Hindlimb kinematics before and after laser fibrotomy in horses with fibrotic myopathy.

REASONS FOR PERFORMING STUDY: Fibrotic myopathy can cause incapacitating gait abnormalities. Transection of the fibrotic mass followed by early post operative exercise is the best treatment for fibrotic myopathy. A laser may be used to transect the fibrotic mass. Assessment of the effectiveness of therapies for fibrotic myopathy has been limited to subjective evaluation.

OBJECTIVES: To objectively assess gait abnormalities associated with fibrotic myopathy before and after laser fibrotomy followed by early post operative exercise.

METHODS: Kinematic evaluation of horses with fibrotic myopathy walking and trotting on a treadmill was used to investigate hindfeet trajectories (n = 8) and lameness (n = 5) before and after laser fibrotomy Hoof flight trajectory length (HFTL), relative protraction length (% PL), maximum hoof height during swing (MXHH), hoof height at end of protraction (HH(pro)) and retraction (HH(ret)) were measured and differences between fibrotic myopathy affected and nonaffected limbs were calculated. Lameness was quantified by measuring maximum and minimum pelvic height differences between right and left halves of the stride.

RESULTS: Before surgery the foot of the fibrotic myopathy affected limb had abnormal trajectories characterised as increased HFTL, MXHH and HH(pro) and decreased % PL and HH(ret) and the 5 horses objectively evaluated for lameness were lame in the fibrotic myopathy affected limb. Immediately after surgery the difference between affected and nonaffected limbs decreased for HFTL, % PL and HH(pro). Six to 11 weeks after surgery, the HFTL difference increased but was still smaller than before surgery, which was interpreted as partial recurrence of the gait abnormality; all horses objectively evaluated for lameness were either improved (n = 1) or not lame (n = 4) in the previously affected, operated limb.

CONCLUSIONS: Fibrotic myopathy affects the foot flight and leads to asymmetric vertical excursion of the pelvis. Laser fibrotomy followed by early post operative exercise can minimise these abnormalities.

POTENTIAL RELEVANCE: Laser fibrotomy combined with early post operative exercise is a viable therapy for fibrotic myopathy.