Cyrus Lashgari
Shoulder pain is the second most common musculoskeletal complaint after back pain encountered by the medical profession. Since Neer's description in 1972, subacromial impingement syndrome has become the most common shoulder diagnosis made by the orthopaedic surgeon. Despite its frequency, care must be taken to ensure the proper diagnosis is made and appropriate treatment instituted.
Pathogenesis
Etiology
The cause of rotator cuff pathology remains controversial. It is unclear if the spectrum of rotator cuff disease is a direct result of mechanical impingement or if intrinsic factors lead to cuff disease and secondarily cause changes within the coracoacromial arch. Neer believed that the rotator cuff impinges on the overlying CA arch, leading to repetitive microtrauma. Progressive extrinsic injury leads to eventual rotator cuff tears. Bigliani et al. showed that acromial morphology could worsen this extrinsic compression by narrowing the subacromial space. Acromions were divided into type I (flat), type II (curved), or type III (hooked). Hooked acromions were associated with 73% of the rotator cuff tears in their cadaver study. In a separate cadaver study, Flatow et al. showed that there was contact between the rotator cuff and acromion. This occurred over the supraspinatus and was more pronounced with type III acromions. Extrinsic compression worsens with a decrease in the subacromial space. This can occur from multiple additional causes such as acromioclavicular spurs, primary bursal swelling, or a laterally sloped acromion.
Abnormal motion of the humeral head with elevation, dynamic impingement, may worsen extrinsic compression. The rotator cuff functions to keep the humeral head centered on the glenoid as the arm is elevated. Several studies have shown that with an injured or weakened rotator cuff, the humeral head moves superiorly abutting the coracoacromial arch. Restoration of rotator cuff strength and function should decrease this dynamic compression.
Other investigators believe that intrinsic causes are more important in the development of rotator cuff pathology. Ogata and Uhthoff have described primary degenerative tendinopathy involving the rotator cuff and suggested that this may lead to tendon tears. Several studies have shown decreased vascularity in the area of the rotator cuff where tears are commonly seen. One study showed a differential pattern of vascularity between the bursal and articular side of the rotator cuff. The articular surface showed a decrease in blood supply relative to the bursal surface. This may help to explain why most partial rotator cuff tears occur on the articular side of the cuff. If extrinsic compression were the only or main cause of rotator cuff tears, it would stand to reason that the tears would be predominately bursal in origin. Although there is currently no consensus, it is probable that a combination of these factors leads to the development of rotator cuff disease.
Classification
Neer described three classes of impingement. These stages consisted of increasing damage to the rotator cuff and appeared age dependent. Further studies using MRI and ultrasound have confirmed an increasing rate of rotator cuff disease as patients age. Stage I consisted of edema and hemorrhage of the cuff and bursa. Stage II consisted of fibrosis and tendonitis of the rotator cuff, whereas stage III disease consisted of rotator cuff tearing. In practice, impingement can be classified according to the status of the rotator cuff. For those patients with intact rotator cuffs, nonoperative measures are exhausted before surgery is indicated. In patients with rotator cuff tears, surgical intervention should
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be discussed sooner, especially in patients younger than 65 years of age. In these patients, prolonged nonoperative therapy may lead to irreversible changes in the rotator cuff. These include muscle atrophy, fatty degeneration, changes in tendon morphology, and degenerative joint changes.
Diagnosis
History
The diagnosis of subacromial impingement syndrome begins with a thorough history. Pain is the most common symptom. It is often described as a dull ache of the anterolateral shoulder radiating to the deltoid insertion. Pain is often worsened by overhead activities or extension of the arm behind the back. Activities with the arm at the side are usually pain free. Night pain often awakening the patient from sleep is a common complaint. Complaints such as stiffness, crepitus, or instability are less commonly associated with impingement syndrome and should alert the physician to the possibility of an alternate diagnosis. Older patients, in particular, should be evaluated for osteoarthritis. Patients younger than 40 years of age with shoulder pain often have instability leading to secondary impingement. Women between the ages of 40 and 60 years, diabetics, and those with thyroid disorders should be carefully evaluated for adhesive capsulitis.
Cervical spine disease commonly masquerades as shoulder pain. Pain radiating past the elbow, often associated with complaints of numbness and tingling, should raise concern about this diagnosis. A history of pain dependent more on neck than arm position also suggests a cervical cause. In contrast to patients with impingement syndrome, patients with cervical disc disease often state that their pain is better with their arm over their head. Pain into the upper trapezius is not necessarily related to the cervical spine. It is a common complaint in patients with shoulder disorders and is secondary to abnormal shoulder mechanics.
