Abstract
Background: Surface anatomy is an essential part of safe clinical practice, and a key component of physical examination. Our knowledge of surface anatomy has been primarily derived from cadaver studies, with all their associated limitations. Surface anatomy needs to be reappraised in the light of modern imaging techniques in healthy living subjects to ensure that it is fit for purpose in the modern evidence based era.
Aims: (i) To determine the consistency with which surface anatomy relevant to cardiothoracic medicine and surgery is reported in contemporary anatomical reference texts, and (ii) to establish evidence based surface markings for the central veins using computerised tomography and ultrasound.
Methods: (i) Major surface anatomy landmarks reported in ten contemporary anatomical reference texts and three popular clinical examination texts were analysed to assess consistency. These were compared to evidence based landmarks derived from scientific studies. (ii) 103 computerised tomographic (CT) scans of the chest (52 female; mean age 64 years [range 19–89 years]) were analysed to establish evidence based surface markings for the central veins and the cardiac apex. In addition, the surface anatomy of the subclavian veins was examined bilaterally using ultrasound in 50 healthy volunteers (25 female; mean age 35 years [range 19–68 years]; mean BMI 24.0 [16.5–37]). The relationship of the subclavian vein to the clavicle was examined both with and without passive shoulder retraction with 10º of head down tilt.
Results: (i) There are numerous inconsistencies in the reporting of many surface anatomy landmarks both between and within reference texts. Few texts address variation with age, gender, ethnicity, body habitus, posture and phase of respiration. Clinical examination texts contain comparatively little surface anatomy. (ii) In most living adults, the brachiocephalic veins are formed posterior to the ipsilateral sternoclavicular joint, the superior vena cava is formed posterior to the right second costal cartilage and enters the right atrium behind the right fourth costal cartilage. The azygos vein typically joins the superior vena cava at the level of the lower half of the fifth thoracic vertebra, 2 cm below the sternal angle. The cardiac apex lies on average in the left fifth intercostal space close to the midclavicular line, about 9 cm from the midline. The subclavian vein lies closest to the clavicle approximately 7 cm from the midline; it has an average diameter of 10 mm, decreasing by approximately 10% after passive shoulder retraction. Age, gender and body mass index affect these variables.
Conclusions: Whilst some commonly accepted thoracic surface markings appear to be reliable when examined in living subjects using modern imaging techniques, others are inaccurate. This is not only relevant to ensuring that modern anatomy teaching is fit for purpose but also important for practical procedures such as central venous catheterisation. Rather than improving successful subclavian vein puncture, passive shoulder retraction may reduce the chances of successful catheterisation by reducing venous diameter. Surface anatomy must be reappraised in living subjects using modern imaging techniques if it is to be accurate and remain useful in clinical practice.