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Morphometry of the suprascapular notch: correlation with scapular dimensions and clinical relevance
© Albino et al.; licensee BioMed Central Ltd. 2013
Received: 17 September 2012
Accepted: 24 April 2013
Published: 24 May 2013
Better knowledge of the suprascapular notch anatomy may help to prevent and to assess more accurately suprascapular nerve entrapment syndrome. Our purposes were to verify the reliability of the existing data, to assess the differences between the two genders, to verify the correlation between the dimensions of the scapula and the suprascapular notch, and to investigate the relationship between the suprascapular notch and the postero-superior limit of the safe zone for the suprascapular nerve.
We examined 500 dried scapulae, measuring seven distances related to the scapular body and suprascapular notch; they were also catalogued according to gender, age and side. Suprascapular notch was classified in accordance with Rengachary’s method. For each class, we also took into consideration the width/depth ratio. Furthermore, Pearson's correlation was calculated.
The frequencies were: Type I 12.4%, Type II 19.8%, Type III 22.8%, Type IV 31.1%, Type V 10.2%, Type VI 3.6%. Width and depth did not demonstrate a statistical significant difference when analyzed according to gender and side; however, a significant difference was found between the depth means elaborated according to median age (73 y.o.). Correlation indexes were weak or not statistically significant. The differences among the postero-superior limits of the safe zone in the six types of notches was not statistically significant.
Patient’s characteristics (gender, age and scapular dimensions) are not related to the characteristics of the suprascapular notch (dimensions and Type); our data suggest that the entrapment syndrome is more likely to be associated with a Type III notch because of its specific features.
The suprascapular notch (SN) serves as passage to the suprascapular nerve (SSN) and it is converted into a foramen by the superior transverse scapular ligament. The first description of suprascapular nerve entrapment syndrome at the site of the suprascapular notch was made by Kopell and Thompson. Over the years, many studies have investigated and have identified the pathologic factors related to this syndrome. The following proved to be involved in the aetiology as well as iatrogenic lesions during open or arthroscopic surgical procedures[3–5]: anterior shoulder dislocation; injury from direct trauma; ganglion cysts; synovial and Ewing’s sarcomas; and chondrosarcoma and lipoma.
In Type I the superior border of the scapula present a depression from the medial superior angle to the base of the coracoid process; Type II is described as a wide blunded “V”-shaped notch, occupying nearly a third of the superior border with the widest point along the superior border. Type III is a simmetric and “U”-shaped notch while Type IV is described as a very small “V”-shaped notch, frequently presenting a shallow groove near the notch; Type V is similar to type III, with partial ossification of the medial border of the notch and with the minimal diameter along the superior border of the scapula. Type VI is described as a bony foramen with a completely ossified STSL.
The suprascapular nerve may be accidentally injured in many surgical procedures, for example blind drilling during arthroscopic Bankart and SLAP repair[13–15] advancement of rotator cuff during the repair of massive retracted rotator cuff tears[5, 16–23], arthroscopic anterior or double interval slide and also during the decompression of suprascapular nerve entrapment[3, 24]. In order to avoid this complication, previous anatomical studies analyzed the “safe zone”[4, 13, 25–27], considered as an area within which is possible to avoid iatrogenic lesions of the suprascapular nerve. The safe zone presents two safe limits: the posterior represented as the distance measured from the supraglenoid tubercle to the scapular notch and the posterosuperior represented as the distance measured from the midline of the posterior glenoid rim to the base of the scapular spine.
We aimed to verify the reliability of the existing data concerning the anatomy of the SN, by analyzing a considerable number of dried scapulae and comparing our results with literature. Measurements were performed in order to assess the differences between scapulae in the two genders and within each individual subject, by comparing the dimensions of the right and left scapula of the same subject. Furthermore, we assessed potential correlations between the dimensions of the SN and the major dimensions of the scapula. We also evaluated variations of the dimensions and of the area among the different types of the SN, as well as the relationship between different types and the posterosuperior limit of the safe zone for the suprascapular nerve.
