Abstract
Athletes are susceptible to rotator cuff injury as the result of chronic overuse caused by repetitive overhead throwing or a single traumatic event. The diagnosis starts with a thorough understanding of anatomy, which is used to interpret physical examination and diagnostic imaging findings. Caution must be used when interpreting these findings because special maneuvers intended to isolate specific structures about the shoulder are largely nonspecific; rotator cuff tears are found in asymptomatic shoulders and may not be the source of symptoms. After a diagnosis has been made, classification systems exist that may help the clinician formulate a treatment plan and set patient expectations. In summary, an appreciation of the subtleties of diagnosing rotator cuff injuries in athletes is the foundation of successful treatment and outcomes.
Keywords
infraspinatus, magnetic resonance imaging, repetitive injury, rotator cuff tear, subscapularis, supraspinatus, teres minor, throwing athlete, ultrasound
Introduction
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Rotator cuff tears are common in throwers and contact athletes.
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A thorough knowledge of shoulder anatomy is essential to translating patient history, physical examination, and imaging findings into a treatment plan.
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In the athletic population, the mechanism of injury and host factors are often quite different from the typical degenerative tears seen in older patients.
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Many rotator cuff tear classification systems exist, and although no one system alone can guide treatment or provide prognostic certainty, some have been shown to be useful guides when formulating a surgical plan and establishing patient expectations.
Anatomy, Epidemiology, and Pathomechanics
Anatomy
A detailed understanding of the rotator cuff anatomy and its associated structures is required of the treating physician. Consisting of four muscle–tendon units, the rotator cuff originates from the scapula to insert on the proximal humerus. Extending from the anterior surface of the scapula, the subscapularis inserts onto the lesser tuberosity and humeral neck just medial to the long head of the biceps tendon. The subscapularis receives its innervation from both the upper and lower subscapular nerves, which arise from the posterior cord of the brachial plexus. Next, the teres minor takes its origin from the middle third of the lateral border of the scapula and inserts onto the inferior facet of the greater tuberosity of the humerus. The teres minor is innervated by a terminal branch of the brachial plexus, the posterior branch of the axillary nerve. Last, the supraspinatus and infraspinatus arise and travel along their respectively named fossae on the posterior aspect of the scapula and insert onto the greater tuberosity. The supraspinatus has been further described as having an anterior and posterior belly. The infraspinatus and supraspinatus take their nervous supply from the suprascapular nerve, which arises from the upper trunk of the brachial plexus.
The tendinous portions of these four muscles ultimately fuse with one another in addition to blending with the fibrous capsule before their final insertion onto the humerus. Intervals exist both anteriorly between the supraspinatus and subscapularis and posteriorly between the supraspinatus and infraspinatus. Referred to as the rotator interval, the more easily defined anterior interval between the supraspinatus and subscapularis contains the coracohumeral ligament, superior glenohumeral ligament, glenohumeral capsule, and biceps tendon.
The insertion of the rotator cuff and its so-called footprint have been extensively studied. Cadaveric studies have elucidated it both qualitatively and quantitatively and form the basis of anatomic repair. The insertional footprint of the supraspinatus is trapezoidal or triangular in shape with an average length between 6.9 and 23 mm and average width of 12.6 to 16 mm ( ). Normally, there is a 1.5-mm margin of exposed bone between the articular edge and the insertion of the supraspinatus. This normal or expected margin can be used to estimate the amount of detachment of articular-sided tears. The infraspinatus has a trapezoidal footprint with an average length of 10 to 29 mm and width of 19 to 32.7 mm ( Fig. 5.1 ). Additionally, the thickness of the tendons is between 10 and 14 mm.
As mentioned previously, these two tendons are intimately intertwined by the footprint, making anatomic repair difficult without the use of an external landmark. The bare area of the humerus can be used to consistently identify the interval between the infraspinatus and supraspinatus tendons and is a useful arthroscopic landmark. Additionally, the supraspinatus and infraspinatus tendons form a crescent-shaped thickened area of tendon referred to as the rotator cable, which runs from the anterior border of the supraspinatus to the posterior border of the infraspinatus ( Fig. 5.2 ). First described by , this cable protects the tendon–bone interface from the forces generated by the rotator cuff muscles. Some have hypothesized that this may also partially explain why some patients who have an intact cable are able to maintain functional strength despite the presence of a full-thickness tear ( ); conversely, some have hypothesized that the presence of this load-sharing cable may be responsible for tear propagation ( ).
