Abstract
Surface anatomy is routinely taught to medical and anatomy students and is a core component of human anatomy in clinical practice. Accurate surface anatomy and awareness of variations are both essential for safe clinical practice. Our knowledge of surface anatomy is largely derived from cadaver studies and radiographic investigations in living subjects. Numerous inconsistencies in clinically important surface markings exist between and within anatomical reference texts. Moreover, only a few texts comment on anatomical variation and the effects of respiration, posture, ethnicity and body build on surface anatomy. The aim of this thesis is to reassess the accuracy of common and clinically important surface landmarks in vivo using modern imaging techniques including ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI).
All three imaging modalities were selected to investigate different aspect of surface anatomy. Firstly, ultrasound was used to record the calibre and course of the accessory nerve in the posterior triangle of the neck in 50 healthy volunteers (mean age 37 years, range 18-62 years, 56% female). Secondly, 52 CT scans of the neck (mean age 63 years, range 30-94 years; 40% female), 153 thoracic CT scans (mean age 63 years, range 19-89 years, 53% female), 108 abdominal CT scans (mean age 60 years, range 18-97 years; 59% female) and 52 thoracoabdominal CT scans (mean age 61 years, range 26-86 years, 56% female) from supine adults at end tidal respiration were analysed to determine the surface anatomy of the neck (e.g. bony and cartilaginous structures), thorax (e.g. central veins and heart), abdomen (e.g. transpyloric plane and kidneys) and pelvis (e.g. plane of the pubic crest). Patients with distorting space-occupying lesions, scoliosis, abnormal kyphosis and lordosis, obvious visceromegaly, and a previous history of major injury were excluded. Thirdly, 45 cranial MRI scans (mean age 56 years, range 24-84 years; 56% female) were analysed to determine the surface anatomy of the central sulcus of the brain.
Some traditional surface landmarks were found to be accurate and reliable (e.g. the hard palate, cardiac apex, formation of the brachiocephalic veins, transpyloric plane). In contrast, some others were inaccurate and unreliable when compared with in vivo findings: the surface markings of the spinal accessory nerve in the posterior triangle of the neck were very variable with the nerve exiting the posterior border of sternocleidomastoid at a mean of 6.7 (4.0-9.4) cm below the mastoid process and penetrating the anterior border of trapezius 5.4 (2.1-9.2) cm above the clavicle; the central sulcus of the brain was located a mean of 2 ± 0.9 (0.3-4) cm behind the midpoint between the nasion and inion; the spleen was most frequently located between the 10th and 12th ribs (48%) with its long axis in line with the 11th rib (55%); the 11th rib was a posterior relation of the left kidney in only 28% of scans; and the level at which the inferior vena cava and oesophagus traversed the diaphragm was T11.
Whilst the surface anatomy of some structures is consistent with standard descriptions, that of other structures is inaccurate and must be revised in the light of results using modern imaging techniques in living subjects. An evidence-based framework is essential if surface anatomy is to be fit for purpose. The effects of gender, age, posture, respiration, build and ethnicity also deserve greater emphasis.