Yonsei Med J.  2009 Apr;50(2):300-303.

Bifid Rib: Anatomical Considerations in Three Cases

• Song WC
• Kim SH
• Park DK
• Koh KS

Abstract

The present study involved a detailed investigation of 3 cases of bifid rib, focusing on anatomical features, and classified them into 2 types. The bifid ribs were in the right fourth rib of all 3 male cadavers. The upper intercostal spaces of the fourth bifid rib were considerably narrowed, whereas the lower intercostal spaces were widened. Although the size and shape of the bifid space between the upper and lower divisions of the bifid rib were different, the intercostal muscles were present in the bifid space in all cases. The third anterior intercostal artery from the internal thoracic artery supplied the bifid space in all cases. In 2 cases, the fourth intercostal nerve ran along the inferior margin of the fourth bifid rib and innervated the muscles of the bifid space. In the third case, there was another branch from the third intercostal nerve supplying the muscles of the bifid space as well as the fourth intercostal nerve. The bifid ribs are associated with other diseases or develop accidentally or sporadically. Knowledge of this malformation is needed for the differential diagnosis with other diseases, such as a chest wall tumor or costal fracture.

Keyword

Bifid rib; anatomy; development; variation

MeSH Terms

Aged, 80 and over
Cadaver
Humans
Male
Middle Aged
Ribs/*abnormalities/*anatomy & histology/radiography

Figure

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  Fig. 1 External surfaces of Case 1 (A) and 2 (B). Upper intercostal space of the bifid fourth rib was narrow; otherwise lower intercostal space was widened in both cases. Dot lines, the junctions of the rib and its cartilage. III, third rib; IV, fourth rib; V, fifth rib.

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  Fig. 2 Measurement items. 1, upper intercostal space between upper division of fourth bifid rib and third rib; 2, thickness of upper division; 3, vertical distance of the bifid space of bifid rib. 4, thickness of lower division; 5, lower intercostal space between lower division of fourth bifid rib and third rib; 6, transverse distance of the bifid space of bifid rib; 7, distance from sternum to bifid point; 8, thickness of sternal end of fourth costal cartilage. III, third rib; IV, fourth rib; V, fifth rib.

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  Fig. 3 Internal surface of Case 3. Structures around bifid rib (A) and bony components (B). Intercostal nerve (ICN) ran along the costal superior and inferior margin from lateral side to medial side. Note the intercostal nerve running along the superior margin and upper division of the fourth rib. It innervated to the muscles in the bifid space formed by upper and lower division of the fourth rib. Anterior intercostal arteries and veins (AICA & V) supplied the medial portion around the area of the bifid rib. Upper intercostal space was much narrowed. The arteries were painted reddish and the nerves were painted with yellowish to find easily. Dot lines, the junctions of the rib and its cartilage. III, third rib; IV, fourth rib.

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  Fig. 4 Developmental course of bifid rib and its derivatives. A, Normally developing ribs; B, Cleavage of rib; C, Outgrowth of rib; D, Fork type of bifid rib; E, Widened rib-derivative of D; F, Hole type of bifid rib; G, Incomplete hole type of bifid rib.

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