INTRODUCTION

Scapulae have a complex anatomy due to their spesific irregular shape. This flat, triangular bone has two surfaces (costal and dorsal), three margins (superior, lateral and medial), three angles (superior, inferior and lateral) and three bony projections (spine, acromion and coracoid process). It is a major component of the pectoral girdle playing an important role in the varied and complex movements of the upper limb. It articulates with the clavicle and humerus forming the shoulder complex. The three bony projections give attachment to a number of muscles and ligaments (^{Romanes, 1995}; ^{Soames, 1995}). Clinical changes associated with the various projections may modify the biomechanics of the upper limb. Anomalies of the shoulder joint, including fractures, dislocations, arthritis, inflammatory and pathological conditions may also arise. Many surgical approaches, such as arthroplasty, glenohumeral arthrodesis, internal fixation for the stabilization of fractures, acromioplasty and acromionectomy for rotator cuff tendinitis all involve the scapula. A detailed knowledge of scapular anatomy is therefore essential for successful total shoulder arthroplasty or surgical treatment of disorders related to scapula and shoulder, as well as shoulder arthroscopy (^{Ebraheim et al., 2000}; ^{von Schroeder et al., 2001}). Furthermore, a clear understanding of the morphology of the acromion, glenoid fossa, coracoid process and subacromial space is necessary to alleviate shoulder pain and rotator cuff insufficiency (^{Aktan et al., 1996}; ^{Getz et al., 1996}; ^{Taskınalp et al., 2001}). The cause of subacromial syndrome is compression of the soft tissues (rotator cuff muscles and subacromial bursae) in the subacromial space by the head of the humerus, acromion, coracoacromial ligament and coracoid process (Ertem et al., 1990; Romanes; Aktan et al.; Unal et al., 1997; Ebraheim et al.; Taskınalp et al.; von Schroeder et al.). Morphometric studies on the subacromial space have confirmed the importance of this region.

The variations of the suprascapular notch (SN) have clinical significance for suprascapular impingement syndrome, while the determination of acromion type is important in shoulder impingement (^{Aydinlioglu. et al., 1997}; ^{Prescher, 2000}). ^{Rengachary et al. (1979}) reported six distinct types of SN (^{Urguden et al. 2004}): it can be turned into a foramen by ossification of the transverse ligament of the scapula. The foramen then serves as a conduit for the suprascapular nerve, which gives sensory branches to ligamentous structures associated with the acromioclavicular and shoulder joints and motor branches to supraspinatus and infraspinatus (Aydinlioglu et al.; ^{Bayramoglu et al., 2003}; Urguden et al., 2004; ^{Sabanciogullari et al., 2006}; ^{Ofusori et al., 2008}). In some cases variation of the transverse ligament accompany NS variations: these may play a role in entrapment neuropathies. Injury to the suprascapular nerve may result in loss of function of the rotator cuff muscles (Aydinlioglu et al.; ^{Ticker et al., 1998}; Urguden et al., 2004; Sabanciogullari et al.; Ofusori et al.).

The acromion partly covers the humeral head: it articulates with the clavicle and gives attachment to the anterolateral portion of deltoid and coracoacromial ligament. Its association with chronic pain and shoulder dysfunction has been observed (^{Voisin et al., 2014}; ^{Nyffeler & Meyer, 2017}). The morphometry of the acromion process is important as it is related to pectoral girdle pathologies (^{Saha & Vasudeva, 2017}). Investigations into acromial morphology have largely been restricted to its shape and tilt (^{Natsis et al., 2007}). Nevertheless, it has been classified into three different types: type I, flat; type II, curved; type III, hooked (^{Bigliani et al., 1986}; ^{MacGillivray et al., 1998}; ^{Mayerhoefer et al., 2005}; Natsis et al.). Type I is most common, while types II and III are considered important factors in the development of subacromial impingement syndrome (Mayerhoefer et al. 2005). There is a significant association between aspects of acromial morphology and rotatory cuff ruptures, as well as subacromial impingement syndrome, commonly observed in orthopedic examination (Mayerhoefer et al., 2005).

This current study was conducted to determine the clinical importance of scapular morphometry, particularly of the suprascapular notch and acromion, and its variations.

MATERIAL AND METHOD

Seventy three intact adult scapulae of unknown age and sex from the anatomy laboratory of Cukurova University Medical Faculty were selected and examined. The suprascapular notch (SN) was classified according to the definition of Rengachary et al. (Fig. 1): its width and depth, the distance from the supraglenoid tubercle to its deepest point were determind (Fig. 2). In addition, acromial length and the distance from the acromion to the coracoid process was also determined (Fig. 2). The angle between the lateral margin of the SN, the superior angle and root of the spine was measured and considered as the upper scapular angle (USA), while the angle between root of the spine, the inferior angle and infraglenoid tubercle was measured and considered as the lower scapular angle (LSA) (Fig. 2). The shape of the acromion was assessed as being type I (cobra), type II (square) and type III (intermediate) (Fig. 3) and its tilt as type I (flat) or type II (curved) (Fig. 4).

