C5 palsy is a specific neurological deficit affecting the movement and sensation of the shoulder and upper arm. It is characterized by weakness or paralysis in the muscles controlled by the fifth cervical nerve root, which originates in the cervical spine. This condition significantly impairs a person’s ability to perform daily activities requiring arm elevation and elbow bending. The onset of this weakness is often sudden, and it is a recognized complication following certain neck procedures.
Understanding the C5 Nerve Root and Function
The C5 nerve root is one of eight pairs of cervical nerve roots exiting the spinal cord in the neck. It emerges from the spinal column between the fourth (C4) and fifth (C5) cervical vertebrae, forming the uppermost part of the brachial plexus. The brachial plexus is a network of nerves that transmits signals from the spinal cord to the shoulder, arm, and hand.
This nerve root is responsible for motor function in two muscle groups: the deltoid and the biceps brachii. The deltoid muscle allows for raising the arm away from the body (shoulder abduction). The biceps muscle is responsible for bending the elbow and rotating the forearm.
A “palsy” refers to a loss of movement or significant weakness in the affected muscles. Damage or irritation to the C5 nerve root interrupts the electrical signals traveling to these muscles. Since the C5 root controls these specific functions, the resulting weakness in shoulder and elbow movement is characteristic of C5 palsy.
Primary Causes and Contributing Factors
C5 palsy is most commonly recognized as an iatrogenic complication, meaning it occurs as an unintended result of medical intervention, particularly following cervical spine surgery. Procedures such as anterior cervical decompression and fusion (ACDF) or laminoplasty are the most frequent settings for its development. The overall incidence following cervical decompression surgery is estimated to be around 6% to 8.5% of cases.
The exact mechanism remains debated, but the accepted theory involves a “tethering effect” on the nerve root. When the spinal cord is decompressed and the neck’s natural curvature is restored, the spinal cord can shift backward. This shift places tension or traction on the C5 nerve root, which has a relatively short and fixed course as it exits the spinal column.
This stretching can lead to a temporary disruption of nerve signaling (neuropraxia), or it can cause ischemia (a reduction in blood flow to the nerve tissue). Risk factors that increase the likelihood of developing C5 palsy include:
- Having multiple levels of the spine decompressed.
- An excessive correction of the neck’s curvature.
- Underlying conditions such as severe stenosis of the C4-C5 foramen or ossification of the posterior longitudinal ligament.
Acute trauma, such as whiplash or a sports injury, can also cause C5 palsy, though the postoperative complication is the most studied form. Symptoms typically occur within one week of surgery.
Recognizing the Clinical Signs
The presentation of C5 palsy is defined by a specific pattern of motor weakness corresponding to the nerve root’s function. The most noticeable sign is weakness in shoulder abduction, meaning the patient struggles to lift the arm away from the side of the body. This results from the impaired function of the deltoid muscle.
Weakness in elbow flexion, controlled by the biceps muscle, is also a characteristic finding. Physicians use the Manual Muscle Test (MMT) scale to grade the severity of this weakness. A reduction of one grade or more in deltoid strength is the standard diagnostic criterion. Severe C5 palsy is often characterized by an MMT grade of 2 or less, indicating only trace movement or movement that cannot overcome gravity.
While motor weakness dominates the presentation, sensory changes may also be present. Patients can experience numbness, tingling, or pain in the C5 dermatome, which covers the shoulder and the outer upper arm. The palsy is unilateral in the majority of cases, affecting only one arm, but bilateral involvement is possible.
Treatment Pathways and Recovery Outlook
The management of C5 palsy typically begins with a conservative approach, as the condition is often transient and resolves spontaneously. Initial treatment focuses on protecting the weakened muscles and maintaining joint mobility through physical therapy. Passive and active-assisted range-of-motion exercises prevent the shoulder and elbow joints from becoming stiff or frozen.
Pain management is also a significant part of the early treatment plan, often involving anti-inflammatory medications. As a post-surgical complication, C5 palsy is expected to improve, with recovery occurring in most patients. The majority of patients experience full or substantial recovery of motor function.
Recovery is a gradual process, often taking weeks to months, though full recovery can take up to 6 months or longer. For patients with severe weakness (MMT grade 2 or less) showing no improvement after several months, surgical options may be considered. These interventions, such as nerve transfer procedures, aim to restore motor function by rerouting a healthy nerve to the affected muscles. The prognosis is generally good, but the ultimate recovery is influenced by the severity of the initial nerve injury and the patient’s underlying health status.