AAEP FOCUS ON SOFT TISSUE LAMENESS IN THE PERFORMANCE HORSE PROCEEDINGS / 2016
What is New About Hindlimb Proximal Suspensory
Desmopathy in Sports Horses?
Sue Dyson, VetMB, PhD

Take Home Message—Proximal suspensory desmopathy (PSD) is
a multifactorial condition, which is primarily degenerative in
nature. Repetitive overload may predispose to clinical signs.
Straight hock conformation or dynamic hyperextension of the
hind fetlocks may enhance risk of injury. Good quality
ultrasonographic images are reliable for diagnosis. Injuries may
be complicated by concurrent suspensory branch injury or
sacroiliac joint region pain, or concurrent injury of the accessory
ligament of the suspensory ligament or the accessory ligament of
the deep digital flexor tendon. Failure of treatment of primary
PSD by surgery may be due to pre-existent adhesions.
no abnormalities. Gross post mortem examination revealed
substantial adhesions between the proximal aspect of the SL
and adjacent soft tissues in 10/37 (27.0%) lame limbs; in 10/37
(27.0%) limbs there were adhesions between the body of the SL
and the mid plantar aspect of the third metatarsal bone,
extending distally in 6 (16.2%) limbs. Histology revealed
abnormalities (grades 1-3) of the collagenous tissue in 25/36
(69.4%) limbs; muscle was abnormal (grades 1-3) in 35/36
(97.2%) limbs and adipose tissue (grades 1-3) in 16/36 (44.4%)
limbs. In one lame limb no histological abnormalities were
identified, but there were extensive adhesions between the SL
and adjacent structures at gross post mortem examination. It
was concluded that ultrasonography was reliable for the
detection of SL pathology based on histology as the gold
standard.
Author’s address—Centre for Equine Studies, Animal Health
Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU,
UK; e-mail: [email protected].
In Part 2 of the study, three horses with recurrent lameness after
surgical management of PSD and four with PSD were assessed
ultrasonographically and post mortem. Adhesions between the
SL and adjacent soft tissues were predicted ultrasonographically and confirmed post mortem. The presence of
such adhesions may explain why some horses fail to respond
adequately to surgical treatment.
I. ULTRASONOGRAPHY AND THE DIAGNOSIS OF
HINDLIMB PSD
H
indlimb proximal desmopathy can be a challenging
diagnosis. It has been suggested that ultrasonography is
unreliable for the detection of hindlimb proximal suspensory
desmopathy (PSD) based on comparison between
ultrasonographic and magnetic resonance (MR) images.1 A
retrospective study was performed to compare ultrasonography
with gross and histopathological post mortem examination in
horses with PSD diagnosed based on ultrasonography and
control horses.2,3 In Part 1, 19 horses with hindlimb PSD and 10
control horses were humanely destroyed. All horses with PSD
had multiple problems contributing to pain and poor
performance and were humanely destroyed for reasons
unrelated to the study. Twenty control limbs and 37 lame limbs
were examined grossly and 40 suspensory ligaments (SLs) were
examined histologically at predetermined anatomical sites and
graded blindly.
II. ULTRASONOGRAPHY: LOAD BEARING VERSUS THE
RESTING LIMB, OBLIQUE ANGLE
Ultrasonographic examination of the plantar metatarsal soft
tissue structures has conventionally been performed in weight
bearing limbs; however, with the limb non-weight bearing a
larger proportion of the cross-sectional area of the SL can be
assessed.4,5 By tilting the transducer, the ultrasound beam is no
longer perpendicular to the collagen fibres which therefore
appear anechogenic. In contrast, the muscle and adipose tissue
remains echogenic. The bilobed structure of the SL in the
middle third of the metatarsus is clear to see. The acquired
image is therefore a more accurate representation of the
architecture of the SL. Fibrosis within the collagen tissue
indicative of chronic injury will remain echogenic.
