INTRODUCTION

The first rib is an atypical rib and is an important anatomical landmark. It is one of the borders of the superior thoracic aperture and also forms the medial boundary of the inlet of the axilla.

The first rib has a head, neck, and shaft, but lacks a discrete angle. The shaft is indented laterally by the groove for the subclavian artery, which contains the lower trunk of the brachial plexus trunk as well as the subclavian artery. Anterior to the scalene tubercle is another groove for the subclavian vein. It has two tubercles:

Ribs, like any other part of the body, may show variations, which may be of clinical, racial, or regional significance. Ribs are essential components of the bony thoracic cage. Anomalous ribs are rare anatomical findings usually discovered as an incidental finding on a routine chest radiograph, or as a part of systemic disease or syndrome Around 22 syndromes are described that involve the rib anomalies.¹

Anomalies of the first rib are commonly associated with postfixed brachial plexus, with main contribution from the second thoracic nerve. Both first and second thoracic nerves may be stretched over the shaft resulting in neurological problems.²

Some first rib anomalies create a space through which the brachial plexus and the subclavian vessels pass, like fusion of cervical and first rib or fusion of first and second ribs. In this, there is compression of the neurovascular bundle.³

Coastal exostosis of rib can cause a hemothorax due to direct traumatic injury to the pleura.^4-8 Certain anomalies of first rib like presence of cervical rib, hypertrophic scalenus anterior, and other factors, such as obliterate interscapular space or costoclavicular space lead to thoracic outlet syndrome.^9,10

The present study focused on first rib variations in the light of available literature to draw conclusions and significances. Abnormalities of first rib were detected in this study that included certain features like:

MATERIALS AND METHODS

Fifty first ribs of the Museum of Anatomy Department of Rohilkand Medical College & Hospital, Bareilly, Uttar Pradesh, India, were studied for anomalies of:

RESULTS

Findings are mentioned in Table 1. Also presented in Figures 1 to 3.

DISCUSSION

Rib anomalies are traditionally classified into (1) numerical and (2) structural. Numerical anomalies include supernumery (e.g., cervical rib, lumbar rib) and deficient pair of 11th ribs. Structural defects include short rib, bifid or forked rib, fused or bridged ribs, and pseudoarthrosis of first rib.¹¹

Fig. 3

Head small and tubercle small

There have been studies on anomalies of ribs including first rib. Many of these studies are clinical and radiological.

One of the most extensive studies was done radiologically in 40,000 cases by Etter.¹² These studies mentioned many variants, such as congenital rib anomalies in 1.4% and cervical rib in 0.2%. The most frequent anomaly that Etter found was the forked rib in 0.6%. This most often involved the fourth rib. The fusion of bone bridging in 0.3% most often involved the first and second ribs. The rudimentary or hypoplastic rib usually involved the first rib and was found in 0.2% cases. Pseudoarthrosis of first rib was present in 0.1% – this anomaly may stimulate a healing fracture.¹³

Others include

The present study detected only one case of trauma/growth (2% incidence).

In our study, the scalene tubercle was found to be absent or very ill defined in a significant 46%; rudimentary was present in 20%.

Number of cases of vascular grooves on the superior surface which were insignificant or absent was 28%.

Incidence of rudimentary tubercle was 12% and rudimentary head was 24%; the oblique ridge of 34% was also seen in the present study.

CONCLUSION

The incidence of absence of both ill-defined scalene tubercle and vascular grooves separated by ridge was found to be surprisingly higher in our study besides the incidences of rudimentary tubercle and head of the first rib.

Findings are of considerable racial, regional, and clinical significance.

The incidence and significance are of considerable clinical importance. It may cause musculoskeletal pain, intercostal nerve entrapment, or vascular compression. Awareness of these anomalies is important for the radiologist for diagnostic purposes and for surgeons for performing various clinical and surgical procedures.

CLINICAL SIGNIFICANCE

Structural malformations of first rib are common. When present, they may lead to compression of neurovascular bundle at the root of neck causing thoracic outlet syndrome. Awareness of such anomalies is important for anatomists, radiologists, and thoracic surgeons dealing with this region. The first rib anomalies can cause compression of structures, as they create a narrow space through which the brachial plexus and subclavian vessels pass.