VASCULAR SUPPLY AND LYMPHATIC DRAINAGE

Iliac vessels and external iliac arteries and veins

The iliac vessels are described on page 1086, and the external iliac arteries and veins on pages 1089, and page 1090 respectively.

ARTERIES

Gluteal vessels

The superior and inferior gluteal arteries (Fig. 80.27) are described on pages 1087, 1089.

Fig. 80.27 The arteries of the gluteal region.

(From Drake, Vogl, Mitchell, Tibbitts and Richardson 2008.)

Arteria comitans nervi ischiadici (artery to sciatic nerve)

The arteria comitans nervi ischiadici is a branch of the internal iliac artery, and runs on the surface of, or within, the sciatic nerve. It represents the primitive axial artery of the lower limb. The artery is usually a very small vessel; occasionally it persists as a large vessel, in which case the femoral artery is correspondingly reduced in size. The artery may participate in collateral circulatory pathways.

Femoral artery

The femoral artery (Figs 80.2, 80.3, 80.28, 80.29) is a continuation of the external iliac artery. It begins behind the inguinal ligament, midway between the anterior superior iliac spine and the pubic symphysis, descends along the anteromedial part of the thigh in the femoral triangle, enters and passes through the adductor (subsartorial) canal, and becomes the popliteal artery as it passes through an opening in adductor magnus near the junction of the middle and distal thirds of the thigh. Its first three or four centimetres are enclosed, with the femoral vein, in the femoral sheath. The femoral artery gives off several branches in the proximal thigh, including the superficial epigastric, superficial circumflex iliac, superficial external pudendal, deep external pudendal and profunda femoris arteries. It gives off the descending genicular artery within the adductor canal. In clinical parlance, the part of the femoral artery proximal to the origin of profunda femoris is often termed the common femoral artery, while that distal to the origin of the profunda is termed the superficial femoral artery.

Fig. 80.28 The left femoral vessels.

(From Sobotta 2006.)

Fig. 80.29 The profunda femoris artery and its branches.

(From Sobotta 2006.)

Rarely, the femoral artery divides, distal to the origin of the profunda femoris artery, into two trunks that reunite near the adductor opening. It may be replaced by the inferior gluteal artery, accompanying the sciatic nerve to the popliteal fossa and representing a persistence of the original axial artery. The external iliac artery is then small, ending as the profunda femoris artery.

Relations

Anterior to the artery in the femoral triangle are the skin, superficial fascia, superficial inguinal lymph nodes, fascia lata, femoral sheath, superficial circumflex iliac vein (crossing in the superficial fascia) and the femoral branch of the genitofemoral nerve (which is at first lateral then anterior). Near the apex of the triangle, the medial femoral cutaneous nerve crosses in front of the artery from the lateral to the medial side. Posteriorly, the posterior wall of the femoral sheath separates the artery from the tendons of psoas, pectineus and adductor longus. The artery is separated from the hip joint by the tendon of psoas major, from pectineus by the femoral vein and profunda vessels, and from adductor longus by the femoral vein. Proximally, the nerve to pectineus passes medially behind the artery. The femoral nerve lies lateral to the artery, outside the femoral sheath. The femoral vein is medial to the artery in the proximal part of the triangle and becomes posterior distally at the apex.

Within the adductor canal, the artery is covered by skin, superficial and deep fasciae, sartorius and the fibrous roof (subsartorial fascia) of the canal. The saphenous nerve lies at first lateral, then anterior and finally medial to the artery. Adductor longus and adductor magnus are posterior, vastus medialis and its nerve are anterolateral, and the femoral vein is also posterior proximally, but it becomes lateral distally (Fig. 80.28).

Compression of the femoral artery is most effective just distal to the inguinal ligament, where it is superficial and separated from the bone (iliopubic ramus) only by the psoas tendon. For this reason arterial injury proximal to the inguinal ligament, such as laceration by a knife, cannot be controlled simply by compression. Gaining proximal control of bleeding involves major exposure of the more proximal arteries as a life-saving manoeuvre.

Branches

Superficial epigastric artery

The superficial epigastric artery arises anteriorly from the femoral artery approximately 1 cm distal to the inguinal ligament and traverses the cribriform fascia to ascend anterior to the ligament and run in the abdominal superficial fascia almost to the umbilicus. It supplies the superficial inguinal lymph nodes and superficial fascia and skin, and anastomoses with branches of the inferior epigastric artery and its contralateral fellow (Fig. 80.28).

Superficial circumflex iliac artery

The superficial circumflex iliac artery is the smallest superficial branch of the femoral artery and arises near or with the superficial epigastric artery. It usually emerges through the fascia lata, lateral to the saphenous opening, and turns laterally distal to the inguinal ligament towards the anterior superior iliac spine. It supplies the skin, superficial fascia and superficial inguinal lymph nodes, anastomosing with the deep circumflex iliac, superior gluteal and lateral circumflex femoral arteries.

The superficial circumflex iliac artery is the basis for the important axial-pattern pedicled groin skin flap. Free flaps based on the vessel may also be raised.