Most of the horses exhibited mild to moderate lameness, in
many horses only seen when ridden. Ultrasonographic lesions
were graded moderate in 31/38 (81.6%) and severe in 7/38
(18.4%) lame limbs; in 4/37 (10.8%) limbs adhesion formation
between the proximal aspect of the SL and the accessory ligament of the deep digital flexor tendon was predicted. Gross post
mortem and histological examinations of control limbs revealed
Acquisition of these images in a horse, which has required
heavy sedation for clipping, can be challenging. Determining
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AAEP FOCUS ON SOFT TISSUE LAMENESS IN THE PERFORMANCE HORSE PROCEEDINGS / 2016
the precise proximodistal location of lesions is not as easy as
when images are acquired with the limb bearing weight.
been harrowed. No effect of arena surface type was observed in
the final multivariable models. This may be due to the effect of
small sample size, horses accustomed to being worked on these
types of surfaces, or that we only determined kinematic values
at midstance. At midstance the limb is being fully loaded and
the base of the surface influences a lot of the characteristics that
the horse experiences.12 Characteristics such as cushioning, grip
and dampening will have more influence at impact and pushoff12 and these may influence the kinematics of the horse at this
point of the stride. The surfaces we evaluated did have
differences in surface characteristics (unpublished data), but
these differences were more likely to affect the top of the
surface and the horse’s interaction with it at impact and pushoff. Epidemiological and clinical data suggests that injury risk
is linked to arena surface characteristics such as unevenness and
poor maintenance.13,14 Further investigation is required to
evaluate the effect of surface on kinematics at different points
of the stride.
III. RISK FACTORS FOR PROXIMAL SUSPENSORY
DESMOPATHY
Risk factors for proximal suspensory desmopathy have been
poorly documented. It has been suggested that conformation
may play a role.6-8 A causal relationship between straight hock
conformation and PSD is difficult to prove. However, an
association has been noted,6 and we have growing evidence to
support this. Static or dynamic hyperextension of the
metatarsophalangeal joints may be a result of PSD or possibly
contribute to causation. The potential role of side to side
oscillation or sideways rotation of the hocks during the stance
phase of the stride merits further study. The role of the relative
heights of the withers and tubera sacrale also needs further
investigation. We also need to understand better the role of
epaxial and abdominal muscle development, fitness and
strength in prevention of injury.
IV. FAILURE OR POST-OPERATIVE COMPLICATIONS OF
MANAGEMENT OF HINDLIMB PSD BY NEURECTOMY OF
THE DEEP BRANCH OF THE LATERAL PLANTAR NERVE
AND PLANTAR FASCIOTOMY
Sports discipline is a risk factor, with dressage horses being
particularly susceptible.9 This may be related to the way in
which they work and the surfaces on which they work. In such
horses, PSD may represent a repetitive strain injury. A high
incidence of hindlimb PSD has been seen in young dressage
horses shortly after sale through high performance sales, at
which they have been repetitively ridden to show extravagant
paces.10
Neurectomy of the deep branch of the lateral plantar nerve and
plantar fasciotomy continues to be a highly successful method
of management of chronic hindlimb proximal suspensory
desmopathy, with careful patient selection i.e., resolution of
lameness after perineural analgesia of the deep branch of the
lateral plantar nerve (or identification of another treatable
source of pain), definitive evidence of proximal suspensory
desmopathy
and
no
predisposing
conformational
abnormalities.15 Pre-existing straight hindlimb conformation
(hock angle > 165°) is a risk factor for progressive degenerative
change of the ligament and failure of surgery.
In a pilot study comparing extended trot with collected trot,
there is increased flexion of the hock and extension of the
fetlock in midstance in extended trot, thus increasing load on
the suspensory apparatus.11 In a larger study, 20 clinically
sound horses in active dressage training were used: 1) ten young
(≤ 6 years) were assessed at collected and medium trot; 2) ten
mature (≥9 years) were assessed at collected and extended trot.
