THE MERCK VETERINARY MANUAL
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Spinal Processes and Associated Ligaments in Horses

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Kissing Spines

The most common location of these lesions is the vertebral segment between T10 and T18, although kissing spines are not rare between L1 and L6. Abnormal findings can be seen in the dorsal part of the spinous processes where their identification is easy; they include kissing and overriding lesions. Different grades can be identified (grade 1: narrowing of the interspinal space; grade 2: densification of the margins; grade 3: bone lysis adjacent to the margins; grade 4: severe remodeling). Abnormal findings can also be seen in the ventral part of the spinous processes and may involve the interspinal ligaments or be associated with osteoarthrosis of the articular processes. Their severity can be established using the same grading system; their clinical incidence seems higher.

The incidence of kissing spines seems to vary according to the horse discipline and biomechanical effects of specific gaits and exercises on the back. In general, these lesions are commonly found in racing Thoroughbreds and seem to be tolerated in many of them. They are quite rare in Standardbreds, but when present, their likelihood of causing pain seems higher. Intermediate frequency and signs are observed in sport horses. Kissing spines can be found in performance race and sport horses without back pain and even with normal thoracolumbar active and passive mobilization. Thus, in each case, the clinical significance of these lesions must be carefully assessed. Diagnosis can be aided by injection of local anesthetic into the affected interspinous spaces. Management includes local injections of steroids, mesotherapy, and/or shockwave therapy, as well as rehabilitation using tolerated exercises after progressive warmup at a slow canter.

Fractures

Multiple fractures of the spinous processes of T4–T10 are sometimes seen in horses that have reared and fallen over backward. The summits and centers of ossification are fractured and displaced laterally. After the initial pain and local reaction have subsided, recovery is often satisfactory. Usually, there is no permanent effect on performance, but a persistent deformation of the withers may require use of a special saddle.

Desmopathies

(Supraspinal ligament injuries)

Acute or subacute desmopathies induce dorsoventral or transverse thickening of the ligament, reduced echogenicity, and severe alteration of the linear pattern. They can be found in the median plane or asymmetrically. In old or chronic injuries, the ligament often remains thicker with a reduced echogenicity and an irregular architectural pattern. Hyperechogenic images with or without acoustic shadows are compatible with mineralization or calcification of the supraspinous ligament. Alteration of the bone surface of the top of the spinous processes indicates insertional desmopathy (enthesopathy) of the supraspinous ligament.

Last full review/revision March 2012 by Stephen B. Adams, DVM, MS, DACVS; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS; James K. Belknap, DVM, PhD, DACVS; Jane C. Boswell, MA, VetMB, CertVA, CertES (Orth), DECVS, MRCVS; Peter Clegg, MA, Vet MB, PhD, CertEO, DECVS, MRCVS; Andrew L. Crawford, BVetMed, CertES (Orth), MRCVS; Jean-Marie Denoix, DVM, PhD, Agregé; Marcus J. Head, BVetMed, MRCVS; C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS, DACVSMR; James Schumacher, DVM, MS, DACVS, MRCVS; John Schumacher, DVM, MS, DACVIM; Roger K. W. Smith, MA, VetMB, PhD, DEO, DECVS, MRCVS; Chris Whitton, BVSc, FACVSc, PhD

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