The cubital tunnel is a narrow passageway located on the inside, or medial side, of the elbow. This location is often involved in conditions affecting the arm and hand. Understanding the anatomy of this small space is the first step in addressing issues that arise when the structures passing through it become compressed. The tunnel acts as a conduit for one of the main nerves supplying the forearm and hand.
Anatomy: Identifying the Cubital Tunnel Location
The physical boundaries of the cubital tunnel are formed by bony structures of the elbow joint. It is situated on the posterior-medial aspect, just behind the prominent bump felt on the inner side of the elbow. This bump is the medial epicondyle of the humerus, which forms the front wall of the tunnel.
The back wall is created by the olecranon process, the bony tip of the ulna that forms the point of the elbow. These two bony landmarks create a groove that the nerve travels through. The floor of the tunnel is the elbow joint capsule itself.
The roof of the cubital tunnel is a fibrous band known as Osborne’s ligament or Osborne’s fascia. This connective tissue stretches across the bony groove, enclosing the nerve within a defined space. This fascial roof can sometimes become taut, contributing to the nerve’s vulnerability.
This location is often referred to informally as the “funny bone” area. A direct hit here causes an immediate, sharp, and radiating sensation because the nerve is superficially located in this small, bony canal.
The Ulnar Nerve: Function and Route
The primary structure coursing through the cubital tunnel is the ulnar nerve. It originates in the shoulder area from the brachial plexus and travels down the arm before entering the elbow’s medial groove. After exiting the tunnel, the nerve continues down the forearm to provide both motor and sensory function to the hand.
The pathway through the cubital tunnel is vulnerable because the nerve navigates a sharp corner. When the elbow is bent, or flexed, the tunnel volume decreases significantly. This can stretch or compress the nerve against the surrounding bony and ligamentous structures, making the ulnar nerve susceptible to irritation and injury.
The ulnar nerve’s sensory function provides feeling to the skin of the little finger and the adjacent half of the ring finger. It also supplies sensation to the corresponding palm area. Disruption to the nerve’s signaling at the elbow is often first perceived as numbness or tingling in these specific digits.
Motor control relies on the ulnar nerve, which innervates most of the small intrinsic muscles within the hand. These muscles are responsible for functions like gripping, spreading the fingers apart, and bringing them together. The nerve also supplies motor function to two forearm muscles that assist with wrist flexion and digit movement.
Understanding Cubital Tunnel Syndrome
When the ulnar nerve becomes compressed or irritated as it travels through the cubital tunnel, the resulting condition is known as cubital tunnel syndrome. This is a common compressive neuropathy, second only to carpal tunnel syndrome in frequency among nerve entrapments in the upper extremity. The syndrome directly affects the nerve’s ability to transmit signals, leading to a predictable set of symptoms in the areas it supplies.
One recognizable symptom is paresthesia, the sensation of tingling, “pins and needles,” or numbness in the hand. This feeling typically follows the specific sensory distribution of the ulnar nerve, affecting the little finger and the ring finger. These sensations may initially come and go but can become constant as compression progresses.
Pain is a frequent complaint, usually localized to the inside of the elbow where the tunnel is located. This discomfort often radiates down the forearm towards the hand and may include tenderness upon touching the medial elbow. The pain is frequently exacerbated by activities that require prolonged or repetitive elbow bending.
As the syndrome progresses, the nerve’s motor function becomes compromised, leading to progressive weakness and muscle atrophy. Patients may notice difficulty performing fine motor tasks, such as buttoning a shirt or picking up small objects. This weakness can manifest as clumsiness or a noticeable loss of grip strength, particularly in the muscles controlling finger separation and adduction.
Compression can be caused by various factors, including repeated and sustained elbow flexion, which mechanically stretches the nerve. Prolonged pressure, such as habitually leaning on the elbow while sitting, can also directly injure the superficial nerve. Trauma or anatomical abnormalities, like a bony spur, can also contribute to the nerve’s entrapment.
Diagnosis and Non-Surgical Management
Diagnosing cubital tunnel syndrome begins with a physical examination and an assessment of the patient’s symptoms and medical history. A provider often performs specific maneuvers to provoke symptoms. One maneuver is tapping gently over the nerve at the cubital tunnel, known as Tinel’s sign. This tapping can elicit a distinctive tingling sensation, confirming the nerve’s hypersensitivity at that location.
To confirm the diagnosis and determine the severity of nerve damage, nerve conduction studies (NCS) are utilized. These tests measure how quickly electrical signals pass through the ulnar nerve at the elbow. A significant slowing of the signal across the cubital tunnel segment indicates a site of compression.
Initial management focuses on conservative, non-surgical interventions designed to relieve pressure on the nerve. Activity modification is a primary strategy, involving avoiding positions that require the elbow to be sharply bent for extended periods. This includes not resting the elbow on hard surfaces and being mindful of sleeping positions.
Night splinting or bracing is a common non-surgical treatment aimed at keeping the elbow straight while sleeping. This prevents the sustained flexion that exacerbates nerve compression overnight. Over-the-counter non-steroidal anti-inflammatory medications may also be recommended to help reduce swelling or irritation around the nerve.