-The objective of this study was to assess the effects of asymmetric placement of the foot on the three-dimensional motions of the interphalangeal joints. Four isolated forelimbs were used. Trihedrons, made of three axes fitted with reflective markers, were screwed into each phalanx. They allowed to establish a local frame associated with each bone and thus to define the spatial orientation of the phalanges. The limbs were then placed under a power press, and subjected to compression with gradually increasing force (from 500 to 6 000 N). The procedure was performed in neutral position and with the lateral or medial part of the foot raised by a 12 o wedge. Flexion, collateromotion (passive abduction/adduction) and axial rotation of the interphalangeal joints were measured using a cardan angle decomposition according to the principle of the "Joint Coordinate System" described by Grood and Suntay. Raising the lateral or medial part of the hoof induced collateromotion (about 5.6 o ± 0.8) and axial rotation (about 6.5 o ± 0.5) of the distal interphalangeal joint. The proximal interphalangeal joint underwent axial rotation (about 4.7 o ± 0.5 at 6 000 N) and slight collateromotion. Both interphalangeal joints underwent collateromotion in the direction of the raised part of the foot (i.e., narrowing of the articular space on the side of the wedge), whereas axial rotation occurred in the direction opposite to the raised part of the foot. These results confirm the functional importance of interphalangeal joint movements outside the sagittal plane. In particular they demonstrate the involvement of the proximal interphalangeal joint in the digital balance. These data are helpful for the identification of biomechanical factors that may predispose to interphalangeal joint injury. Also the data may be of use for the rational decision making with respect to exercise management and corrective shoeing of the lame horse. Résumé -Étude cinématique tridimensionnelle des articulations interphalangiennes chez le cheval: influence de l'appui asymétrique du pied. L'objectif de cette étude était de déterminer les effets de l'appui asymétrique du pied sur le comportement tridimensionnel des articulations interphalangiennes. Quatre membres isolés ont été utilisés. Des systèmes de suivi cinématique, pourvus de 3 axes portant des marqueurs réfléchissants ont été vissés dans chaque phalange. Ces systèmes permettaient de déterminer, pour chaque segment osseux, un repère local définissant l'orientation du segment. Les membres ainsi équipés étaient placés sous une machine de compression et soumis à des cycles de mise en charge de 500 à 6 000 N, en modifiant l'orientation du sabot par l'apposition d'une cale de 12 o sous le quartier latéral ou médial. Les angles de flexion, collatéromotion (abduction/adduction passive) et rotation axiale des articulations interphalangiennes ont été calculés selon le principe du « Système d'Axes Articulaires » énoncé par Grood et Suntay. Les modifications de l'appui transversal du pied ont provoqué un mou...

Summary The purpose of this study was to quantify small amplitude rotational movements in the metacarpophalangeal joint (MPJ) of the horse and to measure the influence of asymmetric placement of the foot on these articular angles. Trihedrons, supporting kinematic markers defining a local frame, were screwed into the third metacarpal bone and the proximal phalanx of 4 isolated forelimbs. The limbs were loaded in a press, and the lateral or medial aspects of the foot were raised alternately by a 12° wedge. The use of the joint coordinate system permitted the simultaneous and continuous computing of the 3 angles of rotation of the joint. During neutral loading, the extension of the MP.I*** (38.4 ± 8.7°) was associated with lateral axial rotation of the proximal phalanx (1.8 ± 0.9°). Addition of a lateral wedge induced medial rotation (‐0.9 ± 0.2°) and abduction (2.1 ° 0.4) of the proximal phalanx. The opposite phenomenon was observed with a medial wedge. These quantitative results confirmed the combination of axial rotation and widening of the articular space on the opposite side to the raised part of the foot that had earlier been observed in semi‐quantitative studies. Despite the high congruence of this joint, this study demonstrated the significant influence of uneven bearing of the foot on the three‐dimensional (3‐D) behaviour of the MPJ. Even though the amplitude of these movements remained small, their biomechanical effects should be considered to improve our understanding of MPJ injuries and to rationalise exercise management and corrective shoeing in the lame horse.

Summary The proximal interphalangeal joint (PIPJ) has always been considered as a low‐motion joint with an almost constant angle during loading of the limb. Until very recently, its motion was not taken into account in kinematic studies in vivo. Recent in vivo studies yielded surprisingly high ranges of motion in this joint. The aim of this study was to measure, in terms of the 3 possible rotations (flexion/extension, collateromotion and axial rotation), the movements of the PIPJ in vitro during limb loading in a neutral position (500‐6000 N) and after the addition of heel and toe wedges (6° and 12°). The joint coordinate system, as it was recently described for use in the horse, was used to compute the 3 components of rotation. With the hoof in neutral position, low‐amplitude flexion movements (7.9°) were observed. They were not associated with collateromotion or axial rotation. The flexion of the joint increased exponentially with load suggesting that, during the midstance phase, heavy loads are necessary to evoke substantial flexion. Raising the heels induced an early flexion of the joint with an increase of its total amplitude. Raising the toe produced an extension at 500 N, beyond which the amount of flexion was reduced. These results show that PIPJ flexion/extension during in vitro loading remains substantially smaller than suggested by in vivo studies based on skin markers. Raising the toe or heel directly affects the behaviour of this joint, but does not induce motion outside the sagittal plane. Hoof wedges are commonly used in clinical practice for purposes other than affecting PIPJ motion. In these cases, their biomechanical effects on this joint should be taken into account.

In page 303, the global matrix should read:In page 304, Section 2.2.2.3, the elementary angles should read:, θ 2 = asin r 23 , . θ 3 = -atan r 21 r 22 θ 1 = -atan r 13 r 33. .

-A method is detailed allowing the computation of three-dimensional (3D) joint angles. Each joint of the equine digit is modelled as a sequence of three single axis rotary joints. The Joint Coordinate System was used; it involves a specific sequence of cardanic angles. The decomposition of the angles was chosen so that the three elementary angles coincide with the flexion/extension, passive abduction/adduction and lateral/medial rotations. The algorithms and kinematic procedures were described for the equine front digital joints. This method was tested in vitro on four forelimbs. For each limb, angle values were measured while the member was loaded by a press (from 500 to 6 000 N). These tests were repeated while a wedge raised one part of the hoof (toe, heel, lateral and medial sides) in order to induce modifications of the angular patterns of the joints. This method allowed a precise quantitative determination of 3D joint movements. The modifications occurring with the wedges are clearly identified and confirm some previously published semi-quantitative observations. Moreover, this method provides a way to collect objective data on the functional anatomy of joints and could be used to study connective shoeing thoroughly. It may be directly applied to other species and may be used by researchers interested in discreet articular movements, especially occurring in other planes than the sagittal one.horse / kinematics / digital joint / joint coordinate system / cardanic angles Vet. Res. 31 (2000) 297-311 297

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