Subacromial impingement syndrome, or symptomatic irritation of the rotator cuff tendons and subacromial bursa within the subacromial space, is the most common cause of shoulder pain, representing between 44 and 65 percent of shoulder disorders.^1,2 Impingement disorders are more common in individuals who participate in prolonged and repetitive overhead activities, including sports and manual labor.^3,4 Further, studies have shown that the incidence of shoulder impingement increases with age, and peak incidence is between ages sixty and sixty-nine.^3,5-7 Other factors that increase the likelihood of development of impingement syndrome include curved or hooked acromial morphology.

Anatomy

The subacromial space is an anatomic region of the shoulder defined as the space between the coracoacromial arch, consisting of the acromion, coracoacromial ligament, and coracoid process; the greater tuberosity; and the rotator cuff attachments.³ Within the subacromial space, there is the presence of soft tissue structures, including the tendons of the rotator cuff, the coracoacromial ligament, the subacromial bursa, and the long head of the biceps tendon. On radiographs, the distance between the superior and inferior borders of the subacromial space has been measured between 0.8 and 1.2 centimeters.³ The shape of the acromion has been classified, according to Bigliani et al., into three categories: type I (flat), type II (curved), and type III (hooked).³ Bigliani et al. initially noted an association of the type II and III acromia with rotator cuff pathology, while other studies have found different associations with rotator cuff pathology.^3,8,9

Pathophysiology

There are several proposed mechanisms that contribute to the development of subacromial impingement.^1,3,4 Extrinsic compression of the rotator cuff tendons occurs between the head of the humerus and the anterior acromion, the coracoacromial ligament, or the acromioclavicular joint. Processes that narrow the subacromial space and can lead to rotator cuff tendon compression include the development of subacromial spurs, osteophytes at the AC joint, and hypertrophy of the coracoacromial ligament, in addition to acromial morphology.^1,3,4 Factors contributing to subacromial impingement include:

• Anterior acromion morphology
• Subacromial spur
• Coracoacromial ligament
• Acromioclavicular joint

Further, repetitive motion and overuse of the shoulder may lead to bursitis and inflammation of the soft tissues within the subacromial space.

History

Initial evaluation of subacromial impingement begins with a thorough history. The most common presenting symptom is pain of the shoulder with overhead activity.³ Classically, this pain occurs on forward elevation of the affected arm between 70 and 120 degrees.³ Patients may additionally report pain upon overhead motion, pain when lying on the affected shoulder, and nighttime pain. Symptoms such as stiffness and weakness may be present but are more often secondary to pain.³ The pain is often relieved by rest, ice, and non-steroidal anti-inflammatory drugs (NSAIDs), and exacerbated by motions including overhead motions, abduction, and internal rotation (i.e., reaching for a back pocket or hooking a bra). In addition to a thorough evaluation of the characteristics of pain, the duration of the symptoms should be determined. Subacromial impingement typically has an insidious course, with symptoms gradually worsening over a period of weeks to months.^2,3 Further, all previous interventions, including lifestyle changes, physical therapy, NSAIDs, corticosteroid injections, and surgical procedures, on the affected shoulder should be noted.

Physical Examination

A thorough physical examination, including inspection, palpation, range of motion, and specific physical examination maneuvers, are crucial for establishing a diagnosis of subacromial impingement. Inspection of the shoulder should be performed when standing in front of, on the side of, and behind the patient, and a comparison of the affected shoulder with the unaffected shoulder should be made. In subacromial impingement, palpation of the CA ligament and anterior acromion may elicit tenderness.¹⁰ Additionally, it is important to perform a thorough examination of the cervical spine, as radiculopathy and degenerative processes can manifest similarly to impingement syndrome.³ This includes palpating the cervical spinous processes for any tenderness, examining full range of motion of the neck, and performing a thorough neurological examination. Active and passive range of motion of the bilateral shoulders should be assessed in the following order: forward elevation, abduction, external rotation at the side, external rotation in abduction, internal rotation in abduction, and internal rotation to vertebral height (video 1.1). Strength of the affected shoulder should be compared to that of the unaffected shoulder. Weakness, although not always present, typically manifests as deficits of abduction and external rotation.

Special Tests

Several physical examination maneuvers have been described for impingement syndrome, including the Neer impingement sign, the Neer impingement test, and the Hawkins test. The Neer sign involves the examiner stabilizing the scapula of the affected shoulder with one hand and passively elevating the arm with the other hand (video 1.2; figure 1.1).¹¹ Pain that is elicited in the arc between 70 and 120 degrees of forward elevation indicates a positive test.³ A variation of the Neer impingement sign is the Neer impingement test.³ A sterile injection of ten milliliters of 1 percent lidocaine is made into the subacromial space, and the technique for the Neer impingement sign is repeated. A positive test is indicated by the relief of pain with the subacromial injection.

The next physical examination maneuver is the Hawkins test, or Hawkins-Kennedy test (video 1.3; figure 1.2).¹¹ The examiner places the patient’s shoulder in 90 degrees of flexion and the patient’s elbow in 90 degrees of flexion and maximally internally rotates the shoulder by applying a downward force to the wrist. A positive test is noted when pain is elicited by the maneuver (video 1.4).

