Introduction
The accessory bones of the foot have been reported by several authors. However, os intermetatarseum is less common than os tibiale externum, os trigonum and os perineum. Gruber et al. [5] first described os intermetatarseum in 1877. The condition is usually asymptomatic.
In 1980, Reichmister [12] reported three cases of painful os intermetatarseum. Compression of the deep peroneal nerve by the os intermetatarseum was described as the pain generator. Naguchi et al. reported a case of painful os intermetatarseum occurring in a soccer player [10]. They suggested that repeated impact on the instep when kicking led to deep peroneal nerve injury above the os intermetatarseum. The current literature regarding this painful condition is reviewed here.
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Epidemiology
The os intermetatarseum is a relatively uncommon accessory bone of the foot, usually found between the base of the first and second metatarsal bones. Gruber first described it in 1877 [5]. The incidence of os intermetatarseum ranges from 1.2 to 14% [2, 3, 11, 14]. Pfitzer et al. [11] documented a 12.5% incidence of it in his report of 520 cadaver dissections. Burman et al. [2] reported 3.3% incidence in a review of 1,000 roentgenograms of the foot. The os intermetatarseum often begins as a separate ossification centre and it may be found at age 2 in females and at age 3 in males. Familial tendencies have been recorded. Most os intermetatarsea are asymptomatic. In the literature, a total of six cases of painful os intermetatarsea have been reported. In 1978, Scarlet et al. [13] reported a case of painful os intermetatarseum. Reichmister [12] described three cases of painful os intermetatarseum.
Clinical presentation
The onset is frequently related to local trauma. Clinically the patients complained of pain and paresthesia with numbness radiating from the dorsum of the foot to the hallux and second toe, increasing with plantar flexion. Tight shoes, ankle instability and cavus feet also aggravated the symptoms. A positive Tinel-like sign was elicited and paresthesia was observed distal to the compression site. There was also weakness of hallux extension. These symptoms are consistent with those of anterior tarsal tunnel syndrome, which is characterized by compression of the deep peroneal nerve by the inferior extensor retinaculum [7‐9].
Diagnostic testing
Standard anteroposterior, lateral and oblique radiographs of the foot should be taken to identify the os intermetatarseum. A CT scan, bone scintigraphy or MRI are useful in accurately determining certain characteristics such as the position, shape and size of a painful os intermetatarseum. Extostosis and calcification in the digital vessels should be ruled out.
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Treatment
The patient should be treated first with conservative treatments including shoe wear modifications, prohibiting participation in sport-activities, nonsteroidal anti-inflammatory drugs (NSAIDs) and local steroid injections. However, in many cases conservative treatments are ineffective. Failure to relieve the patient’s symptoms conservatively could indicate the need for surgical treatment.
In previous reports, all patients except one were surgically treated by excision of the os intermetatarseum [6, 10, 12, 13]. One patient who declined the surgical treatment was not followed up in Reichmister’ s report [12]. With all the cases treated surgically, surgical exploration revealed that the branch of the deep peroneal nerve was located on the os intermetatarseum and compressed by it. Therefore, surgical excision of the os intermetatarseum and nerve decompression relieved the symptoms. All the patients with the painful os intermetatarseum, did not complain of any postoperative symptoms and could return to their employment and sports activity after the excision of the os intermetatarseum.
Pathology
Noguchi et al. [10] reported a case of a painful os intermetatarseum in a soccer player and suspected that the branch of the deep peroneal on the os intermetatarseum was compressed when the patient kicked a soccer ball. Dellon [4] reported the anatomic site of entrapment of the deep peroneal nerve over the dorsum of foot. They documented that anatomic “tightness” of the area where the deep peroneal nerve passes between the extensor hallucis brevis tendon and the first and the second cuneiforms. Any direct injury such as direct contusion to this area or footwear that places a band directly across the bony prominence would increase the pressure within this small space.
Borges et al. [1] described that the deep peroneal nerve was placed under maximum stretch with the foot plantar flexed and toes dorsiflexed. Athletes with an os intermetatarseum may suffer symptoms when combined with these foot and toe positions.
Conclusion
In conclusion, a painful os intermetatarseum should be considered as the cause of dorsal foot pain in athletes. Surgical excision of the os intermetatarseum can be indicated for those patients if conservative treatments fail to reduce their symptoms.
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