Fibril mechanics suggest uneven stress distribution in the equine superficial digital flexor tendon (SDFT)

Fibril mechanics suggest uneven stress distribution in the equine superficial digital flexor tendon (SDFT)

450 Abstracts COMPUTATION OF IN VIVO STRAINPATTFRNSOF TRF,SUSPRNSORY LIGAMWl ANDITS RXTRNSOR BRANCHES IN THE FOREDIGIT OF THEHORSE M.O. Jansen, A. v...

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450

Abstracts

COMPUTATION OF IN VIVO STRAINPATTFRNSOF TRF,SUSPRNSORY LIGAMWl ANDITS RXTRNSOR BRANCHES IN THE FOREDIGIT OF THEHORSE 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.

GROUND REACTION FORCE ANALYSIS AS AN AID TO DIAGNOSIS OF EOUINE DIGITAL FLEXOR TENDON STRAIN A S. M. Dow, J. A Leenderts, 1. A. Silver & A. E. Goodship Comparative Orthopaeadic Research Unit, University of Bristol, U.K. The aim of this studywasto quantifygroundreactionforcesas a meansof identifyiag abnormalities of equine

locomotorperformance priorto theappearanceof overtclinicalsigns. Groundreactionforce datawererecordedfrom 18 horses in jump-racetrainingat monthlyintervals overa period of two years using a commercial force plate. Force-timepatterns for normallocomotionwerecstablisbcdandcompared with patterns from horses with known injuries allowing identification of specific functional components of the gait. Once the changes associated with injury to the superficial digital flexor tendon were isolated horses which were not cBnicaBy lame at the time, but which exhibited similar changes, were identified and their progress was monitored. Six points were chosen for comparison of the vertical (Fz) forces along with two slopes which correlated with the time of maximal extension of the metacarpal-phalangeal joint. Forces were expressed as a percentage of body weight and time measurements as percentage of the contact phase of the gait cycle. The normal variation in force-time patterns was established and compared with data from horses which had or developed cliical tendon injuries. The values of slopes Sl and S2 changed little with time or between normal, Iit horses. An increase in Sl and decrease in S2 correlated with superficial digital flexor tendon injury although the severity varied between horses. Value of Sl and S2 outside the normal population values (P c 0.05) became apparent before clical sign of lameness appeared thus providing an aid in the identification of subclinical tendon injury. This method of locomotor assessment can be an aid in the early diagnosis of specific biomechanical abnormalities.

FIBRIL MECHANICS SUGGEST UNEVEN STRESS DISTBIBUTION IN THE EQUINE SUPEBFICLU DIGITAL FLEXOR TENDON (SDFI’). J.W. WIlmlnk, AM. Wilson and A.E. Guudsbip. Comparative Orthopt~edtc Research Unit, Department of Anatomy, Unlverstty of BrtstoI, Brtstd, U&MI Ktngdom. Locahsed central fibrillar rupture is observed during mechanical tcstiagof equineSDFT. Thii was hypothcsiscd to resultfromlocal variation in fibril mechanics across the tendon. Crimp angle, crimp lengthandtoe limitstrainweremeasured for central (C) and peripheral (P) fibril bundles dissected from the SDPT of four young (GpY, age range 2-3 years) and four old (GpO, age range 10-12 years) thoroughbred horses. The crimp angle and crimp length of the central tibres from GpG was signiticantly less than that for peripheral t&es in GpG and all fibres in GpY. The toe limit strain was lower for central than peripheral 8brc.s in both GpY and GpO; the difference in GpY was 0.3% strain and in GpO 0.6% strain. The shorter toe region of tibres from the centre of the tendon should result in central Bbres experiencing higher stresses than peripheral tibres at a given overall strain magnitude. This may account for the site specific core lesions seen in equine tendon injury.