Accessory ossicles are common in the foot and ankle, and 24 types of accessory ossicles have been reported in the literature . These ossicles are usually asymptomatic and incidentally detected on radiographs. Nevertheless, they could be clinically relevant, especially in trauma, where they can be painful by themselves or simulate a fracture. Knowledge of the anatomy and presentation of these accessory ossicles might therefore be useful for physicians caring for injured patients.
The CS is an accessory ossicle of the anterior facet of the calcaneus, located between the anteromedial aspect of the calcaneus, the proximal aspect of the cuboid and navicular, and the head of the talus . CS is seen in up to 5% of the population [1, 2]. CS is derived from the failure of union of secondary ossification centers and, like other accessory ossicles, it is generally bridged to the calcaneus by poorly mobile synchondrosis but can also be completely independent. The size of this ossicle is generally reported to be 3–4 mm in diameter . One of the largest symptomatic CS was described in a 51-year-old man at 22 mm long and 16 mm high . To our knowledge, the CS described in our case was the largest published so far (35 mm long, 30 mm high, 25 mm width). A sufficient size could cause deformity and/or limitations in the range of motion .
To date, only a few cases of symptomatic CS have been published, mostly in the setting of chronic ankle pain [4,5,6,7]. To our knowledge, no such presentation of an acutely injured large CS has been reported. The diagnosis of symptomatic CS can be challenging for emergency physicians because this accessory bone can easily be mistaken for a fracture of the anterior process or the tuberosity of the calcaneus [3, 4]. Moreover, it has to be differentiated from other accessory ossicles, such as a calcaneus accessorius, cuboideum secundarium, and os sustentaculi . Indeed, the management of a painful CS is very distinct from the treatment of a calcaneus fracture, therefore requiring a well-adapted imaging strategy .
CS can sometimes be diagnosed on a lateral oblique view radiograph showing sclerotic and irregular margins of the calcaneus and cuboid adjacent to the bony fragment, suggestive of a chronic lesion . Frequently, however, both physical examination and conventional radiographs are unable to differentiate a CS from a fracture, especially for emergency physicians not familiar with this presentation. Cross-sectional imaging, such as CT and MRI, is sometimes needed to distinguish CS from a fracture and to understand its clinical relevance. CT scans can confirm the diagnosis of an accessory bone by showing synchondrosis as smoothly and sharply margined well-corticated bones [4, 12]. MRI will confirm the diagnosis of synchondrosis and reveal its recent injury by showing diffuse edema [5, 7, 10].
No consensus exists on the management of an injured CS. Surgical excision of the ossicle is indicated if the symptoms do not resolve with conservative treatment or if the range of motion of the subtalar joint is limited [6,7,8]. Kraft et al. revealed the case of an injured CS in a 51-year-old man treated with an infiltration of steroids and local anesthetic keeping pain free for 1 month. However, the return of symptoms within several weeks requires surgical excision . Furthermore, the case of a 54-year-old woman presenting a symptomatic injured CS that was initially conservatively managed has been reported. However, successful endoscopic resection was performed because she complained of persistent ankle pain . We think that conservative treatment should be proposed, as shown in our case. Ersen et al. described the success of symptomatic therapy (nonsteroidal anti-inflammatory drugs and mobilization after 1 month) . To our knowledge, there are no data in the literature regarding a rehabilitation protocol for symptomatic injured CS. The originality of this case lies in the precise description of a protocol for a conservative approach that has successfully supported a professional soccer player. This example could help clinicians in cases of painful injured CS by adapting the protocol to the pain and patient’s activity.
CS is a frequent cause of chronic ankle pain. However, the diagnosis of a painful injured CS can be considered in cases of acute ankle trauma in which a fracture of the anterior facet of the calcaneus is suspected. If the fracture seems atypical, with, for instance, an excessively large bone fragment or with corticalized borders, CT or MRI seems to be required to first distinguish synchondrosis from fracture and second to assess the acute component of the injury. Conservative treatment is recommended with a rehabilitation protocol based on physiotherapy, tecar therapy and gradual activity. Endoscopic resection should only be proposed in cases where this treatment fails.