Kinematics of the equine back : a method to study the thoracolumbar flexion-extension movements at the trot

HAL Id: hal-02690229

https://hal.inrae.fr/hal-02690229

Submitted on 1 Jun 2020

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Kinematics of the equine back : a method to study the thoracolumbar flexion-extension movements at the trot

Philippe Pourcelot, Fabrice Audigié, C. Degueurce, J.M. Denoix, D. Geiger

To cite this version:

Philippe Pourcelot, Fabrice Audigié, C. Degueurce, J.M. Denoix, D. Geiger. Kinematics of the equine back : a method to study the thoracolumbar flexion-extension movements at the trot. Veterinary Research, BioMed Central, 1998, 29 (6), pp.519-525. �hal-02690229�

Original

Kinematics of the equine ^back:

a

method

study ^the thoracolumbar flexion-extension

the

Philippe

Audigié Christophe Degueurce a

Jean Marie Denoix’ Didier

Geiger

CI Equipe ^{associée Inra} biomécaniquc du cheval. École nationale vétérinaire d’Alfort, 7, Av. du Gal de Gaulle, 94704 Maiaona-Alfiort cedex, ^France

h

Equipe ^{associée CNRS} 7052, Laboratoire de mécanique physique. Université de Paris XII, l, 61, ^{avenue du Gai de} Gaulle, 94010 Creteii cedex, ^France

(Received ²³ April ^1998; accepted 24 July 1998)

Abstract - This study ^{was conducted to evaluate a} method tor quantifying the tlexion-extension movements of the back of horses trotting ^{on a} track in the conditions of the clinical lameness exami- nation. Using ^a 3-D kinematic analysis system, the successive positions of four markers placed ^at reg- ular intervals between the withers and the tuber sacrale ^were recorded. To isolate the flexion-extension

movements of the back, the positions of these four markers were recomputed ^{in a} trunk-related co-ordi-

nate system of the horse. Then, for each frame, the equation of the third-order polynomial that best fit- ted the position of the four markers was determined. Using ^these equations, ^{it was then} possible ^{to inter-} polate the vertical displacement of any point situated between the withers and the tuber sacrale. The accuracy of this method ^was evaluated using three additional markers placed between the four previ-

ous ones. The vertical displacements of these three markers were recorded and compared ^{to the inter-} polated displacements provided by this method. The results showed that the experimental ^and interpolated

values did not present any statistical difference except in the lumbar region, ^{In this} region, ^the general shape of the vertical displacement ^{curve was} conserved but magnified by 17 °;’,. This study showed that

despite the weakness of the _range of the flexion-extension movements of the equine ^{hack at trot, these}

movements can be quantified ^with reliability. This method was then used on a lame horse. The results obtained demonstrated the usefulness of this method to study the tlexion-extension movements of horses suffering from various locomotor disorders. © InraElscvier, Paris.

spine / back / horse / kinematics / lameness

Résumé - Cinématique du dos chez le cheval : une méthode d’étude des mouvements de flexion-extension au trot. L’objectif de ^{cette étude est d’évaluer une} méthode de mesure des mou- vements de flexion-extension du dos de chevaux trottant sur une piste ^{dans les} conditions de l’exa-

men clinique ^des boiteries. À l’aide d’un système d’analyse cinématique ^{3-D, les} positions ^succes-

sives de quatre marqueurs placés à intervalle régulicr ^{entre le} garrot ^et le tuber sacrale ont été

*Correspondence ^and reprints

Tel.: (33) (0) 1 43967049; ^fax: (33) (0) 1 43 96 31 62; c-mail: Pourcelo@vet-alfort.fr

enregistrées. Afin d’isoler les mouvements propres a la colonne vertébrale, ^les positions ^{de ces}

quatre marqueurs ^ont été recalculées dans un repère ^{lié au tronc} du cheval. Puis, pour chaque image, l’équation ^du polynôme du troisième degré passant par ^ces quatre marqueurs ^a été déterminée. À l’aide de ces équations, il fut alors possible d’interpoler ^le déplacement vertical de n’importe quel point ^situé