Superficial external pudendal artery

The superficial external pudendal artery arises medially from the femoral artery, close to the preceding branches. Emerging from the cribriform fascia, it passes medially, usually deep to the long saphenous vein, across the spermatic cord (or round ligament) to supply the lower abdominal, penile, scrotal or labial skin, and anastomoses with branches of the internal pudendal artery.

Deep external pudendal artery

The deep external pudendal artery passes medially across pectineus and anterior or posterior to adductor longus, covered by fascia lata which it pierces to supply the skin of the perineum and scrotum or labium majus. Its branches anastomose with the posterior scrotal or labial branches of the internal pudendal artery.

Muscular branches

These branches supply sartorius, vastus medialis and the adductors.

Profunda femoris

The profunda femoris artery (deep femoral artery) (Figs 80.2B, 80.22, 80.28, 80.29) is a large branch that arises laterally from the femoral artery about 3.5 cm distal to the inguinal ligament. At first lateral to the femoral artery, it spirals posterior to this and the femoral vein to reach the medial side of the femur. It passes between pectineus and adductor longus, then between the latter and adductor brevis, before it descends between adductor longus and adductor magnus. It pierces adductor magnus and anastomoses with the upper muscular branches of the popliteal artery. This terminal part is sometimes named the fourth perforating artery.

The profunda is the main supply to the adductor, extensor and flexor muscles, and also anastomoses with the internal and external iliac arteries above and with the popliteal artery below.

The origin of the profunda femoris is sometimes medial, or rarely posterior on the femoral artery; if the former, it may cross anterior to the femoral vein and then pass backwards around its medial side.

Relations

Posteriorly, in proximodistal order, lie iliacus, pectineus, adductor brevis and adductor magnus. Anteriorly, the femoral and profunda veins, and distally, adductor longus, separate the profunda femoris from the main femoral artery. Laterally vastus medialis separates the proximal part of the artery from the femur.

Branches

The profunda femoris artery gives off the lateral and medial circumflex arteries in the proximal thigh, and perforating and muscular branches more distally.

Lateral circumflex femoral artery

The lateral circumflex femoral artery (Figs 80.27, 80.29) is a laterally running branch given off near the root of the profunda. It passes between the divisions of the femoral nerve, posterior to sartorius and rectus femoris and divides into ascending, transverse and descending branches. The ascending branch ascends along the intertrochanteric line, under tensor fasciae latae, lateral to the hip joint. It anastomoses with the superior gluteal and deep circumflex iliac arteries, supplying the greater trochanter, and, with branches of the medial circumflex femoral, forms an anastomotic ring round the femoral neck, from which ring the femoral neck and head are supplied. The descending branch, sometimes direct from the profunda or the femoral, descends posterior to rectus femoris, along the anterior border of vastus lateralis, which it supplies: a long branch descends in vastus lateralis to the knee, anastomosing with the lateral superior genicular branch of the popliteal, accompanied by the nerve to vastus lateralis. The transverse branch, the smallest, passes laterally anterior to vastus intermedius and pierces vastus lateralis to wind round the femur, just distal to the greater trochanter. It anastomoses with the medial circumflex, inferior gluteal and first perforating arteries (cruciate anastomosis).

The ascending branch forms the pedicle of the tensor fasciae latae musculocutaneous flap. The descending branch supplies the anterolateral thigh fasciocutaneous flap, which is based on the fasciocutaneous perforators that arise from the descending branch.

The lateral circumflex femoral artery may arise from the femoral artery.

Medial circumflex femoral artery

The medial circumflex femoral artery (Figs 80.27, 80.29) usually originates from the posteromedial aspect of the profunda, but often originates from the femoral artery itself. It supplies the adductor muscles and curves medially round the femur between pectineus and psoas major and then obturator externus and adductor brevis, finally appearing between quadratus femoris and the upper border of adductor magnus, dividing into transverse and ascending branches. The transverse branch takes part in the cruciate anastomosis. The ascending branch ascends on the tendon of obturator externus, anterior to quadratus femoris, to the trochanteric fossa, where it anastomoses with branches of the gluteal and lateral circumflex femoral arteries. An acetabular branch at the proximal edge of adductor brevis enters the hip joint under the transverse acetabular ligament with one from the obturator artery. It supplies the fat in the fossa, and reaches the femoral head along its ligament. For details of the blood supply of the proximal end of the femur consult Crock (1996).

