Ultrasonographic Evaluation of the Suspensory Ligament in Quarter Horses Used for Cutting.

Ultrasound remains a mainstay in proximal suspensory ligament (PSL) evaluation. Despite recent improvements facilitating earlier diagnosis/treatment, needs exist for (1) characterization of normal ultrasonographic PSL cross-sectional area (CSA) in specific breeds/disciplines, (2) improved detection of early/subtle changes in the PSL, and (3) an understanding of suspensory ligament (SL) morphology change from work-related stress. The objectives of this study were to establish normal PSL CSA in Quarter Horses (QH) used for cutting via angle contrast ultrasonography, ultrasonographically monitor SL morphology as horses progress through training, and assess the impact of PSL disease on performance (Lifetime Earnings - $LTE). One hundred ten 2-year-old cutting horses had PSL ultrasound examination on all limbs, and examinations were repeated 2 years later on 51 remaining horses. PSL CSA at select locations was compared between time points and entire examinations subjectively graded by an equine radiologist. $LTE was obtained from the National Cutting Horse Association for each horse and analyzed by abnormality number, location, and development over time. A total of 267 PSL ultrasound examinations across both times points were measured and graded. Normal CSA was established by zone for forelimbs and hindlimbs. The prevalence of abnormal limbs increased between the 2-year-old and 4-year-old years, forelimb abnormalities were statistically more prevalent than hindlimb abnormalities at both time points, and osseous attachment abnormalities were statistically more prevalent than ligament abnormalities at both times points. No significant differences in PSL CSA change over time were seen in any group and there was no significant difference in $LTE among or between groups.

Influence of Chronic Lameness on Thoracolumbar Musculus Multifidus Structure in the Horse.

The clinical relationship between equine limb lameness and secondary back dysfunction is largely unknown. Proper function of the spine is critical to maintain the integrity of the kinetic chain and attenuate forces from the appendicular skeleton. The musculus multifidus (m. multifidus) is the primary muscle providing spinal intersegmental stabilization and a functional relationship between m. multifidus hypertrophy and equine postural stability has been established. The relationship between equine thoracolumbar m. multifidus cross-sectional area (CSA) and limb lameness is unknown. The objective was to evaluate ultrasonographic changes in thoracolumbar m. multifidus CSA in horses with chronic single limb lameness, compared with sound horses. We hypothesized that the CSA of m. multifidus, ipsilateral to the lame limb would be smaller than the contralateral side, and within the sound group there would be no difference between sides. Thirty-six horses were enrolled, with twelve horses per group: sound, forelimb lame, and hindlimb lame. M. multifidus CSA was measured ultrasonographically at multiple spinal levels and compared between groups, spinal levels, and sides. M. multifidus CSA at the spinal level T18 was significantly larger than at all other measured levels, regardless of group (P ≤ .05). CSA at all levels was significantly larger in sound horses than the forelimb lame group, regardless of side (P = .002). This is the first study to evaluate the impact of chronic lameness on the axial skeleton and showed a decrease in m. multifidus CSA with forelimb lameness. These results support that axial skeletal adaptation occurs in response to naturally occurring chronic lameness.