Introduction

The geometric anatomy of the scapula is of fundamental importance in the pathomechanics of rotator cuff disease, total shoulder arthroplasty and recurrent shoulder dislocation1. The mechanical impingement on the rotator cuff by the overlying acromial arch and the possibility of rotator cuff impingement by its anteromedial part i.e. the coracoid process was postulated as early as 19092. The coracoacromial anatomy includes the acromion, the coracoacromial ligament, and the tip of the coracoid process3. It is the variation in the height and length of the coracoid process which is responsible for altered size and shape of the space between the coracoacromial arch and the rotator cuff4. It has also been suggested that the problem is functional with anterior instability leading to a narrowing of the coracohumeral distance5.

The subcoracoid space is occupied in vivo by several soft tissue structures, such as the articular capsule of the gleno-humeral joint, the subscapularis tendon and the subacromial bursa. The thickness of these tissues may vary but variations are small and do not affect the width of the subcoracoid space unless there is local pathology. The shape and size of this space depends on its limiting skeletal structures2,6. Therefore, anatomical morphometric studies of these structures may provide information as to the aetiology of the subcoracoid impingement syndrome.

The coracoid process also forms an important part of the scapular glenoid construct and is involved in many surgical procedures on the glenohumeral joint7. Its detailed morphometry is useful in surgical procedures such as hardware fixation, drill hole placement and prosthetic positioning8. Congenital variations and minimal traumatic/iatrogenic changes in this orientation can predispose to subcoracoid dislocation7. 

Materials and Methods

The material for the present study comprised of 100 adult scapulae of unknown sex and age, obtained from the department of Anatomy, Government Medical College, Amritsar, Punjab, India. These were labelled from 1-100 with suffix R (right) or L (left). Of the 100 bones, 50 were of the right side and 50 were of the left side. All the bones were free from any physical deformity or abrasion and were complete in all respects. The following parameters were measured on the coracoid process:

          a) Maximum length: It was measured with the help of vernier calipers from most anterolateral to most posteromedial extension of the coracoid process9 (AB in Fig.1).

          b) Maximum breadth: It was measured with the help of vernier calipers as the maximum width from lateral border to the medial border of the corocoid process10 (CD in Fig.1).

          c) Height of the coracoid process: It was measured with vernier calipers as the distance between supraglenoid tubercle to the top of the ascending portion of the coracoid process along the glenoid axis11 (AB in Fig.2).

          d) Thickness: It was measured with the vernier calipers in the superoinferior direction 1 cm posterior to the tip of the coracoid7.

          e) Coracoglenoid distance (termed as Co-gle by Gallino et al12): It was measured with the vernier calipers as the distance between the tip of the coracoid process to the medial anterior point of the circumference of the glenoid cavity12 (AB in Fig.3).

          f) Height from supraglenoid tubercle to:

                    i) Under surface of coracoid process: It was measured with the vernier calipers as the distance between upper part of supraglenoid tubercle to the mid point of undersurface of the coracoid process (AC in Fig.2).

                    ii) Superior surface of coracoid process: It was measured with the vernier calipers as the distance between upper part of supraglenoid tubercle to the midpoint of superior surface of the coracoid process (AD in Fig.2). 

Figure 1

AB : Maximum length of the coracoid process CD : Maximum breadth of the coracoid process

Figure 2

AB : Height of the coracoid process AC: Height of supraglenoid tubercle to under surface of the coracoid process AD: Height of supraglenoid tubercle to superior surface of the coracoid process

Figure 3

AB : Coracoglenoid Distance

Results

Table 1 depicts the mean value and range of different parameters as observed in the present study and compares the same with the earlier studies.

Table 1

Showing Comparisons Of Different Parameters Of Coracoid Process

Discussion

A true coracoid process is present only in humans and in the non-human primates as a result of the adaptation of moving the upper limbs in a wide range of usually anterior motion. The coracoid process is usually absent in most quadrupeds, reduced to a simple thickening of the supraglenoid tubercle. A representation of the coracoid as an uncinate process is present in most rabbits and rodents, which maintain a certain degree of upper limb mobility in the forward position and in powerful gripping. In all these animals the origin of the short head of the biceps is missing15. From this perspective the coracoid assumes a biomechanical function of a shelf-structure, which is one arm of the lever through which the muscular action of the coracobrachialis, biceps and pectoralis minor muscles exerts a force on the glenoid. Numerous paths of open surgical or arthroscopic access to the shoulder refer to the coracoid16  which has been aptly defined by Matsen et al17 as “the lighthouse of the shoulder”. It has been observed that the position of the apex of the coracoid process varies from one individual to another18.

1. Maximum length of the coracoid process

The mean length of the coracoid process was observed to be 40.43 mm (Range = 29.80-51.07 mm). On the right side, it was 40.70 mm (Range = 29.80-51.03 mm) whereas on the left side, it was 40.16 mm (Range = 31.52-51.07 mm). Thus, the values for the right side were slightly more than the left side.

Earlier Gallino et al12, Von Schroeder et al8, Piyawinijwong et al10 and Coskun et al14 have measured this parameter (see Table 1). It is evident that our results are close to those of Gallino et al12.