Perforating arteries

The perforating arteries (Fig. 80.22) perforate the femoral attachment of adductor magnus to reach the flexor aspect of the thigh. There are three perforating branches, and the terminal part of the profunda itself becomes the fourth perforator. They pass close to the linea aspera under small tendinous arches and give off muscular, cutaneous and anastomotic branches. Diminished, they pass deep to the short head of biceps femoris (the first usually through the attachment of gluteus maximus), traverse the lateral intermuscular septum and enter vastus lateralis. The first arises proximal to adductor brevis, the second anterior and the third distal to the muscle. The first perforating artery passes back between pectineus and adductor brevis (sometimes through the latter), pierces adductor magnus near the linea aspera to supply adductor brevis, adductor magnus, biceps femoris and gluteus maximus, and anastomoses with the inferior gluteal, medial and lateral circumflex femoral and second perforating arteries. The larger second perforating artery, often arising with the first, pierces the attachments of adductor brevis and magnus, divides into the ascending and descending branches supplying the posterior femoral muscles and anastomoses with the first and third perforating arteries. The femoral nutrient artery usually arises from it. When two nutrient arteries exist they usually arise from the first and third perforators. The third perforating artery starts distal to adductor brevis, pierces the attachment of adductor magnus and divides into branches to the posterior femoral muscles. It anastomoses proximally with the perforating arteries, and distally with the end of the profunda and muscular branches of the popliteal. The femoral nutrient artery may arise from it. Side branches of the diaphysial nutrient and other branches of the profunda provide subsidiary cortical arteries.

The perforating arteries form a double chain of anastomoses, initially in the adductor muscles and subsequently near the linea aspera.

Muscular branches

Numerous muscular branches arise from the profunda femoris artery. Some end in the adductors, and others pierce adductor magnus, supply the flexors and anastomose with the medial circumflex femoral artery and superior muscular branches of the popliteal artery. The profunda is thus the main supply to the femoral muscles.

Descending genicular artery

The descending genicular artery (see Fig. 82.1), the distal branch of the femoral artery, arises just proximal to the adductor opening and immediately supplies a saphenous branch. It then descends in vastus medialis, anterior to the tendon of adductor magnus, to the medial side of the knee, where it anastomoses with the medial superior genicular artery. Muscular branches supply vastus medialis and adductor magnus and give off articular branches that anastomose round the knee joint (Ch. 82). One articular branch crosses above the femoral patellar surface, forming an arch with the lateral superior genicular artery and supplying the knee joint. The saphenous branch (saphenous artery) emerges distally through the roof of the adductor canal to accompany the saphenous nerve to the medial side of the knee. It passes between sartorius and gracilis and supplies the skin of the proximomedial area of the leg, and anastomoses with the medial inferior genicular artery.

Arterial anastomoses around the hip

Anastomoses on the back of the thigh

An important chain of anastomoses extends on the back of the thigh from the gluteal region to the popliteal fossa. It is formed in proximodistal order by anastomoses between the gluteal arteries and terminals of the medial circumflex femoral artery; the circumflex femoral arteries and the first perforating artery; the perforating arteries themselves; and between the fourth perforating artery and the superior muscular branches of the popliteal artery (Fig. 80.17). The trochanteric and cruciate anastomoses are the proximal elements of this chain.

Trochanteric anastomosis

The trochanteric anastomosis lies near the trochanteric fossa of the femur and is an anastomosis between the ascending branch of the medial circumflex femoral artery and descending branches of the superior and inferior gluteal arteries (Fig. 80.17). The lateral circumflex femoral artery and the first perforating artery from the profunda may also contribute, creating an extracapsular ‘arterial ring of the femoral neck’ (Crock 1996). Branches from this ring, the retinacular vessels, pierce the capsule and ascend along the femoral neck to give the main blood supply to the head of the femur.

Cruciate anastomosis

The cruciate anastomosis lies at the level of the lesser trochanter, near the lower edge of the femoral attachment of quadratus femoris and is an anastomosis between the transverse branches of the medial and lateral circumflex femoral arteries, a descending branch of the inferior gluteal artery and an ascending branch from the first perforating artery.

Collateral circulation in proximal femoral artery occlusion

After occlusion of the femoral artery proximal to the origin of the profunda femoris artery, five main anastomotic channels are available. These are between branches of the superior and inferior gluteal arteries, the medial and lateral circumflex femoral arteries and the first perforating branch of the profunda femoris artery; the obturator branch of the internal iliac artery and the medial circumflex femoral artery; the internal pudendal branch of the internal iliac artery and the superficial and deep external pudendal branches of the femoral artery; a deep circumflex iliac branch of the external iliac artery, the lateral circumflex femoral branch of the profunda femoris artery and the superficial circumflex iliac branch of the femoral artery; the inferior gluteal branch of the internal iliac artery and perforating branches of the profunda femoris artery.

Perforator flaps in the hip and thigh

Gluteal region

The gluteal region of the lower limb has an average of 21 perforators which arise from three main source arteries, namely the superior and inferior gluteal and internal pudendal arteries. The flaps which are based on these perforators are used as free flaps for breast reconstruction and as local flaps for covering defects in the sacral and perineal region.

Hip and thigh region

The hip and thigh region has six source arteries and an average of 50 arterial perforators. The thigh can be divided into four areas: antero-medial; antero-lateral and trochanteric; postero-medial; postero-lateral. The perforators that supply the antero-medial thigh are derived from the femoral artery, and those for the antero-lateral thigh are derived from branches of the lateral circumflex femoral artery. Perforators that supply the skin over the posteromedial and posterolateral thigh regions are derived from the profunda femoris and the popliteal arteries. Skin flaps based on the superficial circumflex iliac, superficial external pudendal and superficial inferior epigastric arteries have been used as local flaps, tube pedicles and free tissue transfers. Other popular skin flaps are TFL (tensor-fasciae latae) perforator flaps, ALT (anterolateral thigh) and AMT (anteromedial thigh) flaps, gracilis perforator flap and posterior thigh flaps.

