The Anatomy of the Wrist and Hand
Our fingers, hands and arms.. segments of our body that we use every day. Whether it is hitting overhead squats, bench press, holding our cup of coffee, or holding our dog’s leash during a walk, we use our distal upper extremities hundreds if not thousands of times every single day. You will notice this even further if you sustain an injury to any of these areas, life becomes much harder. As we have for every other major joint in the body, we will review over these joints as well, so we can break specific injuries down later on.
In my last article on the elbow we stopped with the proximal radio-ulnar joint, at the top of the forearm. In this article we will start with the distal radio-ulnar joint and work our way down. The distal radio-ulnar joint is a synovial pivot joint, where the radius moves around the mostly stationary distal end of the ulna (for review, the radius is the larger forearm bone on the thumb side of the forearm, whereas the ulna is the smaller forearm bone on the “pinky” side of the forearm. The head of the ulna articulates with the medial side of the distal radius and is connected by the triangular ligament, which provides stability at this joint. The joint is provided further stability with anterior and posterior ligaments which span transversely across the radius to the ulna on both surfaces of the two bones. This joint primarily allows pronation, which occurs when the radius rotates medially and anteriorly over the ulna, and supination, which occurs when the radius rotates laterally and posteriorly over the ulna so the bones return to parallel.
The main wrist joint where many injuries from the “FOOSH (falling on outstretched hand)” mechanism occur. This is the radiocarpal joint, which is a synovial condyloid type of joint. You can easily find this joint by finding the styloid processes of the radius and ulna, which are the two prominent protrusions on each bones at the distal end. These radius and articular disc of the radio-ulnar joint articulate with the 8 carpal bones, which also articulate with the five metacarpals. The ligaments which support this joint are the palmar radiocarpal ligaments, dorsal radiocarpal ligaments, ulnar collateral ligament and radial collateral ligament. These ligaments provide a vast amount of stability for the joint, which is important because many motions occur here. These motions include flexion, extension, adduction, abduction and circumduction. There are a vast amount of muscles and tendons that act on the wrist and hand that originate from the forearm that contract to help these motions occur, these muscles include: the flexor carpi radialis, flexor carpi ulnaris, finger flexors, palmaris longus, abductor pollicus longus, extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, and thumb and finger extensors. The most stable position of the wrist is the “resting position” which is defined as minimal wrist extension.
The intercarpal joints, which are in between the eight carpal bones in both the proximal and distal rows are plane synovial joints. There is only minimal gliding at these joints, which are stabilized by the anterior, posterior and interosseous ligaments. This gliding is added to the motion elsewhere in the surrounding joints and helps with the associated movements at the wrist and hand.
The carpometacarpal and intermetacarpal joints, which are where the carpal bones meet the metacarpals and the articulation of the metacarpals with each other respectively. These are all plane synovial joints which the exception of the CMC joint of the thumb, which is a saddle joint.
The final two joints I want to at least touch on are the metacarpophalangeal and interphalangeal joints. The MCP joints are condyloid synovial joints and the IP joints are hinge synovial joints. These joints provide movements at the phalanges so that we can grip things and basically use our fingers freely to do the things we need in our everyday lives.
I will round out our overview of the anatomy with the cervical section of the spine next week and then we will begin to talk about specific injuries. So if you have had injuries in the past or are currently struggling with things now, let us know so we can get you the information you need and as always, remember to #HealByMoving.