Morphology and morphometric analysis of suprascapular notch

The morphology of the suprascapular notch (SSN) has been associated with suprascapular entrapment neuropathy, and injury to the suprascapular nerve in arthroscopic shoulder procedures. This study aimed to describe the morphology and morphometry of the suprascapular notch in dry scapulae. The present study was done in 314 dry scapulae obtained from B. J. Medical College, Ahmedabad. In the present study the suprascapular notch is classified on the basis of two classifications. According to one classification, SSN was classified into five types, type I without a discrete notch; type II a notch that was longest in transverse diameter; type III a notch that was longest in vertical diameter; type IV a bony foramen; type V a notch and a bony foramen. Based on gross appearance, SSN was classified as ‘U’ shaped, ‘V’ shaped, ‘J’ shaped, absent notch and indentation instead of a notch. The complete and partial ossification of the superior transverse scapular ligament was also noted. According to first classification following observations were made in the present study: type I-29%; type II-52%; type III-16%; type IV-2%; type V-1%. According to another classification, following observations were made: ‘U’ shaped notch 38%, ‘V’ shaped notch 7%, ‘J’ shaped notch 22%, absent notch 18%, and indentation instead of a notch 12%. The complete ossification was seen in 3% and partial ossification of the superior transverse scapular ligament in 2% of cases. This anatomic information is important in the management of entrapment neuropathy or interventional procedure of the SSN.


Introduction
The scapula (shoulder blade) is a triangular flat bone that lies on the posterolateral aspect of the thorax, overlying the 2nd to 7th ribs.The convex posterior surface of the scapula is unevenly divided by the spine of the scapula into a small supraspinous fossa and a much larger infraspinous fossa. The concave costal surface of the scapula has a large subscapular fossa. The triangular body (blade) of the scapula is thin and translucent superior and inferior to the scapular spine. 1 The suprascapular notch is situated in the lateral part of the superior border of the scapula, just adjacent to the base of the coracoid process. This notch is converted into a foramen by the superior transverse scapular ligament and serves as a passage for the suprascapularnerve 2 . The variations in the morphology of SSN are well known. Koepell and Thompson (1959) were the first to describe the suprascapular nerve entrapment syndrome. 3 They reported that abduction or horizontal adduction of the shoulder exerted traction on the suprascapular nerve, which led to its compression against the superior transverse scapular ligament. The anatomical variation of the SSN, which includes the variation in shape, complete or partial ossification of the STSL, is recognized as one of the causes ofsuprascapular nerve entrapment. 3 SSN has been classified by various workers in different populations on the basis of parameters such as vertical length of the notch, transverse diameter of the notch and shape of the notch. 4,5,6,7,8 Knowing the anatomical variations in detail is better for understanding of location and source of the entrapment syndrome.However, the literature focusing on SSN and SN IJBAR (2013) 04 (01) www.ssjournals.com

Abstract
The morphology of the suprascapular notch (SSN) has been associated with suprascapular entrapment neuropathy, and injury to the suprascapular nerve in arthroscopic shoulder procedures. This study aimed to describe the morphology and morphometry of the suprascapular notch in dry scapulae. The present study was done in 314 dry scapulae obtained from B. J. Medical College, Ahmedabad. In the present study the suprascapular notch is classified on the basis of two classifications. According to one classification, SSN was classified into five types, type I without a discrete notch; type II a notch that was longest in transverse diameter; type III a notch that was longest in vertical diameter; type IV a bony foramen; type V a notch and a bony foramen. Based on gross appearance, SSN was classified as 'U' shaped, 'V' shaped, 'J' shaped, absent notch and indentation instead of a notch. The complete and partial ossification of the superior transverse scapular ligament was also noted. According to first classification following observations were made in the present study: type I-29%; type II-52%; type III-16%; type IV-2%; type V-1%. According to another classification, following observations were made: 'U' shaped notch 38%, 'V' shaped notch 7%, 'J' shaped notch 22%, absent notch 18%, and indentation instead of a notch 12%. The complete ossification was seen in 3% and partial ossification of the superior transverse scapular ligament in 2% of cases. This anatomic information is important in the management of entrapment neuropathy or interventional procedure of the SSN.
Keywords:Morphology, Morphometry, Suprascapular notch entrapment in Indian population is scarce. Therefore, the present study was done to obtain the morphological data regarding SSN in the population of Gujarat of India.