VEINS

Femoral vein

The femoral vein accompanies its artery, beginning at the adductor opening as the continuation of the popliteal vein, and ending posterior to the inguinal ligament as the external iliac vein (Figs 80.3, 80.28). The vein is posterolateral to the femoral artery in the distal adductor canal. More proximally in the canal, and in the distal femoral triangle (i.e. at its apex), the vein lies posterior to the artery and proximally, at the base of the triangle, the vein lies medial to the artery. The vein occupies the middle compartment of the femoral sheath, between the femoral artery and femoral canal; fat in the canal permits expansion of the vein.

The femoral vein has numerous muscular tributaries. The profunda femoris vein joins the femoral vein posteriorly 4–12 cm distal to the inguinal ligament, and the long saphenous vein then enters anteriorly. Veins accompanying the superficial epigastric, superficial circumflex iliac and external pudendal arteries join the long saphenous vein before it enters the saphenous opening. Lateral and medial circumflex femoral veins are usually tributaries of the femoral vein. There are usually four or five valves in the femoral vein: the two most constant are just distal to the entry of the profunda femoris vein and near the inguinal ligament.

Profunda femoris vein

The profunda femoris vein lies anterior to its artery, and receives tributaries corresponding to the branches of the artery. Through these tributaries it connects distally with the popliteal and proximally with the inferior gluteal veins. It sometimes drains the medial and lateral circumflex femoral veins and has a valve just before it empties into the femoral vein.

Long saphenous vein

The long saphenous vein (great saphenous vein) (see Fig. 79.9A), the longest vein in the body, starts distally as a continuation of the medial marginal vein of the foot, and ends in the femoral vein a short distance distal to the inguinal ligament. It ascends immediately anterior to the tibial malleolus, crosses the distal third of the medial surface of the tibia obliquely in an anteroposterior direction to reach its medial border, then ascends a little behind the border to the knee. Proximally it is posteromedial to the medial tibial and femoral condyles (lying the breadth of the subject’s hand posterior to the medial edge of the patella), and then ascends the medial aspect of the thigh. It passes through the saphenous opening and finally opens into the femoral vein. The ‘centre’ of the opening is often said to be 2.5–3.5 cm inferolateral to the pubic tubercle, and the vein is then represented by a line drawn from this point to the femoral adductor tubercle. However, the saphenous opening varies greatly in size and disposition so that this ‘centre’ is not a reliable surface marking for the saphenofemoral junction.

In its course through the thigh the long saphenous vein is accompanied by branches of the medial femoral cutaneous nerve. At the knee the saphenous branch of the descending genicular artery (the saphenous artery) and, in the leg and foot, the saphenous nerve, are all anterior to the vein. The vein is often duplicated, especially distal to the knee. It has from 10 to 20 valves, which are more numerous in the leg than in the thigh. One is present just before the vein pierces the cribriform fascia, another at its junction with the femoral vein. In almost its entire extent the vein lies in superficial fascia, but it has many connections with the deep veins, especially in the leg.

Tributaries

At the ankle the long saphenous vein drains the sole by medial marginal veins. In the leg it often connects with the short saphenous vein and with deep veins via perforating veins. Just distal to the knee it usually receives three large tributaries: from the front of the leg, from the tibial malleolar region (connecting with some of the ‘perforating’ veins) and from the calf (communicating with the short saphenous vein). The tributary draining the tibial malleolar region is formed distally from a fine network or ‘corona’ of delicate veins over the medial malleolus, and then ascends the medial aspect of the calf as the posterior arch vein (Dodd & Cockett 1976). This vein was first illustrated by Leonardo da Vinci, whose name is sometimes given to it. It connects with posterior tibial venae comitantes by a series of perforating (communicating) veins. There are usually three, equally spaced between the medial malleolus and the midcalf. More than three such perforators are uncommon, and an arch vein perforator above midcalf is only very rarely found.

Above the posterior crural arch vein, perforating veins join the long saphenous vein or one of its main tributaries at two main sites. The first is at a level in the upper calf indicated by its name, the tibial tubercle perforator; the second is in the lower/intermediate third of the thigh where it perforates the deep fascial roof of the subsartorial canal to join the femoral vein.

