Impingement Syndrome And The Rotator Cuff
Findings associated with pathologic processes involving the rotator cuff relate to tenderness over the rotator cuff, positive impingement signs, and weakness of the rotator cuff demonstrated by the internal and external rotation lag signs. Collectively, these findings are demonstrated in Plates 1-38, 1-40, and 1-43.
The Hawkins and Neer signs are commonly called impingement signs because they are often positive when there is inflammation, degeneration, or tears of the superior and posterior parts of the rotator cuff. The pain associated with these physical examination signs results from contact compression or induced strain on these parts of the rotator cuff under the coracoacromial arch or with contact with the glenoid rim. In some cases of shoulder pain it is not clear to the examiner if the pain is originating from a pathologic process in the subacromial space (e.g., bursitis, partial rotator cuff tear or full tear) when the impingement signs are equivocal. In these cases, the examiner can perform an impingement test with the injection of 10 mL of lidocaine or similar local anesthetic into the subacromial space under sterile conditions. The method of injection is shown in the later discussion on injection techniques. Several minutes after the injection the examiner should repeat the impingement signs of the physical examination. A positive impingement test is defined as a significant improvement in the pain associated with these physical findings that was present before the injection (usually 50% to 100% relief).
Chronic rotator cuff symptoms may be progressive and symptomatic. The acromion along with the coracoid and acromioclavicular ligament form the coracoacromial arch. In many cases these chronic symptoms are associated with narrowing of the subacromial space or subcoracoid space. The subacromial space is defined as the space between the undersurface of the acromion and the rotator cuff that contains a bursa that may become compromised in size by bone spurs that form under the acromion often within the coracoacromial ligament. This mechanical narrowing of the space below the coracoacromial arch can be associated with an acquired bone spur that can cause mechanical irritation of the underlying rotator cuff. It is not certain if the spur forms first and then causes mechanical irritation of the rotator cuff, resulting in partial-thickness or full-thickness rotator cuff tears or if the tear results in weakness of the rotator cuff, resulting in the formation of a spur. In either case, the spur can be part of the pain associated with the impingement.
Subacromial impingement and symptoms may also occur from failure of the ossification centers of the acromion to fuse in early adult life, resulting in a developmental anomaly called an os acromiale. These lesions are associated with a much higher likelihood of having a rotator cuff tear. In cases with this lesion, the tears are often larger and occur in a younger patient population than those tears that typically occur as a result of tendon degeneration. The most common of these types of os acromiale is associated with lack of fusion between the anterior half and posterior half of the acromion, result- ing in two separate bones called a meso os acromiale. These lesions should not be confused with an acute fracture or a nonunion of an acute fracture. The lesions can be asymptomatic. In some cases, a radiolucent line is seen on imaging but the bone is not mobile and is associated with a stable fibrous tissue interface. In about 60% of cases the findings are bilateral. Because a mobile segment of bone is often tilted downward, the anterior half of the acromion can cause mechanical irritation of the cuff and is associated with a large tear; this more often occurs in younger patients than the age group with degenerative or attritional tears. The os acromiale lesions are often best seen on the axillary radiograph, with axial CT, or with MRI. The arthroscopic removal of a lesion is generally reserved for the less active individual. Open reduction and internal fixation with screw fixation and, on occasion, tension band wiring is often done to treat this problem in someone who performs heavier physical activities or heavier labor or participates in certain sporting activities.