Anatomical variations of the human sural nerve and its role in clinical and surgical procedures

Anatomical considerations of the sural nerve in the distal leg: Side branch patterns and significance in nerve harvesting procedures

BACKGROUND

The sural nerve is a somatosensory nerve that provides sensation to the posterolateral aspect of the lower leg and the lateral part of the ankle and foot. Due to its location and anatomical properties, it is often used as an autologous nerve graft. However, the nerve harvest can be complicated by the presence of side branches. The objective of this study was to investigate the anatomy of the sural nerve and to map its side branches. This information can be used to predict the localization of separate incisions during the stair-step incisions technique for nerve harvest, thereby reducing the risk of complications.

METHODS

The study involved the dissection of 50 adult cadaveric legs (25 left and 25 right) obtained from 27 Central European cadavers. The focus of the dissection was to identify the sural nerve, small saphenous vein, and surrounding anatomical structures. Detailed measurements were taken on the side branches of the sural nerve, tributaries of the small saphenous vein, and their interrelationship.

RESULTS

The average number of sural nerve side branches in a single leg was 4.2±1.9. These side branches were categorized into six groups based on their location and course: mediodistal, medioproximal, lateroproximal, laterodistal, medial perpendicular, and lateral perpendicular. Specific patterns of combination of these side branches were also identified and described. The branching point of the sural nerve was found to be 5.8±2.7 cm proximal to the lateral malleolus, whereas the small saphenous vein branching point was located more distally, 4.5 ± 2.8 cm proximal to the lateral malleolus. The highest density of sural nerve side branches was found 2.1-6.0 cm above the lateral malleolus.

CONCLUSION

This study presents valuable data about the relationship between the sural nerve and the surrounding anatomical structures in the distal part of the leg, including the identification of its side branches and their relevance during nerve harvest procedures. On the basis of the most frequent locations of side branches, a three-incision-technique for nerve harvest is proposed.

Morphometry of the sural nerve in diabetic neuropathy: a systematic review

PURPOSE

The aim of this systematic review is to evaluate the usefulness of sural nerve ultrasonography in diagnosing diabetes mellitus (DM) and diabetic polyneuropathy (DPN), the latter of which is a common long-term complication for diabetic patients that frequently involves the sural nerve.

METHODOLOGY

A meta-analysis of the cross-sectional areas (CSAs) of sural nerves in healthy individuals and patients with diabetes mellitus based on a total of 32 ultrasonographic-based studies from 2015 to 2023 was performed. Sub-analyses were performed for factors such as geographical location and measurement site.

RESULTS

The meta-analysis showed that the mean CSA of the sural nerve was significantly larger in DM patients with DPN only compared to healthy individuals across all regions and when pooled together. An age-dependent increase in the CSA of healthy sural nerves is apparent when comparing the paediatric population with adults.

CONCLUSION

Sural nerve ultrasonography can distinguish diabetic adults with DPN from healthy adults based on cross-sectional area measurement. Future studies are needed to clarify the relationships between other parameters, such as body metrics and age, with sural nerve CSAs. Cut-offs for DPN likely need to be specific for different geographical regions.

Variations in sural nerve formation and course in fetuses

To investigate variations regarding the formation and course of the sural nerve (SN). We dissected 60 formalin-fixed Brazilian fetuses (n = 120 lower limbs) aged from the 16th to 34th weeks of gestational age. Three incisions were made in the leg to expose the SN, and the gastrocnemius muscle was retracted to investigate the SN course. Statistical analyses regarding laterality and sex were performed using the Chi-square test. Eight SN formation patterns were classified after analysis. Type 4 (in which the SN is formed by the union of the MSCN with the LSCN) was the most common SN formation pattern. Although there was no statistical association between the formation patterns and the lower limb laterality (p = 0.9725), there was as to sex (p = 0.03973), indicating an association between anatomical variation and sex. The site of branch joining was in the distal leg most time (53.75%). In all lower limbs, the SN or its branches crossed from the medial aspect of the leg to the lateral margin of the calcaneal tendon (CT). Most often, the SN is formed by joining the MSCN and the LSCN in the distal leg. The SN or its branches ran close to the saphenous vein, crossed the CT from medial to lateral, and distributed around the lateral malleolus.