In the thigh the long saphenous vein receives many tributaries. Some open independently, while others converge to form large named channels that frequently pass towards the basal half of the femoral triangle before joining the long saphenous near its termination. These may be grouped as follows: one or more large posteromedial tributaries, one or more large anterolateral tributaries, four or more peri-inguinal veins. The posteromedial vein of the thigh, large and sometimes double, drains a large superficial region indicated by its name: it has (as have the other tributaries) radiological and surgical significance. One of its lower radicles is often continuous with the short saphenous vein. The posteromedial vein is sometimes named the accessory saphenous vein, though some restrict the term accessory to a lower (more distal) posteromedial tributary when two (or more) are present. Another large vessel, the anterolateral vein of the thigh (anterior femoral cutaneous vein), usually commences from an anterior network of veins in the distal thigh and crosses the apex and distal half of the femoral triangle to reach the long saphenous vein. As the latter traverses the saphenous opening, it is joined by the superficial epigastric, superficial circumflex iliac and superficial external pudendal veins. Their mode of union varies. Superficial epigastric and circumflex iliac veins drain the inferior abdominal wall, the latter also receiving tributaries from the proximolateral region of the thigh. The superficial epigastric or the femoral vein may connect with the lateral thoracic veins by means of a thoracoepigastric vein that runs superficially on the anterolateral aspect of the trunk. This vein connects the inferior and superior caval areas of drainage and may be dilated and visible in cases of inferior caval obstruction. Superficial external pudendal veins drain part of the scrotum/labia; one is joined by the superficial dorsal vein of the penis/clitoris. The deep external pudendal veins join the long saphenous vein at the saphenous opening.

The long saphenous vein is often harvested for grafts used both in peripheral and coronary arterial surgery.

LYMPHATIC DRAINAGE

Superficial inguinal nodes

The superficial inguinal nodes form proximal and distal groups. The proximal group usually consists of five or six nodes just distal to the inguinal ligament. Its lateral members receive afferent vessels from the gluteal region and the adjoining infra-umbilical anterior abdominal wall. Medial members receive superficial vessels from the external genitalia (including the inferior vagina), inferior anal canal and perianal region, adjoining abdominal wall, umbilicus and uterine vessels accompanying the round ligament. The distal group usually consists of four or five nodes along the termination of the long saphenous vein. They receive all the superficial vessels of the lower limb, except those from the posterolateral calf. All superficial inguinal nodes drain to the external iliac nodes, some via the femoral canal and others anterior or lateral to the femoral vessels. Numerous vessels interconnect individual nodes.

Superficial inguinal nodes are frequently enlarged in disease or injury in their region of drainage. Thus the proximal inguinal nodes are almost invariably affected in malignant or infective disease of the prepuce, penis, labia majora, scrotum, perineum, anus and lower vagina, or in diseases affecting the skin and superficial structures in these regions, in the infra-umbilical part of the abdominal wall or in the gluteal region. The distal group is implicated only in disease or injury of the limb.

Deep inguinal nodes

The deep inguinal nodes vary from one to three, and are situated medial to the femoral vein. One lies just distal to the saphenofemoral junction, another in the femoral canal, and the most proximal node lies laterally in the femoral ring. The middle node is the most inconstant and the proximal node is often absent. All receive deep lymphatics that accompany the femoral vessels, lymph vessels from the glans penis or clitoris and a few efferents from the superficial inguinal nodes. Their own efferents traverse the femoral canal to the external iliac nodes.

INNERVATION

LUMBAR PLEXUS AND BRANCHES

The lumbar plexus is formed by the first three and most of the fourth, lumbar ventral rami (see p. 1078). The iliohypogastric, iliolingual and genitofemoral nerves are described on pages 1080.

Lateral cutaneous nerve of the thigh

The lateral cutaneous nerve of the thigh arises from the dorsal branches of the second and third lumbar ventral rami and emerges from the lateral border of psoas major, crossing the iliacus obliquely towards the anterior superior iliac spine. It supplies the parietal peritoneum in the iliac fossa. The right nerve passes posterolateral to the caecum, separated from it by the fascia iliaca and peritoneum; the left passes behind the lower part of the descending colon. Both pass behind or through the inguinal ligament, variably medial to the anterior superior iliac spine (commonly 1 cm) and anterior to or through sartorius into the thigh, where they divide into anterior and posterior branches. The anterior branch becomes superficial approximately 10cm distal to the anterior superior iliac spine and supplies the skin of the anterior and lateral thigh as far as the knee. It connects terminally with the cutaneous branches of the anterior division of the femoral nerve and the infrapatellar branch of the saphenous nerve, forming the peripatellar plexus. The posterior branch pierces the fascia lata higher than the anterior, and divides to supply the skin on the lateral surface from the greater trochanter to about midthigh. It may also supply the gluteal skin.

Lesions of the lateral cutaneous nerve of the thigh

The lateral cutaneous nerve of the thigh may become entrapped at three sites along its course: close to the vertebral column; within the abdominal cavity as the nerve travels across the pelvis; as it leaves the pelvis. This last site is where the nerve is most commonly damaged, and entrapment is thought to occur as the nerve passes through or deep to the inguinal ligament just medial to the anterior superior iliac spine. The angulation of the nerve as it crosses the iliac crest means that it is vulnerable to compression during movement, e.g. hip extension may increase angulation and tension on the nerve.

Injury produces an area of impaired sensation, often with pain and paraesthesia on the anterolateral aspect of the thigh (meralgia paraesthetica) in the distal cutaneous distribution of the nerve. This area does not extend across the midline anteriorly, it does not extend below the knee and it does not extend behind the hamstring tendons laterally. Symptoms may be exacerbated when wearing tight belts or tight-waisted clothes or as a result of a recent weight gain or pregnancy. Exceptionally the posterior branch of the lateral cutaneous nerve of the thigh, which supplies a thin strip from the greater trochanter of the femur down about two-thirds of the way to the knee, may be affected separately. This branch leaves the main trunk of the nerve, usually distal to the inguinal ligament, and it then turns laterally to pierce tensor fasciae latae, where it may become entrapped.

