In the foot and ankle, up to forty accessory bones have been described. Most people have at least one of these accessory bones. An accessory bone is a bone that you’re born with, and it may not have any specific function but from time to time it can cause pain and one of the most common accessory bones is the os trigonum. It is thought that 15% to 30% of people may have the presence of an os trigonum.
The os trigonum is located behind the ankle joint next to the talus bone which is referred to as the ankle bone. The os trigonum may be connected to the talus by a fibrous band. When an injury occurs to this area, it is thought the fibrous band might be damaged and therefore allow for more motion of the os trigonum behind the ankle joint and this may cause pain. The pain is located behind the ankle and deep to the Achilles tendon.
The os trigonum lies next to the subtalar joint which is the joint in your foot that works like a universal joint on a car. Therefore, when motion takes place in the foot and ankle which requires a lot of side-to-side motion which is referred to as supination and pronation, it is thought to irritate the os trigonum.
Other terms that are used to describe os trigonum syndrome include talar compression syndrome, posterior tibial talar impingement syndrome, nutcracker type impingement (referred to as nutcracker injury) because the os trigonum gets inched behind the ankle joint when your toes go down, posterior ankle impingement syndrome, and hindfoot impingement syndrome.
Causes of Os Trigonum
Causes can include the following:
Ankle sprains
may inflame the os trigonum bone and may start more consistent chronic pain in this area.
Activities that demand extreme ankle joint motion.
People that are susceptible are people doing ballet, soccer players and football players as their activities might demand the foot to be placed in a downward motion which can irritate the os trigonum behind the ankle joint and they can develop os trigonum pain.
Overuse injuries.
There may be times that there is no direct correlation to an activity or sport, but the bone just gets to be irritated for no specific reason.
Signs and Symptoms of Os Trigonum
Typically, the pain will be a deep, dull pain behind the ankle joint and it seems to be worse when the foot is pointed downwards or pointing your toes. This occurs because the os trigonum may get pinched between the heel bone in the leg bone, the tibia, when the foot is pointed downward to its full range of motion.
Evaluation and Diagnosis of Os Trigonum
When seeing a foot specialist, the suspicion of an os trigonum syndrome is generated by the symptoms that the patient communicates. They will point to an area behind the ankle joint and specifically when they point their foot downwards, it hurts in that area. The doctor will examine the area and press behind the ankles to see if there is pain that is present.
Another test that is frequently done is when the ankle is placed in a very downward position, the doctor might move the big toe up and down and this will also elicit more pain behind the ankle because the flexor tendon that pulls the great toe down is in close proximity to the os trigonum bone on the back of your ankle. X-rays will also be needed to evaluate and seldom is an MRI or CAT scan ordered. If the doctor is suspicious of a fractured os trigonum then an MRI may be useful.
On x-ray view, the os trigonum might appear as the rest of the bone that forms the ankle joint the talus, which is also referred to as ankle bone, when in fact the os trigonum is usually not connected to the talus bone.
Treatment of Os Trigonum Syndrome
Treatment can include the following:
– When the symptoms are acute and of short duration, simple measures such as resting, using nonsteroidal and anti-inflammatories, icing, and potentially immobilizing the area for a week or two in a CAM walker may be useful to get rid of pain and inflammation.
– For more chronic and severe os trigonum symptoms, the following treatments may be offered.
o Orthotics
Orthotics are frequently used because they reduce the pronation and supination on the rearfoot meaning the side-to-side motion that occurs and because the os trigonum is adjacent to the joint where this happens (subtalar joint), it is thought this will irritate the os trigonum bone.
o Cortisone Injections
A series of two and possible three cortisone injections in this area may also benefit.
o Surgical Removal
Rarely is it necessary for surgical removal but when all conservative treatments have failed and if symptoms are significant, surgical results tend to be good.
Early diagnosis and treatment can lead to faster recovery from a painful trigonum. Generally speaking, the prognosis for those suffering from os trigonum pain is generally good.