Ultimately, understanding the anatomy of the rotator cuff and its relationship to the other structures within the shoulder girdle is paramount to successful diagnosis and treatment of rotator cuff injuries.
Epidemiology
Rotator cuff tear is the most common cause of presenting shoulder complaints, and its incidence increases with age. It is estimated that rotator cuff tears result in 4.5 million physician visits annually ( ) with roughly 250,000 repairs performed each year ( ).
Age-related degenerative rotator cuff tears are far more common than traumatic tears in the general population. Similarly, throwing athletes more commonly sustain degenerative tears related to overuse, but other athletes, especially contact athletes, are more likely to sustain traumatic tears during competition or training. A recent systematic review reinforced what has been previously believed, that throwers tend to develop partial-thickness articular-sided tears due to chronic overuse, but nonthrowers are more likely to suffer full-thickness tears during a single traumatic event. This same systematic review noted that studies evaluating rotator cuff tears in patients under the age of 40 years are lacking in both quality and quantity ( ).
It is important to note that not all rotator cuff tears are symptomatic, and care should be taken to determine if the patient’s symptoms correlate to imaging findings. This point is highlighted by ultrasonography, magnetic resonance imaging (MRI), and arthrography findings that have shown full-thickness tears in 4% to 13% of asymptomatic individuals 40 to 60 years old, 20% of subjects 60 to 70 years old, 31% to 50% of subjects 70 to 80 years of age, and 50% to 80% of subjects older than 80 years old. Perhaps more germane to the athlete population, it should also be noted that partial-thickness tears have been found in 4% of asymptomatic patients younger than 40 years ( ).
Pathomechanics
Although all athletes are subject to rotator cuff injury, the pathomechanics discussed in this section are most pertinent to throwing athletes. The other category of tears tends to be acute injuries caused by a single catastrophic event resulting in traumatic avulsion of the rotator cuff. The pathomechanics of rotator cuff injury in the athlete are thought to arise from three proposed mechanisms ( ): internal impingement, external or outlet impingement, or tensile overload.
Thought to be a common cause of partial articular-sided tears in throwers, the pathomechanics of internal impingement are described as abnormal contact of the rotator cuff, glenoid, and labrum during the throwing motion ( Fig. 5.3 ). Because this repetitively occurs during the late cocking and acceleration phase of the overhead throwing motion, it can lead to a predictable pattern of injury involving partial articular-sided tears of the posterior portion of the supraspinatus and the superior portion of the infraspinatus in addition to posterosuperior labral injury. This initial description by was expanded on by , who described a mechanism that placed posterior capsular tightness as the key pathologic change leading to the internal impingement pathway. The proposed pathomechanical cascade begins with the high and repetitive deceleration forces seen by the posterior rotator cuff and capsule. This repetitive stress leads to hypertrophy and capsular contracture that over time forces the humeral head into a less stable posterosuperior position when the arm is abducted and externally rotated. In this less stable position, the humerus is permitted to go into a position of supraphysiologic external rotation that creates increased shearing forces on the rotator cuff and labrum, thereby exacerbating the innate impingement of these structures during the normal overhead throwing motion.
Subacromial or outlet impingement is thought to be a less common cause of rotator cuff tear in throwing athletes. The pathomechanics of rotator cuff tear caused by subacromial impingement are well understood because of its suspected role in older patients with the vastly more common and well-studied degenerative rotator cuff tear. Under normal conditions, the contents of the subacromial space must pass under and through the coracoacromial arch during abduction. As the rotator cuff tendons and the subacromial bursa pass through this anatomic arch formed by the acromion, coracoacromial ligament, and coracoid process, they are subjected to impinging and shearing forces. These forces are further amplified when a thrower has rotator cuff or periscapular weakness caused by fatigue or poor training. Weakness of the rotator cuff can lead to altered throwing mechanics by allowing the deltoid to overpower the weakened or fatigued rotator cuff, disrupting normal force coupling and leading to dynamic superior migration of the humeral head. This superior migration of the humeral head further reduces the volume of the subacromial space and thereby causes further impingement on the rotator cuff tendons and bursa. Periscapular weakness can lead to scapular dyskinesia during the throwing motion, which ultimately leads to compensatory alterations in both scapular and humeral head position, further exacerbating the impinging forces on the rotator cuff. The bursa then becomes inflamed, which may alter the local environment and lead to pain and possible poor tendon tissue quality over time. The rotator cuff tendons have been shown to have altered vascular patterns in response to repetitive stress, thereby reducing the structural strength of the tendon and making it more susceptible to injury ( ); this mechanism is also thought to play a prominent role in tears caused by tensile overload. Regardless of the cause of outlet impingement, during the acceleration phase of the overhead throwing motion, these forces are further amplified and thus can explain bursal-sided or rarely even full-thickness tears of the rotator cuff.
