THE PELVIC GIRDLE AND LOWER LIMB I.
BONES OF THE PELVIC GIRDLE AND LOWER LIMB A.
Bones of the pelvic girdle (Fig. 7.29-7.32) Along with the sacrum, these two bones form a complete ring. Use disarticulated bones and skeletons to study these bones.
Coxal bones (Fig.7.30, 7.31) Know right from left. Each coxa (singular) is formed by the fusion of three irregularly-shaped bones.
Features of the coxal bones Symphysis pubis Acetabulum Anteriorsuperior iliac spine Anterior inferior iliac spine Pelvic inlet
liac crest Ischial tuberosity Ischial spine Sacroiliac joint Obturator foramen Subpubic angle
Bones of the thigh and leg Use the disarticulated bones.
Femur (Fig. 7.33) Know right from left. Head Neck Greater trochanter (“tro-cant-er”) Lesser trochanter
Lateral condyle Medial condyle Lateral epicondyle Medial epicondyle Linea aspera
Patella (Fig. 7.34) You do not need to distinguish right from left.
Tibia (Fig. 7.35) Know right from left. Tibial tuberosity Medial malleolus (“mal-lee-o-lus”)
Fibula (Fig. 7.35) You do not need to distinguish right from left, but recognize the proximal end from the distal end. Head
Bones of the ankle and foot (Fig.7.378) Use the articulated foot bones. 1.
Tarsal bones There are 7, but we will name only the largest two: Talus
Lateral condyle Medial condyle Tibial (anterior) crest
Metatarsals 1-5 (Numbered from medial to lateral.)
Phalanges (fa lan jeez); singular is phalanx (fay-lanks) The hallux (digit 1) has a proximal phalanx and distal phalanx. Digits 2-5 have a proximal, middle and distal phalanx.
Helpful tips for learning these bones 1.
The “features” of bones (Table 7.2) Condyle: the smooth surface of a joint Crest: a ridge along a bone Epicondyle: a rough surface above a condyle for muscle attachment Foramen: an opening in a bone (plural– foramina) Head: a more or less round end of a bone Neck: a narrow part between two larger parts of a bone Notch: a small cut-out part on a bone Process: a part of a bone that projects out Spine: a sharp projection of a bone Trochanter: a large, blunt tuberosity Tuberosity: a large rough bump where a muscle attaches
Observe the articulations of the coxal bones on a skeleton. At the sacroiliac joint, the coxal bone articulates with what other bone? _________________________________ The head of the femur articulates with what part of the coxal bone? ____________________________
Observe the articulations of the knee on a skeleton. The medial and lateral condyles of the femur articulate with the tibia’s ________________________ ________________________ and ________________________ ______________________ . Does the fibula articulate with the femur? (Yes/No) ______ It articulates with the _____________. Finally, notice the position of the patella.
Observe the articulations of the ankle on a skeleton. The lateral malleolus of the _________________ and the medial malleolus of the ___________________ form a strong hinge joint with the _________________ bone.
How many tarsal bones are there? (Count the talus and calcaneus as well as the others that we did not name.) _______
Optional notes on the bones of the pelvic girdle and lower limbs 1.
The neck of the femur is the site of a "broken hip." A "complete hip replacement" is surgery in which a stainless steel head and neck replaces the proximal portion of the femur, and a "cup" replaces the acetabulum.
A child's head is said to be "engaged" when it is lodged within the pelvic inlet prior to its birth.
The ischial spines, if large, can decrease the space available for passage of the fetus at birth.
The subpubic angle is wider in the female pelvis (greater than 90o ) than in the male pelvis (less than 90o ). The pelvic inlet in the female is oval shaped; in the male it is heart-shaped. The female pelvis is wider and shallower than the male pelvis. For other differences between male and female pelvises, see Fig. 7.32.
The weight bearing bone of the leg is the tibia. The fibula serves to stabilize the ankle joint.
MUSCLES THAT ACT ON THE LOWER LIMB
Movement of the thigh (Fig. 10.31-10.33) Use the torso models, and lower limb models. Note that iliopsoas is best seen within the abdomen, on its posterior wall. 1.
