Subcoracoid Impingement

                                       Dr. KS Dhillon

Introduction

Subcoracoid (SC) impingement is the impingement of the subscapularis between the coracoid process and lesser tuberosity of the humerus which can lead to anterior shoulder pain [1]. This condition may be present in association with subcoracoid stenosis. This is characterized by decreased coracohumeral distance on axial and oblique sagittal views, and a variable spectrum of rotator cuff pathology [2]. The rotator cuff pathology can vary from a state of a massive tear to anterosuperior tears of the cuff including the subscapularis tendon [3,4,5].

Some authors state that subcoracoid impingement and massive rotator cuff tears occur when the humeral head translates anteriorly and superiorly toward the coracoid, and the coracohumeral space is reduced [6,7].

Anatomy 

The anatomic configuration plays a role in subcoracoid impingement. The coracoacromial interval includes the tip of the coracoid process, acromion, and the coracoacromial ligament.  The coracoid process is most responsible for altering the volume and shape of the coracoacromial arch. A cadaveric study [8] showed that the coracoid localizes, on average, to the 1:47-o’clock position of the glenoid and 21.5 mm from the nearest portion of the labrum. A study by Renoux et al [9] showed that in most cases a variation in the height and length of the coracoid process is responsible for altering the space between the coracoacromial arch and the rotator cuff. 

Gumina et al [10] in an anatomical morphometric study, described three different configurations of the coracoid process and the coracoglenoid space, of which Type I, occurred in 45% of the scapulae, and it presents the lowest mean values of the coracoglenoid angle and coracoid overlap. This would mean that a short coracohumeral distance is a predisposing factor for coracohumeral impingement. This configuration, however, cannot be directly related to an idiopathic subcoracoid impingement, thus some authors suggest an investigation of this space with a CT scan [11].

Etiology

Subcoracoid impingement can be idiopathic, traumatic, or iatrogenic. Idiopathic SC impingement is related to congenital abnormalities of the coracoid where it projects more laterally than usual. It can be due to calcification or ossification of the subscapularis tendon [12,13,14], subscapularis muscle hypertrophy [15], or ganglion cysts [16,17].

Traumatic causes include displaced humeral or scapular fractures and malunions, humeral head and neck fractures [18–20], and posterior sternoclavicular dislocation [21]. 

Iatrogenic SC impingement is caused by surgical procedures around the shoulder that alter the relationship between the coracoid and lesser tuberosity. Both Bristow/Latarjet and Trillat procedures have been known to produce subcoracoid impingement [18]. An increased anteversion of the glenoid neck, after posterior glenoid osteotomy, can lead to an increased coracoglenoid angle and a decreased coracohumeral distance. This can predispose to impingement [22]. Subcoracoid stenosis may be related to minor anterior shoulder instability [23] or rotator cuff insufficiency and sick scapula syndrome (scapular dyskinesis). This can produce an anterosuperior translation of the humeral head [24,25,26]. This anterosuperior translation of the humeral head leads to a decrease in the coracohumeral distance. Performing an anterior acromioplasty for rotator cuff disorders and a narrow coracohumeral space leads to anterosuperior migration of the humeral head and this can lead to subcoracoid impingement syndrome [5,6].

Clinical diagnosis 

Patients with subcoracoid impingement often give a history of chronic overuse and multiple episodes of microtrauma in overhead activities with the shoulder in a forward-flexion, adducted, and internally rotated position, such as in driving a car, or in the follow-through phase of throwing [27]. The main symptom is a non-specific dull pain in the anterior aspect of the shoulder. The pain is often referred to the upper arm and to the forearm. The pain is exacerbated by forward flexion, adduction, and internal rotation of the shoulder. In patients with iatrogenic syndromes, there is postoperative severe pain often associated with paresthesia which does not correspond with the sensory area of a peripheral nerve or cervical root. Shoulder adduction and internal rotation are limited [28].

