Anatomical variations of the sural nerve

An anatomical study of the formation of the sural nerve (SN) was carried out on 76 Thai cadavers. The results revealed that 67.1% of the SNs were formed by the union of the medial sural cutaneous nerve (MSCN) and the lateral sural cutaneous nerve (LSCN); the MSCN and LSCN are branches of the tibial and the common fibular (peroneal) nerves, respectively. The site of union was variable: 5.9% in the popliteal fossa, 1.9% in the middle third of the leg, 66.7% in the lower third of the leg, and 25.5% at or just below the ankle. One SN (0.7%) was formed by the union of the MSCN and a different branch of the common fibular nerve, running parallel and medial to but not connecting with the LSCN, which joined the MSCN in the lower third of the leg. The remaining 32.2% of the SNs were a direct continuation of the MSCN. The SNs ranged from 6-30 cm (mean = 14.41 cm) in length with a range in diameter of 3.5-3.8 mm (mean = 3.61 mm), and were easily located 1-1.5 cm posterior to the posterior border of the lateral malleolus. The LSCNs were 15-32 cm long (mean = 22.48 cm) with a diameter between 2.7-3.4 mm (mean = 3.22 mm); the MSCNs were 17-31 cm long (mean = 20.42 cm) with a diameter between 2.3-2.5 mm (mean = 2.41 mm). Clinically, the SN is widely used for both diagnostic (biopsy and nerve conduction velocity studies) and therapeutic purposes (nerve grafting) and the LSCN is used for a sensate free flap; thus, a detailed knowledge of the anatomy of the SN and its contributing nerves are important in carrying out these and other procedures.     

Mechanoreceptive afferents in the human sural nerve

Microneurography was used to characterize 104 low-threshold mechanoreceptive afferents in the human sural nerve. The afferents were readily classified into four types using criteria developed for the glabrous skin of the hand: SA I (31%), SA II (11%), FA I (49%), and FA II (9%). The distribution of fascicle fields and receptive fields of individual afferents on the lateral side of the foot indicates that the glabrous skin portion of the innervation territory of the sural nerve is more densely innervated than the non-glabrous skin portion. The different populations in the glabrous and non-glabrous skin regions were similar regarding proportion of unit types, receptive field sizes, and force thresholds. The receptive field sizes of the type I units of the present sample were about twice the size compared to those of the glabrous hand units, and the force threshold were at least three times higher for three of the unit types (SA I, FA I, and FA II). Given their receptive properties, it is likely that mechanoreceptive afferents in the sural nerve provide rich information about contact patterns between the foot and environment during stance and locomotion.     

腓肠神经临床应用解剖及其临床意义的研究进展

目的 探讨腓肠神经的应用解剖及其在相关手术入路中的损伤风险。方法 以“腓肠神经”“解剖”“手术入路”和“sural nerve”“anatomy”“surgical approaches”为中英文关键词,在中国知网、万方数据、SinoMed、PubMed等中英文数据库检索2000年1月-2019年7月间有关腓肠神经临床应用解剖的文献,检索到文献999篇,剔除内容不符合、无法获取原文、重复性研究或存在设计缺陷的文献,最终纳入34篇。总结腓肠神经应用解剖研究成果,重点阐述踝关节骨折的后外侧入路和跟骨骨折的L型入路、跗骨窦入路,以及第五跖骨基底部骨折入路等4种手术入路与腓肠神经的解剖学关系。结果 研究显示,腓肠神经在解剖学上变异类型众多,其走行区域与踝关节骨折的后外侧入路、跟骨骨折的L型入路和跗骨窦入路、第五跖骨基底部骨折入路4种手术入路的关系十分密切。结论术前正确掌握腓肠神经的解剖特点,对足踝骨折手术入路选择以及减少手术中腓肠神经损伤风险至关重要。     

Endoneurial extracellular matrix influences regeneration and maturation of motor nerve axons--a model of acellular nerve graft

