Os Peroneum & Os Vesalianum
- The OS PERONEUM is a sesamoid bone within the peroneus longus tendon where the tendon turns around the cuboid; it is often an incidental, asymptomatic finding (sometimes bipartite/multipartite), but it can be the seat of the PAINFUL OS PERONEUM SYNDROME (POPS), a spectrum of disorders causing lateral and plantar-lateral foot pain.
- POPS has an ACUTE form - typically after a supination/inversion injury that fractures the os peroneum or ruptures the peroneus longus tendon - and a CHRONIC form from recurrent injury or healing with calcific remodelling, producing peroneus longus tenosynovitis/tendinopathy and a risk of subsequent tendon rupture; according to PubMed, simple acute cases can settle with a short course of a non-steroidal anti-inflammatory and rest.
- A KEY EXAM POINT: on radiographs, marked DISPLACEMENT or DIASTASIS of the os peroneum (or wide separation of a fractured/partitioned os, including proximal retraction above the level of the ankle) is used as an imaging SURROGATE for a complete PERONEUS LONGUS TEAR; MRI is needed to characterise the tendon, and the assumption of a complete tear from a retracted os is not absolute - some have only a partial tear.
- The OS VESALIANUM is a rare accessory ossicle at the BASE of the FIFTH METATARSAL, lying within or adjacent to the peroneus brevis insertion; the crucial distinction is from a fifth-metatarsal base AVULSION FRACTURE - the ossicle has smooth, corticated, rounded margins, sits proximal to the metatarsal base, is often bilateral, and the fracture line of an avulsion is sharp and non-corticated (comparison views of the other foot help).
- Other named accessory ossicles of the foot have their own considerations: the OS TRIGONUM (posterior talus, posterior ankle impingement) and the ACCESSORY NAVICULAR (medial navicular, posterior tibial tendon dysfunction) are covered on their own pages - the unifying principle is that an accessory ossicle is usually incidental and only relevant when it is SYMPTOMATIC and corresponds to the site of pain.
- MANAGEMENT of a painful accessory ossicle is NON-OPERATIVE first - activity modification, a period of immobilisation/orthoses, non-steroidal anti-inflammatories and physiotherapy - with SURGERY (excision of the ossicle, debridement or repair/reconstruction of the involved tendon, e.g. peroneus longus to brevis tenodesis where the longus is irreparable) reserved for refractory symptoms or an established tendon rupture; the decision is driven by symptoms and the tendon, not the incidental radiographic finding.
- “Os peroneum = sesamoid IN the peroneus longus at the cuboid; painful os peroneum syndrome (POPS) = lateral/plantar-lateral foot pain (acute # / PL rupture vs chronic tenosynovitis).
- “DISPLACED/DIASTATIC os peroneum (esp. proximally retracted) = surrogate for a PERONEUS LONGUS TEAR - get MRI to characterise the tendon.
- “Os vesalianum (5th-MT base, peroneus brevis) - distinguish from an AVULSION FRACTURE: smooth corticated rounded margins, often bilateral on comparison views, vs a sharp non-corticated fracture line.
Marked displacement/diastasis (especially proximal retraction) of the os peroneum is a surrogate for a peroneus longus rupture - get MRI to characterise the tendon. Do not dismiss it as 'just an ossicle'.
At the fifth-metatarsal base, a smooth, corticated, rounded ossicle (often bilateral) is an os vesalianum, not an avulsion fracture (sharp, non-corticated line). Comparison views help.
Os Peroneum & Painful Os Peroneum Syndrome (POPS)
The os peroneum is a sesamoid bone within the peroneus longus tendon where the tendon turns around the cuboid to cross the sole. It is frequently an incidental, asymptomatic finding (and may be bipartite or multipartite). The painful os peroneum syndrome (POPS) is a spectrum of disorders producing lateral and plantar-lateral foot pain centred on the cuboid. The acute form follows trauma - classically a supination/inversion injury that fractures the os peroneum or ruptures the peroneus longus tendon; the chronic form arises from recurrent injury or healing with calcific remodelling, with peroneus longus tenosynovitis/tendinopathy and a risk of later tendon rupture. Simple acute presentations may settle with a short course of a non-steroidal anti-inflammatory and rest.
On radiographs, marked displacement or diastasis of the os peroneum (or wide separation of a fractured/partitioned os, including proximal retraction of a fragment above the level of the ankle) is used as an imaging surrogate for a complete peroneus longus tendon tear. MRI characterises the tendon and surrounding soft tissue. The relationship is not absolute - a retracted proximal moiety can occur with only a partial peroneus longus tear (the os occupies part of the tendon's cross-section and the eccentric intact fibres remain in continuity) - so MRI provides the full description rather than the radiograph alone.
