Rotator Cuff Injury: Addressing Overhead Overuse
Preston M. Wolin, MD; Joyce A. Tarbet, MD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 25 - NO. 6 - JUNE 97
In Brief: Rotator cuff injuries in sports are usually a result of microtrauma from repetitive movements. Classic, or primary, impingement results directly from overhead motions, and secondary impingement is related to underlying shoulder instability. A variety of physical maneuvers are used to assess pain, muscle weakness, and shoulder stability. The workup also includes plain x-rays, supplemented by other imaging tests if a cuff tear is suspected. Nonoperative treatment, which may include steroid injections, is often effective for an inflamed rotator cuff tendon. Surgery is indicated if the patient has no improvement after at least 6 weeks of physical therapy.
For competitive or recreational athletes involved in baseball, tennis, or swimming, shoulder disorders—especially rotator cuff injuries—can be debilitating. Though medical understanding of rotator cuff injuries has improved greatly, successful diagnosis and treatment of patients still depend on understanding the mechanisms of injury and ruling out shoulder instability, particularly in athletes who use overhead motions. The keys to success include tailoring the treatment to the diagnosis and prescribing appropriate rehabilitation programs, either alone or in combination with surgery.
The subscapularis, supraspinatus, infraspinatus, and teres minor muscles are collectively referred to as the rotator cuff. Together with the deltoid, they place the arm in the overhead position essential in many sports.
Individually, the subscapularis is an internal rotator of the arm. It is innervated by the upper and lower subscapular nerves, branches of the posterior cord of the brachial plexus. The supraspinatus assists the deltoid in abducting the arm, with its greatest contribution being the initiation of abduction (1,2). It is innervated by the suprascapular nerve of the brachial plexus. The infraspinatus and teres minor muscles both externally rotate the arm. The infraspinatus is also supplied by the suprascapular nerve, while the teres minor is innervated by a branch of the axillary nerve. Together, the supraspinatus, infraspinatus, and teres minor muscles abduct and externally rotate the arm into the cocked position for throwing.
In addition, muscles of the rotator cuff, primarily the infraspinatus, teres minor, and subscapularis (1,3,4), depress and stabilize the humeral head. Without them, the humeral head would move upward in the glenoid fossa during arm abduction because of the unopposed pull of the deltoid muscle. This movement would result in constant abutment against the coracoacromial arch.
The coracoacromial arch forms the roof over the rotator cuff (figure 1). The structures forming this arch include the acromion, the acromioclavicular joint, the coracoid process, and the coracoacromial ligament. Variations in the architecture of the coracoacromial arch determine the amount of space available for the rotator cuff. This space is called the supraspinatus outlet (5). Therefore, reduction of this space by a downward sloping anterior acromion or by acromioclavicular osteophytes can result in impingement and injury to the rotator cuff.
Microvascular injection studies of rotator cuffs in human cadavers of all ages have demonstrated an undervascularized zone within the supraspinatus tendon just proximal to its humeral insertion (6,7). In addition, studies have shown that the articular surface is less vascular than the bursal surface in this zone (6). and that there is a significant decrease in vascularity with aging (7). Since most degenerative tears occur in this hypovascular region of the supraspinatus, it is assumed that this localized relative ischemia combined with aging plays a role in the pathogenesis of rotator cuff tears.
Mechanisms of Injury
Several different mechanisms of rotator cuff injury are presently recognized. These can be divided into acute traumatic injuries (macrotrauma) and the more common repetitive overuse injuries (microtrauma) seen in overhead activities.
Acute macrotraumatic rotator cuff injury, although uncommon, can result in partial- and full-thickness tears from a direct contact injury to the shoulder in patients under 40 years old (8). In addition, partial and complete tears of the rotator cuff can occur with traumatic anterior instability of the glenohumeral joint in the over-40 population; rupture of the subscapularis should especially be considered among these patients (9).
Four microtraumatic mechanisms of rotator cuff injury have been described, and several may occur simultaneously in the same patient.
Primary impingement. The first is the classic impingement injury, now called primary impingement (10). Repetitive overhead activity results in impingement of the supraspinatus against the anterior, inferior aspect of the acromion and/or the coracoacromial ligament.
