People with hypermobile Ehlers-Danlos syndrome (hEDS) have larger spaces in the shoulder joint than those without the condition, and this anatomical difference may help to explain their shoulder pain, a study has found.
The findings may also have implications for designing exercise programs for people with hEDS.
The study was published in the Journal of Shoulder and Elbow Surgery, and is titled “Subacromial space outlet in female patients with multidirectional instability based on hypermobile Ehlers-Danlos syndrome and hypermobility spectrum disorder measured by ultrasound.”
hEDS, the most common type of EDS, is characterized by joints that are able to move more than normal and are frequently dislocated. The shoulder is commonly affected in hEDS — an estimated 85% of patients experience shoulder pain, and more than half report shoulder dislocations. The reasons for this, however, aren’t fully understood.
To gain more insight into the shoulder structure of people with hEDS, researchers examined the shoulder joint through ultrasound.
The team was particularly interested in two measurements: the thickness of the supraspinatus tendon (SST), which is the main tendon in the shoulder that helps connect the arm to the chest; and the distance — called acromiohumeral distance (AHD) — between the humerus (the bone in the upper arm) and the acromion (the outer edge of the shoulder).
The researchers measured these parameters in 14 people with hEDS, as well as in 15 people with hypermobility spectrum disorder (HSD), which the researchers described as being clinically similar to hEDS but without fulfilling all of the criteria necessary for an hEDS diagnosis. The two conditions were combined for analysis.
For reference, the researchers also took measurements from 20 healthy people (without hEDS or HSD). The average age was 34 years for hEDS/HSD patients, and 33 years for the controls. All participants were female (hEDS primarily affects females).
Ultrasound results showed that SST thickness in people with hEDS/HSD was not significantly different from unaffected individuals: 5.05 mm in patients, and 5.38 mm in healthy controls.
There were, however, some differences in AHD, with precise values varying depending on the angle of the arm during measurements, but none of these reached statistical significance.
The ratio between SST thickness and AHD — termed the occupation ratio (OcAHD) — was found to be significantly smaller in people with hEDS/HSD when their arms were elevated (mean of 58.94 in the hEDS/HSD group versus 73.72 in healthy controls at 45 degrees of arm elevation; and 57.48 versus 69.77 at 60 degrees of elevation).
“A higher OcAHD means that the SST takes more of the space between the humeral head and the acromion,” the researchers wrote. In other words, people with hEDS/HSD had lower OcAHD values, meaning “a larger available subacromial space outlet compared with healthy individuals.”
Such “free space” in the shoulders was particularly detected when a patient’s arm was elevated than when it was in a resting position.
The researchers speculated that this free space in hEDS/HSD patients may give the bones in the joint more freedom to move in ways that the shoulder is less equipped to handle, ultimately resulting in pain.
Additionally, the team emphasized that this finding could have implications for designing exercise regimes for people with hEDS or HSD. They mentioned that, for instance, using dumbbells or exercises with arm elevations may increase the risk of shoulder dislocation in these individuals.
“The present findings should be taken into account when designing rehabilitation exercise programs for patients with shoulder instability,” the team wrote.