Septic arthritis overview
To say it very simply, Septic arthritis is a condition where any joint gets infection by bacteria. Infection of joint by virus is a separate entity called viral arthritis. Septic arthritis is specific for bacterial infection of joint only. The bacteria may be common pus forming bacteria or may be granule like lesion forming bacteria like tuberculosis. Septic arthritis caused by pus forming bacteria calls for emergency actions by a health team. Typically, this type joint infection develops rapidly and responds to treatment rapidly. However, the chronic infections like tubercular ones may not have significant symptoms but they cause many sufferings to the patient. Pus forming arthritis is sometimes termed as suppurative arthritis. In general, population the incidence of septic arthritis is about 2–10 per lack population. Those with autoimmune disease or prosthetic joint replacement have more chance of getting a joint infected. The incidence in them is about 30–70 per lack population. To prevent septic arthritis we must keep in mind the risk factors and consider appropriate prophylactic therapy for risk groups. To get the maximum benefit of treatment, we must start aggressive treatment promptly. We should consult with experts from orthopedic surgery, rheumatology, infectious diseases, and physical medicine and rehabilitation.
Routes of infection in septic arthritis
The bacteria may reach joint by these ways
- Bacteria may enter joint from infected blood stream.
- A penetrating wound, joint aspiration or corticosteroid injection of a joint, animal or human bites, nail puncture wounds or plant thorn injury, joint surgery, especially hip and knee arthroplasties, prosthesis may pave ways to joint for bacteria.
- Extension of bacteria from osteomyelitis, cellulites, or septic bursitis may spread to joint.
- Tuberculosis related arthritis is caused by infection of a joint with human or rarely bovine tubercle bacilli. Open pulmonary tuberculosis cases are the source of infection in most cases. It can affect all joints. However, the most often affected joints are inter vertebral joints of the thoracic or lumbar spine. The hip and knee are next in frequency. The organisms reach the joint through the blood stream from a focus elsewhere.
Causative organisms for septic arthritis
The commonest organisms for septic arthritis are:
- Staphylococcus aureus
- Streptococcus pneumonia
- Β-Hemolytic streptococci (Lancefield groups A, G, and B)
- Neisseria gonorrhoeae (adult and sexually active adolescent)
- Enterobacteriaceae (age >60 or predisposing condition)
Other pathogens for septic arthritis
- Mycobacterium tuberculosis
- Neisseria meningitides
- Fungi (Sporothrix, dimorphic fungi, Cryptococcus)
- Borrelia burgdorferi
Factors that favor the Development of Septic Arthritis:
- Age greater than 80 years or less than 5 years
- Presence of a prosthetic material in joint
- Recent surgery in joint
- Instrumentation in joint like arthroscopy
- Skin infection
- Previous septic arthritis
- Recent intra articular injection
- Immunosuppressive condition like HIV or AIDS, Diabetes mellitus, End-stage renal disease patient getting dialysis, Advanced hepatic disease, Underlying malignancy, Hypogammaglobulinemia
- Intravenous drug abuse
- Hemophilia with or without AIDS
- Sickle cell disease
- Late complement-component deficiency (susceptible to Neisseria infections)
- Low socioeconomic status with high rate of comorbidities
- Indwelling central venous catheter
- Systemic bacterial infection (especially by Staphylococcus aureus)
Symptoms of septic arthritis
Most of the patients with bacterial septic arthritis present with fever. Fever may come with chills but it is unusual. Old patients may not present with fever. Septic arthritis in child usually presented with fever, malaise, loss of appetite, irritability and avoiding the use of affected limb. Acute bacterial arthritis most commonly affects one joint. In 5% to 8% of pediatric patients and in 10% to 19% of adult patients, septic arthritis may involve more than one joint. Moreover, this type of involvement is mostly found in non-gonococcus infection of joint. The pain and swelling of the joint is the most striking sign.
Patients with gonococcus related joint disease usually present with any of two forms. In the first form, the patient has fever, shaking chills, skin rashes with fluid or pus inside, tendon and synovial inflammation, and joint pain. If we perform blood culture, it shows positive result. However, synovial fluid cultures are not usually positive. Gonococcus culture usually yield from genital, rectal, and pharyngeal sites. Inflammation of multiple tendons of the wrist, fingers, ankle, and toes is a unique feature of this form of gonococcus infection of joint. This feature distinguishes this form of septic arthritis from other forms of infectious arthritis.
In the second form, patients have visible pus in their joints. Most commonly the knee, wrist, or ankles are affected. Multiple joint can be infected simultaneously. Gonococcus culture from the synovial fluid yields positive results.
