The purpose of this study was to evaluate whether walking in the Hibbot affects gait kinematics and dynamics. The mechanism of the Hibbot manages to control all degrees of freedom (3x rotation and 3x translation) at the level of the pelvis and lower trunk. (Figure 1a,1b). The goal is to maximize a child’s own muscle activity and postural control while giving as minimal support as needed. We assume that the design of the Hibbot facilitates correct activation of the gluteal muscles necessary for postural stability. Furthermore, sufficient hip extension movement is required to walk in the Hibbot. When the legs are flexed, fall protection bars touch the ground and locomotion is inhibited.
Our hypothesis is that walking in Hibbot would (a) improve trunk posture and extension in the lower limbs (b) improve weight bearing during the single stance phase. To test these hypotheses, lower limb joint angles and ground reaction forces were compared between walking with the Hibbot and habitual walking in a cross-sectional study.
We performed a cross-sectional study comparing walking in the Hibbot to walking without walking aid/using a habitual walking aid in 5 children diagnosed with CP. The study was approved by the local ethics committee of the Antwerp University Hospital (18/44/509 B300201838159) and retrospective registered as Clinical Trials.gov Protocol Record NCT04172324.
The study was performed in collaboration with a licensed care provider and multifunctional centre directed at children and adolescents with a disability providing directly accessible care, short stay and respite care in Antwerp, Belgium. Participants were recruited in November 2018. Over a period of 3 months, between January 1st and March 31st in 2019, the children were familiarized with the Hibbot by using the walking aid for 30 minutes, twice a week, under the supervision of a physiotherapist. Physical examination and gait analysis were performed before (December 17 – 21, 2018) and after (April 1 – 5, 2019) the familiarization period, at the local gait lab.
Children had to meet the following inclusion criteria: confirmed diagnosis of CP, GMFCS level II-IV, age between 2 and 7 years, stature less than 1.25 meters and body weight less than 30 kilograms. Exclusion criteria were: fixed contractures in the lower limbs, hip dysplasia, infiltration with botulinum toxin 3 months or less prior to the start of the study, orthopaedic operations 6 months or less prior to the start of the study, insufficient mental capacity to understand instructions, insufficient motivation to walk and no prior experience in walking with the Hibbot.
Treating physicians provided the researchers with the information for possible inclusion. Subsequently, study information was provided to parents. After parents had signed an informed consent, patients were screened for eligibility.
To describe the study population age, gender, height, weight, BMI, GMFCS level(4) and mobility by passive range of movement measurement (PROM)(26), strength by manual muscle testing (MMT) (27), spasticity by the Modified Ashworth Scale (MAS)(28) and lower limb selectivity by Selective Control Assessment of the Lower Extremity (SCALE )(29) were assessed. The data of the clinical examination was meaningful by interpretation of the gait parameters i.e. step length, (a)symmetry in, maximal hip and knee extension during stance phase.
Kinematics and kinetics of gait were recorded by an optical motion capture system (8 camera’s, 120 Hz., Qualysis Proreflex, Göteborg, Sweden) surrounding a 10-meter walkway and synchronised with 3 force-platforms (two of 0.5mx0.5m and one of 1.0x0.5m; AMTI Accugait, 1000 Hz., Advanced Medical Technology Inc., Massachussets, USA). Reflective markers were attached to the skin over the processus spinosus of the 7th cervical vertebra (C7), incisura jugulars (IJ), processus xyphoideus (PX) and bilaterally over the clavicular head (CC), major trochanters (TM), lateral epicondyles (LE), lateral malleoli (LM), calcanei (CA) and 2nd metatarsal heads (MT). Marker trajectories were tracked and labelled in QTM (Qualisys Track Manager) software after which kinematic and kinetic data were combined in C3D file format. In addition, two Sony HD video cameras (Type: HDRCX240E, 50Hz.) were placed to record the sagittal and frontal plane kinematics. Children were encouraged to walk at self-selected speed over the walkway in Hibbot and using their habitual walking aid (if necessary, Table 1) in a randomized order. Patients walked either barefoot or with ankle-foot orthoses, if necessary. Prior to gait analysis a standard physical examination was performed by the physiotherapist to assess joint mobility (ranges of motion of hip, knee and ankle towards flexion/extension, ab/adduction and internal/external rotation) and strength, spasticity and selectivity of lower limb muscles (psoas, adductors, quadriceps, hamstrings, gracilis, gastrocnemius and soleus).
Gait analysis data in C3D file format was analysed using visual 3D software (Visual3D Professional v5.01.9, C-motion, Kingston, ON, Canada) and custom models. The body was modelled as an interconnected chain of rigid segments: CC – TM for trunk, TM – LE for thigh, LE – LM for leg and LM – MT for foot. In addition, the thorax was modelled as a 6 – degrees – of – freedom segment with the segment coordinate system definitions partially adapted from the ISB recommendations.(30) The segment origin coincided with IJ; the vertical axis (Z) was defined by the line connecting a virtual point at a fixed distance from PX in the direction of the IJ – C7 axis to the midpoint between IJ and C7 (pointing upwards); the medio-lateral axis (X) was defined as the line connecting the left to right CC; the antero-posterior axis was the common line perpendicular to Z and X, pointing forward.
Events of heel strike and toe off were determined from force plate recordings, CA and MT marker trajectories using the “Automatic Gait Events” command in Visual 3D software. Automatically assigned events were visually inspected.
Hip and knee kinematics in the sagittal plane
Hip flexion and extension were calculated as the planar angle between by CC – TM – LE in the sagittal plane, expressed relative to gait cycle duration (0 – 100%). Knee flexion and extension was characterised as the planar angle between TM – LE – LM as a function of gait cycle duration. The anatomical position with full extension of the hip and knee is characterised by angles of 180°. Angles are calculated against clockwork direction. At the hip, an angle < 180° indicates extension, whereas an angle > 180° indicates flexion. At the knee, an angle < 180° indicates flexion.
Kinematics of the thorax was characterised by Euler/Cardan angles (XYZ) of the thorax coordinate system relative to the global reference frame, normalized to 100% of gait cycle duration. Flexion and extension of the thorax were measured around the X-axis (anteflexion positive, retroflexion negative). Lateral flexion of the thorax was measured around the Y-axis (ipsilateral side positive).
Peak vertical ground reaction force (Fz)
The peak vertical ground reaction force was determined as the maximum value of the vertical component of the ground reaction force vector during stance.
Using the “Temporal Distance Calculations for Gait” command, speed (m/s), normalised speed (statures/second), stride length (m), step length (m), stride width (m), stance time (s), swing time (s) and double limb support time (s) were calculated.
Discrete outcome variables were analysed using the Statistical Package for social Sciences Software (SPSS version 24 for Windows, IBM Statistics). Per subject, data were averaged over different gait cycles (3 – 8 gait cycles per condition). Wilcoxon signed-rank test was performed to evaluate the difference of gait kinematics and kinetics between the Hibbot- and habitual condition. The significance level was set at p<0.05. Data were analysed separately for the before- and after-measurements. Missing data will be treated as missing.
Differences in the time profiles of hip, knee and thorax kinematics across the entire gait cycle were analysed by statistical parametric mapping (spm1d.org) using custom MatLab scripts (version R2018a for Windows). Kinematic time profiles were compared between Hibbot and habitual walking condition, separately for pre- and post-measurements, by means of spm1D paired samples t-test. If the null hypothesis was true, identical curves would be observed in both conditions. The null hypothesis was rejected when the t value exceeded the critical test statistical value t*. Significance level was set at p<0.05.