Spotlight on canine hip dysplasia
Hip dysplasia is a common problem for many dogs and owners, here we highlight the science and symptoms of dysplasia.
Now for the scientific bit; Canine hip dysplasia (CHD) is a polygenic and multifactorial developmental disorder characterised by coxofemoral (hip) joint laxity, degeneration, and osteoarthritis (OA).
There is evidence of genetic predisposition to hip dysplasia with more prevalence in the large breed dogs, however environmental and biomechanical factors such as: overfeeding and excessive exercise during developmental years, also play apart in the development of dysplasia (Lopez and Schachner, 2015).
Hip dysplasia is under constant research to define the exact processes that are thought to cause it, however irregular endochondral ossification and joint laxity are thought to be the two most prevalent. Where there is partial ossification during developmental months, then the acetabulum or femur can become distorted in shape which leads to poor congruency of the joint and increased shearing (Lopez and Schachner, 2015, and Madsen, Reimann, and Svalastoga, 1991).
The affected joint then tends to develop, articular cartilage degeneration and microfractures, subchondral sclerotic changes, inflammation of the synovium and joint capsule thickening and osteophytes, as well as ligament laxity. There has been a direct relationship proposed between the composition of the joint capsule collagen and mechanical properties (Lopez and Schachner, 2015) Abnormal collagen composition with a significantly higher type III:I collagen ratio, may be the cause for increased laxity of the joint capsule and this is linked to the breeds that have a high incidence of hip dysplasia (Madsen et al, 1994).
The clinical presentation of dogs with hip dysplasia is very variable, owners may report hindlimb lameness, which is worse with activity, difficulty jumping or rising from sitting (Fries and Remedios, 2012). Palpation of the hip joint and manipulation into flexion, extension and internal rotation can produce pain (Fitzpatrick et al, 2014 and Fries and Remedios, 1995). Atrophy of the hip muscles is also often present especially in older dogs.
There are two specific tests to examine the laxity of the hip joint, the Ortolani test and Barden’s test, however they can be negative, especially in an older dog where thickening of the joint capsule reduces the amount of laxity. These two tests alone are not sufficient to confirm a diagnosis of hip dysplasia (Lopez and Schachner, 2015).
Radiography is a vital part of diagnosing hip dysplasia and is the gold standard assessment to observe changes in joint morphology and laxity.