Anatomical patterns of the sural nerve: a meta-analysis with clinical and surgical considerations

BACKGROUND

The sural nerve (SN) supplies the posterolateral aspect of the leg and the lateral aspects of the ankle and foot and descends through the gastrocnemius muscle along the lower third of leg. Because in-depth knowledge about SN anatomy is essential for clinical and surgical approaches, our study aims to review SN anatomical patterns.

METHODS

We searched the PubMed, Lilacs, Web of Science, and SpringerLink databases to find relevant articles for meta-analysis. We assessed the quality of the studies using the Anatomical Quality Assessment tool. We used proportion meta-analysis to analyze the SN morphological variables and simple mean meta-analysis to analyze the SN morphometric variables (nerve length and distance to anatomical landmarks).

RESULTS

Thirty-six studies comprised this meta-analysis. Overall, Type 2A (63.68% [95% CI 42.36-82.64]), Type 1A (51.17% [95% CI 33.16-69.04]) and Type 1B (32.19% [95% CI 17.83-48.38]) were the most common SN formation patterns. The lower third of leg (42.40% [95% CI 32.24-52.86]) and middle third of leg (40.00% [95% CI 25.21-53.48]) were the most common SN formation sites. The pooled SN length from nerve formation to the lateral malleolus was 144.54 mm (95% CI 123.23-169.53) in adults, whereas the SN length was 25.10 mm (95% CI 23.20-27.16) in fetuses in the second trimester of gestation and 34.88 mm (95% CI 32.86-37.02) in fetuses in the third trimester of gestation.

CONCLUSIONS

The most prevalent SN formation pattern was the union of the medial sural cutaneous nerve with the lateral sural cutaneous nerve. We found differences regarding geographical subgroup and subject age. The most common SN formation sites were the lower and middle thirds of the leg.

Application of Preoperative Ultrasonography in the Percutaneous Minimally Invasive Repair of Acute Closed Achilles Tendon Rupture

Percutaneous minimally invasive surgery involving Achilles tendon (AT) repair has the advantages of a low rerupture rate and fewer postoperative complications. However, due to the inability to operate under direct vision, the injury of the small saphenous vein (SSV) and sural nerve (SN) remains largely a high risk involving many challenges. We propose to introduce the preoperative application and advantages of ultrasonography in percutaneous minimally invasive surgery for acute AT rupture. Our results indicated that ultrasonography could locate the position of the SN more accurately and reduce the risk of iatrogenic nerve injury. Compared with the traditional surface markers, the preoperative localization and marking of AT, SSV, and SN in ultrasonography significantly reduced the risk of intraoperative accidental injury to blood vessels and nerves, which could reduce postoperative complications and promote early rehabilitation of patients. We ultimately exploit the properties of ultrasonography in percutaneous minimally invasive surgery to treat Achilles tendon rupture.

Intra-operative ultrasound: does it improve the results of percutaneous repair of acute Achilles tendon rupture?

Purpose

Percutaneous repair is a good option for acute Achilles tendon rupture. Although it overcomes the complications of open technique, it carries the risk of sural nerve injury and inadequate repair. In this study, we explore if the use of intra-operative ultrasound with percutaneous technique has any advantageous effect on final results of repair.

Methods

This is a prospective randomized study done between May 2014 and December 2020. It included 91 patients with complete acute Achilles tendon rupture distributed in 2 groups with homogenous clinical and demographic data. Group A (n = 47) included those managed by percutaneous repair with assistant of an intra-operative ultrasound. Group B (n = 44) included those done without the assistant of ultrasound. Post-operative evaluation was done clinically by the American Orthopedic Foot and Ankle Society score, calf muscle circumference and single heel rise test and radiologically by Magnetic Resonance Image.

Results

Patients of both groups reported continuous improvement of the American Orthopedic Foot and Ankle Society score with time. However, patient of group A recorded better functional outcome score at 3 months postoperatively. We recorded longer operative time in group A than those in group B. Continuous improvement of maximum calf circumference was observed in both groups. Satisfactory healing was noticed to happen faster in patients of group A than those of group B. We recorded two cases of re-rupture and two cases of sural nerve injury in group B with no reported complication in group A.

Conclusion

The use of an intra-operative ultrasound with percutaneous repair of acute rupture of Achilles tendon can improve the quality of repair as evidenced by quicker satisfactory healing and earlier regain of activity. Also, it can help in proper localization of sural nerve in relation to lateral edge of Achilles tendon.

