Introduction

Subacromial impingement syndrome (SAIS) is described as pressurization and impingement between the acromion, the bursa under the acromion, and the rotator cuff during the abduction and elevation of the shoulder joint, resulting in pain and a functional disturbance of elevation. It is the most common disorder of shoulder, accounting for 44–65% of all complaints of shoulder pain during a physician’s office visit [1]. The SAIS encompasses a spectrum of subacromial space pathologies including partial thickness rotator cuff tears, rotator cuff tendinosis, calcific tendinitis, and subacromial bursitis [2]. At present, the relationship between subacromial impingement and rotator cuff disease in the etiology of rotator cuff injury is a matter of debate [3]. Neer first detailed this disorder as an independent entity in 1972 [4], and SAIS has since been studied in depth. New evaluation methods have continued to emerge [5,6,7,8]. However, SAIS is easily confused with frozen shoulder because of the common clinical manifestations and age of onset. Sometimes, these two diseases occur concurrently. Additionally, Neer test (NT) is positive in both diseases. Neer identified them using a subacromial bursa injection with lidocaine. We would like to introduce a new method called the modified Neer test (MNT). In this report, the diagnostic accuracy of MNT for SAIS is studied, and its contribution to the diagnosis of frozen shoulder is analyzed.

Patients and methods

This report describes a single-center, prospective study. Between January 2015 and June 2015, 82 consecutive outpatients with shoulder joint disease were treated at Cangzhou Clinical College of Integrated Traditional Chinese and Western Medicine of Hebei Medical University (Cangzhou, China). Fifty males and 32 females (15–65 years old) were enrolled. Among the affected shoulders, there were 48 right shoulders and 37 left shoulders; both shoulders were affected in three patients. The disease course ranged from 2 weeks to 1 decade (average 11 months). Six patients were athletes, and three of these patients practiced judo; the other patients engaged in throwing, weight lifting and volleyball. Seventy-six patients were non-athletes. The inclusion criteria were complaints related to shoulder disease. All patients were examined by one experienced doctor and underwent X-ray examination and magnetic resonance imaging (MRI) contrast scanning of the shoulder. According to the diagnostic criteria described below, of the 82 patients (85 shoulders), 30 patients (32 shoulders) were diagnosed with SAIS; 14 patients (15 shoulders) were diagnosed with frozen shoulder; 13 patients were diagnosed with recurrent dislocation of the shoulder; nine patients were diagnosed with glenoid labrum injuries and rotator cuff tears; and three patients suffered from calcified tendonitis. The other four patients had a partial deltoid tear, a bicep tendon injury, shoulder multi-directional instability and osteoarthritis of the shoulder joint. All adult participants and parents of children provided written informed consent before being enrolled in the study. Study approval was obtained from the Ethics Committee of Cangzhou Clinical College of Integrated Traditional Chinese and Western Medicine of Hebei Medical University.

Diagnostic criteria

The primary diagnostic criteria for SAIS included shoulder pain while raising one’s arm, impingement sign, painful arc, tenderness over the greater tuberosity, subacromial bursa injection with lidocaine, and X-rays, particularly the outlet view of the shoulder, acromion type II or III with sclerosis and entophyte growing both at the acromion and greater tuberosity, and so forth [6, 7]. The primary diagnostic criteria for frozen shoulder included pain and a globally limited range of movement (actively and passively, particularly the inward and outward rotation of the shoulder joint), with no radiological abnormalities or MRI scans displaying thickening and contraction of the joint capsule, except signs of calcific tendonitis and other diseases, such as rheumatoid arthritis [9, 10].

Methods

Neer test (NT)

The patient remains in a sitting position, while the examiner stands by the side of the patient’s body with his scapula in one hand, passively elevating the affected arm from the ventral direction to cause impingement between the greater tuberosity and the acromion; a positive sign was described as pain from 60° to 120° abduction.

Modified Neer test (MNT)

There are two steps to this maneuver. The first step is similar to the traditional impingement sign but with the elbow flexed to 90° and the palm facing downward (Fig. 1). The second step is to abduct the affected arm slightly and then rotate the arm outward to 90° and elevate the affected arm again (Fig. 2). In the former angle, an obvious abatement or disappearance of the shoulder pain was considered to be a positive sign. Aggravation of the pain or the inability to complete the action was considered a negative sign.

Fig. 1
figure 1

The first step of the modified two-step Neer’s impingement sign (M-NT). It is similar to the traditional impingement sign, but the elbow is flexed to 90° and the palm faces downward

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Fig. 2
figure 2

The second step of the M-NT is to abduct the affected arm slightly and then to rotate it outward to 90° and elevate the affected arm again

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Evaluation of the diagnostic test

Based on the clinical epidemiology, we calculated the sensitivity, specificity, positive predictive value, negative predictive value and degree of accuracy for NT, MNT for SAIS, and frozen shoulder. The following calculations were used: sensitivity = true positive/(true positive + false negative); specificity = true negative/(true negative + false positive); positive predictive value = true positive/(true positive + false positive); negative predictive value = true negative/(true negative + false negative); and degree of accuracy = (true positive + true negative)/(true positive + false positive + true negative + false negative). SPSS version 17.0 (SPSS Inc., Chicago, IL, USA) was used for statistical analysis.

