Key Points

The lower back is prone to injury due to high stresses on the spine in this area.

Problems in this area of the spine include disc herniation, nerve root compression and instability of the spine.

Medical therapy may be effective if a permanent life-style changeisenforced.

Surgery is a good option in appropriate cases and may include a dorsal laminectomy, removal of the herniated disc and stabilization of the spine with metal implants.

 

Anatomy

Dogs have seven lumbar vertebrae that form the lower back. This portion of the spine is attached to the pelvic portion of the spine called the sacrum. The pelvis is directly attached to the sacrum via the sacroiliac joint. Because the sacrum is attached to the pelvis, this portion of the spine is somewhat fixed in place. The junction of the 7th lumbar vertebra and the sacrum is under a tremendous amount of stress, as this is the area where the fixed spine meets a very moveable or flexible portion of the spine. Nerves exit the neural foramina (holes in the spine) between each vertebra. The 7th spinal nerve exits the foramina at the lumbosacral junction.

 

Signs

German Shepherds in their mid to later years of life are the most common patient affected by DLSS. Most dogs that have DLSS have clinical signs of pain and may also have hind limb lameness (one limb or both). Reluctance to jump on elevated surfaces may be an overlooked sign of DLSS. Other signs may include crying out in pain or holding a limb off the ground. Commonly, dogs will be referred to us for an orthopedic evaluation, however, we may find that the cause of the lameness is due to a pinched L7 nerve root due to DLSS. Some dogs will have atrophy of the muscles of the hind limbs. In some patients, the cranial tibial muscles (muscles on the front of the shin bone) are atrophied due to profound impairment of the L7 nerve function. With increasing severity of the condition, other signs may include difficulty sitting or rising, hind limb weakness, urinary and fecal incontinence, and impaired tail function. Dogs that have marked clinical signs of ataxia (wobbliness of the hind limbs) should be evaluated for other neurological conditions.

 

Diagnosis

Plain x-rays may be helpful in suggesting a diagnosis of LDSS; however, these are inadequate at providing a definitive diagnosis. Advanced imaging such as CT scan or MRI are the gold standard imaging modalities. MRI is excellent to show additional soft tissue details such as nerve root swelling or compression, thickened spinal ligaments and protrusion of the LS disc. CT is a very good test for DLS,S as it is a relatively fast diagnostic test to perform. Dynamic CT scan or MRI studies should be done. That means a scan is completed with flexion and extension of the spine. With flexion of the spine, pressure is taken off the entrapped nerves. With extension of the spine, the nerves become compresed, as the spine shifts out of alignment (subluxation) and the neural foramina become very narowed (see two images below left 3D CT reconstruction; sagittal spinal image). With flexion, the neural foramina and the spinal canal opens up (see two images below right; 3D CT reconstruction; sagittal spinal image).

Treatment

The type of treatment recommended may be dictated by the findings of the CT scan or MRI. Medical therapy is reserved for milder cases of DLSS and may include rest for 2 months, life-style change (avoid jumping, retirement from working activities), administration of medications such as nonsteroidal anti-inflammatories, epidural cortisone injections, muscle relaxants and nerve pain modulating medications (gabapentin or amantidine). The type of surgery performed will be dictated by the type of problems seen on the CT sacn or MRI. A dorsal laminectomy is commonly done in these cases, which involves removing the roof (lamina) of the spine at the LS junction and removal of the protruding disc. If the spine is unstable (as seen on the dynamic imaging study), then the spine will need to be stabilized (see two x-ray images below of postop stabilization of the spine with two plates and screws). This is achieved by placement of locking plates and screws in the spine to maintain its neutral position which takes pressure off the L7 nerve roots.Atthat time bone graft may be packed around the top of the spine to help promote spinal fusion of the joint of the LS junction.

Care at home

Most dogs that have surgical treatment for LDSS can go home one day after surgery; however, if the patient is quite painful, additional hospitalization may be recommended. The pet that has had surgery for LDSS must have restricted activity for 4 to 6 months. Jumping, running, playing with other dogs or people is forbidden, as this could break of the screws or pins that have been placed in the spine. Return to activity should not be attempted until after 6 months.

 

Prognosis

Most dogs that have surgery for DLSS make a good recovery with resolution of pain and lameness. Return to activity too soon may result in recurrence of clinical signs.