Hip Dysplasia (HD)

Hip Dysplasia (HD)

TABLE OF CONTENTS

What is Hip Dysplasia (HD)?

Hip dysplasia (HD) is essentially laxity of the ligaments of the hip (coxofemoral) joint, which is seen in many different breeds, with some breeds being much more prone to this condition than others.

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Signpost Hub 1: Hip Joint

There is insufficient soft tissue support for the joint which leads to secondary soft tissue and bony changes. The joint laxity appears to be primarily genetically determined but many environmental factors influence this disease process.

Canine HD is a growth disease and has a genetic trait as well as being influenced by environmental factors, so is multi-factorial in nature.

Canine skeleton.
Canine skeleton.

The hip joint consists of the femoral head of the femur and the os coxae of the pelvis. The hip joint is a synovial ball and socket joint.
The hip joint consists of the femoral head of the femur and the os coxae of the pelvis. The hip joint is a synovial ball and socket joint.

Breeds prone to HD

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HD mainly affects medium to large pure bred dogs.

Breed examples prone to HD include;

  • Bloodhound
  • Newfoundland
  • Chesapeake Bay Retriever
  • Sheltie
  • Old English Sheepdog
  • Pug
  • French Bulldog
  • Basset Hound

Pathogenesis

Puppies are born with normal hip joints, which will develop normally if the congruence between the femoral head of the femur and the acetabulum of the pelvis (os coxae) is not affected as the dog grows and matures.

In canine HD, joint laxity is considered to be the cause of the subsequent abnormal hip development which is seen clinically in young dogs of 4 - 10 months of age, correlating to the canine growth spurt around 6 - 9 months of age.

Predisposing factors that decrease the hip congruity may include;

  • Genetic link
  • Overfeeding is associated with HD, due to it's impact on growth rate and obesity
  • Over exercising resulting in additional forces through the hip during the growth period

With joint laxity there will be an abnormal concentration of forces between the femoral head and the dorsal cranial rim of the acetabulum.

At 2 - 3 months of age there is a rounding of the dorsal actebular labrum and wearing of the articular cartilage over the dorsal surface of the femoral head and the abnormal forces result in deformation of the femoral head and neck.

By 5 - 9 months there are microfractures of the dorsal labrum and osteophytes at the points of insertion of the joint capsule on the acetabulum and femoral neck.

By 12 months, the acetabulum and femoral head have remodelled significantly and the microfractures have mostly healed. The peri-articular soft tissues have thickened and restrict joint range of motion (ROM) The result is relative stable joint stability and a decrease in pain.

With age the cartilage erosions become more severe.

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Progressive structural changes at the hip include; joint laxity, subluxation, damage to articular cartilage, swelling, fraying / rupturing of the Teres ligament, shallow articular cavities, eburnation of sub chondral bone, remodelling of acetabulum rim and femoral head, peri-articular formation (osteophytes).

The key question is; when does this occur in the timeline, as this will determine the approach to treatment.

Clinical Signs

Onset of clinical signs are variable and most commonly diagnosed between 6 - 12 months of age and may include;

  • Pain
  • Stiffness on rising
  • Exercise intolerance
  • Difficulty getting up or lying down
  • Difficulty climbing stairs
  • Lameness
  • Pelvic limb gait abnormality ("bunny hopping" when running)
  • Muscle atrophy of hindlimb musculature

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There are 2 fairly distinct populations of affected dogs seen in clinic, juveniles less than 12 months old and older dogs who had HD and present with secondary OA.

HD is bilateral in the majority of dogs, however clinical signs may only be seen in one hip.

Diagnostic Tests

  • Radiography (x-rays); is an imaging technique using X-rays, gamma rays, or similar ionising radiation and non-ionising radiation to view the internal form of an object
  • Computed Tomography (CT); is a medical imaging procedure that uses computer-processed combinations of many X-ray measurements taken from different angles to produce cross-sectional images (virtual "slices") of specific areas of a scanned object
  • Magnetic Resonance Imaging (MRI); is a type of scan that uses strong magnetic fields and radio waves to produce detailed images of the inside of the body
  • Ortolani test; is performed whilst dog is heavily sedated or anaesthetised to assess the laxity in the hip joint

There is very little correlation between the radiographs and the pain the dog is experiencing. Radiographs are not a good indicator of clinical signs.

Management

Puppy's should reach their adult weight at around 15-18 months of age depending on the breed. The aim is to try to get the dog to this age with conservative therapy, however if it is not possible to manage the dogs joint pain, then they will become a surgical candidate.

Conservative (non-surgical)

Young dogs with HD should be encouraged to appropriately exercise to maintain and improve their hip musculature, therefore improving their hip stability.

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Clinical Tip: Reducing the forces through the hip joint is important, so limiting free running, jumping and using stairs while the dog is growing would be beneficial.

