This is a childhood condition of the hip joint usually presenting at the age of between 4 and 8 years of age. It is 3 times commoner in boys than girls and affects about 1 in every 10,000 children. There are hotbeds of the disease in the UK where the incidence is higher than this and the disease more severe. South Wales is unfortunately one of these areas as well as Merseyside and Northern Ireland. In 10% of cases it can affect both hips at different times.
The cause of the disease is unknown, although there are a number of theories ranging from injury to blood disorders. There may be a genetic tendency to developing the disease, although this again is unproven.
The clinical symptoms of the disease are usually a painful limp which develops with no obvious cause. Some children present with just knee pain on the affected side as hip pain can sometimes be felt purely in the knee.
This is known as referred pain.
The cause of the painful limp is that the hip temporarily loses its blood supply and over a prolonged period, the femoral head (ball part of the hip) starts to soften and collapse (fig 1). This causes inflammation in the hip. With time it recovers its blood supply and heals, but all too frequently it does not grow back perfectly round and can become an ovoid shape. The worst possible long term consequence of the disease is therefore premature osteoarthritis of the hip as the hip becomes more like a roller-bearing joint than a normal ball and socket joint (fig 2).
Fig 1 Perthes Disease of right hip
Fig 2: Ovoid shape after healing of Perthes in left hip
As orthopaedic surgeons, although there can be nothing done to prevent the disease occurring, we can influence the final shape of the hip and therefore the risk of osteoarthritis.
Good prognostic factors for the disease are developing the disease at a young age (less than 5), male sex and not having the disease in the whole of the femoral head.
The disease itself has numerous stages and it can take up to 3 yrs from the 1st stage to the final healing (fig 3). It can therefore be a difficult time for the child and parents with regular visits to hospital, regular physiotherapy or swimming and sometimes surgery during this time.
No one knows for sure what the best treatment for the disease is and there is a lot of variation in what is recommended both nationally and internationally.
All surgeons believe that key to a successful outcome is to maintain as much movement in the hip as possible, whilst decreasing the forces through the hip, particularly during the collapse stage of the disease. When the head of the femur is soft and needs to harden or heal, it is comparable to a jelly, and to mould this jelly to as round a shape as possible, it needs to be moving in the centre of the socket, which is the perfect mould. It is recommended therefore that children avoid jumping type activities as well as contact type sports for the duration of the disease. Non weight bearing sports such as swimming and cycling are generally good to do.
Occasionally despite everyone’s best efforts the hip can get stiff and abduction of the hip (sideways movement from the body) can be reduced. It is then essential to try and restore this as early as possible. This is where surgery can be effective.
The type of surgery can range from minimal, where the child is examined under anaesthetic with some dye put into the hip to assess the true shape, to osteotomy, where the femur bone is cut below the head to tilt the head into the joint for it to repair (fig 4 and 5). Often also the surgeon may decide to use plasters to try and stretch the hip for a period of time (fig 6).
The type and extent of surgery is variable in my practice and is tailor made to the individual’s disease and prognostic factors. Obviously this requires detailed consultation with the child and parents as everyone is different. In my experience, I am finding that early surgery, particularly with the older child, is giving better results than conservative therapy. This is an area of ongoing research in my department.