ORIGINAL ARTICLE The clinical anatomy of the musculotendinous part of the diaphragm Maira du Plessis 1 • Daryl Ramai 1 • Sameer Shah 1 • Jessica D. Holland 1 • R. Shane Tubbs 1,2 • Marios Loukas 1 Received: 14 October 2014 / Accepted: 27 April 2015 Ó Springer-Verlag France 2015 Abstract The thoracoabdominal diaphragm is a com- posite musculotendinous structure, separating the thoracic and abdominal cavities. Reemphasis of the already well- delineated variations of the muscular and tendinous por- tions, and blood and nerve supply of the diaphragm is becoming apparent. Scientific reports concerning recon- struction of the pericardium, activation of the muscle and the phrenic nerves by use of laparoscopically placed in- tramuscular electrodes, and repair of congenital and trau- matic hernias reemphasize the importance of the muscular to tendinous relationships. The objective of this study, therefore, was to measure the ratio of the surface area of the tendinous central region to the muscular region of the diaphragm and provide a clear description across various specimens. We classified diaphragmatic measurements from 104 adult human diaphragms into six classes (I–VI) based on the ratio of surface area between its tendinous and muscular components. The majority of specimens, 56.7 %, was attributed to class II and indicated a tendon-to-muscle ratio of between 10 and 15 %; however, a small number of specimens indicated a very large tendon area at the expense of muscle bulk. Future research should be geared toward assessing the relationship between surface area of the musculature and its motor points with focus on interven- tions for herniation repair and recovery. Our results have shown that surgical interventions should be tailored to the individual, as diaphragm size may not necessarily predict tendon-to-muscle ratio. Keywords Septation Á Phrenic nerve Á Diaphragm Á Pericardium Á Esophageal hernia Introduction The diaphragm is a complex muscle studied since at least the ninth century BC by Homer who precisely described wounds of this area in Trojans injured during battle [17]. Standard anatomical textbooks describe the diaphragm as a composite musculotendinous structure, which separates the thoracic and abdominal cavities [4, 5, 11, 12, 17, 18]. The muscular portions of the adult diaphragm can be classified by their points of origin and insertion into sternal (anteri- or), costal (anterolateral), and lumbar (posterior region consisting of the crura and the medial and lateral arcuate ligaments). The point of insertion for all of the diaphragmatic musculature is the fibrous central tendon, which has no bony attachments. The central tendon is typically described as having three leaves, decreasing in size from right to left, and resembling a cloverleaf [4, 7, 11]. The diaphragm is the essential region of separation between the peritoneal sac and the thoracic cavity. Hence, it has a few openings which allow for communication between these compart- ments: the hiatus of the inferior vena cava, the esophageal hiatus, the aortic ‘‘opening’’ which is posterior to the di- aphragm, and the anterior parasternal spaces named for- amina of Morgagni which transmit the superior epigastric vessels. In short, the developed adult diaphragm is a combination of a central tendinous area and its muscular attachments, which radiate to the body’s periphery and & Marios Loukas mloukas@sgu.edu 1 Department of Anatomical Sciences, School of Medicine, St George’s University, Grenada, West Indies 2 Division of Pediatric Neurosurgery, Children’s Hospital, Birmingham, AL, USA 123 Surg Radiol Anat DOI 10.1007/s00276-015-1481-0