Material and Methods
The present study was conducted on 314 dry scapulae obtained from the bone store of the B. J. Medical College, Ahmedabad. Each scapula was observed carefully by two investigators, the scapulae with indentation, absence (type I) or complete ossification of SSN (type IV) were separated. In the remaining scapulae the vertical length (VL) and transverse diameter (TD) of the SSN were measured using digital vernier caliper. Based on the above parameters the suprascapular notch is classified into two classifications. According to one classification, SSN was classified into five types, type I without a discrete notch; type II a notch that was longest in transverse diameter; type III a notch that was longest in vertical diameter; type IV a bony foramen; type V a notch and a bony foramen. Based on gross appearance, SSN was classified as 'U' shaped, 'V' shaped, 'J' shaped, absent notch and indentation instead of a notch. The complete and partial ossification of the superior transverse scapular ligament was also noted. For VL, 2 points were taken; the first point was the midpoint of the imaginary line joining the superior corners of the notch, the second point was at the maximal depth of the notch. For TD the diameter perpendicular to the midpoint of VL was taken [ figure 1].

Fig 1 showing measurements of suprascapular notch
An imaginary line joining the superior corners of the notch Vertical length of the notch Transverse diameter of the notch type IV a bony foramen 2 type V a notch and a bony foramen 1 Table I shows that the most common type of SSN observed in the present study is type II-a notch that was longest in its transverse diameter, the least common is type V where a notch and a bony foramen are present. (TD; transverse diameter, VL; vertical length) Table 2 showing the classification of suprascapular notch on the basis of its shape [ Fig.2 Complete ossification of the superior transverse scapular ligament 3 Table II shows that the U shaped notch is most common, V shaped is least common. The partial ossification of the STSL was seen in 3 'U' Shaped SSN, 1 'V' Shaped SSN and 3 'J' shaped SSN.

Discussion
Rengachary et al classified the SSN into six types based on the inferior shape of the SSN as well as the degree of ossification of STSL. 6 This classification was difficult to use when transition between these types is being found. The classification given by Natsis et al seems to be simple and includes all the anatomical variations based on the vertical and transverse diameters of the SSN. 5 The classification by Iqbal et al also provides an easy method of distinction of SSN based on its shape (U, V, and J) without involving any measurements. 4 The results of the present study show that the most common type of SSN is type II-a notch that is longest in its transverse diameter (52%) and the least common is Type V where both notch and foramen present are present (1%). This corresponds with the results of Wang et al (Chinese population) where also the most common type of SSN reported is Type II (58.6%) , where the notch is longest in transverse diameter and the least common is Type V where both notch and foramen are present (none). 8 Natsis et al in their study reported an equal incidence of types II and III SSN. 5 On gross examination without involving any measurements, the results of the present study correspond with that of Sinkeet et al who also reported the U shaped notch as most common (29%) and the complete ossification of STSL as least common (4%) in Kenyan population. 7 Iqbal et al reported the J shaped notch the commonest (22%) in their study in the population of Pakistan. [4] Variation in the morphology of the STSL which include their partial or complete ossification have been identified to be one of the predisposing factor in cases of suprascapular nerve entrapment in various case reports. 9,10,11 The incidence of complete ossification of STSL varies widely in different populations. In Brazilian population its incidence is reported to be 30.76% 12 as compared to Vallios who reported the incidence to be 6.5% in Italian population 13 and Kajava who reported the incidence of complete ossification of STSL to be 1.5% in Finish Scapulae 14 . In the present study the incidence of complete ossification of STSL was observed in 3% of cases. This indicates that there are differences in different populations, therefore population specific studies are required to know the incidence of complete ossification of the STSL. The differences in morphology of the SSN can be explained by the fact that the shape of the SSN is influenced by the ossification of coracoid process. Odita et al reported that epiphyseal centers of coracoids process appear earlier in Nigerian infants than Caucasians. 15 Although it has been hypothesized that suprascapular nerve entrapment is more likely to be associated with a narrow 'V'shaped notch, no direct correlation between notch type and suprascapular nerve entrapment has been shown clinically. [16] Therefore, rather than the shape and diameter of the notch, the morphology of the STSL has been identified to be associated with suprascapular nerve entrapment.