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.

Objective The aim of this study was to analyse the pelvic fracture distribution and location in a referral centre caseload. Materials and Methods Medical records of 6,717 horses examined in a referral centre over a 7-year period were reviewed to identify all horses diagnosed with a pelvic fracture. Eighty-six horses were identified and divided into three disciplines, namely Thoroughbred racehorses (TBR), Standardbred trotter racehorses (STR) and non-racing sport horses (NRSH). Results A pelvic fracture was diagnosed in 1.3% of the cases examined during the study period. Prevalence was significantly higher in TBR (4.2%) and, regardless of the discipline, in horses under the age of 6 years (2.2%) (p < 0.01). STR were significantly younger than TBR and NRSH at the time of fracture (median ages = 1, 3 and 4 years old, respectively; p < 0.01). The fractures occurred most frequently in the ilium (44/86). No ilial wing fractures were diagnosed in STR and isolated acetabular fractures were only diagnosed in foals and yearlings. Fatigue fractures were diagnosed in TBR alone, affecting 9/22 TBR (foals and yearlings excluded) and most often located in the ilial wing (7 fatigue fractures out of the 12 ilial wing fractures) (p < 0.01). The median age of horses suffering from a pelvic fatigue fracture was 4 years. Clinical Significance This study confirms that young horses (under the age of 6 years) as well as TBR are likely to be at higher risk of a pelvic fracture. Fatigue fractures of the ilial wing seem to be a rare condition in STR while they are more frequent in young TBR in training.

Objective The aim of this study was to evaluate the reliability of fracture location and horse sporting discipline as prognostic indicators after a pelvic fracture in a referral centre caseload. Materials and Methods Data were collected for the short- and long-term follow-up of all cases with a diagnosis of pelvic fracture in a 7-year period. Information was obtained for 75 horses through a postal and internet survey. The proportion of horses returning to competition following fractures was compared between groups according to the competition discipline and the characteristics of the fracture. Results Forty-six of 75 horses returned to or began their intended activity. This proportion was significantly lower in the group of horses that sustained a comminuted fracture irrespective of the fracture location (11/25, p = 0.05). The proportion of Standardbred trotter racehorses returning to a sporting career after pelvic fracture (9/20) was not significantly different from horses competing in other disciplines (37/55). Cases of multiple pelvic fractures in the study population, and particularly those involving the acetabulum, had the worst sports prognosis (2/8 and 0/4). Nevertheless, two foals and one yearling (3/5) with isolated fracture of the acetabulum went on to race. Clinical Significance A clear characterization of the fracture is essential for prognosis, as comminuted fractures seem to entail a poorer athletic prognosis. Despite a lack of significance, prognosis seems poorer for Standardbred trotter racehorses and for cases with acetabulum involvement in multiple fractures. These results should be confirmed in larger samples.

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.

Locomotor disorders involving the spine are a major cause of impaired performance and early retirement in sport horses. Swimming is increasingly incorporated into rehabilitation protocols, but its effects on spinal biomechanics remain poorly understood. This prospective study evaluated changes in thoracolumbar mobility in sixteen sport horses diagnosed with cervical or thoracolumbar axial musculoskeletal lesions over a 12-week rehabilitation program comprising 4 weeks of land-based training followed by 8 weeks during which swimming sessions were incorporated three times per week. Weekly measurements of thoracolumbar flexion–extension range of motion (ROM) were performed during straight-line trot on a hard surface using inertial measurement units attached to the withers, T18, and tubera sacrale. Group-level analyses revealed minimal changes across training phases: in horses with thoracolumbar lesions, mean ROM decreased slightly during the second month of aquatic training (−0.1° [95% CI −0.1; 0], Cohen’s d = 0.2), whereas no significant variation was detected in horses with cervical lesions. As the study did not include a control group, these temporal changes cannot be specifically attributed to swimming and should be interpreted as descriptive rather than causal. Individual trajectories showed heterogeneous patterns, but these were not consistent enough to alter the group-level interpretation. Overall, the findings suggest that thoracolumbar mobility remains relatively stable throughout this type of rehabilitation program, highlighting the importance of individualized monitoring rather than the expectation of a uniform biomechanical response.