Impingement forms are divided into those with
- Glenohumeral centered humeral head (shoulder joint portion of the humerus).
- Decentered humeral head
Neer classification of impingement lesions.
| Stage | Pathology | Typical age | History | Therapy |
| I | Edema (water retention), hemorrhage | <25 years | Reversible | conservative |
| II | Fibrosis (pathological proliferation of connective tissue), tendinitis (inflammation of tendons) | 25-40 years | Load-dependent pain | surgical if necessary |
| III | Bone spur, tendon rupture (tendon tear) | > 40 years | progressive limitation | operational |
Classification into primary or secondary extrinsic and intrinsic impingement:
- Primary-extrinsic impingement
- Subacromial impingement – Cause: changes in the coracoacromial arch that structurally narrow the subacromial space.
- Subcoracoid impingement – Cause: entrapment of the subscapularis tendon (SSC tendon) or the long biceps tendon (LBS) and the biceps pulley system between the lesser tuberosity and the coracoid process (less common)
- Secondary-extrinsic impingement – cause: functional decentration of the shoulder in glenohumeral hyperlaxity or instability).
- Intrinsic impingement – cause: rotator cuff lesions (partial or complete rotator cuff rupture), usually of degenerative genesis (cause).
Classification of internal impingement in:
- Posterosuperior impingement (PSI) – occurrence in sports where the throwing arm is in maximum abduction (lateral displacement or the splaying of a body part away from the center of the body) and external rotation (rotational movement of an extremity about its longitudinal axis; BUT position: “abduction and external rotation”) → overhead sports (baseball, handball, volleyball); microtrauma thus shortens the dorsal joint capsule.
- Anterosuperior impingement (ASI) – cause: repetitive adduction-internal rotation movements leading to lesions of the rotator cuff and pulley system.
