A Strain Study Of The Anterior Ligamentous Complex Of The Shoulder In The Abduction And External Rotation

BackgroundPitcher’s shoulder is an injury caused by the throwing movtion,which is a all-around exercise.The arthrodynia usually is the first symptom[1].Because of the large range of shoulder movement and complex anatomy,the surrounding muscles,ligaments,joint capsule and so on may being demaged in different level,otherwise,because of the low stability of the anterior shoulder,these important structures,including the upper complex[2,3]and the inferior glenohumeral ligamentous complex[4],will be demaged much easier than ohter structures.After the primary injury of the structure,the kinematics of the shoulder will be changed,and insecondary injuries of other structures will appear next,which can eventually develop into joint instability and easily form joint dislocation.The purpose of this study is to investigate the strain of the anterior shoulder ligamentous complex in the abduction and external rotation,analysis the stress of different structure of the ligamentous complex during the kinestate.And further construct the model,which include excise the coracohumeral ligament,excise the glenohumeral ligament and excise both two ligament at the same time,to observe the strain after different structure damage,it will help us to understand the limiting effects of different structure of the shoulder joint in abduction and external rotation,to provide a scientific training basis for sports medicinethe and basis for clinical repair of dislocation of shoulder joint injury.Materials and methods10 fresh adult upper limb specimens were dissected,the muscles around the shoulder joint were removed,including the rotator cuff,and the anterior ligamentous complex was fully exposed.The samples were divided into four groups:N,A,B and C.Which are the normal group,Coracohumeral Ligament excision group,Interior Glenohumeral Ligament-Posterior Bunch excision group and Coracohumeral Ligament+Interior Glenohumeral Ligament-Posterior Bunch excision group.The shoulder joint was loaded by the motorman to simulate the abduction and external rotation,and the full field strain of anterior ligamentous complex was collected by Digital Image Correlation.The variation regularity and trend of strain,the distribution of strain region were observed and recorded.Finally,the specimens were scanned by CT.The important anatomic parameters of the humeral head were measured on the software,to investigate the relationship between the anatomic parameters of the humeral head and the stress of the ligamentous complex.ResultsThe intact group showed that the trend of mean major strain of the anterior ligamentous complex increased with the increase of the external rotation angle.The mean major strain in abduction 60 degree group(13.56+5.33)is smaller than other groups(neutral position:21.63+7.86,30 degree abduction:21+6.78,90 degree abduction:21.10+10.17).The strain distribution of the anterior ligamentous complex observation and analysis of results obtained with anterior shoulder ligament strain distribution of body surface is not equality,but according to the anatomical characteristics,high strain areas are mainly concentrated in the glenohumeral ligament region,especially the region near the scapula(average:29.41+4.65,30 abduction of 30 degree:32.23+7.71,abduction of 60 degrees:20.77+3.71,abduction of 90 degrees:24.89+5.34)more.The comparison between group A and group N showed that the coracohumeral humeral ligament played an important role in the stability of external rotation in neutral position and abduction of 30 degrees,while the comparison between group B and group N showed that the glenohumeral inferior ligament played an important role in shoulder stabilizing joint abduction angle.The results of group C showed that the external rotation stability of the shoulder joint at all angles was affected by the simultaneous damage of the coracohumeral ligament and the glenohumeral ligament.There is no correlation between the anatomical parameters of the humeral head and the strain of the ligamentous complex.Conclusionabduction of 60 degrees of the shoulder joint is more conducive to trauma and postoperative rehabilitation than other positions.In excessive abduction and external rotation of the shoulder,the interior-glenohumeral ligament is more likely to be damaged,especially the region that near the scapula,which is coincide with the Bankart damage in clinic.In the neutral position and abduction of 30 degrees,the coracohumeral ligament contributes great influence on the strain of the anterior ligamentous complex,while the inferior glenohumeral ligament has a significant effect on the anterior ligamentous complex strain in all abduction angles.The experimental results of this paper suggest that there isn’t more relationship between the shape of the humeral head and the strain of the anterior ligamentous complex,but the requirement of the measurement consider thay it is not valid,only as a preliminary discussion,still need further study.