P. 605

N. Fitzpatrick1
1Fitzpatrick Referrals, Eashing, Surrey, UK
Degenerative lumbosacral stenosis (DLSS) is the most common cause of compression of the cauda equina
and seventh lumbar (L7) nerve roots in dogs. DLSS is characterised by lumbosacral (LS) intervertebral disc (IVD) protrusion, subluxation or in ammation of the facet joints with associated thickening of the joint capsule
and hypertrophy of the interarcuate ligament. The lumbosacral joint is the most mobile functional spinal unit (FSU) in dogs. Pathological static or dynamic alteration in load transmission across the L7-S1 joint is thought
to be the most common contributor to lumbosacral intervertebral disc degeneration in dogs. A common sequel to disc-associated DLSS is impingement of the nerve roots or vasculature of the cauda equina and/or L7 nerve roots, either by the disc itself or by secondary in ammatory,  brous or osseous impingement. Abaxial disc protrusion and spondylosis can be a signi cant cause of pain and lameness in large breed dogs whilst lower motor neuron de cits are much less common in our case population in the UK.
Key clinical features are unwillingness to jump, a hunched stance and uni- or bi-lateral pelvic limb lameness, which may occur after prolonged recumbency and lessen with exercise. The sciatic nerve pathway can be palpated per rectum and in the recess of the caudal thigh musculature, whereupon deep digital pressure may produce resentment and vocalisation, though interpretation of
this test is subjective and experience in normal and diseased dogs is important. Focal pressure application
to the dorsal aspect of the lumbo-sacral junction is also important albeit subjective and hyperextension of the lumbosacral junction in isolation without caudal extension of the coxofemoral joints is a useful interrogation during clinical examination. Objective measures of lumbosacral function and pain using kinematics and electrophysiology are evolving and may yield greater accuracy with regard to detection of clinically relevant pain. It is critical to exclude coxofemoral and sti e disease as well as other causes of pelvic limb pain and lameness and infections or neoplastic pathologies must always be considered.
Diagnosis is generally based on clinical examination and advanced imaging. MRI has superior soft tissue contrast resolution and sensitivity for detection of IVD degeneration is high. However, MRI lacks the ability to provide a reliable correlation between severity of clinical signs and the severity of the compression. CT is more
valuable for assessment of de nitive osseous boundaries, but good agreement between MRI and CT  ndings has been documented. MRI is frequently used in canine and human patients to identify primary lumbar foramenal stenosis, since unrecognised or recurrent foramenal stenosis may be associated with “failed back surgery syndrome”. L7-S1 foramenal stenosis and associated compressive radiculopathy has been documented to occur with a reported incidence of 68-90% in dogs presenting with clinical signs associated with DLSS. MRI interrogation of the LS spine in dogs has been used
to divide the L7-S1 intervertebral foramen (IVF) into entrance, middle and exit zones, allowing description
of a foramen as stenotic when loss of the fat signal is complete or when only a minimal rim of fat signal is visible within one of the foramenal zones on parasagittal imaging plane sequences.
It is important to recognise that for some patients, especially working and agility dogs, dynamic imaging is fundamental to diagnosis. In the author’s practice we see a signi cant number of canine athletes that present with performance impairment attributable to dynamic claudication of the cauda equina and L7 nerve roots.
We routinely image lumbosacral spinal motion in neutral and hyperextension and have shown that neuroforaminal dimension varies considerably and that this is clinically relevant in cases of intervertebral disc protrusion with
or without new bone formation. Additionally, the dorsal lamina of the sacrum and articular facet proliferation may encroach dorsally on both the sacral and the L7 nerve roots. These changes may not be apparent on neutral sagittal, parasagittal and transverse imaging planes.
Acquisition of MRI images in conventional parasagittal planes may fail to accurately represent the actual dimensions of the entry, middle and exit zones of the neuroforamena. We have performed both a cadaveric and an in-vivo comparison of standard parasagittal plane image acquisition with parasagittal oblique imaging where images are obtained perpendicular to the L7
nerve pathway rather than parallel to the sagittal plane. These studies have revealed greater sensitivity of oblique parasagittal imaging for detection of encroachment of the L7 nerve pathway in all zones.
Treatment methods for DLSS have been broadly divided into non-surgical and surgical, with the recommended treatment depending on the nature of cauda equina and nerve root compression (static or dynamic, central or lateralised, acute or chronic) the severity and chronicity of clinical signs and the intended use of the dog. Our experience with epidural steroid injections has been favourable for dogs affected by moderate encroachment of the L7 neuroforamenae and pain only.
An Urban Experience

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