Results of a pilot study using serial ultrasonographic measure-ments of multifidus muscle in horses undergoing rehabilitation after medical or surgical treatment for overriding dorsal spinous processes

To assess whether cross- sectional area (CSA) of the equine multifidus muscle changed after treatment in horses with impinging and/or overriding dorsal spinous processes (ORDSP), 45 affected horses were recruited in a descriptive retrospective study. Before any treatment the CSA of the paired (left and right) multifidus muscles was measured by ultrasound at 3 levels: T15, T18 and L2. Horses underwent treatment: either by interspinous ligament desmotomy (ISLD, surgical) or by corticosteroid infiltration into the area of impingement (medical). All followed an exercise program before returning for repeat measurement. The effect of treatment on CSA following rehabilitation was assessed and compared statistically. Thirty-three horses underwent surgery and 12 medical treatment. Overall CSA increased after treatment at each site (percentage increases ranged from 9.6 % to 32.3 %) and the increase was significantly greater than zero at all sites except at L2 for the medical procedure. CSA change differed between sites with T15 having an 8.7 % absolute greater increase than L2 (P < 0.001). Surgical horses had higher radiographic scores than medical (0.962 [95 % CI 0.881-1.043] c.f. 0.424 [95 % CI 0.329-0.518]) and also experienced a greater increase in CSA at all locations (P < 0.001), the greatest being 32.3 % at T15. It was concluded that treatment of ORDSP led to an increase in multifidus CSA, considered to indicate improved spinal functional health. Serial measurement of multifidus CSA provided a useful objective means of assessing response to treatment.