In vivo evaluation of rotator cuff internal impingement during scapular plane abduction in asymptomatic individuals

Abstract

Internal impingement-or entrapment of the undersurface of the rotator cuff tendon against the glenoid during overhead activities-is believed to contribute to articularsided tears. However, little is known about internal impingement outside athletic populations. Therefore, the objectives of this study were to (1) describe glenoid-tofootprint distances and proximity centers during dynamic, in vivo motion in asymptomatic individuals, and (2) determine the extent to which these measures differed between individuals with and without a rotator cuff tear. Shoulder kinematics were assessed in 37 asymptomatic individuals during scapular plane abduction using a high-speed biplane radiographic system. Glenoid-to-footprint distances and proximity center locations were calculated by combining the kinematics with computerized tomography-derived bone models. Glenoid-tofootprint contact was presumed to occur when the minimum distance was less than the estimated labral thickness. The condition of the supraspinatus tendon (intact, torn) was assessed using ultrasound. Minimum distances and proximity centers were compared over humerothoracic elevation angles (90°, 110°, 130°, 150°) and between supraspinatus pathology groups using two-factor mixed model analysis of variances. Glenoid-to-footprint minimum distances decreased consistently across elevation angles (p < 0.01) without a significant difference between groups. Contact was estimated to occur in all participants. Proximity centers were generally located on the anterior half of the rotator cuff footprint and on the posterosuperior glenoid. Statement of Clinical Significance: Internal impingement during overhead motions may be a prevalent mechanism of rotator cuff pathology as contact appears to be common and involves the region of the rotator cuff footprint where degenerative rotator cuff tears are thought to originate.

Investigating the multifactorial etiology of supraspinatus tendon tears

“…The prevalence of internal impingement was also not found to be a significant predictor of a supraspinatus tear. However, the 100% rate of internal impingement observed in the study, while consistent with previous investigations, 27,51 precludes meaningful analysis of its contribution (if any) to tendon tearing. Although typically thought of as a mechanism of pathology, it is possible that impingement is more related to symptom provocation.…”

“…Although typically thought of as a mechanism of pathology, it is possible that impingement is more related to symptom provocation. For example, pain near end‐range humeral elevation is common in patient's seeking care for shoulder pain 52 and may be the result of the entrapment of an inflamed tendon against the glenoid (i.e., internal impingement), 27 even though the injury may have occurred through another mechanism (e.g., overload). Future work will investigate the role of impingement mechanisms in both symptom manifestation and pathology progression.…”

“…First, subacromial impingement was assessed by calculating the proximity between the acromion and rotator cuff footprint, with contact being assumed to occur when the minimum distance at the humeral articular margin was less than the rotator cuff tendon thickness measured during the ultrasound examination 31 (Figure 2A). Second, internal impingement was assessed by calculating the proximity between the glenoid and rotator cuff footprint, with contact being assumed to occur when the minimum distance was less than an estimated labral thickness (4.3 mm) 27 (Figure 2B). Subacromial and internal impingement were operationally defined to be present if contact was estimated to occur during any of the four motion trials.…”

“…Rotator cuff tendon impingement was estimated using a high-speed biplane videoradiography system with methods previously described. 21,27 Briefly, participants were seated and performed four trials of scapular plane abduction with their dominant shoulder (arm raising and lowering with and without a 5 lb. hand weight) while radiographic images were acquired at 60 Hz.…”

Effects of Scapular Angular Deviations on Potential for Rotator Cuff Tendon Mechanical Compression

“…1,2,[7][8][9]16,17 Furthermore, if the arm continues to elevate, the undersurface of the rotator cuff tendon approaches, and may contact, the superior glenoid rim. This distinct mechanism, internal impingement, was identified originally in overhead athletes during combined shoulder abduction and external rotation, 4,39 but it has been observed recently above 90°humeral elevation even without extreme axial rotation, 18,34 suggesting it may not be exclusive to overhead athletes.…”