Relationship between the forces acting on the horse's back and the movements of rider and horse while walking on a treadmill von Peinen, K von Peinen, K. Relationship between the forces acting on the horse's back and the movements of rider and horse while walking on a treadmill. 2009 Relationship between the forces acting on the horse's back and the movements of rider and horse while walking on a treadmill Abstract Reasons for performing the study: The exact relationship between the saddle pressure pattern during one stride cycle and the movements of horse and rider at the walk are poorly understood and have never been investigated in detail. Hypothesis: The movements of rider and horse account for the force distribution pattern under the saddle. Method: Vertical ground reaction forces (GRF), kinematics of horse and rider as well as saddle forces (FS) were measured synchronously in 7 high level dressage horses while being ridden on an instrumented treadmill at walk. Discrete values of the total saddle forces (FStot) were determined for each stride and related to kinematics and GRF. The pressure sensitive mat was divided into halves and sixths to assess the force distribution over the horses back in more detail. Differences were tested using a one sample t-test (p<0.05). Results: FStot of all the horses showed 3 peaks (P1-P3) and 3 minima (M1-M3) in each half-cycle, which were systematically related to the footfall sequence of the walk. Looking at the halves of the mat, force curves were 50% phase-shifted. The analysis of the FS of the 6 sections showed a clear association to the rider's and horse's movements. Conclusion: The saddle force distribution during an entire stride cycle has a distinct pattern although the force fluctuations of the FStot are small. The forces in the front thirds were clearly related to the movement of the front limbs, those in the mid part to the lateral flexion of the horse's spine and the loading of the hind part was mainly influenced by the axial rotation and lateral bending of the back. Potential relevance: This data can be used as a reference for comparing different types of saddle fit.

Objective The aim of this study was to compare the locking compression plate (LCP) with polyaxial locking system (PLS) using single cycle to failure 4-point bending test and to investigate the behaviour of PLS with screws inserted mono- and polyaxially using cyclic fatigue test in two bending directions. Materials and Methods Tests were performed on bone surrogates in a fracture gap model. The 3.5 LCP and 3.5 PLS plates were tested in single cycle to failure. The 3.5 PLS plates with mono- and polyaxial screws were compared in a cyclic fatigue tests in two orthogonal directions. For both experiments, micro-computed tomography (CT) scans were performed pre- and post-testing to investigate the connections between the screw head and the plate hole. Means of forces and cycles needed to failure were statistically compared. Results The PLS plates were on average 30% weaker than LCP plates. Mode of failure was plate bending in the single cycle to failure tests, and plate breakage in the cyclic fatigue tests. Neither screw breakage nor loss of the screw–plate interface occurred. Mono- and polyaxial constructs performed similarly when loaded in the same direction. Micro-CT revealed no additional internal cracks in the plates or screws after testing. It also showed for both PLS and LCP that there was only partial contact of the screw head with the plate hole. Clinical Relevance PLS offers a durable locking system, even when the screws are placed polyaxially. The weaker bending properties of the PLS compared with LCP should be considered during preoperative planning.

Information on the clinical behavior and treatment of cases with an isolated rupture of the short collateral ligaments of the canine tarsus is sparse and contradictory in the veterinary literature. Our objective was to evaluate the function of the short lateral collateral ligaments (SLCLs) of the tarsocrural joint in 90° flexion. Eight canine cadaveric limbs were tested for internal/external rotation and valgus/varus before and after transection of one or both SLCLs. In one group, the fibulocalcaneal ligament was transected first, followed by the fibulotalar. In the second group, the order of ligament transection was reversed. Angular changes between two k-wires were measured and compared. External rotation increased significantly after transection of one or both SLCLs (P = .009 and P &lt; .0005), as did varus (P = .021 and P = .001). Lateral subluxation was only possible when both SLCLs were cut. Unlike the long lateral collateral ligament, which stabilizes against deviation toward medial, both SLCLs are major stabilizers against subluxation toward lateral. This important difference must be considered in clinical patients with isolated rupture of the SLCLs.

Information on the clinical behavior of cases with an isolated rupture of the short collateral ligaments of the canine tarsus is sparse. Our objective was to evaluate the function of the short medial collateral ligaments (SMCLs) in 90° flexion. Eight cadaveric limbs were tested for internal/external rotation and valgus/varus before and after transection of one or both SMCLs. In one group, the tibiocentral ligament was transected first, followed by the tibiotalar. In the second group, the order of transection was reversed. Angular changes between two k-wires were measured and compared. Internal rotation increased significantly after transection of one or both SMCLs (P = .015 and P = .004), with higher angular changes in the group in which the tibiotalar ligament was transected first (P = .003). Transection of this ligament alone was sufficient to cause caudomedial subluxation upon internal rotation. Valgus angulation increased after transection of one ligament (P = .022), but there was also an increase in varus angulation after transection of both ligaments (P = .027). Unlike the long medial collateral ligament, which stabilizes against deviation toward lateral, the SMCL stabilizes against subluxation toward medial, with the tibiotalar ligament being the major stabilizer in flexion. Findings can be used as diagnostic guidance for isolated tarsal short collateral ligament injuries.

To investigate the effect of increasing velocity within one gait on horse and rider movement and to describe the resulting changes in saddle forces, seven ridden dressage horses were examined on an instrumented treadmill. The speed ranged between 1.3-1.8 m/s at walk and 2.6-3.6 m/s at trot. Kinematics of the horse and rider, vertical ground reaction forces and saddle forces were measured simultaneously. Velocity dependency of each variable was assessed for the whole group with linear regression. With increasing velocity, the saddle forces at walk were mainly influenced by the accentuated rocking type of movement and at trot by the higher vertical dynamic and a more rigid horseback which resulted in increased counteracting force between horse and rider. Even small increases of velocity changed the dynamics of the movement pattern of the horse and consequently the forces emerging beneath the saddle: a 10% increase within the indicated speed range resulted in +5% (walk) and +14% (trot) higher total saddle force peaks. Accurate comparison of saddle forces requires speed-matched trials; velocity is therefore a factor which also has to be considered under clinical conditions. IntroductionThe velocity at which a subject is moving within each gait has a fundamental influence on numerous biomechanical variables. In horses, several authors focused their studies on speed-dependent changes in kinetic and kinematic variables and found that increasing velocity reduces stride duration and extends stride length (Clayton, 1994(Clayton, , 1995Dusek et al., 1970;Leach and Drevemo, 1991) and although limb impulses decrease, peak vertical forces increase as a result of reduced relative stance durations (Khumsap et al., 2001a;McLaughlin et al., 1996;Weishaupt et al., 2010). Knowledge of the mathematical functions of these changes enables comparison of individual gait patterns studied at different velocities. On the treadmill, stride duration, stride length and limb impulses change in a linear fashion with increasing velocity, whereas relative stance and suspension duration, as well as peak vertical forces change exponentially . Khumsap et al. (2001bKhumsap et al. ( , 2002 utilised net moment and power of fore-and hindlimb joints to relate ground reaction forces to muscle function and found that with increasing velocity peak moments and power in the joints of the hindlimbs increased, providing more forward propulsion. In the forelimb joints, only minimal velocitydependent changes in net joint energies occurred, indicating that, compared to the hindlimbs, adjustments in muscle activity did not behave in the same way. Increasing velocity also influences back movement. In unridden horses at trot, a reduced flexion-extension movement of the back was observed caused by increased muscle activity of the trunk muscles (Robert et al. 2001a(Robert et al. ,b, 2002. However, there is no information as to how the movement of the horse's back adapt to increasing velocities at walk. Byström et al. (2009Byström et al. ( , 2010 investigate...