Appendicular skeletal system

OBJECTIVES:

1. To be familiar with the bones of the pectoral girdle: scapula and clavicle

2. To identify the bones of the upper limb in addition to their structures

3. To identify the bones of the pelvic girdle: the ilium, ischium and pubis

4. To identify the different bones of the lower limb and their different structures

 

1. THE PECTORAL GIRDLE

         The pectoral girdle is composed of two bones; the scapula which is located posteriorly and the clavicle which is located anteriorly. The clavicle is S-shaped bone with two ends; the rounded end the sternal end which is directed medially and the flattened end the acromial end located laterally. The superior surface of the clavicle is smooth while the inferior one is rough containing the conoid tubercle laterally and costal tuberosity medially. The curvature of the clavicle is convexed medially but concaved laterally.

         The other bone is the scapula, has inverted triangular shape; the wide base is directed superiorly and the narrow apex is directed inferiorly. The straight edge is directed medially and the oblique one is located laterally. The anterior surface is smooth one while the posterior surface has a sharp spine. This bone contains three edges; the superior border, the medial border and the lateral border and also containing three angles; the superior angle, the inferior angle and the glenoid fossa at the lateral superior corner of the bone. At the posterior surface you can find the scapular spine which divides it into two fossae; the supraspinous fossa and the infraspinous fossa while the anterior surface is occupied by the subscapular fossa. The lateral superior corner of the bone contains, in addition, to the glenoid fossa two processes, the most top one is the acromion to articulate with the clavicle and the other is the coracoid processe for muscle attachment. The suprascapular notch exists at the lateral point of the superior border.

2. THE UPPER LIMB

         The upper limb is divided into three regions; the arm, forearm and hand. The arm contains one large bone which is the humerous which is long bone having two ends, the rounded end which located proximally and the flattened end which is directed distally. The straight edge of the humerous is toward the lateral side while the slightly curved edge is directed medially. The anterior surface of the humerous is characterized by being rough and having two fossae distally, while the posterior surface is smooth and contains only one large fossa. The proximal end of the humerous has the most rounded structure of the bone which is the head directed medially to articulate with the glenoid fossa of the scapula. Anteriorly there are two tubercles; the lesser tubercle and greater tubercle which is shifted slightly to the lateral side. The intertubercular sulcus lies between the two tubercles. Down to the body of the bone you can find a wide rough surface laterally called deltoid tuberosity for the deltoid muscle insertion. The distal end of the bone contains two fassae at its anterior side; the coronoid fossa medially for articulation with ulna and the radial fossa laterally to articulate with radius. The distal end of the humerous contains only one fossa posteriorly which is the olecranon fossa. At the most distal point of the bone two rounded processes(condyles) are found ; the lateral one is the capitulum for radius articulation while the medial one is the trochlea for articulation with ulna. On the sides of these two structures the lateral and medial epicondyles are found for muscle attachment.  

         The forearm contains two bones; medially the ulna is located and laterally the radius exists. The radius has a rounded end at its proximal end called the head while the distal end is a wide one which has a needle shaped structure called the styloid process of the radius bone. The anterior surface of the radius proximally has a rounded rough surface called the radial tuberosity. The neck is found between the head and the radial tuberosity. The ulna is the medial bone of the forearm; it contains two processes at its proximal end; the posterior olecranon and the anterior coronoid process having the trochlear notch between them to slide over the trochlea of the humerous during flexion of the elbow joint. Just beneath the proximal end, the radial notch exists at the lateral side. The distal end of the ulna is narrow and contains the needle shaped process called the styloid process of ulna located medially while the head of ulna is at the lateral side.

         The hand is divided into three regions; the wrist, the palm and the digits. The wrist joint is composed of eight bones called the carpals oriented into two rows; proximal and distal. The proximal row contains (from lateral to medial): scaphoid, lunate, triquetrum and pisiform while the distal row contains: trapezium, trapezoid, capitate and hamate. The palm of the hand contains five bones named metacarpal bones numbered I-V. The digits are five containing 14 phalanges, 3 phalanges in each digit except the thumb has only two phalanges. Each bone of the metacarpals and phalanges is composed of three parts; the base (proximal), the shaft (middle) and the base (distal). The hand is concaved anteriorly.