All horses were assessed on two different surfacesa. High-speed
motion capture (240Hz) was used to determine kinematic
variables. Descriptive statistics and mixed effect multilevel
regression analyses were performed. Hock angle and distal
metatarsal coronary band ratio were outcome variables. Speed
and stride length were reduced and stride duration increased at
collected compared with medium and extended trot.
Medium/extended trot was associated with increased fetlock
extension in the hindlimbs. Hock angle was not significantly
influenced by pace. Medium or extended trot increase extension
of the hindlimb fetlock joint compared with collected trot in
both young and mature dressage horses, respectively. The risk
of repetitive strain injuries of the suspensory apparatus or
fetlock may be reduced by avoiding too frequent use of
extended trot and excessively long periods of extended trot.
In horses with acceptable hindlimb conformation, appropriate
post-operative rehabilitation is helpful for best results. This
should ideally include intensive physiotherapy and exercises
designed to enhance core muscle strength and the strength and
fitness of the muscles that stabilise the hindlimbs.
Recognition of concurrent sacroiliac joint region pain,16
sometimes only evident in ridden canter, is important to identify
preoperatively, because this has a large influence on successful
management.16
A small proportion of horses develop low-grade lameness after
resumption of full work associated with tarsometatarsal joint
pain. These horses can generally be successfully managed by
intra-articular medication.
However, despite careful selection, we still have a 24% failure
rate. Generally, these horses have persistent lameness or early
recurrence of lameness and lameness is resolved by infiltration
of local anaesthetic solution around the origin of the suspensory
ligament, or by perineural analgesia of the tibial nerve. Some of
these failures may be due to adhesion formation (see above).
We have previously observed clusters of horses with PSD based
at specific yards and have speculated that arena surfaces may
be a risk factor for injury. All 20 horses were assessed on two
different surfaces: surface A - waxed sand and fibre, which had
been rolled; surface B - unwaxed sand and rubber, which had
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AAEP FOCUS ON SOFT TISSUE LAMENESS IN THE PERFORMANCE HORSE PROCEEDINGS / 2016
accessory ligament of the suspensory ligament was
characterised by marked decrease in echogenicity of the
ligament and loss of parallel alignment of the linear echoes,
which were shorter than normal in longitudinal images.
In a small number of horses, we have identified postoperative
complications. Three of 283 horses have developed proximal
injuries of the accessory ligament of the deep digital flexor
tendon. Four of 278 horses with good hindlimb conformation
have developed progressive degenerative changes of the
suspensory ligament body within three to nine months postoperatively. One horse developed a suspensory branch injury.
VII. CONCURRENT OR SUBSEQUENT INJURY OF THE
ACCESSORY LIGAMENT OF THE DEEP DIGITAL FLEXOR
TENDON
V. PSD AND SUSPENSORY LIGAMENT BRANCH INJURIES
PSD and injury of the proximal aspect of the accessory ligament
of the deep digital flexor tendon (ALDDFT) were identified in
19 horses, 14 with forelimb lameness (unilateral 5, bilateral 9)
and 5 with hindlimb lameness (unilateral 2, bilateral 3).19
Localising clinical signs were seen in 7/31 lame limbs (subtle
thickening in the region of the ALDDFT [n=3], pain on
palpation of the body of the SL [n=6], heat in the proximal
metacarpal or metatarsal region [n=2]). Forelimb lameness was
abolished by perineural analgesia of the palmar metacarpal
(subcarpal) nerves in 17/23 limbs. In the remaining limbs, intraarticular analgesia of the middle carpal joint (n=2) or an ulnar
nerve block (n=4) were required to eliminate the lameness.
Hindlimb lameness was abolished by perineural analgesia of
the deep branch of the lateral plantar nerve (n=2) or local
infiltration of the proximal plantar aspect of the metatarsus
(n=3); a tibial nerve block resolved lameness in the remaining
3 limbs. Lesions of the suspensory ligament (SL) and of the
ALDDFT were characterised ultrasonographically by
enlargement, heterogeneous echogenicity and loss of long
linear echos in longitudinal images. In 3 horses, adhesions
between the ALDDFT and the SL were identified post mortem.