Results

Based on the clinical epidemiology, we calculated the sensitivity, specificity, positive predictive value, negative predictive value and degree of accuracy of this experiment in diagnosing SAIS. The diagnostic accuracy rate of MNT in identifying shoulder SAIS was 90.59%, and the specificity was 95.56%. The sensitivities, specificities, positive predictive values, negative predictive values, and degrees of accuracy of NT and MNT against SAIS are shown in Tables 1, 2, 3 and 4.

Table 1 Results of two tests to diagnose subacromial impingement syndrome
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Table 2 Diagnostic value over subacromial impingement syndrome in the two tests
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Table 3 Results of two tests to diagnose frozen shoulder
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Table 4 Comparison of diagnostic value over frozen shoulder in the two tests
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Discussion

Subacromial impingement syndrome (SAIS) was first identified by Neer [4], and raising-shoulder pain was characterized as a cardinal symptom of SAIS. Dr. Neer developed this test (Neer Impingement Sign) based on his observations during shoulder surgery. He reported that the critical area for degenerative tendonitis and tendon ruptures were focused on the supraspinatus tendon and sometimes involved the anterior infraspinatus and occasionally the long head of biceps. Elevation of the arm in external or internal rotation causes critical areas to pass under the coraco-acromial ligament or anterior acromion. As described above, NT was that the examiner performed maximal passive forward flexion with internal rotation while stabilizing the scapula. However, the diagnostic accuracy of NT for SAIS was limited. Several studies reported that the average sensitivity of the NT was 76.21%, while the average specificity was 36.02% and indicated that the NT had limited use in informing diagnosis for SAIS [11,12,13,14]. In our study, the sensitivity of the NT and MNT was 90.24 and 85.00%, while the specificity was 50.00 and 95.56%, respectively. The results showed that the degree of accuracy of MNT was significantly higher than the NT (90.59 vs 69.41%). It also suggested that the MNT takes little time and are easy to perform.

Several clinical manifestations, including painful arc, tenderness at the greater tuberosity, impingement sign, and a subacromial blocking test, have been shown to be important diagnostic criteria [3, 15, 16]. According to the pathological appearance, subacromial impingement syndrome can be divided into three stages, which are correlated with the clinical and pathological characteristics. In the third stage, patients often suffer from persistent and night shoulder pain, similar to frozen shoulder. Therefore, the differentiation between these two disorders is important. The term “frozen shoulder” was first introduced by Codman in 1934. He described a painful shoulder condition, which is associated with stiffness and difficulty sleeping on the affected side. Codman also identified a significant reduction in forward elevation and external rotation as a sign of disease. Frozen shoulder patients are usually present in the sixth decade of life, and onset before the age of 40 is rare. The peak age was 56 years, slightly higher in women than in men [17]. Frozen shoulders can be a primary or idiopathic problem, or it may be associated with another systemic disease, such as diabetes [18, 19]. In fact, frozen shoulders are a difficult condition to understand, usually involving substantial pain, movement limitation and considerable morbidity. It is also known as adhesitis, however, evidence of capsular adhesion is refuted, and it can be argued that the term should be discarded [20]. There are a few specific laboratory tests or radiolabels used to freeze the shoulder, the diagnosis is basically clinical. Immunological studies (such as the presence of human leukocyte antigen B27), C reactive protein levels, and the erythrocyte sedimentation rate are all normal and would be measured only to exclude other conditions. Most orthopedic surgeons would not investigate a frozen shoulder beyond a standard X-ray. When standard radiographs of the frozen shoulder are taken, they may well be reported as normal, although they may show periarticular osteopenia as a result of disuse. Arthrography shows characteristic findings of a limited capacity of the shoulder joint (5–10 ml compared with 25–30 ml in the normal joint) and a small or non-existent dependent axillary fold. MRI may show a slight thickening in the joint capsule and coracohumeral ligament [21].

SAIS and frozen shoulder are common diseases in the elderly. Night pain can occur in patients with SAIS (stage III) as well as with frozen shoulder. Moreover, NT has been shown to be positive in both types of patients. To distinguish patients with SAIS from patients frozen shoulder and shoulder dislocation, Neer implemented the subacromial bursa blocking test (impingement test). Here, we introduced the MNT without injection. This maneuver can be divided into two steps. The first step is similar to the traditional impingement sign, but the elbow must be flexed 90°. And the palm of the hand must face downward. The second step is to abduct the affected extremity slightly and then externally rotate it and raise the affected arm again. In the same angle, a positive sign is represented by an apparent abatement or disappearance of shoulder pain. A negative sign is represented by an aggravation of shoulder pain or the inability to externally rotate the shoulder. The mechanisms of MNT are as follows. It is believed that subacromial pain originates from the impingement between the greater tuberosity with the anterolateral undersurface of the acromion when the glenohumeral joint is abducted 60°–90°. However, when the arm is externally rotated to 90° the greater tuberosity moves backward and away from the acromion, and the pain lessens or vanishes. Therefore, the positive sign is usually found in patients with SAIS, and we fail to observe a positive sign in patients with frozen shoulder because of limited abduction and outward rotation of the troubled shoulder.

Conclusions

We can conclude that MNT is a reliable and highly accurate maneuver for the diagnosis of SAIS and seems useful to distinguish this syndrome from frozen shoulder. This study adds to the literature because it has shown significant benefit in both subjective and objective outcome by the diagnostic utility of MNT for patients with SAIS.