Impingement Syndrome

Diagnosis

Because impingement involves the rotator cuff, it presents similar to rotator cuff tears. The patient complains of subdeltoid pain with radiation down the lateral arm to the area of the deltoid insertion or down the front of the arm into the biceps muscle. Pain occurs as the arm passes through the arc of 70 to 100 degrees of abduction. Typical activities that are bothersome include reaching overhead (e.g., for items on a high shelf), behind the back (e.g., to fasten a brassiere or belt), or to the side (e.g., to insert an ATM card, use a seatbelt, or access an alarm clock). Patients with severe symptoms may complain of pain that interferes with sleep. The role of trauma is variable; some patients present with symptoms after major injury, but in many others, the pain occurs after repetitive activities without trauma or antecedent injury.

Physical examination normally demonstrates full passive range of motion. Small limitations in elevation and behind-the-back internal rotation are due to the patient's pain rather than true passive glenohumeral joint contracture. Active abduction and behind-the-back internal rotation are painful. The patient often reports pain while actively lowering the arm after the examiner raises it passively. The primary (Neer) and secondary (Hawkins) impingement signs are positive, and pain is relieved with a subacromial lidocaine injection (impingement test). The patient may have pain with palpation over the supraspinatus insertion.

Three special physical exam tests consistent with impingement have been described and are recorded as positive when subacromial pain is produced. The primary (Neer) sign occurs when the examiner places the shoulder in maximal elevation. To demonstrate the secondary (Hawkins) sign, the shoulder is elevated 80 degrees and then maximally internally rotated. The tertiary sign (painful arc) consists of subacromial pain with the shoulder in 90 degrees of abduction. The location of the pain should be carefully noted. A patient with soft tissue pain from rhomboid-trapezius spasm may have increased pain during each of these maneuvers, but the pain is not localized to the subacromial region.

After the physical examination, the surgeon may perform an impingement test. This test consists of injecting local anesthetic into the subacromial space and then attempting to elicit the impingement signs again. If the pain is eliminated or substantially reduced, the test is recorded as positive. The physician must be aware that a positive test result only confirms that the structures producing pain lie within the subacromial space; it is not, by itself, diagnostic of impingement syndrome. Our preferred technique for subacromial injection is posterior, but other surgeons are equally successful with lateral or anterior approaches. We use ultrasound guidance to confirm the location of the injection.

The diagnosis of impingement syndrome is clinical, and arthroscopy does not routinely play a role. A number of conditions that mimic the clinical presentation of impingement are best diagnosed with arthroscopic techniques. Glenohumeral instability, articular surface partial rotator cuff tears, labrum tears, small areas of degenerative arthritis, posterior glenoid–rotator cuff impingement, and lesions of the rotator interval are examples. Glenohumeral instability may result in secondary traction tendinitis, with positive impingement signs as well as a positive impingement test. Successful surgical management of this condition does not involve subacromial decompression, but rather treatment of the underlying glenohumeral instability. Other conditions that may mimic impingement syndrome but cannot be diagnosed with arthroscopic technique include acromioclavicular (AC) joint arthritis, cervical spine disease, and suprascapular neuropathy.

Imaging also plays a limited role and is often not pathognomonic. Historically, plain radiograph osseous findings consistent with subacromial impingement include type 3 acromion, anterior acromial sclerosis, anterior medial spurs (ossification of the coracoacromial ligament), and inferior spurring of the distal clavicle. There is little scientific support for the concept that acromial morphology is significant. Many think the type 3 acromion is actually ossification of the coracoacromial ligament, which is medially positioned and plays no role in subacromial impingement. Magnetic resonance imaging (MRI) findings include tendinosis, bursitis, and lateral acromial downsloping ( Figs. 10.1–10.3 ).

Differential Diagnosis

Pain occurring during abduction can have a number of other causes besides the extrinsic mechanical factors of subacromial impingement, including early rheumatoid arthritis, post-traumatic arthritis, and avascular necrosis. However, these are unusual conditions with clear radiographic findings. An unusual situation is a patient with chondromalacia from early osteoarthrosis. In this case, the plain radiographic findings are normal, and the true cause of the patient's pain is discovered during arthroscopic examination.

There are three common clinical entities that may lead to an erroneous diagnosis: glenohumeral instability, adhesive capsulitis, and musculoskeletal pain syndromes. Fortunately, the surgeon can identify all with appropriate evaluation.

It is likely that the most common error is operating on patients with intrinsic tendinopathy secondary to glenohumeral instability. The repetitive overload of the rotator cuff tendons as they attempt to stabilize the glenohumeral joint causes inflammation and swelling of the tendons. Although the instability may be subtle, the pain from rotator cuff and bursal inflammation may be severe, causing the patient to present for evaluation and treatment. Impingement signs and the impingement test are positive. These patients are usually younger than 40 years and have normal plain radiographs. In this setting, it is advisable to recommend a prolonged period of nonoperative care. Arthroscopic subacromial decompression without correction of the underlying glenohumeral joint lesions will fail. The relationship between rotator cuff lesions and glenohumeral instability is covered in more depth in the section on internal impingement and partial-thickness rotator cuff tears (see Chapter 11 ).

The second most common error occurs when the patient has adhesive capsulitis. The diagnosis of adhesive capsulitis is straightforward when the disease is at its peak, but patients in the very early or late phase may have only a small loss of external rotation that can be missed if the examiner fails to measure both shoulders. Musculoskeletal pain syndromes commonly cause pain in the scapular muscles, and this too can be confused with subacromial impingement. The impingement signs may be positive, but the pain is located in the scapular muscles or trapezius rather than in the classic locations.

