Horizontal moment around the hoof centre of pressure during walking on right and left circles.

REASONS FOR PERFORMING STUDY: Recent research indicates that the digital joints experience some degree of extrasagittal motion during stance and that the moments under the hoof are asymmetric in horses walking in a straight line. On a circle, these have not been defined. OBJECTIVES: To quantify the amplitude and symmetry of horizontal twisting moments around the vertical axis through the hoof's centre of pressure on left and right circles at walk. METHODS: Six Thoroughbred horses were led at walk across a Kistler force platform on a left and a right circle of 5 m radius. The resultant moment around the hoof was calculated from the 4 horizontal forces and their moment arms. RESULTS: Five of the 6 horses exerted an internal moment around their left forehoof, and 4 exerted an internal moment around their right forehoof on the left circle. On the right circle, 5 of the 6 exerted an internal moment around the left forehoof and a weak external moment around the right forehoof. The moments under the hind hooves were bilaterally similar for right and left circles. CONCLUSION: Intrahorse variability in the applied moments is low, but there is some interhorse variability, especially in the forelimb moments, that indicates future studies of movements of the distal limb joints should be bilateral to account for mechanical asymmetry. POTENTIAL RELEVANCE: The finding that horizontal moments vary between forelimbs in some horses will apply to how exercise on a circle is approached, especially in rehabilitation programmes for horses with orthopaedic injury of the distal limb.

Horizontal moment around the hoof's centre of pressure during walking in a straight line.

REASONS FOR PERFORMING STUDY: Joint congruity and ligaments restrain the distal limb joints from excessive motion in the transverse and frontal planes, but the magnitudes and direction of the horizontal twisting moments around the hoof's centre of pressure (CoP) that induce these motions are unknown. OBJECTIVES: To quantify the horizontal moment around the vertical axis through the hoof's CoP at walk, and to determine whether these are symmetric. METHODS: Nine sound Thoroughbred horses (mean age 53 years; mean mass 502 kg) were led at walk in a straight line across a Kistler force platform. Five trials were collected for each fore and hindlimb. The resultant moment around the hoof's CoP was calculated from the horizontal moment arms between the calculated CoP and the 4 horizontal forces in the transverse (X) and cranio-caudal (Y) directions. RESULTS: The calculated moments were consistent within limbs and horses, but variable between horses. Hindlimbs demonstrated a biphasic moment pattern and the largest moments were typically in the first half of stance. Mean +/- s.d. peak moments were internal under both hindlimbs (L: Int 14.1 +/- 4.6 Nm; R: Int 133 +/- 5.5 Nm). In the forelimbs, 7/9 horses demonstrated an asymmetric moment pattern, with the left forelimb exerting an internal moment (L: Int 6.9 +/- 2.9 Nm) and the right forelimb an external moment (R: Ext 8.4 +/- 4.4 Nm), while the remaining 2 horses exerted internal moments in both forelimbs (L: Int 11.7 +/- 1.4 Nm; R:Int 6.6 +/- 1.9 Nm). CONCLUSION: In 7/9 horses, the forelimbs exerted asymmetric horizontal moments around the hoof CoP. The hindlimbs appear to behave with mechanical symmetry during stance, exerting an internal moment during retraction. POTENTIAL RELEVANCE: Extrasagittal joint motions in the forelimb are unlikely to be symmetric and future studies should account for possible bilateral variations.