Functional assessment of inferior glenohumeral joint stiffness using ultrasonography

Subluxation of the affected shoulder in post-stroke patients has been associated with the nerve disorder and muscle fatigue. Clinicians must be able to accurately and reliably measure inferior glenohumeral subluxation of patients in order to provide appropriate treatment. However, the quantitative glenohumeral joint (GHJ) glide and stiffness evaluation methods are still under developing. The aim of this study is to develop a new inferior GHJ glide and stiffness evaluation protocol using ultrasonography under optimal testing conditions and to discuss the effect of GHJ glide and stiffness by using commercially available humerus brace and shoulder brace. In this study, a custom-made chair was used to fix the subjects and multistage inferior testing loads were applied. The glides between anterior-superior surface of humeral head and coracoid in different testing conditions were accessed in 7 healthy volunteers with ultrasonography. The stiffness of the GHJ was defined as the slop of the estimated linear regression line between glides and different testing loads. Testing conditions were defined by different test loading mechanisms (n = 2), shoulder constrain conditions (n = 2), and loading modes (n = 4). The optimal testing condition was defined as the testing condition with the minimal residual variance of measured glides to the calculated stiffness under different testing loads. To compare the effect of inferior GHJ glide and stiffness on using different braces, the paired t-test was utilized. There was no significant difference between the two test loading mechanisms (t = .218, p = .831) and the two shoulder constrain conditions (t = -.235, p = .818). The results concluded the ultrasonographic glides measurement using pulley set loading mechanism might be as well as using direct loading. In addition, constraining the unloading side soulder was proposed because of its lightly lower mean residual variance value. Moreover, bending elbow loading on upper arm posture was suggested because bending elbow loading on forearm may result of an overestimate of the inferior GHJ stiffness and drooping elbow posture would accompany pains at the loading point caused by friction between wide belt and skin. Furthermore, it was interested to note that subjects wearing humerus brace with raising structure had higher stiffness in GHJ than wearing shoulder brace with fixing structure under the proposed testing conditions. This study provides experimental evidences that shoulder brace may reduce the GHJ glide under external load. It is suggested that the appropriate testing condition is using a set of pulleys, constraining the unloading side shoulder, bending elbow and loading on upper arm for measuring the glides and stiffness between anterior-superior surface of humeral head and coracoid. The humeral brace with raising structure is proposed for post-stroke patients.