The nerve is particularly vulnerable to injury when there has been a disruption in the normal anatomy. The most common site of ulnar nerve entrapment is at the elbow, followed by the wrist.Causes or structures which have been reported to cause ulnar nerve entrapment include:
Problems originating at the neck: thoracic outlet syndrome, cervical spine pathology, compression by anterior scalene muscles
Problems originating in the chest: compression by pectoralis minor muscles
Brachial plexus abnormalities
Elbow: fractures, growth plate injuries, cubital tunnel syndrome, flexorpronator aponeurosis, arcade of Struthers
Forearm: tight flexor carpi ulnaris muscles
Wrist: fractures, ulnar tunnel syndrome, hypothenar hammer syndrome
Artery aneurysms or thrombosis
Other: Infections, tumors, diabetes, hypothyroidism, rheumatism, and alcoholism

Cubital tunnel syndrome
The most common location of ulnar nerve impingement at the elbow is within the cubital tunnel, and is known as cubital tunnel syndrome. The tunnel is formed by the medial epicondyle of the humerus, the olecranon process of the ulna and the tendinous arch joining the humeral and ulnar heads of the flexor carpi ulnaris muscle. While most cases of injury are minor and resolve spontaneously with time, chronic compression or repetitive trauma may cause more persistent problems. Commonly cited scenarios include:

Sleeping with the arm folded behind neck, elbows bent. Pressing the elbows upon the arms of a chair while typing. Resting or bracing the elbow on the arm rest of a vehicle. Bench pressing. Intense exercising and strain involving the elbow.Compression of the ulnar nerve at the medial elbow may occasionally be caused by an epitrocheloanconeus muscle, an anatomical variant.
Ulnar nerve entrapment is a condition where the ulnar nerve becomes physically trapped or pinched, resulting in pain, numbness, or weakness, primarily affecting the little finger and ring finger of the hand. Entrapment may occur at any point from the spine at cervical vertebra C7 to the wrist; the most common point of entrapment is in the elbow (Cubital tunnel syndrome). Prevention is mostly through correct posture and avoiding repetitive or constant strain (e.g. "cell phone elbow"). Treatment is usually conservative, including medication, activity modification, and exercise, but may sometimes include surgery. Prognosis is generally good, with mild to moderate symptoms often resolving spontaneously. Signs and symptoms
In general, ulnar neuropathy will result in symptoms in a specific anatomic distribution, affecting the little finger, the ulnar half of the ring finger, and the intrinsic muscles of the hand. The specific symptoms experienced in the characteristic distribution depend on the specific location of ulnar nerve impingement. Symptoms of ulnar neuropathy may be motor, sensory, or both depending on the location of injury. Motor symptoms consistent of muscle weakness; sensory symptoms or paresthesias consist of numbness or tingling in the areas innervated by the ulnar nerve.Proximal impingement is associated with mixed symptoms, as the proximal nerve consists of mixed sensory and motor innervation. Distal impingement is associated with variable symptoms, as the ulnar nerve separates near the hand into distinct motor and sensory branches. In cubital tunnel syndrome (a proximal impingement), sensory and motor symptoms tend to occur in a certain sequence.