Margit Gfoehler

A preliminary model study of the equine back including activity of longissimus dorsi muscle

REASONS FOR PERFORMING STUDY Identifying the underlying problem of equine back pain and diseases of the spine are significant problems in veterinary orthopaedics. A study to validate a preliminary biomechanical model of the equine back based on CT images including longissimus dorsi (LD) muscle is therefore important. OBJECTIVES Validation of the back model by comparing the shortening of LD muscles in the model with integrated EMG (IEMG) at stance during induced lateral flexion of the spine. METHODS Longissimus dorsi muscle activity at stance has been used for validation. EMG electrodes were placed laterally at the level of T12, T16 and L3. Reflective markers have been attached on top of the spinous processes T5, T12, T16, L1 and the sacral bone (OS1, OS2) for motion tracking analysis. A virtual model of the equines back (T1-S5) was built with inclusion of a simplified LD muscle by 2 separate contours left and right of the spine, starting at tuber coxae laterally and attaching to the spinous process T5 medially. Shortening of LD during induced lateral flexion caused by the kinematic data (input) was compared to the 3 EMG signals (T12, T16 and L3) on the active side via correlation. RESULTS Pearson correlation coefficient between IEMG and shortening length of LD in the model was (mean ± s.d.) 0.95 ± 0.07 for the left side and 0.91 ± 0.07 for the right side of LD. CONCLUSIONS Activity of the LD muscles is mainly responsible for stabilisation of the vertebral column with isometric muscle contraction against dynamic forces in walk and trot. This validation requires muscle shortening in the back, like induced lateral flexion at stance. The length of the shortening muscle model and the IEMG show a linear relationship. These findings will help to model the LD for forward simulations, e.g. from force to motion.

Alternative solution of virtual biomodeling based on CT-scans.

In this paper, an alternative method is presented to convert computed tomography (CT)-scans into 3D biomodels. The CT-data of an equine spine was converted into TIF format to work with it in a 2D CAD program. Then the bony structure has been marked manually with closed splines and saved as IGS files for the next procedure with 3D CAD software to create virtual biomodels of every single bone. Therefore, the different layers of the CT-scans were positioned in correct distance and then a closed surface was created to cover all spline-curves. Finally, the cover was filled up with material to create a solid part. This method can be recommended as an alternative way, if CAD software is available only. Especially, if it is necessary to add extra artificial spline-curves to split two or more bones which were unnaturally grown together, working with 3D CAD software is the right solution.

Comparing the Biomechanics of Crouch Gait in Children with Cerebral Palsy to that of Age-Matched Controls and Young Healthy Adults

Cerebral palsy (CP) results from an injury to the developing brain and commonly results in an abnormal gait pattern. Crouch gait is a common gait abnormality associated with CP. The aim of the presented study was to compare kinematics, kinetics and EMG data of CP children walking with a crouched gait with those of aged-matched healthy children and young healthy adults. Gait experiments were performed on two CP children. The main difference in the gait patterns of healthy children and young healthy adults appeared to be in late stance, just before toe off. Children exerted lower torques about the knee and ankle, and they also exerted lower forces on the ground. In crouch gait, the net extensor moment exerted about the hip increased during early stance, which may be due to an increase in the passive force exerted by the hamstrings. Prolonged activity of the biceps femoris and co-contraction with rectus femoris, together with activation of gastrocnemius in late swing, may explain the excessive knee flexion observed in these patients. Early onset of tibialis anterior in the CP patients may also contribute to the reduced amount of ankle plantarflexion observed in these patients.

Comparison of Three Control Strategies for an Upper Arm Rehabilitation Device

The RETRAINER S1 system is an upper limb rehabilitation device designed to be used in repetitive task-oriented training. While the device itself is intrinsically controlled by the wearer, the execution of the training exercises is automatically controlled by a finite-state machine. This contribution discusses three different control strategies tested in a clinical environment.

Passive Light-Weight Arm Exoskeleton: Possible Applications

Upper extremity exoskeletons are useful for humans in different ways: for motor rehabilitation, as assistive devices, or for the reduction of work-related loads on the musculoskeletal system. This paper describes the design of a passive modular and light-weight arm exoskeleton with gravity support and discusses possible fields of application. Tests, carried out with enabled gravity support show reduced muscle activations and forces compared to the same movements with disabled gravity support, indicting the effectiveness of the design.