The shape of the anterior slope of the acromion has been implicated in the development of primary impingement. Three distinct shapes have been described on the basis of a Y view or lateral radiograph of the scapula (figure 2). Type I is a flat acromion, type II is curved, and type III is hooked. Although the cause-effect relationship between acromial shape and rotator cuff disorders is unclear, the occurrence of a full-thickness tear appears to correlate closely with a type II and especially a type III acromion. Bursal side, partial-thickness rotator cuff tears are associated with a type II acromion (5,11).
Primary impingement injury has three stages (10). The first stage is edema and hemorrhage. With repetitive impingement comes the second stage of fibrosis and tendinitis; the subacromial bursa becomes fibrotic and thickened, and the supraspinatus tendon becomes further inflamed. The third stage can be a partial (usually bursal side) or a complete tear of the rotator cuff, with bony changes like spurring of the anterior acromion.
Secondary impingement. The second microtraumatic mechanism is secondary impingement. Individuals who have shoulder instability as a result of congenital laxity, repetitive microtrauma (from participation in overhead sports), or macrotrauma place increased demands on the rotator cuff as it attempts to keep the humeral head centered in the glenoid. These demands are especially pronounced with overhead activities. Fatigue, intrinsic injury (tendinitis), and a partial undersurface tear of the cuff may ensue. If the rotator cuff continues to fatigue, it may no longer center the humeral head in the glenoid, and dynamic cephalad migration of the humeral head in the glenoid occurs, resulting in secondary impingement of the rotator cuff under the coracoacromial arch.
Tensile failure. A third mechanism of microtrauma to the rotator cuff is tensile failure with throwing. The throwing motion has been divided into five phases: wind-up, early cocking, late cocking, acceleration, and follow-through (12). Electromyographic analysis of the throwing motion has demonstrated that the supraspinatus, infraspinatus, and teres minor muscles begin to fire at the end of early cocking phase and become idle at the end of late cocking as the shoulder has achieved maximum external rotation. The subscapularis subsequently fires in late cocking to decelerate the shoulder's external rotation. However, it is during follow-through when all the rotator cuff muscles fire most intensely. As the subscapularis internally rotates the shoulder, the remaining rotator cuff muscles are contracting eccentrically to decelerate the arm. During this repetitive eccentric loading, the rotator cuff is prone to overload, fatigue, tendinitis, and even a partial undersurface tear. Again, as the rotator cuff fatigues, dynamic cephalad migration of the humeral head can occur, resulting in secondary impingement of the rotator cuff under the coracoacromial arch.
Internal or posterior superior glenoid impingement. The fourth and final mechanism of microtrauma is internal or posterior superior glenoid impingement (figure 3) (13). This occurs with repetitive overhead activities, particularly in throwers, when the arm is abducted 90° and maximally externally rotated. In this position, the posterior inferior aspect of the supraspinatus is impinged between the greater tuberosity of the humeral head and the posterior superior labrum, producing fraying of the posterosuperior labrum and an undersurface tear of the posterior aspect of the supraspinatus. In addition, this position puts very high stresses on the anterior inferior capsule. Therefore, glenohumeral instability may be associated with internal impingement.
The symptoms of rotator cuff injury caused by both macro- and microtraumatic mechanisms include pain, weakness, and limitation of active motion. Pain tends to be located in the anterior, superior, and lateral aspects of the shoulder. Patients with acute inflammation of the rotator cuff have intermittent mild pain with overhead activities. Patients with chronic inflammation of the rotator cuff have persistent, moderate pain with overhead activities; there may be pain at rest, but much less than with overhead activities. Patients with partial and full-thickness rotator cuff tears have persistent pain at rest that is often referred to the deltoid insertion. Those with complete cuff tears typically have night pain. The symptoms of weakness and limitation of active motion may be the result of pain or a rotator cuff tear.
Physical examination will usually demonstrate tenderness in the subacromial space. Atrophy may be apparent in the supraspinatus or infraspinatus fossa in patients with full-thickness tears.
Pain and muscle weakness can be evaluated by manual motor testing. The subscapularis lift-off test (figure 4) of Gerber and Krushell (14) is performed with the arm internally rotated behind the back with the elbow flexed. The patient pushes away from the back against resistance, keeping the elbow flexed; inability to push away indicates subscapularis injury.
