Intrinsic subtalar ligaments are primary varus stabilizers of the subtalar joint: A 3D cadaveric motion analysis

The respective roles of subtalar joint intrinsic ligament (cervical ligament [CL], interosseous talocalcaneal ligament [ITCL]) versus the extrinsic calcaneofibular ligament (CFL) are unclear. This study aimed to use 3D opto-electronic analysis to compare their respective contributions to subtalar joint stability.

In this cadaveric comparative study, twenty feet were split into intrinsic or extrinsic groups and underwent sequential sectioning: (1) intact, (2) anterior talo-fibular ligament (ATFL) cut, (3) CFL or CL+ITCL cut, (4) all ligaments cut. At each stage, manual anterior drawer and varus-tilt tests in neutral and dorsiflexion were performed. Angular rotations and ligament elongations were recorded.

In both intrinsic and extrinsic groups, sectioning of the CL+ITCL significantly increased varus rotation in dorsiflexion between the calcaneus-talus (+38.4 % and +71.1 %, respectively; p < 0.05) and calcaneus-tibia (+49.2 % and +82.5 %, respectively; p < 0.05). CFL sectioning increased varus rotation in neutral flexion between the calcaneus-tibia (+36.6 % and +30.9 %, respectively; p < 0.05) and talus-tibia (+77.2 % and +95.3 %, respectively; p < 0.05), while also producing a significant increase in ATFL elongation (+4.5 % and +7.2 %, respectively; p < 0.05).

Intrinsic ligaments primarily stabilize the subtalar joint and the tibio-talo-calcaneal complex against varus stress in dorsiflexion, whereas the CFL provides varus stability to both the ankle and the tibio-talo-calcaneal complex in neutral flexion. Sectioning of the CFL increases ATFL proximal-to-distal distance under varus and inversion stress, underscoring the importance of addressing the CFL in cases of combined ATFL and CFL injuries.