Muscle tears as a primary cause of lameness in horses: 14 cases (2009-2016)

Abstract

This study describes clinical and ultrasonographic findings and outcomes of horses with lameness associated with muscle tears. Records of horses diagnosed with muscle tears were retrospectively evaluated. Horses in which one or more muscle tears were confirmed ultrasonographically and lameness was associated with the tear were included in the study (n = 14). Eight horses had tearing of a single muscle, 6 horses had 2 or more muscles involved. Twelve of 14 horses survived to discharge and were alive at follow-up (8 to 90 months). Recovery time ranged from 6 to 52 weeks (mean: 19.8 weeks); 6 to 16 weeks for single muscle injuries and 12 to 52 weeks for multiple muscle injuries. Of the 12 long-term survivors 3 had chronic lameness/stiffness preventing return to their previous activity level and 9 returned to equal or greater level of activity. No statistically significant difference existed between outcomes and location of injury or number of muscles injured. Key clinical message: This study indicates that conservative management of muscle tears can result in favorable long-term outcomes.

Figure 1

Longitudinal ultrasound image of the left deltoideus muscle of an 8-year-old Thoroughbred mare with left forelimb lameness of 5 weeks duration. A focal area of disruption of the perimysium (arrowheads) with a central area of hypoechoic fluid collection (asterisk) is noted. The muscle in this area shows a marked heterogeneous echogenicity with areas of increased echogenicity commonly seen in muscle injury. The deltoideus muscle has focal increase in thickness as noted by displacement of the epimysium (arrows). The more peripheral aspect of the deltoideus muscle has a normal echogenicity.

Figure 2

Transverse ultrasound image of the right semimembranosus muscle of a 17-year-old Arabian gelding. A focal area of muscle tissue disruption is noted with a central area of hypoechoic fluid (arrowheads). An anechoic rim of fluid (arrows) with thin hyperechoic bands is noted beneath the epimysium dissecting the fascial plane circumferentially around the entire muscle belly from the surrounding musculature; this is suggestive of a circumferential hematoma with mild retraction of the muscle. Additionally, small hyperechoic speckles are noted within or adjacent to the anechoic fluid suggestive of small quantities of air.

Figure 3

Transverse ultrasound images of the right (A) and left (B) cleidobrachialis muscles of a 12-year-old Thoroughbred mare with right forelimb lameness of 8 days duration. A — Right cleidobrachilis muscle has severe loss of normal fiber pattern within the muscle tissue with multiple areas of hypoechoic to anechoic fluid (arrow) most consistent with hematoma formation. The muscle belly is increased in size best noted by the displacement of the epimysium, and overall reduced echogenicity is suggestive of generalized edema and severe fiber disruption. B — Left cleidobrachialis muscle has normal fiber pattern and muscle size with no abnormal accumulation of fluid. The epimysium is smooth in outline (arrows) and the perimysium (arrowheads) wrapping the muscle fiber bundles is apparent.