Beware the hallucal interphalangeal joint sesamoid in first metatarsophalangeal joint arthrodesis

Symptomatic Accessory Ossicles of the Foot and Ankle

Accessory ossicles are small noncalcified, calcified or ossified structures found throughout the body, often noted as incidental findings. Specifically in the foot and ankle, there are at least 24 different ossicles described the majority of which are incidental. However, there are accessory ossicles that can be symptomatic, leading to significant pain and discomfort. While many of the symptomatic ossicles have been described in the literature, there are several that are under-recognized or under-reported for example, os interphalangeus and os calcaneus secundarius syndromes. This manuscript will review common and uncommon accessory ossicles including painful os peroneum, os naviculare, os calcaneus secundarius, os trigonum and os interphalangeus syndromes as well as medial sesamoiditis, with attention to the clinical and imaging findings and with an outline of the current management.

Diagnosis, imaging, and potential morbidities of the hallux interphalangeal joint os interphalangeus

Hallux pain is a common entity with a differential diagnoses including hallux valgus, hallux limitus/rigidus, and gout and specifically at the interphalangeal joint (IPJ), flexor hallucis longus (FHL) tenosynovitis, and joint arthrosis. An under-recognized source of pain is the os interphalangeus, an ossicle typically located at the plantar aspect of the hallucal interphalangeal joint. This ossicle is radiographically visible in its ossified form in 2-13% of individuals, but can also be present as an ossified or non-ossified nodule in patients. The os interphalangeus may be centrally or eccentrically located, and although originally believed to be a sesamoid bone in the FHL tendon, it is an ossicle located in the joint capsule of the IPJ and separated from the tendon by a bursa. When the ossicle is absent, the bursa is also absent and the tendon is attached to the joint capsule. Infrequently, the os may be located eccentrically under the first IPJ and reflect persistence of one of the distal phalanx. Rarely, the os interphalangeus may be dorsal to the IPJ. The os interphalangeus is best evaluated on radiographs, ultrasound, and MRI. Pain is a result of altered mechanics with arthrosis or frictional effects with bursitis, tenosynovitis, or intractable plantar keratosis (IPK). The ossicle may also displace into a dislocated IPJ, preventing reduction. The os interphalangeus may be centrally or eccentrically located, and although originally believed to be a sesamoid bone. This has been found within the plantar joint capsule of the distal hallucal interphalangeal joint and separated from the tendon by a bursa. Uncommonly, the location may be plantar eccentric and reflect persistence of one of the ossification centers of the distal phalanx. Although the ossicle can be imaged with standard AP and lateral radiographs in many cases, in those cases of unexplained pain with no radiographically visible ossicle, and the presence of friction blisters, intractable plantar keratosis (IPK), hyper-extension of the IPJ, hallux limitus/rigidus, or metatarsophalangeal joint (MTPJ) arthrodesis, an MRI or CT should be considered to identify a non-ossified fibrocartilaginous node. This is of particular concern in a patient with a history of underling diabetes mellitus or other metabolic disorders associated with diminished pedal sensation where neurotrophic changes place them most at risk for complications associated with excessive plantar pressure. Pain is a result of altered biomechanics with arthrosis, or frictional effects causing bursitis, tenosynovitis, or IPK. The ossicle may also displace into a dislocated IPJ, preventing reduction. In this article, we will describe the anatomy and imaging appearance of the common os interphalangeus variants and associated complications including frictional effects, arthrosis, and IPK and discuss conservative and surgical management of a symptomatic ossicle.

The hallucal interphalangeal ossicle: anatomy and basis for ultrasound-guided surgical shaving

Painful lesions on the plantar aspect of the first interphalangeal joint (IPJ) of the hallux can be attributed to structures called ossicles, nodules, or sesamoids. The aims of the present study were first to verify that ultrasonography (US) is a high-sensitivity tool for diagnosing an interphalangeal ossicle (IO), and second to prove that US-guided-shaving surgery ("milling") is a safe and feasible technique for remodeling the IO. The study is divided into three parts. In the first part, the prevalence of IOs was estimated in 12 cadaver feet using US, anatomical dissection, and fluoroscopy. In the second, a detailed US and morphological description of the IO was obtained. In the third, six cadaver feet were subjected to surgical milling. IO prevalence was 41.6% in gross anatomy, 41.6% in US examination and just 16.6% in fluoroscopy. The ossicles had a mean length of 4 mm (± 2 mm) and a width of 7 mm (± 2 mm). The ossicles could be completely shaved in all specimens without injuring important anatomical structures. Our results indicate that US is a more precise tool for diagnosing an IO than X-ray. Moreover, our US-guided mini-invasive surgical technique appears feasible and safe.

Concomitant Dislocation of the Hallucal Interphalangeal Joint and Extra-Articular Dislocation of Its Sesamoid: A Case Report

CASE

A 22-year-old man sustained closed dislocation of the hallucal interphalangeal joint (HIPJ). Painful limitation of movements persisted 2 months after closed reduction. Magnetic resonance imaging revealed dislocation of the hallucal interphalangeal joint sesamoid (HIPJS) from its intra-articular attachment on the superior surface of the plantar plate to an extra-articular subcutaneous location, plantar and lateral to the flexor hallucis longus tendon. The HIPJS was enucleated through a plantar approach, and the foot remains pain-free 18 months later.

CONCLUSIONS

This case represents an unusual combination of HIPJ dislocation and extra-articular dislocation of its sesamoid. Raised awareness of the HIPJS, its normal anatomical location, and configuration will avoid delayed diagnosis.