- Research article
- Open Access
- Open Peer Review
Variety of transversus thoracis muscle in relation to the internal thoracic artery: an autopsy study of 120 subjects
© Jelev et al; licensee BioMed Central Ltd. 2011
- Received: 1 September 2010
- Accepted: 27 January 2011
- Published: 27 January 2011
The transversus thoracis muscle is a thin muscular layer on the inner surface of the anterior thoracic wall that is always in concern during harvesting of the internal thoracic artery. Because the muscle is poorly described in the surgical literature, the aim of the present study is to examine in details its variations.
The data was obtained at standard autopsies of 120 Caucasian subjects (Bulgarians) of both sexes (97 males and 23 females), ranging in age from 18 to 91 years (mean age 52.8 ± 17.8 years). The transversus thoracis morphology was thoroughly examined on the inner surface of the chest plates collected after routine incisions.
An overall examination revealed that in majority of cases the transversus thoracis slips formed a complete muscular layer (left - 75.8%, right - 83.3%) or some of the slips (left - 22.5%, right - 15%) or all of them (left - 1.7%, right - 1.7%) were quite separated. Rarely (left - 3.3%, right - 5.8%), some fibrous slips of the transversus thoracis were noted. In 55.8% of the cases there was left/right muscle symmetry; 44.2% of the muscles were asymmetrical. Most commonly, the highest muscle attachment was to the second (left - 53.3%, right - 37.5%) or third rib (left - 29.2%, right - 46.7%). The sixth rib was the most common lowest attachment (left - 94.2%, right - 89.2%). Most frequently, the muscle was composed of four (left - 31.7%, right - 44.2%) or fifth slips (left - 53.3%, right - 40.8%).
This study provides detailed basic information on the variety of the transversus thoracic muscle. It also defines the range of the clearly visible, uncovered by the muscle part of the internal thoracic artery and the completeness of the muscular layer over it. The knowledge of these peculiar muscle-arterial relations would definitely be beneficial to cardiac surgeon in performing fast and safe arterial harvesting.
- Internal Thoracic Artery
- Bare Area
- Costal Cartilage
- Complete Layer
- Axillary Arch
The inner surface of the anterior thoracic wall is covered by a thin muscular layer - transversus thoracis muscle[1–4]. It has a close relation to the internal thoracic artery (ITA), which is now accepted as a superior graft for CABG surgery [1, 2]. According to classical textbook descriptions [3, 4], the fibers of transversus thoracis form four to five slips. Those arise from the xiphoid process, the inferior part of the body of sternum and the adjacent costal cartilages near their sternal ends, and directing supero-laterally they insert from the second to sixth costal cartilages. In literature it is also mentioned that the transversus thoracis shows variations in its attachments not only in different subjects, but also on the opposite sides of the same subject . Consequently, that particular muscle was announced as the most variable in the human body . Anatomists from the XIXth and the beginning of the XXth century have reported the variations of the transversus thoracis only qualitatively [6–8]. Some quantitative evaluation of the rib attachment level of the transverus thoracis slips have been presented only by Loth , Mory  and Satoh .
Surprisingly, in the surgical literature there is quite insufficient data about the most variable human muscle, which is currently having a role in CABG surgery. Acquiring detailed information about the transversus thoracis variations would provide basic anatomical information for the cardiac surgeons while performing ITA harvesting.
The data presented here was gathered in the course of fresh cadaver autopsies carried out in the Department of Forensic Medicine at the Medical University of Sofia, Bulgaria. The medico-legal office and local Ethic Committee approved the study. During the last four years (2006-2009) a total of 120 Caucasian subjects (Bulgarians) of both sexes (97 males and 23 females), ranging in age from 18 to 91 years (mean age 52.8 ± 17.8 years) were examined. None of the autopsied persons had ever undergone any prior thoracic surgical procedure. A standard autopsy protocol was followed for each one of the bodies . After initial midline incision on the anterior thoracic wall, the skin and the subcutaneous tissue were dissected back to expose the underlying muscles and bones. The sternoclavicular joints on both sides were identified and cut. With a bone saw the ribs were cut along the anterior axillary line and the chest plate containing the sternum, the medial part of the upper eight to nine ribs and the surrounding soft tissues was removed from the body. Afterwards, the fat tissue on the inner surface of the chest plate was carefully removed. That helped in observing and recording the characteristics of the transversus thoracis. The following data analysis was done over 240 thoracic halves - 120 left and 120 right ones.
Number of slips of the transversus thoracis muscle.
Scope of the transversus thoracis muscle on the inner thoracic wall.
Comparison of the quantitative literature data concerning the transversus thoracis muscle.
Author (year)[Reference] Population examined
Loth (1931) Poles
Mori (1964) Japanese
Satoh (1971) Japanese
Jelev et al.[present study] Bulgarians
Highest rib attachment
Left side Right side
Lowest rib attachment
Scope (most frequent forms)
Regarding muscle function, transversus thoracis draws down the costal cartilages [3, 4] and takes a stand on the expiration phase of breathing. Unlike dogs where the transversus thoracis is a primary muscle of breathing , in human this muscle is usually silent in supine posture . In standing posture it contributes to the deflation of the rib cage during active expiration . Our data reveals that in most of the cases the transversus thoracis is well developed bilaterally. However, the cases with weakly developed muscle are an evidence of secondary breathing role of the transversus thoracis in human.
The transversus thoracis variations represent theoretical interest with some practical significance. Usually during routine CABG surgery, the harvesting of ITA starts in the bare area on the inner thoracic wall, between the first rib and the highest transversus thoracis slips. At this location the artery is well detectable because it is covered only by the endothoracic fascia and the parietal pleura . By describing the transverusus thoracis variations we provide characteristics of the possible size of this bare area. Usually it reaches second and third ribs and intercostal spaces; rarely it can be missing (the highest muscular attachment is to the 1-st rib) or spreads over almost entire course of the ITA (the highest muscular attachment is to the 5-th rib). On the left side, in 53.3% the bare area reaches below the second rib and intercostal space; in nearly half of the cases (46.7%) the right bare area is larger and reaches the level of third rib and intercostal space.
The data from the present study adds some basic information concerning the surgical anatomy of the anterior thoracic wall. It describes the variety of the transversus thoracis muscle and its relation to the ITA. A complete muscular layer of significant size predominantly covers the artery. Rarely, this muscular layer is quite narrow or separate muscular slips bridge over the artery. Usually, the ITA is clearly visible under the endothoracic fascia and parietal pleura up to the second or third rib level. Sometimes, the artery may be uncovered or completely covered by the muscle fibers through its entire course. All this muscle-arterial relations, quite variable in nature, may be borne in mind during routine ITA harvesting and especially when using minimally invasive approaches and endoscopic harvesting techniques [20–26].
The authors wish to thank Prof. Dr. Radomír Čihák, D.Sc. (Department of Anatomy, 1st Faculty of Medicine, Charles University in Prague, Czech Republic) for locating the work of Loth (1931). The kind help of Dr. Tsvetomir Badov in proofreading of the English text is gratefully acknowledged.
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