Legg-Perthes disease in dogs: hip pain and treatment

Overview

The hip is a ball-and-socket joint in which the rounded head of the femur fits into the pelvis's hip socket. In Legg-Perthes disease, disrupted blood flow weakens the structure of this ball-shaped bone. As the femoral head collapses, the joint surfaces may no longer fit together properly.

The condition is also called Legg-Calvé-Perthes disease. It is uncommon overall, although it occurs in several small breeds. Most dogs have only one affected hip. Without treatment, the hip may develop osteoarthritis and remain painful.

In a healthy hip, the fit between the femoral head and socket allows the leg to move in different directions. Disease that changes this fit reduces joint mobility.

Causes

Disrupted blood flow damages developing bone

When blood flow is interrupted, the bone receives less oxygen and fewer nutrients. This causes bone cell death, or necrosis. The small supporting struts in damaged bone can no longer withstand normal loading. Small fractures develop and the femoral head may collapse.

Restored blood flow triggers new bone formation and remodelling. However, the altered shape may continue to fit the socket poorly. Stiffness and pain may result. The precise trigger for the blood supply problem is unknown.

There is an inherited predisposition. Blood vessels in a growing dog's femoral head may be particularly vulnerable to damage.

Changes develop while the bone's growth plate is still open. The joint's cartilage surface may later crack and change shape.

Risk factors

A typical patient is a growing small dog, particularly a terrier or toy breed. Symptoms usually start at 4–11 months of age. Average age at onset is described as 5–8 months. The overall reported range is 3–13 months.

Small crossbreeds can also be affected. Miniature and Toy Poodles are susceptible varieties. Both male and female dogs develop the disease. Because of inherited susceptibility, disease in relatives is also relevant to breeding decisions.

Other susceptible breeds include Chihuahuas, Pomeranians and Yorkshire Terriers. The disease has been described particularly in small dogs weighing up to 12 kg.

Typical symptoms

Lameness often starts mildly and increases over several weeks. Your dog may eventually hold the painful leg completely off the ground. Apparently sudden pain may emerge even though joint damage has been developing for some time.

• Your dog is lame on a hindleg or avoids bearing weight on it.

• The hindquarters move stiffly and your dog runs less.

• Your dog is reluctant to jump or climb stairs.

• Touching near the hip or hindleg makes your dog irritable.

• One thigh looks thinner as its muscles waste.

• Moving the hip causes pain or a yelp.

• In severe disease, your dog struggles to move or is reluctant to get up.

You may notice leg pain without any preceding accident. Rarely, the disease starts in one leg and later affects the other hip too.

Complications and consequences

An uneven joint and muscle wasting impair function

Deformation of the femoral head gradually leads to osteoarthritis. Reduced leg use causes the muscles supporting the hip to waste. Muscle wasting can also prolong recovery after surgery.

Disease in both hips makes movement particularly difficult. In one clinical study of 43 dogs, both hips were affected in 5 dogs, or 11.63%. One-sided disease occurred in 38 dogs, or 88.37%.

Bilateral disease has also been described in 12–17% of dogs. Other descriptions have called it common, so accounts of its frequency differ.

The leg may remain slightly shorter after surgery. Nevertheless, a functioning false joint can allow good quality of life.

Diagnosis at the vet

The source of lameness and hip movement are assessed

The vet considers age, breed, symptom history and examination findings. Movement is assessed as your dog walks in the practice. Both hindlegs are compared. Hip range of movement may be restricted on examination. Moving the joint may produce a grating sensation called crepitus.

The vet also assesses thigh muscle wasting. The affected limb may seem shorter than the other. Your description of how long lameness has been present helps the assessment.

In the clinical study of 43 dogs, 33, or 76.7%, had pain on palpation. Crepitus occurred in 24 dogs, or 55.8%. Muscle wasting was seen in 17 dogs, or 39.5%.

X-rays show changes in bone structure

Diagnosis is usually confirmed with hip X-rays. These may be taken under sedation or general anaesthesia. Images show uneven bone density in the femoral head and neck. In more advanced disease, the head may be flattened or fragmented. Poor fit between the joint surfaces of the femoral head and socket may also be visible.

Early X-ray changes can be very subtle. Repeat images are sometimes needed to demonstrate developing changes. Imaging both hips helps assess the extent of disease. X-ray changes can be divided into 5 grades of severity.

In the mildest grade, grade 1, femoral head shape may still look normal. However, the joint space may be widened and bone density reduced. In grade 2, the head starts flattening and contains several areas of reduced density. In grade 3, the joint surface becomes irregular. In grade 4, normal head shape is lost. In the most severe grade, grade 5, the head fragments and the joint surface breaks up.

Treatment

Pain relief and deciding on surgery

The vet chooses treatment according to symptoms and the degree of joint damage. Restricted exercise and a non-steroidal anti-inflammatory drug may be tried in mild early disease. However, fewer than 25% of conservatively treated dogs achieve a complete response. An anti-inflammatory painkiller reduces pain but does not repair the underlying joint damage.