We examined 500 dried scapulae belonging to the anatomical collection of the Department of Anatomy from two Universities (53 + 59), the bone collection of the municipality of Rome (70), and a southern Italian region (318). Our research was performed in compliance with the Helsinki Declaration.
The gender and ages of 155 donors were known. Among the donors, we found 131 complete skeletons (67 males, 64 females) while in the remaining 24 (5 males, 19 females) one of the two scapulae was missing. Therefore, there were a total of 147 scapulae belonging to females and 139 to males. An additional 15 complete skeletons, whose gender and age were unknown, were used. The age at the time of death ranged from 22 to 108 years (average age: 71).
The shape of the scapular notch was also classified. We decided to apply Renganchary’s system since it is a simple, reproducible and objective method of classification. In addition, it has already been used in several studies and it allowed us to compare the results.
For each class, we analyzed the width/depth ratio expressing the area occupied by the SN.
All measurements were performed twice with a vernier caliper.
Continuous variables were reported by mean, standard deviation, median. Categorical variable were expressed in numerical (count) and percentage terms. To assess differences between groups we used ANOVA. We also calculated the correlation with Pearson’s r. We also estimated the intra-class correlation coefficient (ICC) in order to assess potential statistical bias related to the measuring method.
A value of p <0.05 was considered statistically significant. All analyses were performed using SPSS v.18.
Descriptive analysis of the major dimensions of the scapula, glenoid fossa and scapular notch
A axis (cm)
Distance E (cm)
Depth SN (cm) width
Frequencies and percentages of the suprascapular notch types
Scapular notch type
Both width and depth of the SN did not show a statistical significant difference when elaborated according to gender (mean width in males: 0.93 cm, mean width in females: 0.94 cm; mean depth in males: 0.61 cm, mean depth in females: 0.58 cm) and side (mean width in right scapulae: 0.96 cm, mean width in left scapulae: 0.95 cm; mean depth in right scapulae: 0.59 cm, mean depth in left scapulae: 0.56 cm).
We found a statistically significant difference (p=0.033) among the mean depths elaborated according to the median age of our sample; subjects over 73 showed a deeper notch (mean: 0.64 cm; 95% IC: 0.59-0.69 cm) than those ≤ 73 (mean: 0.56 cm; 95% IC: 0.51-0.61 cm).
Correlation indexes between the dimensions of the scapula and the dimensions of the scapular notch
Descriptive analysis of the dimensions of the suprascapular notch types
The intraclass correlation coefficient which assesses the error of the vernier calliper was 0.996 with a 95% Confidence Interval: 0.993-0.998.
In the relevant scientific literature, we found many studies[3, 9, 10, 12, 28–32] that investigated the characteristics of the suprascapular notch; unfortunately there is not a univocal standard of classification[3, 10, 33] whereupon the opportunity to compare the different results is reduced.
In fact, taking the cue from Rengachary's study, other authors elaborated the geometric and morphologic features of the notches in order to create and refine new models of classification. In 2007 Nastis et al. presented their classification, distinguishing V classes on the base of the relationship between the vertical and transverse diameter of the SSN and the presence/absence of both notch and foramina. A further system of classification was elaborated by Polguj et al. in. They compared for every single notch 3 distances: the maximal depth, the superior and middle transverse diameter; successively they divided the notches in V main classes basing on morphologic features, with a further division 3 in sub-classes for both type I and III, according to the specific relationship between the 3 distances considered. Although these systems may seem more specific if compared with Rengachary's classification they are quite new, they are not yet fully assessed and they own a low diffusion at the time.
Comparison of the percentages of the different types of suprascapular notch presented in literature
Rengachary et al.
Sinkeet et al.
