Treatment of Type 2 Os Navicular
Type 2 os navicular (accessory navicular synchondrosis) should initially be treated conservatively with immobilization using orthotics or casting, but if symptoms persist after conservative management, surgical excision of the accessory navicular with its synchondrosis is recommended without requiring posterior tibial tendon transposition. 1
Understanding Type 2 Os Navicular
Type 2 accessory navicular represents a synchondrosis (cartilaginous connection) between the accessory bone and the main navicular body, distinguishing it from Type 1 (a separate ossicle within the posterior tibial tendon) and Type 3 (the "cornuate navicular," representing a possible fused end-stage). 1
Pathophysiology
- The pull of the posterior tibial tendon, degree of foot pronation, and location of the accessory navicular relative to the undersurface of the navicular create tension, shear, and compression forces on the synchondrosis. 1
- These forces produce microscopic changes of injury and repair similar to those seen with physeal fractures. 1
- These alterations may not always be visible on plain radiographs but are typically detected by 99mTc methylene diphosphonate bone scans. 1
Treatment Algorithm
Initial Conservative Management
- Begin with rigid immobilization using either orthotics or casting for symptomatic Type 2 accessory naviculars. 1
- Conservative treatment should be attempted first in all cases before considering surgical intervention. 1
- The duration of immobilization should allow adequate time for symptom resolution, though specific timeframes are not well-established in the literature. 1
Surgical Intervention
Indications for surgery:
- Failure of conservative treatment with persistent pain and functional limitation. 1
- Athletes requiring return to sport who have not responded to non-operative measures. 1
Surgical technique:
- Excision of the accessory navicular along with its synchondrosis is the recommended procedure. 1
- Transposition of the posterior tibial tendon is NOT necessary during this procedure, which simplifies the surgical approach and reduces operative complexity. 1
- The goal is to remove the source of mechanical irritation while preserving the integrity of the posterior tibial tendon insertion. 1
Important Clinical Considerations
Diagnostic Workup
- Plain radiographs may not reveal the pathologic changes within the synchondrosis. 1
- Bone scintigraphy (99mTc-MDP scan) is more sensitive for detecting active pathology and should be considered when clinical suspicion is high despite normal radiographs. 1
- Advanced imaging with MRI can help characterize bone marrow edema and soft tissue inflammation around the synchondrosis, though this is based on general orthopedic principles rather than specific evidence for Type 2 os navicular. 2, 3
Common Pitfalls to Avoid
- Do not proceed directly to surgery without attempting conservative management first, as many patients will respond to immobilization and activity modification. 1
- Do not perform unnecessary posterior tibial tendon transposition during surgical excision, as this adds complexity without demonstrated benefit. 1
- Do not rely solely on plain radiographs to rule out symptomatic Type 2 os navicular, as bone scan or MRI may be needed to confirm active pathology. 1
- Be aware that Type 2 os navicular is particularly common in athletes and may be exacerbated by repetitive stress and foot pronation. 1