Most patients will describe a gradual onset of symptoms without a specific traumatic event. A recent onset of a new exercise routine or greater than normal physical activity such as heavy yard work often is described as the initiating event. Treatments initiated by the primary physician or patient should be documented. Activity modifications, medications, injections, and therapy are commonly tried before seeing the orthopaedic surgeon. The effect of these treatments is helpful in making the proper diagnosis. For example, a subacromial injection of cortisone or local anesthetic that relieves the pain is highly suggestive of impingement syndrome.
Physical Exam
The patient should be gowned so that both shoulders, including the scapulas, can be examined. The initial evaluation of the patient should include an examination of the cervical spine. Cervical spondylosis and radiculopathy often mimic intrinsic shoulder pathology. The physical exam includes motor and sensory testing of the entire upper extremity. Specific tests such as the Spurling (extension with rotation of the neck to the involved side) and Lhermitte (compression and flexion of the neck) maneuver are performed. Any reproduction of the patient's symptoms suggests that the cervical spine is at least partially involved. It must be remembered that both neck and shoulder pathology can coexist in the same patient.
The shoulder exam starts with inspection. Muscle wasting, suggestive of a chronic rotator cuff tear or peripheral nerve lesion, is documented. Range of motion is evaluated by standing behind the patient. This allows for evaluation of scapular rhythm and winging as active motion is evaluated. Forward elevation, external rotation in 90 degrees of abduction, external rotation at the side, and internal rotation are recorded both actively and passively. Although there often is a painful arc, the motion in patients with impingement syndrome is usually well preserved. Long-standing cases may show a mild decrease in motion, especially in internal rotation. A more profound loss of both active and passive motion in the shoulder suggests the diagnosis of adhesive capsulitis, assuming there is no significant glenohumeral arthritis.
Strength testing of the rotator cuff is performed next. Supraspinatus strength is examined using the Jobe test. The patient resists a downward force after the arm is placed in the plane of the scapula elevated to shoulder level with the thumb pointed toward the ground. The infraspinatus is tested with resisted external rotation with the arms at the side and elbows flexed to 90 degrees. The arms should be placed in internal rotation at the start of the test to isolate the infraspinatus. The teres minor is isolated with use of the horn blower's test. The arm is brought into 90 degrees of abduction and neutral rotation. The patient is then asked to rotate the shoulder externally to 90 degrees with the thumb pointed posteriorly. The subscapularis is tested either with the lift-off test or abdominal compression test. Patients with impingement syndrome generally have preserved strength although testing may elicit pain. This is especially true with the Jobe test. If there is significant pain, the patient may appear weak although the rotator cuff is intact.
Impingement signs are evaluated after strength testing. The Neer and Hawkins tests are most commonly performed. The Neer sign is performed by elevating the arm in the scapular plane while stabilizing the scapula. The patient complains of pain as the supraspinatus tendon impinges on the acromion usually above 70 degrees of elevation. The Hawkins sign is performed by internally rotating the arm with the arm in 90 degrees of forward flexion with the elbow flexed 90 degrees.
The exam is completed by testing for instability. In the young patient, instability can cause secondary impingement. The apprehension test is performed by bringing the arm into 90 degrees of abduction with the patient supine. Progressive external rotation is performed, trying to elicit apprehension as the patient feels the humeral head sliding anteriorly. The relocation test is then performed by applying a posteriorly directed force on the arm. The test is positive if there is relief of pain and/or apprehension. If instability is suspected as the cause of the impingement, the treatment will differ from that for primary subacromial impingement syndrome. Failure to appreciate mild instability is a leading cause of failed subacromial decompressions.
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Figure 37-1 Diagnostic workup algorithm. |
Differential injections help isolate the anatomic area responsible for the pain. The Neer impingement test consists of an injection of local anesthetic into the subacromial space. If the patient's pain is relieved or decreased, it is assumed that the subacromial space is a source of pain. If an injection of local anesthetic and/or cortisone into the subacromial space does not relieve a patient's symptoms, the diagnosis of impingement syndrome is questioned. In this setting, injections into the acromioclavicular joint or into the glenohumeral joint are helpful in evaluating other possible sources of pain.
Radiologic Testing
Standard radiographs of the shoulder should include an anteroposterior (AP) in internal rotation, scapular AP in external rotation, axillary, and supraspinatus outlet view. These films may reveal other causes of shoulder pain such as calcific tendonitis, osteoarthrosis of the glenohumeral or acromioclavicular joint, or an os acromiale. The supraspinatus outlet view is a lateral view with a 10-degree caudal tilt, affording a better view of acromial morphology. Typically there will be few abnormalities found in a patient with isolated subacromial impingement. Acromial spurring, sclerosis of the greater tuberosity, and subchondral cysts may be present.
