We are continuing BeneFIT Physical Therapy’s Anatomy Blog Series this month with the wrist joint. Each month we will feature a different part of the body. BeneFIT PT’s staff is highly trained in knowing all about human anatomy so that we can effectively help our patients with their specific areas of concern, rehabilitation and strengthening.
Last post we began our discussion of the elbow joint by highlighting the bones, ligaments, and tendons. We talked about everything from hitting your funny bone to the muscle the drive movements. Today were going to talk about the wrist and how this important joint is structured.
The bones in the wrist consist of the forearm bones, carpal
bones, and hand bones. The two largest bones that contribute to the wrist run from the elbow down to the wrist. These bones are known as the radius and the ulna.
- The radius is on the same side as the thumb.
- The ulna is on the little finger side.
The end of the ulna is covered by a triangular-shaped articular disc which is a piece of fibrous cartilage that cushions the wrist bones. This disc connects the ulna bone to the carpal bones and is essential for allowing movements like typing on a computer and drinking out of a cup. Unlike the ulna, the radius directly connects to the carpal bones. The radius bone meets the wrist at the first of two rows of small round bones known as carpal bones:
- Proximal carpals: The row of carpal bones closest to the forearm
- Distal carpals: The row of carpal bones closer to the fingers
There are a total of eight carpal bones and together they are called the carpus. The distal carpals form five joints with the bones that make up the palm. These bones are called metacarpal bones and are long bones that connect the fingers to the wrist.
Joints and Motions of the Wrist
There are several sets of joints in and around the wrist.
- The distal radioulnar joint- located between the radius and the ulna at the wrist. This joint allows for rotation of the forearm. The ulna stays in a stable position while the radius rotates around it.
- The radiocarpal joint– located where the radius meets the first row of carpal bones. This joint is the main joint of the wrist. The radiocarpal joint is a condyloid joint. A condyloid joint allows combined motions in multiple planes, including backward and forward bending motions, side-to-side motions, and circular motions.
- The midcarpal joint– located where the proximal and distal carpals meet. This joint has features of both condyloid and gliding joints. Gliding joints allow the bones to glide up and down, left and right, and diagonally. The midcarpal joint performs up/down and side-to-side movements and works together with the radiocarpal joint to move the wrist.
- The carpometacarpal joints– the five joints between the distal carpals and the metacarpals.
- The carpometacarpal joint– this is a saddle joint and the joint that allows the thumb to have so much movement. This saddle joint allows the thumb to function like a joystick, with forward, backward, and side-to-side motions.
Ligaments of the Wrist
The wrist consists of several ligaments and tendons that help provide strength and flexibility to the hand. Ligaments are fibrous bands of tissue that connect one bone to another. The wrist contains a network of ligaments, including:
- Extrinsic ligaments- connect the wrist bones to the long bones of the forearm and the bones of the hand. Extrinsic ligaments include several volar radiocarpal ligaments, volar ulnocarpal ligaments and dorsal ligaments.
- Intrinsic ligaments- connect the carpal bones to each other. Intrinsic ligaments include several proximal row ligaments, distal row ligaments, and palmar midcarpal ligaments.
Wrist capsule- the radiocarpal joint, where the radius bone and the first row of carpal bones meet, is surrounded by the wrist capsule. The outer layer of this capsule is fibrous and contains some of the extrinsic ligaments. The capsule’s inner layer is made up of a very thin tissue called the synovial membrane. The synovial membrane produces and holds in a special fluid, called synovial fluid. This fluid helps keep the joint lubricated.
Tendons of the Wrist
The motions of the hand and wrist are powered by tendons, which connect muscles to bones. The extrinsic tendons that control the wrist originate from forearm muscles and insert into hand bones. These tendons include:
- Tendons involved in wrist flexion or the action of bending the wrist forward/inward. These tendons also help in rotating the wrist.
- Tendons involved in wrist extension or the action of bending the wrist backward. These tendons also help move the wrist toward the thumb or the little finger.
- Tendons involved in finger flexion and extension, which pass by the wrist on their way to the fingers.
Nerves of the wrist
Three nerves travel through the wrist and into the hand: the median, ulnar, and radial nerves. These nerves are the end branches of a network of nerves called the brachial plexus located in the shoulder. Each nerve travels down from the neck to the shoulder then down the arm, providing sensation to different parts of the hand:
- The median nerve enters the wrist through the carpal tunnel and branches into the thumb, index finger, middle finger, and part of the ring finger. When this nerve becomes compressed in the carpal tunnel, it causes carpal tunnel syndrome.
- The ulnar nerve enters the wrist and travels into the ring and little fingers. Compression of this nerve at the elbow causes cubital tunnel syndrome. This nerve also causes “funny bone” shocks when jarred near the elbow. This nerve can also be compressed at the wrist as it passes through Guyon’s canal, which is called handlebar palsy when it happens in bicyclists.
- The radial nerve supplies the forearm muscles that straighten the wrist and fingers. Radial nerve injury in the upper arm can lead to wrist drop or inability to straighten the wrist. It also provides sensation to part of the back of the hand
If you want to learn more about the hand or wrist give us a call today! With Direct Access in NJ we can get you in for an evaluation without you having to see your Doctor, probably quicker than you could even get that appointment, while also saving you both time and money!
Please, call us to schedule you evaluation at one of BeneFIT’s locations, Bridgewater (908.203.5200) or Chester (908.879.5700) with one of our highly trained Doctors of Physical Therapy!