JOINTS OF THE HAND
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Hand and Wrist Joints
The forearm consists of two individual bones – the radius on the thumb side of the arm, and the ulna on the opposite side. The radius and ulna come together at the carpus, also known as the wrist joint. As a complex joint, the wrist actually consists of many joints and connections between the small bones of the hand and the arm.
The carpus consists of eight small bones separated into two groups of four:
On the topside of the wrist sits the pisiform, triquetrum, lunate and scaphoid. While the bottom side of the hand contains the hamate, capitate, trapezoid and trapezium.
The wrist also contains the radiocarpal joint, which exists where the radius meets the row of bones consisting of the scaphoid, lunate, and triquetrum. A large number of common wrist injuries affect the radiocarpal joint, including fractures to the joint surface. Injuries to this area of the wrist also tend to sprain the scapholunate ligament.
The Lunate and Triquetrum, in addition to connecting to the radiocarpal joint, also connect to the ulnocarpal joint, which includes the ulna on the other side of the arm from the radius. A wrist sprain will commonly involve the Ulnocarpal joint. Actually breaking the wrist can misalign the two bones in the arm, this can lead to the ulna elongating further than the radius, leading to wrist pain that can persist even after healing. If the opposite occurs (a radius elongated further than the ulna), that patient will have a higher risk of developing Kienbock’s disease.
The middle of the hand consists of five long bones known as the metacarpals, which connect to the finger bones called phalanges. Three phalanges make up each finger, and connect to each other at the knuckles.
Each of the phalanges consist of three joints:
- The metacarpophalangeal joints, or “MCP” joints, consist of the meeting point between each metacarpal in the hand and each of the phalanges in the finger. The MCP joints allow you to grab or pinch items, as the main connection between the fingers and hand. The MCP joint gives the fingers their ability to bend, flex, spread, and come together. When the fingers extend, they loosen the collateral ligaments, which allows them to spread more easily than when you curl them. Injuries to the collateral ligaments, along with arthritis, make up common problems associated with the MCP joints. While any of the fingers can suffer a radial sagittal band injury, the middle finger has the highest risk of receiving this injury which causes the extensor tendon to retreat to the little finger side of the hand.
- The proximal interphalangeal joint, or “PIP” Joint. This joint bisects each finger and exists as the first joint after the MCP when going up the hand. The proximal interphalangeal joint allows the fingers to bend and grasp. Injuries to the PIP joint can commonly include sprains, dislocations, fractures, arthritis, Boutonniere Deformity, and hyperextension. These injuries can all cause stiffness in the PIP joint and limit the fingers range of motion.
- The distal interphalangeal joint, or “DIP” joint. This joint sits toward the very tip of the finger, just below the fingernail. While not very flexible, this joint can still suffer from various common conditions such as Mallet Finger, Jersey Finger, arthritis, mucous cysts, and fractures.
The thumbs only have two joints each, rather than three.
Both sides of every joint have a layer of cartilage to help them move smoothly together with minimal pressure and friction. The joints receive further lubrication from the synovial fluid created by the membrane within the joint capsule. If this layer of cartilage breaks down, it can lead to osteoarthritis in the hand.
If you would like to speak to one of our upper extremity Specialist in Dallas, give us a call at 817-697-4038, or contact us over the web. Tele-medicine appointments are also available.