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Shoulder impingement syndrome (SIS) is a common condition often described as shoulder pain exacerbated by overhead activities.1 Several structures can become impinged and thus lead to shoulder impingement syndrome. The impingement that generally takes place is the pinching of a soft tissue structure under a bony structure with associated motions, resulting in many undesirable effects.
General Anatomy of the Shoulder
The shoulder girdle includes the articulation of the humerus, clavicle, sternum, and scapula. The structures that are usually the culprit in shoulder impingement syndrome involves degeneration and/or mechanical compression of the subacromial structures on the anterior undersurface of the acromion. The structures involved include the rotator cuff tendons, the long head of the biceps, and subacromial bursa.
Biomechanics of the Shoulder Girdle
Several movements occur in order for the shoulder complex to function properly. In order for these full shoulder motions to occur, there must also be mobility in spinal segments through the level of T6. This should be considered in discerning the cause of movement disorder in the shoulder girdle. If a clinician decides to perform joint mobilizations, it is imperative for the clinician to understand the biomechanics of the shoulder girdle. Generally speaking, the glenohumeral joint follows the convex on concave rule which results in the roll and glide occurring in the opposite direction of each other. A common reason for the painful arc in shoulder impingement syndrome is because of the lack of inferior glide during abduction of the glenohumeral joint. Knowing the biomechanics of the shoulder girdle will help decide which joint mobilization to apply for the patient. Any disorder in motion occurring at the scapula thoracic joint (STJ), acromionclavicular joint (ACJ), glenohumeral joint (GHJ), or sternoclavicular joint (SCJ) could contribute to dysfunction at another joint.
Impingement of the shoulder girdle can be described by three main processes. These processes involve different dysfunctions, such as abnormal arthokinematic motion during shoulder ROM or from anatomical structural abnormalities of the humerus or acromion.2
Primary shoulder impingement occurs when the rotator cuff tendons, long head of the biceps tendon, glenohumeral joint capsule, and/or subacromial bursa become impinged between the humeral head and anterior acromion. Primary impingement may be due to intrinsic factors such as: rotator cuff (RTC) weakness, chronic inflammation of the RTC tendons and/or subacromial bursa, RTC degenerative tendinopathy, and posterior capsular tightness leading to abnormal anterior/superior translation of the humeral head. Extrinsic factors that can lead to impingement include a curved or hooked acromion, acromial spurs, or postural dysfunction.
Secondary impingement is defined as a relative decrease in the subacromial space due to glenohumeral joint instability or abnormal scapulothoracic kinematics. Commonly seen in athletes engaging in overhead throwing activities, secondary impingement occurs when the RTC becomes impinged on the posterior-superior edge of the glenoid rim when the arm is placed in end-range abduction and external rotation. This positioning becomes pathologic during excessive external rotation, anterior capsular instability, scapular muscle imbalances, and/or upon repetitive overload of the RTC musculature.1 It has been suggested that secondary/internal impingement is most likely caused by fatigue of the muscles of the shoulder girdle resulting from a lack of conditioning or from over-throwing. As the shoulder girdle muscles become fatigued, the humerus drifts out of the scapular plane.2
Coracoid Impingement syndrome is a less common cause of shoulder pain. Symptoms are presumed to occur when the subscapularis tendon impinges between the coracoid process and lesser tuberosity of the humerus. The impinging of the subscapularis tendon can lead to tendinosis and pain. Coracoid impingement presents with activity-related anterior shoulder pain and can co-exist with subacromial impingement. This syndrome occurs most commonly after a history of chronic overuse with multiple episodes of micro trauma, especially when in the exacerbated positions. Typical movements that exacerbate this impingement include forward flexion, adduction, and internal rotation. Causes of coracoid impingement are classified as idiopathic, traumatic, or iatrogenic.3
Impingement can occur indirectly due to overuse and/or due to a chronic injury. Impingement can also occur gradually due to a specific trauma to the GH joint. Secondary/internal impingement typically affects young to middle-aged adults; in most major case series of internal impingement, patients are under 40 years of age and participate in activities involving repetitive ABD and ER arm motions or positions (overhead athletes).4
Patients will typically indicate in the subjective examination pain with over head movement through a particular arc of movement. Upon evaluation of the patients posture, common deviations include: forward head, rounded shoulders, and/or protracted or tilting scapulae. Furthermore, patients will presents with limited range of motion (RoM) in internal rotation, increased pain on active external rotation and abduction of the shoulder. There will be weakness present during manual muscle testing (MMT), these tests could also be painful. Also, the Neer's and Hawkin's-Kennedy tests will be positive for pain. The head of the humerus could appear to sit more anterior and superior in the glenoid fossa compared to the uninvolved side; thus, assessing all active, passive, and passive accessory movements to determine the patients comparable sign is important. Deciphering between rotator cuff, bursa, or AC joint injury occurs based on the location of the pain in the arc of movement.
