The glenohumeral joint (GHJ) capsule and surrounding bursae are important for the control of intra-joint fluid volume and pressure. The relationship between GHJ capsule and bursae was still unclear. The purpose of this study was to examine the kinematics (volume, morphology) of GHJ capsule and subscapular bursa (SSB) during shoulder internal and external rotation (IR, ER) by three dimensional computed tomography (3D-CT) reconstruction images after arthrograms. 6 patients with rotator cuff tear were enrolled in this study. All patients had CT (2-positions : IR, ER) examination after arthrograms. Reconstruction of 3D computer models for contrast medium, GHJ capsule, SSB and subacromial bursa (SAB) from the CT image in the 2 positions was done using a custom-made software program (Mimics, Materialise Inc, Ann Arbor, MI). By measuring the volume of each model, (GHJ capsule, SSB and SAB etc.) the morphology and volume between 2 positions were compared by paired T-test. The volume of SSB decreased at the ER position of shoulder. The volume of the GHJ capsule was maintained during the shoulder rotation. The capusle at the posterior region was stretched at the IR position, and shrunk at the ER position. On the external rotation of the rotator cuff tear shoulders, the subscapularis stretched and the volume of SSB was decreased. Then, SSB fluid leaked out to the GHJ through the Weitbrecht hole, and secondary the fluid in GHJ leaked out to the SAB through the rotator cuff tear site. The morphology and kinematics of capsule and bursae in rotator cuff tear were evaluated by 3DCT images. The subscapularis kinematics was related to the change of SSB volume.