entre le garrot ^et le tuber sacrale. Cette méthode a été évaluée à l’aide de trois marqueurs supplé-

mentaires placés ^{entre les} quatre précédents. ^Les déplacements verticaux de ces trois marqueurs ^ont été enregistrés puis comparés ^aux déplacements théoriques fournis par la méthode. Les résultats obtenus ont montré que les valeurs expérimentales ^et théoriques ^ne présentaient ^aucune différence sta-

tistiquement significative ^{sauf en} région lombaire. Dans cette région, ^{la forme} générale du tracé des

déplacements ^verticaux théoriques n’était pas altérée ; ^{en revanche} l’amplitude ^{de ce tracé se trouvait} amplifiée de 17 %. Les résultats de cette étude ont montré _que malgré la très faible amplitude ^{de mobi-}

lité en flexion-extension du dos d’un cheval au trot, ^ces mouvements peuvent néanmoins être quan- tifiés de façon fiable. Cette méthode a ensuite été exploitée ^{sur un} cheval boiteux. Les résultats obte-

nus ont montré l’intérêt de cette méthode dans l’étude quantitative ^des mouvements de flexion-extension du dos de chevaux souffrant d’affections de l’appareil loconurieur. © Inra/Elsevier, Paris.

colonne vertébrale / dos / cheval / cinématique ^{/ boiterie}

1. INTRODUCTION

Pathological patterns of locomotion are

sometimes observed on horses suffering

from back pains [4, 6, 8]; inversely, ^limb-

related lamenesses may have significant repercussions ^on the kinematics of the

equine ^back.

Many ^{in vitro} studies of the mobility ^of

the equine spine ^{have been} reported [5, 7, 15-17J, ^{but no} in vivo kinematic analysis

of the back movements of horses trotting

on a track has been carried out. This _may be due to the weakness of the _{range of} motion of the spine ^and consequently ^the difficulty ⁱⁿ obtaining reliable data.

The aim of this study ^{is to describe a}

method for quantifying the flexion-exten- sion movements of the back of horses trot-

ting ^{on a track in} the conditions of the rou-

tine lameness examination. This method will be illustrated with results from a sound horse and a lame horse.

2. MATERIALS AND METHODS

2.1. Method

Four markers are placed ^{at specific levels on}

the dorsal midline of the back of a horse (grey

markers infïgure /). ^The first marker (MI) ^is placed ^{over the tuber sacrale,} the second one

(M2) is placed ^{at the} top ^{of the} spinous process of the eighteenth thoracic vertebra or first lumbar vertebra, the third one (M3) ^at the level of the twelfth or thirteenth thoracic vertebra and the fourth one (M4) ^{on the} withers, i.e. at the level of the fifth or sixth thoracic vertebra. The trajecto-

ries of these markers are then collected using ^a

3-D kinematic analysis system.

The first step ^{of data} processing ^{is to filter}

the vertical displacements (z-co-ordinates) ^of

these markers using Fourier series. The filtered

displacements ^consist only of the first and second harmonic waves [ I I ] calculated ^{over one stride}

duration (figure 2). To isolate the tlexion!xten- sion movements of the back, ^the displacements ^of

the markers are expressed ^{in the} following ^trunk-

related co-ordinate system (figiii-e I):

- the origin of this co-ordinate system is rep- resented by the tuber sacrale marker (M 1 );

- the longitudinal ^axis (x-axis) ^{is defined as the}

line joining the tuber sacrate (Ml) ^{and with-}

ers (M4) markers;

- the transversal axis (y-axis) is nonnal to x-

axis and parallel ^{to the} ground;

- the vertical axis (z-axis) ^{is normal to x-} and y- axis.

The trajectories of the four markers are recom-

puted ^{in this new} co-ordinate system. ^{As this co-} ordinate system ^is trunk-related, the tuber sacrale marker (M I ) appeared static and the withers marker (M4) ^can only ^move along the x-axis.

For each frame of the stride, the third-order

polynomial that best fitted the (x, z) co-ordinates of the four markers is determined. The equation

of this polynomial permits computation ^{of inter-} polated points along the thoracolumbar spine

between the withers and the tuber sacrale.

