|Year : 2021 | Volume
| Issue : 1 | Page : 17-20
Study of Scalene Tubercle and Morphological Features of the First Rib with Clinical Implications
S Keerthi, PR Prefulla, BJ Bhuvaneswari, E Mohanapriya
Assistant Professor, Institute of Anatomy, Madras Medical College, Chennai, Tamil Nadu, India
|Date of Submission||16-Jun-2020|
|Date of Decision||18-Jul-2020|
|Date of Acceptance||25-Aug-2020|
|Date of Web Publication||27-Jan-2021|
Institute of Anatomy, Madras Medical College, Chennai - 600 003, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Aim and Objectives: The study aims to study the scalene tubercle and morphological features of the first rib with clinical importance. Materials and Methods: Two hundred and forty adult human dry first ribs of unknown sex were studied. The morphological features studied were scalene tubercle, vascular groove, oblique ridge, tubercle, and the head of the first rib. The obtained data were recorded and analyzed. Results: Scalene tubercle was absent in 13.75%, rudimentary in 23.33%, and hypertrophied in 1.67%. Of 240 first ribs, 1.25% was found with the attached cervical rib. The vascular groove was absent in 11.25%. Oblique ridge was absent in 5.83%. The head and tubercle were observed to be rudimentary in 16.67% and 12.5%, respectively. Conclusions: The findings of the present study will be useful for anatomists, anesthetists, forensic surgeons, and general surgeons for the identification of the first rib and management of anomalies related to the first rib.
Keywords: Cervical rib, hypertrophied scalene tubercle, oblique ridge, scalenus anterior, subclavian vessels
|How to cite this article:|
Keerthi S, Prefulla P R, Bhuvaneswari B J, Mohanapriya E. Study of Scalene Tubercle and Morphological Features of the First Rib with Clinical Implications. Natl J Clin Anat 2021;10:17-20
|How to cite this URL:|
Keerthi S, Prefulla P R, Bhuvaneswari B J, Mohanapriya E. Study of Scalene Tubercle and Morphological Features of the First Rib with Clinical Implications. Natl J Clin Anat [serial online] 2021 [cited 2021 Jun 18];10:17-20. Available from: http://www.njca.info/text.asp?2021/10/1/17/308115
| Introduction|| |
The first rib is an atypical, the shortest, and the most curved rib. Its parts are the head, neck, tubercle, and shaft. The head of the first rib is small and round. It bears an articular facet, which is circular in shape. Its neck is rounded and the tubercle has an oval articular facet medially. Since the first rib is bent at its tubercle, its angle and tubercle coincide. The flat superior surface of the shaft is obliquely crossed by two shallow grooves. These are separated by a slight ridge, which ends at the internal border. The scalene tubercle is a small projection which is located at this point at the internal border. It provides attachment for the scalenus anterior muscle. The size and disposition of this muscle vary and its tendon may curve posteriorly around the subclavian artery to form a snare. The subclavian vein lies in a groove that is anterior to the scalene tubercle. The posterior groove is related to the subclavian artery and the lower trunk of the brachial plexus. The scalene tubercle may not be present always, but the muscular ridge for the insertion of the scalenus anterior muscle is almost always present. It generally extends up to the medial one-third of the superior surface. The scalenus medius muscle is inserted on the superior surface of the first rib, between the tubercle and the groove for the subclavian artery. This attachment is represented as the oblique ridge of the first rib. The scalene tubercle is present near the midpoint of the internal border of the first rib, which is concave. The Sibson's fascia is attached to this internal border. The external border is convex and is thick posteriorly. This part is related to the scalenus posterior, which descends to the second rib for insertion. The shaft of the first rib ossifies from one primary center of ossification, the head, and the tubercle ossify from secondary centers. The aim of the present study is to provide additional information to the present limited data on morphological variations of the first rib with its clinical importance.
| Materials and Methods|| |
Two hundred and forty (120 right and 120 left) adult human dry first ribs of unknown sex were studied. All normal and variant first ribs were included in the study. Those with ossified first costal cartilage and damaged or broken ribs were excluded from the study. The morphological features studied were scalene tubercle, vascular grooves, oblique ridge, tubercle, and head of the first rib. Scalene tubercle which is palpable along the internal border was considered as a prominent one. The absence of a palpable scalene tubercle along the internal border, with a muscular ridge on the superior surface, was considered to be rudimentary scalene tubercle. The obtained data were recorded and analyzed. The morphological features were studied with the naked eye and confirmed by the digital palpation method.
| Results|| |
Many variations in the morphological features of the first rib were observed in the present study [Table 1].
|Table 1: Incidence of variations in the different morphological features of the first rib|
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The different morphological variations in the scalene tubercle of the first rib, namely, prominent, rudimentary, absent [Figure 1]a,[Figure 1]b,[Figure 1]c, and hypertrophied [Figure 2] were noted. The absence of scalene tubercle was noted in 13.75%. Out of four ribs with hypertrophied scalene tubercle, three were left-sided and one was right-sided. The various locations of hypertrophied scalene tubercle are shown in [Figure 2].
