A novel radiation-free shoulder joint stiffness evaluation protocol using non-invasive ultrasonographic images

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 developed. The purpose of this study was to find an optimal testing condition to evaluate the inferior GHJ stiffness. A custom-made chair was used to position subjects stably and applying multistage inferior testing loads (0N, 30N, 60N, 90N and 120N), the glides between anterior-superior surface of humeral head and coracoid in different testing conditions were accessed in 7 healthy volunteers with ultrasonography. Eight testing conditions were defined by different test loading mechanisms (DL and IDL), shoulder constrain conditions (CS and NCS), and loading modes (DW, DUA, BUA and BFA). Reliability of measurements was tested between measurements in the same subjects under the same testing conditions with the interval of 24 h. The experiment results showed that the ICC value between measurements is 0.85. There were no statistically significant difference of measurements between DL and IDL (t = 0.218, p = 0.831) and between CS and NCS (t = -0.235, p = 0.818). There were statistically significant relationship of assessments between DW and DUA (r = 0.849, p = 0.016), between DW and BUA (r = 0.821, p = 0.023) and between DUA and BUA (r = 0.854, p = 0.015). It is suggested that the testing condition using a set of pulleys, constraining the unloaded shoulder, bending elbow and loading on upper arm might be the optimal testing condition for measuring the inferior GHJ stiffness. Under the optimal testing condition, the average inferior GHJ stiffness is 23.2N/mm.