Exploration of the clinical course of frozen shoulder: A longitudinal multicenter prospective study of functional impairments.

Background: Contradictory evidence exists regarding the clinical course of frozen shoulder (FS).

Objectives: To explore the clinical course of FS regarding disabilities, pain, range of motion (ROM), muscle strength, scapular upward rotation, and proprioception and to establish longitudinal correlations between these variables.

Methods: Patients with FS were prospectively followed for 9 months at 3-month intervals. Assessment included the Disabilities of the Arm, Shoulder and Hand questionnaire; visual analogue scale for pain; an inclinometer for shoulder external rotation (ER), internal rotation (IR), flexion, and abduction ROM, and scapular upward rotation and proprioception, as well as handheld dynamometry for muscle strength in shoulder abduction, ER, and IR.

Results: Initially, 149 patients (98 females; mean (SD) age 53 (9) years) were included, with 88 completing all follow-up assessments. Most variables showed early improvement in the clinical course of FS, particularly ER and IR at 90° abduction, which continued to improve from 6 to 9 months of follow-up. Associations were observed between disabilities and pain (r = 0.61), disabilities/pain and ROM (r=-0.62 to -0.59 and r=-0.47 to -0.39, respectively), disabilities/pain and muscle strength (r=-0.24 to -0.35 and r=-0.36 to -0.17, respectively), and between disabilities/pain and scapular upward rotation below shoulder level (r = 0.23 to 0.38 and r = 0.24 to 0.30, respectively). ROM correlated with muscle strength (r = 0.14 to 0.44), while both ROM and ER muscle strength correlated with scapular upward rotation below shoulder level (r=-0.37 to -0.23 and r=-0.17 to -0.12, respectively). Muscle strength correlated with scapular upward rotation above shoulder level (r = 0.28 to 0.38) and lift-off muscle strength correlated with joint repositioning (r=-0.17 to -0.15).

Conclusion: Almost all factors improved in the early phase (3-6 months) after baseline assessment, while ER and IR ROM at shoulder level continued to improve long term.