Physical examination may show deformities in the shoulder area and previous scars. Often there is tenderness on the soft tissues around the coracoid process or between the coracoid and the lesser tuberosity. The coracoid impingement test is positive. The test is similar to the Kennedy-Hawkins impingement sign, except that the patient’s shoulder is placed in a position of cross-arm adduction, forward elevation, and internal rotation to bring the lesser tuberosity in contact with the coracoid [18]. Shoulder elevation is most painful between 80° and 130°.  Abduction to 90° combined with internal rotation is limited and painful as well as horizontal cross-adduction [28]. Clinical evaluation of the subscapularis functions is carried out. The most reliable tests such as Napoleon, Belly-press, lift off, and bear hug tests, as well as the evaluation of passive pathological external rotation, should be performed [29].

The supine Napoleon test is performed by placing the patient's hand on their belly while they lay supine with an examiner holding their hand and shoulder to prevent compensatory motion. The patient was asked to move their elbow upward and the test was considered positive if they were unable to do so.

The bear hug test is performed by asking the patient to place the palm of the affected side on the opposite shoulder, with the fingers extended and the elbow anterior to the body. The patient is asked to maintain the arm position. The therapist then applies an external rotation resisting force perpendicular on the patient’s forearm, the patient resists the therapist by performing internal rotation. The test is positive if the patient could not maintain the position of the hand against the shoulder or showed weakness in resisted internal rotation greater than 20% compared to the opposite side.

The belly press test is performed by the examiner putting his backhand against the patient's belly and asking the patient to press against your hand. This test is positive, if you detect weakness compared to the other side, or if your patient reports pain.

The lift off test also known as Garber’s test is performed with the patient standing. The patient’s arm is placed in internal rotation with the hand behind the mid-lumbar spine. The dorsum of the hand (back of the hand) is against the patient’s lumbar spine.

The patient attempts to move the hand away from the lower back by extending and further internally rotating the arm. The examiner can also provide resistance to this movement if the patient is able to complete the movement. The Lift-Off Test is considered positive if the patient is unable to move the hand away from the back or is very weak in doing so. The test is also positive if pain is reported.

Radiology

Standard radiographic AP and axillary views perpendicular to the plane of the scapula are done. Abnormalities of the bony elements, which narrow the coracohumeral space can be detected. Some authors suggest that the supraspinatus outlet view for a chevron-shaped coracoid process be done, which is synonymous with coracoid impingement [30].

CT scans and magnetic resonance imaging are useful for further delineating the coracoid and subcoracoid anatomy [27,31,32,33]. The coracohumeral distance in both the axial and sagittal views should be measured in patients presenting with subscapularis tears, especially if surgical intervention is planned [2]. Cine or kinematic, MRI may be used to evaluate the dynamic aspects of subcoracoid impingement [27].

A CT axial view can be used to evaluate the coracoid index. It is a measurement of the lateral projection of the coracoid beyond a line tangential to the articular surface of the glenoid. Dines et al [18] reported that its mean value in 67 normal shoulders was 8.2 mm.

Measurement of the coracohumeral interval is another way to quantify anatomic variation in this region. The coracohumeral interval (CHI) is the minimal distance between the coracoid process and lesser tuberosity, as measured on an axial MRI scan with the humerus in maximum internal rotation [34]. Some authors found that the coracohumeral interval in asymptomatic patients averaged 11 mm [27], with none less than 4 mm. The mean coracohumeral interval in symptomatic patients was 5.5 mm. The average coracohumeral interval for females is 3 mm smaller than that for males [31]. Friedman et al [27] also found that there is no redundancy of the subscapularis tendon in asymptomatic subjects. Patients with subcoracoid impingement usually demonstrate increased soft tissue in the subcoracoid space. This is because of redundancy or folding of the subscapularis tendon and capsular tissues when the shoulder is in maximum internal rotation. Edema located at the ACP level, a subscapular tendon injury, changes in the rotator interval, thickening of the coracoacromial ligament and the clavipectoral fascia, as well as the reduction in the coracoid index, can be seen with an MRI. The sensitivity of the internal rotation position in detecting coracoid impingement on MRI is only 5.3% with specificity at 97.6%. This suggests that coracoid impingement is largely a clinical diagnosis that may be supported, but not established, by MRI [31].  Subcoracoid impingement could be a cause of persistent shoulder pain following supraspinatus repair [6]. 

