A broken foot, also known as an ankle sprain, is most commonly associated with ligament damage, particularly a sprain of the lateral collateral ligament.
Because the medial side of the ankle is shorter than the lateral side, and because the lateral collateral ligament is weaker than the medial side, when the foot is not adjusted or coordinated in time to twist inwards when stepping on stairs or breaking the foot, the injury occurs when the lateral ligament is overstretched beyond the maximum force, and the force of the overstretched ligament is then transferred to the attached bone, causing a bone fracture.