Biomechanical and Morphological Characterization of the Foot in Patients With Posterior Tibial Tendon Dysfunction.

Posterior tibial tendon dysfunction (PTTD) is a progressive condition of the tendon of the tibialis posterior muscle with symptoms of tendinopathy or even rupture. Functionally, it is associated with the inability to lock the mid foot and thus manifests itself as a main contributor to adult acquired flatfoot deformity. Importantly, this condition is associated with severe pain, inability to walk, collapse of the foot arch and dislocation and destruction of foot joints, causing serious disability with respect to activities of daily living and professional activities.

Concerning treatment, clinical decision making is currently based on a classification integrating various parameters as pain, flexibility of the foot joints, the condition of the posterior tibial tendon assessed through ultrasound imaging and radiographic assessment of arthritic changes. PTTD stage 1 is characterized by tendinopathy and is suggested to be mainly treated conservatively. Stage 2 is characterized by a flexible flat foot deformation, mostly combined with a tear of the posterior tibial tendon. Here, treatment is suggested through osteotomies and soft tissue surgery. Stage 3 encompasses a rigid flat foot deformity associated with a fully dysfunctional posterior tibial tendon and degenerative changes of the hind foot joints. At this stage fusion of the affected joints should be considered. During recent decades, this classification has been extended with additional subgroups as well as a stage 4 which adds onto stage 3 with excessive tibio-talar valgus and is mainly treated by a complementary fusion of the ankle joint.

Surprisingly, this classification does not consider any morphologic characteristics (the shape of a bone or joint) or functional, biomechanical characteristics of the foot and ankle, i.e. based on kinematics (e.g. range of motion) and/or kinetics (center of pressure, angular velocity, moment, power absorption and power generation of a joint).

Detailed biomechanical characteristics of the foot and ankle can be reliably collected by instrumented gait analysis wherein a 3D camera system is combined with a force plate and plantar pressure platform. Kinematic studies in the field of PTTD typically considered the foot as a structure consisting of three segments: hind foot, forefoot and hallux. Consequently, the mid foot segment (the Chopart and Lisfranc joints) has been neglected, although it is this segment that is particularly affected in PTTD patients. While kinematic studies focus on joint motion, kinetic studies focus on the loading and impact associated with motion of the joints.

Besides documenting specific biomechanical characteristics of the different stages of PTTD, it is essential to explore the relation of these biomechanical characteristics with the bone morphology of the involved osseous structures.