The Impact of Decreased Scapulothoracic Upward Rotation on Subacromial Proximities

Abstract

BACKGROUND: Decreased scapulothoracic upward rotation has been theorized to increase an individual's risk for rotator cuff compression by reducing the clearance for the tendons in the subacromial space (ie, subacromial proximities). However, the impact of decreased scapulothoracic upward rotation on subacromial proximities has not been tested during dynamic in vivo shoulder motion. OBJECTIVE:To determine the impact of decreased scapulothoracic upward rotation on subacromial proximities. METHODS:Shoulder kinematics were quantified in 40 participants, classified as having high or low scapulothoracic upward rotation, during scapular plane abduction using single-plane fluoroscopy and 2-D/3-D shape-matching. Subacromial proximities were calculated as (1) the normalized minimum distance between the coracoacromial arch and humeral rotator cuff insertion, and (2) the surface area of the humeral rotator cuff insertion in immediate proximity to the coracoacromial arch. The effect of decreased scapulothoracic upward rotation on subacromial proximities was assessed using 2-factor mixed-model analyses of variance. The prevalence of contact between the coracoacromial arch and rotator cuff was also quantified. RESULTS:Subacromial distances were generally smallest below 70° of humerothoracic elevation. With the arm at the side, the normalized minimum distance for participants in the low scapulothoracic upward rotation group was 34.8% smaller compared to those in the high upward rotation group (P = .049). Contact between the coracoacromial arch and rotator cuff tendon occurred in 45% of participants.CONCLUSION: Decreased scapulothoracic upward rotation shifts the range of risk for subacromial rotator cuff compression to lower angles.

Shoulder kinematics impact subacromial proximities: a review of the literature

“…Initial work by Thomas et al 35 suggested acromiohumeral distance (measured via ultrasound) was not significantly correlated with scapular upward rotation angular position when the arm was at the side or at 90 • humerothoracic elevation in asymptomatic college baseball players. Recent work, 37 however, suggests the relationship between scapulothoracic upward rotation and subacromial proximities is not absolute, but depends on the angle of humerothoracic elevation. The study quantified shoulder kinematics and minimum distance (normalized to the rotator cuff tendon thickness) in 40 symptomatic and asymptomatic individuals during dynamic scapular plane abduction.…”

“…Three-dimensional methods used to quantify subacromial proximities include kinematic tracking and modeling using either single- 37 or bi-plane radiography, 7,38,39 stereophotogrammetry, 28 3D image reconstruction, 40 or computational modeling. 41,42 Although these 3D approaches provide higher accuracy, they often require custom equipment and data processing algorithms, and significant data processing time, which hinder broad use, clinical translation, and large sample sizes.…”

“…As such, normalizing the minimum distance to a measure of the rotator cuff tendon thickness may aid data interpretation. 37 In addition to the limitations just described, distance measures alone may not provide a comprehensive assessment of subacromial space. Consequently, other geometric descriptions have been used.…”

“…subacromial proximity areas) has also been reported. 28,37,41 Like minimum distance, however, subacromial proximity areas may be difficult to interpret without information on the rotator cuff thickness.…”

Fatigue-Induced Scapular Dyskinesis in Healthy Overhead Athletes

“…Other Authors reported a range of apparently contrasting results concerning the increment or decrement of scapular rotations in various athletes populations (Su et al, 2004;Ebaugh et al, 2006;Maenhout et al, 2015). Discrepancies between studies can be attributed to the degree of humeral elevation and the postural arrangement adopted in the fatigue protocols (prone, sitting or standing position), the applied load (bottle, elastic band, and sport-specific actions) or upper limb movement (elevation or abduction) (Lawrence et al, 2019).…”