Clinical results of functional reinnervation after application of autogeneous nerve grafts obtained from cutaneous nerves have not always been satisfactory. A foreign extracellular condition especially for regeneration of motor axons is assumed to be one of the reasons explaining these unsuccessful results. The role of endoneurial extracellular matrix in regeneration and maturation of motor axons was studied using acellular nerve segment prepared from muscular or cutaneous nerves applied between stumps of transected motor branch of the femoral nerve. No differences were found in the numbers of regenerated axons and related motoneurons through the motor and cutaneous nerve grafts 1 month after operation. Two months from grafting, however, the numbers of motoneurons and regenerated axons were increased significantly in the motor grafts while these were decreased after regeneration through the cutaneous grafts compared with 1 month. Axons' diameter and thickness of their myelin sheaths were similar in the cutaneous grafts 1 and 2 months after grafting. In comparison to 1 month, axons had larger diameter and thicker myelin in the motor than cutaneous nerve grafts 2 months from their application. Results of morphometric analysis indicate more beneficial extracellular conditions for regeneration and maturation of myelinated motor nerve axons in the acellular motor than cutaneous nerve graft. Generally, the results revealed that the endoneurial extracellular matrix of motor fibers has a positive effect on regeneration and maturation of motor nerve axons after lesion.     

腓肠神经的交感成分及其对腓肠神经营养血管皮瓣血流动力学影响的探查

目的　探讨腓肠神经是否有发出交感纤维支配其伴行血管及腓肠神经切段后近端蒂腓肠神经营养血管皮瓣的血流动力学会出现何种相应变化。 方法　在探明兔下肢腓肠神经及其伴行血管相应解剖后,取17只白兔,其中2只白兔直接处死,取腓肠神经血管束。其余15只（30侧后肢）随机等分入神经保留组与神经切断组。神经保留组白兔在行皮瓣切取术后,不对腓肠神经进行处理;神经切断组则在皮瓣掀起后将腓肠神经在其起点处切断。在相应时间点处死两组动物,取腓肠神经营养血管束行乙醛酸染色。利用红外热像仪对上述两组皮瓣术后24 h皮瓣的平均温度进行测量。 结果　神经切断组术后3、5及7 d 3个时间点腓肠神经内荧光点及其伴行动脉外膜荧光出现高度一致性的下降,组间荧光评分具有显著性差异(F=13.563, P=0.004)。神经保留组在术后整个过程中荧光强度未出现明显改变。术后2 h起,神经保留组皮瓣平均温度低于神经切断组,两者差异具有统计学意义（P＜0.05）。 结论　腓肠神经有发出交感纤维至其伴行血管,调节其伴行血管张力。腓肠神经切段后,近端蒂腓肠神经营养血管皮瓣的微循环会出现相应改善,皮瓣存活率有可能增加。     

Clinical significance of selective nerve fascicular degeneration on sural nerve biopsy specimen

Eight cases of selective nerve fascicular degeneration (SNFD) on sural nerve were identified from 250 consecutive biopsy specimens. In six patients, SNFD was associated with angiopathic changes. This study suggests that SNFD is a distinctive finding seen in 3% of nerve biopsy specimens, and its presence alone may indicate an angiopathic disorder. Selective nerve fascicular degeneration is associated with a variety of clinical presentations, ranging from chronic distal symmetrical polyneuropathy to mononeuropathy multiplex.     

Formation and location of the sural nerve in the newborn

In this study, the location and formation of the sural nerve were examined in 40 legs of new-born cadavers. The sural nerve was formed by the peroneal communicating branch from the common peroneal nerve joining the medial sural cutaneous nerve in 27 of 40 legs (67.5%). It was formed by the peroneal communicating branch from the lateral sural cutaneous nerve joining the medial sural cutaneous nerve in 4 (10%). It was formed by the peroneal communicating branch from the common peroneal nerve and fibers from the posterior femoral cutaneous nerve joining the medial sural cutaneous nerve in 2 (5%). In 5 of 40 legs (12.5%), the medial sural cutaneous nerve was in the place of the sural nerve without joining any other nerve. In one case (5%), the sural nerve was not formed bilaterally.     

The relative contributions of the medial sural and peroneal communicating nerves to the sural nerve

