Preliminary report into the function of the shoulder using a novel imaging and motion capture approach.

REASONS FOR PERFORMING STUDY: The function of the forelimb is fundamental to understanding both sound and pathological locomotion. The precise movements of the equine shoulder are hidden by layers of skin and muscle and hence the shoulder is normally modelled as a simple pivot during locomotion which assumes that any translational motion is negligible. OBJECTIVES: To record and quantify the sliding motion of the scapula during locomotion, using a novel imaging technique. METHODS: Scapula motion during locomotion in the horse was calculated by tracking the ripple of the shoulder blade's movement under an array of markers placed over the soft tissue. RESULTS: Interstride variability was low. Sliding of up to 80 mm in the plane of progression (cranio-caudal) was observed; however, the limits of motion varied by <5 mm in the gaits examined, despite variations in stride length. Stride length appeared to be increased by scapula rotation in the plane of progression, and this flexion-extension was largest in trot and was not significantly different between walk and canter. This was in agreement with the distance travelled by the trunk whilst the hoof was on the ground. Substantial sliding in a dorsal-ventral direction was shown and varied with the gait used, both in magnitude and timing, possibly providing a shock absorption mechanism. The sliding did not increase as much as would be expected in canter and this coincided with a more lateral positioning of the scapula and increased impact on the ribcage. CONCLUSIONS: It has been assumed that scapula-thoracic sliding increases stride length and hence economically increases locomotor speed. The extra motion of the scapula recorded appeared to absorb shock from forelimb impact and maintain the economy of locomotion, but did not increase with speed and the muscular pretensioning implied could actually impair ventilation.

The role of tendon stiffness in development of equine locomotion with age.

REASONS FOR PERFORMING STUDY: The flexor tendons support the metacarpophalangeal (MCP) and distal interphalangeal (DIP) joints during stance phase and since tendon stiffness and strain changes with age, it is likely that kinematics are also age-dependent. HYPOTHESIS: Maximum MCP and DIP angles decrease in the young horse, plateau in the mature horse and increase towards senescence. METHODS: The distal limbs of 57 walking horses age 3-212 months were filmed and digitised with an automated tracking system. Maximum MCP and DIP angles during stance phase were used to calculate strain in the superficial and deep digital flexor tendons. Horses were divided into 3 age groups; young (3-35 months), mature (36-99 months) and older horses (100-212 months). Pearson's correlation coefficients were calculated to determine the relationship between age and kinematics. RESULTS: Tendon strain decreased in young horses, stayed constant in mature horses and increased in older horses. Joint angles showed significant negative correlation in young horses, with coefficients of -0.88 (MCP) and -0.81 (DIP). In mature horses, correlations were not significant (P = 0.2 for MCP; P = 0.5 for DIP). In older horses, angles showed significant positive correlation, with coefficients of 0.62 (MCP) and 0.48 (DIP). CONCLUSIONS: Joint angles decreased in the young horse as tendon stiffness increases, remained constant in the mature horse where tendon stiffness is constant and increased in older horses as tendons weakens and stiffness decreases. Strain patterns were similar to those found in vitro. POTENTIAL RELEVANCE: Changing tendon stiffness appeared to influence the development and degeneration of gait. This has implications for studying musculoskeletal development, especially for identification of normal and pathological development.

Prediction of the hip joint centre in adults, children, and patients with cerebral palsy based on magnetic resonance imaging.

The location of the hip joint centre (HJC) is required for calculations of hip moments, the location and orientation of the femur, and muscle lengths and lever arms. In clinical gait analysis, the HJC is normally estimated using regression equations based on normative data obtained from adult populations. There is limited relevant anthropometric data available for children, despite the fact that clinical gait analysis is predominantly used for the assessment of children with cerebral palsy. In this study, pelvic MRI scans were taken of eight adults (ages 23-40), 14 healthy children (ages 5-13) and 10 children with spastic diplegic cerebral palsy (ages 6-13). Relevant anatomical landmarks were located in the scans, and the HJC location in pelvic coordinates was found by fitting a sphere to points identified on the femoral head. The predictions of three common regression equations for HJC location were compared to those found directly from MRI. Maximum absolute errors of 31 mm were found in adults, 26 mm in children, and 31 mm in the cerebral palsy group. Results from regression analysis and leave-one-out cross-validation techniques on the MRI data suggested that the best predictors of HJC location were: pelvic depth for the antero-posterior direction; pelvic width and leg length for the supero-inferior direction; and pelvic depth and pelvic width for the medio-lateral direction. For single-variable regression, the exclusion of leg length and pelvic depth from the latter two regression equations is proposed. Regression equations could be generalised across adults, children and the cerebral palsy group.