Friedman et al [27] assessed the CHI in 50 asymptomatic volunteers and 75 patients with symptomatic shoulders, all of whom underwent a cine MRI of the shoulder. They found that cine MRI provides valuable information about the subcoracoid region that is not obtainable with other imaging modalities. 

Giaroli et al [32] compared preoperative MRI scans in a group of 19 patients with demonstrable coracoid impingement at the time of surgery with a control group. The study showed low sensitivity of MRI. The authors concluded that this imaging technique could support the clinical diagnosis, but not establish it.

Ultrasonography has been shown to be a valuable, easily available, and cost effective method to image the subcoracoid recess and diagnose subcoracoid impingement [35]. A significant difference has been found between the CHI in normal asymptomatic shoulders and the CHI in shoulders with symptoms consistent with coracoid impingement. 

Treatment

Treatment has to commence after careful evaluation of the patient with a resistant or recurrent subcoracoid impingement syndrome [18,19,20,23,28]. There should be functional evaluation of the shoulder for possible muscular imbalance, capsular contracture, and scapular dyskinesis, which has to be addressed [26].

The first line of treatment is rest, ice, activity modification, NSAIDs, and corticosteroid injections. There has to be a program of activity modification, with avoidance of the provocative positions of forward flexion and medial rotation, and physical therapy to strengthen rotator cuff muscles and scapular stabilizer musculature.

Surgical decompression of the subcoracoid space may be undertaken if the above conservative measures fail.

Coracoplasty will be indicated in patients with mechanical volume expanding anatomical changes such as calcification or ossification of the subscapularis tendon [12–14], ganglion cysts [16,17], previous humeral head and neck fractures, displaced humeral or scapular fractures and malunions [18–20], or changes of coracoid orientation due to surgical procedures [18,28].

Coracoplasty can be carried out either with open or arthroscopic techniques [3,18,18,36]. Dines et al [18] described an open coracohumeral decompression by excision of the lateral 1.5 cm of the coracoid with re-attachment of the conjoined tendon. The operation is performed through a deltopectoral incision dissecting the lateral insertion of the conjoined tendon. Gerber et al [28] suggested a combination of resection of the coracoacromial ligament, acromioplasty, and resection of conjoined tendon because they believed that isolated coracoid impingement was rare.

Arthroscopic treatment of coracoid impingement can be also performed. The coracoid and subcoracoid spaces are thoroughly examined in patients with long-head biceps and biceps reflection pulley tears, subscapularis tears, and anterior supraspinatus tears [3,37].

The long head biceps tendon must be evaluated. Tears or degeneration of the tendon of more than 50% of its thickness and/or lesions of the biceps pulley system must be addressed by biceps tenodesis [3] or tenotomy.

The coracoplasty can be performed by a trans-articular approach [37] (through the rotator interval) or an extra-articular [38] approach from an anterolateral subacromial portal. The subscapularis must be intact to allow an appropriate orientation of the coracoplasty [37]. Outcome studies detailing this relatively rare diagnosis are limited. Authors typically report reasonable outcomes for both open and arthroscopic procedures [3,4,18–20,23,28,36,37,38].

Conclusion

Subcoracoid impingement has a simple etiology. A decrease in the distance between the coracoid and the lesser tuberosity of the humerus causes impingement that leads to anterior shoulder pain and tendinosis of the subscapularis tendon. The diagnosis is usually clinical. However, the overlapping clinical manifestations of various shoulder pathologies make diagnosis difficult with physical examination alone. MRI modalities have become very effective at isolating this pathology. MRI, however, can be expensive, time consuming, and limited by patients' body habitus or implantable devices. Ultrasonography has proven to be an accurate and cost-efficient option. 

Conservative treatment of subcoracoid impingement is the first line of treatment and can be successfully implemented for most patients. In a  minority of patients where conservative treatment fails, they will require surgical intervention for this pathology. Both open and arthroscopic techniques are available. Despite early promising results for arthroscopic coracoplasty, there are no comparative studies yet to show a definitive clinical benefit. A major deficiency exists in level 1 evidence on this topic. 

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