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 paper (10).
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