Lastly, the Jobe test is performed for the assessment of subacromial impingement and/or rotator cuff pathology (video 1.5; figure 1.3).¹¹ The patient’s arms are placed in 90 degrees of abduction, angled forward 30 degrees, and internally rotated so that the thumbs face the floor. The examiner applies a downward force to the patient’s arm, asking the patient to resist the force and keep their arm level. A test is considered positive if pain and/or weakness are elicited with the maneuver (video 1.6). It is critical to remember that a positive Jobe test does NOT necessarily indicate a rotator cuff tear—pain from the associated bursitis often causes inhibition of the muscles, and the patient simply cannot hold the arm against resistance.

A thorough and efficient examination for subacromial impingement involves all these tests for impingement performed in succession (video 1.7). Recent studies have examined the accuracy of these physical examination maneuvers in the diagnosis of subacromial impingement syndrome.^11,12 In an analysis of 1127 patients, Park et al. noted that the sensitivity, specificity, positive predictive value, and negative predictive value of these tests varied considerably and were influenced by the severity of the impingement syndrome.¹¹ In a systematic review and meta-analysis, Alqunaee et al. determined that these three tests of impingement were more useful in ruling out than ruling in subacromial impingement, as the pooled sensitivity (0.69–0.78) was greater than the pooled specificity (range, 0.57–0.62).¹² Regardless, these three physical examination maneuvers are critical in evaluating the patient for suspected subacromial impingement.

Sensitivities and specificities for all examinations described in chapter 1 are outlined in table 1.1.^12-14

Key Terminology

Hawkins Test 

A test for subacromial impingement where the examiner places the patient’s shoulder in 90 degrees of flexion and the patient’s elbow in 90 degrees of flexion and maximally internally rotates the shoulder by applying a downward force to the wrist. A positive test is noted when pain is elicited by the maneuver. ↵

Jobe Test 

A test for the assessment of subacromial impingement and/or rotator cuff (supraspinatus) pathology. The patient’s arms are placed in 90 degrees of abduction, angled forward 30 degrees, and internally rotated so that the thumbs face the floor. The examiner applies a downward force to the patient’s arm, asking the patient to resist the force and keep their arm level. A positive test is noted if pain and/or weakness is elicited by the maneuver. ↵

Neer Impingement Sign 

A test for subacromial impingement where the examiner stabilizes the scapula of the affected shoulder with one hand and passively elevates the arm with the other hand. A positive test is indicated by pain in the arc between 70 degrees and 120 degrees of forward elevation. ↵

Neer Impingement Test

A variation of the Neer impingement sign, where a sterile injection of 1 percent lidocaine is made into the subacromial space, and the technique for the Neer impingement sign is repeated. A positive test result is indicated by the relief of pain with the subacromial injection. ↵

Subacromial Impingement Syndrome

Disorder characterized by the symptomatic irritation of the rotator cuff tendons and subacromial bursa within the subacromial space. ↵

Subacromial Space

Anatomic region of the shoulder defined as the space between the coracoacromial arch, consisting of the acromion, coracoacromial ligament, and coracoid process, and the greater tuberosity and the rotator cuff attachments. ↵

References

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2. Umer M, Qadir I, Azam M. Subacromial impingement syndrome. Orthop Rev (Pavia). 2012;4(2):e18. ↵

3. Bigliani LU, Levine WN. Subacromial impingement syndrome. J Bone Joint Surg Am. 1997;79(12):1854-1868. ↵

4. Harrison AK, Flatow EL. Subacromial impingement syndrome. J Am Acad Orthop Surg. 2011;19(11):701-708. ↵

5. Garving C, Jakob S, Bauer I, Nadjar R, Brunner UH. Impingement syndrome of the shoulder. Dtsch Arztebl Int. 2017;114(45):765-776. ↵

6. Yamaguchi K, Ditsios K, Middleton WD, Hildebolt CF, Galatz LM, Teefey SA. The demographic and morphological features of rotator cuff disease: a comparison of asymptomatic and symptomatic shoulders. J Bone Joint Surg Am. 2006;88(8):1699-1704. ↵

7. Hsiao MS, Cameron KL, Tucker CJ, Benigni M, Blaine TA, Owens BD. Shoulder impingement in the United States military. J Shoulder Elbow Surg. 2015;24(9):1486-1492. ↵

8. McLean A, Taylor F. Classifications in brief: Bigliani classification of acromial morphology. Clin Orthop Relat Res. 2019;477(8):1958-1961. ↵

9. Pandey V, Vijayan D, Tapashetti S, et al. Does scapular morphology affect the integrity of the rotator cuff? J Shoulder Elbow Surg. 2016;25(3):413-421. ↵

10. Toprak U, Ustuner E, Ozer D, et al. Palpation tests versus impingement tests in Neer stage I and II subacromial impingement syndrome. Knee Surg Sports Traumatol Arthrosc. 2013;21(2):424-429. ↵

11. Park HB, Yokota A, Gill HS, El Rassi G, McFarland EG. Diagnostic accuracy of clinical tests for the different degrees of subacromial impingement syndrome. J Bone Joint Surg Am. 2005;87(7):1446-1455. ↵

12. Alqunaee M, Galvin R, Fahey T. Diagnostic accuracy of clinical tests for subacromial impingement syndrome: a systematic review and meta-analysis. Arch Phys Med Rehabil. 2012;93(2):229-236. ↵

13. Hegedus EJ, Goode A, Campbell S, et al. Physical examination tests of the shoulder: a systematic review with meta-analysis of individual tests. Br J Sports Med. 2008;42(2):80-92; discussion. ↵

14. Jain NB, Luz J, Higgins LD, et al. The diagnostic accuracy of special tests for rotator cuff tear: the ROW cohort study. Am J Phys Med Rehabil. 2017;96(3):176-183. ↵