A routine implementing this method was

developed ^{and added to a more} general computer program that tracks the markers ^on the 2-D video

images, calculates the 3-D co-ordinates of the markers and computes ^various parameters.

2.2. Experimental ^evaluation

of the method

A horse clinically free of lameness was fit- ted with four skin markers placed ^at specific ^lev-

els on the dorsal midline of its back, ^{as described} in the method. To evaluate the reliability ^{of this} method, ^{a second set} of three markers (m 1-2, m2-3, m3-4) ^was placed in the middle of the three segments ^defined by ^{the four} previous

markers (figure 1). Moreover, ^to identify ^the

stance phase, ^one additional marker was glued

to the dorsolateral wall of each fore hoof. The horse was then led by ^{hand at a slow trot} (3. I ^{1 ±}

0.22 m/s) and filmed trotting ^{on a track in a} straight line until six correct runs were com-

pleted. ^The recordings ^{were realised as} previ- ously ^described [12, 14] using four 8-mm video

cameras (Sony ^FX 700E, ⁵⁰ Hz, ) placed ^{in such}

a way that each side of the horse was filmed by

two cameras. The cameras were focused to image

a 5.50-m-long field of view and were synchro-

nised using ^{a method} previously ^described [ 13 1.

After digitisation of the 2-D video recordings,

the 3-D trajectories of the markers were calcu- lated using the direct linear transformation (D.L.T.) ^method [1,9, )0i. 1.

To assess the accuracy of the results provided by ^{this method, the} interpolated ^and experimen-

tal vertical displacements (z-axis) of the three markers m 1-2, ^{m2-3 and m3-4 were} compared.

The interpolated ^vertical displacements ^were computed using ^the equation of the third-order

polynomial calculated by the method. For each trial, ^one complete ^{stride was} analysed ^{and two}

different parameters ^were considered.

1) For each marker (ml-2, m2-3, m3-4), ^the

coefficient of correlation between the exper- imental and interpolated ^vertical displace-

ments was calculated.

2) ^{For each} stride, ^two ranges of vertical dis-

placement ^were calculated, ^one for the left

diagonal ^stance phase (left forelimb, right hindlimb) ^{and one for the} right diagonal

stance phase (right ^{forelimb, left} hindlimb).

These calculations were performed ^{for both} experimental ^and interpolated displacements.

For each marker, ^the interpolated ^values

obtained were compared ^{to the} experimental

ones using ^a paired ^{t-test. A P value < 0.05}

was considered to be significant.

2.3. Example ^{of use} of this method A horse, moderately ^{lame at a trot,} suffering

from a right tarsal osteoarthritis (bone spavin)

fitted with four markers on its back was recorded

as described above. Using the method previously

described the trajectories ^{of 20} interpolated points regularly spaced along its thoracolumbar spine

were calculated. Such a number of points ^was

chosen because it corresponds ^to the number of vertebrae situated between the withers and the tuber sacrale.

3. RESULTS

3.1. Experimental ^evaluation

In tab(e I the coefficients of correlation obtained between the experimental ^{and inter-} polated ^vertical displacements ^are presented.

These coefficients were all larger ^{than 0.96} except ^for trial number 5 where a value of 0.94 was observed for m3-4.

Table II presents ^{the mean} ranges of the vertical displacements ^{for both} experimen-

tal and interpolated displacements. ^{The inter-} polated values obtained for the ml-2 were

significantly higher (+17 %) ^{than the} exper- imental ones.

3.2. Results obtained for a lame horse

Figure 3 presents ^the trajectories ^{of the}

20 interpolated points ^obtained during ^the

first of the six trials. Numbering ^the points

from left (tuber sacrale) ^to right (withers),

the maximal _range of vertical displacement (average ^{of six} trials) ^was observed for point

number 1 1 for the sound diagonal ^stance phase. ^This point corresponds approximately

to the fifteenth thoracic vertebra. Its mean

value was 2.1 1 ± 0.14 cm. This value was

significantly higher (P ^< 0.05) ^{than the one} obtained for the lame diagonal ^stance phase

for which a mean value of 1.61 ± 0.12 cm

was found. Moreover, this value was not observed for point ^{number 1 1 but for} point

number 13, ^{that is to} say approximately ^the

thirteenth thoracic vertebra.

