European Journal of Cardiovascular Medicine

The scapula, or shoulder blade, is a flat triangular bone situated on the posterolateral thoracic wall, extending from the second to the seventh ribs. It has three borders and three angles, with the superior border being the thinnest and shortest [1]. Near the base of the coracoid process, this border shows a depression called the suprascapular notch, which is bridged by the superior transverse scapular ligament (STSL), converting it into a foramen. The suprascapular nerve passes through this foramen to supply the supraspinatus and infraspinatus muscles, while the suprascapular vessels usually course above the ligament. Occasionally, the STSL undergoes ossification, altering the anatomy of this region [2]. Several variations of the STSL have been reported, including calcification and multiple bands [3], bifurcation [4], trifurcation [5], and hypertrophy [6]. In some animals, the notch is completely bridged by bone instead of a ligament [7]. Clinically, this site is important because the suprascapular nerve is prone to compression at the suprascapular notch or spinoglenoid notch, leading to suprascapular nerve entrapment syndrome, first described by Kopell and Thompson in 1959 [8]. Ossification of the STSL significantly increases the risk of compression, causing pain, weakness of abduction and external rotation, and atrophy of supraspinatus and infraspinatus muscles.

Ossification of the STSL is relatively rare but shows wide variability among populations, with important implications for clinicians, surgeons, and anaesthetists. The suprascapular nerve, derived from the upper trunk of the brachial plexus (C5–C6, occasionally C4), also provides sensory supply to the shoulder joints and lateral arm, making its entrapment clinically significant. Despite several studies worldwide, there is limited data available from North India, particularly Eastern Uttar Pradesh, where genetic and lifestyle factors may influence the prevalence of such anatomical variations. Therefore, the present study aims to determine the incidence of complete ossification of the STSL in this population, compare it with other races, and analyze the morphometry of the suprascapular foramen and ossified ligament, to better understand their role in nerve compression.

The present study was conducted on 200 dried human scapulae (100 right and 100 left-sided) of unknown age and sex, obtained from the Department of Anatomy, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh. Each specimen was carefully examined for the presence of complete ossification of the superior transverse scapular ligament (STSL) along the superior border of the scapula. In cases where ossification was observed, the vertical and transverse diameters of the resulting suprascapular foramen, as well as the thickness of the ossified STSL, were measured using a standard digital sliding vernier caliper.

Inclusion Criteria:

• Scapulae with well-preserved superior borders and suprascapular notch region.
• Both right and left scapulae included for comparison.

Exclusion Criteria:

• Damaged, fractured, or eroded scapulae obscuring the suprascapular notch or coracoid process.
• Scapulae with pathological changes (tumors, congenital deformities, or post-traumatic irregularities) affecting the superior border.
• Incomplete or unidentifiable scapulae (missing anatomical landmarks needed for morphometry).
• Specimens with prior surgical intervention or prosthetic reconstruction (in case of radiological study on patients).

Statistical Analysis:

All data collected from the study were entered into Microsoft Excel and analyzed using the Statistical Package for the Social Sciences (SPSS), version 25.0. Categorical variables were expressed as frequencies and percentages, while continuous variables were summarized as mean ± standard deviation (SD). Side-to-side differences (right vs. left) were assessed using the Chi-square test for categorical variables and the paired t-test for continuous measurements. A p-value of less than 0.05 was considered statistically significant.

Out of 200 scapulae examined, complete ossification of the superior transverse scapular ligament (STSL) was observed in 26 specimens (13%). Among these, 16 cases (8%) were on the right side and 10 cases (5%) on the left side. The difference between sides was not statistically significant (P = 0.207). While the completely ossified STSL were more common on the right side. The remaining 174 scapulae (87%) showed no ossification of the STSL [Table 1, Figures 1, 2, and 3].

The mean vertical diameter of the suprascapular foramen (SSF) was found to be 9.28±1.04 mm on the right side and 9.09±0.99 mm on the left side, with an overall mean of 9.19±1.01 mm; the difference was not statistically significant (p=0.171). The mean transverse diameter of the SSF measured 5.91±1.06 mm on the right side and 5.53±0.85 mm on the left side, with an overall mean of 5.72±0.97 mm, showing a statistically significant difference (p=0.005). The thickness of the ossified superior transverse scapular ligament (STSL) was 2.78±0.43 mm on the right side and 1.96±0.43 mm on the left side, with an overall mean of 2.37±0.59 mm, and this difference was highly significant (p<0.0001) [Table 2].

Table 1: Sidewise allocation of the completely ossified superior transverse scapular ligament

[STSL: Superior transverse scapular ligament]

Figure 1: Distribution of scapulae with and without a completely ossified superior transverse scapular ligament (STSL) on the right and left sides.

Table 2: Shows the mean vertical diameter, mean transverse diameter of the suprascapular foramen, and thickness of the ossified STSL (in mm).

[SSF: Suprascapular foramen and STSL: Superior transverse scapular ligament]

Figure 2: Dorsal view of completely ossified STSL in the right and left-sided scapula.

