Can my shoulder's anatomy increase my risk of impingement?

Yes, the shape of the acromion (Type II curved or Type III hooked), acromial spurs, osteophytes, and thickening of the coracoacromial ligament are anatomical factors that can narrow the subacromial space.

Are there specific movement patterns that contribute to shoulder impingement?

Dysfunctional movement patterns like scapular dyskinesis, rotator cuff muscle imbalances (e.g., weak external rotators), poor posture, and limited thoracic spine mobility are critical biomechanical risk factors.

Do my daily activities or exercise habits affect my risk?

Yes, repetitive overhead activities in sports or occupations, improper technique during exercises, and sudden increases in training volume or intensity can significantly raise the risk.

What other general health factors can influence shoulder impingement risk?

Age, previous shoulder injuries, systemic inflammatory conditions like rheumatoid arthritis, and poor overall physical conditioning can all play a role in increasing vulnerability to shoulder impingement.

What are the risk factors for shoulder impingement?

Shoulder impingement syndrome is a common condition characterized by the compression of soft tissues, such as the rotator cuff tendons and bursa, within the subacromial space. This multifactorial condition arises from a complex interplay of anatomical, biomechanical, activity-related, and systemic factors that narrow this space and irritate the structures passing through it.

Anatomical and Structural Factors

Certain inherent structural characteristics or acquired changes in the shoulder can predispose an individual to impingement.

Acromial Morphology: The shape of the acromion, the bony projection of the shoulder blade that forms the roof of the subacromial space, is a significant factor.
- Type I (Flat): Least common to be associated with impingement.
- Type II (Curved): More common and increases the risk.
- Type III (Hooked): Most strongly associated with impingement due to the significantly reduced subacromial space.
Acromial Spurs and Osteophytes: Bony growths (spurs) on the underside of the acromion or osteophytes forming at the acromioclavicular (AC) joint can directly narrow the subacromial space.
Thickening of the Coracoacromial Ligament: This ligament spans between the coracoid process and the acromion, forming part of the subacromial arch. Thickening can reduce the available space.
Rotator Cuff Tendon Degeneration/Calcification: Age-related wear and tear, or the deposition of calcium within the tendons (calcific tendinopathy), can thicken the tendons, making them more susceptible to impingement.
Bursitis: Inflammation and swelling of the subacromial bursa, a fluid-filled sac that reduces friction, can itself contribute to impingement by occupying more space within the subacromial area.

Biomechanical and Movement Factors

Dysfunctional movement patterns and muscular imbalances around the shoulder complex are critical contributors to impingement.

Scapular Dyskinesis: Abnormal movement or positioning of the scapula (shoulder blade) is a primary risk factor. This can include:
- Poor Upward Rotation: The scapula fails to upwardly rotate sufficiently during arm elevation, reducing the subacromial space.
- Excessive Anterior Tilt or Downward Rotation: These positions can bring the acromion closer to the humeral head.
- Lack of Scapular Stability: Weakness or poor coordination of the scapular stabilizing muscles (e.g., serratus anterior, trapezius) can lead to uncontrolled scapular motion.
Rotator Cuff Muscle Imbalances:
- Weakness of External Rotators: The external rotators (infraspinatus, teres minor) help depress the humeral head during arm elevation, preventing superior migration. Weakness can lead to upward translation and impingement.
- Impaired Timing/Coordination: Even with adequate strength, poor activation sequencing of the rotator cuff muscles can compromise glenohumeral centering.
Poor Posture: Chronic forward head posture and rounded shoulders (thoracic kyphosis) can alter scapular resting position and movement, contributing to a reduced subacromial space.
Glenohumeral Joint Laxity/Instability: Excessive looseness in the shoulder joint can lead to uncontrolled humeral head translation, particularly superiorly, during dynamic movements.
Limited Thoracic Spine Mobility: Stiffness in the upper back can force more motion from the glenohumeral joint and alter scapular mechanics, increasing impingement risk.

The nature and demands of physical activities significantly influence the risk of impingement.

Repetitive Overhead Activities: Sports (e.g., swimming, baseball, tennis, volleyball, basketball) and occupations (e.g., painting, construction, electricians) that involve frequent or sustained arm elevation are high-risk.
Improper Technique: Incorrect form during weightlifting (e.g., upright rows, overhead presses with poor scapular control) or throwing motions can place excessive stress on the subacromial structures.
Sudden Increase in Training Volume or Intensity: Rapid progression without adequate conditioning or recovery can overload the rotator cuff and surrounding tissues, leading to inflammation and impingement.
Inadequate Warm-up and Cool-down: Failing to properly prepare the shoulder for activity or neglecting post-activity recovery can increase tissue vulnerability.

Systemic and Intrinsic Factors

General health status and individual characteristics can also play a role.

Age: As individuals age, tendons naturally undergo degenerative changes, becoming less elastic and more prone to micro-trauma and inflammation. Bone spurs are also more common with age.
Previous Shoulder Injury: A history of rotator cuff tears, tendinitis, or other shoulder pathologies can alter mechanics and increase the likelihood of subsequent impingement.
Systemic Inflammatory Conditions: Diseases like rheumatoid arthritis can cause widespread inflammation, including in the shoulder joint and bursa, contributing to impingement.
Poor Overall Physical Conditioning: General muscle weakness, fatigue, and lack of core stability can indirectly affect shoulder mechanics and increase vulnerability.
Genetics: While not a direct cause, genetic predisposition may influence anatomical variations, such as acromial shape, in some individuals.

Understanding these diverse risk factors is crucial for both prevention and effective management of shoulder impingement syndrome. By addressing modifiable factors through targeted exercise, posture correction, and proper movement mechanics, individuals can significantly reduce their risk and promote long-term shoulder health.

Shoulder impingement is a multifactorial condition resulting from anatomical, biomechanical, activity-related, and systemic factors.
Anatomical features like acromial morphology (especially Type III hooked), bone spurs, and thickened ligaments can directly narrow the subacromial space.
Biomechanical issues such as scapular dyskinesis, rotator cuff imbalances, poor posture, and limited thoracic mobility are significant contributors.
Repetitive overhead activities, improper technique, and rapid increases in training intensity are common activity-related risk factors.
Systemic factors like age, previous shoulder injuries, inflammatory conditions, and overall physical conditioning also influence impingement risk.

Shoulder Impingement: Anatomical, Biomechanical, and Lifestyle Risk Factors