Radiological medial safe zone - Protecting the posterior tibial tendon during ankle or pilon fracture fixation

B. Jones, A. Bond, K. Roughneen, L. Mason

Background: The surgical treatment of pilon and posterior malleolar fractures can risk damage to the posterior tibial tendon. The lateral safe zone has been confirmed previously to prevent syndesmosis incisura encroachment, however the risks to the tibialis posterior tendon medially has not been investigated. Our aim in this study was to identify the fluoroscopic safe zone medially, to prevent inadvertent injury to the tibialis posterior tendon during both direct and indirect fixation techniques.

Methods: A cadaveric study was performed using 9 fresh frozen cadaveric specimens. A medial posteromedial approach was performed on each specimen to expose the tibialis posterior sheath. A flexible wire was placed down the lateral aspect of the tibialis posterior sheath as a radio opaque marker. Fluoroscopic imaging was performed in the anteroposterior and lateral position to identify a medial safe zone.

Results: In all specimens, the wire was located medial to a vertical line corresponding to the articular surface (the medial safe zone line) of the medial malleolus on anteroposterior imaging. On lateral imaging, the radiopaque marker followed the medial malleolus obliquity and continued to correspond to 30% of the posterior plafond.

Conclusion: This study demonstrated that a medial safe zone fluoroscopic landmark is unambiguous in localizing the tibialis posterior sheath and that any metal work medial to this line is likely to be at risk of damaging the tibialis posterior tendon. The lateral radiograph showed that any anteroposterior screw could involve the tibialis posterior sheath even if the penetration is only 70% across the tibial width.

Clinical relevance: This article describes a radiographic and clinical safe zone for fixation and hardware placement during open reduction internal fixation (ORIF) of PMFs. This information will assist surgeons in avoiding posterior tibial hardware placement.