|Figure 1: Scalene tubercle of the first rib- Right side (a) Prominent (b) Rudimentary (c) Absent|
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|Figure 2: The presence of hypertrophied scalene tubercle (HST) and its location in three left ribs (a) little anterior to the midpoint of the internal border (b) Near the midpoint (c) just behind the anterior end of the first rib, in the right rib (d) little anterior to the midpoint of internal border|
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The presence of completely ossified cervical rib was found in three ribs which include two left and one right ribs. The shaft of the cervical rib fused with the superior surface of the first rib behind the vascular groove, encroaching the internal border. The head, neck, and the tubercle of the cervical rib were free from the posterior end of the first rib [Figure 3]a and [Figure 3]b.
|Figure 3: Cervical Rib (*) attached to the first rib (a) left side and (b) right side|
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Vascular groove for subclavian vessels was prominent in most of the ribs and it was absent in 11.25%. In eight right and seven left first ribs, we found the absence of both scalene tubercle and vascular groove. This accounted for about 6.25%.
Oblique ridge on the posterosuperior part of the shaft was present in 94.17% [Figure 4]a and [Figure 4]b and it was absent [Figure 4]c in 5.83%. This percentage is less compared to that of the absence of vascular groove and scalene tubercle in 11.25%, 13.75%, respectively.
|Figure 4: Oblique ridge (OR) on the superior surface of the first rib shaft – left side (a) Prominent (POR) (b) Rudimentary (ROR) (c) Absent|
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All the first ribs showed the presence of the head and tubercle. The percentage of the rudimentary head (16.67) was higher than that of rudimentary tubercle (12.5%) [Figure 5]a and [Figure 5]b. Ten first ribs (8 Right and 2 Left) showed both head and tubercle to be rudimentary [Figure 5]c. Hypertrophy or absence of both the head and the tubercle together were not observed in any of the ribs.
|Figure 5: Right first rib showing (a) rudimentary head, (b) rudimentary tubercle (c) both head and tubercle are rudimentary|
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| Discussion|| |
The structural morphological variations in the ribs, especially the first rib, have been documented mostly in clinical and radiological studies. Studies to show the presence of morphological variations in the first rib in dry bones are limited.
In the present study, the scalene tubercle was prominent along the internal border in 61.25%. Rudimentary scalene tubercle was found in 23.33%. This coincides with the study of Rashia and Zaidi, with rudimentary scalene tubercle in 20%. The present study showed the absence of scalene tubercle in 13.75%, this incidence was less when compared to other studies, with 46% and 18.75%.
The present study observed that in four ribs scalene tubercle was hypertrophied. In one out of four ribs, a hypertrophied scalene tubercle was observed just behind the anterior end of the first rib. This shows the anterior attachment of the muscle. Since the subclavian vein anterior to scalene tubercle is commonly used to obtain central venous access, the knowledge of this type of hypertrophied scalene tubercle and variations in the muscle attachment is important for surgeons and clinicians. There are studies reporting that abnormal anterior insertion of the scalenus anterior may be a cause of venous compression syndromes in the root of the neck. This can also cause difficulties while doing cannulation of the subclavian vein. The danger of inadvertent puncture of the subclavian artery during attempted venous cannulation due to anteroinferior displacement of subclavian vessels is also possible.,
A small additional rib (cervical rib) may be present at the root of the neck. It develops in association with the seventh cervical vertebra. It is frequently fibrous in nature, but in some cases, it may be ossified. Of 240 first ribs studied, three were found with the cervical rib attached behind the middle of the first rib shaft. Morphological anomalies such as fusion of the cervical and first thoracic ribs, or first and second thoracic ribs can cause compression of the neurovascular bundle. Variations such as cervical rib and hypertrophic scalenus anterior muscle can lead to compression of neurovascular structure in the inter scalene triangle. Kurki explained that anomalies of ribs such as a cervical rib, pelvic rib, bifid rib, and bicipital rib whether pathological or normal variants, often indicate an underlying systemic disorder. The fused ribs affect chest wall expansion and may lead to respiratory complications.
In the present study, though the incidence of rudimentary tubercle (12.5%) was similar (12%), the rudimentary head had a low incidence (16.67%), when compared to that of Rashia and Zaidi (24%).
Yogesh et al. clearly demonstrated that the course of roots of brachial plexus can be variable in relation to the scalene muscles attached to the first rib. These variations should be given due significance by radiologists, anesthetists, and surgeons working at the root of the neck. Adequate knowledge about the morphology of the first rib and its variations is important for surgeons while doing resection of the first rib or scalenectomy for recurrent thoracic outlet syndrome.
The first rib has low fragility and often preserved when compared to other skeletal elements, such as the fourth rib and pubic symphysis. Therefore, the likelihood of its persistence in archaeological and forensic contexts is high. Knowledge of morphological features and variations helps in the identification of the first rib correctly.
| Conclusions|| |
For the identification of the first rib in undergraduate teaching, one of the features we look at is the scalene tubercle. The present study concludes that the scalene tubercle is not a constant feature to identify the first rib. The knowledge of normal morphological features of the first rib and its relations to the neurovascular bundle is important to understand various clinical presentations related to common variations present near the root of the neck. The findings of the present study will be useful for anatomists, forensic surgeons, anesthetists, and general surgeons in the identification of the first rib, choosing landmarks for cannulation, and in the management of anomalies of the first rib.
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Conflicts of interest
There are no conflicts of interest.
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