Clinical History
A 38-year old patient is referred for chronic pain in lateral plantar region of the right foot.
Complaints started after running.
Imaging Findings
Fig. 1: Reformatted proton density weighted fat saturated MRI image. Striped arrow: os peroneum incorporated in the peroneal tendon. White arrow: hyperintense signal intensity localized in the peroneal tendon at the level of the os peroneum.
Discussion
Painful os peroneum syndrome (POPS) is a condition usually characterized by acute fracture of the sesamoid os peroneum (or diastasis of a multipartite os peroneum), chronic partial tendon rupture, tendon chronic entrapment or even prominent calcaneal tubercle. [1] POPS is a relatively new recognized entity and still an underdiagnosed condition. Operative treatment can be performed when conservative therapy fails and pain persists. A peroneal disorder needs to be documented very excessively before an operation can safely be performed. The procedure usually consists of tendon debridement, tenosynovectomy and excision of the os peroneum (combined with removal of the hypertrophied peroneal tubercle, if present). Delayed diagnosis may lead to sequels, such as inflammation of the peroneus longus tendon, ankle instability, and peroneal compartment syndrome.
If plain radiography shows unusual accessory bony variation, US or MRI can make the differential diagnosis, and guide further therapeutic management. Radiographic differentiation between fractured os peroneum and multipartite os peroneum can be troublesome. Fracture margins appear relatively nonsclerotic in acute presentations and the bone fragments resemble fitting “pieces of puzzle”, whereas finding rounded, smooth, sclerotic borders are suggestive of multipartite os peroneum. [2] It is conceivable that remodelling of fracture fragments could give the appearance of a multipartite os peroneum. Displacement of an os peroneum fragment can be helpful in the differential diagnosis. The distracted proximal fragment in case of a fracture may be located several centimetres proximal to the calcaneocuboid joint. Assessing this displacement pattern can be useful in differentiating between an os peroneum fracture and normal distraction in multipartite os peroneum. Pain or discomfort when applying direct ultrasound transducer pressure, combined with a large gap (6 mm or more is highly suggestive for POPS) between sesamoid particles with irregular margins requires further exploration.[2] When distance is less, like our patient exhibits (2mm), chronic impingement or a healing fracture is more likely.
Sonographic diagnostic accuracy can be elevated by the presence of associated peroneus longus tendon abnormality. Posterior acoustic shadowing is only present in larger bone fragments. MRI can be helpful when mid-foot peroneus longus tendon tear is suspected. Findings on fluid-sensitive sequences like STIR or PD-fat-saturation, include tears portrayed by a risen signal-intensity, near the site of the tear, and morphologic tendon abnormalities. Other secondary findings such as hypertrophic peroneal tubercle, bone marrow oedema of the tubercle, lateral calcaneal wall or cuboid bone can occasionally be identified. [2] Our patient was treated conservatively and recuperated well.
Differential Diagnosis List
Painful os peroneum syndrome (POPS)
Fractured os peroneum
Multipartite os peroneum
Final Diagnosis
Painful os peroneum syndrome (POPS)
