Human Anatomy Lesson 24
Hip Joint, Gluteal Region
We are now turning our attention from the upper limb to the lower liimb. Although very different, their organization is similar - we will start in this lesson with the hip joint and gluteal region, which is equivalent to the shoulder joint and rotator cuff/posterior scapular muscles. Then, we turn in lesson #25 to the thigh, which is equivalent to the arm in the upper limb, and finish off with the leg, ankle, and foot in lesson #26, which is equivalent to the forearm, wrist, and hand.
Learning Objectives - By the end of this lesson, you should be able to ...
- Describe movements of the thigh at the hip joint
- List and describe the bones and ligaments that make up part of the hip joint, including different parts of the pelvis, proximal femur, and the ligaments surrounding the femoral head and neck
- Describe "gateways" where structures pass from the abdominopelvic cavity into the perineum and lower limb, and to the gluteal region in particular
- List the origins, insertions, innervations, and actions of 9 gluteal muscles
- Understand how nerves running to the lower limb are branches off the lumbosacral plexus and carry L1 to S5 fibers
- List 9 nerves running between the abdominopelvic cavity and lower limb, and list the structures innervated by 4 of these nerves that terminate in the gluteal region
- Name the branches of the internal iliac arteries and veins that supply and drain blood to/from the gluteal region
The lower limb is crucial for support and locomotion and, indeed, the human lower limb exhibits several adaptations that facilitate bipedal walking (walking on two limbs). We need to work our way up to analyzing the traits that facilitate locomotion, but for now we can concentrate on "simpler" movements of the lower limb, particularly those at the hip joint, which is the subject of this lesson.
- Flexion/extension: anterior (flexion) and posterior (extension) movements of the thigh at the hip joint in the sagittal plane. Flexion and extension are important components of bipedal walking, although not the whole story.
- AB-duction/AD-duction: movement of the thigh at the hip joint in the coronal plane, away from the midline (AB-duction) and toward the midline (AD-duction). AB-duction and AD-duction are important components of walking, especially considering that AB-duction on a fixed pelvis allows one to stand on one leg, as is necessary during the swing phase of walking (more on this later).
- Medial rotation/lateral rotation: movement of the thigh at the hip joint in the transverse plane around a supero-inferior axis.
- Circumduction: a combination of the above movements. Note that the degree of movement, and circumduction, possible at the hip joint is less than is possible at the shoulder joint, since the hip joint is a standard ball-and-socket joint and the humerus is attached to the axial skeleton at the shoulder joint largely by muscles and ligaments, not bone-on-bone connection.
Bones and Joints
- Bony pelvis: the muscles in the gluteal region all have their origin on the outer aspect of the bony pelvis and attach to the proximal part of the femur. We have reviewed much of this information previously, so this section will be something of a refresher, with a few new tidbits thrown in.
- Ilium: the gluteal muscles originate on and around the outer surface of the ilium and adjacent sacrum/coccyx. There are 3 gluteal lines on the outer surface of the ilium: (1) the inferior gluteal line, which runs from just superior to the anterior inferior iliac spine to the posterior margin of the acetabulum. The rectus femoris muscle (one of the quadriceps muscles in the anterior compartment of the leg - see lesson #25) originates from the anterior inferior iliac spine and the region between the inferior gluteal line and acetabulum. (2) Anterior gluteal line, which runs from the tuberculum of iliac crest posteriorly and inferiorly to the upper margin of the greater sciatic notch. The gluteus minimus muscle (see below) originates from between the anterior and inferior gluteal lines. (3) Posterior gluteal line, which runs from the posterior portion of the iliac crest inferiorly to the posterior superior iliac spine. The gluteus medius muscle originates between the anterior and posterior gluteal lines, and the gluteus maximus muscle attaches posterior to the posterior gluteal line (see below).
- Ischium: the ischial spine is the attachment area for the sacrospinous ligament, which runs from the ischium to the sacrum and adjacent parts of the coccyx and divides the space posterior to the ilium and ischium into upper and lower halves. The sacrotuberous ligament encloses this space completely, running from the ischial tuberosity to the sacrum, coccyx, and iliac crest as far superiorly as the posterior superior iliac spine. This creates 2 foramina: the greater sciatic foramen, which is bordered by the greater sciatic notch of the ilium superiorly and anteriorly, the sacrospinous ligament inferiorly, and the sacrotuberous ligament posteriorly; and the lesser sciatic foramen, which is bordered by the lesser sciatic notch anteriorly, the sacrospinous ligament superiorly, and the sacrotuberous ligament posteriorly and inferiorly. These two foramina are important sites of passage from the pelvis into the gluteal region (for the greater sciatic foramen) and from the gluteal region into the perineum (lesser sciatic foramen).
- Hip joint: the head of the femur articulates into the acetabulum, which forms a ball-and-socket-style synovial joint. Three ligaments (iliofemoral ligament, pubofemoral ligament, ischiofemoral ligament) tightly bind the femoral head and acetabulum together, and the ligament of head of femur attaches the femoral head (at the fovea) to fascia in the acetabular fossa. We will not consider this joint further.
