Management Of Hip Dysplasia
The discussion below covering what Hip Dysplasia (HD) is and how it can be managed is summarised in this algorithm
What is Hip Dysplasia?
Good hips – ball well seated Dysplastic hips – not well seated
The hip joint is a “ball and socket” joint that allows a large range of movement. A capsule is attached to the rim of the socket and the neck of the ball and a ligament passes from the centre of the socket to the ball (a and b in Fig 1a). Although these help to stop the ball dislocating from the socket they are not very strong and in an adult dog it is the muscular support for the hip that keeps it stable through its whole range of movement (c and d in Fig 1a).
Fig 1a Fig 1b
Hip dysplasia is a laxity of the joint that may occur in puppies. As the dog takes weight on that leg the ball rides out of the socket (Fig 1b). They are not born with it but develop it in early life. The cause of hip dysplasia is multifactorial, that is to say no one thing controls whether a puppy will have it or not. There is certainly a genetic predisposition but environmental factors (e.g. nutrition and exercise levels) also play a role. Any breed can be affected but not all puppies that are affected by laxity show any clinical signs. If they do develop signs as puppies then these tend to appear as the dog’s bodyweight and activity levels increase.
How can we control Hip Dysplasia?
In the U.K., the dominant control scheme involves evaluation of radiographs (X-rays) taken of potential breeding dogs and bitches. The X-rays are scored by a panel of experts working on behalf of the Kennel Club and British Veterinary Association. The lower the score (maximum for each hip is 53) the better and the general rule of thumb is to breed from animals that have scores below that breed’s average. Although this is the best control method currently available in the U.K., it is flawed in that it measures something that is not related to the degree of laxity in a simple way. This is highlighted by the fact that one-third of puppies born to parents with good hip scores will themselves have poor scores, whilst one-third of puppies born to parents with poor scores will have reasonably good scores. Improving the way in which we are able to control hip dysplasia may come from gene typing but this is not yet possible and it is unlikely that a single gene will be responsible for the disease.
There are other schemes that have been developed around the world and the one in which there is considerable interest was developed by Professor Gail Smith in Pennsylvania. His system measures how far the ball can be distracted from the socket and, from this, a ratio is calculated known as the Distraction Index. The DI correlates strongly with the likelihood of a dog developing OA as measured on Xrays. It also shows a high heritability and so might be influenced strongly by an appropriate breeding programme. The scheme has yet to take off in the UK, partly because of difficulty in obtaining the necessary Xrays without contravening the Ionising Regulations in the UK, and partly because of the training required and quality control demanded by the people who run the PennHIP scheme.
One very important point in relation to X-ray scores is that they are for breeding purposes only, they cannot and should not be used as a predictor of whether any given dog will develop clinical signs relating to hip dysplasia, either as a puppy or as an adult (see below).
What signs can Hip Dysplasia cause?
The signs caused by hip dysplasia relate to pain from one or both hip joints :-
- Difficulty getting up or climbing stairs / into the car
- Stiffness after rest
- An awkward, almost inco-ordinate, hindlimb gait
- Lameness at exercise
- Tendency to “bunny hop” at faster paces
These signs are not specific for the hips and can also result from problems in, for example, both stifles (knees) or the lower back.
In the young (immature) dog these signs result from the damage caused by the laxity of the joints. As the dog moves the ball comes out of the socket, causing stretching of the capsule (1 in Fig 1b), damage to the cartilage over the rim of the socket and apposing area on the ball (2 in Fig 1b) and stretching of the muscles (3 in Fig 1b). All these may cause pain during exercise or inflammation which then produces stiffness after the dog has rested.
In the adult dog the signs are related to osteoarthritic changes in the joints which are a result of laxity as a puppy. The reasons why arthritic joints cause pain is complex and not fully understood but the resulting signs are as listed above.
What can be done to manage Hip Dysplasia in the Immature Dog?
