Sunday, June 13, 2010

Appendicular Skeleton

The appendicular skeleton has one primary function: facilitate movement! Within the appendicular skeleton, there are 126 bones in for areas.  The upper limbs have 60, the lower limbs have 60, the pectoral girdle has 4 and the pelvic girdle has 2.

The pectoral girdle is also known as the shoulder.  There are two of them, therefore two of each bone.  The pectoral girdle is made of the scapula and the clavicle.  The clavicle is an s-shaped bone.  The medial curve is convex posteriorly, while the lateral curve is concave anteriorly. It extends from the sternum to the scapula, above the first rib.  Where the two curves meet is a common fracture site. The medial side articulates with the manubrium of the sternum forming the sternoclavicular joint.  The lateral end articulates with the acromium forming the acromioclavicular joint.  Ligaments attached to the clavicle to stabilize its position.
The scapula is also called the shoulder blade.  For the amount of work that it does, it is extremely thin.  It is triangular is shape.  It articulates with both the radius and the humerus.  It is held in place posteriorly by complex shoulder and back musculature.  The medial borders of the scapulae lie about 5 cm from the vertebral column.  The scapula has four main features.  The spine is a large process on the posterior of the scapula that ends laterally as the acromion.  The acromian is the flattened portion of the spine on the scapula.  The coracoid process is a protruding projection that provides the point of attachment for the biceps trachiae.  The gelnoid is a shallow concavity that articulates with the head of the humerus.

Each upper limb consists of 30 bones.  The humerus, ulna, radius, carpals, metacarpals and phalanges.  Joints include the shoulder, elbow, wrist, metacarpophalageal and interphalageal.  
The humerus is the largest and longest bone of the upper limb.  It articulates proximally at the scapula at the glenoid cavity and distally with the ulna and radius at the elbow.  At the proximal end of the humerus, we find a rounded head, a greater tubercle (the lateral projection, distal to the neck), lesser tubercles for muscle attachment, the deltoid tuberosity and the body.  The distal end of the humerus has 2 condyles.  The capitulum laterally articulates with the the head of the radius.  The trochlea is the medial articulation with the ulna.  Medial and lateral epichondyles are the attachment sites for muscles.  
The radius and ulna make up the forearm.  On the medial side is the ulna.  The radius is on the lateral side.  The radius turns the radio (with the thumb).  Each bone articulates with the humerus and three carpal bones.  At the proximal end of the forearm, the ulna has the olecranon process that forms the point of the elbow.  The radius head articulates with the capitulum of the humerus and radial notch of ulna tuberosity for the biceps attachment. At the distal end of the forearm, the styloid process of the ulna is the site of attachment for wrist ligaments.  The radius forms wrist joints with carpals.
Eight carpal bones bound together by ligaments form the wrist.  Five metacarpal bones are in the palm of the hand (one for each finger and the thumb).  These make up knuckles.  14 phalanges are create the fingers and the thumb.

The Pelvic girdle is also known as the hip girdle.  This area provides strong and stable support for the lower appendages.  It also allows for some flexibility.  There is less flexibility than the pectoral girdle however, because it it more stable.  There are two hip bones that are also known as coxal bones or ossa coxae.  Each hip bone is composed of three bones at birth, the illium, ischium and the pubis.  These three bones fuse at the acetabelum during childhood to form the socket for the hip joint.  The ischium is the inferior, posterior portion of the hipbone.  The ischial spine and tuberosity are located here.  It forms the obturator foramen with the pubis which is the largest foramen in the body.  The pubis is the body that is superior and inferior to ramus.  It is the area that is linked to pubic symphysis.  The illium forms the illiac crest, a site for muscle attachment.  It is anterior and superior to the iliac spine. It can be felt laterally to groin.  The greater sciatic notch is here for the sciatic nerve.  The pelvis is made of the sacrum, coccyx and 2 hip bones.  The pelvic brim is from the top of the symphysis to the sacral promontory.  The false pelvis is above the brim, while the true pelvis is below the brim.

Each of the lower limbs, like the upper limbs has 30 bones.  The femur and patella within in the thigh, the tibia and fibula are in the leg, the tarsals in the ankle. the metatarsals are the foot and the phalanges are the toes.  The joints include the hip, knee and ankle, proximal and distal tibiofibular, and metatarsophalangeal.

The femur is aka the thighbone.  It is the largest, heaviest and strongest bone in the body.  It articulates with the hip bone and tibia.  The head of the femur articulates with the acetabulum.  The tibia articulates with both the medial and lateral condyles.  The neck of the femur is a constricted region distal to the head and it is a common fracture site among the elderly.  The trochanters are a bony landmark that can only be found on the hip bone.  There are greater and lesser trochanters, linea aspera and muscle attachments.

The patella, aka the kneecap, is the only sesamoid bone in the body and is located anterior to the knee joint.  It functions to increase the leverage of the tendon of the quadriceps femoris to maintain the position of the tendon when the knee is bend and to protect the joint.

The tibia is the shin bone and does all of the weight bearing.  It is larger and medial to the fibula.  The fibula is lateral and parallel to the tibia.  The tibia has lateral and medial condyles that articulate with the femur.  The tibial tuberosity os for the patellar ligaments of the quadricep femoris.  The medial malleolus is at the ankle and is the articulation point for the talus. The fibula is not in the knee.  Its main function is for attachment of muscles.  There is a lateral malleolus at the ankle.

There are seven tarsals that make the ankle and share the weight associated with walking. Five metatarsal bones are contained in the foot.  Dancers, especially ballet, fracture their metatarsals.  The arrangement of the phalanges in the toes is the same as the phalanges of the hand and is the same as described above.  The big toe is known as the hallux.

The ankle is made of seven tarsal bones.  The talus is the ankle bone and articulates with the medial malleolus of the tibia and the lateral malleolus of the fibula.  The calcaneous is the heel bone and is the largest and strongest bone in the foot.

The bones of the foot are arranged in two arches held together by ligaments and tendons.  They enable the foot to support and distribute body weight over the hard and soft tissues and provide leverage while walking.  The arches are fully developed by about age 12-13.  Flatfoot (decline), clawfoot (elevation) and clubfoot (rotation) are caused by the medial longitudinal arches.  Arches provide yield and spring back when weight is lifted.  Longitudinal arches from heel to toe along each side and the transverse arch is across the midfoot region.

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