Bowed tendons - different treatment options - new ultrasound technology - ultrasound tissue characterisation
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By Sarah Plevin
Overstrain injuries to the superficial digital flexor tendon (SDFT) are among the most common musculoskeletal injuries for all athletic equine disciplines but account for a significant amount of wastage in the Thoroughbred (TB) racehorse.
Treatment options for such ‘bowed tendons’ are many and varied, but all have a couple of things in common: time out of training; expense and no guarantee of success.
It makes sense then, that prevention of injury should always be the goal, and failing that, a method to optimally guide rehabilitation is needed.
Unfortunately, limitations of current imaging diagnostics have restricted their use for accurately monitoring the tendon.
A new ultrasound technology, however, called ultrasound tissue characterisation, may get us one step closer to achieving the goals of injury prevention and optimal rehabilitation.
What would the ideal tendon imaging modality allow us to do?
Monitor the effects of exercise on the tendon
Early detection of overstrain injuries
Be able to stage the lesion, i.e., determine the level of degenerative change within the tendon structure
Fine-tune therapy
Guide rehabilitation
Why are tendon injuries so tricky?
Figure 1: Functionally normal healthy aligned tendon bundles.
A normal healthy tendon is made from aligned organized tendon bundles. (Figure 1) Deterioration of this structure ranges on a spectrum from complete disruption (core lesion) to more minor changes, but all affect the ability of the tendon to function optimally.
Degenerative changes within the tendon matrix are not uniform—meaning that not all overstrain injuries to the SDFT are represented by the same level of deterioration or structural change, so there is not a one-size-fits-all pathology or diagnosis, and therefore there cannot be a cure-all treatment.
Most tendon injuries have a sneaky onset with tendon degeneration developing initially without clinical signs, so problems start without you or your horse even knowing about them. Often by the time you realize there is a problem, tendon matrix degradation has already begun.
Staging the structural integrity of the tendon or classifying the extent of structural deterioration present is, therefore, imperative—not only for optimal therapy selection and appropriate rehabilitation guidance but also if prevention of injury is ever to be achieved.
Why isn’t conventional ultrasound enough?
Unfortunately, although conventional ultrasound has historically been used to evaluate equine tendon, limitations have restricted its ability to accurately monitor tendon structure, predict injury or guide rehabilitation.
Clinical improvement is usually not accurately correlated with changes in imaging status using conventional ultrasound, especially in the later stages of healing with conventional ultrasound not demonstrating enough sensitivity to determine the type of tendon tissue under investigation.
So, while regular ultrasound can easily demonstrate the presence of a core lesion when it first appears, by about two months post injury, its capacity to provide information regarding the health of the tendon is limited. Because of its inability to interpret the integrity of the underlying tendon structure accurately, along with inconsistencies in imaging, reliance on operator skills and the inherent lack of ability of a 2D conventional ultrasound image to fully decipher a 3D tendon structure, its ability to reliably evaluate and monitor the SDFT following the initial acute period is severely restricted.
What is ultrasound tissue characterisation?
Ultrasound tissue characterisation is a relatively new technique intended to alleviate some of the problems encountered with conventional ultrasound by improving objective tendon characterisation. It does this by providing a 3D reconstruction of the tendon and by classifying and then quantifying tendon tissue into one of four colour-coded echo types based on the integrity of the tendon structure.
It can assess in detail the structural integrity of the tendon; it can discriminate a variety of pathological states and is sensitive enough to detect the effect of changing loads on the tendon within days.
Figure 2: Color-coded ultrasound tissue characterization echo types represent the stability of echo pattern over contiguous images related to tendon matrix integrity.
What do the colors mean? (Figure 2)
Green (type 1 echoes) are normal, well-aligned and organized tendon bundles, and at least 85-90% of this echo type should be found in a healthy tendon (SDFT). Blue (type 2 echoes) are areas of wavy or swollen tendon bundles. They can represent remodeling and adapting tendon or inferior repair. Red (type 3 echoes) represents fibrillar tissue (the smaller basic unit or building block of tendon). This echo type can represent partial rupture of the tendon where they reflect breakdown of normal structure or they can represent initial healing as the tendon begins to rebuild. Black (type 4 echoes) are areas of cells or fluid and represent core lesions where no normal tendon tissue exists.
How is ultrasound tissue characterization currently used?
The aim of ultrasound tissue characterization is not to replace conventional ultrasound but on the contrary, it is recommended to perform an evaluation with both conventional B mode ultrasound and ultrasound tissue characterization to achieve a complete picture of tendon health.
Figure 3: Ultrasound tissue characterization tracker frame with attached ultrasound probe.
Currently it is used successfully in elite human athletes such as NBA and soccer players to monitor the health of their tendons (Achilles tendon and patellar tendons) and to guide exercise regimens post injury.
In the equine field, it is used in elite sport horses as part of routine maintenance evaluations to direct exercise, to monitor tendon health and guide rehabilitation following an injury.
How does it work?
It consists of a standard linear ultrasound probe mounted onto a motorized tracking device (Figure 3). Due to the sensitivity of this equipment, the limbs should be clipped in order to obtain good quality images.
The probe moves non-invasively and automatically down the tendon from top to bottom over a 12-cm scanning distance (see Introphoto) …
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