Evidence-based surface anatomy

Authors


… if surface anatomy is not evidence-based …it will rightly be perceived as being of limited clinical value and belonging to a bygone era… (Hale et al., 2010).

Being able to locate structures under the skin by reference to palpable surface features such as bony protuberances and tendons is a core clinical skill. An appropriate knowledge of anatomy, particularly of surface anatomy, is needed to undertake physical examinations and interventional procedures safely and effectively and to interpret diagnostic images. For many general practitioners, the vast majority of the anatomy that they use may be surface anatomy (Kotzé et al., 2012). For interventionists, direct visualization techniques, e.g., ultrasound guidance in regional anesthesia, have not displaced the need to know the relevant anatomy, including surface anatomy: for anesthetists and anesthesiologists, the mantra that “regional anesthesia is applied anatomy…” still holds (Marhofer et al., 2010). For surgeons, familiarity with relevant surface landmarks is a prerequisite for the successful placing of incisions to optimize access to organs and vessels (Sayeed and Darling, 2007) and for donor site reconstruction (Cunningham et al., 2004). For all clinicians undertaking a physical examination, whether generalist or specialist, surface anatomy has not yet been usurped by technology (Verghese and Horwitz, 2009). For medical students, surface anatomy and living anatomy help to contextualize cadaveric topographical anatomy and provide important bridges between lab and clinic (Boon et al., 2002; Aggarwal et al., 2006; Ganguly and Chan, 2008). The subject is of more than academic interest.

Figure  .

Susan Standring.

Surface anatomy was born out of the clinical need to visualize the internal landscape of the body from the outside by looking, listening, and palpating. Surface landmarks that are used today were established by cadaveric dissection and measurement decades ago, many of them during the nineteenth century (Thomson, 1894; Dwight, 1894; George, 1935; Anson and McVay, 1936). More recent cadaveric anatomical studies are still prompted by clinical need, for example, for more accurate interpretation of radiological images (e.g., Ribeiro et al., 2006), the only difference being that cadavers may now be soft fixed or frozen/thawed rather than formalin fixed (Cunningham et al., 2004). Surface anatomy landmarks have also been explored using plain and contrast radiography (e.g., Aubert and Koumare, 1975; Karim et al., 1990) and latterly by the use of ultrasound sonography, magnetic resonance imaging, and computed tomography (Chukwuemeka et al., 1997; Chithriki et al., 2002; Lee et al., 2004; Yang et al., 2011). How reliable are the surface landmarks that have been derived in so many different ways?

Intuitively, the notion that “one size fits all” when relating surface features to underlying deeper structures does not sit easily with demographic variations in body mass index, height, gender, age and ethnicity, nor does it take dynamic factors such as posture or respiration into account. Surface anatomy is not an exact science: descriptions may be influenced by anatomical variations and by methodological limitations such as post-mortem distortion in cadavers and geometric assumptions about acquired data. Inconsistencies in values of published landmarks for specific structures should not therefore be summarily dismissed as inaccurate or unreliable, but neither should they be decontextualized. Descriptions of surface anatomy landmarks lacking any indication that they may be approximations have always seemed to me to be the anatomical equivalent of the elusive 70 kg man so beloved of undergraduate physiology textbooks (Burton, 2000), i.e., useful in principle, but less useful in practice.

In a series of papers in this issue, Professor Mark Stringer and his colleagues add weight to their recent proposal that surface anatomy must be evidence-based if it is to remain a reliable and useful educational and clinical tool in an era of evidence-based medicine. Using measurements from modern cross-sectional images obtained from healthy living subjects they have examined conventional surface landmarks and compared their results with those published in a number of current anatomical texts. Taken together with their earlier papers on inconsistencies in surface anatomy landmarks in current textbooks (Hale et al., 2010) and the surface anatomy of the major planes of the trunk (Mirjalili et al., 2012), they present a detailed, systematic analysis of the surface anatomy of the head, neck, and trunk. The same experimental design is used throughout the series, rendering the complete study more powerful than the sum of its parts. The results confirm some traditional landmarks, offer image-based evidence for re-appraising others, and recommend excluding several on the basis of unreliability. The message that surface landmarks must be contextually reliable is well taken—hopefully other groups will be stimulated by this work to re-examine clinically relevant surface markings in the context of variables such as age, sex, ethnicity, BMI, etc. and will share their results with the readership of Clinical Anatomy.

There is a further point to consider. Assuming that surface anatomy, hopefully evidence-based, is not consigned to the long grass, when and how it should be taught? Novel pedagogic approaches, such as using body painting or drawing on a “translucent cadaver” (laminated photographs of full body digital X-rays), appear to engage students in the process of knowledge acquisition (Op Den Akker et al., 2002; Aggarwal et al., 2006; McMenamin, 2008; Finn and McLachlan, 2010; Finn et al., 2011), but do not necessarily aid the subsequent implementation of that knowledge in the clinic (Kotzé et al., 2012). This resonates with my experience that the surface anatomical knowledge of some recent medical graduates and surgical trainees often bears a striking resemblance to the childhood guessing game of “pin the tail on the donkey.” The finding is not new, as I realized when re-reading Whitnall's monograph on the study of anatomy: “Many a student first realizes [the] importance [of surface anatomy] only when brought to the bedside or the operating table of his patient, when the first thing he is faced with is the last and least he has considered” (Whitnall, 1933). Surely evidence-based surface anatomy should be reinforced by practical application in the clinic and at the bedside from the earliest days of an undergraduate medical program?

I am not convinced that surface anatomy is under growing threat from modern imaging technology, paradoxically, its salvation may be provided courtesy of that technology.

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