Postoperative Shoulder

Description

Through an open or arthroscopic approach, a combination of shavers and burs are used to remove the anteroinferior aspect of the acromion from the level of the acromioclavicular (AC) joint to the level of the deltoid insertion (see eFig. 107-1 ). The subacromial bursa, if inflamed, is often resected at the time of the subacromial decompression. The coracoacromial ligament, if thickened, may be resected at the level of its attachment to the acromion. Many orthopedic surgeons, however, will choose to débride rather than resect the ligament, especially in younger patients, in an attempt to prevent superior migration of the humeral head. In the setting of advanced AC joint degenerative change, the AC joint may be resected along with the distal 2.5 cm of the clavicle, referred to as a Mumford procedure ( Fig. 107-1 ). Prominent osteophytes may also be resected.

Indications, Contraindications, Purpose, and Underlying Mechanics

The basic goal of subacromial decompression is to treat extrinsic impingement of the rotator cuff by resecting those areas of the osseous outlet and acromion that result in narrowing of the supraspinatus outlet. Pain over the anterolateral and superior aspects of the shoulder may be elicited or exacerbated by passive forward elevation of the arm (Neer sign) or by internal rotation that brings the greater tuberosity beneath the anterior aspect of the acromion (Hawkins sign). The impingement test involves injection of lidocaine into the subacromial space. Significant relief of symptoms after injection is considered specific in ascribing pain to rotator cuff pathology that may benefit from subacromial decompression.

Nonoperative management of overuse syndromes includes rehabilitation, such as capsular stretching, rotator cuff and scapulothoracic strengthening, and patient education with regard to alterations in athletic participation and training or job modification. Modification of activity is geared to reducing repetitive overhead use of the arm. Oral anti-inflammatory agents or corticosteroid injections may help reduce inflammation associated with impingement. Chronic rotator cuff problems often lead to limitations of movement and may require capsular stretching exercises as a prelude to eventual rotator cuff strengthening. Nonoperative management is typically less successful for those younger patients with a rotator cuff tear. Small chronic rotator cuff tears in older, less active patients with normal range of motion may respond more favorably to nonoperative management. Failure to respond to nonoperative management is an indication of subacromial decompression.

Preoperative MR findings of the coracoacromial arch associated with the clinical syndrome of impingement include extensive capsular hypertrophy or a large inferiorly directed osteophyte at the level of the AC joint, resulting in mass effect on the underlying cuff. Anatomic abnormalities of the anterior aspect of the acromion that can be associated with impingement include a subacromial spur or a type 3 acromial configuration. Finally, thickening of the coracoacromial ligament (>3 mm) may also predispose to impingement of the anterior rotator cuff.

Although there are no absolute contraindications to subacromial decompression, some factors, such as age, activity level, general medical condition, patient expectations, and the severity of disease, will determine the likelihood of proceeding to surgery. The partial-thickness tear in a young throwing athlete must be approached cautiously and examined for occult instability leading to eccentric loading of the rotator cuff or internal glenoid impingement. Acromioplasty is not indicated in this patient with occult instability unless bursal pathology is also present (see Tables 107-2 and 107-3 ).

Expected Appearance on Relevant Modalities

Comparison with preoperative imaging studies is of particular importance in accurately assessing the postsurgical changes as they relate to impingement. Understanding of the patient's presurgical anatomy enables the radiologist to give a more accurate description of the changes to the osseous outlet. After acromioplasty, MRI may demonstrate a change from a curved or hooked acromial configuration to a flat undersurface ( Fig. 107-2 ). Low signal artifact from small metal fragments is often present as a result of burring of the acromion, and, typically, the anterior third of the acromion is not visualized because of resection (see eFig. 107-2 ). Residual microscopic metal shavings resulting from burring of the acromion often result in extensive susceptibility artifact on MRI. If AC joint pathology was considered the source of impingement, postoperative changes may include absence of the distal 1.5 to 2.0 cm of the clavicle (Mumford procedure) or widening of the AC joint ( Fig. 107-3 ). Fibrosis often develops at the site of acromioplasty, resulting in low T1- and T2-weighted signal within the remaining acromion (see eFig. 107-3 ).

