Legg-Calve-Perthes disease, also called Legg-Perthes disease, Perthes disease or aseptic necrosis of the femoral head, happens when the blood supply to the ball of the hip joint is interrupted. Without blood, the bone of the femoral head dies. The dog keeps bearing weight on a femoral head that is no longer structurally sound, so it develops microfractures, collapses and fragments, and the hip joint becomes incongruent and arthritic.
Who Gets It
This is a disease of young, small-breed dogs, most often diagnosed between three and thirteen months of age with a peak around six to eight months. Chihuahuas, Bichons Frises, Poodles, Pomeranians and terriers are over-represented, and a hereditary component is well recognised, with a recessive pattern proposed in Manchester Terriers. Somewhere between one in eight and one in five cases involve both hips. Cats can be affected too, and trauma to the hip can produce a similar picture.
The underlying mechanism is well described even though the trigger is not. The first change is death of the bone in the proximal femoral growth area while the cartilage covering it stays alive, which is why the joint does not look inflamed. Continued weight-bearing then produces microfractures in the dead bone, collapse of the supporting layer below the cartilage, and damage to the growth plate. New blood vessels eventually grow back into the femoral head, but by then it is mechanically weakened and fragments under normal loads. The end result is a deformed femoral head, an incongruent joint and osteoarthritis of the hip.
Signs to Watch For
- Slowly worsening hind-limb lameness over weeks, with no obvious injury
- Reluctance to bear weight, or a hind leg that looks shorter
- Reduced hip range of motion and muscle wasting over the thigh
- Irritability or grumpiness that owners later link to joint pain
- Occasionally sudden severe lameness when a weakened femoral head collapses
In the earliest phase many dogs are not yet painful, because the dead bone itself has no nerve supply and the cartilage surface is still intact. That is why the lameness can be mistaken for a soft-tissue strain or a growing-pain phase, and why cases are often only recognised once the joint has already collapsed and become irregular. Owners sometimes describe a dog that no longer wants to jump onto the sofa, or one that has become short-tempered when the hindquarters are handled.
How It Is Diagnosed
Diagnosis rests on history, physical examination and radiographs. X-rays typically show a misshapen femoral head, a shortened or eroded femoral neck, and mottled areas of reduced bone density, sometimes described as a moth-eaten appearance. A flexed hip view helps show the abnormal shape. CT can be useful when the femoral head still looks relatively normal but destruction inside it is suspected. Because medial patellar luxation, hip dysplasia and growth-plate injuries of the femur can look similar, and can occur alongside this disease, the knee and hip are usually assessed together.
Treatment Direction
Conservative management, meaning anti-inflammatory pain relief plus restricted or non-weight-bearing activity such as swimming, helps only a minority of dogs, and many are diagnosed after the femoral head has already collapsed. The surgical treatment of choice is femoral head and neck ostectomy (FHO), in which the diseased femoral head and neck are removed and the body forms a fibrous false joint. Larger dogs may be candidates for total hip replacement instead.
Recovery is usually good. Most dogs are running and playing within months, though a small proportion have ongoing mild lameness and may need long-term anti-inflammatory medication. Physiotherapy started soon after surgery improves mobility. If a dog is not willing to bear weight within the first couple of weeks after surgery, passive range-of-motion exercises are often added, and if lameness appears in the opposite hind leg, the other hip is reassessed with X-rays. Because the condition is inherited, affected dogs should not be bred.
When to Call Your Vet
A young small-breed dog with a hind-leg limp that has been building for weeks deserves an examination and X-rays rather than a wait-and-see approach. Early diagnosis is the only chance to weigh options before the joint collapses.