The Relationship Between The Corachohumeral Ligament's Thickness And Primary Frozen Shoulder

Background and ObjectivePrimary Frozen Shoulder (PFS) is a chronic disease, which usually perplexes the middle-aged people, the incidence rate is 2%-5% .The course of this disease is so long that it makes the patients suffering in work and family life .The diagnostic criteria of imageology vary greatly, which lead to numerous difficulties in treatment. Recently, many researches have showed that the rotator interval (RI), including the coracohumeral ligament (CHL), played an important role in the development of the PFS.CHL is a special structure of the shoulder; the anatomic features are still controversial. Many authors thought that it arised from the lateral aspect of the coracoid process (CP), but the insertions are various, such as the humerus at the greater and lesser tuberosities, the superspinatus tendon, subscapularis tendon, rotator interval et al. The histological source of the CHL is in dispute too, many researches have showed that the CHL was capsular thickening and a ligament biomechanically. However, others thought it was a distinct ligament.Recent studies have showed that the CHL in PFS thickened on magnetic resonance arthrography (MRA) (4.1mm) and ultrasound (3mm) examination. However, some authors emphasized that the CHL's thickness is normal on Magnetic Resonance Image (MRI) and ultrasound exmination. Based on the researches above, the anatomic features and the imageology appearance of the CHL remain poorly defined.The present study will start from the anatomic features of the CHL, then set up a method of scanning the CHL on MRI, and finally, discuss the relationship between the thickness of CHL and PFS in order to provide the theoretical evidence for the diagnosis and treatment of the PFS.Materials and methods1. Firstly,26 shoulders were dissected, and then observe the position and morphology of the CHL and their relationship with the Superior Glenohumeral Ligament ( SGHL).In 20 shoulders, the following parameters were measured respectively: the full length of CHL, The length from the top of CP to the anterior border of the origin of CHL, the length from the extremity of CP to the posterior border of the origin of CHL, the base width of CHL, the width, where it confluences with the joint capsule, the base thickness, and the thickness where it confluences with the joint capsule, And in 3 shoulders, determine the CHL's histologic features in comparison with the joint capsule and coracoacromial ligament (CAL).2. Both shoulders of eight normal adults'were scanned by MRI with three different locating methods on axial plane: parallel to the underlayer of glenohumeral joint space; parallel to the upperlayer of glenohumeral joint space; perpendicular to the long axis of the supraspinatus tendon. Scanning sequence and parameter are identical in the three methods, observing the CHL's morphology features. One fresh normal cadaveric shoulder was scanned by MRI with five methods: the coronal oblique (CO) parallel the CHL which can be observed on axial view; the sagittal oblique (SO) plane perpendicular to the CHL which can be observed on axial view; the plane parallel the base of the CP; the SO plane parallel the underlayer of the glenohumeral joint space; the plane perpendicular to the CHL which can be observed on SO plane. And, measuring and comparing the thickness of the CHL on MRI and fresh cadaveric shoulder.3. Both shoulders of 10 patients with PFS in one side and both shoulders of 10 healthy adults were scanned by MRI. The thickest portion of the CHL was measured on SO image and analyzed with the paired t-test between the affected side and the unaffected side of the patients with PFS, and between the left side and the right side of the healthy adults.Results1. The CHLs were all located at the RI, with an irregular trapezoidal structure. Above and below the CHLs were the subacromial bursa and the subcoracoid bursa, respectively. The CHLs all originated from the lateral aspect of the base of the CP, whereas in 11 shoulders, the CHLs inserted into the RI. In 11 other shoulders, the CHLs inserted into the supraspinatus tendon. The CHLs in 3 shoulders, however, were split and inserted into both the supraspinatus and subscapularis tendons, respectively. Finally, the CHL in 1 shoulder only inserted into the subscapularis tendon. In addition, in 4 normal cadavers, the pectoralis minor tendon was found to pass over the CP and insert into the CHL. Eleven shoulders had a complex of the CHL and the SGHL. The full length was 35.7±6.0 mm (26.2~48.1 mm), and the length from the top of the CP to the anterior border of the origin of CHL 12.0±4.4 mm (4.0~19.2 mm), the length from the extremity of the CP to the posterior border of the origin of CHL 17.5±4.0mm (6.0~21.1 mm),the base width 21.0±3.5mm (15.1~29.0 mm), the width, where it confluences with the joint capsule 15.8±2.4 mm (12.1~20.1 mm), the base thickness 2.15±0.70 mm (1.18~3.60 mm), the thickness, where it confluences with the joint capsule 1.83±0.69 mm (1.02~3.46 mm), respectively. Histologically, the CHL was found to be similar to the joint capsule without any ligament features.2. The CHL can be observed with three different locating methods, there are no difference in morphology among these methods, and no difference between the left and right side of the same shoulder. 6 shoulders are trapezoidal structure, 10 shoulders are paralleled structure .The thickness of CHL on the coronal oblique (CO) plane parallel this ligament which can be observed on axial view is 3.5mm;The thickness on the SO plane perpendicular to this ligament which can be observed on axial view is 2.6mm; The thickness on the plane parallel the base of the CP is 3.0mm; The thickness on the SO plane parallel the underlayer of the glenohumeral joint space is 3.7mm;The thickness on the plane perpendicular to the CHL which can be observed on SO plane is 3.0mm; The thickness on fresh cadaveric shoulder is 3.38mm.3. There was no significant difference in the thickness of the CHL between the affected side and the unaffected side (respectively3.0±1.16 mm, 2.8±1.36 mm, the paired t-test p>0.05). There was also no significant difference in the thickness of the CHL between the left and the right side (respectively 2.8±1.33 mm,2.8±1.35mm, the paired t-test p>0.05).Conclusions1. The position, morphology, and origin of the CHL did not change much, but its insertion varied greatly. The CHLs gradually become narrow and thin from its origin to insertion. The anatomical datum of CHL are greatly variable among different specimens, which implies that it is not helpful for the diagnosis and treatment of frozen shoulder, depending on the anatomical datum of different specimens. Histologically, the CHL had the histologic feature of a capsule, not a ligament.2. The thickness on the CO plane parallel the CHL which can be observed on axial view and the SO plane parallel the underlayer of the glenohumeral joint space is mostly near to the data on specimen.3. There was no association between the thickness of CHL and PFS, and the thickness of the CHL can not be considered as the most characteristic MR finding in primary frozen shoulder.