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Ulnar Nerve Definition
One of the three primary nerves in the human arm is the ulnar nerve, sometimes known as the “funny bone.” It includes both motor and sensory functions, and it controls the majority of the hand’s motions, including delicate finger movements. The ulnar nerve is frequently damaged as a result of compression or trauma, although most lesions are typically treatable.
Ulnar Nerve Anatomy
The median nerve, ulnar nerve, and radial nerve are the three main nerves in the arm. The ulnar nerve is named after the ulnar bone, which is the innermost of the two bones in the forearm (the other being the radial bone).
The ulnar nerve is one of five nerves that emerge from the brachial plexus, a group of nerves that transmit impulses from the spinal cord to the upper arm and hand. The ulnar nerve, in particular, is a continuation of the brachial plexus’s medial cord.
The ulnar nerve runs from the neck to the wrists, hands, and fingers, passing via the upper arm and forearm. It travels down the arm’s medial side (i.e., the inner arm).
It descends beyond the humerus’s medial epicondyle, which is the area where tendons and ligaments join the bone at the elbow. This section of the ulnar nerve is particularly vulnerable to damage.
It divides into three branches as it reaches the forearm: muscle branches, palmar cutaneous branch, and dorsal cutaneous branch.
1. Two muscles of the forearm are innervated by the muscular branches (the flexor carpi ulnaris and the flexor digitorum profundus).
2. The palmar cutaneous branch is a tiny branch that innervates the palm’s core.
3. The little and ring fingers receive sensation from the dorsal cutaneous branch.
The ulnar nerve enters the hand through the ulnar canal, also known as Guyon’s canal, at the wrist. It divides into two branches in the hand: the superficial branch (which serves mostly sensory tasks) and the deep branch (which serves primarily motor activities) (mainly motor functions).
The ulnar nerve is the scientific term for the so-called “funny bone,” which is not a bone at all. Its closeness to the humerus bone may have given it this name. The odd sensation that happens when the ulnar nerve is hit, which is a tingling feeling with a dull aching, is another possibility.
Ulnar Nerve Function
The ulnar nerve is a mixed nerve, which means it has axons that are both sensory and motor. It controls the majority of the hand and a portion of the forearm. It feeds the skin in the centre of the forearm, wrist, and two fingers with sensory nerves.
i. Motor Function
The ulnar nerve’s motor duties include controlling the motions of the hand and part of the forearm. It controls the tiny motions of the fingers by innervating virtually all of the hand’s muscles. As a result, it’s sometimes referred to as the musician’s nerve.
The thenar muscles (thumb muscles) and the two lateral lumbricals are the only muscles in the hand that it does not regulate (the muscles that flex the index and middle fingers). The ulnar nerve also controls the movement of two forearm muscles.
The flexor carpi ulnaris, which flexes the wrist, and the medial part of the flexor digitorum profundus, which flexes the fingers, are these muscles.
ii. Sensory Function
The ulnar nerve innervates the medial one and a half fingers, as well as the palm region, and serves as a sensory nerve. In other words, it sends external impulses to the brain from the area covering the little finger and half of the ring finger, as well as the palm underneath them.
Damage and Injury to the Ulnar Nerve
The ulnar nerve is frequently injured. This is due to the fact that it is the human body’s biggest nerve that is not protected by muscle or bone. Trauma, such as a fracture or a blunt force injury, can cause ulnar nerve damage.
Injury to the ulnar nerve, on the other hand, is generally caused by the nerve being pinched (also called compression of the nerve, or entrapment).
Ulnar Nerve Entrapment
Ulnar nerve entrapment (also known as ulnar nerve compression) can cause both motor and sensory symptoms (such as muscular weakness) (such as numbness or tingling). It can also cause a lot of discomfort.
Cubital tunnel syndrome is a typical occurrence of ulnar nerve entrapment around the elbow, particularly at the inner elbow. It can, however, occur anywhere along the nerve that connects the wrist to the upper arm.
The effects of the damage are determined by where the lesion happened along the nerve. The sensations are usually felt in the hand and occur more frequently when the elbow is bent.
Numbness in the ring and pinky fingers, a shaky grasp, and trouble regulating fine motor skills in the fingers are all symptoms.
Ulnar Nerve Diagnosis
Because of its influence over movement and feelings in the hands, ulnar nerve injury is quickly identified. The Froment’s Sign is a test that is used to diagnose ulnar nerve injury (ulnar nerve palsy).
If ulnar nerve entrapment is present, this test will be positive. The patient will do the test by holding a sheet of paper between their thumb and index finger. After then, the doctor will tug on the paper.
If the ulnar nerve is functioning, the person should be able to comfortably grip the paper. If the ulnar nerve is damaged, they will be unable to resist the physician’s pulling and will have to release the paper or compensate by squeezing it at the tip of their thumb.
An ‘ulnar claw’ may appear in more advanced forms of the disease. When the ulnar nerve is injured, it causes a malformation in the hand. This disease prevents people from completely extending their little and ring fingers.
Milder instances of ulnar nerve compression are generally treated without surgery. Anti-inflammatory medications are used to reduce swelling and discomfort, splints are used to straighten the joint when sleeping or resting, and exercises are used to ease the nerve into the proper position.
The ulnar nerve glide is a typical exercise in which you make a ‘okay’ sign with your hand, bend your elbow, and repeatedly elevate your forearm towards your shoulder. If these methods fail, surgery may be considered.
If non-surgical options fail or the symptoms become too severe, surgery may be recommended. These procedures can even be done with only a local anaesthetic. Cubital tunnel release is a procedure for releasing the ulnar nerve from its entrapment at the elbow.
Any tissue that is tight around the nerve will be taken away, relieving the pressure. Ulnar nerve anterior transposition is a procedure in which the surgeon moves the ulnar nerve’s location in order to relieve pressure.
The medial epicondyle, which is the bone lump on the inside of your elbow, is removed during a medial epicondylectomy.
The ulnar nerve is relieved of pressure as a result of this. People with ulnar nerve entrapment usually recover completely (or nearly completely) on their own or with treatment.
Repeated elbow bending is the most common cause of ulnar nerve injury or entrapment. For example, smoking cigarettes, playing tennis, golfing, working while leaning on a desk, or constantly using a cell phone.
Reduced ulnar nerve injury can be avoided by reducing these duties. Simply learning to lean less on your elbow and to straighten your arm as much as possible will help to relieve pressure on the nerve.
Ulnar Nerve Citations
- Management of ulnar nerve injuries. J Hand Surg Am . 2015 Jan;40(1):173-81.
- Ulnar Nerve Management with Distal Humerus Fracture Fixation: A Meta-Analysis. Hand Clin . 2018 Feb;34(1):97-103.
- Ulnar Nerve Entrapment. PMID: 32310389