Erb’s Palsy, also known as Erb-Duchenne paralysis, is a condition involving weakness or paralysis of the arm resulting from damage to specific nerves. This injury primarily affects movement and sensation in the shoulder and upper arm. It is most frequently associated with the physical stresses of childbirth, leading to a loss of muscle function that can range from temporary weakness to permanent disability. This is the most common type of birth-related nerve damage affecting the upper limb.
Defining Erb’s Palsy
Erb’s Palsy is caused by an injury to the brachial plexus, a complex network of five nerve roots that originate in the spinal cord in the neck and shoulder area. This nerve network controls all movement and sensation in the shoulder, arm, and hand. The injury specifically affects the upper two nerve roots of this plexus, designated as cervical nerves C5 and C6.
Damage to the C5 and C6 nerve roots results in weakness or paralysis of the muscles they supply, particularly the deltoid, biceps, and brachialis. The loss of function leads to a characteristic physical manifestation known as the “waiter’s tip” posture. In this position, the affected arm hangs limply by the side, the shoulder is internally rotated, and the forearm is turned with the palm facing backward. This paralysis prevents the infant from raising the arm or bending the elbow.
Incidence and Epidemiology
Erb’s Palsy is considered one of the more frequently occurring birth injuries, though reported rates show some variability. The estimated incidence rate typically falls within a range of 0.9 to 4 cases per 1,000 live births. This range reflects variations in reporting methods and the inclusion of transient cases.
A large majority of cases, often between 80% and 90%, represent transient injuries that resolve spontaneously within the first few months of life. This recovery occurs as the nerves, which were only stretched or bruised, regain their function. However, the remaining 10% to 20% of cases result in a lasting functional deficit that requires intervention and long-term care.
Incidence rates are influenced by improvements in obstetrical care and changes in delivery practices. Some regional studies have noted a decrease in the overall rate of obstetric brachial plexus injuries over recent decades. Despite this, the condition remains a persistent concern worldwide, with similar rates reported globally.
Primary Causes and Associated Risk Factors
The mechanism that causes Erb’s Palsy is mechanical trauma involving excessive traction or stretching of the infant’s neck during a difficult vaginal delivery. This stretching force pulls the head and neck in one direction while the shoulders are held back, causing injury to the delicate brachial plexus nerves. The injury can occur whether the delivery is assisted or unassisted.
The primary contributing factor to this mechanical stress is shoulder dystocia, a situation where the baby’s shoulder becomes lodged behind the mother’s pubic bone after the head has been delivered. When this obstruction occurs, excessive force may be applied to free the shoulder, leading to nerve damage. Shoulder dystocia is rare, but it is strongly correlated with this type of nerve injury.
Other factors increase the likelihood of Erb’s Palsy by increasing the size of the fetus or complicating the delivery process. High birth weight, termed macrosomia (a baby weighing over 8 pounds 13 ounces), is a known risk factor. Maternal conditions such as diabetes can lead to macrosomia, raising the risk. Prolonged labor, the use of instruments like forceps or vacuum extractors, and a previous delivery complicated by shoulder dystocia are also associated risk factors.
Classifying Severity and Long-Term Outlook
The prognosis for Erb’s Palsy is directly linked to the type and severity of the nerve damage sustained. Injuries are classified into four types, ranging from mild stretching to complete separation. The least severe type, neurapraxia, involves a temporary shock or bruising to the nerve without tearing the tissue, and these cases typically resolve completely within three months.
More severe injuries include rupture, where the nerve is torn but remains connected, and neuroma, where scar tissue forms, blocking signal transmission. The most severe type is avulsion, where the nerve is completely torn from its spinal cord attachment, causing permanent loss of function. Ruptures and neuromas often require surgical repair, while avulsions are difficult to treat due to the complete separation.
Since the vast majority of cases are mild stretching injuries, the overall long-term outlook is favorable, with a high rate of complete recovery. For the small percentage of infants with severe ruptures or avulsions, the outlook is less certain and often requires specialized surgical procedures, such as nerve grafts or nerve transfers. Even after surgery, these severe injuries may result in permanent weakness, limited range of motion, and reduced muscle development in the affected limb.