Hip dysplasia (HD) is an abnormality of one or both hip joints (dysplasia means “not well-formed”). With a healthy hip joint, the head of the thighbone and the bowl of the pelvis fit together precisely. This means that the cartilage of the head of the thighbone is in contact with the cartilage of the bowl of the pelvis over a large surface area. The development of the hips in young, growing cats is sometimes not quite normal, causing malformed joints.
HD is usually caused by a combination of hereditary predisposition and external factors.
It is a hereditary defect, which can be positively or negatively affected by external influences such as growth rate, body weight, exercise, muscle development, nutritional supplements, and nutrition. An animal that has no predisposition can get a deformed hip due to external factors. An animal that does have a predisposition can also be positively affected by external factors, resulting in less deformity. Because of the differences during growing up, animals with the same hereditary disposition can eventually develop different hips.
HD is mainly known from the dog world and usually occurs in dogs of large and medium-sized breeds. Still, other animals (or people) and even smaller breeds can also develop HD. HD is also regularly found in animals in the wild. So it is not necessarily a deviation, which is caused by wrong breeding policies. Two animals with good hips can still get offspring with HD, and out of two animals with a light form of HD can get HD free offspring. Despite years of extensive health programs in dog breeding, the number of dogs with HD is not strongly influenced.
With a well-formed hip joint, it consists of a head-turning in a bowl. The smooth, convex head of the thighbone rotates in a deep bowl of the pelvis. The head is held in place by a firm joint capsule and surrounding muscles. Dogs/cats that have had sufficient exercise while growing up will suffer less from hip dysplasia because the muscles and capsules are stronger. This keeps the head better in the bowl. Because the skull can rotate in the bowl, the animal can move forward. When turning, the head must fit well in the bowl. This strong connection of the head in the bowl is not only necessary for a proper function of the joint, but is also essential for the healthy development of the joint of young, still growing animals.
Hip joints can form as follows:
- The round head fits well into the deep bowl.
- A round head that fits moderately in a somewhat shallow bowl.
- A flat head with a poor connection in a shallow bowl.
- The head fits moderately in the shallow bowl, in addition to bone growth around the head and bowl.
- Various combinations of the shapes mentioned above are also possible.