European Journal of Cardiovascular Medicine

Coracoacromial ligament (CAL) was described in early 1970s by Neer as a generator of pain. The CAL bridge the gap between flat acromion process of scapula and curved coracoid. It is triangular in shape with its apex being attached with area in front of the articular facet for clavicle on acromion process, and its broad base attached with lateral aspect of coracoid process.¹

Protection to the head of a humerus and Glenohumeral joint stability during abduction is provided by coracoacromial arch formed of this ligament along with flat acromion process and beaklike coracoid process of the scapula. The arch is superiorly related to the clavicle and under deltoid muscle surface, whereas, it is inferiorly related to supraspinatus fossa of scapula with sub acromial bursa interposed in between. The bursa helps in smooth movements between this arch formed of two scapular processes and glenohumeral joint and supraspinatus tendon.²

The osseoligamentous structure forms a stable protective arch that extends between acromion and coracoid processes of scapula. Utilizing this arch, humeral head is prevented from superior displacement from glenoid cavity of scapula. Coracoacromial arch is strong that superior thrust of the humerus will not fracture it. A triangular band is seen anterior to the joint which is formed between acromion and coracoid processes of scapula, the coracoacromial ligament spreads out and is present above the humeral head for increasing surface that provide support to humerus head. It is separated from muscle of rotator cuff by subacromial bursa.³ 

During shoulder joint abduction, a vital role is played by supra humeral articulation of the shoulder joint. The supra humeral articulation is comprised of acromion and coracoid processes of scapula and coracoacromial ligament joining the two. It protects humerus head during shoulder joint abduction with intervening of subacromial bursa to allow smooth movement in these bony components, The arch avoid upward dislocation of humerus head, however, under normal situations, a small space is seen between bony components of the articulation. Also, during normal abduction, upper humerus end will tend to impinge the arch at 90 degrees to abduction.⁴  

Sometimes, it is seen that CAL comprises of two strong marginal bands with thin center. Anatomic variants are usually seen following shape of this ligament. Sometimes, it is Y-shaped, rectangular, or quadrangular in shape. Different morphological shapes of CAL are described in literature. It has a vital role in shoulder impingement syndrome as ligament as ligament thickening can lead to shoulder arthropathy or impingement syndrome. Surgical CAL release with other ligaments of glenohumeral joint plays a vital role in relieving pain from this condition.⁵

The present study was aimed to study various types of coracoacromial ligaments in Indian cadavers and their role in shoulder joint biomechanics and surgical significance. The study cadavers were from the Department of Anatomy  at Mamata academy of medical sciences Hyderabad Telangana, The Oxford medical college hospital and research centre Bangalore Karnataka and Neelima institute of medical scinces Hyderabad Telangana . Permissions were taken from higher authorities and ethics committee of the institution before starting the dissection in the departments. 

The study assessed 80 cadavers that were finally included and were embalmed in 10% formalin and the dissection following guidelines and recommendations was done. The inclusion criteria for the cadavers in present study was intact shoulder joints and exclusion criteria for the study were disarticulated shoulder joint.

The final cadaver size in the present study was 80 cadavers that were used in undergraduate study. Dissection was done following the steps of Cunningham’s Manual of Practical Anatomy.⁶ On the shoulder joint, the skin was reflected and the deltoid muscle exposure was done. For further dissection of the shoulder joint in the cadaver, middle and anterior fibers of the deltoid muscle were reflected and cut.

The superior surface of the acromion and coracoid process were exposed. Margins of coracoacromial ligament were cleared and its shape and attachments were studied. All the variations in the shaped and varying morphological types of CAL were noted.

The data gathered were analyzed statistically using SPSS (Statistical Package for the Social Sciences) software version 24.0 (IBM Corp., Armonk. NY, USA) for assessment of descriptive measures, Student t-test, ANOVA (analysis of variance), and Chi-square test. The results were expressed as mean and standard deviation and frequency and percentages. The p-value of <0.05 was considered.

The present study assessed 160 dissected specimens from 80 cadavers comprising of 80 left and 80 right specimens. Coracoacromial ligament depicted varying morphological types and shapes following classification of Rothenberg et al.⁷ In triangular shape, the ligament has its base attached with coracoid process and the apex was attached to acromion process. This type of shape was seen in 35% subjects.

