Musculoskeletal Developmental Conditions
Note: Essential reading before completing this Master Class™ – Musculoskeletal Anatomy.
Hip dysplasia (HD) literally means bad growth. Bad growth of the hip joint results from a combination of genetic and nutritional factors acting on the hip of a growing large breed dog. The hip is a ball and socket joint; in dysplasia the ball becomes flattened and the socket becomes shallow. This creates an unstable joint so as the pet moves the ball wobbles within the socket. This wobbling motion stretches the soft supporting tissues of the joint causing pain. The ball wobbling within the socket causes early loss of the cartilage and subsequent arthritis; signs of this do not usually occur until after 3 or 4 years of age.
Hip Dysplasia is more common in large and giant breed dogs especially Labradors, Golden Retrievers, German Shepherds, Rottweilers and Mastiffs.
The radiograph on the left (1) shows normal hips and the picture on the right (2) shows a Labrador suffering from hip dysplasia. In the hip dysplasia radiograph can see two things happening: the head of the femur does not sit well into the acetabulum which cause the hip to wobble and the shape of the joint is no longer round and even which causes abnormal wear and tear within the joint as the dog moves.
The body responds to the laxity and wear and tear in the hip joint by trying to repair the damage to the cartilage and laying down more bone (osteophytes) on the edge of the joint to try to stabilize the joint. This inflammatory process causes pain and lameness. It is important to note that there is not a strong correlation between the severity of changes on x-ray and the degree of pain an animal is experiencing. The dog may be in severe pain and have quite good x-rays or have very bad x-rays and little pain.
The condition presents around three years of age but can arise from 18 months onwards. The symptoms are stiffness or soreness after rest, reluctance to exercise, bunny-hopping or other abnormal gaits ( e.g. legs moving together when running rather than swinging alternately), lameness, pain, reluctance to stand on rear legs, jump up, or climb stairs, subluxation or dislocation of the hip joint, or wasting away of the muscle mass in the hip area.
Hip dysplasia is preventable if diagnosed before skeletal maturity. All susceptible breeds should be radiographed at 12 weeks of age. If hip dysplasia is present then the growth plate at the pelvic symphisis can be fused preventing the problem from developing. This must be performed before 5 months of age but sooner is better. Because hip dysplasia is a developmental partly caused by the differing rates of muscle and bone development, feeding large breed dogs a restricted diet and not over exercising them can reduce the severity of hip dysplasia.
There are several different methods of evaluating radiographs for hip dysplasia. PennHIP (an acronym for “University of Pennsylvania Hip Improvement Program”) is the recommended method. The PennHIP method of diagnosis consists of three radiographs taken from different angles, which are then analyzed in order to make an assessment.
If hip dysplasia has not been prevented there are medical treatments and salvage surgery procedures that will reduce pain:
- NSAIDs such as Rimadyl, Metacam and Deramax are recommended to reduce inflammation and relieve pain. These drugs inhibit the action of an enzyme cyclooxygenase which triggers the inflammatory pathways in the body. The side-effects of these drugs are gastric irritation and kidney damage.
- Aqequan injection contains polysulfated glycosaminoglycan. This stimulates cartilage repair processes, binds to damage cartilage and suppresses the enzymes that eat away at the joints. It helps to keep joints lubricated, making movement easier and reduces pain and inflammation.
- Cosequin contains include glucosamine hydrochloride, chondroitin sulphate and manganese which all help to maintain healthy joint junction by promoting cartilage repair and lubricating the joint.
- Hill Prescription Diet™j/d contains high levels of EPA (Eicosapentanoic Acid), an omega-3 fatty acid found in high concentrations in fish oil. Research has shown that EPA can help maintain joint function. Enhanced levels of glucosamine and chondroitin provide the building blocks of healthy cartilage, and L-carnitine, which helps maintain optimum body weight.
- Weight management is an important aspect of minimizing hip dysplasia symptoms. Reducing excess weight can reduce arthritis symptoms as much as NSAIDs can. Hills Prescription Diet™ w/d or r/d should be recommended for overweight dogs.
- Exercise needs to be regular and moderate. 20 to 30 minutes three times a day is about right for most dogs. Dogs with hip dysplasia should never be exercised for so long they get tired or allowed to lie still for prolonged periods. Swimming is the ideal exercise for arthritic dogs.
- Surgery such as total hip replacement or femoral head excision can be carried out to prevent pain in refractory cases.
Patellar Luxation in Dogs and Cats
The patella sits in a grove at the distal end of the femur. The patellar ligament joints the femur to the tibia and keeps the leg in a straight line while it flexes and straightens. Luxation occurs when the patella moves outside the grove. This happens because the joint groove is too shallow, the joint capsule is lax or the tibial crest is pulling the patella off to one side because it is not in a straight line. The patella can luxate to the inside of the joint – medial or to the outside of the joint – lateral. Medial luxations are most common in small breeds of dogs and cats, lateral luxations are more common in large breeds of dogs. The condition can affect either or both hind legs.
Breeds showing a predisposition for medial patellar luxation include miniature and toy poodles, Maltese, Yorkshire terriers, Pomeranians, Pekingese, Chihuahuas and Boston Terriers. Large breed dogs are also affected and the Labrador retriever seems particularly predisposed. Patellar luxation is less common in cats than in dogs. Predisposed breeds include the Devon Rex and the Abyssinian.
Patellar luxation can be detected in puppies from 8 weeks of age although symptoms do not appear until later in life at around 4 to 6 months of age. The characteristic sign of patellar luxation is a hopping gait for a few steps then back to normal as the patella slips out of the joint and then back in. As the condition becomes more severe the lameness becomes more frequent.
Patellar luxation is graded in four stages:
|I Patella can be manually luxated but returns to the grove when released, lameness if present is very mild||Not usually required|
|II Patella can be manually luxated or can spontaneously luxate during flexion it returns to normal position easily during extension, lameness is intermittent||NSAIDs may be required if arthritis develops, surgery is required if condition is painful|
|III Patella is luxated most of the time but it can be manually reduced when the stifle is flexed, lameness is frequent||Surgery is always recommended|
|IV Patella is permanently luxated and there may be up to 90% rotation of the tibial plateau lameness is marked||Surgery is always recommended, tibial crest transposition will be required|
A range of surgical procedures are used to correct patellar luxation, they involve deepening the groove (sulcoplasty or trochleoplasty), tightening the joint capsule on the luxating side (joint capsule imbrication) or loosening the joint capsule or the non-luxating side (desmotomy) and moving the tibial crest to straighten the patellar ligament (tibial crest transposition). Usually a combination of techniques is used on the joint depending on the severity of the condition.