Hindfoot Instability Test-Introduction and Validation of an Intraoperative Diagnostic Test of Hindfoot Instability in Deltoid Ligament Injury Associated With Ankle Fractures.

The deltoid ligament complex (DLC) is well-known as an ankle joint stabilizer; however, through the superficial DLC, it also acts at the subtalar joint and helps to maintain the medial longitudinal arch. DLC repair in the presence of an ankle fracture remains a topic of controversy in the current literature. There is a paucity within the literature surrounding clinical tests that could be performed to assess for hindfoot instability in patients with DLC injuries associated with ankle fracture. However, hindfoot instability has been observed intraoperatively under fluoroscopy via valgus stressing of the calcaneus, while maintaining a congruent medial clear space. In cases of hindfoot instability, the calcaneal tuberosity crosses the lateral fibular line. We aim to validate this technique as a method for detecting hindfoot instability radiographically with DLC injury when undertaking ankle fracture fixation. For this, 10 morphologically normal cadaveric leg specimens were used to validate the hindfoot instability test. Specimens were radiographed before and after transecting both the superficial and deep fibers of the DLC. A line was drawn along the lateral aspect of the fibula on the radiographs. The position of the calcaneal tuberosity in relation to this line was used to determine if the specimen had hindfoot instability. Pre-transecting the DLC, the calcaneal tuberosity did not cross the lateral fibular line on hindfoot valgus stressing. Post-transecting the DLC, the calcaneal tuberosity crossed the lateral fibular line in all specimens on repeat valgus stressing of the hindfoot. Post-DLC repair, the calcaneal tuberosity did not cross the lateral fibular line on hindfoot valgus stressing. We demonstrated that the hindfoot instability test may provide a useful intraoperative adjunct to determine hindfoot instability in the presence of a DLC injury and can be used to guide repair of the DLC in cases of ankle fractures.