The use of sonoelastography to assess the recovery of stiffness after equine superficial digital flexor tendon injuries: A preliminary prospective longitudinal study of the healing process.

Background: The objective assessment of the mechanical properties of the superficial digital flexor tendon (SDFT) could provide useful information for the rehabilitation of horses with SDFT injuries. Assessment of strain ratio (the strain of a standard reference divided by that of lesions) is a quantitative method in sonoelastography for evaluating tissue stiffness in vivo. As yet, no longitudinal studies have used strain ratio to evaluate the progression of stiffness in SDFT injuries.

Objectives: To test the hypothesis that strain ratio can evaluate the recovery of stiffness during the healing of SDFT injuries.

Study Design: Prospective and longitudinal study with observer-blinded evaluation.

Methods: Ultrasonography, including sonoelastography, was performed in seven Thoroughbred horses with naturally occurring SDFT injuries at five time points: within 20 days of the injury, and at 2, 3, 6 and 9 months after the injury. Blinded sonoelastographic images were independently evaluated by two veterinarians to assess interobserver agreement. The recovery of stiffness and echogenicity in lesions were evaluated using the strain ratio and grey-scale ratio (echogenicity of lesions divided by that of the surrounding area), respectively.

Results: Interobserver agreement was assessed as 'almost perfect'. Strain ratios were significantly higher at 9 months after injury than at the other time points (all P<0.05). Strain ratios at 6 months after injury were significantly higher than those at earlier time points (P<0.05). Grey-scale ratios within 20 days of injury were significantly lower than those at the other time points (all P<0.05).

Main Limitations: Validations of SDFT status were evaluated only by recovery of the echogenicity in lesions and not by histopathological examination.

Conclusions: Although further studies are needed to validate the relationships between injured SDFT status and sonoelastographic findings, this preliminary study shows that strain ratio may provide a means to monitor the recovery of stiffness in lesions during rehabilitation, even when the grey-scale ratio remains unchanged from a few months after SDFT injury. The Summary is available in Chinese - see Supporting Information.