Soft tissue impingement describes the process that occurs when soft tissues are compressed between two or more solid surfaces that move.
In the shoulder this most commonly occours as impingement of the rotator cuff tendons, causing compromise of the tendon and sub acromial bursa.
In extrinsic impingement this occours between the undersurface of the greater tuberosity/ superior aspect of thehumerus and the coracoacromial arch ( formed of the acromium and the coracoacromial ligament).
Anterior impingement beneath the coracoacromial arch is the most common presentation.
Neer’s classification of impingement into three stages is still utilised today.
This is most commonly seen the patients under the age of 25 years.
Stage II – Impingement presents as irreversible changes such as fibrosis and tendinitis of the rotator cuff and is usually seen the patients 25 – 40 years of age.
Stage III – Chronic changes such as rotator cuff tears are found. Neer later added a further classification dividing lesions into outlet and non-outlet.
Outlet lesions occur when the coracoacromial arch encroaches on the rotator cuff, e.g acromial spurs; calcified coracoacromial ligament; inferiorly angulated anterior acromium ( Bigliani type III acromial morphology).
Non outlet or “Cuff” lesions, thickening and hypertrophy of the rotator cuff, contribute to uncoordinated rotator cuff/extrinsic muscle activity; often in combination with excessive gleno-humeral joint laxity , causing secondary impingement. This is most common in the younger age group.
Signs and Symptoms
Pain is the most common symptom. Weakness and stiffness are secondary and should resolve once pain dissipates.
If weakness persists there may be a secondary rotator cuff tear or neurological problem.
If stiffness persists conditions such as frozen shoulder, inflammatory arthritis or calcific tendinitis may be the cause.
Overhead activities, above shoulder height, predispose to impingement and repetitive movements above the head aggravate pain. Most symptoms of impingement begin insidiously and get progressively worse with time. Impingement is more common in persons over the age 40. Younger people presenting with symptoms are mostly related to sporting activities and should also be evaluated for mild instability.
These include extrinsic causative factors, exterior to the rotator cuff tendon and intrinsic factors within the rotator cuff muscles or tendons themselves.