Figure 3: Costal view of completely ossified STSL in the right and left-sided scapula

The ossification of the suprascapular ligament appears to be multifactorial, and its reported frequency varies considerably across different populations worldwide, as summarized in Tables 3 and 4. In the present study, we observed a 13% incidence of completely ossified STSL, which is comparable to the findings of Jadhav et al. [9] (10.57%). By contrast, Silva et al. [10] reported a much higher incidence of 30.76% in the Brazilian population, while our data showed only 13%. In some regions, ossification is quite rare, with incidences as low as 0.3% in Alaskan Eskimos and 2.1–2.9% in Native Americans [6]. In Nigeria, Osuagwu et al. [11] described a single case of complete ossification, while Khan [7] and Das et al. [12] also documented isolated cases in India. Within Indian populations, reported incidences range widely from 1.93% to 19.44%. Many authors, like Jadhav et al. [9], Kalpana T et al. [13], Natsis et al. [14], and Sinkeet et al. [15], did not assess partial ossification of the STSL. Bony bridges of this type are reported more frequently in Caucasian males [6]. Interestingly, Cohen et al. [4] described a familial occurrence of STSL calcification in both a father and son, resulting in suprascapular nerve entrapment, suggesting a possible genetic predisposition.

In our morphometric analysis, the mean vertical diameter of the suprascapular foramen (SSF) measured 9.28±1.04 mm on the right and 9.09±0.99 mm on the left (overall 9.19±1.01 mm), with no statistically significant difference (p=0.171). The mean transverse diameter was 5.91±1.06 mm on the right and 5.53±0.85 mm on the left (overall 5.72±0.97 mm), which showed a significant difference (p=0.005). The mean thickness of the ossified STSL was 2.78±0.43 mm on the right and 1.96±0.43 mm on the left (overall 2.37±0.59 mm), with a highly significant difference (p<0.0001). Mistry et al. [16] documented a mean thickness of 2.8±0.96 mm in Indian specimens. Sandow and Ilic [17] further noted that suprascapular nerve compression is particularly common among volleyball players due to repetitive movements such as abduction combined with external rotation. Rangachary et al. [18, 19] classified suprascapular notches into six types, with type VI representing a completely ossified STSL forming a bony foramen. Conversely, Natsis et al. [14] proposed a five-type classification, in which type IV denotes the bony foramen. From a surgical perspective, De Mulder et al. [20] and Warner et al. [21] emphasized that the distance between the glenoid cavity and the suprascapular notch is critical during open shoulder procedures. To minimize iatrogenic nerve injury, they defined a “safe zone” of 1.4 cm from the posterior glenoid margin at the scapular spine base and 2.3 cm from the superior glenoid rim [22]. Surgeons must remain mindful of this zone during interventions around the shoulder joint.

Anatomical variations of the STSL have also been reported. Polguj M. [23] observed bifid STSL in 3.1% of cases, while Ticker JB et al. [5] identified trifid ligaments in 3%. Bayramoglu et al. [24] described five morphological types: the commonest fan-shaped type, a variant with an additional anterior coracoscapular ligament, a two-part (anterior and posterior) type, and the least frequent calcified type. Additionally, Wang HJ [25] reported a rare case of a double suprascapular foramen in the Chinese population.

Functionally, the suprascapular nerve provides motor innervation to the supraspinatus and infraspinatus muscles but has no cutaneous branches. Therefore, its irritation often causes poorly localized deep pain. By the time patients present clinically, muscle atrophy may already be evident [8]. Early and accurate diagnosis requires detailed anatomical knowledge of the nerve’s course and compression sites, which are most commonly (a) at the suprascapular notch and (b) at the scapular spine base. Thompson et al. [8] noted that compression typically occurs against the STSL during shoulder abduction and horizontal adduction, a risk that increases when the ligament is ossified [7]. Clinically, suprascapular nerve entrapment syndrome initially manifests as burning sensations, numbness, and hand weakness, later progressing to weakness of abduction and external rotation of the shoulder, as described by Black KP and Lombardo JA [26]. Diagnostic tools such as radiography, CT, MRI, EMG, NCV, and arthrography assist in confirming the condition. Importantly, an ossified STSL may complicate surgical decompression of the suprascapular notch if not recognized beforehand. It may also alter the attachment of the omohyoid muscle, which lies close to the ligament. In some cases, lateral scapular projections may distort the omohyoid attachment and, consequently, its function.

Table 3: Comparison of Incidences of completely ossified STSL in different populations of the world

Table 4: Comparison of Incidences of Completely Ossified STSL in the Indian population

Awareness of anatomical variations in the suprascapular region, particularly ossification of the STSL, is crucial for anatomists, clinicians, radiologists, anaesthetists, and surgeons to minimize iatrogenic injury and improve diagnostic accuracy. Since suprascapular neuropathy is an established cause of chronic shoulder pain and functional impairment, especially in athletes, early recognition and timely management are essential. Special attention should be given to the possibility of an ossified ligament during open or arthroscopic interventions, and procedures such as suprascapular nerve blocks are best performed under ultrasound guidance with due caution.

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