1.    Primary extrinsic impingement syndrome with subacromial bursitis and/or cuff tendinosis with type II or III acromion.

2.    Chronic secondary impingement with adaptive pathologic subacromial bony/soft tissue changes (e. g., anterior acromial traction spur or undersurface acromial fraying or bursal cuff degeneration).

3.    Lack of response to diligent conservative treatment program including scapular and rotator cuff retraining, nonsteroidal anti-inflammatory drugs, subacromial injection, and activity modification for 6 to 12 months.

1.    Secondary impingement with underlying subluxation

2.    Internal posterior-superior impingement with/without superior labrum anterior and posterior (SLAP) lesion

3.    Anterior subcoracoid impingement

4.    Pseudo-impingement

1.    Pain with impingement maneuvers (Neer and Hawkins signs) relieved with subacromial injection of lidocaine

2.    Tenderness to palpation of anterior acromion and anterior and superior cuff when arm is extended

3.    Pain with resisted abduction and flexion (cuff tendinosis) and/or positive Speed’s test (biceps tendinosis)

1.    Standard shoulder radiographs including outlet, glenohumeral anteroposterior (AP), axillary, and acromioclavicular (AC) views to evaluate acromial morphology and AC disease

2.    Magnetic resonance imaging, arthrogram, or ultrasound may be utilized to further evaluate rotator cuff and biceps tendon

3.    Selective lidocaine injections into subacromial space versus AC joint versus bicipital groove to delineate pathology

1.    Outlet and axillary views are key to evaluating the acromion. AP of AC joint and axillary views are key for the AC joint.

2.    Determine the shape (should be type II or III or you are likely performing an inappropriate procedure) and thickness of acromion on outlet view. Draw two lines: one on the undersurface of the acromion from the front tip to the back edge; a second line along the posterior one half of the undersurface of the acromion extending through the anterior acromion. The distance between these two lines approximates the amount of undersurface anterior bone that will be resected (Fig. 10–1A).

3.    Visualize the AC joint and acromion on the axillary view to determine the amount of anterior acromial protuberance that extends anterior to the AC joint. This approximates the amount of bone that will be taken off anteriorly as one resects the AC spur in addition to the undersurface bone (Fig. 10–1B).

4.    It is important on the outlet view to evaluate the thickness and shape of the acromion because those that are very thin and curved will not be candidates for the “cutting block” technique as too much bone would be resected, risking acromial fracture or deltoid detachment. A limited resection of the anterior hook would be more appropriate in these cases (Fig. 10–2).