Lab 14 Pre-Lab Exercise:
The hind limb is directly attached to the axial skeleton through the os coxae or hip bone ("innominate bone"). The two innominate bones join with the sacrum to form the pelvis. The os coxae are formed ontogenetically by the fusion of the ilium, ischium, and the pubis.
The ilium (pl. ilia) is the largest bone of the innominate, and serves as the origin for the gluteal muscles. It is the thin, blade-like section superior to the hip socket. In the lateral aspect, the most obvious landmark of the innominate is the acetabulum, which provides the articulation for the femoral head. Other landmarks include the iliac crest, which defines the superior border of the ilium, and the sciatic notch, an indentation on the postero-inferior surface of the ilium, just superior and dorsal to the acetabulum.
The ischium (pl. ischia) is the most inferior bone of the innominate. The body of the ischium defines the border of the obturator foramen. The most caudal portion of the ischium is marked by the ischial tuberosity (what you sit on- it’s the bone that carries the weight of the trunk in a sitting person).
The pubis is the most anterior bone of the innominate. Left and right pubic bones articulate at the pubic symphysis, which aligns with the sagittal midline of the trunk. The pubis has superior (iliopubic) and inferior (ischiopubic) rami (sing. ramus) that surround the obturator foramen.
1. Examine an innominate and identify the following:
- The points of attachment of the sacrospinous, sacrotuberous, and posterior sacroiliac ligaments. These ligaments resist sacroiliac dislocation and rotation of the sacrum.
- The ischial tuberosity, bears the weight of the trunk when we sit, and serves as the site of attachment of the hamstring muscles
- The C-shaped articular surface of the acetabulum
- The anterior superior iliac spine, where the inguinal ligament and sartorius muscle attach
- The anterior inferior iliac spine, where the rectus femoris muscle and the iliofemoral ligament attach. Note also the osseous parts of the boundaries of the greater and lesser sciatic foramina, separated by the sacrospinous ligament, and completed medially by the sacrotuberous ligament.
The femur is the largest long bone in the body and the only bone in the thigh (as the humerus is the only bone in the arm). Proximally, it is marked by the large, globular femoral head, the femoral neck, and the greater trochanter. The femoral head articulates with the acetabulum of the innominate (note the smooth surface of the femoral head at this articulation).
The femoral shaft (diaphysis) is generally very robust with a slight anterior curvature. Dorsomedialy, the shaft is marked near its proximal end by the lesser trochanter. At its distal end, the femoral shaft expands into the lateral and medial femoral condyles. These condyles provide articulation with the proximal tibia, forming the knee joint. However the femur is not in direct line with the tibia; it angles medially from the acetabulum toward the knee (valgus knee). The articular surface of the condyes is expanded anteriorly to provide a groove for the patella (knee cap).
1. Examine a disarticulated femur. Locate the most important sites of muscle attachment to this bone:
- The greater trochanter (insertions of the deeper glutei and lateral rotator muscles)
- The lesser trochanter (insertion of the iliopsoas muscle)
- The linea aspera along the whole length of the posterior surface of the shaft (origin of the medial and lateral vasti muscles and the short head of the biceps femoris; insertion of the adductors muscles, pectineus, and gluteus maximus)
- Medial and lateral epicondyles (origin of the plantaris and gastrocnemius muscles)
- The adductor tubercle (insertion of the adductor magnus muscle - hamstring portion).
3. Bony landmarks of the gluteal region
Tendons, muscles and bony landmarks in the lower limb are used to locate major arteries, veins, and nerves. Because vessels are large, they can be used as entry points to the vascular system and in addition, the vessels in the lower limb are farthest from the heart and most inferior in the body. Therefore, the nature of peripheral pulses in the lower limb can give important information about the status of the circulatory system in general.
Pelvis: the hip bones (innominate) meet anteriorly at the pubic symphysis and articulates with the sacrum posteriorly. The posterior surface of the gluteal region is formed by the sacrum and coccyx. The tip of the coccyx is located in the anal cleft. In the anatomical position, the pubic tubercles (lateral to the pubic symphysis) and the anterior superior iliac spines (ASIS) are in the same vertical (coronal) plane). Superiorly, both iliac crests can be palpated throughout their lengths. The posterior superior iliac spine (PSIS) can be found at the level of S2 spinous process and marks the middle of the sacroiliac joint. At the surface, both PSIS are found as depressions of skin (dimples) posteriorly. The ischial tuberosity overlaps the inferior border of gluteus maximus when the hip is extended. It is palpable when the hip is flexed just above the gluteal fold: it becomes prominent because the muscle no longer covers the tuberosities (only overlying bursa and a pad of fat separate the tuberosities from skin).
Femur: the femur articulates proximally with the innominate at the acetabulum. The greater trochanter is a hard bony protuberance that can be palpated laterally as you medially and laterally rotate and abduct the femur. It is about a hand’s width inferior to the midpoint of the iliac crest.
4. Soft tissue of the gluteal region
Sensation and muscle action in the lower limb are tested to assess lumbar and sacral regions of the spinal cord.
Gluteus maximus: is the large and most superficial muscle that can be palpated when the hip is extended against resistance.
Gluteus medius: can be felt inferior to the iliac crest as it contracts in supporting the body weight on one leg (palpate on the side of the supporting leg). The gluteus medius is stabilizing the pelvis to prevent sagging of the pelvis to the opposite side.
5. The sciatic nerve
The sciatic nerve innervates muscles in the posterior compartment of the thigh, muscles in the leg and foot, and an appreciable area of the skin. It enters the lower limb in the gluteal region and passes inferiorly midway between two major palpable bony landmarks: the greater trochanter and the ischial tuberosity.
The gluteal region can be divided into quadrants by two lines positioned using palpable bony landmarks. One line descends vertically from the highest point of the iliac crest. The other line passes horizontally through the first line midway between the highest point of the iliac crest and the horizontal plane through the ischial tuberosities.
The sciatic nerve curves through the upper lateral corner of the lower medial quadrant and descends along the lateral margin of the lower medial quadrant. Injections can be carried out in the anterior corner of the upper lateral quadrant to avoid injury to the sciatic nerve and major vessels in the region.