This study aimed to assess the SFN anatomy. The existence and pooled prevalence of two branching patterns of this nerve with regard to the deep fascia and five branching patterns concerning the ankle joint level have been reported. Knowing these anatomical variations is of great importance to avoid iatrogenic injuries to this nerve in ankle and leg surgical procedures, just as for the proper performance of regional anesthesia on the leg and foot.
SFN is the most commonly injured structure in ankle arthroscopy due to its high anatomical variability [3, 18, 32]. Considering the level of the ankle joint, type 1 and type 3 were more prevalent in Asian populations (26% and 12.4%, respectively), while type 2 was more common in South American populations (69%). Type 4 was most prevalent in populations from Oceania (17.5%), and type 5 was most common in populations from North America (10.2%). Significant differences were found between the aforementioned geographical groups. These data may indicate the need for caution when performing surgical procedures, since the SFN anatomy may vary by geography.
An important clinical application of SFN anatomy is in entrapment syndrome of this nerve. This clinical condition may occur when this nerve pierces the deep fascia to become subcutaneous at the leg distal third and is compressed by this fascia at its emergence site [17]. The basis of the symptomatology of this syndrome is due precisely to the point at which the SFN emerges from the deep fascia [30], as this is the most common site of nerve entrapment [14]. The anatomy of this nerve has a direct influence on the symptomatology and therapeutics in this entrapment syndrome. Subgroup analysis showed that type 1 was more prevalent in all geographical subgroups, with significant differences between all these groups. These data may alert to caution with fascial release procedures in patients of different nationalities.
Another important therapeutic application of SFN is for its use as a nervous graft [17, 24], although it is still underestimated for this [36]. Nervous grafts are the better option for filling the space left between proximal and distal stumps of an injured peripheral nerve. SFN provides a lengthy graft and also has a relatively foreseeable course. Also, it can be harvested without major problems for the donor, as the lack of its sensory portion only affects the sensitivity of the dorsum of the foot [24]. Knowing the anatomical variants of this nerve ensures, in addition to better nerve utilization, a greater chance of preventing injuries to the distal branches involved in its harvesting procedure [24]. Simple electroneuromyography tests may be used for the non-invasive ascertainment of possible variations in the SFN terminal branching [11]. The preoperative application of these tests can be of great value to avoid iatrogenic injury to this nerve.
It is possible to verify SFN anatomical variations through imaging methods. In this regard, ultrasonography is of great value, as previously demonstrated [6, 7]. Certain comorbid conditions (e.g., morbid obesity, arteriopathies, or heart failure) can cause imaging obstruction by excess tissue or subcutaneous fluid. In these cases, anatomical knowledge of the SFN becomes even more vital. The primary use of this ultrasound-applied information is during the SFN local blockage technique. These groups derive the greatest benefits from the use of regional anesthesia, avoiding the harm that general anesthesia in surgical procedures can bring. Clinical and surgical practices have shown the importance of anatomical knowledge regarding the SFN location and branching for the treatment of diseases, syndromes, or injuries associated with it [6].