Close apposition of these structures seen ultrasonographically
may indicate adhesion formation. It was concluded that the
clinical features of PSD and concurrent injury of the ALDDFT
are similar to those for PSD alone, highlighting the need for
comprehensive and systematic ultrasonographic assessment.
Proximal injuries of the ALDDFT have also been seen as a
sequel to hindlimb PSD.20
We routinely examine the suspensory ligament in its entirety
and suspensory branch injuries and/or periligamentous fibrosis
can be present despite failure to recognise improvement in
lameness after perineural analgesia of the plantar (at the
junction of the proximal ¾ and distal ¼ of the metatarsus) and
plantar metatarsal nerves (‘low 4-point-block’)b. In addition, we
also see horses in which there is partial improvement in
lameness after a ‘low-4-point-block’ and abolition of lameness
after perineural analgesia of the deep branch of the lateral
plantar nerve, associated with concurrent PSD and suspensory
ligament branch injury.17 Although some horses have palpable
enlargement of the suspensory ligament branch or
periligamentous enlargement, and may show resentment of
passive flexion of the fetlock and exacerbation of lameness after
flexion, the absence of localising clinical signs does not
preclude injury.
Recent gross post mortem studies indicate that the extent of
periligamentous reaction on the axial aspect of the suspensory
ligament
branches
may
be
difficult
to
assess
ultrasonographicallyc.
VI. CONCURRENT INJURY OF THE ACCESSORY
LIGAMENT OF THE SUSPENSORY LIGAMENT
The accessory ligament of the hindlimb suspensory ligament
arises from the plantar aspect of the calcaneus and fourth tarsal
bones and blends with the suspensory ligament in the proximal
aspect of the metatarsus. The accessory ligament of the
suspensory ligament of both hindlimbs of 12 mature horses,
with no history of hindlimb lameness, was assessed
ultrasonographically. The ligament comprised linear parallel
echoes which were consistently shorter than those of the lateral
digital flexor tendon; the dorsal and plantar borders were
parallel.18 Lameness associated with injury of the accessory
ligament of the suspensory ligament was identified in six of
eight lame hindlimbs of five horses, unilaterally in four horses
and bilaterally in one horse.18 In all horses there was concurrent
proximal suspensory desmopathy. There was localised
oedematous swelling on the distal medial aspect of the chestnut
extending distally in two horses. Lameness was best identified
when the horses were ridden. Perineural analgesia of the deep
branch of the lateral plantar nerve abolished lameness in three
horses, but perineural analgesia of the tibial nerve was required
to abolish lameness in the hindlimb with injury of the accessory
ligament of the suspensory ligament in two horses. Injury of the
VIII. CONCURRENT SACROILIAC JOINT REGION PAIN
Sacroiliac joint region pain is frequently seen in association
with hindlimb PSD.16 We presume that it may develop
secondarily, but it is equally plausible that it may be primary.
Clinical signs are almost invariably worst ridden and may only
be apparent ridden, especially in canter. Thus the condition may
be missed unless horses are seen ridden. Lameness may be
substantially improved by perineural analgesia of the deep
branch of the lateral plantar nerve, with residual lameness being
abolished by infiltration of local anaesthetic solution around the
sacroiliac joint regions. In other horses, lameness is abolished
by perineural analgesia of the deep branch of the lateral plantar
nerve, but the horse still appears uncomfortable, especially in
canter. In a small proportion of horses although baseline
lameness may be substantially improved by perineural
analgesia of the deep branch of the lateral plantar nerve, the
horse’s demeanour, willingness to work and quality of the
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AAEP FOCUS ON SOFT TISSUE LAMENESS IN THE PERFORMANCE HORSE PROCEEDINGS / 2016
canter may deteriorate. These features are substantially
improved by infiltration of local anaesthetic solution around the
sacroiliac joint regions.