- Proximal femur: the gluteal muscles attach to the greater trochanter, lesser trochanter, intertrochanteric line, and intertrochanteric crest. The greater trochanter is positioned laterally across the neck from the femoral head. Seven out of nine gluteal muscle insert onto the greater trochanter. The lesser trochanter is positioned posteromedially on the proximal femur just below the neck, and provides an attachment site for the iliopsoas musculature, which we reviewed with the abdomen and pelvis. The intertrochanteric line runs between the two trochanters on the anterior and medial surface of the proximal femur, and is continuous with the pectineal line and linea aspera on the posterior aspect of the femur. The intertrochanteric crest on the posterior surface of the femur runs directly between the two trochanters and provides attachment area for the quadratus femoris muscle (see below).
"Gateways" to the Lower Limb
In this lesson and the next two lessons, it will be of primary concern how muscles, vessels, and other structure pass from the abdominopelvic cavity into the hip, gluteal region, thigh, leg, and (for just a few long-running structures), into the ankle and foot. There are only a few passageways through the pelvis, described below. It might be useful if you glance over this information now and then come back at the end of each lesson to get a better appreciation of how structures course from the abdominopelvic cavity into the lower limb.
- Obturator canal: the obturator nerve and obturator vessels pass from the abdominopelvic region into the medial compartment of the thigh through the obturator canal, a small hole that is not covered by obturator membrane like the rest of the obturator foramen.
- Greater sciatic foramen: the piriformis muscle runs through this foramen and splits it into superior and inferior sections. The superior gluteal nerve and vessels pass superior to piriformis, and a number of other nerves and vessels traveling to the gluteal region pass through this foramen. We will cover these in detail in this lesson.
- Lesser sciatic foramen: the tendon of obturator internus passes into the gluteal region through this foramen. In addition, the pudendal nerve and internal pudendal vessels pass OUT OF the greater sciatic foramen and INTO the perineum through the lesser sciatic foramen. These vessels form the main nerve and blood supply, respectively, of the perineum.
- "Under" the inguinal ligament: the iliopsoas and pectineus muscles take this route between the abdomen and anteromedial part of the thigh, as do the femoral artery, femoral vein, and femoral nerve, among other nerves and vessels.
A set of muscles lies posterolateral to the bony pelvis and proximal end of the femur. These muscles mainly AB-duct, extend, and laterally rotate the femur in the hip joint. As noted above, nerves and other vessels run through the greater and lesser sciatic foramina from the pelvis and perineum to the thigh. There are two groups of gluteal muscles: a deep group and a superficial group. The deep group, which includes piriformis, obturator internus, gemellus superior, gemellus inferior, and quadratis femoris, are mainly lateral rotators of the femur at the hip joint. The superficial group, which includes the three gluteal muscles and tensor fascia lata, mainly AB-duct and extend the hip, in addition to stabilizing the knee.
- Piriformis: runs from the anterior surface of the sacrum through the greater sciatic foramen to insert onto the superior border of the greater trochanter of the femur. Innervated directly by anterior rami of L5, S1, and S2 spinal nerve. Laterally rotates the extended femur at the hip joint and AB-ducts the flexed femur.
- Obturator internus: runs from the deep surface of the obturator membrane and surrounding bone to the medial side of the greater trochanter of the femur by passing through the lesser sciatic foramen. Innervated by nerve to obturator internus (L5 to S1). Laterally rotates the extended femur at the hip joint and AB-ducts the flexed femur.
- Gemellus superior: runs from ischial spine to the greater trochanter of the femur along with the obturator internus tendon. Innervated by nerve to obturator internus. Laterally rotates the extended femur at the hip joint and AB-ducts the flexed femur.
- Gemellus inferior: runs from the ischial tuberosity to the greater trochanter of the femur along with the obturator internus tendon. Gemellus superior and gemellus inferior sandwich the obturator internus muscle, and both gemelli (the plural of gemellus) attach partially along the obturator internus tendon. Innervated by nerve to quadratus femoris. Note that innervation for the two gemelli muscles "piggybacks" on surrounding muscles, obturator internus for gemellus superior and quadratis femoris for gemellus inferior. Laterally rotates the extended femur at the hip joint and AB-ducts the flexed femur.
- Quadratus femoris: the most inferior of the deep muscles, quadratus femoris runs from the lateral part of the ischium just inferior to the ischial tuberosity to the intertrochanteric crest of the proximal femur. Innervated by nerve to quadratus femoris (L5 to S1). Laterally rotates the femur at the hip joint. All of the above muscles belong to the deep group of gluteal muscles.
- Gluteus minimus: runs from the external surface of the ilium to the anterolateral aspect of the greater trochanter. Innervated by the superior gluteal nerve. AB-ducts the femur at the hip joint and medially rotates the thigh.
- Gluteus medius: runs from the external surface of the ilium to the lateral surface of the greater trochanter, around the anterior side. Innervated by the superior gluteal nerve. AB-ducts the femur at the hip joint and medially rotates the thigh.
