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Painful Os Peroneum Syndrome (POPS) occurs when an accessory ossicle located within the peroneus longus tendon becomes symptomatic. While there are many accessory bones of the foot, not all of them are clinically significant. However, the os peroneum can become symptomatic due to a variety of conditions, often presenting as lateral midfoot pain. Its rarity and the lack of clinical suspicion by practitioners make it easy to overlook during diagnosis. POPS is a rare clinically entity who’s epidemiology is limited to a series of case reports
Illustration of os peroneum and location of pain when symptomatic.
POPS can be involved in various pathological conditions, including acute or stress fractures, diastasis, tenosynovitis, multipartite formation, or rupture of the peroneus longus tendon. Rupture may occur due to a strong contraction of the muscle combined with sudden inversion or supination of the foot. The presence of the Os Peroneum is thought to predispose individuals to tendon rupture, likely due to increased friction with adjacent structures.
Acute os peroneum fracture from trauma.
Acute POPS typically occurs due to trauma, such as an ankle sprain or supination injury, leading to a fracture of the ossicle. It may or may not be associated with a rupture of the peroneus longus tendon. Chronic POPS, on the other hand, is linked to the healing of a fracture, often accompanied by calcification, remodeling, or diastasis. This chronic condition can result in tenosynovitis of the peroneus longus tendon.
The Os Peroneum is located on the lateral aspect of the cuboid, near the cubital tunnel and the calcaneocuboid joint, and is embedded within the peroneus longus tendon. While it is present in a cartilaginous form in everyone, it ossifies in up to 26% of the population and is best visualized on oblique radiographs of the foot. The peroneus longus muscle originates from the fibula and intermuscular septa, inserting on the medial cuneiform and the plantar aspect of the fifth metatarsal. Its primary actions are plantarflexion and eversion of the foot.
Location of pain and tenderness of Os Peroneum
Patients with Os Peroneum-related issues often present with a history of lateral midfoot pain that worsens with weight-bearing activities. On physical examination, swelling may be observed over the cuboid, accompanied by tenderness to palpation of the ossicle. Pain can also be provoked by movements such as plantarflexion and inversion of the foot.
Radiographs of the foot are the initial imaging modality of choice and can easily identify os peroneum. This is best seen on the oblique view. Common findings include displacement, fractures, diastasis, or a bipartite sesamoid. Displacement of the Os Peroneum can serve as an indirect indicator of a tendon rupture. Differentiating between a fracture and a bipartite Os Peroneum can be challenging, as acute fractures typically show nonsclerotic margins, with the bony fragments appearing to “fit together.”
On MRI, Os Peroneum is typically iso-intense to bone marrow and is most often located near the cuboid. Clinically, it presents with increased intrasubstance signal within the peroneus longus tendon. On ultrasound, it is easily identified due to its characteristic hypoechoic appearance, appearing as a curved echogenic focus with posterior acoustic shadow, and is readily found within the peroneus longus tendon. CT imaging can reveal displacement, fractures, diastasis, or a bipartite sesamoid, with displacement potentially serving as an indirect indicator of tendon rupture.
Nonoperative management is the first-line therapy for most cases of POPS. Treatment includes immobilization in a tall walking boot, the use of NSAIDs, initiation of physical therapy, and discontinuation of aggravating activities. Additional options may include corticosteroid injections or the use of shoe insoles to address pes planus. Emerging treatments, such as shockwave therapy, have also been reported in case studies. Surgical intervention is reserved for cases where conservative management fails. Operative techniques typically involve excision of the ossicle and repair of the peroneus longus tendon.
There are no guidelines for rehabilitation, although any program should target the peroneal tendons. There are no return to work or play guidelines. Prognosis is unknown and complications include chronic pain.
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