The surface anatomy of the anterior leg compartment

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1 Surgical Anatomy of the Saphenous Nerve Victor Dayan, MD, Leandro Cura, MD, Santiago Cubas, MD, and Guillermo Carriquiry, MD Cardiovascular Surgery Department of the National Institute of Cardiac Surgery, and Anatomy Department of the Medicine School of Uruguay, Montevideo, Uruguay Background. During harvest of the saphenous vein (SV), the most important relationship to take into account is the saphenous nerve (SN) to avoid pain and paresthesias after surgery. Methods. We harvested the SV and SN in 20 cadaveric lower limbs. Relationships between both structures were recorded using a millimetric ruler, and distances were measured from the medial malleolus at the ankle. Results. The SV was superficial to the leg fascia 32 cm above the malleolus in 95% of the legs. During its course in the leg, 40% of SNs are posterior to the SV; 40% are anterior and then posterior to the SV; and 10% are posterior and then hidden by the SV. The SN crosses the SV in 55% of the legs. Three constant branches of the SN were identified: middle-posterior, middle-anterior, and inferior-anterior. The SN ends by splitting 5.9 cm above the malleolus. A vulnerable region occurs in the lowest 13.2 cm, where the SN adheres to the SV. At this level the SN gives off the inferior-anterior branch that crosses the SV in 66% of the legs. Between 21.6 cm and 28.8 cm the SN crosses deep to the SV. Conclusions. During harvest of the SV, the most vulnerable area is the inferior third of the leg because of venonervous adhesion. (Ann Thorac Surg 2008;85: ) 2008 by The Society of Thoracic Surgeons The surface anatomy of the anterior leg compartment has focused its attention on the saphenous vein (SV), neglecting the saphenous nerve (SN). The SV is frequently used as a graft during vascular bypass procedures. During harvest of the SV, the most important relationship that the surgeon must pay attention to is with the SN. A careless dissection or lack of knowledge of the anatomy of this nerve, or its branches, will lead to sensory alterations (pain, paresthesias, and anesthesia) in the medial aspect of the leg. Saphenous neuralgia [1] describes the symptom complex that includes anesthesia, hyperesthesia, and pain within the distribution of the SN. Besides its description after SV harvesting for coronary artery bypass graft procedures [2], it has also been described after varicose vein [3], arterial [4], and orthopedic [5] procedures. We centered our attention on the SN in the leg, as it is in this region in which relationships with the SV matter and where the SN is at its greatest risk of being injured. Material and Methods The study protocol was reviewed and approved by the National Institute of Cardiac Surgery and Medical School institutional review board, and did not require individual patient consent. Twenty cadaveric lower limbs were studied, 8 of them from male cadavers and 12 from female cadavers. We harvested the SN in the superficial medial aspect of the Accepted for publication Nov 12, Address correspondence to Dr Dayan, Instituto Nacional de Cirugía Cardiaca, 26 de Marzo 3459, Apt 602, Montevideo, Uruguay; vdayan@adinet.com.uy. leg up to the superficial fasciae. A continuous incision was made from the medial malleolus at the ankle to the medial condyle at the knee. Two flaps were made to expose the SN and SV. We considered the medial malleolus at the ankle as the initial site from which distances were recorded. Measurements were made using a millimetric ruler and expressed in centimeters. Distances were always recorded by the same observer and correlated to the lower limb longitude to minimize the errors of using absolute measures. Distances recorded were divided by the distance between the medial malleolus at the ankle and the knee fold. Therefore, 0% corresponded to the medial malleolus and 100% to the knee fold. The data recorded were the level of surface of the SN, relationships the SN has with the SV down its passage in the leg, the number of branches the SN gives off, relationships of these branches with the SV and their skin innervation territory, ending site, and delimitation of safe and vulnerable regions where the SN could be damaged. We defined a safe region as one in which the separation between the nerve or its branches with the vein were greatest, therefore the risk of nerve injury during SV harvest would be minimal. The vulnerable regions were those in which the SV and SN were in close contact or adhered and where branches given off by the SN crossed the SV. At these regions, the SN or its branches would be at greatest risk of injury during harvest of the SV. Results Origin The surface point of the SN was in 95% of the legs (n 19) below the knee fold, whereas in a single case (5%), the 2008 by The Society of Thoracic Surgeons /08/$34.00 Published by Elsevier Inc doi: /j.athoracsur

