Subacromial impingement is a common condition that causes pain in the shoulder and upper arm. It occurs when the tendons of the rotator cuff or the space (bursa) overlying them become pinched in a tunnel called the subacromial space.
The rotator cuff is a group of four muscles that wrap closely around the shoulder joint. The muscles originate from the shoulder blade and connect to the arm bone (humerus) via four tendons. These tendons run through a tunnel that is called the subacromial space (so named because it is beneath the acromion bone). Narrowing of this tunnel, which can occur either because of a bony spur or injury and thickening of the tendons, can cause the tendons to catch in the tunnel. This is referred to as Subacromial Impingement.
Patients complain of shoulder pain occurring when abducting the arm, or with overhead activities. Putting the arm into a sleeve of clothing often exacerbates symptoms. Pain at night can also occur, which may disrupt sleep.
The range of movement is not normally significantly restricted.
Positive examination findings will include a painful arc (pain from 70-120 degrees of shoulder abduction). Improvement in this pain following an injection of local anaesthetic (+/- corticosteroid) into the subacromial space can also help to confirm the diagnosis (see below).
Hawkins Test – The examiner brings the arm forward to 90 degrees with the elbow bent at 90 degrees. The arm is then internally rotated (i.e. the hand is pushed towards the ground) This squashes the rotator cuff tendons between the greater tuberosity (of the humerus) and the acromion. It will cause pain with impingement syndrome.
Plain radiographs: AP and trans-scapular lateral views. These will assess bony morphology. They may demonstrate acromial hooking, arthritis or calcific tendonitis.
Either modality can provide further information regarding the integrity of the rotator cuff, if a tear is suspected.
Here are treatments for for Subacromial Impingement
This can be highly effective. Avoiding activities which worsen the shoulder pain will help to reduce the stress on the tendons and promote healing.
Pain killers and anti-inflammatory medication may help to reduce and control symptoms, particularly in mild cases. Physiotherapy can also help to improve shoulder posture and the strength of the rotator cuff tendons, improving symptoms.
An injection of local anaesthetic and steroid may also be given into the subacromial space to help reduce inflammation around the tendons. This can be painful for the first 24 hours but, in combination with physiotherapy, can be very effective in reducing symptoms. A combination of 5mls of 0.5% Marcain and 20-40mgs Kenalog are utilised. The subacromial space can be injected from the lateral aspect of the acromion or from the posterior aspect of the shoulder.
This is often performed as a day case procedure. It will successfully treat symptoms in 85% of patients. If there is a tear to the rotator cuff tendons, this may be repaired at the same time.