Septic arthritis is an infection of a joint, which if not treated promptly can lead to irreparable damage to the joint surfaces. This condition is mainly seen in children, sometimes after a trivial fall or injury. Under normal conditions, it is very unlikely for an infection to reach a joint. This is because of the joint capsule and synovium forming a barrier around it. However, children have a poorly developed joint capsule, which makes them prone to get joint infections. This is especially seen in children who have weak immunity or frequent blood transfusions (sickle cell anemia, thalassemia).
Why is Septic Arthritis an Emergency ?
Septic arthritis involves the interaction of the immune system with the infecting organism within the joint space. The infecting organisms release several toxins as a part of their life-cycle. The immune system also releases numerous toxins to penetrate and kill the infecting organism. The pus that is formed in this process contains dead organisms, dead immune system cells, and harmful toxins. These toxins cause injury to the articular cartilage covering the joint surfaces. If the pus remains in contact with the articular cartilage for more than 12 hours, it leads to permanent damage to the cartilage in the form of erosion or even scraping off of the cartilage in places. A once damaged cartilage does not regenerate, leading to lifelong arthritis. Hence, appropriate treatment should be started as soon as possible.
Diagnosis of Septic Arthritis
A child having septic arthritis has severe pain of the involved joint. The joint becomes red, swollen, and warm to feel. Fever, if present, is of the high grade type, and is present throughout the day. The joints commonly involved are the joints of the leg and so walking or even standing is unbearable for the child. On a hospital visit, the orthopedic surgeon should be consulted in the emergency section.
The following investigations are generally done for septic arthritis:
- Blood tests which include complete blood count (CBC), erythrocyte sedimentation rate (ESR), c-reactive protein titre (CRP). The CBC helps to know the severity of the infection as well as measures the way in which the immune system is responding to the infection. It also helps in conforming the diagnosis along with ESR and CRP, have to be repeated after a couple of days and then after a week.. The values of ESR and CRP are raised in an active infection. Their falling trend after starting the antibiotics tells us that the correct treatment has been given.
- X-rays of the involved part is done to rule out the presence of any fracture or bone tumor, which may give rise to similar symptoms. A routine chest x-ray is also done to look for an infective focus in the lungs, which is a commonly known to be the origin of the joint infection.
- Sonography of the joint reveals the presence of fluid (pus) within the joint.
- Joint aspiration with the fluid sent for a routine and microbiological examination to know the infecting organism. The joint aspiration has to be through in order to reduce the burden of infectious organisms over the immune system of the body. If the microbiological examination reveals an infective organism, it is cultured and tested with several antibiotics to know the sensitivity pattern. This helps in selecting the right drugs for the treatment. It may have to be repeated after a week to check the response to treatment or changes in the infecting organism.
Treatment of Septic Arthritis
The treatment begins in the emergency department of a hospital with urgent blood investigations, x-rays, and joint aspiration. The child is given injectable analgesics and antipyretics to allay the pain and fever till reports of the investigations become available.
As soon as the diagnosis of septic arthritis is established, based on the reports of the investigations, antibiotics are started to help kill the infective organisms. A small procedure consisting of surgically opening the joint space for the drainage of pus, can be done to further aid in getting rid of the toxins. This is called as arthrotomy.
In order to give rest to the involved joint, it has to be placed in a traction unit. A traction unit consists of a weight tied to the leg with a belt and hung over a pulley at the foot end of the bed. This can be highly discomforting and also a bit painful in the beginning, especially for children who naturally do not understand its significance. It can become necessary to convince the child in his own way about the need for the traction.
The mainstay of the treatment is the intravenous antibiotics which have to be given for a week. This is followed by gradual mobilization of the joint and oral antibiotics for 3 weeks. The completion of the course is very critical as the infectious organisms can persist and spread to the adjacent bones leading to more disastrous consequences. Bone infections are extremely difficult to heal and may persist for the lifetime. Follow up visits to the hospital are important as the joint as well as the adjacent bones are assessed for the presence of infection. If there are signs of a persistent infection, a course of higher antibiotics for a couple of weeks is necessary.
Children may resume their normal activities when all the signs of infection have subsided and the course of gradual mobilization and physical therapy is complete, which normally takes around 2-3 months.