Appendicular Skeleton

Human Physiology

Lesson 13 : Appendicular Skeleton

Appendicular Skeleton

  • Upperlimbs

The clavicle (collar bone) forms a rigid strut between the shoulder joint and the sternum. This probably reflects the difference between primates – which predominantly move using their hindlegs or by swinging from their arms – and quadrupeds which continuously need a shock-absorbing system at the front end, especially if they gallop or jump. The spine of the scapula is often palpable on its lateral surface and extends down almost to the shoulder joint. This is a ball & socket joint between the scapula and humerus and much support is provided by the adjacent muscles.

The distal part of the humerus is usually palpable; you can feel the two epicondyles which lie just above the articular regions, called the condyles. The distal humerus articulates with both the radius and ulna at the elbow joint, which permits flexion and extension. The ulna lies caudal to the radius at the elbow, and is easily palpated at the olecranon (or point of the elbow). Moving distally along the forearm, the relationship of the radius to the ulna alters, so that the radius comes to lie medial to the ulna, and both bones are normally palpable in the distal forearm.

The carpus (wrist) is made up of two rows of short bones. It is a complex joint, and allows articulation between the distal forearm and the metacarpus. Individual bones of the carpus are rarely palpable, except for the accessory carpal bone which lies on the caudal and lateral surface of the carpus.

Articulating with the distal row of carpal bones are the five metacarpal bones. The first metacarpal bone lies medially and is very small. The four main metacarpal bones articulate with the proximal phalanx of a digit. Each digit has three phalanges, the distal phalanx being partly covered by the nails. The bones of the digits are most easily palpated from the dorsal surface since their palmer surface is covered by the thicker keratin layer.

  • Lower Limbs

Unlike the upper limb, there is rigid connection between the lower limb and the vertebral column, by means of the sacroiliac joint.

The hip bone is made up of three bones, the ilium, ischium and pubis, fused together. The wing of the ilium is normally palpable, lateral to the vertebral column. The ischium lies more caudally, and a prominence, the ischial tuberosity, is normally palpable lateral and ventral to the anus. The third component of the hip bone is the pubis, which is positioned more ventrally and can be palpated in the region of the groin. The two hip bones meet at the pubic symphysis, a cartilaginous joint, and lying lateral to this is a large hole, the obturator foramen. This is clearly visible on radiographs made for the assessment of hip dysplasia. As a whole, the pelvis provides a protective enclosure for various organs including the bladder and part of the uterus, until advanced pregnancy.

The ilium, ischium and pubis all meet at the acetabulum. This is deep cavity which articulates with the head of the femur to form the hip joint. A small ligament runs in the joint from the centre of the acetabulum to the head of the femur. Extension and flexion, and abduction and adduction are all possible at the hip joint, because of its ‘ball and socket’ shape.

At the distal femur, the lateral and medial condyles are normally palpable. Lying cranial to them is the patella (kneecap) which lies in a small groove, the trochlea. A radiograph of the knee reveals two, or often three, small sesamoid bones lying in the muscles caudal to the knee joint. Movement at the knee joint normally involves extension and flexion.

The femur articulates with the tibia and fibula at the knee joint. The fibula is a thin, almost stick-like bone, which lies lateral to the much larger tibia. Proximally, the tibia is expanded to form the tibial crest which is easily palpated on the cranial surface of the leg. Distally, the tibia and fibula articulate with the bones of the ankle joint which is composed of numerous short bones, arranged in three rows. Movement is normally restricted to extension and flexion between the distal tibia and the proximal row of tarsal bones. The calcaneus extends caudally from to form the point of ankle which is the site of insertion of the Achilles tendon, and is easily palpable.

The arrangement of the metatarsal bones and phalanges is very similar to the arrangement of the metacarpal bones described for the forelimb.

Last modified: Tuesday, 10 April 2012, 6:30 AM