Other classes of medicine may also be used for pain when needed. Most dogs require surgery. Surgery is particularly indicated once the bone has collapsed and osteoarthritis has developed.

Removing the femoral head and neck creates a false joint

The usual operation removes the damaged femoral head and neck. It is also known as femoral head ostectomy, or FHO. Removal stops painful bone surfaces rubbing against one another. A fibrous false joint develops between the femur and hip socket.

The muscles around the hip support the limb in its new situation. The false joint does not have the same structure as the original ball-and-socket joint. Its range of movement may be smaller than that of a normal hip. A young small dog often does not need an artificial joint to replace the removed bone.

Hip replacement is an alternative for some dogs. This replaces the damaged joint with artificial components. A vet specialising in orthopaedics performs the replacement. If both hips are operated on separately, the more severely affected side may be treated first. The other side may be operated on 4–6 weeks later.

Femoral head and neck removal is performed under general anaesthesia. Hospitalisation may last from hours to several days, depending on the dog. Your dog may not yet bear weight on the operated leg immediately after discharge. A protective collar can prevent wound licking.

Rehabilitation progresses from rest to controlled movement

Early postoperative care focuses on pain control and tissue healing. Gentle rehabilitation may begin after just 1–2 days of rest. Exercise is often increased after about a week, according to the vet's plan. Movement helps prevent excessive tightening of scar tissue in the false joint.

Slow walking encourages weight-bearing on the operated leg. When running, a dog is more likely to hold the leg up. Rough play and sudden twisting movements are avoided for the first 30 days. Painful passive movement exercises are not continued.

Recovery may progress to normal activity in about 6 weeks. Restrictions on vigorous activity may also last 2–3 months. A rehabilitation programme supports the return of muscle strength, range of movement and normal leg use.

The outlook after surgery is generally good. However, some dogs retain lameness or discomfort. A remaining painful bone spur may require another operation.

Initially, outings may be limited to short toilet trips on a lead. Wound checking and removal of non-dissolving stitches may take place after 10–12 days. Dissolving stitches under the skin do not always need separate removal.

Good muscle mass supports joint stability and may speed the return to pain-free movement. If there is no clear improvement at 6 weeks, the need for supervised rehabilitation is assessed.

Prevention

Some breeding guidance excludes affected dogs from breeding. However, the precise inheritance pattern has not been confirmed. An effect of a single gene has been suspected. Several genes may also be involved.

A genetic study compared DNA from 85 affected and 102 healthy dogs. A possible disease-associated region was found on chromosome 6. The aim was still to identify the precise predisposing mutation or mutations.

Avoiding excess weight reduces loading on the treated hip. Early recognition and treatment may prevent progression of severe deformity and osteoarthritis.

Important for dog owners

Take a short video of your dog walking on level ground if it can move without being forced. Note which leg is lame, when symptoms began and how leg use has changed. Also record willingness to play, get up from lying down and manage usual walks.

Some Poodle breed clubs accept reports of a diagnosis for a disease register supported by veterinary documentation. Under such reporting schemes, the document must show the diagnosis and identify the dog. Identification may be a registration number, microchip number or registered name.

At discharge, ask for a written exercise and rehabilitation plan. Agree when leg use should improve and what to do if pain increases. Record completed exercises and movement afterwards. Give medicines as prescribed and report any adverse effects you notice.

Frequently asked questions

What does necrosis of the femoral head mean?

In Legg-Perthes disease, the main damage is death of the femoral head caused by disrupted blood flow. X-rays show its changing shape and possible collapse. Confirmation relies on hip imaging as well as the symptoms. Bone remodelling changes reduce the fit between the femoral head and socket.

Can both hips be affected?

Yes, although most dogs have only one affected hip. Bilateral damage was found in 5 dogs in a study of 43. The examination therefore compares both hindlegs and the structure of both hips. Damage to both hips complicates rehabilitation as well as movement.

Can painkillers cure it without surgery?

Restricted exercise and a non-steroidal anti-inflammatory drug may be tried in mild early disease. However, fewer than 25% of conservatively treated dogs respond completely. Surgery is the usual treatment for a collapsed, arthritic hip. The damaged femoral head and neck are removed.

How can my dog walk without the femoral head?

A cushioning fibrous false joint develops between the femur and hip socket. Muscles support the limb. Rehabilitation helps restore muscle strength and leg use. Most dogs regain good function after treatment. However, the operated limb may remain slightly shorter than before.

When should my dog use the leg after surgery?

Controlled leg use is encouraged early, according to the vet's rehabilitation plan. Exercise is often increased after about a week. Typical recovery may take about 6 weeks. Long-standing muscle wasting may prolong this. Rough play is avoided for the first 30 days after surgery.