Trial registration

Clinical Trials.gov Identifier: NCT04935281.

Low to moderate risk of nerve damage during peroneus longus tendon autograft harvest

PURPOSE

This study aims to evaluate the proximity of the tendon stripper to both the peroneal and sural nerves during peroneus longus tendon (PLT) autograft harvesting.

METHODS

Ten fresh-frozen human cadaveric lower extremities were used to harvest a full-thickness PLT autograft using a standard closed blunt-ended tendon stripper. The distance to the sural nerve from the PLT (at 0, 1, 2 and 3 cm proximal to lateral malleolus (LM), and the distance to the peroneal nerve and its branches from the end of the tendon stripper were measured by two separate observers using ImageJ software.

RESULTS

The average distance from the PLT to the sural nerve increased significantly from 0 to 2 cm proximal to LM. The average distance to the sural nerve at the LM was 4.9 ± 1.5 mm and increased to 10.8 ± 2.4 mm (2 cm proximal to LM). The average distance from the tendon stripper to the deep peroneal nerve was 52.9 ± 11.4 mm. The average distance to the PLT branch of peroneal nerve was 29.3 ± 4.2 mm. The superficial peroneal nerve, which coursed parallel and deep to the tendon stripper, was on average 5.2 ± 0.7 mm from the end of the stripper. No transection injuries of the nerves were observed in any of the ten legs after harvesting.

CONCLUSION

This cadaver study found during a full-thickness PLT harvest, the distances between the tendon stripper and the nerves were greater than 5 mm with an initial incision at 2 cm proximal to LM which is recommended.

Sural nerve harvest for infants: integrated with information based on anatomical dissections

Background/aim

The aim of the present study was to determine the course and possible variations of the sural nerve with all anatomical details in human fetal cadavers.

Materials and methods

This study was performed on 60 fetal cadavers. Formation type and level of the sural nerve was detected.

Results

According to trimesters, it was determined that the mean transverse and vertical distance between the lowest point of the LM and the SN varied between 1.1 and 2.9 mm and 1.54 and 3.58 mm, respectively. Type 2 was the most common seen type of sural nerve (35.83%). It was determined that the sural nerve was mostly formed at the middle third of the leg (42.5%).

Conclusion

Sural nerve graft with the knowledge of the anatomical details may be used for peripheral nerve reconstruction is required in congenital lesions, such as facial paralysis, obstetric brachial paralysis, and posttraumatic lesions in infants and children.

Intraoperative ultrasonography assistance for minimally invasive repair of the acute Achilles tendon rupture

Background

Minimally invasive repair is a better option for Achilles tendon rupture with low re-rupture and wound-related complications than conservative treatment or traditional open repair. The major problem is sural nerve injury. The purpose of this study was to evaluate the effect and advantage of the intraoperative ultrasonography assistance for minimally invasive repair of the acute Achilles tendon rupture.

Methods

A retrospective study was performed on 36 cases of acute Achilles tendon rupture treated with minimally invasive repair assisted with intraoperative ultrasonography from January 2015 to December 2017. The relationship of the sural nerve and small saphenous vein was confirmed on the preoperative MRI. The course of the small saphenous vein and the sural nerve was identified and marked by intraoperative ultrasonography. The ruptured Achilles tendon was repaired with minimally invasive Bunnell suture on the medial side of the small saphenous vein (SSV).

Results

All patients were followed up for at least 12 months. No sural nerve injury or other complications was found intraoperatively and postoperatively. All the patients returned to work and light sporting activities at a mean of 12.78 ± 1.40 weeks and 17.28 ± 2.34 weeks, respectively. The Mean American Orthopaedic Foot & Ankle Society (AOFAS) scores improved from 59.17 ± 5.31 preoperatively to 98.92 ± 1.63 at the time of 12 months follow-up. There was a statistically significant difference (P < 0.001). No patient complained of a negative effect on their life.

Conclusions

The minimally invasive repair assisted with intraoperative ultrasonography can yield good clinical outcomes, less surgical time, and less complications, especially sural nerve injury. It is an efficient, reliable, and safe method for acute Achilles tendon (AT) rupture.

