Synostosis

Modern Study Review (AI-Generated)

High-Yield Summary

Synostosis is a pathological bony fusion between adjacent bones, most commonly seen as a complication after forearm or tibial fractures. It leads to significant functional impairment by restricting normal joint or interosseous membrane motion. Early recognition and differentiation from heterotopic ossification are essential for appropriate management. Surgical excision remains the mainstay of treatment after maturation, with careful timing to optimize outcomes and minimize recurrence.

Key Diagnostic Findings

Anatomy

• Forearm: Radius and ulna are normally separated by the interosseous membrane allowing pronation and supination.
• Tibia and Fibula: Normally have slight motion at the distal tibiofibular syndesmosis to accommodate ankle movement.

Clinical Presentation

• Loss of forearm rotation (pronation/supination) or ankle motion depending on location.
• History of prior fracture with risk factors such as severe displacement or delayed treatment.
• May present months after injury with progressive stiffness.

Imaging

• X-rays: Show bridging bone between radius and ulna or tibia and fibula.
• CT scan: Useful for detailed assessment of the extent and maturity of the synostosis.
• Differentiate from heterotopic ossification by location and pattern (synostosis is continuous bone fusion between two bones).

Classification Systems

• No widely adopted formal classification system specific to synostosis; however, the location and extent guide treatment decisions.

Current Gold Standard Treatment

Non-operative

• Observation if minimal functional impairment.
• Early aggressive physical therapy is generally ineffective once synostosis is established.

Operative

• Indications: Significant functional limitation, mature synostosis (usually >12 months post-injury), and failure of conservative measures.
• Procedure: Surgical excision of the bony bridge with removal of periosteum to reduce recurrence risk.
• Adjuncts: Interposition of autologous fat or muscle graft to prevent re-ossification.
• Forearm: Dual incision approach for ORIF to minimize risk; excision after maturation if synostosis develops.
• Tibia: Excision of synostosis or partial fibular resection with distal fibular fixation to tibial epiphysis (analogous to Sauvé-Kapandji procedure) to restore ankle motion.

Modern Complications & Outcomes

Complications

Outcomes

• Functional improvement in rotation or ankle motion is achievable with timely excision.
• Delay in surgery beyond 12 months reduces recurrence but may limit functional gains.
• Fat or muscle interposition grafts reduce recurrence rates.
• Early recognition and prevention during initial fracture management remain critical.

Classic Clinical Notes

Synostosis

Complications – Synostosis

• Rare and serious complication of forearm fractures or tibia fractures.
• Must distinguish it from heterotopic bone.

Forearm

• Try to do both bones forearm ORIF through two incisions (but even then you can still see this problem).
• Predisposing factors include:
• Severe initial displacement
• Residual displacement
• Periosteal interposition
• Delayed surgery
• Re-manipulation
• Fracture at the same level of the radius and ulna.
• Treat with excision after waiting at least 1 year. Remove the bone and periosteum, lay in fat.

Tibia

• There is some normal motion between the tibia and fibula at the ankle joint which gets obliterated with synostosis.
• Try to excise the synostosis, or resect part of the fibula and do screw fixation of the distal fibula to tibial epiphysis (kinda like a Sauve-Kapandji of the distal tibia).

Last Updated on January 25, 2026 by orthonet