2 Ann Thorac Surg DAYAN ET AL 2008;85: SURGICAL ANATOMY OF THE SAPHENOUS NERVE 897 CARDIOVASCULAR Fig 1. The surface point of the saphenous nerve (SN) at the knee fold is deeper than the saphenous vein (SV). Both are separated by an important adipose layer. The middle-posterior branch does not cross the saphenous vein. The middle-anterior branch crosses superficially the saphenous vein. supraaponeurotic origin was above. The distance from the medial malleolus at the ankle was 32 4 cm (89% 7%) in 50% of the cases, with maximum values of 40 cm and a minimum of 27 cm. The relationship with the SV at this level showed that in 45% (n 9) of cases the SN was posterior to the vein, in 45% (n 9) anterior, and hidden by the vein in 10% (Fig 1). Course During its course down the leg, the position of the SN with regard to the SV changes. The SN was posterior to the SV in 40% (n 8) of cases. In another 40% (n 8), the SN was anterior to the SV initially and posterior to it Fig 2. The saphenous nerve (SN) ends splitting in a supramalleolar and dorsomedial branch. In this area of the leg, the saphenous nerve and saphenous vein are adhered. The inferior-anterior branch given off by the saphenous nerve crosses the saphenous vein superficially. This branch is at great risk of injury during the saphenous vein harvest. Fig 3. As the nerve descends along the leg, it approaches the saphenous vein and determines a safe and vulnerable region. later. In 5% (n 1) the SN was hidden by the SV all along its course, and in 5% (n 1) it was hidden initially and later was posterior to the SV. In 10% (n 2), the SN was posterior and then became hidden by the SV. The SN crossed the SV in 55% (n 11) of the legs, with the SV superficial to the SN at the crossing point in 90% (n 18) of them. The crossing area in 50% (n 10) of the legs was at cm (63% 13%) from the medial malleolus with a maximum of 30 cm and minimum of 13 cm. Branches of the Saphenous Nerve The most frequent presentation was the presence of three branches: middle-posterior, middle-anterior, and inferior-anterior branch. The middle-anterior branch ended at the anterior middle third of the leg; the inferioranterior branch ended at the anterior distal third of the leg, and the middle-posterior branch ended at the posterior middle third of the leg. The middle-anterior branch originated in 50% of the legs at cm (56% 15%) with a maximum of 32 cm and minimum of 13 cm. The middle-posterior branch originated in 50% of the legs at cm (67% 18%) with a maximum of 34 cm and minimum of 11 cm. The inferior-anterior branch originated in 50% at cm (33% 15%) with a maximum of 30 cm and minimum of 6 cm. These three branches were present in 100% of the legs. Other less frequent branches had the following designations: anterior proximal third of the leg (present in 35% of the legs), posterior distal third (in 30% of the legs), and posterior proximal third (in 10% of the legs). Ending of the Saphenous Nerve The SN ended in 50% of the legs at cm (15% 7%) with a maximum of 11 cm and minimum of 1 cm. In 95% of the legs, the nerve divided into a supramalleolar and dorsomedial branch that follows the SV to the dorsum of the foot. In 1 case (5%), the nerve did not divide and continued as a dorsal branch (Fig 2).

3 898 DAYAN ET AL Ann Thorac Surg SURGICAL ANATOMY OF THE SAPHENOUS NERVE 2008;85: Safe Region The safe region extended from the point the SN surfaces to cm (68% 9%) of the medial malleolus in 50% of the legs. The maximum extension was up to 20 cm, whereas the minimum was 30 cm. In these cases, the nerve was located 1 or 2 cm deeper and anterior or posterior to the vein, separated by an adipose layer. These values varied according to the adipose layer of the leg. In legs of female cadavers, the safe zone extended up to cm of the medial malleolus in 50% of the legs. In men it was up to cm of the medial malleolus (Fig 1). In 35% of legs another safe region could be delimited in which the nerve was located more than 0.5 cm posterior to the vein but at the same depth level. This zone was between 15.8 cm (45%) and 24.4 cm (68%). Vulnerable Region At the distal end of the leg, the SN was adhered to the vein, covered by a common fascia. This intimate relationship between both structures extended in 50% of the cases, from the medial malleolus at the ankle to cm (37% 17%), with a maximum extension of 25 cm (78%) and a minimum of 3 cm (9%). At this region, the SN was hidden by the SV in 15% (n 3) and was posterior to it in 85% (n 17) of legs. As we previously stated, a vulnerable region corresponded to the crossing point of the SV and SN, which was between 21.6 and 28.8 cm (61% to 80%). The last vulnerable segment extended from 7.2 to 10.8 cm. (21% to 30%) of the medial malleolus; in this section, the inferioranterior branch of the SN crossed the SV in 90% (n 18) of the legs (Fig 3). There were no differences between the right and left lower limbs. Between those of male and female cadavers, their differences were based on the thickness of the fatty layer and therefore in the extension of the safe region. Comment The saphenous nerve is the terminal sensory branch of the femoral nerve (L2, L3, and L4) supplying the