The athleticism of the horse owes much to the superficial digital flexor tendons in the front legs. These energy‐storing tendons play a crucial role in the efficiency of the gallop and trot.
However, they are highly susceptible to injury. Indeed, injuries to the superficial digital flexor tendons are one of the most commonly reported causes of lameness in the performance horse.
Researchers Claire O’Brien, Neil Marr and Chavaunne Thorpe, in a review published in the Equine Veterinary Journal, have explored the biomechanical and biothermal effects of strain on this key tendon and how they contribute to the accumulation of microdamage.
The trio also explored the effect of age‐related alterations on strain response and subsequent injury risk to the tendon.
Given that tendon injuries are slow to heal and poor at regenerating tissue, prompt detection of early stages of problems and timely adaptations to training protocols are likely to have a better outcome than advances in treatment, they say.
“Early screening tools and detection protocols could subsequently be of benefit in identifying subclinical signs of degeneration during the training programme.”
This, they say, would provide an opportunity for preventative strategies to be implemented to minimise the number of injuries and reduce recovery periods in elite performance horses.
The authors, who cited 140 scientific papers in their review, said most superficial digital flexor tendon injuries occur during fitness work in training regimes.
“Previous studies have established that there is a lack of evidence‐based practices in current equine conditioning programmes, which may increase incidences of injury during training and limit the validity of previous research findings in the training environment.”
Variations in training frequency, training intensity, training effects, surfaces and equipment have all been identified as potential risk factors for injuries to these keys tendons.
In addition, individual risk factors such as age, breed and sex, as well as individual variations in tendon blood supply, flexibility and strength may also contribute to the initiation of acute/chronic tendon injuries and longer recovery rates.
The review team said early detection of subclinical changes may provide trainers with the chance to take preventative action during the training programme to minimise more serious injury and reduce recovery periods.
This could include standardised training regimes built around the scientific principles of training, which would aim to ensure progressive loading of the various systems and provide sufficient recovery times.
The authors stressed that while the superficial digital flexor tendon is an energy‐storing structure essential for efficient locomotion and performance, it has a narrow mechanical margin for error. This is what makes it susceptible to injury.
Scientific understanding of the mechanisms and causes behind such injuries have developed in recent years, but it has not translated to a reported reduction in injury rates in the performance horse industry.
Nevertheless, the evidence suggests that trainers are considerably more interested in measures to prevent such injuries rather than treatment, because of the destructive nature of such injuries.
This highlighted the benefits of evidence‐based training practices and standardised protocols aimed at reducing the risk of musculoskeletal injuries during training.
The review team identified several areas requiring further research so that suitable recommendations can be made for training programmes that specifically aim to prevent injuries to the tendon:
- An understanding of the physiological demands of the different types of high‐intensity training sessions is imperative for trainers.
- The effects of extraneous factors, such as surface type, gradient, ambient temperatures, fence height and bandaging, as these have a direct influence on tendon strain and temperature values during training.
- The frequency of training sessions that subject the tendons to extreme stresses which mimic the competition environment should be monitored closely and repeated a minimum of 72 hours apart in order to allow tendons enough time to repair and adapt. Individual factors, such as the horse’s age, previous competition experience and history of injuries would play an important role in deciding the frequency of intense sessions, and so require further investigation.
- Objective measures to gauge the physiological responses of individual animals to training sessions should contribute to decisions on when to increase training intensity, and this should be increased incrementally over an appropriate length of time. Routine veterinary consultation and screening/prevention protocols should be employed to detect potential tendon problems as soon as possible.
- Temperature manipulation may play an important role in managing the inflammatory response associated with high‐intensity work. But, again, standardised protocols in horses have not been established, which means there is scope for further investigation.
O’Brien is with the University of Winchester, in Winchester, England. Marr and Thorpe are with the Royal Veterinary College.
Microdamage in the equine superficial digital flexor tendon
Claire O’Brien, Neil Marr and Chavaunne Thorpe
Equine Veterinary Journal, First published: 08 August 2020 https://doi.org/10.1111/evj.13331