A true os trigonum is a secondary ossification center that has not fully fused with the talus and is connected by fibrous or cartilaginous tissue. (yellow arrow) Frequently it is incorrectly described as a fracture of Stieda’s process which is an enlargement of the posterior process of the talus which is the foot bone that makes up the ankle joint, along with the tibia and fibula bones. This accessory bone lies in the posterior or back part of the ankle.
It is estimated that this accessory bone or ossicle occurs in 7-9 percent of the population and by and large it is asymptomatic.
Injury can occur to this bone when the foot is forced into severe plantarflexion (where the foot is bent down and away from the body). This can occur in sports or in dance such as point in ballet. This injury can also occur in repetitive lesser traumatic plantarflexion of the foot. An example would be someone who climbs up and down flights of stairs carrying heavy weights such as furniture movers or delivery men.
As the foot is being forced into plantarflexion the posterior process of the talus (Steida's process) as well as the os trigonum (depending on the pathology) is pressed against one of the tendons running in the back of the ankle (flexor hallucis tendon) causing excessive pressure and further exacerbated by the pressure of the posterior part of the ankle, thus resulting in irritation of the Steida's process or the os trigonum.
When seen in the office the doctor will attempt to reproduce this motion by plantarflexing the foot. If in doing so the patient experiences pain, the doctor should be suspicious of an irritation of the os trigonum or perhaps a fractured posterior talus .
Standard x-rays should differentiate between a fractured talar process or os trigonum syndrome. Typically x-rays are taken of both feet for comparison. When a clear diagnosis is difficult, an MRI may be ordered for better clarity.
Symptoms of os trigonum syndrome include a deep pain in the back of the ankle aggravated mostly when the foot is plantarflexed (toes bending downwards). An example would be walking down steep stairs or performing point in ballet. There may also be swelling and tenderness in the back of the ankle. This condition may be mimicked by fracture of Steida's process, as described, as well as achilles tendonitis or ankle sprain.
Conservative care is the treatment of choice in these situations and there is a very high success rate of os trigonum syndrome.
Surgical intervention should be considered in those individuals who do not respond to conservative care or those who seem prone to constant recurrence. This extra bone or in the case of Steida's process is not needed for everyday function. The procedure is done as an out patient and requires removal of either the accessory bone or the removal of the broken Steida's process. The patient will have to wear a cast for another few weeks during the healing process. The major complication of this procedure is irritation to the sural nerve which is a sensory nerve that runs down the posterior lateral side of the ankle and down the lateral side of the foot. This may result in sensory loss on the lateral side of the ankle joint and foot which can lead to disability.
Want more information? CLICK HERE
I've been doing some aggressive research lately (it's how I found your incredible website) and realize now that my symptoms are not consistant with the diagnosis.
Michael D. Ebeling
Tampa, Florida 33624
Thanks for a most interesting website, which has helped a lot.
I usually do my research on the Mayo clinic website. I think your website is the most informative site I have found when researching foot pain.
I thank you for putting together this incredible website.
....I have been told that it is not hard enough to be cut off. Please help, I am not sure what to do now! THANKS FOR A WONDERFUL AND VERY HELPFUL SITE!
You have an unusually clear, informative and well-written website for laypersons. Thank you for that.
Mansfield Ctr, CT
First, I'd like to thank you for all the information that you provide on your website and the opportunity to write to you.
First, I want to let you know that you have the best web site I've found related to foot issues. (The only thing I had difficulty finding was the "ask a question" page.)
I received the orthotics Monday afternoon and began wearing them Tuesday. After two days I would say that I have noticed a huge improvement in the discomfort I have been experiencing. My foot feels better than it has in months.
I greatly admire someone like you who would donate and dedicate so much time and effort to helping strangers with no compensation. Truly, it is uncommonly kind. And your site is so intelligently arranged.
Pacific Grove, CA
I used to work for a podiatrist (front desk) back during summers in
college years ago, so I know the benefits of good care. Again, I want
to thank you for an EXCELLENT website. It was so great to get to your
site (top of google search) and actually find all the answers I needed
EASILY and QUICKLY! Clearly you put a ton of work into it and I really
All the best,
By the way, millions of websites could use yours as a guideline on how to organize information and make the site user-friendly. Kudos to you!
Thank you for your very interesting and informative site!
By Marc Mitnick DPM © 2006-2018, foot-pain-explained.com LLC
Solo Build It!