Femoral nerve

The femoral nerve is the largest branch of the lumbar plexus and arises from the dorsal branches (posterior divisions) of the second to fourth lumbar ventral rami (Fig. 80.30). It descends through psoas major, emerging low on its lateral border, and then passes between psoas and iliacus, deep to the iliac fascia. Passing behind the inguinal ligament into the thigh, it is split into anterior and posterior divisions by the lateral circumflex femoral artery. Behind the inguinal ligament it is separated from the femoral artery by part of psoas major. In the abdomen the nerve supplies small branches to iliacus and pectineus and a branch to the proximal part of the femoral artery; the latter branch sometimes arises in the thigh.

Fig. 80.30 The nerves of the left thigh: anterior aspect.

(From Sobotta 2006.)

Nerve to pectineus

The nerve to pectineus branches from the medial side of the femoral nerve near the inguinal ligament. It passes behind the femoral sheath and enters the anterior aspect of the muscle.

Anterior division of the femoral nerve

The anterior division of the femoral nerve supplies intermediate and medial cutaneous nerves of the thigh and branches to sartorius.

Medial cutaneous nerve of the thigh

The medial cutaneous nerve of the thigh is at first lateral to the femoral artery. It crosses anterior to the artery at the apex of the femoral triangle, and divides into anterior and posterior branches. Before doing so, it sends a few rami through the fascia lata to supply the skin of the medial side of the thigh, near the long saphenous vein: one ramus emerges via the saphenous opening, another becomes subcutaneous about midthigh. The anterior branch descends on sartorius, perforates the fascia lata beyond midthigh, and divides into a branch which supplies the skin as low as the medial side of the knee, and another which runs lateral to the former and connects with the infrapatellar branch of the saphenous nerve. The posterior branch descends along the posterior border of sartorius to the knee, pierces the fascia lata, connects with the saphenous nerve, and gives off several cutaneous rami, some as far as the medial side of the leg. The nerve contributes to the subsartorial plexus (see below).

Intermediate cutaneous nerve of the thigh

The intermediate cutaneous nerve of the thigh usually pierces the fascia lata 8 cm below the inguinal ligament, either as two branches or as one trunk that quickly divides into two. These descend on the front of the thigh, supplying the skin as far as the knee and ending in the peripatellar plexus. The lateral branch of the intermediate cutaneous nerve communicates with the femoral branch of the genitofemoral nerve, frequently piercing sartorius and sometimes supplying it.

Nerve to sartorius

The main nerve to sartorius arises from the femoral nerve in common with the intermediate cutaneous nerve of the thigh.

Posterior division of the femoral nerve

The branches of the posterior division of the femoral nerve are the saphenous nerve and branches to quadriceps femoris and the knee joint.

Saphenous nerve

See page 1409.

Muscular branches

The muscular branches of the posterior division of the femoral nerve supply quadriceps femoris. A branch to rectus femoris enters its proximal posterior surface and also supplies the hip joint. A larger branch to vastus lateralis forms a neurovascular bundle with the descending branch of the lateral circumflex femoral artery in its distal part and also supplies the knee joint. A branch to vastus medialis descends through the proximal part of the adductor canal, lateral to the saphenous nerve and femoral vessels, and enters the muscle at about its midpoint, sending a long articular filament distally along the muscle to the knee. Two or three branches to vastus intermedius enter its anterior surface about midthigh; a small branch from one of these descends through the muscle to supply articularis genu and the knee joint.

Vascular branches

Vascular branches of the femoral nerve supply the femoral artery and its branches.

Lesions of the femoral nerve

The main trunk of the femoral nerve is not subject to an entrapment neuropathy, but it may be compressed by retroperitoneal tumours or retroperitoneal haemorrhage in patients on anticoagulants or with a bleeding diathesis. A localized lesion of the femoral nerve may occur in diabetes mellitus (one of the forms of diabetic amyotrophy). The most striking feature of femoral neuropathy is wasting and weakness of quadriceps femoris, which results in considerable difficulty in walking and a tendency for the leg to collapse. Pain and paraesthesia may occur on the anterior and medial aspect of the thigh, extending down the medial aspect of the leg in the distribution of the saphenous branch of the femoral nerve.

Obturator nerve

The obturator nerve arises from the ventral branches of the second to fourth lumbar ventral rami. The branch from the third is the largest while that from the second is often very small. The nerve descends in psoas major, emerging from its medial border at the pelvic brim to pass behind the common iliac vessels and lateral to the internal iliac vessels. It then descends forwards along the lateral wall of the lesser pelvis on obturator internus, anterosuperior to the obturator vessels, to the obturator foramen, entering the thigh by its upper part. Near the foramen it divides into anterior and posterior branches, separated at first by part of obturator externus and lower down by adductor brevis.

