Hip Dysplasia

Introduction

Hip dysplasia is a developmental trait characterised by an instability of the hip joint.

The hip joint laxity is responsible for early clinical signs and joint changes. The abnormal motion of the hip stretches the fibrous joint capsule and ligament connecting the head of the femur to the pelvis, producing pain and lameness. The acetabulum is easily deformed by continual movement of the femoral head. Micro fractures of the acetabular bone may occur, causing further pain and lameness in the immature dog. The dog’s physiologic response to joint laxity is proliferative fibroplasia of the joint capsule and formation of osteophytes on the rim of the acetabulum and the femoral neck. This helps to stabilise the hip joint but results in the chronic signs of degenerative joint disease, which progresses over the lifetime of the dog.

It primarily affects large and giant breed dogs, but can also occur in smaller dogs and cats.

The causes of hip dysplasia are multifactorial, and include hereditary and environmental factors. Overnutrition during growth has been implicated, as well as mild repeated trauma causing synovial inflammation. Obesity increases the severity of clinical signs.

Clinical Signs

Lameness is the most common presenting sign for most cases.

Dogs may present between 5-10 months of age with gait abnormalities and a severe form of the disease. There may be pain, a reluctance to rise or jump, and a clunking sound when walking.

Chronic, mildly painful lameness is more common in older dogs, who might have difficult in rising after exercise or sleep.

There may be muscle atrophy of the pelvic limbs.

Signs are usually more severe if the patient is overweight.

There may be luxation of the femoral head due to ligament rupture, which will present as acute and painful lameness.

Diagnosis

History and clinical findings will be suggestive.

Evaluation of the lameness at a walk and trot is useful: affected dogs may carry their heads low to reduce the amount of weight carried on the hip, there will be a shortened swing phase and stance phase in the affected limb, or a bunny-hopping gait if both limbs are affected.

The Ortolani test should be performed with the dog under sedation.

1. Dog is placed in dorsal recumbency with both femurs vertical.
2. Axial pressure is put on the femurs and the femoral heads will subluxate if hip dysplasia is present.
3. The limbs are then abducted and a click or pop will be heard and felt as the femoral head returns to the acetabulum: the angle at which this occurs is the angle of reduction.
4. As the limbs are adducted, the femoral head may subluxate again: this is known as the angle of subluxation.

Radiography is essential, and the most common view is a ventro-dorsal view of the pelvis with the limbs extended.

There may be evidence of hip subluxation: shallow acetabulum, less than 50-60% of the femoral head inside the dorsal rim of the acetabulum.

Degenerative joint disease may also be evidence: osteophyte proliferation, thickened femoral neck, spurring, flattening of the femoral head, sclerosis of the subchondral bone.

The hip dysplasia can usually be scored radiographically by licenced technicians.

Treatment

Options are varied depending on the dog's age and degree of discomfort, physical and radiographic findings and the owner's wishes and finances.

Conservative and surgical options are available.

Most immature animals are best treated with conservative and medical management. 75% of dogs respond favourably to this option, and 25% require further treatment or surgery.

Conservative treatment involves exercise restriction and the use of NSAIDs for pain flare-ups. Neutraceuticals may be considered.

A surgical option for immature dogs with joint laxity but no osteoarthritis is: triple pelvic osteotomy. This involves osteotomies of the ilium, pubis and ischium in order to increase the capture of the femoral head in the acetabulum. This stabilises the hip joint and slows the progress of osteoarthritis.

Mature dogs with hip dysplasia who show no clinical signs do not need treatment. Radiographic signs do not always correlate with clinical severity. Weight loss and muscle development should be encouraged to support the hip as well as possible.

Occasional lameness can be treated with NSAIDs and rest.

If medical therapy fails to control the pain and lameness, surgery as a salvage procedure may be the only option. Two options exist:

Femoral Head and Neck Excision: most effective in small and medium-sized dogs

Total Hip Replacement: only possible in animals heavier than 15-20kg. Many complications may occur and the surgery must be performed in a specialist facility.

Results following surgery are good to excellent, but owners have to be fully committed to aftercare and physiotherapy.

Hip Dysplasia Learning Resources
Flashcards Test your knowledge using flashcard type questions	Small Animal Orthopaedics Q&A 08

References

Merck and Co (2008) Merck Veterinary Manual Merial

Pasquini, C. (1999) Tschauner's Guide to Small Animal Clinics Sudz Publishing

Slatter, D. (2002) Textbook of small animal surgery Elsevier Health Sciences

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