4. DISCUSSION

To record the kinematics of two strides of

a horse trotting ^{on a track, a} 5.50-m-long

field of view is needed. As mentioned in the

Introduction, the range of motion of the

spine is very small and consequently ^{it is}

necessary ^to filter the random errors (noise)

caused by ^the digitisation process ^to obtain reliable data. If we assume that the vertical

displacements of markers placed ^{on the back}

of a sound or a lame trotting ^{horse are} 1 ) periodic ^and 2) ^{consist of an} asymmetrical part ^{and a} symmetrical part [ 11 these ^dis- placements ^can be modelled using ^Fourier

series. It is then possible ^{to filter these ver-}

tical displacements by calculating only ^the

first (asymmetrical part) and the second

(symmetrical part) ^{harmonic waves.}

As proved by ^the high values of coeffi- cients of correlation observed between the

experimental ^and interpolated vertical dis-

placements, this method does not alter the

general shape ^{of the curves. In the same}

way, the interpolated ranges of the vertical

displacement ^{were not altered} using ^this

method except for the marker m 1-2 where

a significant difference was observed with the experimental ranges. For this marker the

general shape ^{of the} interpolated ^vertical displacement ^was maintained but its _range

was magnified.

This method provides ^a non-invasive

means of evaluating ^the mobility of the back.

Nevertheless, ^{two main} types ^{of error} may alter the results.

1 ) The resolution of the system may affect the 3-D co-ordinates of the markers. In the

experimental conditions used in this study,

the resolution of the system has been eval- uated at 0.4 cm. This value is the maximal

error of location of a moving ^{marker in an}

absolute co-ordinate system. ^{This error is} mainly ^{due to} systematic ^errors resulting

from lens distortions [3] and, consequently,

is dependent ^on the location of the marker in the workspace. On the other hand, ^{the rela-} tive error made on the displacement ^{of a} moving ^{marker in a} part ^of the field of view is lower and estimated at 1 mm in our exper- imental conditions.

2) ^{The use of skin markers} introduces a sec-

ond source of error. First, errors are made in marker placement, and second the move- ments recorded are those of the skin and not

those of the underlying ^skeletal structures.

Audigié ^{et al.} [2J showed that errors in marker placement ^{can reach 2 cm for the} proximal joints of the limbs while Van Weeren [18j quantified ^{the skin} displace-

ments with respect ^{to the} underlying ^bones

of the limbs but no systematic study ^{of the}

effects of these errors for markers placed

over spinous processes has been reported.

Our technique ^{has a} clinical usefulness and was mainly developed for that purpose.

We used the lame horse merely as an exam-

ple. ^{It is not the} purpose ^{here to} make an assessment of the effects of a lameness, ^but

to show that the possibility ^exists.

The results obtained in this method demonstrate the interest of kinematic tech-

niques ^{to measure} phenomena ^{difficult to} quantify by visual observation. Using ^this approach, ^a systematic study ^{will be under-}

taken to compare the flexion-extension of the back of a group of sound horses with those of horses suffering from various loco-

motor disorders.

ACKNOWLEDGEMENTS

The authors wish to acknowledge ^their gratitude ^to Patricia Perrot and Benoit Bousseau for their important contributions.

This study ^was supported by the Institut national de la recherche agronomique ^and

the Service des haras et de 1’equitation.

REFERENCES

[ 1 ] Abdel-Aziz Y.1., ^Karara H.M., Direct linear trans- formation from comparator co-ordinates into

object-space co-ordinates in close-range pho- togrammetry, ^{Proc. Am. Soc. for} Photogramme- try, Urbana, Illinois, January, ¹⁹⁷ pp. ^1-18.

