Lumbosacral transitional vertebra in dogs: LTV explained

Overview

An LTV lies at the boundary between the lumbar spine and sacrum. Dogs normally have 7 lumbar vertebrae. The sacrum usually consists of 3 fused vertebrae. Its joint surfaces connect it to the iliac bones of the pelvis.

Before the sacrum, a dog's spine normally has 27 vertebrae in total, divided between the neck, chest and lumbar regions.

An LTV may look the same on the right and left sides. In an asymmetrical form, its two sides differ. An abnormal vertebra does not always cause noticeable problems. The mildest change, termed LTV1 in the grading scheme described below, is not currently considered to cause symptoms.

The same dog may also have a transitional vertebra at the thoracic–lumbar boundary. An abnormality there may involve incompletely developed ribs.

Causes

An LTV forms during spinal development before a puppy is born. The change is inherited, but its precise inheritance mechanism is unknown. In sacralisation, the last lumbar vertebra, L7, acquires sacral features. In lumbarisation, the first sacral vertebra, S1, instead resembles a lumbar vertebra.

Complete lumbarisation may appear as 8 lumbar vertebrae. With complete sacralisation, there may be 6. The shape of the abnormal vertebra's transverse processes and their connection to the ilium may vary.

Normally, the ossification centre of the first sacral vertebral body appears on day 40 of pregnancy. The developing structures of all 3 sacral vertebrae are visible by day 43. Normal fusion of the sacral vertebral bodies is completed at about 6 months of age.

Before fusion, fibrocartilaginous tissue normally lies between the vertebrae.

Risk factors

LTV occurs in many breeds. Frequency varies between breeds, and comprehensive information is lacking for many. Previously reported proportions in German Shepherd Dogs have ranged from 4.3–29.0%.

In a northern European group of 228 German Shepherd Dogs, LTV was found in 92 dogs, or 40%. The group included screened dogs, dogs retired from service and dogs imaged at veterinary visits for various reasons. The high proportion partly reflected inclusion of mild separation of the median sacral crest as an abnormality.

This crest separation was found in 62 dogs, or 27% of the whole group. In 6 dogs, the only abnormal finding was a short additional lumbar vertebra positioned further back than usual.

Working or sporting use may affect an LTV's clinical significance. Symptoms of degenerative lumbosacral stenosis usually begin at 3–7 years of age. This later-developing narrowing is particularly common in large dogs.

Typical symptoms

Possible signs of lumbosacral pain or nerve compression include:

• Your dog gets up slowly or looks stiff when starting to move.

• Your dog becomes reluctant to jump, climb stairs or walk up a steep slope.

• The lower back is painful, and your dog may cry out or avoid touch.

• Your dog starts limping on a hindleg or seems to lose hindquarter strength.

• Hindleg muscle mass may decrease with a longer-standing problem.

• The tail moves less than before or seems weak.

• Urine or faeces may leak if nerve function is severely disrupted.

An LTV1 finding alone is not currently expected to explain these symptoms. A dog graded LTV2–LTV4 may also be entirely symptom-free.

Complications and consequences

An LTV may predispose the lumbosacral junction to premature degeneration. Abnormal vertebral connections can alter twisting forces in the area. Narrowing of the spinal canal or nerve root channels can compress the local nerve roots.

The disc at the lumbosacral junction may degenerate and bulge towards the nerve roots. Thickening of a ligament in the spinal canal may also reduce space for nerves. Partial dislocation of the lumbosacral junction is a less common change associated with narrowing.

Cauda equina is the name of the nerve root bundle in the lower back. Compression can cause pain and sometimes neurological dysfunction. In the most severe cases, hindleg paralysis may develop.

An asymmetrical LTV3 may be associated with congenital pelvic tilt. One-sided hip dysplasia may occur with the same change. An affected dog may cope fairly well as a pet. A return to demanding work or sports is less certain.

Diagnosis at the vet

Identifying an LTV requires side-view X-rays of the thoracic and lumbar spine. An image of the sacrum with the dog lying on its back is also taken, and may form part of hip imaging. Different views complement each other when assessing vertebral structure.

A side view helps identify an additional lumbar vertebra. Separation of the median crest may be apparent only in the image taken on the dog's back. Under some official screening schemes, an LTV assessment can be issued from 12 months of age. An official assessment of this congenital change is issued only once under such a scheme.

Screening aims to identify hidden inherited abnormalities even in symptom-free dogs. Results are always given as a grade on a predefined scale. In some schemes, only assessment grades appear in the breeding database. Additional details can be checked in the owner's PDF assessment report.

What do LTV grades mean?

In this grading scheme, LTV0 means no classifiable changes are found.

LTV1 is the mildest structural abnormality. It includes, for example, separation of the median sacral crest. Despite crest separation, the sacral body may be normally fused.

LTV1 can also include an L7 that is shorter and positioned further back than normal. Another LTV1 form is a sacrum made up of 4 vertebrae, with the first tail vertebra fused to it.

Incomplete development of the first part of the median sacral crest can also result in LTV1. In a rare mild form, a gap remains between the second and third sacral vertebrae.

LTV2 is a symmetrical form with identical sides. A gap remains between the first and second sacral vertebral bodies. In LTV3, one side resembles a lumbar vertebra more closely and the other a sacral vertebra.

