ESSENTIALS OF DIAGNOSIS
Anterior shoulder pain that is often atraumatic.
Discomfort frequently worse with repetitive or overhead activities.
Strength often maintained on exam.
The term subacromial impingement syndrome defines any entity that compromises the subacromial space and irritates the enclosed rotator cuff tendons. It is not clearly or consistently defined and may represent a variety of disorders from subacromial bursitis to calcific tendinosis. Often these entities arise in a similar fashion and may be difficult to differentiate. Diagnosis is based on a meticulous history and physical exam and appropriate imaging.
Diagnosis of subacromial impingement is primarily clinical. The patient complains of dull shoulder pain of insidious onset over weeks to months. Less often, these symptoms arise following trauma. Pain is typically localized to the anterolateral acromion and radiates to the lateral deltoid. Pain is often aggravated by repetitive overhead activities, such as a carpenter swinging a hammer or a baseball player throwing a ball. Individuals often complain of pain when they roll onto the shoulder at night and will awaken with symptoms if the arm is positioned over the head.
Physical exam usually reveals normal range of motion, although the patient may experience pain on reaching the maximum forward flexion and abduction. Muscular weakness can be seen but is often secondary to pain and not secondary to loss of function. In other words, a patient who is coached to try to resist on manual muscle testing despite pain will often exhibit near-full strength. The maintenance of strength can help differentiate between inflammation and a high-grade cuff tear.
Radiographs that may aid in diagnosis include anteroposterior (AP), outlet, and axillary views of the affected shoulder. The outlet view provides visualization of acromial morphology exhibiting curvature or spurs that may contribute to the underlying pathology. Plain films may also provide evidence of tendon calcification, underlying degenerative disease, and cystic changes in the humeral head. MRI can confirm the diagnosis but seldom changes the treatment plan.
Provocative testing includes the Neer test and the Hawkins test. The Neer test involves passive elevation of an internally rotated, forward-flexed arm. In the Hawkins test the arm is positioned in 90° of forward flexion and is internally rotated with a bent elbow. These motions cause “impingement” of the supraspinatous tendon against the acromion. Pain with either maneuver is considered a positive test; however, these tests may also be positive in patients with other pathology.
Differential diagnosis includes acromioclavicular joint arthritis, rotator cuff tear, glenohumeral instability, arthritis, supraspinatus nerve entrapment, and cervical disk disease.