What is the Os Peroneum?

The Os Peroneum is a small sesamoid bone (or ossicle) found within the peroneus longus tendon as it passes along the outside of the foot. It is usually located adjacent to the cuboid bone, near the lateral side of the foot’s mid-arch.

Present in roughly 5–30% of the population, sometimes on one foot (unilateral) or both (bilateral).

How it works biomechanically

• Location: Embedded in the peroneus longus tendon at (or just proximal to) the cuboid groove.

• Function:

  • Acts as a sesamoid pulley, changing the direction of the tendon’s pull as it curves under the foot.

  • Increases the mechanical advantage of the tendon by slightly elevating its line of action away from the joint, similar to how the patella works in the knee.

  • Reduces friction and distributes pressure across the cuboid surface during plantarflexion and eversion.

• Clinical note: While often asymptomatic, the os peroneum can fracture or become involved in os peroneum syndrome, which may impair the “pulley” action of the peroneus longus and cause lateral foot pain.

Normal Variations

• Can be ossified (true bone) or fibrocartilaginous (soft tissue-like).

• May be single or multipartite (naturally in two or more pieces).

Pathology & Clinical Relevance

The term “Painful Os Peroneum Syndrome” (POPS) describes conditions involving the os peroneum and its tendon, such as:

• Fracture of the os peroneum – often from ankle inversion or direct trauma.

• Diastasis of a multipartite os peroneum – separation of its natural segments due to tendon injury.

• Peroneus longus tendon tear or rupture – can occur at or near the os peroneum.

• Os peroneum entrapment or impingement – due to bony or soft tissue crowding.

Symptoms

• Lateral midfoot pain, sometimes radiating to the outer ankle.

• Swelling or tenderness over the cuboid area.

• Pain aggravated by pushing off the foot or resisted eversion (outward foot movement).

• Weakness in eversion or plantarflexion of the first ray (big toe joint area).

Diagnosis

• Clinical exam – tenderness along the peroneus longus tendon course.

• X-rays – may show an ossicle near the cuboid; comparison with the opposite foot helps identify fracture vs. normal variant.

• Ultrasound – dynamic assessment of tendon integrity.

• MRI – for tendon tears, bone marrow oedema, or associated injury.

Treatment for Os Peroneum Conditions

(Including Painful Os Peroneum Syndrome)

1. Conservative (Non-Surgical) Treatment

Used for mild to moderate pain, early injuries, or overuse cases.

• Rest & Activity Modification – Avoid activities that aggravate symptoms, like running, jumping, or walking barefoot on hard surfaces.

• Ice Therapy – 15–20 minutes several times a day to reduce swelling.

• Anti-inflammatory medication (if appropriate) – NSAIDs to help with pain and inflammation.

• Immobilisation – Short-term use of a walking boot or stiff-soled shoe to protect the area while healing.

• Orthotic Support – Custom or prefabricated orthotics to offload the lateral foot and support the peroneus longus tendon.

• Physiotherapy / Podiatric Rehab – Strengthening, stretching, balance training, and soft tissue release techniques.

• Taping or Bracing – Limits painful tendon movement during activity.

2. Injection Therapy

• Corticosteroid injections – Rarely used near the tendon due to rupture risk, but may be considered in certain soft tissue inflammation cases.

• PRP (Platelet-Rich Plasma) – In some chronic tendon injuries, to stimulate healing.

3. Surgical Treatment

Considered when:

• The os peroneum is fractured with displacement

• There’s a complete or severe tear of the peroneus longus tendon

• Conservative care has failed after 3–6 months

Surgical options include:

• Os Peroneum Excision – Removal of the bone fragment.

• Tendon Repair or Reconstruction – Stitching or grafting to restore tendon strength.

• Debridement – Cleaning out damaged tissue to reduce pain and improve function.

Recovery Times

Conservative treatment time frames are typically 4–8 weeks for mild injuries, although can be longer if the condition has been chronic.

Surgical recovery can take 8–12 weeks for basic repair, up to 6 months for complex tendon reconstruction.

If you or someone you know is struggling with reoccuring pain and would like a solution, the podiatrists at Relief Podiatry are here to help.