Rotator cuff tendon compression is influenced by upper scapular rotation.
When the humerus and scapula move together during shoulder abduction, they form a rhythm known as the scapulohumeral rhythm. Each two degrees of movement in the humerus causes one degree of rotation in the scapula upward. The scapula, which is often affected by arthritis, is just one of two bones that work together to move the joint. As a result, shoulder injuries such as rotator cuff tears are frequently linked to scapular dyskinesia.
Scapular upward rotation (UR) has been shown to have an effect on the muscles of the rotator cuff (RC). When the angle of elevation is less than 60 degrees, the researchers hypothesised that those with a lower UR would have a narrower distance between their coracoacromial arch and the insertion of RC muscles on the upper arm.
Dozens of tests Groups of people with symptomatic shoulders were separated from those who did not have any symptoms at all. They were divided into groups based on their gender, age, and dominant hand. Everyone had scapulothoracic rotation measured at 30 degrees of humeral elevation. A scapular UR score was used to divide the participants into three equal groups: those with high, mid, and low UR scores were included in the analysis
A 3-D computer model of each subject’s shoulder was created using magnetic resonance imaging. Those with a mid-range UR were left out of the study entirely. The C-arm fluoroscopy and motion caption cameras were used to examine the subjects’ shoulder motion after that. Researchers were able to take into account each participant’s unique anatomy by superimposing a 3-D model onto the motion films. The distance between the coracoacromial arch and the insertion of the RC was measured using the superimposed model at various scapular plane abduction angles. In reference to the distance, they stated this.
thickness of the RC at the time of insertion.. Therefore, if the distance between the insertion and the arch was less than 100%, the tendon filled the space and the two were in contact.
Compression and contact with the RC are frequently blamed for RC pathology. All participants, regardless of whether they were symptomatic or not, showed contact at some point in the elevation arc, regardless of which UR group they belonged to. There was no statistically significant difference in the number of subjects in each UR group who showed contact. An additional third were at an elevation of 60 degrees or higher when they demonstrated RC-arch contact.
Clinical implication
This content is private. please select our membership plan to unlock the private content features.
Click here
And unlock the content.
Upper arm elevation tends to cause rotator cuff discomfort. As a result, most people assumed that the RC was compressed at 80° of flexion or more. Between 50 and 70 degrees of scapular flexion, however, the distances between the arch and the RC were found to be the smallest. This is consistent with other 3-D studies that have found the same thing. How can impingement occur at lower elevations cause pain at higher elevations if it does? It’s possible that an already irritated tendon is exacerbated by the greater force required to move a longer lever arm through the mid-range of motion,” the researchers write. According to this theory, RC compression-related pain may actually be the result of another structure being compressed, such as the bursa of the subacromial-subdeltoid joint (SASD).
The arch-to-tendon space narrowed 9 degrees less in the low UR group than in the high UR group during motion arc. A decrease in scapular rotation may not increase compression or be clinically significant at higher angles because this difference was not statistically significant. This is of particular significance when treating overhead athletes who experience pain at the mid-arc or higher. Scapular dyskinesia at lower ranges of motion that is associated with symptoms should be addressed by correcting the UR.
The distribution of symptomatic individuals between the high and low UR groups was not statistically significant, as was previously reported. As a result, both high and low UR are associated with shoulder pain, while no shoulder pain occurs when UR is either high or low. Is scapular UR a clinically significant finding? It’s impossible to answer this question in the context of this study, but clinicians should be aware that scapular motion isn’t the sole cause of all dysfunction. Only about half of people with RC pathology see any improvement in their functional abilities, so practitioners should take their approach to rehabilitation and their exercise goals very seriously.
Referance
- JOSPT March 2019
