Subacromial injection is a useful procedure to counteract shoulder impingement syndrome. With the aid of high-resolution ultrasound, the needle can be introduced precisely into the subacromial/subdeltoid bursa located between the acromion above and the supraspinatus tendon below. The standardized method allows the injectate to distribute along the subdeltoid bursa, further reliving pain from subacromial/subdeltoid impingement. In a substantial part of shoulder pain patients, it is common to accompany pain along the bicipital groove, which the biceps long head tendon courses through. The biceps long head tendon is attached to the superior labrum of the glenoid cavity and acts as the second important structure to prevent upward migration of the humeral head, following the supraspinatus tendon. Overuse injury of the biceps tendon is a likely cause of anterior shoulder pain. Concomitant administration of medication into the subacromial bursa and biceps tendon sheath is theoretically more effective than injection to the subacromial bursa only because the formal procedure targets two vulnerable structures in shoulder impingement syndrome at once. Regarding the standard ultrasound-guided subacromial injection. Therefore, we will conduct a randomized controlled trial investigating the effectiveness of standard subacromial injection in comparison with a novel approach simultaneously injecting the subacromial bursa and biceps tendon sheath.

Introduction Subacromial injection is a useful procedure to counteract shoulder impingement syndrome. With the aid of high-resolution ultrasound, the needle can be introduced precisely into the subacromial/subdeltoid bursa located between the acromion above and the supraspinatus tendon below. The standardized method allows the injectate to distribute along the subdeltoid bursa, further reliving pain from subacromial/subdeltoid impingement. In a substantial part of shoulder pain patients, it is common to accompany pain along the bicipital groove, which the biceps long head tendon courses through. The biceps long head tendon is attached to the superior labrum of the glenoid cavity and acts as the second important structure to prevent upward migration of the humeral head, following the supraspinatus tendon. Overuse injury of the biceps tendon is a likely cause of anterior shoulder pain. Concomitant administration of medication into the subacromial bursa and biceps tendon sheath is theoretically more effective than injection to the subacromial bursa only because the formal procedure targets two vulnerable structures in shoulder impingement syndrome at once. Regarding the standard ultrasound-guided subacromial injection. Therefore, we will conduct a randomized controlled trial investigating the effectiveness of standard subacromial injection in comparison with a novel approach simultaneously injecting the subacromial bursa and biceps tendon sheath.

Material and methods:

Participants: adult patients (>20 year old) with shoulder impingement syndrome Inclusion criteria: shoulder pain>3 weeks; no contraindication for local injection; Visual analogue scale of pain>4 Participant number: at least 30 at each treatment arm Exclusion criteria: systemic rheumatologic disease, Ankylosing spondylitis, malignancy, major trauma or recent injections on the affected shoulder Study design: single center double blind randomized controlled trial Randomization method: block randomization (block size: 4), computerized random sequence generation, allocation concealment (+) Detail of the intervention

1. Control group: ultrasound guided injection into the subacromial bursa with 40 mg triamcinolone acetonide plus 3 mL of lidocaine
2. Experimental group: ultrasound guided injection into the subacromial bursa and biceps tendon sheath with 40 mg triamcinolone acetonide plus 3 mL of lidocaine

Outcome measurement:

Visual analogue scale of pain, physical examination(bicipital groove compression test, Speed's test, Yergason's test, empty can test, Neer's impingement test, Hawkins-Kennedy impingement test, painful arc test), range of motion, shoulder pain and disability index (SPADI), shoulder sonography (gray-scale/elastography)

Statistical analysis:

Continuous variables

1. Student's t test: fit assumption of normal distribution
2. Mann-Whitney test: does not fit the assumption of normal distribution Categorical variables

(1) Chi-square test (2) Fisher exact test: sparse data

Multivariate analysis:

1. Linear regression
2. Logistic regression Keywords: ultrasonography, corticosteroid, subacromial impingement syndrome, shoulder pain

Inclusion Criteria:

• shoulder pain>3 weeks; no contraindication for local injection; Visual analogue scale of pain>4

Exclusion Criteria:

• systemic rheumatologic disease, Ankylosing spondylitis, malignancy, major trauma or recent injections on the affected shoulder

The treatment is double blind to the participants and outcome assessors. Only the physician performs the injection knows which kind of intervention the patients receive.