The medial sural cutaneous nerve (MSCN) and peroneal communicating nerve (PCN) conjoin in the calf area to form the sural nerve (SN). In previous anatomic studies, there was unresolved debate as to the main contributor to the sural nerve, and the relative contributions of MSCN and PCN had not been studied. The purpose of this study is to determine their relative neurophysiologic contributions to the SN by nerve conduction study (NCS). A total of 47 healthy subjects (25 males and 22 females, mean age 29.6 +/- 10.4 yrs, range 20-59 yrs) participated in the study. This study employed the orthodromic nerve conduction technique: stimulation at the ankle and recording at the mid calf (SN); specifically, we preformed stimulation at the mid calf (MSCN, PCN) and recording at 14 cm proximal to the middle of the popliteal fossa (MSCN) and fibular head (PCN). The onset and peak latencies (ms) were SN 2.3 +/- 0.2 and 3.0 +/- 0.2; MSCN 2.1 +/- 0.2 and 2.8 +/- 0.2; and PCN 2.1 +/- 0.2 and 2.8 +/- 0.2. The peak-to-peak amplitudes (microV) and areas (nVsec) of the SN, MSCN, and PCN were 9.7 +/- 3.9, 7.0 +/- 4.7, and 5.0 +/- 3.2; and 7.2 +/- 2.9, 5.7 +/- 3.4, and 4.0 +/- 2.4, respectively. The side-to-side difference was not statistically significant. The main contributor to the SN was found to be the MSCN. The relative contribution ratio of the MSCN to the PCN was 1.37:1 by amplitude and 1.42:1 by area. However, in 32.9% of the subjects, the contribution of the PCN was greater than that of the MSCN.     

Peripheral nerve amyloidosis in sural nerve biopsies: a clinicopathologic analysis of 13 cases

OBJECTIVE: Amyloidosis is a well-recognized but uncommon cause of peripheral neuropathy. Our objectives were to determine the overall prevalence of peripheral nerve amyloidosis in sural nerve biopsies and to evaluate the clinical and pathologic features of these lesions. METHODS: All available histologic and ultrastructural materials on biopsy tissue from 13 cases of peripheral nerve amyloidosis were examined. Muscle biopsies performed at the same time as the nerve biopsy were reviewed when available. Clinical data were collected on all patients. RESULTS: The prevalence of amyloidosis in sural nerve biopsies at our institution was 13 (1.2%) of 1098 cases over a 15.8-year period. These patients ranged in age from 41 to 82 years (median, 61 years) at initial presentation and included 10 men and 3 women. Presenting neuropathy symptoms were sensory in 6 of the 13 patients, motor in 2 cases, and mixed in 5 cases. Cardiac, renal, or gastrointestinal involvement was present in 7 of 13 cases. Two patients had myeloma and 7 had systemic autonomic symptoms. Two patients had probable familial amyloid polyneuropathy, and 1 patient demonstrated an alanine 60 point mutation. Amyloid, identified as amorphous eosinophilic extracellular deposits demonstrating apple green birefringence on Congo red stain or recognized by its characteristic fibrillar ultrastructure by electron microscopy, was identified in the endoneurium in 12 nerves, perineurium in 2 nerves, and epineurium in 9 nerves. Chronic inflammation was identified in 5 nerves. Axonal loss was recorded as mild (<25%) in 1 nerve, moderate (25% to 75%) in 8 nerves, and severe (>75%) in 4 nerves. Axonal degeneration predominated over demyelination in 8 of 10 cases that could be evaluated. Concomitant muscle biopsies contained amyloid deposits in 8 of 9 cases. CONCLUSIONS: Amyloidosis is a rare (1.2% in our series) cause of peripheral neuropathy with a distinct microscopic and ultrastructural appearance. Just over half the patients in our study had visceral organ involvement and systemic autonomic symptoms. The peripheral neuropathy was associated with axonal degeneration and a moderate to severe axonal loss in the majority of cases. Amyloid deposition was present in 8 out of 9 muscle biopsies performed at the same time.     

Formation and distribution of the sural nerve based on nerve fascicle and nerve fiber analyses

The formation and distribution of the sural nerve are presented on the basis of an investigation of 31 legs of Japanese cadavers using nerve fascicle and fiber analyses. Nerve fibers constituting the medial sural cutaneous nerve were designated as 'T', whereas those constituting the peroneal communicating branch were designated as 'F'. In 74.2% of cases (23/31), the T and F fibers joined each other in the leg, whereas in 9.7% of cases (3/31) they descended separately. In 16.1% of cases (5/31), the sural nerve was formed of only the T fibers. The sural nerve gave off lateral calcaneal branches and medial and lateral branches at the ankle. The lateral calcaneal branches always contained T fibers. The medial branches consisted of only T fibers, whereas most of the lateral branches consisted of only F fibers (71.0%; 22/31). In addition to the T and F fibers, P fibers, which derived from the superficial and deep peroneal nerves, formed the dorsal digital nerves. The P fibers were entirely supplied to the medial four and one-half toes. However, they were gradually replaced by the T and F fibers in the lateral direction. The 10th proper dorsal digital nerve consisted of T fibers only (38.7%; 12/31), of F fibers only (19.4%; 6/31) or of both T and F fibers (38.7%; 12/31). These findings suggest that the T fibers are essential nerve components for the skin and deep structures of the ankle and heel rather than the skin of the lateral side of the fifth toe. The designation of the medial sural cutaneous nerve should be avoided and only the T fibers are appropriate components for naming as the sural nerve.     