121 Audigi6 ^{F., Pourcelot P.,} Degueurce C., ^Denoix J.M., Geiger ^G., Bortolussi C., Asymmetry ⁱⁿ placement of bilateral skin markers on horses and effects of asymmetric skin marker placement ^on

kinematic variable, Am. J. Vet. Res. 59 (1998) 938-944

[31 ^Chen L., Armstrong C.W., Raftopoulos D.D., ^An investigation ^on the accuracy of three-dimen- sional space reconstruction using the direct linear

transformation technique, J. Biomech. 27 ( 1994) 493-500.

141 ^Dalin G., Magnusson L.E., Thafvelin B.C., Ret-

rospective study ^of hindquartcr asymmetry ⁱⁿ Standardbred Trotters and its correlation with

performance, Equine ^Vet. J. 17 (1985) ^292-296.

[5] ^{Denoix J.M.,} Kinematics of the thoracolumbar

spine of the horse during dorsoventral move- ments: a prcliminary report, ^in: Gillespie ^J.R.,

Robinson N.E. (Eds.), Proc. 2nd Int. Conference

on Equine ^Exercise Physiol., ^San Diego, ^Cali- fornia, August, 1986, pp. 607-614.

[6] ^Jcffcott L.B., Disorders of the thoracolumbar

spine of the horse-- survey of 443 ^cases, Equine

Vct. J. 12 (1980) ^197-210.

[71 Jeffcott L.B., Dalin G., ^Natural rigidity ^{of the}

horse’s backbone, Equine ^{Vet. J. 12} (1980) 101-108.

18] ^Jeffcott L.B., ^Dalin G., ^Drevemo S., Fredricson I., Bjorne K., Bergqvist ^A., Induction of back pain ⁱⁿ trotting horses and its effect on performance,

Svensk Veterinartidning ³⁵ (1983) ^110-113.

[9] ^Marzan G.T., Karara H.M., A computer program for direct linear transformation solution of col-

inearity condition, ^{and some} applications ^{of it,}

Proc. Symp. ^on Close-Range Photogrammetric Systems, Falls Church, VA, 1975, pp. 420-476.

[ 10! ^Miller N.R., Shapiro R., McLaughlin ^{T.M., A} technique ^for obtaining spatial kinematic param- eters of segments of biomechanical systems ^from cinematographic data, J. Biomech. 13 (1980) 535-547.

[111 I ! Peham C., ^Scheidl M., ^Licka T., A method of

signal processing ^{in motion} analysis ^{of the} trotting horse, J. Biomech. 29 (1996) 11 1 1-I 1 14.

j )2] ^Pourcelot P., Audigi6 ^F., Degueurce C., ^Denoix J.M., Geiger G., ^Kinematic Symmetry ^{Index: a}

method for quantifying the horse locomotion sym- metry using ^{kinematic data,} Vet. Res. 28 (1997) 525-538.

[ 13] ^Pourcclot P., Audigi6 F., Degueurce C., Geiger ^G.,

Denoix J.M., A numerical method to synchro-

nize home video cameras using ^{D.L.T. method,}

Med. Biol. Eng. Comput. ³⁵ (1997) ^715.

! 14] ^Pourcelot P., Degueurce C., Audigi6 ^{F., Denoix} J.M., Geiger G., ^Kinematic analysis of the loco- motion symmetry of sound horses at a slow trot,

Equine ^{Vet. J.} Suppl. ²³ (1997) ^93-96.

[151 ^Townsend H.G.G., ^Leach D.H., Relationship

between intervertebral joint morphology ^and mobility ^{in the} equine thoracolumbar spine, Equine ^{Vet. J. 16} (1984) ^461-465.

! 16! ^{Townsend H.G.G, Leach D.H., Fretz P.B., Kine-} matics of the equine thoracolumbar spine, Equine Vet. J. 15 (1983) ^{I 17-122.}

[17] ^{Townsend H.G.G., Leach D.H.,} Doige C.E., Kirkaldy-Willis ^W.H., Relationship ^between spinal biomechanics and pathological changes ⁱⁿ

the equine thoracolumbar spine, Equine ^{Vet. J.}

18 (1986) ^{107-I 12.}

[)8j Van Weeren P.R., ^Skin displacement ⁱⁿ equine

kinematic gait analysis, thesis, Utrecht, ^1989.