Resistance testing of the supraspinatus is performed with the arms abducted 90° in the scapular plane (30° anterior to the coronal plane of the body) and internally rotated so that the thumbs point toward the floor. The examiner applies a downward force, while the patient attempts to maintain the arms parallel to the floor. Inability to resist the examiner's downward force demonstrates isolated supraspinatus weakness.
The infraspinatus and teres minor muscles are examined together. Patients position their arms at their sides, elbows flexed. Weakness of external rotation against resistance is abnormal.
The impingement sign of Neer (15) is positive when forcibly forward flexing the arm—jamming the greater tuberosity against the anterior inferior surface of the acromion (15)—causes pain. Another method of demonstrating impingement is by forward flexing the shoulder to 90° and internally rotating the proximal humerus, driving the greater tuberosity under the coracoacromial ligament (16). The impingement test involves administering 10 mL of 1% lidocaine hydrochloride into the subacromial space and repeating the impingement sign of Neer (10). Pain relief confirms the diagnosis of impingement syndrome. If pain relief eliminates weakness, then a complete tear is unlikely.
The diagnosis of instability and therefore secondary impingement must always be ruled out. Stability testing is initially performed with the patient supine. To test for anterior translation of a patient's right shoulder, the patient's right hand is placed in the examiner's right axilla and held by the examiner. The patient remains completely relaxed. The right shoulder is held in 90° abduction and neutral external rotation. The patient's scapula is stabilized by the examiner's left hand by pressing the scapular spine forward with the index and middle fingers and applying counterpressure with the thumb on the coracoid process. The examiner's right hand grasps the patient's right humerus and an attempt is made to lever the humeral head over the rim of the glenoid anteriorly. Anterior translation is measured as grade 0 (no motion), grade 1 (humeral head to the glenoid rim), grade 2 (humeral head over the glenoid rim), and grade 3 (frank dislocation). Posterior translation is similarly recorded.
The apprehension and relocation tests are also for anterior instability. With the patient supine, the apprehension test is performed by abducting the patient's arm to 90°, externally rotating it, and trying to translate the humeral head anteriorly. Patient apprehension is noted with the development of anxiety and the sensation of impending subluxation. (The patient may say, "My shoulder feels like it is coming out.") The relocation test is then performed by placing a hand on the anterior aspect of the patient's shoulder and applying a posteriorly directed force (to prevent anterior translation of the humeral head), while doing the apprehension test. A positive relocation test is obtained when the hand pressure eliminates the patient's apprehension.
The sulcus sign is performed to demonstrate inferior instability, a component of multidirectional instability. This test is done with the patient sitting upright with the shoulder in neutral position. The examiner applies downward traction on the humerus and looks and feels for the development of a sulcus between the greater tuberosity of the humerus and acromion.
Radiographic evaluation of the shoulder starts with a routine shoulder series, including anteroposterior (AP) views with both internal and external rotation of the humerus. These views profile the acromioclavicular and glenohumeral joints and the tuberosities of the humerus and provide information regarding fractures, dislocations, arthritic changes, and calcific deposits. An acromiohumeral distance of less than 7 mm on the AP internal rotation view indicates the static cephalad migration of the humeral head in chronic rotator cuff tear (figure 5). An axillary view allows better visualization of the glenohumeral joint and glenoid margin as well as the acromion. A scapular Y view assesses the anterior slope of the acromion. The Stryker notch view best evaluates the presence of humeral head defects (Hill-Sachs lesions) seen in anterior instability.
Special diagnostic imaging, such as arthrography, ultrasonography, and magnetic resonance imaging (MRI), may aid in evaluating the rotator cuff. The goal of any special test is to provide information regarding the presence of a partial- or full-thickness tear of the rotator cuff, the size of the tear (retraction), and the quality of the muscle. Such information is especially important if surgery is being considered.
Shoulder arthrography (both single and double contrast) can help in diagnosing full-thickness rotator cuff tears. However, its ability to detect partial undersurface tears remains controversial, and bursal side partial tears will go undetected. In addition, it cannot evaluate the size of a tear or the quality of the muscle. Arthrography, although inexpensive to perform, is invasive.
Ultrasonography is noninvasive, painless, and inexpensive. Although it is widely used in Europe, its reliability is controversial, and its diagnostic accuracy appears to depend on the skill of the sonographer.