skin of the anteromedial aspect of the leg through its two major divisions: the sartorial and infrapatellar nerves. After its origin at the inguinal region, the SN travels with the femoral artery through the femoral canal. It perforates the anterior wall of the canal and becomes superficial. At this point the SN comes in close proximity with the SV, and the risk of a lesion increases as it descends down the leg. The presence of saphenous neuralgia as a complication of SV harvesting has been previously described [6]. Its incidence was reported by Mountney and Wilkinson [2] in 35 (90%) of the lower limbs examined 3 days after surgery, with 23 (72%) still symptomatic in a mean follow-up of 20 months. The main symptom was anesthesia, whereas hyperesthesia and pain were less frequently encountered. Budillon and associates [7] report saphenous neuralgia after harvesting of the SV as a rare consequence. The main symptom reported was anesthesia, which lasted no longer than 2 months. After an extensive review of the current bibliography, we could not find any descriptive anatomy of the SN at this area that could explain the sensory deficits after SV harvest. To analyze the collected data, we will discuss the anatomy of the supraaponeurotic segment of the SN with regard to its origin, course, relationships, branches, and ending, comparing it in each case with those published. Origin The origin was found in most of the legs below the knee fold. At this level the SN perforates the superficial fascia between the gracilis and sartorius muscles. There is no published description as to the superficial origin of the nerve. Course The SN descended through the medial aspect of the tibia from the medial condyle at the knee fold to the medial malleolus at the ankle, following an anterior concave course. A compartment occupied by the SV and the SN throughout their course in the leg was described by Caggiati [8]. This compartment is limited deeply by the muscular fascia and superficially by the superficial fascia; laterally both fascia are fused, following two lines that go from the medial condyle at the knee to the medial malleolus at the ankle. Relationships The SN relationships were basically with the SV and varied throughout the leg. At its origin, the nerve lay deeper than the vein. This depth varied from 1 to 2 cm and depended on the adipose layer of the leg. The nerve was located anterior or posterior to the SV, and the frequency was similar in both cases. The separation in depth between the SN and SV diminished as it descended, with both existing at the same depth level in the distal half of the leg. To take its final location in the distal half of the leg, the course of the SN at the proximal half was different according to the superficial origin. In those cases in which the SN originated anterior to the vein, the nerve crossed the vein along its course. This crossing was deep with respect to the vein in 90% of legs and occurred at the proximal half of the leg. The crossing point is separated by adipose tissue and protects the nerve from being damaged by the surgeon. This segment represents a safe region, which will depend on the adipose content of the leg. The SN reaches its definitive position at the distal half of its course. This position was in 85% posterior to the vein and hidden in 15%. Our findings differ from a previously published report that states an anterior position of the nerve with respect to the SV in 70% of the legs [12]. We deduce that the SN variability in position with respect to the vein is the consequence of the venous variability, because as a general rule, vein anatomy is much more variable than nerve anatomy.

4 Ann Thorac Surg DAYAN ET AL 2008;85: SURGICAL ANATOMY OF THE SAPHENOUS NERVE 899 The second branch we called the middle-anterior branch. It originated between the superior and middle third of the leg, went downward and anterior, crossing the vein deeply in those cases in which the SN was posterior to the SV. The last branch was called the inferior-anterior branch. It originated between the middle and inferior third of the leg and went downward and anterior, crossing the vein in 100% of the legs, as at this segment the SN was hidden or posterior to the vein. The crossing was generally superficial to the SV. Mountney and Wilkinson [2] described three areas as the most frequent sites of anesthesia in their patients, which correlate with the innervation territory of the three branches of the SN described. This means that the sensory deficit could be explained by careless injury to the SN branches. There is no descriptive systematization of the SN branches in the bibliography reviewed. They are described simply as anterior and posterior branches [9 11]. Branches found with lesser frequency were called superior-anterior, superior-posterior, and inferior-posterior. CARDIOVASCULAR Ending of the Saphenous Nerve The ending of the nerve was practically constant and in accordance with the bibliography reviewed [12, 13]. At the distal fifth of the leg, it splits into a dorsomedial