Indications and Goals of Surgery

The indications for arthroscopic treatment include pain or weakness that interferes with work, sports, or activities of daily living, and is unresponsive to appropriate nonoperative treatment. The usual nonoperative regimen consists of oral anti-inflammatory medication, cortisone injections into the subacromial space, activity modification, selective rest, and a rehabilitation program. The rehabilitation program is designed to restore or maintain movement and to improve strength in the deltoid, scapular stabilizers, and rotator cuff muscles. The recommended duration of this nonoperative approach varies, but it seems reasonable to consider surgery if the patient's pain continues for 12 months or is increasing in severity after 6 months. Additionally, an unusual indication for operative treatment is a superiorly displaced, healed greater tuberosity fracture. Arthroscopic subacromial decompression treats the deformity by increasing clearance for the malunited bone.

Surgery generally addresses two potential sites of pathology or sources of pain. First, the subacromial bursa is excised. This may simply represent a denervation procedure as the bursa may mediate pain. It is the barrier between the bursal surface of the rotator cuff and overlying acromion that is compressed or irritated with repeated contact. Resection of a hypertrophic or inflamed bursa likely contributes to the relief of pain. Second, the anterolateral acromion is beveled or flattened. This potentially reduces the contact between the bursal surface of the rotator cuff and the acromion.

Literature Review

A number of reports in the orthopedic surgery literature describe the arthroscopic management of impingement syndrome. Several authors have reported 70% to 90% success rates with arthroscopic acromioplasty. All authors stress that arthroscopic surgery is successful when impingement is due to extrinsic compression on the tendon by the structures of the coracoacromial arch. It is not successful when impingement is intrinsic, as may be seen with the increased demand on rotator cuff tendons in patients with glenohumeral subluxation or scapulothoracic dyskinesis. Other studies have compared the open and arthroscopic techniques. Matsen and colleagues found that although the open technique produced a slightly higher success rate, the return to function was superior with arthroscopic treatment. Norlin found that the arthroscopic technique produced better results and a more rapid return of function. Van Holsbeeck and associates reported marginally better results with the open technique, but advised arthroscopic decompression for patient convenience and satisfaction. Other literature has focused on the dynamic cause of some cases of impingement syndrome. It is well known that alterations in scapular biomechanics can cause subacromial pain. Treatment in these individuals is not surgical, but it involves a comprehensive physical therapy program. The best work on this topic is by Kibler.

The concept of acromioplasty itself is controversial, with some surgeons believing that acromioplasty is unnecessary. It is Matsen's opinion that contact between the rotator cuff and the acromial undersurface is normal and that acromial spurs are the result of—not the cause of—a primary tendon abnormality. He treats patients demonstrating impingement with débridement of abnormal bursa and adhesions, and then initiates a vigorous rehabilitation program. Nirschl's view is that impingement is an intrinsic tendinopathy and that acromioplasty is not needed. Conversely, numerous articles have reported good results with acromioplasty. At present, there is little scientific evidence to guide orthopedic surgeons, who must consider these conflicting opinions within the context of their own experience.

Arthroscopic Findings

Most surgeons examine the glenohumeral joint for unsuspected lesions before arthroscopic subacromial decompression. Subtle Bankart or superior labrum from anterior to posterior (SLAP) lesions, labral fraying, early adhesive capsulitis, and small areas of cartilage loss are some examples of pathology that may be identified. Subacromial findings in impingement are variable. The space may be clear, or a dense, fibrous bursal reaction may be found. Impingement syndrome may exist even in the presence of a clear, well-defined subacromial space. In some individuals, contact between the rotator cuff and the acromion produces pain, but it does not incite an inflammatory bursitis reaction. Tendon erosion, fraying, or partial-thickness tears may be found on the superior (bursal) surface of the cuff. Erosions on the acromial undersurface near the anterior edge may be noted, as are small areas of inflammation. The surgeon may also observe coracoacromial ligament fraying ( Fig. 10.4 ). Although these findings are suggestive of subacromial impingement, they are not necessarily diagnostic.

Treatment

Arthroscopic treatment of impingement involves examination under anesthesia to document range of motion and translation, followed by inspection of the glenohumeral joint and treatment, if indicated, of any coexisting intra-articular lesions.

Subacromial treatment includes excision of the bursa and flattening of the acromion. Certainly, more attention is paid to resecting an inflamed and hypertrophied bursa than a thin, normal-appearing bursa as the patient has greater potential for symptom improvement. The acromial pathology is assessed by clearing the undersurface of the acromion anteriorly and laterally to define the acromial morphology. In order to do this, the coracoacromial ligament may need to be resected or reflected. As noted earlier, some may elect not to perform acromioplasty or coracoacromial ligament resection, limiting treatment to bursectomy.

We prefer to reflect the coracoacromial ligament, without fully detaching it, in order to identify the acromial morphology to convert it to a flat (type 1) structure. We clear the entire undersurface of the acromion medially to the scapular spine for therapeutic denervation, to release any adhesions to the rotator cuff, and to allow for a good perspective of acromial morphology before and after resection. Beveling or flattening of the acromion is accomplished with a power bur placed in either the lateral or the posterior portal, depending on the surgeon's preference.

Operative Technique ( Video 10.1 )