Caution urged in thermal imaging’s role in assessing saddle fit

The thermal grid reference used when quantifying thermal temperatures of the thoracic region (left) and ventral aspect of the saddle (right). A mask (grey area) was applied to areas of the grid which did not correspond to the horse’s back. Images:

Researchers urge caution in relying only on thermal imaging on horses to assess pressure under the saddle.

Thermography is a non-invasive method for measuring surface temperatures, which has raised the possibility of it being used as a convenient way of identifying warm and cool areas under a saddle that may be related to saddle pressures.

Russell MacKechnie-Guire and his colleagues, in a study reported this week in the journal Animals, noted that the effects of saddle fit and design on equine health and performance are becoming better understood.

“Incorrect saddle fit is thought to be a potential contributing factor in the context of back problems, poor attitude to work and poor performance.”

One way of quantifying saddle fit is the use of an electronic pressure mat beneath a saddle. It has been shown to be a reliable and accurate way to quantify saddle pressure distribution.

However, the costs and time associated with data collection and processing is a limiting factor for its use outside a laboratory setting.

Thermography has been used in veterinary medicine and specifically as part of a diagnostic technique when evaluating back-related conditions.

Thermographs of the undersides of saddles used in the study. A had correct saddle width, B was narrow and C was assessed as too wide. Thermographs were taken from three horses who had the highest mean and peak saddle pressures (kPa) during the standardised ridden exercise test. Images:

So, what of its potential role in quantifying saddle fit by evaluating thermal pattern distribution? Thermal imaging cameras can detect hyperthermic activity (due to friction/pressure) with more than 10 times higher sensitivity than the human hand.

“The overarching biological assumption appears to be that areas with an increased magnitude in pressure (related to incorrect saddle fit) will alter the heat emitted from the affected region of the thoracic spine as a function of pressure.

“There is, however, an apparent lack of evidence specifically quantifying the association between saddle pressures (using an electronic pressure mapping system) and thermographic assessments.”

For their study, MacKechnie-Guire and his colleagues set out to quantify thermal patterns and saddle pressure distribution in a group of non-lame sport horses ridden by the same rider following a standardised exercise test.

Eight adult elite jumping horses were recruited for the study, ridden in the exercise test in all cases by a 69kg man with experience as an international showjumper.

On the day, saddles were assessed independently by five qualified saddle fitters. All saddles were checked for fit both statically and dynamically following the Society of Master Saddlers published guidelines.

Three were found to be too narrow, three were too wide and two were assessed as a correct fit.

A thermal camera was used to gather minimum, maximum and average temperatures at specific locations under the saddle (left/right) of the thoracic region at three-time points: Baseline, after lunging, and after a standardised ridden test.

A pressure mat determined the average and peak saddle pressures.

The underside of each saddle was also thermographically imaged immediately after removal.

The study team found that the thermal activity beneath the saddle did not appear to be representative of increased saddle pressure values.

“The sole use of thermal imaging for saddle fitting should be applied with caution,” they said.

The researchers, discussing their findings, said the idea that thermal activity may be a useful mechanism for identifying incorrect saddle fit appears of merit, since the magnitude of pressure, as a result of incorrect saddle fit, may affect blood flow.

Whilst several studies provide partial support for the use of thermography as a means of quantifying saddle fit, they are essentially based on the biological assumption that areas with an increased magnitude of pressure (as a result of saddle fit) will lead to warm or cool areas as a function of increased or decreased blood flow in the corresponding areas of the horse’s back.

They said the inclusion of horses with varying saddle fit provided a “real-life” opportunity to compare thermography and saddle pressure measurements to describe saddle fit.

They noted that, during ridden exercise, the saddles which were classified as a correct saddle fit showed uniform pressure distribution. In the saddles classified as too narrow and too wide, the magnitude of pressure was increased in the front region of the saddle.

They said that while areas of high pressures were found in the front region for the narrow and wide saddles, this was not reflected in thermal activity seen.

No differences were found in thermal activity between the unridden and unsaddled lunge test and the ridden test.

“The increase in thermal activity in the thoracic region found in the present study was as a function of exercise and not saddle fit.”

The researchers said the thermograms of the underside of the saddle did not appear to reflect the findings of the saddle fit assessment.

“Our findings,” they concluded, “did not provide evidence supporting a direct link between thermal activity and areas with an increased magnitude of pressure under the saddle.

“We did, however, find consistent exercise-induced changes in thermal activity. This complicates the use of thermal imaging for assessing dynamic saddle fitting.”

The study team comprised MacKechnie-Guire, with Centaur Biomechanics and the Royal Veterinary College; Mark Fisher and Diana Fisher, with Woolcroft Saddlery in Wisbech; Helen Mathie, with Helen Mathie Physiotherapy; Kat Kuczynska, with Vet-IR in Manchester; Vanessa Fairfax, with Fairfax Saddles; and Thilo Pfau, with the Royal Veterinary College.

MacKechnie-Guire, R.; Fisher, M.; Mathie, H.; Kuczynska, K.; Fairfax, V.; Fisher, D.; Pfau, T. A Systematic Approach to Comparing Thermal Activity of the Thoracic Region and Saddle Pressure Distribution beneath the Saddle in a Group of Non-Lame Sports Horses. Animals 2021, 11, 1105.

The study, published under a Creative Commons License, can be read here.

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