James Cowles Prichard advanced a similar concept he called moral insanity, which would be used to diagnose patients for some decades. Moral in this sense referred to affect (emotion or mood) rather than ethics, but it was arguably based in part on religious, social and moral beliefs, with a pessimism about medical intervention so social control should take precedence. These categories were much different and broader than later definitions of personality disorder, while also being developed by some into a more specific meaning of moral degeneracy akin to later ideas about psychopaths. Separately, Richard von Krafft-Ebing popularized the terms sadism and masochism, as well as homosexuality, as psychiatric issues. The German psychiatrist Koch sought to make the moral insanity concept more scientific, and in 1891 suggested the phrase psychopathic inferiority, theorized to be a congenital disorder. This referred to continual and rigid patterns of misconduct or dysfunction in the absence of apparent "mental retardation" or illness, supposedly without a moral judgment. Described as deeply rooted in his Christian faith, his work established the concept of personality disorder as used today. 20th century
In the early 20th century, another German psychiatrist, Emil Kraepelin, included a chapter on psychopathic inferiority in his influential work on clinical psychiatry for students and physicians. He suggested six types – excitable, unstable, eccentric, liar, swindler and quarrelsome. The categories were essentially defined by the most disordered criminal offenders observed, distinguished between criminals by impulse, professional criminals, and morbid vagabonds who wandered through life.
In most cases, the first three fuse at 15–18 years, whereas the base part fuses to the scapular spine at 12 years. However, in between 1% and 15% of cases, this osseous union fails and the acromion remains separate as an accessory bone. This condition is referred to as os acromiale, but rarely causes pain. Earlier estimates of its prevalence were as low as 1.4%, and this higher estimate was made by Sammarco in the year 2000, based on radiographic and anatomical studies.Four types of os acromiale can be distinguished:
A non-union between the meso- and meta-acromia, the most common or typical os acromiale
A non-union between the pre- and meso-acromia
A non-union between the pre- and meso-acromia; and between the meso- and meta-acromia, atypical
A non-union between the pre- and meso-acromia; between the pre- and meso-acromia; and between the meta- and basi-acromiaThis feature was common in skeletons recovered from the Mary Rose shipwreck: it is thought that in those men, much archery practice from childhood on with the mediaeval war bow (which needs a pull three times as strong as the modern standard Olympic bow) pulled at the acromion so much that it prevented bony fusion of the acromion with the scapula. Although historically regarded as an incidental finding, the os acromiale may occasionally produce symptoms from subacromial impingement or instability at the site of non-union. In people with symptoms of  os acromiale, dynamic ultrasound sometimes shows hypermobility in the area during shoulder movement, or graded compression with the probe.