Diagnostic Protocol for Degenerative Suspensory Ligament Desmitis

By Dr. Mero ~ Revised March 12, 2006

1. SIGNALMENT- Breeds such as Warmbloods, Arabians, Quarter Horses and race horses tend to contract DSLD at ages older than 15 years.^3,4,5 Exceptions to this occur in broodmares, horses that are subjected to intense work loads, or have sustained a prior suspensory desmitis (injury).^3,4,5 In breeds other than Peruvians DSLD occurs usually in the rear limbs only. Peruvian Pasos appear to develop DSLD differently than other breeds. They most commonly develop DSLD in all four limbs, with a widespread age range from weanlings to over 20 years of age.^6,9 Average age of onset in Peruvians is between 4-10 years with both sexes roughly affected in equal numbers.⁹ And unlike other breeds, Peruvians Pasos can develop disease regardless of athletic function, i.e. no work is needed for disease to occur.⁹ (*Note- latest research has found other breeds also develop DSLD in all limbs and at early ages without work or injury)

2. MEDICAL HISTORY- This is always a quadrilateral (4 limb) or bilateral (2 limb) disease. Early cases can develop obscure signs such as generalized stiffness, changes in attitude, reluctance to work and back pain.⁹ As disease progresses horses often are painful for the farrier. Others can appear extremely stiff and unwilling to move after inactivity and then seem to work out of it with exercise. Obscure, intermittent or chronic lameness is common. End stage cases become reluctant to move about, spend much of their time lying down and often dig holes to stand in to relieve pressure off of their sore limbs.

3. PHYSICAL EXAM-
A. Conformation changes: Over 90% of the time DSLD starts and predominantly affects the suspensory ligament (SL) branches.⁹ Similar lesions can occur in other soft tissues structures such as the flexor tendons. ^2,6 The classic signs of swollen, dropped fetlocks, with coon shaped hooves and straight leg angles occur in less than 1/2 of cases even with advanced disease.⁹ Early onset cases usually have no visual abnormalities. As disease progresses diffuse swelling and wind puffs about the fetlocks sometimes are noticed.^1,2,5,6,9 Visible enlargements specifically involving the branches of the suspensory can also be seen.

B. Palpation of Suspensory Ligaments: Initially cases may or may not exhibit pain response and will have no thickening on palpation. By early to mid stage a marked pain response occurs to SL branch palpation.6,9 Usually a palpable thickening and enlargement of the SL branches will occur by mid to late stages^.6,9

C. Baseline Lameness: In early stages lameness is often not apparent. Even advanced cases may not be obviously lame due to more than one limb being painful.⁹ Front limb cases can look tight and appear reluctant to move out and extend their gait. Hind and four limb cases move stiffly, will not drive in the rear and will have a marked widening of their hocks and lower limbs during gaiting as viewed from the rear. Many rear limb cases stab their toes into the ground and appear reluctant to load their heel regions. Tight circles will usually exacerbate lameness.

D. Flexion Tests: In all cases, even initial cases, flexion tests are ALWAYS positive.9 Early onset cases may show only a mild response of 1-2/5. By mid to late stage disease responses to flexion tests are usually dramatic with horses being crippled after the test with responses of 4-5/5 for several minutes.⁹ It can often be difficult to flex contralateral limbs as pain can be residual for some time post flexion test.

4. ULTRASOUND EXAMINATION of Suspensory Ligaments- What distinguishes DSLD apart from just an injury is the progressive, continual enlargement of the suspensory ligaments, primarily in the branches, over time, in more than one limb.^1,7,9 Early onset cases often are only slightly enlarged and may warrant a second exam in 3-6 months to document continual enlargement. Typically, the SL branches at their largest are no more than 1.1cm2 on area, or 1.1cm in the lateral to medial, or the palmar/plantar to dorsal plane.^8,9 The SL body can range up to 2cm just below the hock or the knee. Views of the individual SL branches in the lateral to medial plane are best for accurate measurements.
In Peruvians 0.7cm squared for the suspensory ligament branches in zones 3A or 4A and up to 1.3 cm for the suspensory ligament body at midcannon are considered the cut offs or high normal sizes for the suspensory ligaments in these areas, according to Dr. Mero's paper¹⁰.

Other ultrasound lesions present can be a diffuse loss of fiber patterns both in the cross sectional and the longitudinal plane.^1,3,5,9 An overall increase in the hyperehocogenicity (whiteness) of the affected tissues is typical.^1,3,5,9 Most commonly in zones 3A/4A to 3B/4B the SL branches will appear enlarged and often are bright white on the distal ultrasound screen in cross section. Less commonly will discrete hypoechoic (black) lesions, often thought of as tears, be noted in the SL branches and/or the SL body.⁹ On post mortem these represent areas of degeneration and widespread tissue destruction.

5. SUMMARY- Consistent clinical findings: Pain on palpation of suspensory branches, lameness of some kind though often subtle and seen as only stiffness, and positive fetlock flexion tests. The presence of positive flexion tests in more than one fetlock, especially severe responses in horses with seemingly no visual abnormalities and only mild palpation findings, should raise the examiner's index of suspicion for DSLD. Some of the worst affected cases have not had any appreciable ankle swellings, no obvious lameness and no ankles that dropped below the horizontal. Four limb cases in Peruvians seems to be more common, and routine scanning of all four limbs of any Peruvian suspected of having DSLD is recommended. Four limb cases usually are more painful and often deteriorate faster. Some bilateral cases can remain at least pasture sound for several years. Re-exams 3-6 months from the initial exam will usually distinguish DSLD from a healing injury, by the presence of worsening clinical signs and progressive enlargements of the suspensory ligaments on ultrasound.

Copyright 2002 DSLD Research Inc. All Rights Reserved. (*Reprinting permitted for diagnostic purposes)

REFERENCES

1. Young, JH. Degenerative Suspensory Ligament Desmitis. Hoofcare and Lameness. 1993;(61)6-19.
2. Pryor, PB, Pool, RR, Wheat, JD. Failure of the suspensory apparatus in Peruvian Paso horses, in Abstracts. ACVS meeting 1984; 56.
3. Dyson, S. Diagnosis and prognosis of suspensory desmitis. In: Proceedings of the 1st Dubai International Symposium, Ed:ML Hauser, Matthew R. Rantanen Design, USA, 1996: 207-225
4. Dyson, S, Arthur, RM, Palmer, DE, et al. Suspensory ligament desmitis. Vet Clin. N. Am: Equine Pract. 1995;11: 177-215
5. Gibson, KT, Steel, CM. Conditions of the suspensory ligament causing lameness in horses. Equine Vet Ed 2002;4: 50-64
6. Pryor, PB, Pool, RR, Wheat, JD. Clinical and pathological characterization of suspensory apparatus failure in Peruvian Paso horses. Unpublished paper. 1984.
7. Yeager, A. Ithaca, NY (personal communication) March 13, 2002.
8. Cuesta, IC, Riber, C, Pinedo, M, et al. Ultrasonographic measurement of palmar metacarpal tendon and ligament structures in the horse. Vet Radiol Ultrasound 1995: 131-136.
9. Mero, JL, Pool, RR. 20 Cases of Degenerative Suspensory Ligament Desmitis in Peruvian Paso Horses, in Proceedings. American Association of Equine Practitioners Mtg.2002;48:329-334
10. Mero, JL, Scarlett, JM. Diagnostic Criteria for Degenerative Suspensory Ligament Desmitis in Peruvian Paso horses. Journal of Equine Veterinary Science 2005;5