## 4 Discussion  
Our major findings showed that the posterior glide and inferior glide joint mobilization (80 N, 5 Hz, 30 min for each treatment course, three times a week for eight continuous weeks) applied by the joint mobilization apparatus plus regular therapy, improved shoulder flexion ROM 36%, abduction ROM 51%, internal rotation ROM 81%, external rotation ROM 88%, and decreased visual analogue scale (VAS) pain scores 62% for the patients with frozen shoulder (FS). Furthermore, the shoulder flexion, abduction, internal rotation, and external rotation of the patients who received the joint mobilization apparatus plus regular therapy was 11%, 25%, 41%, and 24% higher than that of patients who received regular therapy only. No complaints and no side effects were found during the usage of the joint mobilization apparatus and after the treatment. In this study, the mobilization directions used in the joint mobilization apparatus are posterior glide and inferior glide. According to the principle of the joint mobilization and concave-convex rule, the shoulder joint inferior glide can improve shoulder abduction and the posterior glide can improve shoulder flexion and internal rotation [24, 25]. Previous studies had tried to add manual inferior glide shoulder joint mobilization to help patients with FS to increase the shoulder ROM in abduction [15, 29]. [PERSON] et al. found that patients with FS who received manual shoulder joint mobilization combined with stretching were better physically, rather than stretching alone in the evaluation of shoulder abduction. This study showed that the shoulder abduction in patients with FS who received four directions (inferior, posterior, anterior, distraction) manual shoulder joint mobilization (every direction 1-2 min, repeated 3-4 times, three times a week for six continuous weeks) combined with stretching were 10% higher than those in patients with FS who received stretching only after treatment [15]. [PERSON] et al. confirmed that the manual shoulder joint mobilization technique when combined with exercise had the efficacy to improve shoulder abduction in patients with FS. This study showed that, when combined with exercise, the shoulder abduction in patients with FS who received two directions (inferior, anterior) of manual shoulder joint mobilization (every direction 30 sec, repeated five sets, three times per week for four continuous week) was 10% higher than those of patients who received exercise only after treatment [29]. Comparatively, in our study, the shoulder abduction in patients with FS who received the posterior glide and inferior glide joint mobilization (30 min each treatment course, three times a week) applied by the joint mobilization apparatus plus regular therapy for eight weeks was 25% higher than those of patients who received regular physical therapy. Furthermore, some previous studies had tried to add manual posterior glide shoulder joint mobilization to help patients with FS increase the shoulder flexion or internal rotation ROM [30, 31, 32, 33]. [PERSON] et al. reported that high-grade and low-grade manual mobilization techniques using four directions (posterior, inferior, anterior, lateral) for 12 weeks (30 min each treatment course, two times per week) are both effective to improve shoulder flexion. This study showed that the patients with FS in the high-grade mobilization group and the low-grade mobilization group improved their mean shoulder flexion 27.6\({}^{\circ}\) and 24.9\({}^{\circ}\) after treatment [30]. [PERSON] et al. found that the posterior glide of the Kaltenborn and Maitland manual shoulder mobilization techniques were able to effectively improve the shoulder internal rotation about 17% and 16% (10 min each treatment course, three times per week for four weeks) in patients with FS after the treatment [31].