Function upper ankle joint
The upper ankle joint is a pure hinge joint, so there is only one axis of motion with two possible movements: Starting from the neutral-zero position of the joint (i.e. the foot resting flat on the ground), dorsal extension up to a maximum of 30 degrees and plantar flexion up to a maximum of 50 degrees is possible. In dorsal extension, the front part of the lower joint surface, the trochlea tali, is wedged firmly into the malleolar fork, since its width in the front part fits perfectly into the malleolar fork. Since it is 4-5 mm narrower in the rear part, i.e. at the front, this also means that the malleolar fork is too wide for the trochlea tali in the case of plantar flexion. This explains why the foot is most stable in a squatting position (e.g. when skiing downhill), while the foot is most unstable and thus most prone to injury when walking downhill or even when simply tiptoeing or climbing stairs.This is why ligament injuries to the upper ankle joint caused by twisting are more common in situations where the foot is currently plantarly deflected.
- The dorsal extension (elevation) and
- Plantar flexion (flexion) of the foot.
Clinical case
The most common ankle injury is the so-called supination or inversion trauma of the upper ankle joint. In this case, the foot bends inwards, which leads to overstretching and possibly to a rupture (tear) of the outer ligaments. Such an injury can be accompanied by a fracture of the lateral malleolus, the lowest part of the fibula.
