The os trigonum is an accessory bone found in the posterior
foot. It is seen directly behind the
lateral tubercle of the body of the talus in 2.5% to 14% of people. It is a round, triangular, or oval shaped
bone that is variable in size, but is typically quite small compared to the
surrounding bones.
Os trigonum syndrome may be seen in people with the
anatomical variant, and presents as pain in the back of the ankle. This is due to impingement of the bone, and
the condition is sometimes referred to as a posterior impingement
syndrome. Pain may be reproduced when
the patient goes up on their toes, thus adding pressure to the posterior
ankle. This is particularly noticeable
in ballet dancers or in athletes that spend time on their toes.
Diagnosis of the condition is made largely on clinical
suspicion and presentation, and is confirmed with x-rays. The accessory bone may be seen on x-ray. In conditions where the bone is not seen on
x-ray, an MRI may be ordered to further assess the area. MRI may show a separation between the body of
the talus and the accessory bone, as well as any swelling in the area.
Conservative therapy such as rest, ice, and orthotics may be
beneficial to some, although surgical excision is usually necessary to relieve
the symptoms. The accessory bone may be
removed completely, in an attempt to relive pain and restore function. For the competitive athlete or ballet dancer,
this may mean a period of rest from activity while their surgical site heals.
Os trigonum syndrome should be differentiated from other
possible etiologies of pain, such as tendinitis of the flexor hallucis longus
tendon, which runs in close proximity to the os trigonum. Fractures and osteochondral defects of the
talus should also be ruled out, particularly in cases with a report of trauma
to the area. Space-occupying lesions
such as soft tissue tumors (usually benign in nature) should also be ruled out,
particularly when there is no evidence of accessory bone on plain film x-ray. The entire foot and ankle complex should be
thoroughly evaluated for an other sprains and strains that may be present.
Remember that pain is an indication that something is wrong,
and should never be considered “normal”.
Athletes are notorious for “playing through the pain”, but should be evaluated
by a foot and ankle surgeon for any acute or chronic pain that they may be
having.
Central Florida Foot & Ankle Center, LLC
101 6th Street N.W.
Winter Haven, FL 33881
Phone: 863-299-4551
www.FLFootandAnkle.com