RTC muscles act to maintain the head of the humerus in the glenoid fossa, essentially depressing and centralizing the humeral head as the arm is elevated and abducted. Weakness in the RTC muscles causes dysfunction in the depression and centralization of the humeral head whilst the joint is moved through any movements above ninety degrees. In SIS, as the arm is elevated, the greater tubercle of the humerus comes in contact with the acromion and thus causes impingement of RTC tendons, or the subacromial bursa.
|Table 1 Causes of Shoulder Impingement Syndrome|
|Type 2 and Type 3 acromions|
|Osteoarthritic spurs of AC joint|
|Thickened or calcified coracocacromial ligament|
|Loss of RTC muscles causing superior migration of humerus|
|Secondary impingement from unstable shoulder|
|Anterior or posterior capsular contractures|
|Table from: http:www.aafp.org/afp/980215ap/fongemie.html|
Diagnostic tests for SIS include x-ray and MRI arthrography. Radiographic views include: AP, axillary and Y-view – minimal findings are typically present on X-ray. Changes of the greater tuberosity, rounding or remodeling of the posterior glenoid rim, or characteristics of the acromion process are observed. MRI is the optimal choice of diagnostic tool and is considered to be the gold standard. Another imaging method, MR arthrography findings include articular-sided partial-thickness RTC of the supraspinatus, infraspinatus, or both tendons, and posterior or superior labral lesions.4
X-ray of Shoulder Impingement
MRI image of Shoulder Impingement
Evaluation/Special Orthopedic Tests
There are numerous tests for the shoulder complex; however the most commonly used tests for impingement are Neer's, Hawkins-Kennedy, and Impingement Sign. Presence of pain with each of these tests indicates that the test is positive. In overhead athletes, posterior GH joint line tenderness, increased external rotation, and decreased internal rotation are also typically noted. The description of each special test along with an image and video is included below.
This test is performed with the patient sitting or standing. The physical therapist stabilizes the clavicle and scapula with one hand and passively flexes the patient's internally rotated arm with the other hand. Reproduction of pain indicates a positive test.
Image from http://ajs.sagepub.com/content/31/1/154.full
Hawkin's Kennedy Test
This test is performed with the patient standing or sitting with the examiner passively flexing the shoulder to 90 degrees with the elbow in 90 degrees flexion. A forceful internal rotation force is applied as the arm is moved in different angles of horizontal adduction and flexion. Reproduction of pain indicates a positive test.
Image from http://ajs.sagepub.com/content/31/1/154.full
This test is performed with the patient seated or in supine while the examiner moves arm to 90 degrees of abduction and full external rotation. Reproduction of symptoms or anterior/posterior shoulder pain suggests positive test. Reverse impingement sign should alleviate symptoms if impingement is present. [Reverse impingement is performed with an inferior glide to the humerus while moving arm through abduction].
There are several different avenues for conservative management of SIS. Physical therapy is the most common first approach to treating SIS. Specifically, glenohumeral (GH) mobilizations combined with exercises is currently the most effective means of conservative management.1 Specific GH mobilization techniques discussed in research that have shown significant effects on pain reduction and improvements in shoulder function include: GH joint anterior, posterior, and inferior glides, and long-axis distraction passive accessory motions (PAM).
GH Joint Mobilizations: Anterior, Inferior, and Posterior
Mulligan’s technique of mobilization with movement (MWM) has also shown significant reduction in shoulder pain with improved function when used in concert with therapeutic exercises such as: strengthening the rotator cuff and scapular stabilizing musculature and stretching to decrease capsular tightness.1 Kirchhoff and Imhoff4 provide a specific rehabilitation protocol for internal impingement of the overhead athlete. This protocol is broken down into four phases:
Phase I: Acute Phase: allow injured tissue to heal, modify activity, decrease pain and inflammation, correct muscle balance, and restore proprioception. [use ice, US, and e-stimulation to reduce pain and inflammation]. Stretching of the posterior RTC muscles.
Phase II: Intermediate Phase: intensify the strengthening program, continue to improve flexibility, facilitate neuromuscular control. Progress to more aggressive isotonic strengthening activities. Stretch posterior capsule, increase IR (sleeper stretch). Scapular strengthening, core strengthening, running program, UE stretching to maintain flexibility
Phase III: Advanced Strengthening: Phase initiate aggressive strengthening drills, enhance power and endurance, perform functional drills and gradually initiate throwing activities. “Thrower’s ten”7, manual resistance stabilization drills, plyometric training, initial throwing program.
Phase IV: Return-to-throwing Phase: progression of interval throwing and neuromuscular maintenance.4
Another means of conservative management of SIS is the use of subacromial corticosteroid injection (CSI). Research shows that CSI is the most common procedure for the management of shoulder pain used by orthopaedists, rheumatologists and general practitioners. Though the long-term efficacy of CSI has not been established yet, an injection is a very appealing means of treatment since the CSI provides immediate reduction of the inflammatory response.5
Image from: http://orthoinfo.aaos.org/topic.cfm?topic=a00032
Surgery & post-op treatment
A traditional means of surgical management is an acromioplasty. There has been a significant increase in the number of acromioplasties performed over the past two decades. The switch from an open approach to an arthroscopic approach has been a factor in this increase. Arthroscopic surgery can be performed to the acromion to increase the subacromial space and thus relieve impingement of the greater tuberosity into the acromion.6 Post-operatively patients will be placed in a sling most often restricting motion into internal rotation. Goals of physical therapy include pain management and restoring full ROM as indicated by the surgeon.
Exercise in the treatment of rotator cuff impingement: A systematic review and synthesized evidence based rehabilitation protocol by John E. Kuhn, MD