Compound nerve action potential of common peroneal nerve and sural nerve action potential in common peroneal neuropathy

To enhance the accuracy for determining the precise localization, the findings of the compound nerve action potentials (CNAPs) of the common peroneal nerve (CPN) were investigated in patients with common peroneal mononeuropathy (CPM) in the knee, and the sural sensory nerve action potentials (SNAPs) were also analyzed. Twenty-five patients with CPM in the knee were retrospectively reviewed. The findings of the CNAPs of the CPN recorded at the fibular neck and the sural SNAPs were analyzed. The lesion was localized at the fibular head (abnormal CNAPs) and at or distal to the fibular head (normal CNAPs). Seven patients were diagnosed as having a lesion at or distal to the fibular neck, and 18 cases were diagnosed as having a fibular head lesion. The sural SNAPs were normal in all the cases of lesion at or distal to the fibular neck. Among 18 cases of fibular head lesion, the sural SNAPs were normal in 7 patients: two cases of conduction block and 5 cases of mild axon loss. Eleven patients showed abnormal sural SNAPs. Of those, 9 cases were severe axon loss lesions and 2 patients were diagnosed as having severe axon loss with conduction block. The recording of the CNAPs may enhance precise localization of CPM in the knee. Moreover, the sural SNAPs could be affected by severe axonal lesion at the fibular head.     

Origin and make up of the human sural nerve

Abstract The dissection of 37 cadavers has shown that in only a third of cases, the sural nerve comes from the communication between the medial cutaneous nerve, derived from the tibial nerve, and the communicating branch of the lateral cutaneous nerve of the leg which comes from the lateral popliteal nerve. The communication is most often at the junction between the proximal two-thirds and distal third of the leg, on average 2 mm below the transverse crease of the popliteal fossa. The medial cutaneous nerve was absent in only one case. On the other hand, in 11 cases the lateral cutaneous nerve or its communicating branch was missing. In 12 cases without any anastomoses, the route of the sural nerve was followed by the medial cutaneous nerve of the leg in 9 cases and by the lateral cutaneous nerve in 3 cases. The majority of branches to the proximal half of the calf came from the lateral cutaneous nerve. In the lower part of the leg, the sural nerve and/or the medial cutaneous nerve gave numerous branches to the Achilles’ tendon and to the integuments of the lateral aspect of the heel and lateral malleolus.     

Clinicopathologic study of 43 patients with sural nerve vasculitis

Vasculitis is a relatively uncommon finding in sural nerve biopsy specimens and is associated with significant morbidity. This study retrospectively reviewed the clinicopathologic features of 43 patients (44 sural nerve biopsy specimens) with sural nerve vasculitis, defined as infiltration of vessel walls by inflammatory cells. These biopsy specimens were obtained over a 19-year period, during which 1503 nerve specimens were reviewed. The study group comprised 29 females and 14 males, ranging in age from 19 to 94 years (mean, 72.5 years) at the time of biopsy. The most frequent clinical presentations included paresthesias in 19 patients (61%), pain in 17 patients (57%), weakness in 10 patients (32%), and weight loss in 9 patients (29%). Histologically, 26 of 44 biopsy specimens (59%) demonstrated necrotizing vasculitis. The remaining 18 biopsy specimens demonstrated a nonnecrotizing lymphocytic vasculitis. Eosinophils were identified in 4 biopsy specimens, intravascular thrombi in 10 (22%) specimens, and granulomatous inflammation in 1 specimen. In 39 biopsy specimens (89%), multiple vessels were involved by vasculitis. Epineurial vessels were the most common target of vasculitis, (n = 42; 95%). Evidence of vascular wall scarring, indicative of healed vasculitis, was observed in 13 biopsy specimens (30%). All biopsy specimens showed evidence of axonopathy, with mild axonal loss noted in 14 specimens (32%), moderate loss in 18 specimens (41%), and severe loss in 12 specimens (27%). Concomitant muscle biopsy was performed in 31 patients. Fifteen muscle biopsy specimens demonstrated evidence of vasculitis (48%), which was necrotizing in 11 cases. All muscle biopsy specimens demonstrated features of neurogenic atrophy. Twenty-five out of 32 patients were known to have been treated with steroids and demonstrated some degree of clinical improvement. In conclusion, sural nerve vasculitis is a relatively uncommon pathological finding (prevalence of 2.9% in this study). In most cases, multiple vessels were involved. Concomitant vasculitis was also identified in about half of the muscle biopsy specimens obtained at the time of nerve biopsy. In most patients, the vasculitis appeared to be at least partially responsive to immunosuppressive therapy.     

