Margot O. Jansen

In vivo Tendon Forces in the Forelimb of Ponies at the Walk, Validated by Ground Reaction Force Measurements

The load distribution over tendinous structures in the equine forelimb was studied by computing forces from in vivo signals of implanted liquid-metal strain gauges in 5 ponies. For validation, these tendon forces were converted to joint moments, which were summed and compared to the calculated joint moments caused by the ground reaction force. Mean peak forces per kilogram body weight (n = 5) amounted to 5.2 N/kg for the superficial digital flexor tendon, 3.8 N/kg for the deep digital flexor tendon, 7.3 N/kg for the distal accessory (check) ligament and 8.4 N/kg for the third interosseous muscle (suspensory ligament). The maximal moment exerted by the tendons about the fetlock joint differed 11 +/- 7% (average +/- SD, n = 5) from the maximal ground reaction force moment, which difference amounted to 17 +/- 15% for the coffin joint moments. These differences appeared to result to a substantial extent from errors in the moment arms. Therefore, the computed tendon forces were considered to be sufficiently reliable.

Strain of the Musculus interosseus medius and Its Rami extensorii in the Horse, Deduced from in vivo Kinematics

The in vivo strains of the musculus interosseus medius (suspensory ligament) and its rami extensorii (extensor branches) in the forelimb of the horse were determined from angular changes of the metacarpophalangeal and the distal interphalangeal joints. For this purpose, regression models were fitted to strains and joint angle combinations measured in in vitro limb loading experiments. The in vivo strains were computed from the kinematics of 8 horses at the walk, the trot and the canter. It was found that the extensor branches were strained about 1.0% at hoof impact, which indicates that they passively extend the interphalangeal joints just prior to impact and prevent flexion of the pastern joint just thereafter. The maximal strain of the suspensory ligament amounted to 3.4% at the walk, 5.6% at the trot and 6.3% at a slow canter.

A kinematic and strain gauge study of the reciprocal apparatus in the equine hind limb

Hind limb kinematics were recorded in five horses at walk and trot using an opto-electronic CODA-3 system. Simultaneously, in vivo strain in the completely tendinous peroneus tertius muscle was registered by implanted mercury-in-silastic strain gauges. The origin-insertion length patterns of the peroneus tertius were calculated from raw kinematic data and from data corrected for the error caused by skin displacement, and compared with the directly measured strain. The strain patterns calculated from externally measured kinematic data appeared to be in accordance with the directly measured strain gauge data. However, a correction for skin displacement is an obligatory prerequisite to obtain reliable results. The amplitudes of strain did not exceed 3% and appeared to be of about the same magnitude at both walk and trot.

MECHANICAL PROPERTIES OF THE TENDINOUS EQUINE INTEROSSEUS MUSCLE ARE AFFECTED BY IN VIVO TRANSDUCER IMPLANTATION

Liquid metal strain gauges (LMSGs) were implanted in the tendinous interosseous muscle, also called suspensory ligament (SL), in the forelimbs of 6 ponies in order to quantify in vivo strains and forces. Kinematics and ground reaction forces were recorded simultaneously with LMSG signals at the walk and the trot prior to implantation, and 3 and 4 days thereafter. The ponies were euthanised and tensile and failure tests were performed on the instrumented tendons and on the tendons of the contra lateral limb, which were instrumented post mortem. The origo-insertional (OI) strain of the SL was computed from pre- and post-operative kinematics, using a 2D geometrical model. The LMSG-recorded peak strain of the SL was 5.4+/-0.9% at the walk and 9.1+/-1.3% at the trot. Failure occurred at 15.4+/-2.1% (mean+/-S.D.). The LMSG strain was higher than the simultaneously recorded OI strain 0.5+/-0.7% strain at the walk and 2.2+/-1.1% strain at the trot. Post-operative OI strains were only slightly higher than pre-operative values. Failure strains of in vivo instrumented SLs were 2.0+/-1.2% strain higher, and failure forces were slightly lower, than those of the contra lateral SLs that were instrumented post mortem. SL strains appeared to be considerably higher than those found in earlier acute experiments. Differences between in vivo LMSG and OI strains, supported by lower failure strains comparing in vivo and post mortem instrumented SLs, revealed that local changes in tendon mechanical properties occurred within 3 to 4 days after transducer implantation. Therefore, measurements of normal physiological tendon strains should be performed as soon as possible after transducer implantation.

Computation of in vivo strain patterns of the suspensory ligament and its extensor branches in the fore digit of the horse

COMPUTATION OF IN VIVO STRAIN PATTFRNS OF TRF, SUSPRNSORY LIGAMWl AND ITS RXTRNSOR BRANCHES IN THE FORE DIGIT OF THE HORSE M.O. Jansen, A. van Buiten and A.J. van den Bogart Department of veterinary anatomy, University of Utrecht P.O. Box 80.157, 3508 TD Utrecht, The Netherlands. Investigation of the function of these passive structures required knowledge about their in vivo strain behaviour. -The relationships between distal joint angles and strain of the extensor branches (EB), resp. suspensory ligament (SL) were derived from in vitro -experiments on 6 fore limbs. Using a least squares method, a linear model was fitted to the SL strain and an exponential model was fitted to the F.B strain (average fitting error of 0.2 X strain for both models). These regression models were used to calculate SL and RB strains from kinematical data. These data were recorded during walk and trot, using a modified CODA-3 gaitanalysis system. The SL strain showed peak values of 2.7 4 at the walk and 4.7 X at the trot, which is consistent with earlier direct SL strain measurements. The RB patterns revealed, that at initial ground contact of the hoof they were already strained 1 X and reached their peak value at an early stage of the stance phase, with little difference between walk and trot. It was concluded, that the major function of the passive RB is to take care of positioning the hoof ‘automatically’ just prior to ground contact.