We believe that the difference between the mean depths, elaborated according to our median age, may be due to the most frequent presence of partial/total ossification of the superior transverse scapular ligament in the population over 73 years old. At the same time, we are aware that our sample, which is made up of dry scapulae from cadavers, is not homogeneous in terms of age (95.8% of the sample was over 50 years old). Therefore it is worth further investigating this assumption.
The correlation indexes developed in this study showed a weak relationship between the dimensions of the suprascapular notch and the glenoid fossa, while the relationship between the dimensions of the suprascapular notch and the scapular body was absent. The strongest correlation was found between the posterosuperior limit of the safe zone and the width of the suprascapular notch. Unfortunately this relationship may be facilitated by a geometric element. Both distances share a little segment of the scapula (from the lateral angle of the suprascapular notch to the middle part of the notch itself) and we suppose that the overlapping may affect the results. As far as our analysis is concerned, we can state that the dimensions of the scapula could not be considered as predictive parameters to determine the dimensions of the suprascapular notch; those should be considered independent variables.
Recently, Polguj et al. analyzed a sample of 86 dried scapulae and demonstrated the existence of a direct correlation between the scapular length (corresponding to A axis in our study) and the SN depth (R=0.265) and an inverse correlation between the ratio length/width of the scapular body and the SN depth (R=−0.327). In our opinion, the different statistical method used to determine the correlation (Spearman’s rank correlation coefficient) as well as the size of the sample considered may have led to a discrepancy in the results of the two works.
Comparison of the averages and ranges of the scapular notch dimensions presented in literature
Average ± SD (cm)
Range min-max (cm)
Rengachary et al.
Thicker et al.
Wang et al.
In analyzing the trends reported in this study, we found that Type III, V and VI have the lowest width/depth ratio (indicative of the area occupied by the suprascapular notch). Dunkelgrun et al. stated that type III notches had a larger area than Type IV notches, leading to the assumption that a V-shaped notch would be more likely connected with nerve entrapment. At the same time, Rengachary et al. concluded their work asserting that patients with Type IV notch are more likely to suffer from the suprascapular nerve entrapment syndrome; but in clinical practice, because of the higher frequency of Type III scapulae and its associated small size, it is more likely to encounter an entrapment syndrome associated with this type of notch. We agree with Regngachary’s assumption that patients with Type III notch are more likely to have suprascapular entrapment neuropathy than patients with Type IV notch. But we believe that the main pattern that predisposes patients to the entrapment syndrome involves the specific anatomical characteristics of Type III notches instead of the frequency, which proved to be almost nine percentage points higher for Type IV. In fact, comparing the width/depth ratio between the two classes, we observed that Type III notch presents averagely a lower value and consequently a smaller space available for the suprascapular nerve, increasing the possibility to have a case of suprscapular nerve entrapment. Because our analysis oppose to those presented by Dunkelgrun et al., we believe that the different aims and methods of the two studies may explain the difference in the results.
Sinkeet et al. reported that Type III notches were associated with the lowest value of the posterosuperior limit (difference among such types are not statistically significant). Wang et al. found that Type IV notches have the shortest posterosuperior limit and their conclusions were corroborated by the work of Urgüden et al.. Our findings agree with Sinkeet et al’s work. We have also demonstrated that the posterosuperior limit of the safe zone does not change considerably from Type I to Type VI and, at the same time, the difference among them was not statistically significant.
One of the limits of our study is due to the sample composed of dried scapulae. In fact, the anatomical variations of the anterior coracoscapular ligament as well as the existence of a bifid or trifid STSL, that are important anatomical factors influencing the incidence of the suprascapular nerve entrapment syndrome[39–42] can only be evaluated in vivo. Further studies are required to investigate this specific issue.
In conclusion, we believe that the characteristics of the patient (gender, age and dimensions of the scapula) are not related to the characteristics of the suprascapular notch (dimensions and Type). Our findings demonstrated that entrapment syndrome is more likely to be associated with a Type III notch because of its specific features.
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