Tensile overload refers to attritional degeneration and eventual tear of the rotator cuff in response to the cumulative and repetitive stresses caused by overhead throwing. Most of the injury and preceding stress placed on the rotator cuff in this setting occur during the deceleration phase of throwing, as eccentric contracture of the posterior rotator cuff attempts to slow the arm from its maximum angular velocity. As these posterior structures slow the arm, they experience considerable strain, leading to the aforementioned vascular changes, which creates the conditions for articular-sided wear and eventually partial-thickness tear. These attritional injuries occur most commonly in the posterior portion of the supraspinatus and anterior half of the infraspinatus, as the rotator cuff maintains the humeral head within the glenoid while simultaneously slowing the arm against tremendous force. The deceleration phase is also implicated as the pathologic force in Burkhart’s mechanism of internal impingement-driven rotator cuff injury in throwers previously discussed in this chapter.
Although each mechanism is described separately, it is important to recognize that significant overlap likely occurs in throwers presenting with suspected rotator cuff injury. An understanding of these mechanisms highlights the need for strength training, proper throwing mechanics, and rest for the throwing athlete so that intervention can be made proactively before significant injury occurs.
History, Physical Examination, Imaging, and Classification
History
As with any clinical encounter, a thorough history is paramount to guiding the clinician to a timely and accurate diagnosis. Questioning should be targeted at determining the acuity or chronicity of the chief complaint as well as aggravating and alleviating activities. Areas of special focus include the sport, position, level of participation, and expectations of the patient. Previous treatments as well as the patient’s response should be recorded.
Throwers may present with a variety of complaints, from discomfort, decreased velocity or stamina, to a generalized ache and inability to throw. A detailed throwing history should be obtained, including any recent changes in mechanics, training program, or workload. High-level throwers can often identify the exact phase of their throwing motion where symptoms occur. Throwing or contact athletes may complain of persistent symptoms or acute onset that correlates to a traumatic event. Symptoms of rotator cuff injury are often localized to the subdeltoid region and exacerbated by activities of daily living that place the arm away from the body or overhead. Complaints of night pain are common.
Patients with acute traumatic tears often present with severe pain accompanied by profound loss of function after an identifiable inciting event. An inability to elevate the arm for days to weeks after the injury is not uncommon. A contact athlete with an acute rotator cuff tear may report a history of shoulder dislocation at the time of injury.
Physical Examination
Evaluating the rotator cuff via physical examination can be challenging because of its intimate relationship with other commonly injured structures in and about the shoulder. Common pathologies in this patient population that have significant examination findings that overlap with rotator cuff injury findings include proximal biceps tendon pathology, labral injury, acromioclavicular joint arthrosis, and symptomatic os acromiale. It should not be surprising then that many of the physical examination findings described have been reported to have modest sensitivity and even lower specificity for rotator cuff tear ( Table 5.1 ).
| Physical Examination Maneuver | Reported Sensitivity/Specificity (%) | References |
|---|---|---|
| Infraspinatus | ||
| External rotation lag | 46–98/72–98 | |
| Supraspinatus | ||
| Jobe or empty can | 53–89/65–82 | |
| Drop arm | 10–73/77–98 | |
| Teres Minor | ||
| Hornblower’s sign | 100/93 | |
| Subscapularis | ||
| Lift off/lag | 17–100/60–98 | |
| Belly press | 40–43/93–98 | |
| Bear hug | 60/92 | |
Inspection
The physical examination should commence with careful inspection of the patient’s undressed shoulder girdle from multiple perspectives, noting symmetry, muscular bulk and tone, swelling, bruising, scarring, and deformity. Asymmetry may be due to normal hand dominance or may be a pathologic sign of guarding or atrophy. Muscular atrophy should always be interpreted as abnormal and may be a sign of rotator cuff tear or central or peripheral nerve compression.