12. Hobbs S, Northrop A, Mahaffey C, et al. Equine
Surfaces White Paper. 2014. Available at:
http://www.fei.org/fei/about-fei/publications/fei-books
13. Murray R, Walters J, Snart H, et al. Identification of risk
factors for lameness in dressage horses. Vet J
2010;184:27-36.
14. Murray R, Walters J, Snart H, et al. How do features of
dressage arenas influence training surface properties
which are potentially associated with lameness? Vet J
2010;186:172-179.
15. Dyson S, Murray R. Management of hindlimb proximal
suspensory desmopathy by neurectomy of the deep branch
of the lateral plantar nerve and plantar fasciotomy: 155
horses (2003 – 2008). Equine Vet J 2012;44:361-367.
16. Barstow A, Dyson S. Clinical features and diagnosis of
sacroiliac joint region pain in 296 horses: 2004 – 2014.
Equine Vet Educ 2015;27:637-647.
17. Marneris D, Dyson S. Clinical features, diagnostic imaging
findings and concurrent injuries in 71 sports horses with
suspensory branch injuries. Equine Vet Educ 2014;26:312321.
18. Dyson S. Hindlimb lameness associated with proximal
suspensory desmopathy and injury of the accessory
ligament of the suspensory ligament: five horses. Equine
Vet Educ 2014;26:538-542.
19. Plowright E, Dyson S. Concurrent proximal suspensory
desmopathy and injury of the accessory ligament of the
deep digital flexor tendon in forelimbs or hindlimbs of 19
horses. Equine Vet Educ 2015;27:355-364.
20. Dyson S. Proximal injuries of the accessory ligament of the
deep digital flexor tendon in forelimbs and hindlimbs: 12
horses (2006 – 2010) Equine Vet Educ 2012;24:134-142.
ACKNOWLEDGMENTS
Declaration of Ethics
The Author has adhered to the Principles of the Veterinary
Medical Ethics of the AVMA.
Conflicts of Interest
The Author has no conflicts of interest. Referenced studies
were approved by the Ethical Review Committee of the
Animal Health Trust.
REFERENCES AND FOOTNOTES
1.
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magnetic resonance and sonographic findings in horses
with proximal plantar metatarsal pain. Vet Radiol
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2. Dyson S, Pinilla M. Proximal suspensory desmopathy in
hindlimbs: a correlative clinical, ultrasonographic, gross
post mortem and histological study, in Proceedings. Am
Assoc Equine Pract 2015;61:359.
3. Dyson S, Murray R, Pinilla M. Proximal suspensory
desmopathy in hindlimbs: a correlative clinical,
ultrasonographic, gross post mortem and histological
study. Equine Vet J 2016; doi: 10.1111/evj.12563
4. Werpy N, Denoix J-M, McIlwraith C, et al. Comparison
between standard ultrasonography, angle contrast
ultrasonography and magnetic resonance imaging
characteristics of the normal proximal suspensory
ligament. Vet Radiol Ultrasound 2013;54:1-12.
5. Denoix J-M, Bertoni L. The angle contrast ultrasound
technique in the flexed limb improved assessment of
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pelvic limb. Equine Vet Educ 2015;27:209-217.
6. Dyson S. Proximal suspensory desmitis in the hindlimb:
42 cases. British Vet J 1994;150:279-291.
7. Dyson S. Proximal suspensory desmitis in the hindlimb.
Equine Vet Educ1995;7:275-278.
8. Dyson S. Is degenerative change within hindlimb
suspensory ligaments a prelude to all types of injury?
Equine Vet Educ 2010;22 271–274.
9. Murray R, Dyson S, Tranquille C, et al. Association of
type of sport and performance level with anatomical site
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10. Kold S, Dyson S. Lameness in the dressage horse. In: Ross
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flexion and fetlock extension at collected and extended
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a.
b.
c.
11
Walker V, Tranquille C, Newton R, et al. Effect of
medium or extended trot, compared with collected
trot, on the kinematics of the forelimbs and hindlimbs
in two groups of dressage horses on two different
surfaces. Submitted for publication 2016.
Dyson S, unpublished data.
Dyson S, unpublished data.