Joint structure and function by cynthia norkin pdf free download

Joint structure and function by cynthia norkin pdf free download joints and is therefore described separately. Bones of a human wrist. In this photo both the free position and saddle shape of the first CMC joint and the proximal transverse palmar arch are clearly visible.

Pronation-supination of the first metacarpal is especially important for the action of opposition. The movements of the first CMC are limited by the shape of the joint, by the capsulo-ligamentous complex surrounding the joint, and by the balance among involved muscles. The capsule is sufficiently slack to allow a wide range of movements and a distraction of roughly 3 mm, while reinforcing ligaments and tendons give stability to the joint. It is slightly thicker on its dorsal side than on the other.

The description of the number and names of the ligaments of the first CMC varies considerably in anatomical literature. A strong, thick, and intracapsular ligament originating on the palmar tubercle of the trapezium to be inserted on the palmar tubercle of the first metacarpal. It is taut in abduction, extension, and pronation, and has been reported to have an important retaining function and to be elongated or absent in CMC joint arthritis. An extracapsular ligament, the UCL is located ulnarly to the AOL. It is taut in abduction, extension, and pronation, and often found elongated in connection to CMC joint arthritis.

The importance ascribed to the UCL varies considerably among researchers. Connecting the bases of the second and first metacarpals, this ligament inserts onto the ulnopalmar tubercle of the first metacarpal where its fibers intermingle with those of the UCL. It is taut in abduction, opposition, and supination. It has been reported to be the most important restraining structure of the first CMC joint by several researchers. Some consider it too weak to be able to stabilize the joint by itself, yet accept that together with the UCL it represents an important restraining structure. An intracapsular ligament stretching from the dorsoulnar side of the trapezium to the ulno-palmar tubercle of the first metacarpal.

Not considered an important ligament to the first CMC joint, it tightens during forced adduction and radial abduction. Like the previous ligament, the DRL is not considered important to the first CMC. It connects the dorsal sides of the trapezium and the first metacarpal. In this articulation the movements permitted are flexion and extension in the plane of the palm of the hand, abduction and adduction in a plane at right angles to the palm, circumduction, and opposition. It is by the movement of opposition that the tip of the thumb is brought into contact with the volar surfaces of the slightly flexed fingers.

The flexor muscles pull the corresponding part of the articular surface of the metacarpal bone on to this facet, and the movement of opposition is then carried out by the adductors. The thumb’s MP and CMC joints abduct and adduct in a plane perpendicular to the palm, a movement also referred to as “palmar abduction. The same joints flex and extend in a plane parallel to the palm, also referred to as “radial abduction,” because the thumb moves toward the hand’s radial side. Abduction and adduction occur around an antero-posterior axis, while flexion and extension occur around a lateral axis. For ease of orientation, the thumbnail can be considered as resting in the thumb’s frontal plane.

CMC, MP, and IP joints occur in a plane that is perpendicular to the thumbnail. This remains true regardless of how the first metacarpal bone is being rotated during opposition and reposition. Male and female thumb CMC joints are different in some aspects. In women, the trapezial articular surface is significantly smaller than the metacarpal surface, and its shape also differs from that of males.

While most thumb CMC joints are more congruent in the radioulnar direction than the dorsovolar, female CMC joints are less globally congruent than male joints. The shape of the human TMC joint dates back about 5 million years ago. The fifth metacarpal articulates with the hamate. The range of motions in these joints decrease from the fifth to the second CMCs.

The second and third joints are however essentially immobile and can be considered to have zero degrees of freedom in practice. These two CMC provide the other three CMCs with a fixed and stable axis. Together the movements of the fourth and fifth CMCs facilitates for their fingers to oppose the thumb. The function of the finger CMC joints and their segments overall is to contribute to the palmar arch system together with the thumb. The proximal transverse arch of the palm is formed by the distal row of carpal bones. For each finger there is also a longitudinal arch. Furthermore, as the amount of surface contact is maximized, stability is enhanced and sensory feedback increases.