Iliopsoas (“il-e-o-so-as”) (Iliacus and psoas major)
Origin: Ilium Insertion: Greater trochanter Actions: Extends and abducts thigh
Origin: Ilium Insertion: Greater trochanter Action: Abducts thigh
Origin: Pubis Insertion: Linea aspera Actions (2): Adducts and flexes thigh
(Adductor longus, brevis and magnus)
Origin: Ilium, lumbar vertebra Insertion: Lesser trochanter Action: Flexes thigh
Movement of the thigh and leg (Fig. 10.30, 10.33) 1.
Quadriceps femoris group Origin: Femur, anterior inferior iliac spine (Rectus femoris Insertion: Tibial tuberosity vastus lateralis, etc.) Actions (2): Flexes thigh; extends leg
Hamstring group (semimembranosus semitendinosus, biceps femoris)
Origin: Ischial tuberosity Insertion: Tibia and fibula Action (2): Extends thigh; flexes leg Origin: Anterior superior iliac spine Insertion: Tibia Actions (3): Flexes and laterally rotates thigh; flexes leg (tailor sitting position)
Movement of the foot and toes (Fig. 10.36; 10.37 [10.38, 10.39]) 1.
Peroneus (fibularis) longus Actions (2): Plantarflexes and everts foot
Action: Extends toes
Actions: Dorsiflexes and inverts foot
Action: Flexes toes
Insertion: Calcaneus via Achilles' tendon Action: Plantarflexes foot
(A “PET Fat Goldfish” can help you learn names and locations on the leg.)
Anatomy is a precise descriptive science based on observation. Unlike the common misconception, it is not based on rote memory! 1.
Each name is meant to identify some characteristic of the muscle. Make the muscle “show” you its name as you observe its location, shape, size, or action.
On the trunk origins are more medial; insertions are more lateral. On the limbs origins are more proximal; insertions are more distal.
Make the muscle “show” you its origin or insertion by observing it. In most but not all muscles, you can see the assigned origin and insertion on the models.
Muscles on the limbs usually cause movement of the part of the limb distal to their belly.
Make the muscle “show” you its action by its position. Muscles cause movement by shortening (contracting), which pulls one bone toward or away from another bone. Notice the direction of the fibers of the muscle, which are the parts that shorten.
As you learn each muscle, draw your fingers slowly along the belly from the origin to the insertion. Say the name. Name the origin and name the insertion as you touch each end on the models or yourself. Then, perform the actions with your own muscles as you
17 say the name of the actions aloud. In lab, use the models and your own muscles. At home, use your own muscles.
Optional notes on the muscles that act on the lower limbs: 1.
The gluteus maximus is a common site for intramuscular injections, since it is the thickest muscle of the body. However, the thickest nerve of the body, the sciatic nerve, runs deep to the gluteus maximus, making an understanding of the anatomy essential to know before attempting an intramuscular injection in this region.
Iliopsoas is located primarily in the posterior wall of the abdomen. It shortens with prolonged sitting and contributes importantly to lower backache. The "fencer's position" (one thigh and knee flexed; the other thigh extended posteriorly with knee straight) is a common exercise specifically designed to stretch the iliopsoas. The “cat back” (on hands and knees the back is arched upward) is another exercise which stretches the iliopsoas.
The adductor muscles are the ones that ache a day after horseback riding.
A "pulled groin" is a sharply painful injury to the origin of the adductors, on the pubis.
A "pulled hamstring" is a similarly painful injury to the origin of the hamstring muscles, on the ischial tuberosities.
"Sartorius" comes from the Latin word meaning "tailor." To remember its three actions, sit crossed-legged (tailor sitting).
Achilles' tendon is named for Achilles, the Greek mythological hero whose mother held him by the heel and dipped him in the river Styx when he was a baby, to make him invincible. As an adult he died of a poisoned arrow to the calcaneus, which didn't get dipped....
The Spanish word for socks is "calcetines;" it is related to the Latin calcaneus (heel). Peroneus longus means "long pin" in Latin. Observe its shape.
Tibialis anterior is a muscle which can be involved in painful "shin splints.”