Os Vesalianum vs Fifth-Metatarsal Base Avulsion
| Feature | Os vesalianum (accessory ossicle) | Avulsion fracture (zone 1) |
|---|---|---|
| Margins | Smooth, corticated, rounded | Sharp, non-corticated fracture line |
| Location | Proximal to the 5th-MT base (in peroneus brevis) | At the 5th-MT tuberosity/base |
| Bilaterality | Often bilateral (comparison views help) | Unilateral, follows the injury |
| Mechanism | Developmental (incidental); pain if symptomatic | Inversion injury - acute pain/tenderness |
| Clue | No acute injury / chronic/incidental | Acute injury with focal bony tenderness |
A rounded, corticated ossicle at the fifth-metatarsal base - especially if bilateral and without an acute injury - is an os vesalianum, not an avulsion fracture. Conversely, do not dismiss a genuine zone 1 avulsion as an ossicle. The os vesalianum is usually asymptomatic and incidental; treat it only when it is the clear source of symptoms, and then non-operatively first.
Management Principles
- Non-operative first: activity modification, a period of immobilisation and/or orthoses, non-steroidal anti-inflammatories and physiotherapy - most symptomatic ossicles settle.
- Image to define the tendon: for POPS, a displaced/diastatic os peroneum should prompt MRI to define the peroneus longus (intact, partial tear, complete rupture).
- Surgery for refractory pain or tendon rupture: excision of the symptomatic ossicle, with debridement or repair/reconstruction of the involved tendon - where the peroneus longus is irreparable, a peroneus longus to brevis tenodesis restores eversion.
- Decide on symptoms and the tendon - an incidental, smooth, corticated ossicle that does not match the site of pain needs no treatment.
The clinically important lesson of the painful os peroneum syndrome is that a displaced or diastatic os peroneum on a radiograph is not simply an incidental ossicle - it can be the only clue to a peroneus longus tendon tear, which alters management (immobilisation/repair rather than reassurance) and, if missed, leaves a weak eversion and ongoing lateral-foot pain. Whenever the os peroneum is displaced, fragmented, or proximally retracted, obtain an MRI to characterise the tendon before deciding treatment. Equally, at the fifth-metatarsal base, do not mislabel an acute zone 1 avulsion fracture as an os vesalianum (or vice versa); use the margin characteristics and comparison views, and correlate with the history and the site of tenderness.
Evidence & Key Studies
Painful os peroneum syndrome: presentation and management
- The painful os peroneum syndrome is subdivided into acute and chronic forms; the acute presentation usually follows trauma - most commonly a supination or inversion of the ankle - which can fracture the os peroneum or rupture the peroneus longus tendon.
- The chronic presentation results from recurrent foot injury or healing of a fracture with calcific remodelling of the sesamoid, producing peroneus longus tendinopathy/tenosynovitis and a risk of subsequent tendon rupture.
- MRI characterised the os peroneum, surrounding soft-tissue swelling and peroneus longus tendinopathy; the reported case settled with a short course of a non-steroidal anti-inflammatory.
Retracted os peroneum with partial integrity of the peroneus longus tendon
- Marked displacement of the proximal fragment of the os peroneum on radiographs is often used as an imaging surrogate for a complete peroneus longus tendon tear.
- A retracted proximal os peroneum (even above the level of the ankle) can occur with only an incomplete peroneus longus tear, because the os occupies part of the tendon's cross-section and eccentric intact fibres remain in continuity.
- MRI is required to provide a full description of the tendon, and a complete tear should not be assumed from a retracted os on radiography alone.
According to PubMed, the acute/chronic spectrum of the painful os peroneum syndrome and its conservative resolution come from the cited Henrique Segatt report, and the use (and limitation) of a displaced/retracted os peroneum as a surrogate for a peroneus longus tear - with MRI for full characterisation - from the cited Lee report. The anatomy of the os peroneum (sesamoid in the peroneus longus at the cuboid) and os vesalianum (fifth metatarsal base, peroneus brevis) and their distinction from avulsion fractures are standard, well-established teaching. (See also our Os Trigonum, Accessory Navicular, Peroneal Tendon Disorders and Fifth Metatarsal Fractures topics.)
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A patient has chronic lateral midfoot pain. The radiograph shows a displaced, fragmented os peroneum. What is your concern and what do you do?”
“A radiograph of an ankle injury shows a bony fragment at the base of the fifth metatarsal. How do you decide whether it is an avulsion fracture or an os vesalianum?”
Mnemonics & Memory Aids
POPS
Hook:POPS: Peroneus longus sesamoid, Os displaced = tear (MRI), Pain lateral foot, Start non-operative.
Os peroneum
- Sesamoid within the peroneus longus at the cuboid (often incidental/bipartite)
- Painful os peroneum syndrome (POPS): acute (# / PL rupture) vs chronic (tenosynovitis)
- Displaced/diastatic/retracted os = surrogate for a peroneus longus tear - get MRI
Os vesalianum
- Accessory ossicle at the 5th-MT base (peroneus brevis insertion)
- Smooth/corticated/rounded, often bilateral - NOT an avulsion fracture
- Avulsion = sharp non-corticated line, unilateral, post-inversion (comparison views help)
Management
- Non-operative first: activity modification, immobilisation/orthoses, NSAIDs, physiotherapy
- Surgery for refractory pain or tendon rupture: ossicle excision + tendon repair/reconstruction
- Irreparable peroneus longus -> peroneus longus to brevis tenodesis
Don't forget
- Os trigonum (posterior talus) and accessory navicular have their own pages
- Treat the symptom and the tendon, not the incidental ossicle
- Correlate radiograph with history + site of tenderness