What is the os peroneum?

Os Peroneum: Anatomy, Clinical Significance, and Management

The os peroneum is a small sesamoid bone located within the peroneus longus tendon near the cuboid bone on the lateral aspect of the foot. It is present in approximately 26% of the population and can be a source of lateral foot pain when injured 1.

Anatomical Characteristics

• The os peroneum is typically round or oval-shaped, situated within the substance of the peroneus longus tendon as it courses around the cuboid bone 2.
• Average dimensions of the os peroneum are approximately 13.35 mm in length, 8.96 mm in breadth, and 4.11 mm in thickness 2.
• The deep (articular) surface of the os peroneum is concave, smooth, and sometimes divided into two parts, forming a synovial joint with a convex articular facet on the cuboid bone 2.
• The os peroneum develops from ossification centers that fail to fuse with the main bone during development 3.

Clinical Significance

• Painful os peroneum syndrome (POPS) refers to conditions causing pain in the lateral aspect of the cuboid area 4.
• POPS can result from:
  • Acute trauma (e.g., ankle sprains) 4
  • Chronic overuse injuries 4, 1
  • Direct trauma to the lateral foot 1
  • Forceful muscle contraction 1
• Fractures of the os peroneum are rare but can cause significant lateral foot pain 5, 1.
• The os peroneum can be involved in tears of the peroneus longus tendon, with changes in its morphology or position depending on the location of the tear 4.

Classification of Peroneus Longus Tendon Tears Related to Os Peroneum

Peroneus longus tendon tears can be classified into three subtypes based on the location relative to the os peroneum 4:

• Type I: Tears proximal to the os peroneum
• Type II: Tears at the level of the os peroneum
• Type III: Tears distal to the os peroneum

Diagnostic Imaging

• Radiography is the initial imaging modality to identify the os peroneum and potential fractures 4.
• MRI is generally accepted to achieve high sensitivities (>90%) in diagnosing ankle tendon tears and can help evaluate the peroneus longus tendon and os peroneum 6.
• Ultrasound can be useful for evaluating the peroneal tendons, with one study showing 100% sensitivity and 90% accuracy in diagnosing peroneal tendon tears 6.
• Dynamic ultrasound assessment is particularly valuable for evaluating tendon subluxation and dislocation, with a reported positive predictive value of 100% compared with surgical findings 6.

Management

• Fractures of the os peroneum can often be managed conservatively, even in active patients 5.
• Conservative treatment typically includes:
  • Restricted weightbearing for approximately 2 weeks 5
  • Physical therapy and gradual return to activities 5
  • Analgesics for pain management 3
• Surgical options may include:
  • Fixation of the fracture 5
  • Excision of the bone with direct repair of the tendon 5
  • Tenodesis of the peroneus longus to the peroneus brevis 5

Clinical Considerations

• Os peroneum may be discovered incidentally after trauma to the ankle or foot 3.
• It can be a confounding factor in the diagnosis of foot and ankle pain, potentially leading to misdiagnosis if not properly identified 3.
• Failure to recognize the presence of an os peroneum might result in unnecessary immobilization or surgery 3.
• In cases of lateral foot pain, the os peroneum should be considered in the differential diagnosis, especially when pain is localized to the lateral aspect of the cuboid 4, 1.

Treatment Outcomes

• Nonoperative treatment of minimally displaced fractures of the os peroneum can lead to excellent outcomes, even in high-level athletes 5.
• In one documented case, a professional tennis coach with a minimally displaced fracture returned to tennis 8 weeks after injury with full strength, full motion, and a radiographically healed os peroneum 5.