Objective—To develop a method that allows quantification of the 3 anatomic rotations in the digital joints of moving horses and measure these rotations when horses are walking in a straight line on a hard track. Animals—4 healthy French Trotter horses. Procedure—Triads of ultrasonic kinematic markers were surgically linked to the 4 distal segments of the digits of the left forelimb of each horse. Three-dimensional (3-D) coordinates of these markers were recorded in horses walking in a straight line. The three angles of rotation of each digital joint were calculated by use of a joint coordinate system as well as the 3-D orientation of the hoof and third metacarpal bone. A calibration procedure was developed to convert data from measurements within a technical coordinate system to data in relation to an anatomically relevant coordinate system. Results—Precision of the method was 0.5^o, and repeatability of the calibrations resulted in variations of 1.4^o. Extrasagittal movements of the proximal and distal interphalangeal joints were obvious during landing because the impact of the hoof was on the lateral side. Mean ± SD extension of the proximal interphalangeal joint was 10.0 ± 2.5^o. Conclusions and Clinical Relevance—This study provides a description of the technical background, error analysis, and procedures used to measure the 3-D rotations of the 4 distal segments of the forelimb in walking horses. As a major result substantial involvement of the proximal interphalangeal joint in the sagittal and extrasagittal planes,should incline investigators and clinicians to consider the functional importance of this joint. (Am J Vet Res 2004;65:447–455)

The sagittal alteration of hoof balance is a common intervention in horses, with corrective shoeing being one of the most frequently applied methods of managing tendonitis. However, the effect of toe or heel elevation on tendon strains is poorly understood. This study aimed to examine the effect of toe and heel wedges on the superficial digital flexor tendon, deep digital flexor tendon, and the third interosseous muscle or suspensory ligament strains usingin vivodata and an accurate subject‐specific model. Kinematic data were recorded using invasive markers at the walk and trot. Computerized tomography was then used to create a subject‐specific model of an equine distal forelimb and strains were calculated for the superficial digital flexor tendon, the deep digital flexor tendon accessory ligament and the suspensory ligament for seven trials each of normal shoes, and toe and heel elevation. As the proximal interphalangeal joint is often ignored in strain calculations, its influence on the strain calculations was also tested. The deep ligament showed the same results for walk and trot with the heel wedge decreasing peak strain and the toe wedge increasing it. The opposite results were seen in the suspensory ligament and the superficial digital flexor tendon with the heel wedge increasing peak strain and the toe wedge decreasing it. The proximal interphalangeal joint was shown to be influential on the strains calculated with normal shoes and the calculated effect of the wedges. Our results imply that corrective shoeing appears to decrease strain in the tendon being targeted; the possibility of increases in strain in other structures should also be considered.