Clinical Implication: While Codman19 expressed doubt about existence of idiopathic subcoracoid impingement syndrome, Gerber et al20  blamed a long coracoid process for the same. It was further supported by Dines et al21  who treated all seven patients of coracoid impingement by surgical excision of the coracoid tip.

2. Maximum breadth of the coracoid process

The mean breadth of the coracoid process was found to be 13.77 mm (Range = 9.60-18.04 mm). On the right side, it was 13.68 mm (Range = 9.60-18.04 mm) whereas on the left side, it was 13.87 mm (Rang e= 9.98-17.73 mm). On comparing the two sides, it was seen that there was slight difference between the values of both the sides with slightly higher value for the left side.

Piyawinijwong et al10 had also measured this parameter before and found the value to be 13.5 mm (Range = 10.8-18.1 mm) which is almost similar to the one found in the present study.

3. Height of the coracoid process

The mean height of the coracoid process was 15.62 mm (Rang e= 6.0-24.0 mm). On the right side, it was 15.71 mm (Range = 6.0-24.0 mm) whereas on the left side, it was 15.53 mm (Range = 10.0-20.0 mm). Thus, it was seen that there was slight difference between the values of both the sides with slightly higher value for the right side.

Earlier Cho and Kang11, Piyawinijwong et al10 and Coskun et al14 had measured this parameter. It is evident from table 1 that our results are near to those of Coskun et al14.

4. Thickness of the coracoid process

The mean thickness of the coracoid process was 7.83 mm (Range = 5.61-10.79 mm). On the right side, it was 7.80 mm (Range = 5.61-10.79 mm) whereas on the left side, it was 7.85 mm (Range = 5.64-10.21 mm). Thus, it was slightly higher on the left side.

Table 1 compares the studies already undertaken by Gumina et al13, Von Schroeder et al8 and Piyawinijwong et al10. Our results were in consonance with those of Gumina et al13.

5. Coracoglenoid distance

The mean value for coracoglenoid distance was 27.05 mm (Range = 18.84-33.98 mm). On the right side, it was 27.53 mm (Range = 18.84-33.37 mm) whereas on the left side, it was 26.56 mm (Range = 21.13-33.98 mm). Thus, it was higher on the right side than the left side.

Table 1 compares our study with those performed earlier. While Gumina et al13 and Piyawinijwong et al10 found it to be 16.23 mm and 14.8mm, Von Schroeder et al8 found it to be 50.7 mm. Such a wide variation in the value of this parameter in these two studies is unexplainable. However, our values fall in between these two studies (vide supra).

Gallino et al12 reported that surgical techniques that recommend transporting the coracoid to the anterior rim of the glenoid fossa to stabilize the glenohumeral joint in recurrent dislocation22,23  are successful. Because the distance from the apex of the coracoid and the mid-anterior point of the glenoid rim is on average 2.10 cm with a minimum of 1.09 cm in the smallest scapula. In such interventions the point of application of the force of the coracobrachialis and biceps muscles would be significantly nearer to the geometric center of the joint and would thus create more stability. However, the mean value of this distance in the present study was found to be on a higher side as compared to theirs. Also the minimum distance on smallest scapula was larger than that.

6. Height from supraglenoid tubercle to

         i. Undersurface of the coracoid process:

The mean height from the supraglenoid tubercle to theundersurface of the coracoid  process was found to be 15.18 mm (Range = 9.23-22.53 mm). On the right side, it was 14.06 mm (Range = 9.23-20.13 mm) whereas on the left side, it was 16.31 mm (Range = 11.68-22.53 mm). On comparing the two sides, it was seen that the mean value on left side was higher than the right side.

Clinical Implication:

(a)  Gumina et al13 had blamed severe narrowing of coracoglenoid space as a risk factor for development of idiopathic subcoracoid impingement syndrome. Thus a knowledge of this distance is important for assigning the risk of this syndrome to any patient.
(b)  Renoux et al4 opened that it is the height and length of the coracoid process which is responsible for altering the size and shape of space between the coracoacromial arch and rotator cuff. If these are diminished, the chances of idiopathic subcoracoid impingement syndrome increase and vice versa.

         ii. Superior surface of the coracoid process:

The mean height of the supraglenoid tubercle to the superior surface of the coracoid process was found to be 21.59 mm (Range = 13.35-31.33 mm). On the right side, it was 21.46 mm (Range = 15.24-31.33 mm) whereas on the left side, it was 21.72 mm (Range = 13.35-27.36 mm). When comparing the two sides, it was also found to be increased on the left side.

            Thus the study provides a baseline data for the various morphometric parameters of the coracoid process. Also an attempt has been made to discuss their clinical importance in causation of idiopathic subcoracoid impingement syndrome. These values of different parameters of coracoid process may be useful for the orthopaedicians dealing with this entity.

Conclusions

To summarise, the present study discusses the role of various parameters of the coracoid process in the aetiology of  subcoracoid impingement syndrome and  also provides a base line data for the same. These findings could be of great value in the further exploration of their role in causation and surgical management of this syndrome.