Figure 1: Infected cemented hip, notice the lucent line around the cup
The rate of deep infection in total hip replacements is about 1-2% and can vary from surgeon to surgeon and hospital to hospital. The most common organisms are not MRSA but bacteria that are normally present on the skin and only cause a problem when in the wrong place. Infection will either occur early, often due to contamination at the time of surgery or later due to spread via the blood stream (haematogenous spread). Patients will usually complain of a deep seated pain. There may have been a history of wound infection at the time of surgery. Often, the patient will say that the joint "never felt right". Clinically there may be little to find but x-rays may show evidence of loosening and blood tests will be abnormal. The patient will have an abnormal bone scan due to the increased blood supply around the hip and a positive white cell scan indicating the bodys' attempt to eradicate the infection.
A joint aspiration is carried out in order to confirm the diagnosis of infection and to test which antibiotics it is sensitive to.
Once the diagnosis is made and the patient is optimised, then the revision is carried out over two stages. During the first, the old implants and cement are removed. Any infected tissue is also removed, leaving only healthy tissue behind. A temporary hip made out of antibiotic laden cement is inserted and the patient remains on intravenous then oral antibiotics for 4-6 weeks.
Once the tissues have healed and the blood tests have returned to normal, then the patient undergoes a second procedure where the spacer is removed and a new hip is inserted.
This type of surgery is called a 2 stage revision. It is possible to do a 1 stage revision but only if the organism is known and not too virulent, bone graft is not needed and a cemented hip is re-inserted. The success rate for 2 stage is 90-95% and that for 1 stage is slightly less at 85-90%.