Mapping of Posterior Talar Dome Access through Standard Posteromedial and Posterolateral Approaches With or Without an External Fixator Distraction: A Match-paired Cadaveric Study

Abstract

Category: Trauma; Ankle; Other Introduction/Purpose: Posterior talar body fractures (AO/OTA 81.1.B/C) are rare injuries that present unique challenges in their access to the treating surgeon. Accessibility to this structure has been investigated extensively in the context of osteochondral lesion interventions, normally requiring perpendicular access to perform operative procedures. However, techniques in gaining this access regarding fracture repair, requiring only adequate visualization, has not been described in literature. Generally, a pre-operative decision is made between a posterior, soft-tissue based approach or a peri-articular osteotomy, which is associated with comparatively higher morbidity and complication rates. The aim of this study is to evaluate the accessible area of the talar dome via two standard posterior approaches (posteromedial; PM, and posterolateral; PL) with and without external fixator distraction. Methods: Eight male through-knee matched-paired cadaveric legs (mean age: 49.0 +- 14.6; mean BMI: 24.5+- 3.9 kg/m2) were included in this study. A standard PM or PL approach was performed using a randomized crossover design for surgical sequences. The accessible area without distraction was initially outlined by drilling a 1.6-mm Kirschner wire around the periphery of the visualized talus. Five millimeters of distraction, confirmed with fluoroscopy, was then applied to the specimens using an external fixator. The accessible area was again marked using the same method. The tali specimens were then explanted and imaged using a Micro-CT scanner to acquire 3 dimensional reconstructions. The accessible area was calculated as a percentage of the total talar dome surface area. The Mann-Whitney U test was used to compare the reported areas among the two surgical approaches, where the Wilcoxon signed rank test was utilized to compare values among distracted and non-distracted conditions. Results: In reference, the average total surface area of the talus is 16.94 +- 2.47 cm2. No statistically significant differences were found among match-paired specimens (p=0.63). The PM approach allowed access to 17.1% (11.1 to 23.6%, SD 5.4) of the talar dome surface without distraction and 29.3% (20.0 to 38.6%, SD 8.6) of the talar dome surface with distraction. The PL approach provided access to 7.4% (4.7 to 11.8%, SD 3.1) and 17.0% (11.0 to 26.1%, SD 6.5) of the talar dome surface with and without distraction, respectively. A statistically significant difference was observed in talar dome accessibility among distracted and non- distracted conditions in both surgical approaches (p=0.008). Additionally, the PM approach provided significantly more access to the talar dome relative to the PL approach (p=0.043). Conclusion: This matched-paired cadaveric study provides roadmap that can assist in the pre-operative planning of talar dome access in the treatment of talar body and posterior tubercle fractures. We found no advantage to a PL approach over a PM approach to access these challenging fractures. Additionally, added distraction using an external fixator consistently increased visualization of the talar dome by a magnitude of at least 40% greater than the non-distracted conditions. These methods can be applied clinically to gain appropriate access to the talar dome, allowing fracture repair.