Important conservative treatments embracing a multimodal approach;

  • Physiotherapy
  • Hydrotherapy
  • Pain management
  • Exercise modification
  • Bodyweight control + monitoring
  • Nutritionally balanced diet

Intermediate goals of conservative treatment;

  • Manage / control PAIN
  • Minimise joint damage and promote repair
  • Minimise joint incongruency
  • Minimise formation of osteoarthritis (OA)
  • Promote fibrous and muscular strengthening
  • Optimise joint function and hind quarter stability

For each dog their SMART goal setting (short, mid + long term) will respond to their assessment findings and specific prioritised problem list. Every case is different!

Preventative measures

Minimising joint pain is the most important factor when it comes to the conservative management of canine hip dysplasia. These overlap with conservative treatment approaches and include;

  • Dietary management
  • Exercise management
  • Population screening

A hip score is a measure of evidence of hip dysplasia. Scores for each hip are added together to get an overall hip score for a dog. Scores range from 0 to 106, with the lower the score the better. The advice to breeders is to ideally breed only from dogs which score below the breed average.

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The Hip Dysplasia Scheme was established by BVA and the Kennel Club in 1965 to reduce the incidence and severity of the condition. HD can have serious effects on the health, behaviour and welfare of dogs. The scheme uses X-rays to screen for signs of abnormalities (irregular or poorly shaped hip joints) caused by hip dysplasia. X-rays are reviewed and scored by BVA-appointed expert veterinary surgeons.

Dog's must be at least one year old to have X-rays taken and scored, but there is no upper age limit.

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The most important aspect of conservative management is controlling joint pain with pharmaceuticals because without effective pain relief nothing else matters.

Surgical

Juvenile Pubic Symphysiodesis (JPS); is a procedure to induce premature fusion (electrical cauterisation) of part of the pelvis (pubis) to alter growth so the location of the femoral head within the acetabulum is improved.

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This surgery has to be performed on dogs less than 5 months of age and they need to have mild to moderate laxity confirmed by radiographic and manipulative tests.

Triple Pelvic Osteotomy (TPO); this is the surgical modification of the existing hip joint to improve the fit of the ball in the existing socket. Three cuts are created in the bones around the cup and the cut segment is rotated to a point that allows the best fit for the hip. The bone segments are fixed in their new position using a custom plate and screws. Bone healing takes 4 - 6 weeks.

Schematic drawing showing position of osteotomies for completion of a triple pelvic osteotomy (TPO) with ilial stabilisation using a bone plate and screws.
Schematic drawing showing position of osteotomies for completion of a triple pelvic osteotomy (TPO) with ilial stabilisation using a bone plate and screws.

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TPO is only effective in dogs that have hip laxity and no secondary remodelling of the bones or subsequent osteoarthritis (OA).

Total Hip Replacement (THR); THR involves surgically removing all of the diseased hip joint. The femoral head is replaced with a metal implant and the acetabulum is replaced with a plastic / metal implant. The implants can be attached to the bone by using bone cement or may have a porous coating into which the bone grows.

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Dogs with persistent joint pain may be suitable for a THR or Excision Arthroplasty.

Femoral Head + Neck Excision (FHNE); this is a salvage procedure which is usually only considered in cases where a THR cannot be performed. The femoral head and neck are completely removed allowing a "false joint" to form.

Pain is relieved as the bony contact between the femoral head and acetabulum has been removed, however the resulting "false joint" is typically limited in its function.

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Clinical Tip: For great outcomes following an FHNE, physiotherapy and hydrotherapy need to be administered from day 10 post operatively onwards to optimise the new fibrous joint function.

HD is the commonest canine orthopaedic condition and all dogs with HD develop secondary OA of the affected hip joint.

References

Alexander, J.W. The Pathogenesis of Canine Hip Dysplasia, Veterinary Clinics of North America: Small Animal Practice, 1992, 22 (3), pp. 503-511.

Flückiger, M. Scoring radiographs for canine hip dysplasia. European Journal of Companion Animal Practice, 2007 proceedings.

Kapatkin A.S. et al. Canine hip dysplasia: The disease and its diagnosis. Compendium on Continuing Education for the Practicing Veterinarian. 2002, 24 (7), pp. 526-538.

Krontveit, R.I. et al. Housing- and exercise-related risk factors associated with the development of hip dysplasia as determined by radiographic evaluation in a prospective cohort of Newfoundlands, Labrador Retrievers, Leonbergers, and Irish Wolfhounds in Norway. American Journal of Veterinary Research. 2012, 73 (6), pp. 838-846.

Madsen, J.S. The joint capsule and joint laxity in dogs with hip dysplasia. Journal of the American Veterinary Medical Association. 1997 210 (10), pp. 1463-1465.

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