The distribution pattern of the dorsal cutaneous nerves of the foot and its clinical implications

Iatrogenic injury to subcutaneous nerves on the dorsum of the foot is an established risk factor during the surgical procedures resulting in postoperative pain, sensation loss and painful neuroma. Previous studies have reported on the distribution pattern of the superficial peroneal, deep peroneal and sural nerves (SNs) and their branches with various classifications about specific populations. The purpose of the present study was to evaluate the distribution pattern and classification of the nerves on the dorsum of the foot and analyze the location of these nerves into five zones with clinical implications. Fifty-four lower limbs of fresh frozen cadavers were used in the present study. The anatomical patterns of the superficial peroneal, deep peroneal, SN and their branches were classified into eight, two and five patterns respectively. Type VI pattern, a classic distribution pattern of the superficial peroneal nerve was the most frequent type with a prevalence of 13 limbs (25.00%). In Zone 5, where the arthroscopic portal placements for the first metatarsophalangeal joint arthrodesis, 29 limbs (55.77%) showed three nerve branches located in this zone. The results of the present study provide anatomical knowledge that may help the surgeon to choose the appropriate treatment for their patients and reducing the rate of complications in surgery.

Mini-invasive foam sclerotherapy-assisted ligation versus surgical flush ligation for incompetent sapheno-popliteal junction treatment

Objectives

Comparison of a flush sapheno-popliteal junction ligation versus a mini-invasive foam sclerotherapy-assisted ligation.

Methods

Forty-eight chronic venous disease patients underwent sapheno-popliteal junction flush ligation (group A). Forty-one patients underwent small saphenous vein ligation by means of mini-invasive incision with foam sclerotherapy of the popliteal stump (group B).

Results

At 4.1 ± 3.3 years mean follow-up, sapheno-popliteal junction recurrence was detected in four patients of group A (4/48; 8.3%) and in two cases of group B (3/41; 7.3%) ( P= ns). Mean procedural time was 36 ± 11 minutes versus 21 ± 6 minutes ( p<0.0001). A mild post-operative paresthesia lasting more than 24 h was reported in 6.3% (3/48) of group A versus 2.4% (1/41) ( p<0.009) of group B. At one-year check-up, Aberdeen Varicose Vein Questionnaire significantly improved in both groups with no significant difference between group A and B.

Conclusions

Foam-assisted mini-invasive sapheno-popliteal ligation represents a time and clinical-effective option, associated with a decrease in post-operative paresthesia risk.

A review of main anatomical and sonographic features of subcutaneous nerve injuries related to orthopedic surgery

Lesion to subcutaneous nerves is a well-known risk of orthopedic surgery and a significant cause of postoperative pain and dissatisfaction in patients. High-resolution ultrasound can be used to visualize the vast majority of small subcutaneous nerves of the upper and lower limbs. Ultrasound detects nerve abnormalities such as focal hypoechoic thickening, stump neuroma, and scar encasement, and provides information not only about the peripheral nerve itself but also about its relationship to adjacent anatomical structures. The purpose of this review is to provide an overview of the anatomy of the main subcutaneous nerves damaged during orthopedic surgery, recall at-risk procedures, and offer useful anatomic landmarks to help the sonographer identify and follow the nerves when an iatrogenic lesion is suspected.

Use of Vascularized Sural Nerve Grafts for Sciatic Nerve Reconstruction After Malignant Bone and Soft Tissue Tumor Resection in the Lower Legs

BACKGROUND

Vascularized nerve grafting is normally associated with a good outcome, but can be difficult to use for nerve reconstruction in patients with long defects of the sciatic nerve given the graft thickness. We report 3 cases of large defect sciatic nerve reconstruction using the bilateral sural nerves of the lower legs harvested together with the fascia and lesser saphenous vein to form a vascularized flap.

METHODS

The subjects were 3 patients who required the reconstruction of a 10-cm or longer segment of the sciatic nerve. Priority was given to restoring sensation in the plantar region such that reconstruction of the sensory nerves corresponding to the tibial region.

RESULTS

Two patients were followed up for long term. There was some persistent perceptual deficit in the foot, minimal protective sensation had been achieved.

CONCLUSIONS

We were able to selectively reconstruct the sensory nerves to achieve sensation in the soles of the feet by using sural nerve grafts from both legs. As the prognosis for the underlying condition in cases necessitating this procedure is often poor, the costs and benefits of reconstruction should always be weighed carefully for each individual patient.