3. THE PELVIC GIRDLE

         The pelvic girdle is composed of two bones; the hip bones articulate anteromedially with each other forming the pubic symphasis, posteriorly the articulation is mediated by the presence of the sacram forming the iliosacral joint. Each hip bone is built up from three different bones; the superior one is the ilium, and inferiorly; the anterior bone is the pubis and the posterior bone is the ischium. The wide end of the bone is directed superiorly while the narrower one is inferiorly directed. The smooth surface of the bone is medially situated, while the lateral side is characterized by having a large rounded depressed surface called the acetabulum, the inferior edge of the bone is pointed anteriorly and rounded posteriorly. The largest bone of the hip bone is the ilium occupies the superior part of the hip, having the iliac crest at the most superior line and having four spines; the anterior superior and the anterior inferior iliac spines and the posterior superior and posterior inferior iliac spines. The superior part of the ilium is the iliac ala containing the iliac tuberosity at its posteromeial point to articulate with the sacrum. Medial surface of the ilium is the iliac fossa. Inferiorly the ilium participates in forming the acetabulum. The greater sciatic notch is a large invagination of the bone located posteriorly. The pubis lies at the anterior inferior part of the hip bone forming the pointed inferior end. The body of the pubis contributes to form the pubic symphasis branches to have two rami; the superior pubic ramus participates to form the acetabulum and the inferior pubic ramus participates to form the inferior edge of the hip bone. The ischium is the inferior posterior bone of the hip bone, having one ramus; the ischial ramus contributes to form the inferior edge of the hip bone and the body of ischium which participates to form the acetabulum superiorly. The ischial tuberosity exists at the posterior surface of ischium. The obturator foramen which is the largest foramen of the body is located between pubis and ischium.

4. THE LOWER LIMB

         The lower limb is divided to three regions: the thigh, the leg and the foot. The thigh is built up from one bone, which is the femur. Femur is the largest, heaviest and strongest bone in the body. The femur has two ends; the one that has rounded structure with an angle is located proximally, while the other end with two rounded processes is located distally. The rounded structure is directed to the medial side while the lateral side is straight one. The anterior surface of the bone is smooth while the posterior surface has rough surface. The rounded large structure is the head articulates with the acetabulum of the hip bone, the head contains rounded spot called the fovea capitis from which a ligament emerges to enter the acetabulum of the hip. Just distal to the head of the femur, the neck of the femur is located at an angle with its body, according to this angle the width of the pelvis is determined. The posterior side of the proximal end contains two trochanters; the greater trochanter superiorly and the lesser trochanter inferiorly, between the two trochanters there is intertrochantric line anteriorly and intertrochantric crest posteriorly. The gluteal tuberosity is a wide rough surface exists just beneath the lesser trochanter, at the posterior surface of the body, the linea aspra is found for the attachment of muscles. The distal end of the femur contains two rounded processes; the medial condyle at the side of the head and the lateral condyle on the other side. On the sides of the two condyles there are the medial epicondyle and the lateral epicondyle respectively for muscle attachment. The intercondylar fossa exists between the two condyles.

         The leg contains two long bones; the tibia and fibula. The tibia is bigger and located at the medial side, it has two ends; the bigger one is the proximal end while the smaller one is the distal end, the posterior surface of the tibia is concaved, while the anterior one is straight. Proximally; the tibia has the medial and the lateral condyles that articulate with those of the femur superiorly. Between the two condyles there is the intercondyler imminence, at the anterior surface of the bone the tibial tuberrosity exists. The anterior crest of tibia exists anteriorly as a longitudinal edge. The distal end of tibia has the medial malleolus of tibia medially while the fibular notch is located laterally. The fibula is a thin long bone located at the lateral side of the leg, has two ends; the rounded one is the proximal end while the pointed one is the distal end, the fibula is slightly curved to the medial side to articulate only with the tibia proximally. Proximally; the head of the fibula is located then the shaft of the fibula. The distal end of the fibula has the lateral malleolus.

         The foot contains three groups of bones: the tarsal bones forming the ankle joint, the metatarsal bones forming the intermediate piece of foot and the phalanges forming the toes of the foot. There are seven tarsal bones: superiorly; the talus articulates with the tibia and fibula superiorly, inferiorly at the most posterior point of the foot the calcaneous bone is located. Anterior to talus; the navicular bone exists, then three cuniform bones are found: medial, intermediate and lateral cuniforms. Anterior to the calcaneous, the cuboid bone is located. There are five metatarsal bones numbered I-V from medial to lateral. The phalanges are 14; three phalanges in each toe (distal, intermediate and distal phalanges) except the big toe has only two (proximal and distal) phalanges, each phalanx is formed from base, shaft and head (from proximal to distal end).