In the immature dog any clinical signs present tend to be a direct result of joint laxity. In some cases this laxity can be eliminated using one of a number of “corrective” surgical techniques. The one used most often at this clinic involves moving the socket around the ball so as to “capture” it and prevent it slipping out when the dog takes weight through the hip. The procedure is illustrated in Fig 2.
It involves cutting the pelvis in three places (hence it is referred to as a triple pelvic osteotomy) which allows the segment of pelvis containing the socket to be mobilised and rotated over the top of the ball. Once the socket is in this position it is held in place with a special plate that is cast with an “angle of rotation” built into it. It is probable that all hip joints that are lax through hip dysplasia could be made stable by this procedure at some stage in their progression. Unfortunately, with time the socket begins to “fill in” with bone (see below) and rotating it will not capture the ball properly, and this may already be the situation by the time clinical signs are noted. Deciding whether a particular dog with clinical signs is a suitable candidate for this and this may already be the situation by the time clinical signs are noted. Deciding whether a particular dog with clinical signs is a suitable candidate for this surgery requires assessment under anaesthesia involving both manipulation and radiography (X-raying) of the hips.
The success rate for this surgical procedure is high with about 95% of cases recovering good, pain free limb function. However, the careful selection of patients and attention to surgical detail is paramount in achieving this level of success.
For puppies showing clinical signs where surgery is excluded either because the hip is “too far gone” for it to be successful or due to financial constraints, then the only option is to manage them conservatively. With time the lax hip will become stable naturally by virtue of:-
- Thickening of the joint capsule (i)
- Formation of new bone around the rim of the socket (ii)
- The socket becoming in-filled with new bone (iii)
- Increased strength of the supporting muscles (iv)
Due to this improvement in stability about 75% of owners will report that their pet has recovered an acceptable level of activity by 15-16 months of age. The cause of continued signs in those not considered satisfactory is the osteoarthritis that is created during the stabilisation process (i, ii and iii in Fig 3). If it were possible to “tip the balance” in favour of improved muscle strength stabilising the joint rather than osteoarthritic changes then that might lead to a higher success rate, better overall function and less chance of clinical arthritis being seen later in life. In recent years, Veterinary Physiotherapyhas become more available and this has an important role to play in the management of puppies with HD, particularly those treated non-surgically. A structured programme of exercise aimed at building up support for the hip joints so that they become functionally stable appears not only to have improved both the proportion of puppies that achieve satisfactory function by 12-15 months of age but also the quality of their mobility. In general, if surgery has been ruled out for whatever reason then this approach is to be recommended.
The use of medications to relieve pain should only be considered in puppies that are struggling to manage even very basic levels of exercise. They should not be used to make them feel or behave normally as this will serve to traumatise the unstable hip joints further.
Many compounds are now being marketed with claims to help dogs suffering with a whole host of problems. Most of these will do no harm but there is little evidence to suggest that they influence the clinical outcome in hip dysplasia.
What can be done to manage Hip Dysplasia in the Mature Dog?
In dogs with signs that persist beyond 15-16 months of age, or else don’t develop until a much later age, the problem being faced is one of pain from an arthritic hip rather than an unstable joint. Therefore, the approach to management is completely different. Details of the options of management can be found under “Osteoarthritis” within “Common Treatments” but a brief outline of the options is given here
Pain or symptom control may be achieved using conventional medications (anti-inflammatory drugs), physiotherapy, acupuncture, nutraceuticals, homeopathy. Obviously such strategies may require continual dosing with a given preparation or repeat course of treatment.
There are two surgical options and which is chosen is governed by the size of the dog and financial constraints. In the past, surgical management revolved around a procedure to remove the ball of the hip(excision arthroplasty) joint and leave nature to form a so-called “false joint” (though this should not be confused with a hip replacement). The results of doing this are generally good in smaller patients but less so in the larger breeds, although there has been some improvement in these results with the advent of post-operative physiotherapy. Total hip replacement is becoming a more frequent procedure in the dog and can result in a return to normal limb function. It involves removal of the socket, which is replaced by a plastic cup, and the ball, which is replaced by a cobalt chrome ball sitting on a stem that fits into the thigh bone.