The aim of this study is to investigate the impact on gait and morphology of the calf muscle in children with Cerebral Palsy with equinus gait pattern following serial casting and Botulinum toxin (Btx) interventions.

Toe walking is a common feature of a number of orthopaedic and neurological problems (e.g. cerebral palsy, idiopathic toe walking and stroke). Patients who toe walk often develop contractures in their calf muscles and in the longer term may suffer from foot or calf pain and foot deformities. Toe walking also causes difficulties with balance and leads to secondary compensations and deformities. The causes of toe walking are not always clear for individual patients. Current interventions target the perceived causes (e.g. surgery, stretching or orthotics for contracture or botulinum toxin injections for excessive activity) but the relationship between toe walking and the impairment in muscle morphology and control is not fully understood. Clinical movement analysis is used to quantify joint motion and loading during gait. This is done according to established local departmental protocol and is part of routine clinical practice. This is done using the Video Based Motion Analysis System Ltd (VICON), which is a 3D movement analysis modality which makes use of small, spherical reflective markers, between 5mm and 25mm in diameter that are attached to the skin over key anatomical landmarks (located during the clinical examination). Special infrared cameras are used to track the movements of reflective markers in three dimensions. This is combined with AMTI force plates; which together give the kinematics and kinetics of the subject. Electromyography (EMG) of the Triceps Surae and Tibialis Anterior enables observation of muscle activity in conjunction with the gait cycle during different movements. After obtaining participant consent and ensuring that the participant fully understands the scope of the tasks, the session is undertaken. In brief, using local ORLAU department protocol, a clinician places reflective markers on the subject and anthropometric measurements are taken. After the subject is prepared, they are asked to walk along a 10-metre walkway at a self selected speed and a minimum of 6 trials are collected with adequate strikes with each foot landing on the force plate to obtain desired kinematic and kinetic data. EMG recordings are performed simultaneously on the Medial \& Lateral Gastrocnemius, Soleus, and Tibialis Anterior to record muscle activity during the movement.

To obtain information about the morphology, the modality of B-mode ultrasound evaluated the muscle morphology and obtains key information such as muscle fibre length, fibre orientation, pennation angle, cross sectional area, and muscle thickness. After obtaining consent and ensuring that the participant understands fully the scope of the session, they are asked to lie prone on the plinth with lower legs exposed so that the assessor has access to the calf muscles. The assessor then uses the b-mode ultrasound protocol to obtain the key parameters of the calf muscle. Muscle lengths are measured using a Vernier caliper.

In addition, the imaging modality elastography is used. This uses mechanical force, from manual pressure or through a shear wave impulse generated within the ultrasound probe, to detect the change in deformation of the examined tissue and therefore to determine the stiffness. The stiffness of soft tissues can be an indication of pathology. Elastography uses harmless ultrasound waves and allows for the visualisation of strain across a tissue, by superimposing the colour coded elasticity map onto a conventional B-mode image. The colours represent the stiffness of the tissue ranging from red to green to blue, with the exact scale varying between vendors. Shear wave elastography has the added advantage of being able to provide velocity measurements within a defined region of interest, thus quantifying tissue stiffness.

Prior to beginning the session, consent from the subject is obtained and the scope of the session is explained. After consent from the participant, the subject is asked to lie prone on the plinth with their lower legs exposed. The consultant radiologist undertakes elastography measures on the calf muscles (medial, lateral gastrocnemius, soleus) in longitudinal and transverse planes according to the protocol. These are then saved after the key information is obtained and analysed after the session.

Computer modelling can estimate muscle forces during gait, and it is used to study a wide range of conditions such as spastic paresis and crouch gait. Ultrasound can provide information about muscle parameters such as volume, length, anatomical cross-sectional area and pennation angle. This information can be used to adjust the parameters of the musculoskeletal model to fit the characteristics of each patient. The musculoskeletal model can then estimate personalised muscle forces and help understand the individual impairments which lead to toe walking. Future prospects Clinical- The computer models will assist with the precise identification of impairments (eg muscle atrophy, contracture and spasticity) and hence allow more objective specification and targeting of interventions. Combining the data collected from B mode ultrasound, elastography and gait analysis, the effects of clinical interventions in muscle properties can be observed. This can be applied to other interventions, including orthopaedic surgery and orthotic devices. Elastography can also be a vital tool in understanding the elastic muscle properties associated with myopathies and can help optimise and personalise care by selecting the most effective intervention based on an individual's baseline features.