Posterior Internal Impingement of the Rotator Cuff in Throwers
ABSTRACT & COMMENTARY
Synopsis: One hundred percent of symptomatic throwers demonstrated internal impingement of the undersurface of the rotator cuff against the glenoid rim on arthroscopic examination.
Source: Paley KJ, et al. Arthroscopic findings in the overhand throwing athlete: Evidence for posterior internal impingement of the rotator cuff. Arthroscopy 2000;16:35-40.
Classic impingement syndrome of the rotator cuff involves outlet impingement beneath the coracoacromial arch, and responds well to surgical decompression of the subacromial space. Young, throwing athletes often are the exception, with difficulty demonstrated on attempts to return to throwing activities. The concept of internal impingement secondary to instability has been proposed as an etiology of nonoutlet impingement that would not respond to subacromial decompression.
Paley and colleagues present their arthroscopic findings in 41 consecutive, male professional throwing athletes to help us understand these complex shoulder relationships. All patients complained of pain during the late cocking or acceleration phase that limited their throwing ability. The dominant arm was involved in all subjects, and none described a single traumatic episode. On exam, 26% demonstrated classic impingement (Neer or Hawkins signs). Subtle instability, as demonstrated by the relocation test or pain on the apprehension test, was evident in about 63%. However, none of the patients had true apprehension or gross instability. These patients were examined arthroscopically prior to being treated with anterior capsular labral reconstruction.
Paley et al found that 100% of patients had internal impingement with the arm in 90° of abduction and maximal external rotation (the cocking phase of throwing). They defined internal impingement as contact between the undersurface of the rotator cuff and the posterior superior glenoid rim, or osteochondral lesions on the humeral head (17%). Partial thickness tears (fraying) of the rotator cuff were present in 93%, and posterosuperior labral fraying was present in 88%. Anterior pathology included anterior labral fraying (36%), Bankart lesions (10%), and SLAP lesions (10%). A positive relocation test was associated with posterior pathology in all cases, while a negative relocation test was associated with combined anterior and posterior pathology in 44% of cases.
Comment by David R. Diduch, MS, MD
This paper by Paley et al helps us better understand the etiology of nonoutlet impingement by providing arthroscopic, physical examination, and patient history correlations. While Paley et al do not attempt to evaluate treatment outcomes, they effectively demonstrate internal impingement findings at arthroscopy. These undersurface rotator cuff tears and osteochondral injuries would not likely be improved by subacromial decompression.
I believe that this is the important thing to be learned from their observations. When a young patient, especially a throwing athlete, presents with impingement findings, we should consider internal impingement due to microinstability as an etiology as opposed to classic, outlet impingement. The treatment will likely be quite different. Throwing athletes develop excessive external rotation to help achieve velocity. This comes at the expense of anterior capsular stretch from repetitive microtrauma, or possibly due to traumatic avulsion (Bankart lesion). When the shoulder is in the cocking phase of throwing, the anterior capsular laxity allows forward translation and secondary posterior pinching or impingement of the rotator cuff. Paley et al also found the Jobe relocation test (posterior pain on abduction, external rotation that is relieved by a posteriorly directed force) to be helpful diagnostically.
This well-focused study effectively demonstrates internal impingement of the rotator cuff between the posterosuperior glenoid rim and the humeral head in the throwing athlete. The paper also outlines elements of the history, examination, and arthroscopic findings that will help in making the proper diagnosis so that patients can receive the proper treatment.
Internal, nonoutlet impingement of the rotator cuff is associated with all of the following except:
a. undersurface rotator cuff fraying.
b. subtle anterior glenohumeral laxity.
c. throwing athletes.
d. a tight coracoacromial arch.