branch that follows the course of the SN and a supramalleolar branch to the medial malleolus. Fig 4. In this sketch, the leg is divided into thirds. The three constant branches of the saphenous nerve (SN) arise at the superior third (middle-posterior branch), between the superior and middle third (middleanterior branch), and between the middle and distal third of the leg (inferior-anterior branch). (SV saphenous vein.) In the last segment, the nerve remained adhered to the vein, surrounded by a common fascia, being difficult to dissect between both structures. Branches There were only three constant branches. We named them according to their skin distribution at the medial aspect of the leg (Fig 4). The first one was the middle-posterior branch. It originated at the superior third of the leg and traveled obliquely downward and posterior. There was no crossing with the vein unless the SN was located anterior to the vein; in this case, the crossing was deep owing to the deeper position of the nerve with respect to the SV at this region. Vulnerable Region We concluded that the region of greatest precaution during the harvest of the SV is the inferior third of the leg. At this sector, the nerve is adhered to the vein by a common fascia. The nerve is located posterior to the SV or hidden by the vein. This last disposition increases the complexity of the dissection. Between 7.2 and 10.8 cm (20% to 30%) from the medial malleolus at the ankle, the SN gives off the inferioranterior branch, which crosses superficially the SV in two thirds and deeply in one third of the legs. We consider this last disposition of great importance; not taking it into account probably would lead to damaging the inferioranterior branch of the SN and the presence of sensory deficits after surgery (Fig 3). The importance of this region was demonstrated by Mountney and Wilkinson [2] in which the most common affected area (of the three they describe) after SV harvest was the anterior and distal third of the medial leg. The high incidence of sensory effect in this area could be explained by injury to the inferior-anterior branch of the SN during harvest of the SV. In patients with little adipose tissue, the crossing of the SN with the vein, which is seen approximately in the inferior third of superior half of the leg, represents another vulnerable region. Safe Region The safe region is located at the superior half of the leg. Here, an adipose layer separates the SN and SV. During

5 900 DAYAN ET AL Ann Thorac Surg SURGICAL ANATOMY OF THE SAPHENOUS NERVE 2008;85: the dissection of female lower limbs, this region was greater, owing to a thicker layer of adipose tissue. Conclusions Little has been described regarding the surgical anatomy of the SN at the leg. We consider the correct anatomic knowledge of this sector of the nerve of great importance because of the relationships with the SV, and therefore it is of importance in cardiac surgery or any vascular procedure that seeks this conduit. The most significant vulnerable region found in our work was at the distal third of the leg. This is where sensory alterations appear most frequently after SV harvesting as demonstrated by Mountney and Wilkinson [2]. Future studies should be aimed at establishing the presence of sensory deficits after harvest of the SV, in which the SN branches described here are correctly identified and preserved. Although the number of samples is small to reach definitive conclusions, this study constitutes a line of investigation to be continued. References 1. Adar R, Meyer E, Zweig A. Saphenous neuralgia: a complication of vascular reconstruction below the inguinal ligament. Ann Surg 1979;190: Mountney J, Wilkinson GA. Saphenous neuralgia after coronary artery bypass grafting. Eur J Cardiothorac Surg 1999; 16: Wellwood JM, Cox SJ, Martin A, Cockett FB, Browse NL. Sensory changes following stripping of the long saphenous vein. J Cardiovasc Surg (Torino) 1975;16: Urayama H, Misaki T, Watanabe Y, Bunko H. Saphenous neuralgia and limb edema after femoropopliteal artery bypass. J Cardiovasc Surg (Torino) 1993;34: Hunter LY, Louis DS, Riccardi JR, O Connor GA. The saphenous nerve: its course and importance in medial arthrotomy. Am J Sports Med 1979;7: Lavee J, Schneidermann J, Yorav S, Schewach-Mileet M, Adar R. Complications of saphenous vein harvesting following coronary artery bypass surgery. J Cardiovasc Surg (Torino) 1989;30: Budillon AM, Zoffoli G, Nicolini F, et al. Neurologic symptoms after great saphenous vein harvesting for coronary artery bypass grafting. J Cardiovasc Surg (Torino) 2003;44: Caggiati A. Surgical and radiologic anatomy. 1999:21, Rouviere H. Anatomía humana. Barcelona: Masson, 1987: Testut L, Latarjet A. Tratado de anatomía humana, vol 3. Barcelona: Salvat, 1951: Bannister LH, Berry MM, Collins P, Dyson M, Dussek JE, Ferguson MWJ, eds. Gray s Anatomy. Edinburgh, Great Britain: Churchill Livingstone, 1995: Garnjobst W. Surgery gynaecology and obstetrics. 1964:119, Lazorthes G. Le systeme nerveux peripherique. Paris: Masson, 1976:270.