Changes of histology and capsular collagen in a rat shoulder immobilization model

Shoulder immobilization can induce adhesion of the joint, capsular contracture or lead to the condition of frozen shoulder. However, little is known about the histological effects of immobilization on the shoulder joint. This study aimed to explore the effect of immobility on the subscapular bursa （SSB） and the joint capsular content, including the distribution of typesⅠ and Ⅲcollagen, within an immobilized rat shoulder. Methods Forty-six Sprague-Dawley rats were randomly divided into one control group （n=6） and four immobilization groups （n=10 in each group）, in which the left shoulders were immobilized with plaster for 1,2, 3 and 4 weeks. At the end of each time point, 2 rats from each group were euthanized and shoulders prepared for serial histological observations of the glenohumeral joints, as well as picrosirius red and immunohistochemical observation of type Ⅲcollagen. Histological sections of the remaining rat shoulders were used for the immunohistochemical detection of the capsular content of types Ⅰand Ⅲcollagen. Results The hyperplastic synovium of the anterior capsule obstructed the communication between the SSB and the glenohumeral joint cavity at 2 and 3 weeks. The adhesion of the SSB appeared at 3 and 4 weeks. The quantitative and qualitative results showed that the capsular contents of types Ⅰand Ⅲcollagen progressively increased at 2, 3 and 4 weeks, and that type Ⅲcollagen was distributed extensively within the joint capsule at 2 and 3 weeks. Conclusion Immobilization of the rat shoulder induced synovial hyperplasia of the joint capsule, adhesion of the SSB and an increase of the capsular content of types Ⅰ and Ⅲcollagen.

Subject-specific Finite Element Modelling of the Human Shoulder Complex Part 1:Model Construction and Quasi-static Abduction Simulation

Human shoulder joints exhibit stable but highly active characteristics due to a large amount of soft tissues.Finite Element(FE)modelling plays an important role in enhancing our understanding of the mechanism of shoulder disorders.However,the previous FE shoulder models largely neglected the Three-Dimensional(3D)volume of soft tissues and their sophisticated interactions with the skeletons.This study develops a 3D model of the rotator cuff and deltoid muscles and tendons.It also includes cartilage and,for the first time,main ligaments around the joint to provide a better computational representation of the delicate interaction of the soft tissues.This model has potential value for studying the force transfer mechanism and overall joint stability variation caused by 3D pathological changes of rotator cuff tendons.Motion analysis systems and Magnetic Resonance(MR)scans were used to collect shoulder movement and geometric data from a young healthy subject,respectively.Based on MR images,a FE model with detailed representations of the musculoskeletal components was constructed.A multi-body model and the measured motion data were utilised to estimate the loading and boundary conditions.Quasi-static FE analyses simulated four instants of the measured scapular abduction.Simultaneously determined glenohumeral motion,stress/strain distribution in soft tissues,contact area,and mean/peak contact pressure were found to increase monotonically from 0°to 30°of abduction.The results of muscle forces,bone-on-bone contact force,and superior-inferior movement of the humeral centre during motion were consistent with previous experimental and numerical results.It is concluded that the constructed FE shoulder model can accurately estimate the biomechanics in the investigated range of motion and may be further used for the comprehensive study of shoulder musculoskeletal disorders.