Orthopedic Coding Alert

Question: What is os trigonum syndrome and which ICD-10-CM code should I report for this condition?

California Subscriber

Answer: You should report ICD-10-CM code Q74.2 (Other congenital malformations of lower limb(s), including pelvic girdle) for os trigonum syndrome.

Posterior ankle impingement syndrome (PAIS) is a term used to describe a musculoskeletal disorder created from the repeated abutment of the posterior process of the talus or os trigonum between the tibia and calcaneus during plantar flexion of the ankle. When the os trigonum is the cause, it is described as os trigonum syndrome. Podiatrists might refer to this condition as os trigonum syndrome, talar compression syndrome, PAIS, or posterior tibiotalar impingement syndrome (PTTIS).

The os trigonum is an extra (accessory) bone that lies behind the ankle joint that exists when one area of bone does not fuse with the rest of the talus (ankle bone) during growth. The os trigonum varies in size, and it is attached to the posterior aspect of the talus by a fibrous band of tissue.