Bilateral Forelimb Lameness in
an 11 year-old Thoroughbred
Drs. Karyn Labbe and Beth Biscoe, Washington State University
Dr. John Mattoon, Washington State University
Bilateral forelimb lameness in an 11
year-old Thoroughbred
• Patient is a previous racehorse acquired by the
owner with the intended use of barrel racing
• History of intermittent lameness in both
forelimbs noticed by the owner 9 months prior
• No improvement was seen with a prolonged
period of stall rest
Primary Veterinarian Workup
• Injection of both fore coffin joints resulted in
transient lameness improvement for 3 months
• Referring radiographs of the left front foot
revealed moderate navicular bone degeneration
Lameness evaluation at presentation
• Patient showed a grade II/V left fore lameness,
which was exacerbated by left circling
• Left fore palmar digital nerve analgesia resolved
the left fore lameness and resulted in the horse
displaying a grade III/V right fore lameness
• Right fore palmar digital nerve analgesia
improved the RF lameness greater than 75%
Further Imaging
• The decision was made for MRI of both fore feet
• Nail screening radiography prior to MRI identified
a type II fracture of the right fore third phalanx
Advanced Imaging
MRI Left Front Foot Region
• MRI Proton Density (PD) transverse images shown
• Distal to proximal
• 2 vitamin E capsules were placed along lateral side
MRI Left Front Foot Region
Sagittal Plane
• Proton Density sagittal plane
• Lateral to medial
MRI Findings Left Front Foot Region
• Multifocal areas of hyperintensity associated with
both lobes of the deep digital flexor tendon
• Symmetrical biaxial lobes of tissue isointense to
the DDFT that span from the palmar margin of
the distal navicular suspensory ligament
proximally and axially to merge with the DDFT
lobes/fibrocartilaginous dorsal DDFT border
• Hypointense tissue in the navicular bursa
between the navicular suspensory ligament and
dorsal-axial margin of the DDFT lobes, likely
represent adhesions
MRI Findings (continued)
• Enlargement and heterogenous intensity of the
impar ligament
• Avulsion fragment of the distolateral border of
the navicular bone at the impar attachment
• Marked thickening of the distal digital annular
ligament
Follow-Up
• Due to the poor prognosis for competitive use as
a barrel horse, the patient was retired
Commentary
• This case was selected because of the described
biaxial symmetrical lobes of tissue between the
navicular suspensory ligament and the DDFT
• A symmetrical finding was found in the
contralateral forelimb
• Due to the bilateral symmetry, the tissue likely
represents a congenital anatomic variant
Right Front, PD transverse
Commentary (continued)
• It is considered that the relationship of the tissue
connecting the DDFT dorsal border and the
navicular suspensory ligament may have altered
the biomechanics of the distal limb (especially
with extension of the DIP joint)
• This may have placed additional strain on the
DDFT distal to the site of tissue attachment,
predisposing it to tendinopathy
Commentary (continued)
• The palmar carpal ligament extends distally to
form the accessory ligament of the DDFT (inferior
check ligament). No reports of additional DDFT
accessory ligaments or a tripartite DDFT at the
level of P2 were found in a literature search but
are considered present in this horse, discovered
in both the left and right forelimbs
Commentary (continued)
• The “T ligament” is described anatomically as
vascular connective tissue separating synovial
structures in the palmar foot, including palmar
pouch of the coffin joint, proximal recess of the
navicular bursa and distal recess of the digital
tendon sheath
• Although the observed tissue in the sagittal
images was in a similar location as the T ligament,
the tissue displayed hypointense signal similar to
dense collagen connective tissue comprising
tendons and not the typical “T ligament”
Commentary (continued)
• Fibrinous adhesions can form between the
navicular suspensory ligament and DDFT. Over
time collagen can be deposited resulting in a
fibrous adhesion. However, due to the biaxial
symmetry as well as bilateral symmetry of the
discrete bundles discovered in this horse, fibrous
adhesions are thought a less likely explanation
Commentary (continued)
• It was also interesting to evaluate the right fore
type II third phalanx fracture on MRI
• The bone margins at the fracture site were PD
hypointense consistent with sclerosis, but did not
demonstrate hyperintensity on STIR sequences
Commentary (continued)
• Characteristics of this fracture on MRI support a
chronic fracture that has healed by a fibrous
union, associated with the vestigial periosteum of
the coffin bone (Butler JA, Colles CM, Dyson SJ, Kold SE, Poulos PW.
Clinical Radiology of the Horse, 3rd ed., p.88, 2008, Wiley-Blackwell)
• This case demonstrates the potential advantage
of utilizing additional imaging diagnostics like MRI
to evaluate soft tissue structures in the foot for a
cause of lameness even though obvious bony
lesions were identified on radiographs
Right Front, Type II P3 fracture
Transverse, PD
Transverse, STIR
Right Front, Type II P3 fracture
Dorsal, 3D
Right Front, Type II P3 fracture
60-degree dorsoproximalpalmarodistal oblique
Lateral 45 degree proximalmedial distal oblique