Management of severely injured or neurologic horses is challenging, with ambulatory support limited to static lifts and rescue slings. The aim of this study was initial testing and adjustment of a novel computer-integrated dynamic lift system, including measuring effects of increasing weight compensation (i.e. load reduction) and time attached to the lift. This automated system was developed to improve outcomes and reduce complications in horses with ambulatory difficulties, allowing for controlled mobility and varying load carried by the horse with independent front and hind limb support. Two healthy Thoroughbred horses were studied using the Anderson rescue sling. The lift was programmed to respond to weight and movement of horses. Weight compensation (% bodyweight) was incrementally increased, for front and hind limbs, to maximum percent tolerated, based on heart/respiratory rates and behavioural scoring. The time attached to the lift was then incrementally increased at maximum tolerated weight compensation previously determined. Measures included heart/respiratory rates, behavioural scoring, muscle enzyme activity and blood flow to distal limbs. Results were analysed descriptively. Avoidance behaviour was observed at front and hind end weight compensation of 18 and 4%, respectively. Average maximum time attached to the lift was 2.25 hours. After 60 minutes, respiratory rate increased >20 breaths (b)/minute, reaching 60 b/minute in one horse and 36 b/minute in the other, with shallow breathing. Other measures remained normal. In conclusion, lift programming was successful for weight compensation and mobility during lift support. Complications included avoidance behaviour and respiratory distress at >20% weight compensation, likely caused by the Anderson rescue sling. To address these limitations, a new rehabilitation harness better suited for long-term use is under development.
Development of a rehabilitation harness to aid in recovery from musculoskeletal injuries is needed because serious complications can arise from long-term use of rescue slings. This study’s objective was to determine the anatomical structures of the horse that can bear significant weight, the potential complications that could arise if a horse is not properly supported by the harness and the % weight compensation achievable with the newly developed harness when used together with a dynamic rehabilitation lift. This dynamic lift can reduce the load the limbs carry, either withers-to-pelvis or left-to-right when used in combination with the rehabilitation harness under development. The rehabilitation harness prototype described here was made of cotton/nylon with sheepskin inserts, forming a blanket with high-strength strapping supporting the load-bearing structures of the horse. This prototype was load tested up to 600 kg, for safety, with no sign of failure. In an adult horse, the harness allowed for 40% load reduction from both front (125 of 303 kg [60% of 506 kg]) and hind (80 of 203 kg [40% of 506 kg]) legs before complications (abnormal posture) occurred. Pressure was measured to determine areas of high pressure which lead to the addition of an H-frame and a figure-eight pattern of strapping to the forelimb support reducing pressure, improving posture and achieving greater load reduction (46% [140 of 301.2 kg]). Abnormalities in respiratory rate or pattern were not observed. Future research will include testing the harness longer term (up to six weeks) with the incorporation of an air-pressurised breastplate to detect high-pressure, high-temperature, high-moisture areas, modifying the design further for improved horse-comfort reducing the risk of complications and enabling long-term use of the harness during rehabilitation.
Quantitative tracking of equine movement during stall confinement has the potential to detect subtle changes in mobility due to injury. These changes may warn of potential complications, providing vital information to direct rehabilitation protocols. Inertial measurement units (IMUs) are readily available and easily attached to a limb or surcingle to objectively record step count in horses. The objectives of this study were: (1) to compare IMU-based step counts to a visually-based criterion measure (video) for three different types of movements in a stall environment, and (2) to compare three different sensor positions to determine the ideal location on the horse to assess movement. An IMU was attached at the withers, right forelimb and hindlimb of six horses to assess free-movement, circles, and figure-eights recorded in 5 min intervals and to determine the best location, through analysis of all three axes of the triaxial accelerometer, for step count during stall confinement. Mean step count difference, absolute error (%) and intraclass correlation coefficients (ICCs) were determined to assess the sensor's ability to track steps compared to the criterion measure. When comparing sensor location for all movement conditions, the right-forelimb vertical-axis produced the best results (ICC = 1.0, % error = 6.8, mean step count difference = 1.3) followed closely by the right-hindlimb (ICC = 0.999, % error = 15.2, mean step count difference = 1.8). Limitations included the small number of horse participants and the lack of random selection due to limited availability and accessibility. Overall, the findings demonstrate excellent levels of agreement between the IMU's vertical axis and the video-based criterion at the forelimb and hindlimb locations for all movement conditions.
Summary Equine musculoskeletal injuries, or other causes of reduced movement, can have a poor prognosis partially due to the secondary complications that may develop during recovery or rehabilitation. These can include supporting limb laminitis due to excessive weightbearing on healthy limbs and also problems associated with ventilation or perfusion due to prolonged recumbency. The risk of these complications is reported to increase with increasing body weight. While many methods have been attempted to reduce load and prevent complications, there is no current standard practice when managing horses with ambulatory difficulties. One critical consideration with load reduction devices is maintaining sufficient mobility to allow for blood flow and the prevention of muscle wasting. One of the most challenging obstacles with any weight reduction method or device is preventing pressure sores/ulcers or other tissue trauma because load is redistributed away from the limbs and onto regions of the body unaccustomed to weightbearing. Reported methods to aid in recovery and rehabilitation include rescue slings, forced recumbency, flotation tanks, water treadmills and aquatic therapy. While these methods have been successful in some horses, significant complications have also been reported. If too much weight is removed, muscle wasting or osteopenia occurs; conversely, if insufficient weight is lifted blood flow is hindered. The optimal load reduction is not known because each individual horse will have different requirements depending on the severity of the injury. The goal would be to restore normal weight distribution on the noninjured limbs, while supporting the weight that would normally be placed on the injured limb.
In horses, severe limb injuries and other problems affecting ambulation are challenging to manage. Offloading the injured limb can result in secondary complications such as supporting limb laminitis (SLL), severely affecting quality of life and sometimes necessitating euthanasia. SLL results from increased load and decreased blood flow to the foot. There is a need to develop a dynamic device to reduce the load on the limbs while maintaining mobility and blood flow for the rehabilitation of horses with ambulatory difficulties. In this study, the unique biomechanics of the horse were considered in the design of a dynamic front limb weight support system. The development further had to consider complications associated with its use, such as pressure ulcers and other tissue trauma. Therefore, the design included silicone air pockets to be inflated and deflated in a programmable cycle. A series of three prototypes resulted in a front limb support (breastplate) intended for use with a computer-controlled rehabilitation lift. Iterative design modifications of the breastplate allowed to safely provide up to 50% front limb weight reduction while maintaining horse comfort. This is a significant step towards adjustable, dynamic ambulatory support with the ability to customize rehabilitation programs for horses with ambulatory difficulties.
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