Decoding (patho-)mechanical joint loading patterns and intrinsic foot muscle properties in subjects with chronic ankle instability

Lateral ankle sprain (LAS) is the most common lower limb musculoskeletal injury in active persons. Up to 40% of them will develop chronic ankle instability (CAI), characterized by recurrent ankle giving way and sprains, ongoing symptoms, and altered function. Literature highlights that subjects with LAS and CAI show altered foot and ankle joint kinematics during locomotor tasks, which are associated to the high risk of injury recurrence that characterize this population. Lower limb kinetics are altered in those subjects too, however, critical appraisal of the current evidence highlights that there is no insight into the foot and ankle joint specific kinetics during locomotor and functional tasks. Following recent development, this phenomenon can now be studied using multi-segment joint foot kinetic models. These detailed data will provide relevant information regarding the underlying (mal)adaptive joint loading patterns in these subjects. In addition, there is growing literature regarding the multiple roles of the intrinsic foot muscles and their interest into rehabilitation of lower limb injuries, as they act as sensors and local stabilisers of the foot arches. Fatigue of those muscles led to decreased static support of the medial longitudinal arc in healthy, and it is known that their strength and volume are reduced in adults with CAI. However, the effect of intrinsic foot muscle fatigue on multi-segment foot kinematics and kinetics in patients with CAI remains poorly understood. This will enable a better understanding of the altered kinematics and kinetics referred above and provide the basis for developing new therapeutic interventions through foot muscle strengthening, which was successfully implemented into rehabilitation of other pathologies. Therefore, the main purpose of this thesis is to study kinetics at different foot levels (rear-, middle-, and fore-foot) in order to better understand pathological mechanisms in CAI. The second purpose is to assess the effect of foot muscle fatigue and strengthening. Through a collaboration between UCLouvain and KU Leuven, two studies involving 72 subjects in total are planned: (1) An observational study to compare kinetics and patient reported measures between subjects with CAI, subjects with LAS, and healthy subjects during walking, running and functional tasks. This study will also record foot muscle volume (ultrasound) and assess the impact of a foot muscle fatigue protocol in those three groups on the same outcomes. (2) A randomized controlled trial to assess the impact of an eight-week intrinsic foot muscle strengthening treatment in subjects with CAI.