Apostrophe use and eponyms

Apostrophes are used according to standard English grammar rules. They are used for possessives and to indicate missing letters. 

When using a possessive it's usually by adding "'s" at the end, e.g. "the patient's disease". Apostrophes should not be used for pluralisation, e.g. "apostrophes" and not "apostrophe's".

The other main use is to indicate missing letters in so-called 'contractions', e.g. "it's", "don't" and "you're". Some of these forms have notorious counterparts without an apostrophe that have a different meaning, e.g. its (possessive of it), your (possessive of you). Although in written English, and hence Radiopaedia, generally the non-contracted form is preferred e.g. "cannot" instead of "can't", "we would" instead of "we'd" etc.

Although apostrophes were previously also used in the pluralisation of letters (B's), numbers and acronyms (ICD's) this use is becoming obsolete and we, therefore, advise against it and would write: Bs, ICDs, 5s, and Ss (for plural of 'S'). Read more about acronyms.

At Radiopaedia.org we think that the use of apostrophes should be as limited as possible. In general, terms that often include apostrophes are mostly used in an adjectival sense and only in a very limited number of cases should the possessive nature of apostrophes be maintained for grammatical reasons.

Apostrophes in eponyms

A particular note should be made on eponyms as the use of apostrophes in eponyms is debated. Many diseases, anatomical structures and landmarks are named after a person, either a patient, a doctor or someone entirely different (also see Stigler's law of eponymy). There is variation in the spelling of such eponyms when it comes to the inclusion of an apostrophe, effectively alternating between using a possessive form (Down's syndrome) or a non-possessive form (Down syndrome). 

The non-possessive form (without apostrophe) is becoming more common ¹. Radiopaedia.org aims for uniformity both regarding its own content and in the larger medical community and for this reason alone we prefer the non-possessive form. Furthermore, the use of an apostrophe can lead to ambiguity related to the genitive use (Cushing's disease does not usually indicate that Cushing is diseased).

The non-possessive form, however, is more simple and easier to use, having fewer letters and symbols (which are not always easy to find on any particular keyboard). The dedicated employment of the non-possessive form will contribute to more simplicity, more efficient literature search strategies and less ambiguity.

Although dropping the apostrophe from well-known terms and eponyms might feel awkward initially, it's fairly easy to get used to and at Radiopaedia.org we would like to set an example.

When to use apostrophes

Generally speaking, and mostly because of the plea above, Radiopaedia.org is in favor of omitting apostrophes wherever possible. However, there are still some cases where it's necessary. These include:

• anatomical structures that cannot be pluralised without becoming nonsense: Arnold's nerve, Waldeyer's ring, Bochdalek's flower basket, Lister's tubercle, Hoffa's fat pad
  • by using the rule of thumb with plurals other terms can do without an apostrophe: Morgagni hernia, Bochdalek hernia, Hoffa fracture, Meckel diverticulum
• terms that include a fixed phrase that includes an apostrophe: shepherd's crook deformity, bull's eye sign

When not to use apostrophes

In all other cases, Radiopaedia.org strongly encourages not using an apostrophe. This includes many terms for which many people actually include an apostrophe and versions with or without apostrophes can be observed throughout the literature, clinical practice or presentations.

A non-exhaustive list of terms that can do without apostrophes:

• diseases: Parkinson disease, Huntington disease, De Quervain tenosynovitis
• syndromes: Down syndrome, Chilaiditi syndrome, Löfgren syndrome
• signs: Westermark sign, Rigler sign, Chilaiditi sign
• lines: Shenton line, Perkin line, McGregor line