MRI is very accurate at depicting full thickness rotator cuff tears (figure 6). The sensitivity and specificity for full thickness tears are 100% and 95%, respectively (17). The advantage of MRI is its ability to show the location, size, and retraction of the tear as well as co-existing pathology, such as labral tears. It can also assess the quality of the muscle; in chronic tears, the muscle degenerates and fat infiltrates, preventing normal muscle performance even if the tendon is repaired to bone. MRI can aid in diagnosing partial tears with 82% sensitivity and 85% specificity. Its major disadvantage is cost.
Suprascapular nerve entrapment should always be included in the differential diagnosis of patients with shoulder weakness. These patients present with weakness of external rotation and occasionally abduction that can be accompanied by atrophy of the infraspinatus and/or supraspinatus. Pain is not usually a significant symptom but, if present, tends to be a dull ache in the posterior aspect of the shoulder. Electrodiagnostic studies, such as electromyography and nerve conduction velocity, should be obtained. MRI is recommended to assess the possible causes of nerve entrapment, such as a ganglion cyst.
Nonoperative management is often effective for treating acute and chronic inflammation of the rotator cuff, and a supervised program of physical therapy is the mainstay. The first phase of therapy aims to reduce rotator cuff inflammation and improve range of motion. Rest from the inciting activity is often accompanied by cryotherapy and short-term nonsteroidal anti-inflammatory drugs, if not contraindicated. The glenohumeral joint is mobilized with passive and active assisted range of motion; the arc of motion should be increased as pain permits. Overhead athletes commonly have limited internal rotation (and therefore a tight posterior capsule) and increased external rotation. However, a tight posterior capsule may aggravate impingement because it forces the humeral head against the anteroinferior acromion as the shoulder is forward flexed (5). Therefore, local heat or ultrasound followed by gentle stretching of the posterior capsule in cross-body adduction and internal rotation can be helpful.
A subacromial corticosteroid injection, which bathes the tendon, can provide significant pain relief in impingement cases (18). However, injection into the tendon must be avoided since adverse reactions, including a significant loss of ultimate tensile strength and spontaneous rupture, have been well-documented (19). Since local corticosteroid injection is associated with tendon weakness caused by collagen necrosis and the disruption of the normal parallel collagen arrangement, corticosteroid use in partial tears is a concern. The following are guidelines for corticosteroid use:
The second phase of physical therapy emphasizes full and painless range-of-motion exercise. Progressive isometric exercises, performed in the nonpainful planes below shoulder level, should include the scapular stabilizers, the trapezius, levator scapulae, rhomboid major and minor, and serratus anterior muscles. Strengthening the stabilizers can restore proper scapulohumeral motion.
The third phase of therapy introduces isotonic exercises to strengthen the rotator cuff, deltoid, and scapular stabilizers in order to stabilize the humeral head in the glenoid and prevent the dynamic, proximal migration leading to impingement. These exercises, initially done with light weights or elastic bands, are performed below shoulder level and with the arm at the side to prevent irritation of the inflamed cuff. Exercises that isolate specific cuff muscles, especially the supraspinatus at greater than 90° abduction, should be avoided to prevent reinjury. In addition, the thumb should be turned upward during exercise to externally rotate the humerus, moving the greater tuberosity away from the acromion.
Weight-bearing, closed-chain exercises promote dynamic strengthening with proprioceptive input; in one such exercise the patient "walks" on his or her arms while the trunk is supported by a Swiss ball or a low stool. Plyometric and sport-specific activities, such as high-speed tubing exercises, come last and often accompany isokinetic concentric and eccentric training. An athlete recovering from an impingement disorder should gradually return to sports activity while continuing to work with an athletic trainer and coach to ensure proper mechanics.
Surgical treatment of chronic inflammation of the rotator cuff is indicated only if the patient fails to progress after a minimum of 6 weeks of supervised physical therapy (5). Individuals with a flat acromion (type I), demonstrated on a scapular Y view, are likely to have secondary impingement, and the underlying instability will need to be addressed. Those with a type II (curved) or type III (hooked) acromion may undergo subacromial decompression whereby the anterior inferior acromion is resected, converting it to type I. This is also referred to as an anterior acromioplasty. Subacromial decompression can be performed through open or arthroscopic approaches. Arthroscopic subacromial decompression has an overall patient satisfaction rate of 92% (20). The only disadvantage of the arthroscopic technique is its technical difficulty.