If inflamed, the subacromial/subdeltoid bursa is often resected at the time of acromioplasty, resulting in scar tissue and residual fluid in the region of the bursa. As a result, fluid in the location of the bursa is not a useful secondary sign of cuff injury or bursal inflammation after acromioplasty (see eFig. 107-4 ). The coracoacromial ligament may also be lysed or débrided at the time of the surgery, typically near its attachment to the acromion ( Fig. 107-4 ).

After subacromial decompression, without rotator cuff repair, there may be slight improvement in the altered MR signal intensity seen within the rotator cuff tendon and peritendinous tissues; however, most changes of tendinosis and additional alterations in the tendon, such as bursal or articular surface fraying or partial tear, usually persist.

Potential Complications and Radiologic Appearance

There are many potential sources of continued or recurrent pain after subacromial decompression. One source of pain is inadequate acromioplasty. Sagittal and coronal MR images are typically most helpful in assessing for the presence of persistent anatomic changes of the osseous outlet that may be associated with continued impingement, such as residual spur formation along the undersurface of the acromion that indents the supraspinatus muscle or tendon (see eFig. 107-5 ). After acromioplasty, the patient may continue to have pain because of osteoarthritis of the AC joint that was not addressed at the time of surgery or progression of disease in the region of the AC joint ( Fig. 107-5 ). An additional cause for persistent impingement would be the formation of extensive postoperative scarring interposed between the cuff tendon and the remaining acromion.

The persistence or progression of rotator cuff disease is also a common source of pain after acromioplasty (see eFig. 107-6 ). This may occur because of inadequate decompression or the natural progression of cuff disease not treated at the time of acromioplasty. Because many of these patients, to some degree, have coexisting disease of the rotator cuff disease, MRI is indicated in the setting of persistent postoperative symptoms. Clinical findings, such as night pain, loss of motion, and weakness, are not considered to be specific. Rotator cuff tendinosis may progress to a tear, or unrecognized partial or small complete tears may extend (see eFig. 107-6 ).

The assessment of cuff integrity after surgery is complicated by the possibility of a persistent signal in the cuff tendons after acromioplasty. However, MRI remains sensitive but not as specific in this setting for the assessment of cuff tear. It is fairly sensitive (84%) and specific (87%) for residual impingement, according to a study by Magee and colleagues. The typical criteria for a cuff tear in which there is tendon discontinuity and a fluid signal defect on long repetition-time/echo-time sequences still apply. MR arthrography may also be helpful in further evaluating for more subtle cuff tears because contrast agent extravasation through a cuff defect may be more readily apparent.

Another potential cause of unsuccessful acromioplasty is failure to recognize and treat an unstable os acromiale. A persistent unstable os acromiale can lead to continued impingement on the rotator cuff during deltoid contraction and continued symptoms of impingement ( eFig. 107-7 ). Finally, in some patients, symptoms of impingement result from unrecognized glenohumeral instability rather than from extrinsic impingement, and acromioplasty can, in fact, worsen the situation in these patients.

Open surgical procedures for subacromial decompression and rotator cuff repair carry the risk of deltoid detachment or atrophy because this procedure involves a deltoid takedown in an open approach or a deltoid-splitting procedure in a mini-open approach ( Fig. 107-6 ). The mini-open procedure may carry a lower risk of this complication ( Table 107-3 ). During ultrasound examination of postoperative subacromial decompression, using an open or mini-open approach, a few months after surgery, closure sutures appear in the middle part of the deltoid muscle or in the proximal part of the muscle as small linear or curved hyperechogenic artifacts without shadowing. Residual fluid may persist over the supraspinatus muscle, in cases of subacromial bursectomy ( Fig. 107-7 ).