腓肠神经及其两根的应用解剖学观测

目的观测人腓肠神经的构成类型,长、宽以及构成腓肠神经的两根的位置、长度、宽度,以补充国人腓肠神经的解剖学资料为临床腓肠神经的移植提供依据。方法利用直尺及游标卡尺（精确度0．02mm）对腓肠神经,腓肠内、外侧皮神经的长、宽进行测量,对腓肠内、外侧皮神经位置及腓肠神经的组成型式进行观测统计。结果腓肠神经的构成型式较前人的观察更为复杂,因此本文采用了新的分型方法。腓肠内、外侧皮神经的发出位置多变,腓肠神经起始部、中点及外踝平面宽度不同。结论腓肠神经及其两根型式复杂,临床选择移植体时应充分考虑其型式及长度、宽度,以便更加适应受区特征。     

Schmidt-Lanterman clefts: A morphometric study in human sural nerve

In the human sural nerve, large myelinated fibers contained. 35 Schmidt-Lanterman (SL) clefts per mm, and small myelinated fibers contained only eight SL clefts per mm. The incidence of SL clefts is linearly related to myelin thickness. The SL clefts extended over 13 μm in large and over 9 μm in small fibers, the total extent of the SL region amounting to nearly 50% of internodal length in large and to 6% in small fibers. In the SL region, the fiber diameter was 6% larger than outside this region, and the axon was 17% smaller in large and 28% smaller in small fibers. The paranodal-nodal region occupied less than 2% of internodal length in large fibers and 6.5% in small fibers; in the nodal region the axon diameter was reduced by 40–50%.     

Anatomic study of the superficial sural artery and its implication in the neurocutaneous vascularized sural nerve free flap

Combined extended nerve and soft tissue defects of the upper extremity require nerve reconstruction and adequate soft tissue coverage. This study focuses on the reliability of the free vascularized sural nerve graft combined with a fasciocutaneous posterior calf flap within this indication. An anatomical study was performed on 26 cadaveric lower extremities that had been Thiel fixated and color silicone injected. Dissection of the fasciocutaneous posterior calf flap involved the medial sural nerve and superficial sural artery (SSA) with its septocutaneous perforators, extended laterally to include the lateral cutaneous branch of the sural nerve and continued to the popliteal origin of the vascular pedicle and the nerves. The vessel and nerves diameter were measured with an eyepiece reticle at 4.5× magnification. Length and diameter of the nerves and vessels were carefully assessed and reported in the dissection book. A total of 26 flaps were dissected. The SSA originated from the medial sural artery (13 cases), the popliteal artery (12 cases), or the lateral sural artery (one case). The average size of the SSA was 1.4 ± 0.4 mm. The mean pedicle length before the artery joined the sural nerve was 4.5 ± 1.9 cm. A comitant vein was present in 21 cases with an average diameter of 2.0 ± 0.8 mm, in 5 cases a separate vein needed to be dissected with an average diameter of 3.5 ± 0.4 mm. The mean medial vascularized sural nerve length was 21.2 ± 8.9 cm. Because of inclusion of the vascularized part of the lateral branch of the sural nerve (mean length of 16.7 ± 4.8 cm), a total of 35.0 ± 9.6 cm mean length of vascularized nerve could be gained from each extremity. The free vascularized sural nerve graft combined with a fasciocutaneous posterior calf flap pedicled on the SSA offers a reliable solution for complex tissue and nerve defect. Clin. Anat. 26:903–910, 2013. © 2012 Wiley Periodicals, Inc.