Hydrotherapy has been utilized in horse rehabilitation programs for over four decades. However, a comprehensive description of the swimming cycle of horses is still lacking. One of the challenges in studying this motion is 3D underwater motion capture, which holds potential not only for understanding equine locomotion but also for enhancing human swimming performance. In this study, a marker-based system that combines underwater cameras and markers drawn on horses is developed. This system enables the reconstruction of the 3D motion of the front and hind limbs of six horses throughout an entire swimming cycle, with a total of twelve recordings. The procedures for pre- and post-processing the videos are described in detail, along with an assessment of the estimated error. This study estimates the reconstruction error on a checkerboard and computes an estimated error of less than 10 mm for segments of tens of centimeters and less than 1 degree for angles of tens of degrees. This study computes the 3D joint angles of the front limbs (shoulder, elbow, carpus, and front fetlock) and hind limbs (hip, stifle, tarsus, and hind fetlock) during a complete swimming cycle for the six horses. The ranges of motion observed are as follows: shoulder: 17 ± 3°; elbow: 76 ± 11°; carpus: 99 ± 10°; front fetlock: 68 ± 12°; hip: 39 ± 3°; stifle: 68 ± 7°; tarsus: 99 ± 6°; hind fetlock: 94 ± 8°. By comparing the joint angles during a swimming cycle to those observed during classical gaits, this study reveals a greater range of motion (ROM) for most joints during swimming, except for the front and hind fetlocks. This larger ROM is usually achieved through a larger maximal flexion angle (smaller minimal angle of the joints). Finally, the versatility of the system allows us to imagine applications outside the scope of horses, including other large animals and even humans.

Aquatic training has been integrated into equine rehabilitation and training programs for several decades. While the cardiovascular effects of this training have been explored in previous studies, limited research exists on the locomotor patterns exhibited during the swimming cycle. This study aimed to analyze three distinct swimming strategies, identified by veterinarians, based on the propulsion phases of each limb: (S1) two-beat cycle with lateral overlap, (S2) two-beat cycle with diagonal overlap, and (S3) four-beat cycle. 125 underwater videos from eleven horses accustomed to swimming were examined to quantify the differences in locomotor patterns between these strategies. Initially, a classifier was developed to categorize 125 video segments into four groups (CatA to CatD). The results demonstrated that these categories correspond to specific swimming strategies, with CatA aligning with S1, CatB with S2, and CatC and CatD representing variations of S3. This classification highlights that two key parameters, lateral and diagonal ratios, are indeed effective in distinguishing between the different swimming strategies. Additionally, coordination patterns were analyzed in relation to these swimming strategies. One of the primary findings is the variability in swimming strategies both within and between individual horses. While five horses consistently maintained the same strategy throughout their swimming sessions, six others exhibited variations in their strategy between laps. This suggests that factors such as swimming direction, pauses between laps, and fatigue may influence the selection of swimming strategy. This study offers new insights into the locomotor patterns of horses during aquatic training and has implications for enhancing the design of rehabilitation protocols.

Summary: Fractures of the third trochanter of the femur are an uncommon cause of hindlimb lameness in the horse. The diagnosis is easily made with ultrasonography. Reported prognosis is good after a period of rest and a progressive return to exercise. This case report describes a third trochanter fracture in a 5‐year‐old trotter mare, which is atypical in terms of both its clinical presentation and management. At the dynamic examination, a left hind lameness was only observed when harnessed at the track. Nuclear scintigraphic examination revealed a marked increase in radiopharmaceutical uptake on the third trochanter of the left femur. Radiographic and ultrasonographic findings confirmed an old complete fracture of the third trochanter of the left femur, with a displaced fragment. The mare was referred for surgical treatment in order to remove the fractured third trochanter. At the follow‐up examination, the mare was sound in hand and imaging revealed successful resection of the main fractured fragment. After a period of stall rest, the mare progressively resumed training and then racing 7.5 months after the surgery, performing at its expected level. Surgical treatment may be an option for chronic fractures of the third trochanter.

Objective: To quantify changes in the cross-sectional area (CSA) of the midmetacarpal superficial digital flexor tendon (SDFT) in young Trotters during training. Methods: In this experimental study, 12 healthy 3-year-old French Trotters, assigned to either a soft-track or a hard-track group, were trained for 4 months (June through September of 2012 and 2013). Both groups followed the same exercise program of increasing intensity. Ultrasonographic examinations of both forelimb SDFTs of each horse were performed before the beginning of training (D0), after 2 months of training (M2), and after 4 months of training (M4). The tendon CSA at the midmetacarpus was measured at each session, and the percentage of change over time was calculated. Results: 3 of 6 horses trained on the hard track developed bilateral SDFT tendinopathy at M4 (n = 6 tendons). The tendon CSA in horses without tendinopathy (n = 18 tendons) significantly increased: +6.8% at M2 and +4.3% at M4, compared to D0; the CSA change from M2 to M4 was −2.3% while exercise intensity increased. Although the tendons that developed tendinopathy at M4 were asymptomatic at M2, a posteriori analysis revealed that their CSA percentage of increase from D0 to M2 (+13%) was significantly larger compared with tendons that remained uninjured. The CSA continued to increase from M2 to M4 in these tendons (+27.9%). Conclusions: Increased SDFT CSA in Trotters during the initial phase of training and a greater rate of CSA increase for those with early tendon damage suggest adaptive changes to exercise and injury. Clinical Relevance: Early tendon damage should be suspected when CSA increase reaches 10% or more in 2 months.