We obtained the novel findings that the rotator interval and the joint capsules in the symptomatic group with night pain of the frozen shoulder joint significantly thickened in comparison with those in the asymptomatic group and in the normal group with MRI PETRA imaging which made it possible to visualize joint capsules as high signal images.
Using ultra-short echo time (TE), Pointwise encoding time reduction with radial acquisition (PETRA) has the potential to visualize ligaments, tendons, and joint capsules which have a very short T2*, as high signal images while conventional MR imaging visualizes them only as low signal images. The purpose of this study is to evaluate the difference of the thickness of the rotator interval and the joint capsules in the axillary pouch, depending on the stage or the symptom of patients with frozen shoulder, which conventionally have been visible with the contrast of surrounding tissues.
Materials And Methods
Subjects consisted 21 healthy volunteers and 25 patients with frozen shoulder. We defined frozen shoulder as follows: range of motion< 100° in forward flexion, <20° in external rotation, and <L5 in internal rotation. These patients were divided into two groups. 16 patients with night pain were classified to symptomatic group and 9 patients without night pain were classified to asymptomatic group. The thickness of the rotator interval and the joint capsule in the axillary pouch were measured. A 3T MRI scanner (MAGNETOM Skyra VD13A; Siemens Healthcare) was used to all MR studies. For PETRA imaging, parameters were as follows: TR 4.0 ms, TE 0.1 ms, TI 500 ms, FA 6 deg, base resolution 288, radial views 30000, voxel size 1 x 1 x 1 mm. The thickness of the joint capsule in the axillary pouch was measured with ZIOSTATION2 (Ver2.4). Two observers measured the thickness and Pearson's correlation coefficient was calculated.
Patients in the symptomatic group had a significantly thickened joint capsule in the axillary pouch (2.2 mm vs 1.8 mm in the asymptomatic group; p<0.05 for both comparisons, Wilcoxon signed-rank test) and a thickened joint capsule in the rotator interval (1.8 mm vs 1.6 mm in the asymptomatic group, 1.4mm in the normal shoulder group; p<0.05 for 3 groups comparisons, Steel-Dwass test).
It is said that the symptomatic frozen shoulder patients with night pain is caused by the inflammation of the synovial membrane inside the joint capsules. With conventional MR imaging, it has been difficult to visualize the joint capsules because of their rapid T2* decay. However, with PETRA imaging, it is possible to visualize ligaments and tendons as high signal images because its echo time (TE) is 0.1ms, which is very short. We obtained the novel findings that the rotator interval and the joint capsules in the symptomatic group significantly were thickened in comparison with those in the asymptomatic group and in the normal group with PETRA imaging. In this study, we proved the potential of PETRA imaging to visualize capsules and ligaments which used to be difficult to be visualized without arthrography. Since these results was related to the symptom of the patients, it was indicated that using PETRA imaging can be the useful method for the stage classification of the patients who are suffered from shoulder diseases.