- Gluteus maximus: runs from the fascia covering gluteus medius, external surface of ilium behind the attachment of gluteus medius, posterior and lateral surfaces of the sacrum and coccyx, and sacrotuberous ligament to the gluteal tuberosity and iliotibial tract of fascia lata. Innervated by the inferior gluteal nerve. Extends the flexed femur at the hip joint and stabilizes the hip and knee joints, in addition to laterally rotating and AB-ducting the thigh. It is active during running but not during walking at normal speed.
- Tensor fascia lata: runs from the lateral part of the iliac crest between ASIS and tubercle and the iliotibial tract. Innervated by the superior gluteal nerve. Stabilizes the knee in extension.
Nerves in the Gluteal Region
Nerves that enter the lower limb from the abdominopelvic cavity are terminal branches of the lumbosacral plexus, which is made up of anterior rami of L1 to L3 (and part of L4) spinal nerves (lumbar plexus), anterior rami of the rest of L4 and L5 (lumbosacral trunk), and anterior rami of S1 to S3 (and part of S4) spinal nerves (sacral plexus). We will not focus the same amount of time on the lumbosacral plexus as we did on the brachial plexus, except to note the names of the terminal nerves: femoral nerve (L2-L4), obturator nerve (L2-L4), sciatic nerve (L4-S3), superior gluteal nerve (L4-S1), inferior gluteal nerve (L5-S2), ilio-inguinal nerve (L1), genitofemoral nerve (L1-L2), lateral cutaneous nerve of thigh (L2-L3), nerve to quadratus femoris (L4-S1), nerve to obturator internus (L5-S2), posterior cutaneous nerve of thigh (S1-S3), perforating cutaneous nerve (S2-S3). Six of these nerves enter the gluteal region through the greater sciatic foramen (+ the pudendal nerve, which is not a terminal branch off the lumbosacral plexus):
- Superior gluteal nerve: runs through the greater sciatic foramen between gluteus minimus and the piriformis muscle, and runs superiorly in the plane between gluteus minimus and gluteus medius, supplying these two muscles + tensor fascia lata.
- Sciatic nerve: enters the gluteal region through the greater sciatic foramen inferior to piriformis, descending in the plane between the superficial and deep gluteal muscles and crossing over obturator internus, the gemelli muscles, and quadratus femoris, and running halfway in-between the ischial tuberosity and greater trochanter to enter the posterior thigh. This large nerve innervates all of the muscles in the posterior (flexor) compartment of the thigh and provides motor innervation to all of the muscles that move the ankle and foot, in addition to sensory innervation to skin in the lower limb.
- Nerve to quadratus femoris: enters the gluteal region through the greater sciatic foramen inferior to piriformis and deep to the sciatic nerve, anterior to the deep muscles. As noted above, it innervates quadratus femoris and gemellus inferior.
- Nerve to obturator internus: enters the gluteal region through the greater sciatic foramen inferior to the piriformis muscle. As noted above, it provides motor innervation to gemellus superior and, after passing back into the perineum from the gluteal region, it supplies obturator internus from its deep surface.
- Posterior cutaneous nerve of the thigh: like many of the nerves above, this nerve enters the gluteal region through the greater sciatic foramen inferior to the piriformis muscle, and runs on the medial side of the sciatic nerve down into the thigh. This nerve provides sensory cutaneous innervation to gluteal folds, part of the perineum, and the posterior thigh and leg.
- Pudendal nerve: enters the gluteal region through the greater sciatic foramen inferior to the piriformis muscle, and immediately takes a sharp turn to enter the perineum through the lesser sciatic foramen. It provides somatic (motor and sensory) innervation to the perineum.
- Inferior gluteal nerve: enters the gluteal region through the greater sciatic foramen inferior to piriformis along the posterior edge of the sciatic nerve. It provides motor innervation to the gluteus maximus.
- Perforating cutaneous nerve: unlike the other nerves in the gluteal region, this small nerve actually pierces the sacrotuberous ligament and loops around the lower border of the gluteus maximus to supply skin over its medial aspect.
Vasculature of the Gluteal Region
In the abdominopelvic cavity, the aorta splits at L4 to form right and left common iliac arteries, which split at the auricles on each side of the sacrum to form an internal iliac artery that innervates pelvic, perineal, and gluteal structures, and an external iliac artery that continues under the inguinal ligament to become the femoral artery, the primary artery of the thigh and leg. The external and internal arteries and veins are shown in the figures below - the internal iliac artery and vein are labeled in these pictures as the hypogastric artery.
- Arteries: the inferior gluteal artery and superior gluteal artery run from the pelvic cavity to the gluteal region through the greater sciatic foramen. The inferior gluteal artery is from the anterior trunk of the internal iliac artery in the pelvic cavity, and the superior gluteal artery is from the posterior trunk of the internal iliac artery. These two vessels pass through the greater sciatic foramen below and above the piriformis muscle, respectively.
- Veins: inferior and superior gluteal veins drain into the femoral vein, one of the two primary veins of the thigh (the other being the great saphenous vein). That is all.
© 2014 Robert McCarthy