Contribution of the sural nerve to postural stability and cutaneous sensation of the lower limb

BACKGROUND

The sural nerve is a cutaneous nerve of the lower limb that innervates the posterolateral aspect of the lower leg, ankle, and foot. Considering this pattern, it is plausible that it contributes to the maintenance of postural stability. However, the implications of sensory loss following sural nerve injury have yet to be thoroughly investigated. Therefore, the aim of this study was to investigate the immediate effect of sural nerve sensory loss on postural stability and its variability of innervation to the lower limb.

METHODS

Twenty-five healthy adult subjects participated in an observational study with a repeated-measures design. Each participant underwent a postural stability assessment using the Neurocom Balance Master under 2 conditions: 1) with the sural nerve functioning normally and 2) following a bilateral ultrasound-guided sural nerve block. The cutaneous distribution of the sural nerve was mapped for descriptive purposes.

RESULTS

There were no statistically significant differences between conditions for the primary outcome measure (unilateral stance on the dominant leg with eyes closed). A statistically significant reduction in postural stability was detected during unilateral stance on the nondominant leg (with eyes closed) following the nerve block (mean increase, 2.25 deg/s; 95% confidence interval, -0.48 to 2.91; t = 2.75; df = 24; P = .01). The mean area of plantar skin innervated by the sural nerve was 17% ± 11%, and the mean area of lateral skin was 50% ± 6%.

CONCLUSION

Our findings demonstrate that a loss in sural nerve function is unlikely to reduce postural stability during daily activities. The sural nerve has a variable innervation pattern that can involve the third digit and the plantar medial border of the heel.

CLINICAL RELEVANCE

Practitioners should consider this variability when assessing for potential sensory deficits and when planning procedures requiring anesthesia to the plantar surface of the foot.

Risk of sural nerve injury during lateral distal Achilles tendinoscopy: a cadaver study

BACKGROUND

The risk of damage to cutaneous sensory nerves located near portals has been evaluated for both conventional arthroscopy and extra-articular posterior ankle endoscopy. The objective of the anatomic study reported here was to assess the risk of injury to the sural nerve or lateral calcaneal nerve while using the distal lateral portal for the Achilles tendinoscopy procedure described by Vega et al. in 2008.

MATERIALS AND METHODS

We dissected the sural nerve and its branch, the lateral calcaneal nerve, of 13 human cadaver ankles in the prone position. We defined P as the point where the Achilles peritendon was opened during the distal lateral approach used for the study technique. P was adjacent to the lateral edge of the Achilles tendon, 2 cm proximal to the postero-superior edge of the calcaneal tuberosity. T was defined as the attachment site of the most lateral fibres of the Achilles tendon to the postero-superior edge of the calcaneal tuberosity. We evaluated the origin of the lateral calcaneal nerve relative to T and we measured the shortest distances separating P from the sural nerve and lateral calcaneal nerve.

RESULTS

A lateral calcaneal nerve was identified in 10 (77%) ankles and originated a mean of 39.1mm (range, 25.0-65.0mm) proximal to T. P was at a mean distance from the sural nerve of 12.3mm (range, 5.0-18.0mm) and from the lateral calcaneal nerve of 6.8mm (range, 4.0-9.0mm). The median difference between these two distances was statistically significant (P=0.002).

DISCUSSION

While using the distal lateral portal for Achilles tendinoscopy, the lateral calcaneal nerve is at greater risk for injury than is the sural nerve.

LEVEL OF EVIDENCE

Level IV. Anatomic Study.

Study of sural nerve complex in human cadavers

Aim. The sural nerve complex (SNC) consists of four named components: medial sural cutaneous nerve (MSCN), lateral sural cutaneous nerve (LSCN), peroneal communicating nerve (PCN), and sural nerve (SN). The formation and distribution of the sural nerve vary in different individuals. SN is universally recognized by surgeons as a site for harvesting an autologous nerve graft. The nerve is widely used for electrophysiological studies. Hence the study of sural nerve complex was taken up. Method. SNC was observed by dissecting 100 lower limbs in the department of anatomy at three different medical colleges, over a period of 10 years. Result. Typical SN was observed in 60% of the cases. MSCN was present in all the cases; in 15% of the cases the MSCN followed an intramural course. LSCN was present in 80% of the cases. PCN was present in 70% of the cases and in most of the cases calibre was larger than that of MSCN. Conclusion. The knowledge about the variation in the origin and course of the SN is important in evaluating sensory axonal loss in distal axonal neuropathies and should be borne in mind by clinicians and surgeons.