Assessing inferior glanohumeral stiffness: A quantified and non-invasive ultrasonographic method

The aim of this study was to develop a new real-time inferior glanohumeral joint (GHJ) glide and stiffness evaluation protocol using non-invasive, radiation-free ultrasonography. Besides, to compare GHJ glide and stiffness between different testing conditions, and to discuss the effect of GHJ glide and stiffness on using commercial available humerus brace and shoulder brace. In this study, using a custom-chair to fix the subject stably and apply multistage inferior forces. Commercial ultrasonographic device were utilized to assess the displacement of inferior GHJ glide and stiffness. To determine the optimum testing conditions of the measurement, the glides between anterior-superior surface of humeral head and coracoid in different testing conditions were evaluated. To compare the effect of inferior GHJ glide and stiffness on using different braces, the t-test was utilized. Intraclass correlation coefficients were high for intra-test measurement (ICC = 0.85). The optimal testing conditions for GHJ glide and stiffness measurement are loading on bending elbow upper arm, indirect loading by pulley set and applying constrain on unloading side shoulder. Under the optimal testing condition, the average glide between anterior-superior surface of humeral head and coracoid is proportional to external force, the inferior GHJ stiffness is 23.2 N/mm.. It is interested to note that wearing "Humerus brace" (brace A) will provide higher stiffness in GHJ than wearing "Shoulder brace" (brace B) under the proposed testing conditions. This study provides experimental evidences that shoulder brace A may reduce the shoulder subluxation under external loads.