2.2.2 Gait assessment
Gait analysis was performed in the institutional’s Clinical Movement Analysis Laboratory. Data were obtained when the subjects walked along 10-meter walkway, surrounded by an optoelectronic motion capture consisting of 10 T-10 cameras (100 Hz, Vicon Motion Systems Ltd., Oxford, United Kingdom). A force plate (Advanced Mechanical Technology, Watertown, MA, USA) and a superimposed pressure plate (Footscan, dimensions 0.5 m ∙ 0.4 m, 4096 sensors, 2.8 sensors/cm2; RSscan International, Paal, Belgium) were an integral part of the walkway. Both plates were dimensionally matched and were built into the floor. An RSscan 3D synchronization box was used to synchronize and calibrate the plantar pressure and force data. Sampling of these force and pressure plate data was done at 200 Hz.
Multisegment foot kinematics and kinetics were assessed by placing retroreflective markers (Ø = 10 mm) to the participants’ feet and shanks following the marker placement protocol of the Instituto Ortopedico Rizzoli (IOR) Foot Model(20). Subsequently, the patients were instructed to walk along the aforementioned walkway at their own pace until at least five representative trials were recorded.
Data processing incorporated manual marker labelling and definition of the individual gait cycles using Nexus software (Vicon Motion System Ltd, Oxford Metrics, Oxford, UK). Following this post-processing routine, the IOR-4segment-model-1 described by Deschamps et al. (2017) was applied(21). This model calculates 3D intersegment joint rotations between the following adjacent segments: shank-calcaneus (Sha-Cal), the calcaneus-midfoot (Cal-Mid), midfoot-metatarsus (Mid-Met), hallux and metatarsus (Hallux); as well as the following non-adjacent segments: calcaneus and metatarsus (Cal-Met). The following terminology was used with respect to the aforementioned adjacent inter-segment angle calculations (joints): Ankle between shank and calcaneus, Chopart between calcaneus and midfoot, Lisfranc between midfoot and metatarsus, and the first metatarsophalangeal joint (MTP 1) between hallux and metatarsus.
Joint centers were respectively defined as the midpoint between both malleoli (Ankle), the midpoint between the navicular and cuboid bone (Chopart), the second metatarsal base (Lisfranc), and the projection of the MTP1 marker halfway to the floor (MTP1). Subsequently, ground reaction forces and moments (captured by the force and pressure plate) were distributed over the different segments of the IOR-4segment-model-1 using a validated proportionality scheme(22). For every time frame of the gait cycle, the resulting pressure in each of these segments, compared with the total pressure, provided the proportion of the total ground reaction force to each corresponding segment. Then, we calculated inertial parameters based on the mass of each segment and their geometric solids. The mass of the foot was distributed at a 30/30/30/10 (rearfoot/midfoot/forefoot/hallux) percent rate. Joint kinetics were computed starting from the distal joint and progressing proximally, using Newton-Euler equations using an in-house custom inverse dynamic analysis program (ACEP-Manager, Matlab2016a, The Mathworks, Natick, US). Following data-processing, normalization of all waveforms for a full stance phase was performed.
Regarding the joint kinematics the following outcome variables were investigated: 1) range of motion (RoM), defined as the difference between the maximum and minimum value in a kinematic waveform, and calculated for three subphases of stance including loading response (0–20% stance phase), midstance and terminal stance together (21–83% stance phase) and pre-swing (84–100% stance phase)(23), 2) the degree of kinematic coupling between the following inter-segment angles: Sha-Cal (Inversion/Eversion) and Sha-Cal (adduction/abduction), Sha-Cal (Inversion/Eversion) and Cal-Met (dorsiflexion/plantarflexion), Sha-Cal (Inversion/Eversion) and Cal-Met (Inversion/Eversion), Sha-Cal (Inversion/Eversion) and Cal-Met (Adduction/Abduction).
Finally, peak internal joint moment, peak dorsiflexion and plantarflexion angular velocity and peak power generation and absorption (joint moment multiplied with angular velocity) at the different joints were quantified as kinetic outcome measures.