The classic presentation of septic arthritis other than gonococcus related arthritis is the quick onset of pain and swelling in a single joint. Non-gonococcus arthritis have predilection to large joints. In adults, the knee is the only joint that is affected in more than 50% of cases. Hip, ankle, and shoulder are on the list of affected joint in ascending order. In infants and small children, the hip is most common site for septic arthritis.
In case of tubercular arthritis, the symptoms are nearly same. But, the onset and course of arthritis is long standing. Children and young adults are most commonly affected by this type arthritis. There is often a history of contact with a patient with active pulmonary tuberculosis. An abscess or sinus is often apparent. Tuberculosis may be found elsewhere in the body.
On examination of joint, it shows redness, warmth and swelling. The swelling is partly from fluid effusion and partly from thickening of the synovial membrane. If the affected joint is superficial, the overlying skin is warm. The joint is usually reddened. Movements of the joint are reduced. Body prevents the movement due protective muscle spasm due to pain. In severe cases, the movements are almost totally prevented. Attempted or forced movement increases the pain.
Diagnosis of septic arthritis
Needle aspiration of synovial fluid and synovial fluid analysis is mandatory for all patients clinically suspected for inflammatory arthritis. Normal joints contain a small amount of synovial fluid. Normal synovial fluid is clear, highly viscous and has very few leucocytes (WBCs). The protein concentration is approximately one third that of plasma and the glucose concentration is similar to that of plasma. Infected synovial fluid is usually purulent with an elevated leukocyte count typically greater than 50,000 WBC/mm3 with neutrophil predominance. Low synovial fluid glucose (<40 mg/dl) and an elevated lactate dehydrogenase (LDH) suggest bacterial infection but they are not sufficiently sensitive or specific for the diagnosis.
The C-reactive protein and the erythrocyte sedimentation rate in blood are raised. Radiographs in the early stages show no change from normal. An ultrasound scan may show presence of fluid in the affected joint. Later, if the infection persists, there may be diffuse thinning of bone adjacent to the joint, reduction of cartilage space, and possibly destruction of bone. Radioisotope bone scanning shows increased uptake of the isotope in the region of the joint.
The earliest radiological change in tubercular arthritis is diffuse thinning of a wide area of bone adjacent to the joint. If we treat tuberculosis early, there may be no further change. But, if the infection progresses the cartilage space is narrowed and the underlying bone is eroded. As the disease heals, the bones harden up again and the bone density is restored to normal. Radioisotope bone scanning shows increased uptake of the isotope in the region of the joint.
Gram stain of aspirated synovial fluid is done routinely. However, this shows positive result in only about one-third of infected cases. Culture of a causative organism in synovial fluid is positive in 80–90 per cent of cases of septic arthritis. Therefore, culture of organism is more helpful to diagnose and treat septic arthritis. However, bacteria take time ranging from 2-3 days to grow and then we identify the organism in the laboratory. The number of white cells seen is not diagnostic of infected joint. Crystals may also be seen in infected joints like gout or pseudo-gout. Now, we have the diagnostic dilemma. If we take culture of organism as diagnostic, it will delay treatment and lead to complication. If we like to take microscopy and Gram staining as differentiating one, it will mislead us. As its sensitivity and specificity is very low. But, we cannot delay early treatment for the infection. So, until culture report obtained, the initial decision is based on doctor’s clinical assumption.
Septic arthritis treatment
There are only three steps for proper treatment of septic arthritis: prompt diagnosis, immediate institution of appropriate antibiotics, and adequate drainage of joint.
We must start treatment of septic arthritis quickly after the clinical suspicion. The joint must be drained adequately both for therapeutic and diagnostic purpose.
Antibiotics are usually given for 3–6 weeks (of which the first 2 weeks are commonly given intravenously). Until culture and sensitivity report is available, treatment should be begun with broad spectrum antibiotics. Third generation cephalosporin, quinolol, clindamycin or penicillins with gentamycin is a good choice. They usually have high anti-staphylococcal activity. For children Nafcillin alone or along with cefotaxime or Cefuroxime will be a good choice. For tubercular arthritis, anti-tubercular drug must be continued for 9 months. Other local managements are same as septic arthritis.
The joint must be given rest, usually in a plaster splint. Passive or active stretching is advised to prevent stiffness. If hip or knee joint is infected, sustained traction by weight relieves spasm and pain. The fluid is removed by aspiration or, if necessary, by incision. We should repeat aspiration, if fluid is formed again. If any bursa gets infected, it is best treated with repeated aspiration and antibiotics.