Additional imaging includes plain film arthrogram, MRI, and ultrasound. These tests are often ordered to evaluate for tears of the rotator cuff. MRI gives the most additional information, allowing for evaluation of the labrum, AC joint, and biceps tendon. In well-trained hands, ultrasound is an inexpensive alternative for evaluation of the cuff. Although not
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needed for the diagnosis and management of impingement syndrome, additional imaging is often obtained if nonoperative measures fail (Fig. 37-1).
Treatment
Nonsurgical Treatment
Historically, nonsurgical management has proved quite successful for subacromial impingement. Success rates of 70% to 80% have been seen across several studies. Options include activity modification, nonsteroidal anti-inflammatory drugs (NSAIDs), rehabilitation exercises, cortisone injections, and modalities such as ultrasound. Although these options are well established, few controlled trials have been done proving their efficacy.
NSAIDs, which have both anti-inflammatory and analgesic properties, are an integral part of most nonsurgical protocols. With the recent concern about cardiovascular side effects with these medications, it is advisable to try to limit their use to short periods (1 to 3 months) at the smallest effective dose. Acetaminophen can be tried as the first line of medication. If the pain is not well controlled with these medications, the use of cortisone injections into the subacromial space is indicated. Because of their deleterious effects on normal tissue, cortisone injections are used judiciously. In general, cortisone should be limited to three injections spaced at least 3 months apart. Steroid injections are particularly helpful in patients experiencing significant night pain.
Exercise is the most important aspect of nonsurgical therapy. After rest and medication have reduced the acute inflammation and pain, stretching and strengthening exercises can begin. The goal of stretching exercises is to restore a full range of motion through long, slow stretches with minimal pain. After range of motion is improved, strengthening of the rotator cuff and surrounding musculature can begin. Opinions differ as to the need for supervision by a physical therapist. Physical therapists may help those who need more encouragement and guidance. They also have the ability to use modalities such as ultrasound, phonophoresis, and iontophoresis to improve pain control. Despite these potential advantages, studies have shown no difference between supervised and unsupervised therapy.
Operative Treatment
If the patient's symptoms persist for 3 to 6 months despite appropriate nonsurgical treatment, operative intervention is indicated. Surgery consists of an anterior acromioplasty, bursectomy, and resection of the coracoacromial ligament. Routine resection of the distal clavicle is not recommended. Distal clavicle resection is indicated for patients with tenderness on exam or in those with inferior spurring of the AC joint that is thought to aggravate impingement. The goal of a subacromial decompression is to remove sufficient bone from the anterolateral acromion to create a type I, or flat, acromion. Similar results have been obtained using both open and arthroscopic techniques. Good to excellent results are seen in approximately 90% of patients with either method. The open acromioplasty remains an effective operation and is less likely to result in insufficient bone removal. An arthroscopic decompression allows inspection of the glenohumeral joint for additional pathology and decreases iatrogenic injury to the deltoid. The decision ultimately depends on surgeon experience. Postoperatively, NSAIDs and therapy are important to reduce residual inflammation and maximize return of function. The stretching and strengthening exercises used for nonoperative treatment are instituted in the early postoperative period. These should commence in the first few days after surgery.
Conclusions
Subacromial impingement syndrome is a common diagnosis made by the practicing physician. Proper diagnosis depends on a thorough history and physical exam. Nonsurgical management is extremely successful and consists of both relief of inflammation and rehabilitation. An arthroscopic or open acromioplasty is performed only after failure of a 3-to 6-month course of nonsurgical treatment.
Suggested Readings
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Bigliani LU, Morrison DS, April EW. The morphology of the acromion and its relationship to rotator cuff tears. Orthop Trans. 1986,10:228.
Ellma H. Arthroscopic subacromial decompression: analysis of one- to three-year results. Arthroscopy. 1987;3:173–181.
Flatow EL, Soslowsky LJ, Ticker JB, et al. Excursion of the rotator cuff under the acromion: patterns of subacromial contact. Am J Sports Med. 1994;22:779–788.
Liotard JP, Cochard P, Walch G. Critical analysis of the supraspinatus outlet view: rationale for a standard scapular Y-view. J Shoulder Elbow Surg. 1998;7:134–139.
Morrison DS, Frogameni AD, Woodworth P. Non-operative treatment of subacromial impingement syndrome. J Bone Joint Surg Am. 1997;79:732–737.
Neer CS II. Anterior acromioplasty for the chronic impingement syndrome in the shoulder: a preliminary report. J Bone Joint Surg Am. 1972;54:41–50.
Ogata S, Uhthoff HK. Acromial enthesopathy and rotator cuff tear: a radiologic and histologic postmortem investigation of the coracoacromial arch. Clin Orthop. 1990;254:39–48.
Spangehl MJ, Hawkins RH, McCormick RG, et al. Arthroscopic verus open acromioplasty: a prospective, randomized, blinded study. J Shoulder Elbow Surg. 2002;11:101–107.