Shoulder Subluxation In Stroke Patients: Causes And Mechanisms

Shoulder subluxation, or glenohumeral subluxation (GHS), is a common complication following a stroke, affecting up to 80% of survivors. It occurs when the upper arm bone, the humerus, becomes partially or completely dislocated from the shoulder socket due to muscle weakness, paralysis, or spasticity. The glenohumeral joint is multi-axial and has a wider range of motion than other joints, sacrificing stability for mobility. After a stroke, the muscles around the shoulder, the rotator cuff, can become weak or paralysed, and gravity pulls the humerus down in the socket, resulting in subluxation. This can cause pain and loss of function, impacting a person's quality of life.

Muscle weakness or paralysis

During the initial period following a stroke, the hemiplegic arm is often flaccid or hypotonic. The arm's weight, combined with the downward pull of gravity, may be enough to cause subluxation. The trunk tends to lean towards the hemiplegic side, causing the scapula to descend from its normal position. The trapezius and serratus anterior muscles become weak, causing the scapula to rotate downwards. This further impairs the ability of the rotator cuff to maintain the integrity of the GHJ.

During the spastic stage of recovery, the pectoralis major and minor, rhomboids, levator scapulae and latissimus dorsi can become hypertonic, further rotating the scapula downwards and causing GHS.

Other factors that can contribute to subluxation include improper positioning, lack of support when sitting or standing, and tension on the hemiplegic arm when the patient is being moved.

Changes in muscle tone

During the flaccid stage of stroke recovery, the patient's body tends to lean towards the hemiplegic side, causing the scapula (shoulder blade) to descend from its normal position. The trapezius and serratus anterior muscles, which are responsible for posture and shoulder blade movement, become weak and soft, causing the shoulder blade to rotate downward. Without normal muscle tone, the rotator cuff can no longer hold the arm in the shoulder joint, resulting in shoulder subluxation.

Additionally, trunk and pelvis malalignment from weakened core muscles is common after a stroke. This affects the entire body, including the diaphragm, lung expansion, voice production, swallowing, and balance. Orthopedic consequences can also develop when there are postural alignment issues in the neck, spine, and hips. Muscular imbalances in the back, shoulder blade region, and neck may contribute to the pulling of the humeral head and subsequent shoulder subluxation.

To prevent and treat shoulder subluxation, it is crucial to focus on upper limb rehabilitation, including range-of-motion and strength exercises, as well as supportive devices such as slings, lap trays, pillows, and foam support.

Trunk and pelvis malalignment

The trunk's tendency to lean or shorten toward the hemiplegic side during the flaccid stage after a stroke causes the scapula to descend from its normal position, contributing to glenohumeral subluxation (GHS). The trapezius and serratus anterior muscles become weak, causing the scapula to rotate downward. This downward rotation of the scapula is further exacerbated during the spastic stage due to hypertonicity in the pectoralis major and minor, rhomboids, levator scapulae, and latissimus dorsi muscles.

The impact of trunk and pelvis malalignment extends beyond the shoulder. The decreased capacity of the diaphragm and lung expansion can lead to impaired breathing. Additionally, the strain on the voice production mechanism may result in difficulties with speech. Impaired swallowing, balance issues, and orthopedic consequences related to postural alignment problems in the neck, spine, and hips can also occur.

To address trunk and pelvis malalignment, it is crucial to focus on core strengthening exercises and postural correction. Seeking guidance from a physical therapist or occupational therapist can help identify specific exercises to improve stability, strength, and mechanics of the trunk and pelvis. Additionally, they can recommend supportive devices or orthoses to improve alignment and provide external support during rehabilitation.

Overall, addressing trunk and pelvis malalignment is essential not only for preventing and managing shoulder subluxation but also for improving overall functional mobility and quality of life following a stroke.

Damage from external influences

Improper positioning of the body can cause the head of the humerus to be forced or gradually pulled out of its socket. This can happen during sleep, while walking, or even when sitting. For example, if the patient adopts an incorrect sleeping posture, this can cause the shoulder joint to subluxate. Additionally, if the patient is moved from one place to another, the tension on the hemiplegic arm can cause the shoulder to subluxate.

Orthopedic trauma can also cause shoulder subluxation and further damage. This can occur when the arm is pulled during a transfer or when the arm is passively stretched beyond its limits.

Engaging in daily activities and promoting movement in the arm is important, but muscle imbalances along the chain of the trunk, scapular muscles, and shoulder can cause microtears in the shoulder muscles, leading to pain, reluctance to use the arm, stiffness, and weakness. This can then factor into impingement, subluxation, or gradual tearing.

Orthopedic trauma

During the initial flaccid or hypotonic stage after a stroke, the shoulder muscles may be too weak to keep the arm within the shoulder joint, and the arm's weight, combined with the downward pull of gravity, can cause the humerus to "drop" lower in the socket, leading to subluxation. This can be exacerbated by improper positioning, such as incorrect sleeping postures, lack of support when sitting or standing, or tension on the arm during transfers.

To prevent and treat shoulder subluxation in stroke patients, early intervention is critical. Supportive devices such as slings, lap trays, pillows, and foam supports can be used to keep the arm and shoulder in the correct position and reduce the risk of subluxation. In addition, physical and occupational therapy, including exercises to strengthen the rotator cuff and improve range of motion, can help prevent and treat subluxation. Kinesiology taping, electrical stimulation, medications, and injections may also be used to manage this condition.

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