique of the NSC applied to the SN is useful to diagnose generalized or focal neuropathies [23], such as compressive, post-traumatic, diffuse polyneuropathic, lumbosacral plexus, and sciatic and tibial nerve injuries [27]. Sural nerve variations can influence the stimulation of SN complex and affect the amplitude and latency parameters of the sensory nerve action potential, causing erroneous and misinterpretations of diagnostic findings [23]. Sural nerve biopsy is a valuable method to investigate the cause of peripheral neuropathies [12].
The SN formation site was also studied. Uluutku et al. stated that SN formation was most common in the middle third of the leg [30]. Büyükmumcu et al. reported similar results [4]. Mestdagh et al. [15] reported nerve branch communication more frequently in the distal half of the leg. Nuri et al. [17] reported most of the medial and lateral branch junctions in the distal leg, and Eid et al. [8] reported that the joining between MSCN and FCB was more prevalent in the distal leg. Similarly, our study reported that branch union was more common in the distal leg.
Surgeons recognize the SN and its components as ideal for grafting [24]. Using the SN graft in treating peripheral nerve injuries is broad for facial paralysis, post-obstetric brachial plexus palsy, and post-traumatic injuries [4, 30]. Depending on anatomical variations, surgical procedures or incisions for reconstructions or repair of the CT, subtalar arthrodesis, and distal fibula fractures [1] can injure the SN or its branches. Therefore, researchers report the need to use anatomical knowledge and ultrasonography preoperatively for the surgical success of procedures [3, 11, 21, 31].
The present study was limited in the analysis of the SSV course in relation to the SN due to the sample (40 lower limbs). This small sample was because of the difficult visibility of the SSV in fetuses with lower gestational age and the ease of venous injury during dissection.