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The Importance of the Saphenous Nerve in Ankle Surgery

Eglitis, Nicholas MD; Horn, Jean-Louis MD; Benninger, Brion MD, MSc; Nelsen, Sylvia PhD

doi: 10.1213/ANE.0000000000001168
Regional Anesthesia: Brief Report

BACKGROUND: Recent evidence suggests that the saphenous nerve may be involved in the innervation of deeper structures at the medial ankle. In this study, we sought to determine the consistency and variability of the saphenous nerve innervation at the distal tibia and medial ankle joint capsule.

METHODS: One hundred three lower extremities from 52 embalmed cadavers were dissected to identify the deep branches of saphenous nerve along its distal course.

RESULTS: In all specimens, the saphenous nerve had branches, emerging between 3.9 and 8.2 cm above the medial malleolus, to the periosteum of the distal tibia and the medial capsule of the ankle joint.

CONCLUSIONS: Deep branches of the saphenous nerve innervate the periosteum of the distal tibia and talocrural capsule.

Supplemental Digital Content is available in the text.Published ahead of print February 8, 2016

From the *Department of Anesthesiology, Perioperative, and Pain Medicine, Stanford University School of Medicine, Stanford, California; Medical Anatomy Center, Western University of Health Sciences, Lebanon, Oregon; and Integrative Biosciences Department, Oregon Health and Science University, Portland, Oregon.

Accepted for publication December 16, 2015.

Published ahead of print February 8, 2016

Funding: None.

Conflict of Interest: See Disclosures at the end of the article.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website.

This report was previously presented, in part, at the 2013 Spring American Society of Regional Anesthesia and Pain Medicine meeting.

Reprints will not be available from the authors.

Address correspondence to Jean-Louis Horn, MD, Department of Anesthesiology, Perioperative, and Pain Medicine, Stanford University School of Medicine, 450 Serra Mall, Stanford, CA 94305. Address e-mail to hornj@stanford.edu.

Clinical experience with regional anesthetic techniques used for surgery involving the medial and anterior ankle joint demonstrates that a sciatic block is often insufficient in providing complete surgical anesthesia and/or postoperative pain control. This suggests that the innervation of the bony structures adjacent to the ankle and the capsule itself are not simply innervated by terminal branches from the sciatic nerve alone but rather at least in part by the saphenous nerve. This distribution provides reason as to why saphenous and sciatic nerve blocks are necessary to obtain adequate analgesia and/or anesthesia of the ankle even when the skin overlying the anteromedial ankle is not in the surgical site.

The saphenous nerve is a terminal branch of the femoral nerve that provides sensory innervation to the soft tissues and skin of the anterior and medial lower extremity.1 Its course is relatively direct as it branches from the femoral nerve in the thigh coursing medially and accompanying the descending genicular artery through the adductor canal to reach the lower extremity.2 At this point, it typically gives off several infrapatellar branches to serve the soft tissues of the anterior knee3,4 before continuing distally to terminate within the soft tissues of the medial and anterior lower extremity and dorsum of the foot. As the saphenous nerve makes its way to the dorsum of the foot, it runs parallel to the distal tibia and branches into anterior and posterior divisions proximal to the medial malleolus before continuing distally.5

The ankle joint is also known as the talocrural joint, which is a synovial hinge joint located at the interface of the tibia and talus bones.6Gray’s Anatomy, a classic anatomical text, describes the innervation of the ankle joint and cites the saphenous nerve as a contributor; however, this fact often remains disputed in clinical practice and in other anatomy textbooks.6 One study reported that the saphenous nerve does play a role in the innervation of the medial malleolus and ankle joint capsule although the extent of this contribution is not known.7 The aim of this study was to determine the relation of the saphenous nerve innervating the bony structures of the ankle and distal tibia with regard to its consistency among subjects and variability thereof.

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METHODS

This study was approved by the IRBs of Oregon Health and Science University and Western University of Health Sciences. Dissections were conducted on 52 (103 lower extremities: 51 right and 52 left) embalmed cadavers. We dissected all available cadavers allotted to the school of medicine for learning and research to ensure a large sample representation.