The open technique of subacromial decompression is technically easier to perform than the arthroscopic technique. However, it does not allow inspection of the glenohumeral joint for co-existing pathologies, such as labral tears, biceps tendon tears, or undersurface partial-thickness rotator cuff tears. In addition, the open technique requires some detachment of the deltoid from the acromion to facilitate exposure. The detached deltoid is surgically reattached but requires postoperative protection, thus retarding rehabilitation and possibly resulting in residual weakness.
Partial-thickness rotator cuff tears can be approached in two ways. Tears affecting less than 40% of the total cuff thickness can be treated by arthroscopic debridement with subacromial decompression to remove the anterior curve of the acromion that is impinging on the rotator cuff. Partial-thickness tears greater than 40% of the cuff thickness over an area of more than 1 cm2 should be excised and repaired.
Repair of full-thickness rotator cuff tears varies. If a tear is less than 1 cm long (anterior to posterior), it can be treated with debridement and subacromial decompression. Tears longer than 1 cm should be treated with subacromial decompression and repair. Surgeons use one of three general approaches, depending on their preference and the size of the tear. The all arthroscopic rotator cuff repair done solely through arthroscopy is presently investigational. The mini-open deltoid splitting technique, which has demonstrated an 83% good to excellent result (21), has the advantage of splitting rather than detaching the deltoid from the acromion; however, exposing massive tears with this technique is technically difficult. The classic open approach, while requiring deltoid detachment, may be required for massive tears. If a massive tear has been neglected, successful repair is not always possible; if the posterior and anterior cuff is intact, however, patients with such massive tears can obtain significant pain relief with arthroscopic subacromial decompression and debridement (4). No matter what the operative procedure, the goals of rotator cuff repair are to preserve the deltoid and make a good repair that allows early range-of-motion exercise and thus reduces the likelihood of a stiff shoulder.
Postoperative rehabilitation varies with the surgical procedure performed. Patients with partial-thickness rotator cuff tears treated with arthroscopic subacromial decompression and debridement are placed in a simple sling. Active-assisted range-of-motion exercise begins immediately. Full active motion is achieved within 2 weeks. Resistive exercises and progressive strengthening start during the second week and continue for up to 12 weeks. Full return to sports activities requires 2 to 3 months, but high-level overhead athletes may take longer.
Following mini-open rotator cuff repair, patients use a simple sling only. Many surgeons prescribe an abduction pillow to prevent stretching of the repair. When the tendon is repaired with the arm at the side, passive range-of-motion exercises begin immediately. Active-assisted motion is started at 4 weeks, allowing for initial healing of the repair, and active motion is started at 6 weeks. Resistive exercises are then introduced. Full rehabilitation takes approximately 4 to 6 months.
The classic open technique requires prolonged postoperative protection of the deltoid, so rehabilitation is slower, taking about 9 to 12 months for full rehabilitation. The phases of rehabilitation, though delayed and extended, are essentially the same as those described above.
Coaches and athletic trainers can help develop and carry out sound programs for preventing rotator cuff injuries. Preseason conditioning should address the flexibility, strength, and endurance of the shoulder muscles, particularly the scapular stabilizers and external rotators of the rotator cuff. The conditioning program must be tailored to the sport and fitness level of the athletes. Learning the correct mechanics of the sport and choosing proper equipment are also important. In-season training must be adjusted to avoid overuse injuries, and a proper warm-up and cool-down period should be routine with practice or competition. Such measures will not only help prevent injury, but will also make athletes more successful.
Dr Wolin is director of the Center for Athletic Medicine in Chicago, team physician for Depaul University, and assistant clinical professor at the University of Illinois at Chicago. He is a fellow of the American College of Sports Medicine and a member of the American Orthopaedic Society for Sports Medicine. Dr Tarbet is associate orthopedic surgeon sports medicine specialist at the Center for Athletic Medicine in Chicago and a fellow of the Royal College of Surgeons of Canada. Address correspondence to Joyce A. Tarbet, MD, Center for Athletic Medicine, 711 W North Ave, Suite 206, Chicago, IL 60610.
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