Anterior branch

The anterior branch (Fig. 80.30) leaves the pelvis anterior to obturator externus, descending in front of adductor brevis, behind pectineus and adductor longus. At the lower border of adductor longus it communicates with the medial cutaneous and saphenous branches of the femoral nerve, to form a subsartorial plexus that supplies the skin on the medial side of the thigh (see below). It descends on, and supplies, the femoral artery. Near the obturator foramen the anterior branch supplies the hip joint. Behind pectineus it supplies adductor longus, gracilis, usually adductor brevis and often pectineus, and connects with the accessory obturator nerve (when this nerve is present). Occasionally the communicating branch to the femoral medial cutaneous and saphenous branches continues as a cutaneous branch to the thigh and leg. When this occurs, the nerve emerges from behind the distal border of adductor longus to descend along the posterior margin of sartorius to the knee, where it pierces the deep fascia and connects with the saphenous nerve to supply the skin halfway down the medial side of the leg.

Subsartorial nerve plexus

The medial cutaneous nerve of the thigh forms a subsartorial plexus with branches of the saphenous and obturator nerves, deep to the fascia lata, at the lower border of adductor longus. When the communicating branch of the obturator nerve is large and reaches the leg, the posterior branch of the medial cutaneous nerve is small, and ends in the plexus from which it gives rise to a few cutaneous filaments.

Posterior branch

The posterior branch pierces obturator externus anteriorly, supplies it and passes behind adductor brevis to the front of adductor magnus, dividing into branches to this and adductor brevis when the latter is not supplied by the anterior division. It usually sends an articular filament to the knee joint which either perforates adductor magnus distally or traverses its opening with the femoral artery to enter the popliteal fossa. Within the fossa the nerve descends on the popliteal artery to the back of the knee, pierces its oblique posterior ligament and supplies the articular capsule. It gives filaments to the popliteal artery.

Lesions of the obturator nerve

Isolated lesions of the obturator nerve are extremely rare, but may occasionally occur as a result of direct trauma (sometimes during parturition) or in anterior dislocations of the hip. The nerve may also be damaged by a rare obturator hernia, or be involved together with the femoral nerve in retroperitoneal lesions that occur close to the origins of the lumbar plexus. A nerve entrapment syndrome causing chronic medial thigh pain is described in athletes with large adductor muscles.

Accessory obturator nerve

Occasionally present (10%), the accessory obturator nerve is small and arises from the ventral branches of the third and fourth lumbar ventral rami. It descends along the medial border of psoas major, crosses the superior pubic ramus behind pectineus and divides into branches: one branch enters the deep surface of pectineus, another supplies the hip joint, and a third connects with the anterior branch of the obturator nerve. Sometimes the accessory obturator nerve is very small and only supplies pectineus. Any branch may be absent and others may occur: an additional branch sometimes supplies adductor longus.

SACRAL PLEXUS AND BRANCHES

The branches of the sacral plexus (see Fig. 79.11) are:

	Ventral divisions	Dorsal divisions
To quadratus femoris and gemellus inferior	L4, 5, S1
To obturator internus and gemellus superior	L5, S1, 2
To piriformis		S(1), 2
Superior gluteal		L4, 5, S1
Inferior gluteal		L5, S1, 2
Posterior femoral cutaneous	S2, 3	S1, 2
Tibial (sciatic)	L4, 5, S1, 2, 3
Common fibular (sciatic)		L4, 5, S1, 2
Perforating cutaneous		S2, 3
Pudendal	S2, 3, 4
To levator ani, coccygeus and sphincter ani externus	S4
Pelvic splanchnic	S2, 3, (4).

Sciatic nerve

The sciatic nerve is 2 cm wide at its origin and is the thickest nerve in the body. It leaves the pelvis via the greater sciatic foramen below piriformis and descends between the greater trochanter and ischial tuberosity, along the back of the thigh, dividing into the tibial and common fibular nerves at a varying level proximal to the knee. Superiorly it lies deep to gluteus maximus, resting first on the posterior ischial surface with the nerve to quadratus femoris between them. It then crosses posterior to obturator internus, the gemelli and quadratus femoris, separated by the latter from obturator externus and the hip joint. It is accompanied medially by the posterior femoral cutaneous nerve and the inferior gluteal artery. More distally it lies behind adductor magnus and is crossed posteriorly by the long head of biceps femoris. It corresponds to a line drawn from just medial to the midpoint between the ischial tuberosity and greater trochanter to the apex of the popliteal fossa.

Articular branches arise proximally to supply the hip joint through its posterior capsule; these are sometimes derived directly from the sacral plexus. Muscular branches are distributed to biceps femoris, semitendinosus, semimembranosus and the ischial part of adductor magnus.

The point of division of the sciatic nerve into its major components (tibial and common fibular) is very variable. The common site is at the junction of the middle and lower thirds of the thigh, near the apex of the popliteal fossa, but the division may occur at any level above this point, and rarely may occur below it. It is not uncommon for the major components to leave the sacral plexus separately, in which case the common fibular component usually passes through piriformis at the greater sciatic notch while the tibial component passes below the muscle.