Each lower extremity was opened with a superficial skin flap. The saphenous vein was identified in each dissection. After this, the accompanying saphenous nerve was identified and dissected. Small branches of the saphenous nerve reaching deep to the anatomic plane were of particular interest, and great care was taken to preserve them in their entirety to identify their relation to structures toward which they headed. The distance from the medial malleolus and the first tibial branch of the saphenous nerve was measured and recorded (median and range). A Wilcoxon signed-rank test was performed after the data were gathered given its nonnormal distribution to compare the right- and left-sided findings. The Clopper Pearson method was used to calculate a confidence limit of the findings.

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RESULTS

In the sample of 52 cadavers, each lower extremity in this sample had an identifiable saphenous vein and nerve. Every leg also had ≥1 identifiable branch of the saphenous nerve traveling deep and becoming continuous with the periosteum of the distal tibia (Fig. 1) giving a lower 1-sided confidence limit of 94.4% consistency. The measurements of the saphenous nerve from the medial malleolus to the first tibial branch of the saphenous nerve revealed the following (Supplement Digital Content, http://links.lww.com/AA/B360): right-sided measurements demonstrated a range of 3.9 to 8.2 cm with a median of 6.2 cm. Left-sided measurements had a range of 4 to 8.1 cm with a median of 6.05 cm. When combining both right and left measurements, the range was 3.9 to 8.2 cm with a median of 6.1 cm. No statistical significance was found between the right- and left-sided dissections (Z score, −0.611 with P = 0.729).

Figure 1

Figure 1

Figure 2

Figure 2

Each saphenous nerve also had identifiable branches that traveled deep to become continuous with the joint capsule of the medial ankle joint at the talocrural joint (Fig. 2). These branches were identified around the level of the medial malleolus.

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DISCUSSION

This study confirms that the saphenous nerve is a contributor to distal tibia and medial ankle joint capsule innervation. The dissections we performed show consistent saphenous nerve branches to the distal tibia and the medial ankle joint capsule among our sample of 52 cadavers. The relation of the terminal branches of the nerve at these sites to the underlying structures supports this conclusion because the nerve fibers can be seen to integrate with the periosteum directly overlying the bone and joint capsule, respectively. These branches can be difficult to identify in routine dissection because they are often discarded when looking for more substantial structures; however, they can be traced once their branch point from the nerve is identified. The branches to the distal tibia and medial joint capsule are clinically important because they provide an anatomic basis for the transmission of pain from these bony and articular structures even when the overlying skin is undisturbed.

Several studies have described the innervation of the ankle joint. A feline study in 1965 demonstrated that the ankle joint was innervated by branches of the saphenous nerve and posterior/anterior tibial nerves.8 Another human study in 2001 demonstrated that the sinus tali (a structure subjacent to the subtalar joint) was innervated by the deep peroneal nerve and occasionally by branches of the sural nerve.9 This is significant because it demonstrates not only the diversity of nerves serving a portion of the ankle joint but also what was once thought to be a purely cutaneous nerve (the sural nerve) can have branches to serve deeper structures. A histologic study in 1968 on 2 fetal cadavers demonstrated the innervation of the ankle joint with nerve stains by several branches of the sciatic nerve and the saphenous nerve as well10; this study served as the basis for the information presented in Gray’s Anatomy regarding the innervation of the ankle joint in part by the saphenous nerve.6 A study by Clendenen and Whalen7 demonstrated the contribution of the saphenous nerve to the innervation of the medial malleolus and distal tibia with gross dissection and histology, although the consistency and variability of this contribution were not assessed.

