![]() Ĭomputed tomography (CT) and magnetic resonance imaging (MRI) are able to detect the associated bone and soft tissue abnormalities. The posterior impingement view has been shown to be more sensitive than the lateral view in the detection of an os trigonum. Radiographs can detect the presence of an os trigonum however, their sensitivity is limited in the assessment of early bone changes occurring with the development of pathology. The os trigonum syndrome constitutes a subtype of posterior ankle impingement syndrome. Symptoms of os trigonum syndrome may result from all the situations mentioned above and consist of chronic or recurrent pain with stiffness, soft tissue swelling and tenderness to palpation in the postero-lateral aspect. In these cases of repetitive trauma, there can be involvement of the soft tissues, which results in irritation manifested as local synovitis, flexor hallucis longus (FHL) tenosynovitis or entrapment. Repetitive plantar flexion is a continuous requirement in activities such as ballet, basketball or soccer. Ī single traumatic episode of forced plantar flexion or repetitive forced plantar flexion may result in degeneration or tear of the synchondrosis (Fig. Os trigoni may have a round, oval or triangular morphology. The os trigonum is normally an incidental finding, with no associated pathology. It is connected to the lateral tubercle of the posterior process of the talus by a fibrocartilaginous synchondrosis and in close vicinity to the flexor hallucis longus tendon. Currently, this is viewed as a developmental skeletal variation, likely resulting from failure of fusion of a secondary lateral tubercle ossification centre that forms at about 7–13 years of age, and normally fuses at about 14 years of age. Initially, this was interpreted as a non-united fracture. ![]() Its prevalence is estimated in between 1 and 25%. The os trigonum is one of the most common accessory ossicles in the ankle and foot. Our aim with this review is to illustrate the imaging findings related to the presence of accessory ossicles and muscles in the ankle and hindfoot through different techniques, with special attention to those variants that associate factors of clinical relevance or, in the case of the ossicles, that would pose a challenge in the differential with fractures.īone coalitions, given their complexity and frequent clinical implications, deserve separate analysis and will not be the object of this review. Occasionally, they will manifest clinically, presenting as mass lesions or causing compression syndromes such as tarsal tunnel syndrome, chronic pain or impingement. Īccessory muscles are also generally asymptomatic and discovered incidentally on imaging studies. With respect to accessory sesamoid bones, the os peroneum is the most frequently found. The most common accessory ossicles in the ankle and foot are the os trigonum, the accessory navicular (among the different three types, type II is the most common) and the os intermetatarseum, in this order. They functionally represent components of a gliding mechanism and are at least partially embedded in tendons, reducing friction and protecting the tendon structure. ![]() Sesamoid bones have a different anatomical nature. They are seen as subdivisions of existing bones or free elements in the vicinity of the normal bone structures. Īccessory ossicles in most cases are a result of unfused ossification centres. Most of them represent developmental abnormalities that constitute incidental radiographic findings. These include accessory ossicles, additional sesamoid bones, variations in number and configuration of sesamoid bones, coalitions, bipartitions and variants in the soft tissues, such as accessory muscles. A number of anatomical variations can be found in the ankle and hindfoot.
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