have always used hammertoe n/m - 1mt

one word - hammertoe

2 words according to Stedman and Dorland - 1 word according to some English dictionaries - Just another opinion

According to Stedman and Dorland Dictionaries, it is two words.

hammer toe

 Definition: permanent flexion deformity of a toe at an interphalangeal joint

Stedman's Medical Dictionary

Interestingly enough, Webster and other American English dictionaries have one word as their preference, while medical dictionaries and text books use two words:

From an Orthopedic Text Book:  

- Anatomy and Discussion:
    - term describes abnormal flexion posture of PIP joint of one of lesser 4 toes;
    - the hammer toe deformity is similar to the curly toe deformity but is not malrotated;
    - flexion deformity of PIP may be fixed or supple;

Typing it as one word could be one of those instances where the word has just evolved from so many people typing it that way (like “alright”) and not officially a word in the dictionary.  

So, it really depends on how strict your MTSO/client is about perfect English.  If they allow slang, then you can leave it as one word, hammertoe.  If they are strictly “by the medical book,” then it would be two words, hammer toe.  

Just another opinion.

In my Stedeman's ortho words it is hammertoe, one word and that is the way I have always typed - orthogirl