Fig. 1 Types of suprascapular notch: adapted from ^{Rengachary et al. (1979}). 

Fig. 2 Morphometric measurements of the scapula. SNW, suprascapular notch width; SND, suprascapular notch depth; TS-SN, distance between the supraglenoid tubercle and deepest point of the suprascapular notch AL; acromion length; A-CP, distance between the acromion and coracoid process; USA, upper scapular angle; LSA; lower scapular angle. 

Fig. 3 Type of acromion according to shape. Type I; cobra, Type II, square; Tpye III; intermediate. 

Fig. 4 Type of acromion according to tilt. Type I; flat, Type II; hooked. 

RESULTS

Table I shows the linear measurements and angles associated with different SN types. The SN types observed were; as type I (28.8 %), type II (23.3 %), type III (13.7 %), type IV (20.5 %), type V (2.7 %), type VI (5.5 %): a notch was absence in 5.5 % of specimens (Table I). According to its shape the acromion the majority were type III (47.0 %), closely followed by type I (45.5 %) and then type II (7.5 %) (Table II), while according to tilt 84.8 % were type II and 15.2 % type I (Table III). The associated measurements for each type of acromion are also presented in Tables II and III.

Table I Linear measurements of different types of suprascapular notch, together with the mean scapular angles. 

^{SN, suprascapular notch; SNW, suprascapular notch width; SND, suprascapular notch depth; TS-SN, distance from the supraglenoid tubercle to the deepest point of the suprascapular notch; USA, upper scapular angle LSA; lower scapular angle; n, number of scapulae}.

Table II Acromion type according to shape, number of scapulae and associated acromial measurements. A-CP; distance from the acromion to the coracoid process, AL; acromion length. 

Table III Types of acromion according to tilt number of scapulae and associated acromial measurements. A-CP; distance from the acromion to the coracoid process. 

DISCUSSION

For shoulder arthroscopy the distance of certain structures from palpable bone landmarks is vital to determine entrance points. The suprascapular nerve can be injured during arthroscopy associated with the suprascapular notch (von Schroeder et al.). ^{Taser & Basaloglu (2003}) demonstrated significant differences between sexes in the distance between the edge of coracoid process and the suprascapular notch, while von Schroeder et al. observed that all measurements of the coracoid process were different between sexes.

Rengachary et al. classified the SN into 6 distinct types. Using this classification ^{Urgüden et al. (2004}), reported that 6 % of SNs were type I, 24 % type II, 40 % type III, 13 % type IV, 11 % type V and 6 % type VI . Earlier Aydinlioglu et al. had reported normal SN in 64 %, an absent SN in 18 %, partial bridge formation in 16 % and complete bridge formation in 2 %. In their study Sabanciogulları et al. (2006), reported the SN to be type I in 28 %, type II in 5.3 %, type III in 29.3 %, type IV in 14.6 %, type V in 13.4 % and type VI in 9.4 %. In contrast in the current study 28.8 % of scapulae showed type I SN, 23.3 % type II, 13.7 % type III, 20.5 % type IV, 2.7 % type V, 5.5 % type VI and 5.5 % having no SN. The above suggests racial and/or ethnic differences in the type of SN present; these differences should therefore be taken into account during arthroscopic examination and surgery to avoid potential damage to the suprascapular nerve and vessels.

In the current study the lower scapular angle was 58.7º, the upper scapular angle was 95.5º, the distance between supraglenoid tubercle and SN was 28.2 mm, SN width 8.3 mm and depth 6.5 mm. ^{Sabanciogullari et al. (2006}), reported similar values from their study, being 51.2º, 102.9º, 26.5 mm, 7.3 mm and 5.3 mm respectively.

In the current study the type of acromion according to shape was 45.5 % type I, 7.5 % type II and 47 % type III, while according to tilt there were 15.2 % type I and 84.8 % type II. Acromion length was 42.1 mm and the distance between acromion and coracoid process was 37.7 mm. ^{Kosar et al. (2006}), have reported the similar values, being 29.3 %, 32 % and 38.7 % for acromion shape, 50.7 % and 41.3 % for acromial tilt, and 46.1 mm and 29.3 mm for acromial length and distance between the acromion and coracoid process respectively. They have observed the hooked type of acromion (type III) in 8 % of their specimens, in contrast to the current study which observed no type III acromion.

Restricted movement of the pectoral girdle and upper limb has been observed when acromial length exceeds normal values (Aktan et al.). Aktan et al. have reported that the longest acromions are the cobra type having a mean length of 50.23±7.29, whereas Taser & Basaloglu give a range of 41.5 to 45.3 mm being significantly less than Aktan et al.

Knowledge of the morphology of the adult acromion process will help define the bony landmarks to be used in assisting surgeons undertaking specific operative procedures and technique. In agreement with Saha & Vasudeva it is concluded that the current observations in an Anatolian population combined with the findings from earlier studies will provide a more precise guide for clinicians undertaking surgical procedures involving the shoulder.