Palpation
The examiner should attempt to identify areas of tenderness about the shoulder girdle. Areas of interest include the acromioclavicular joint, long head of the biceps tendon–bicipital groove, deltoid, posterior capsule, and rotator cuff muscles and their insertions.
Range of Motion
Active and passive range of motion (ROM) should be assessed in all planes. Instability and apprehension can be tested as part of the passive ROM examination. Overhead athletes often exhibit increased external rotation and concomitantly decreased internal rotation as a result of adaptive changes caused by repetitive throwing; this is commonly referred to as glenohumeral internal rotation deficit . Normal laxity is often present in athletes such as swimmers and overhead throwers and should not be interpreted as pathologic. However, limited internal rotation may also reflect posterior capsule tightness secondary to early pathology in throwers. Deficits in active and passive ROM should be noted. Pain with active ROM within the so-called painful arc between 60 and 120 degrees of flexion in the scapular plane has been associated with rotator cuff pathology. During ROM testing, it is important to observe both scapulae from behind the patient as the arm is brought through the full range of abduction and forward flexion. Care should be taken to examine for the presence of winging and abnormal or asymmetric motion concerning for scapula dyskinesia, which can be a common cause of shoulder pain in throwers and may accompany a rotator cuff injury.
Strength Testing and Special Maneuvers Specific to the Rotator Cuff
Infraspinatus. Strength of the infraspinatus is tested by resisted external shoulder rotation with the arm fully adducted and in a neutral to slightly internally rotated position. In addition to strength testing, pain may be elicited in the aforementioned position in patients with infraspinatus pathology.
External rotation lag at 0 and 90 degrees can be used to test for infraspinatus competence. To test at 0 degrees, the seated patient’s back is to the physician with the elbow flexed to 90 degrees and the shoulder positioned 20 degrees in the scapular plane. While supporting the limb at the elbow, the examiner grasps the wrist and brings the shoulder to near maximal external rotation. Care should be taken not to place the patient in maximal external rotation because this will cause a false-positive result when the arm recoils; a false-positive result may also be appreciated in patients with an anterior capsular contracture, but a false-negative result may be caused by subscapularis insufficiency. The patient then attempts to maintain the position of external rotation as the examiner releases the wrist while support of the limb at the elbow is maintained. The test is considered positive when the arm falls into internal rotation. The test can be performed similarly with the arm held at 90 degrees of abduction and near maximal external rotation. Neither of these tests is thought to completely isolate the infraspinatus, and as such, sensitivity and specificity are 46% to 98% and 72% to 98%, respectively, in the literature.
Supraspinatus. Strength of the supraspinatus is tested with resisted elevation in the scapular plane with the arm held in 90 degrees of abduction and neutral rotation. As with infraspinatus testing, pain may be a sign of supraspinatus pathology even in the setting of full manual strength, and this is the basis of the Jobe or empty can maneuver.
Special maneuvers thought to be more specific for supraspinatus pathology are the Jobe (also known as “empty can”) test and the drop sign. To perform the Jobe or empty can test, the arm is placed in 90 degrees of abduction and brought forward 30 degrees into the scapular plane. Internally rotating the arm rotates the thumb toward the ground, and the patient attempts to resist a downward force. Pain or weakness is interpreted as a positive test result; however, with a reported sensitivity and specificity of 53% to 89% and 65% to 82%, respectively, it should be noted that this test can also be a sign of impingement. The drop arm sign is elicited by having the patient abduct the arm past 90 degrees before slowly adducting the arm back to his or her side. The test result is considered positive if at any time the patient drops the arm to the side because of pain or weakness.
Teres minor. Strength of the teres minor is tested by having the patient externally rotate against resistance with the arm held in 90 degrees of abduction.
The hornblower sign has been shown to have high sensitivity and specificity for teres minor pathology. Originally described in the obstetrics literature in the context of birth-related brachial plexus injury and later adapted by as a test for rotator cuff tears involving the teres minor, this special maneuver has been variously described. Ultimately, the test is used to demonstrate profound external rotation weakness with the arm held in the position of strength testing described earlier. The test result is considered positive when the patient’s hand falls into internal rotation requiring abduction of the shoulder to bring hand to mouth, thereby assuming the characteristic “hornblower” position ( Fig. 5.4 ).