Our study demonstrated the saphenous nerve as a consistent contributor to the distal tibia and ankle joint innervation and with minimal variability. In our methodology, the branch points of the articular branches to the joint and the distal tibia were recorded and measured because these branches are the ones likely carrying pain signals from these structures. If a saphenous block was performed at a distal location and 1 or several of these branches were not included in sensory blockade, anesthesia at the ankle would be incomplete because there is variation of blocked territory at the ankle in response to block location.11 We also reported variation in the distance with which the branches to the distal tibia branch from the nerve proper. However, our results suggest that a block at 8.2 cm proximal to the medial malleolus includes all the articular branches of the saphenous nerve to the ankle joint and capsule.

The limitations of our findings are that this was a purely anatomic study. Although the macroscopic appearance of the saphenous nerve and its branches can be readily identified and traced, its exact relationship to the joint capsule and distal tibia periosteum cannot be definitively demonstrated except through histologic sections. In addition, studies with nerve tracers would also be beneficial because they would label the exact course of the nerve within its anatomic plane(s) and could show the extent of the territory served by the saphenous nerve.

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CONCLUSIONS

In conclusion, transmission of pain signals from the distal tibia and medial ankle joint capsule is most likely conducted by the saphenous nerve. This innervation has variability in the extent of its territory, nevertheless, is a consistent contributor to the distal tibia and medial ankle joint capsule. Therefore, a saphenous nerve block should be added to a sciatic nerve block for surgery involving the medial ankle, even when the skin overlying said structures remains undisturbed.

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DISCLOSURES

Name: Nicholas Eglitis, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Nicholas Eglitis has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: The authors declare no conflicts of interest.

Name: Jean-Louis Horn, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Jean-Louis Horn has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Conflicts of Interest: Jean-Louis Horn consulted for Halyard Health, TeleFlex, and Edan Medical.

Name: Brion Benninger, MD, MSc.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Brion Benninger has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: The authors declare no conflicts of interest.

Name: Sylvia Nelsen, PhD.

Contribution: This author helped design the study, conduct the study, and write the manuscript.

Attestation: Sylvia Nelsen has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: The authors declare no conflicts of interest.

This manuscript was handled by: Terese T. Horlocker, MD.

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ACKNOWLEDGMENTS

We would like to thank all those who graciously donated their bodies so that this research was possible. We would also like to thank the Medical Anatomy Center and The McDaniel Surgical and Radiological Anatomy Research Lab in Lebanon, Oregon.

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REFERENCES

1. Benninger B, Brueckner J, Carmichael S, Granger N, Hansen J, Tubbs R, Netter FH Lower limb. In: Atlas of Human Anatomy. 20105th ed. Philadelphia, PA Saunders:488–9
2. Horn JL, Pitsch T, Salinas F, Benninger B. Anatomic basis to the ultrasound-guided approach for saphenous nerve blockade. Reg Anesth Pain Med. 2009;34:486–9
3. Pannell WC, Wisco JJ. A novel saphenous nerve plexus with important clinical correlations. Clin Anat. 2011;24:994–6
4. Esmer AF, Orbay H, Apaydin N, Şen T, Elhan A. Variation of infrapatellar sensory innervation: a case report and review of the literature. Int J Exp Clin Anat. 2009;3:62–4
5. Mercer D, Morrell NT, Fitzpatrick J, Silva S, Child Z, Miller R, DeCoster TA. The course of the distal saphenous nerve: a cadaveric investigation and clinical implications. Iowa Orthop J. 2011;31:231–5
6. Standring S Ankle and foot. In: Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 200840th ed. New York, NY Churchill Livingstone:1442
7. Clendenen SR, Whalen JL. Saphenous nerve innervation of the medial ankle. Local Reg Anesth. 2013;6:13–6
8. Freeman MA, Wyke B. Reflex innervation of the ankle joint. Nature. 1965;207:196
9. Rab M, Ebmer J, Dellon AL. Innervation of the sinus tarsi and implications for treating anterolateral ankle pain. Ann Plast Surg. 2001;47:500–4
10. Gardner E, Gray DJ. The innervation of the joints of the foot. Anat Rec. 1968;161:141–8
11. Benzon HT, Sharma S, Calimaran A. Comparison of the different approaches to saphenous nerve block. Anesthesiology. 2005;102:633–8

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