Use of magnetic resonance imaging to assess soft tissue damage in the foot following penetrating injury in 3 horses

Magnetic resonance imaging (MRI) uses the magnetic properties of tissues to create a high resolution image, taken in any anatomical plane. The use of MRI in equine diagnostics is still in its infancy, but the technique has great potential in the investigation of many equine diseases, especially diseases of the foot. Conventional imaging modalities, including radiography, diagnostic ultrasonography and nuclear scintigraphy, have significant limitations in assessing the structures within the foot. Magnetic resonance imaging, on the other hand, can provide 3-dimensional images of the entire foot, including both osseous and soft tissue structures. There have been a small number of studies describing the use of MRI in the evaluation of foot pain (Denoix et al. 1993; Whitton et al. 1998; Widmer et al. 2000; Dyson et al. 2003); these reports demonstrate the potential for use of the modality in lameness diagnosis. A study of the correlation between MRI images with histological sections confirmed that all of the anatomical structures in the equine digit can be evaluated by MRI (Kleiter et al. 1999). Conventional open and cylindrical human MRI scanners necessitate general anaesthesia in order to scan the horse’s leg. A MRI system for use in the standing sedated equine patient has recently become available (Mair et al. 2003). It incorporates an open, mobile, 0.2T magnet and a radiofrequency coil that fits around the foot. This system was recently installed at our clinic, and since June 2002 over 300 horses have been scanned in the unit. While both the system and imaging protocols are still under refinement, it has already been particularly beneficial in identifying soft tissue lesions within the foot. Penetrating foot wounds are a common clinical presentation. Standard investigative procedures of these lesions make use of synoviocentesis and contrast radiography (arthrography, bursography and/or fistulography) to assess synovial (navicular bursa, distal interphalangeal joint and digital tendon sheath) involvement. To date, there has been no universally reliable method of assessing damage to many of the other soft tissue structures within the foot, particularly the deep digital flexor tendon. Diagnostic ultrasonography of the region, performed through the frog and distal pastern, can be helpful but is technically difficult and yields limited information. Previously, those horses that had suffered penetrating wounds which did not recover as predicted may have been assumed to have suffered undiagnosed synovial involvement or tendon/soft tissue damage. Accurate diagnosis and prognosis were therefore hampered by uncertainty. This case series discusses 3 horses with unresolved lameness following penetrating foot wounds. MRI studies revealed deep digital flexor tendon (DDFT) lesions, presumed to have occurred at the time of the original penetration.