Internal Impingement

What is impingement?

  • The word impingement basically means 'rubbing' or 'catching' of structures. In this context, we refer to structures within the shoulder. It is the impingement of the rotator cuff (muscles and tendons within the shoulder which play a large part in lifting and twisting the arm) against other structures within the shoulder which form the basis of impingement syndromes.
  • There are several ways in which impingement can be classified. Here we will refer to internal and external.
    • External impingment (also known as Subacromial Impingement) is where the rotator cuff is impinged in a part of the shoulder known as the sub-acromial space.
    • Internal impingement involves other structures within the main shoulder joint itself (Glenohumeral joint).

Who gets it?

The condition is mainly seen in athletes, where overhead activity is a major part of their sport, particularly throwing athletes. In-fact, the condition is sometimes called "The Throwers Shoulder" and is also seen in the "Swimmer's Shoulder". It is for this reason that it is mainly seen in a younger athletic population.

Why throwing?

There are four phases involved in throwing. They are:

  1. Wind up
  2. Cocking
  3. Acceleration
  4. Deceleration or Follow-through

It is during cocking that internal impingement can occur.
The action of cocking can be summarised in three descriptive movements that all occur at the shoulder.

  • Abduction: The movement of bringing your arms up from your side to clap above your head.
  • External rotation: The movement done when your arms are flexed to 90°, elbows kept by your sides and you swing your hands outwards. It is similar to the motion of reaching behind you to put on a seat belt.
  • Extension: Reaching behind your body with your arms.
    It is this motion that creates a unique position within the shoulder joint, producing internal impingement.

This diagram shows how all of the components of the shoulder come together during throwing, with the red star indicating the point at which the rotator cuff tendon is being impinged.

The combination of abduction and external rotation in the cocking phase of throwing causes an impingement of the underside of the rotator cuff against the posterior (back) superior (top) labrum.

Image showing how the rotator cuff gets 'pinched' (impinged) between the glenoid labrum and the humeral head in full abduction and external rotation.

This is something which occurs to everyone during throwing. Therefore internal impingement in itself is not an injury. It becomes an injury when over time, microtrauma from repetitive throwing results in damage to the rotator cuff (see rotator cuff tears) or the superior portion of the labrum (see SLAP tears).

The 'impingement' lesions on the labrum and rotator cuff are known as 'kissing lesions'. The image below shows a view of the lesions at arthroscopy (viewing from anterior):


The main symptom patients with internal impingement usually complain of is pain. This is usually made worse by over-head activity or throwing. The pain is a result of inflammation and irritation to the tendons which are being impinged. This is called a tendonitis. Also affected is the bursa. This is a fat pad within the shoulder to allow tendons and muscles to glide over bones easily. If this becomes inflamed and irritated it is called bursitis. There may also be shoulder instability as a result of the damage done to the labrum. The damage done to the rotator cuff may cause a weakness in the movements of the shoulder, particularly abduction and external rotation, the movements discussed above as being crucial to throwing.


Internal impingement is usually diagnosed on clinical examination. 
Special tests such as a MR arthrogram may be useful. This is a specific type of MRI scan in which a dye is injected into the joint space to allow tears in the labrum to be seen. Fluid around tendons and in the joint could also point to impingement. It may also show up tears in the rotator cuff. Similar things may also be picked up on an ultrasound scan


Treatment can be divided into five phases:

  1. Rest: This allows inflammation in the tendons, joint capsule and bursa to subside.
  2. NSAIDS and steroid injection: To help facilitate the decrease in inflammation, NSAIDs such as ibuprofen can be helpful, as can a steroid injection into the joint such as Kenalog.
  3. Strengthening programme: Aimed at the rotator cuff muscles and other muscles of the shoulder and upper back.
  4. Sports / Job specific training: Rehab aimed at a specific area of performance; in this case it is likely to be throwing.
  5. Surgery: If rehab fails to provide satisfactory results then surgery is indicated. This is aimed at repairing rotator cuff damage or labral damage. If the rotator cuff is badly damaged, then early repair must be considered. Controlled 'rebalancing' of the capsule may also be performed.


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