For trapezoid shape of the ligament, wide portion was attached with coracoid process and narrow portion was attached to the acromion process. Trapezoidal shape of ligament was seen in 10% of the study subjects. Rectangular shape of CAL was seen with both the attachments nearly equal in size. Rectangular CAL was seen in 32.5% of the limbs. Y-shaped ligament shape was seen depicting single attachment at the coracoid process, whereas, its attachment in acromion process was at two places depicting bifurcation responsible for Y shape. This type was seen in 12.5% of assessed limbs.

Bipartite type depicted CAL present as two separate bands. Majority of the times, the medial portion is broad and the lateral portion is narrow. Bipartite type was seen in 7.5% of the limbs. Tripartite depicted CAL as three separate bands where one was broad and others were narrow as strips. It was found in 2.5% of the limbs.

It was seen that for various shapes of coracoacromial ligament seen in study subjects, tripartite shape was see in 2 subjects each from right and left limbs, bipartite in 6 subjects each from right and left limbs, trapezoid in 8 subjects each from right and left limbs, Y-shaped in 10 subjects each from right and left limbs, rectangular in 26 subjects each from right and left limbs, and triangular in 28 subjects each from right and left limbs (Table 1).

Table 1: Various shapes of coracoacromial ligament seen in study subjects

In the present study, 160 dissected specimens were assessed in the study from 80 cadavers comprising of 80 left and 80 right specimens. Coracoacromial ligament depicted varying morphological types and shapes following classification of Rothenberg et al.⁷ In triangular shape, the ligament has its base attached with coracoid process and the apex was attached to acromion process. This type of shape was seen in 35% subjects. This was similar to the previous studies of Demir M et al⁸ in 2019 and Alraddadi A et al⁹ in 2017 where authors assessed subjects with characteristics of coracoacrmial ligament characteristics similar to the present study in their respective studies.

Concerning the trapezoid shape of the ligament, wide portion was attached with coracoid process and narrow portion was attached to the acromion process. Trapezoidal shape of ligament was seen in 10% of the study subjects. Rectangular shape of CAL was seen with both the attachments nearly equal in size. Rectangular CAL was seen in 32.5% of the limbs. Y-shaped ligament shape was seen depicting single attachment at the coracoid process, whereas, its attachment in acromion process was at two places depicting bifurcation responsible for Y shape. This type was seen in 12.5% of assessed limbs. These results were consistent with the studies of Fagelman M et al¹⁰ in 2007 and Wang YC et al¹¹ in 2009 where trapezoidal and rectangular CAL reported by the authors in their studies was comparable to the results of the present study.

It was seen that Bipartite type depicted CAL present as two separate bands. Majority of the times, the medial portion is broad and the lateral portion is narrow. Bipartite type was seen in 7.5% of the limbs. Tripartite depicted CAL as three separate bands where one was broad and others were narrow as strips. It was found in 2.5% of the limbs. These findings were in agreement with the results of Dietrich TJ et al¹² in 2016 and Yomamoto N et al¹³ in 2010 where bipartite and tripartite CAL shape comparable to the present study was also reported by the authors in their respective studies.

The study results showed that for various shapes of coracoacromial ligament seen in study subjects, tripartite shape was seen in 2 subjects each from right and left limbs, bipartite in 6 subjects each from right and left limbs, trapezoid in 8 subjects each from right and left limbs, Y-shaped in 10 subjects each from right and left limbs, rectangular in 26 subjects each from right and left limbs, and triangular in 28 subjects each from right and left limbs. These results were in line with the findings of Wu CH et al¹⁴ in 2010 and Wellmann M et al¹⁵ in 2008 where results concerning shape of the present study similar to the present study was also reported by the authors in their studies.

The present study, considering its limitations concludes that advancements in understanding of coracoacromial ligament via research outcomes can help in contributing to higher intraoperative decision making for the surgeons performing arthroscopic surgeries. However, further studies with a greater number of limbs and in different geographical background are needed to reach a definitive conclusion.

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