LTV4 is structurally furthest from normal. It includes 6 or 8 lumbar vertebrae. Under this scheme, a very mild borderline case appears in the breeding database as a normal LTV0 result.

If the total number of vertebrae is unknown, distinguishing lumbarisation from sacralisation may be difficult. Pelvic bones can obscure the abnormal vertebra's transverse processes on X-rays.

Investigating the cause of symptoms

History and clinical examination are central to investigating back pain. Lower back and hip pain can be difficult to distinguish. Degenerative changes on X-rays may also be symptom-free findings.

Disc infection may also underlie nerve compression. A spinal tumour can likewise compress nerves in this area.

If nerve compression is suspected, MRI shows nerves and surrounding soft tissues. CT shows the local bony structures in detail. The relationship between imaging findings and this individual dog's symptoms determines their clinical significance.

Treatment

Treatment targets the symptoms identified and their cause. Back symptoms associated with LTV can be managed with rest and pain relief prescribed by the vet. The most severe symptoms may require surgery.

Pain management and adjusting activity

In degenerative lumbosacral stenosis, mild pain alone may ease with 4–6 weeks of rest. After initial rest, controlled lead exercise can be reintroduced. Activities involving jumping and strong twisting movements are modified.

Weight loss in an overweight dog is part of conservative back care. Painkillers may relieve symptoms temporarily. Physiotherapy may help, particularly in long-term management.

Strengthening lower back support muscles may form part of conservative care for degenerative narrowing.

About 50% of dogs with degenerative lumbosacral stenosis can be treated successfully without surgery. Recurrent symptoms may require another period of rest and pain management. Lasting changes in everyday activity may be needed even after symptoms settle.

Surgery for nerve compression

Surgery is considered when pain does not respond to other treatment. Neurological dysfunction may also be an indication. A common decompression procedure removes part of the vertebral roof and disc material when needed. A nerve root's passage may be widened separately in some cases. Fixation devices can also stabilise the lumbosacral junction.

Removing part of the vertebral roof alone may not adequately reach narrowing in the lateral part of a nerve root channel. Stabilisation screws can bend or loosen. Broken screws may also impair fixation. Bone removal at the fixation site can weaken a vertebral joint process and predispose it to fracture.

Symptoms improve in about 70–95% of dogs operated on for degenerative narrowing. However, existing urinary incontinence does not always resolve. Permanent nerve damage may remain despite successful decompression.

Rest and pain management continue after surgery. Rehabilitation is planned according to the procedure and remaining symptoms. In some dogs, symptoms may recur later despite surgery.

Prevention

Spinal imaging of breeding dogs helps reduce inherited LTV. Some breed-club guidance recommends excluding symptomatic dogs from breeding. Under such guidance, an LTV1–LTV4 result in a symptom-free dog does not automatically prevent breeding.

A symptom-free dog graded LTV1–LTV4 is recommended to be paired only with an LTV0 dog. Spinal imaging is recommended for offspring from these matings. Examining offspring builds information about the inheritance and significance of the changes.

Under such official screening schemes, spinal assessment results appear in a breeding database. Consistent grading scales make results comparable between dogs when gathering breeding information.

Important for dog owners

Keep the official LTV report and original images. Record when your dog gets up slowly, avoids stairs or becomes lame. Note whether changes occur after rest or with activity. Show the vet previous hip and spinal assessment reports too.

An LTV finding may be symptom-free. New pain may also originate in the hip joint.

Agree activity limits and a return to training for an affected dog according to examination findings and treatment response. Monitor hindleg strength, tail function and continence separately. Before breeding, ask for the proposed mate's LTV result too, and record examination results in the resulting puppies.

Frequently asked questions

Does LTV1 mean my dog has a painful back?

LTV1 changes are not currently considered to cause symptoms. Separation of the median crest may occur with an otherwise normally fused sacrum. Clinical examination investigates the cause of back pain. Hip pain may also resemble lower back pain. MRI or CT may be used to investigate symptoms when needed.

Is LTV4 always a serious disease?

LTV4 describes the vertebral structure that differs most from the usual lumbosacral junction. The dog has 6 or 8 lumbar vertebrae. LTV2–LTV4 changes may predispose to degenerative disease. Nevertheless, many of these dogs have no symptoms. Working or sporting use may influence the finding's clinical significance.

What breeding guidance applies to a dog with LTV?

Some breed-club guidance recommends excluding symptomatic dogs from breeding. It recommends an LTV0 mate for a symptom-free LTV1–LTV4 dog. Imaging of offspring is recommended. This gathers information on inheritance and significance for future breeding decisions. Under such schemes, official results appear in a breeding database to support others' breeding choices too.

Can an ordinary hip X-ray show LTV?

A hip image taken with the dog on its back can form part of an LTV examination. Side views of the thoracic and lumbar spine are also needed. A side view helps identify an additional lumbar vertebra. Different views help assess the abnormal area as a whole. Pelvic bones may obscure transverse processes from some directions.

Does LTV always need surgery?

A dog can be symptom-free despite an LTV2–LTV4 finding. Back symptoms may be treated with rest and pain relief. In degenerative narrowing, surgery is considered if pain does not respond to other care. Neurological deficits can also lead to surgery. The approach is chosen according to the location and nature of the nerve compression identified.