Posterior superior Internal Impingement: Evidence Based Review

Over the last decade, the concept of internal impingement has continued to evolve, and the frequency with which this condition is recognised continues to increase. This syndrome should be clearly differentiated from the classical (external) impingement that is thought to be caused by compression of the subacromial bursa, long head of the biceps tendon and rotator cuff (RC) by the coraco-acromial arch. Internal (posterosuperior) impingement syndrome is typified by a painful shoulder due to impingement of the soft tissue, including the RC, joint capsule and the posterosuperior part of the glenoid. The aetiology of this syndrome is unclear, but hypotheses include anterior shoulder instability or micro- instability, contracture of the posterior capsule, reduced humeral retroversion and scapular dyskinesis. Non- operative therapy represents the first line of treatment for this syndrome and includes the management of pain, stretching of the posterior capsule and a muscle strengthening programme. Surgical treatment should only be considered when conservative management fails. A number of different surgical procedures have been proposed, but the results are variable. The success rate is generally improved when the subtle instability, associated with internal impingement, is also addressed. INTRODUCTION Classic shoulder impingement, as described by Neer,1 is caused by extrinsic compression of the subacromial bursa, long head of the biceps ten- don and rotator cuff (RC) by the coraco-acromial arch. Over the past decade, the concept of internal impingement has continued to evolve and is now accepted as a major cause of shoulder pain and discomfort. The internal or non-outlet impinge- ment syndrome is the result of an impingement of soft tissues between the articular surfaces of the humeral head (HH) and the glenoid. The joint capsule may also be involved along with the gle- noid rim (where the impingement may involve the labrum). Minor internal impingement is fre- quently seen in asymptomatic shoulders, with- out any evidence of pathological change, when the arm is brought into abduction and external rotation (ABER). Over time, constant repetition of this movement may result in injury at the site of impingement (the posterosuperior aspect of the labrum and the undersurface of the RC), cre- ating a need for treatment of the pathology as well as the factors causing the impingement.2–6 The aim of this review is to evaluate the differ- ent aetiological theories proposed to explain internal impingement. The different anatomical structures involved in impingement are described, the clinical findings are presented, and treatment guidelines are suggested.