Objective To establish a finite element model of rotator cuff which can be used to simulate the rotator cuff injury and to evaluate the biomechanical effects of rotator cuff surgery.Methods The Dicom CT images of the right shoulder of a Chinese healthy volunteer were used to establish models of the scapula,humerus and clavicle.The rotator cuff structures were separated and modeled based on the MRI images and anatomical knowledge.After the rotator cuff model was introduced into the finite element analysis software Abaqus 6.12,the anatomical positions were simulated when the shoulder was at 30° internal rotation,30° external rotation,30° abduction,30° adduction,30° flexion and 30° extension.Results When the shoulder was in 30° flexion,the average stress was 52.2 kPa on the supraspinatus,223.0 kPa on the inffaspinatus and the teres minor,and 90.4 kPa on the subscapularis.When the shoulder was in 30° extension,the average stress was 105.0 kPa on the supraspinatus,78.2 kPa on the infraspinatus and the teres minor,and 55.7 kPa on the subscapularis,indicating that the muscle and tendon of the supraspinatus was subjected to greater stress and the humerus and the scapula produced less stress compared with the shoulder in 30° flexion.Conclusion Since our finite element model of the rotator cuff can simulate common activities of the shoulder joint and obtain stress values of the corresponding rotator cuff muscles,it can be used in simulation of rotator cuff injury and its surgery.

Objective To study the effects of exercise after myocardial infarction on the survival rate and the dynamic functioning of the left ventricle ( LV) . Methods Ninety-six male Sprague-Dawley rats were randomly assigned to a sedentary sham operation group ( Sed-Sh) , a previous exercise and sham operation group ( PreE-Sh) , a sedentary myocardial infarction ( MI) group ( Sed-MI) , a previous exercise MI group ( PreE-MI) , a post exercise MI group (PostE-MI) and a combined exercise MI group (ComE-MI), each of 16.All of the rats underwent either MI in-duction or a sham MI operation, the PreE groups after exercising for 5 weeks on a treadmill. The Sed groups did not exercise. The Post E-MI group did not exercise before the operation, but performed treadmill exercises for 4 weeks be-ginning 8 weeks after the operation. The ComE-MI group exercised for 5 weeks before and 4 weeks after the operation. All the exercising rats ran on the treadmill for 60 minutes daily, 5 d/wk. Life situation and spontaneous mortality were recorded, and echocardiographic measurements were performed on the4thday and 2, 4, 8 and 12weeks after the oper-ation. All of the rats were sacrificed at the end of the experiment. Results Compared with the Sed-Sh group, the Sed-MI group had significantly larger average LV dimensions at the end of both the diastol ( LVEDd) and the systol (LVEDs, but it had lower average fractional shortening (FS) and a smaller average ejection fraction(EF) at all of the different measuring times. The PreE-MI group had significantly lower average LVEDd and LVEDs, but a signifi-cantly higher FS and EF than the Sed-MI group on the 4th day. However, 2 weeks after the intervention the difference in LVEDd between the two groups was no longer significant. Significantly higher FS and EF were observed in the PostE-MI group at 12 weeks compared to the Sed-MI group. The ComE-MI group had significantly lower average LVEDd and LVEDs, but significantly higher FS and EF at all the time points than the Sed-MI group. The ComE-MI group had a significantly lower average LVEDs but a higher average FS and EF than the PreE-MI group at 12 weeks after the intervention. Conclusion Pre-MI exercise improves LV function significantly at the early stage, though the difference is temporary. Post-MI exercise improves LV function in the longer term. Combined exercise improves LV function the most effectively.