CASE 9166 Published on 15.05.2011
0

The migrated os peronaeum

Section

Musculoskeletal system

Case Type

Clinical Cases

Authors

Schubert R, Radiologie am Europa-Center, Berlin, Germany.

Connected authors
Patient

58 years, female

Categories
Area of Interest Extremities ; No Imaging Technique
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Clinical History
A 58-year-old lady was referred for imaging studies after suffering a pedestrian accident three weeks before. She had twisted her right foot with an audible snap, as she had slipped off the kerb.
Imaging Findings
X-rays of the right foot in two planes (Fig. 1) showed pronounced soft-tissue swelling at the lateral foot border, most prominently at the level of the calcaneocuboid joint. A proximally displaced os peroneum (OP) with an irregular distal contour was present. More distally, at the level of the cuboid notch, some tiny bone fragments appeared within the soft-tissue opacity, probably representing bony avulsions. Given the patient's history and the radiographic findings, peroneus longus tendon (PLT) injury was suspected, and an MRI of the right foot and ankle was performed, showing replacement of the normally dark tendon by diffuse T1- and T2-hyperintense signal, that extended from the retracted sesamoid down to the cuboid notch. The distance of the OP to the calcaneocuboid joint measured on sagittal MR images was about 12 mm (Fig. 2). Coronal T2-weighted images showed complete discontinuity of the PLT on several contiguous slices (Fig. 3).
Discussion
The os peroneum (OP) is a sesamoid bone of variable shape and size in the peroneus longus tendon (PLT). It is normally situated at the lateral calcaneocuboid joint, proximally to the plantar inflection of the tendon. In old-world monkeys, the OP is a regular bone of the foot, articulating with a facet of the cuboid, whereas in humans, it has undergone regression with the loss of hallux opposability [1]. Its prevalence has been reported between 4.7 and 30% [2, 3]. The OP may rarely be affected by, or associated with, acute traumatic or chronic attrition injuries of the PLT, especially with inversion stress in a cavovarus foot [4]. However, the mere presence of an OP apparently does not predispose to degenerative disease [3]. PLT tears are injuries, that are commonly overlooked, and the final diagnosis may be delayed up to several months or even years [5]. Complete tears are more likely to occur in the distal PLT segment at the cuboid notch [6]. Foot mechanics may be seriously impaired by these ruptures. However, asymptomatic cases have also been described [7]. PLT ruptures typically present either as a fracture through the OP with diastasis of the fragments or as posterior dislocation of the whole OP [8]. Radiographic measurements of fragment separation and displacement relative to the calcaneocuboid joint have been carried out by Brigido and co-workers. Accordingly, a gap between fragments of 6 mm or more or proximal OP displacement of 10 mm or more are indicative of a full-thickness tear of the PLT [9].
MRI is very accurate in predicting partial or complete PLT tears, especially if oblique coronal T2-weighted images, perpendicular to the tendon course, are included [6, 10]. Although comparative studies with ultrasound are lacking, MRI is probably the imaging method of choice to secure a suspected PLT rupture or to detect alternative causes of lateral foot pain, not only in the setting of acute trauma.
Differential Diagnosis List
Complete peroneus longus tendon rupture
Os peroneum stress fracture
Bipartite os peroneum
Proximal PLT rupture (mostly split tears)
Peroneus longus tendinosis
Calcaneocuboid joint injury
Final Diagnosis
Complete peroneus longus tendon rupture
Case information
URL: https://www.eurorad.org/case/9166
DOI: 10.1594/EURORAD/CASE.9166
ISSN: 1563-4086
Figure 1

Plain radiographs of the right foot

Plain radiographs of the right foot
Dorsoplantar view. Marked soft-tissue swelling over the calceneocuboid joint region down to the 5th metatarsal base (arrowheads). Accessory bone lateral to the calcaneus (arrow).
Plain radiographs of the right foot
Lateral oblique view. The os peroneum (arrow) is displaced proximally. Some tiny bone islands are seen in the soft tissue near the cuboid (arrowhead).
Figure 2

Sagittal and transverse MR images

Sagittal and transverse MR images
Three contiguous sagittal STIR images showing the proximal (arrow) and distal (arrowheads) ends of a ruptured PLT. The gap between them is filled with hyperintense fluid signal (*).
Sagittal and transverse MR images
Two contiguous sagittal and a transverse T1-weighted image showing the position of the proximal end of the PLT with an adherent os peroneum (arrow) near the peroneal tubercle of the calcaneus.
Figure 3

Coronal T2 FSE

Coronal T2 FSE
3 mm slices from the peroneal tubercle to the metatarsus. Absence of the dark tendon signal on 3 contiguous slices distal to the OP (PLT encircled). The brevis tendon (above) can be followed through.