Lesions of the sciatic nerve

The sciatic nerve supplies the knee flexors and all the muscles below the knee, which means that a complete palsy of the sciatic nerve results in a flail foot and severe difficulty in walking. Fortunately complete sciatic nerve palsy is very rare. The nerve is vulnerable in posterior dislocation of the hip. As it leaves the pelvis it passes either behind piriformis or sometimes through the muscle and at that point it may very rarely become entrapped or tethered: the piriformis syndrome is a controversial condition in which an anomalous relationship between piriformis and the sciatic nerve is thought to cause pain in the buttocks and along the course of the sciatic nerve. External compression over the buttock, e.g. in patients who lie immobile on a hard surface for a considerable length of time, can injure the nerve. However, the most common cause of serious sciatic nerve injury (and of the resulting major medicolegal claims) is iatrogenic. The nerve may be damaged in misplaced therapeutic injections into gluteus maximus (Ch. 79). Sciatic nerve palsy occurs after total hip replacement or similar surgery in 1% of cases, and may be caused by sharp injury, burning from bone cement, traction from instruments, manipulation of the hip, inadvertent lengthening of the femur, or haematoma surrounding the nerve. For some reason, possibly anatomical, the common fibular component of the sciatic nerve is more usually affected: the patient has a foot drop and a high stepping gait.

Inferior gluteal nerve

The inferior gluteal nerve arises from the dorsal branches of the fifth lumbar and first and second sacral ventral rami. It leaves the pelvis via the greater sciatic foramen below piriformis, and divides into branches that enter the deep surface of gluteus maximus.

Superior gluteal nerve

The superior gluteal nerve arises from the dorsal branches of the fourth and fifth lumbar and first sacral ventral rami. Accompanied by the superior gluteal vessels, the nerve leaves the pelvis via the greater sciatic foramen above piriformis, and divides into superior and inferior branches. The superior branch accompanies the upper branch of the deep division of the superior gluteal artery to supply gluteus medius and occasionally gluteus minimus. The inferior branch runs with the lower ramus of the deep division of the superior gluteal artery across gluteus minimus, supplies the glutei medius and minimus and ends in tensor fasciae latae.

Pudendal nerve

See Fig. 62.15 and page 1081.

Perforating cutaneous nerve

The perforating cutaneous nerve usually arises from the posterior aspects of the second and third sacral ventral spinal rami. It pierces the sacrotuberous ligament, curves round the inferior border of gluteus maximus and supplies the skin over the inferomedial aspect of this muscle. The nerve may arise from the pudendal nerve or it may be absent, in which case it may be replaced either by a branch from the posterior femoral cutaneous nerve or from the third and fourth, or fourth and fifth, sacral ventral rami.

Nerve to quadratus femoris and gemellus inferior

The nerve to quadratus femoris and gemellus inferior arises from the ventral branches of the fourth lumbar to the first sacral ventral rami. It leaves the pelvis via the greater sciatic foramen below piriformis, descends on the ischium deep to the sciatic nerve, the gemelli and the tendon of obturator internus, and supplies gemellus inferior, quadratus femoris and the hip joint.

Nerve to obturator internus and gemellus superior

The nerve to obturator internus and gemellus superior arises from the ventral branches of the fifth lumbar and first and second sacral ventral rami. It leaves the pelvis via the greater sciatic foramen below piriformis, supplies a branch to the upper posterior surface of gemellus superior, crosses the ischial spine lateral to the internal pudendal vessels, re-enters the pelvis via the lesser sciatic foramen, and enters the pelvic surface of obturator internus.

Posterior cutaneous nerve of the thigh

The posterior cutaneous nerve of the thigh arises from the dorsal branches of the first and second, and the ventral branches of the second and third sacral rami. It leaves the pelvis via the greater sciatic foramen below piriformis and descends under gluteus maximus with the inferior gluteal vessels, lying posterior or medial to the sciatic nerve. It descends in the back of the thigh superficial to the long head of biceps femoris, deep to the fascia lata. It pierces the deep fascia behind the knee and accompanies the short saphenous vein to midcalf, its terminal twigs connecting with the sural nerve. Its branches are all cutaneous and are distributed to the gluteal region, perineum and the flexor aspect of the thigh and leg.

Three or four gluteal branches curl round the lower border of gluteus maximus to supply the skin over the inferolateral portion of the muscle. The perineal branch supplies the superomedial skin in the thigh, curves forwards across the hamstrings below the ischial tuberosity, pierces the fascia lata and then runs in the superficial perineal fascia to the scrotal or labial skin. It communicates with the inferior rectal and posterior scrotal or labial branches of the perineal nerve, and gives numerous branches to the skin of the back and medial side of the thigh, the popliteal fossa and the proximal part of the back of the leg.

Nerve to piriformis

The nerve to piriformis usually arises from the dorsal branches of the first and second sacral ventral rami (sometimes only the second) and enters the anterior surface of piriformis.

Visceral and pelvic muscular branches of sacral plexus

Visceral branches of the sacral plexus are described on page 1092. For pelvic muscular branches, see page 1083.