Lameness associated with foot pain: results of magnetic resonance imaging in 199 horses (January 2001--December 2003) and response to treatment.

REASONS FOR PERFORMING STUDY: The diagnosis of foot-related lameness often remains elusive and it can be difficult to offer rational treatment, or to predict outcome.
OBJECTIVES: To describe the spectrum of injuries of the foot identified using magnetic resonance imaging (MRI), to determine their relative prevalence among MRI diagnoses and to establish the long-term results of treatment.
METHODS: The MR images of horses examined from January 2001--December 2003 were reviewed. Horses were selected for MRI if the pain causing lameness was localised to the foot using perineural analgesia but any clinical, radiological or ultrasonographic abnormalities were insufficient to explain the degree of lameness. The clinical significance of lesions identified using MRI was determined with reference to the results of local analgesia, radiography, ultrasonography and nuclear scintigraphy. Follow-up information was obtained in January 2004 for horses which had been examined 6-36 months previously and the outcome classified as excellent (horse returned to full athletic function without recurrent lameness), moderate (sound, but only in light work), or poor (persistent or recurrent lameness).
RESULTS: One hundred and ninety-nine horses underwent MRI examinations. Deep digital flexor (DDF) tendonitis was the most common injury (59%) with primary injury in 65 horses (33%) and a further 27 horses (14%) having lesions of the DDF tendon and navicular bone. Seventeen percent of horses had injuries to multiple structures, including 24 with DDF tendonitis. Desmitis of a collateral ligament (CL) of the distal interphalangeal (DIP) joint was the second most common injury (62 horses, 31%), with primary injuries in 30 horses (15%) and a further 32 horses (16%) that had CL desmitis in conjunction with other injuries. Prognosis was best for horses with traumatic injuries of the middle or distal phalanges, with 5 of 7 horses (71%) having an excellent outcome. Horses with primary lesions of the DDF tendon or CL of the DIP joint had excellent results in only 13 of 47 (28%) and 5 of 17 horses (29%), respectively. Horses with combined injuries of the DDF tendon and navicular bone, or primary navicular bone abnormalities, had a poor outcome, with the majority of horses suffering persistent lameness.
CONCLUSIONS: A wide variety of lesions associated with foot pain were identified using MRI, a high proportion of which were primary soft tissue injuries with a guarded prognosis for return to full athletic function. POTENTIAL RELEVANCE: It is now possible to propose more rational treatment strategies for the variety of foot injuries identified using MRI than had previously been possible; however, further information concerning aetiopathogenesis of these injuries is needed to improve their management.