SEPTIC ARTHRITIS

This is an arthritis caused by pyogenic organisms. Typically it presents as an acute painful arthirits, but it may present as subacute or chronic arthritis.
Other terms often used to describe this condition are pyogenic arthritis, infective arthritis or suppurative arthritis

Aetiopathogenesis

It is more common in children and males are more susceptible. Other predisposing facots are poor hygiene, poor resistance, diabetes etc. Staph aureus is the commonest causative organism. Other organisms are streptococcus pneumococcus and gonococcus.
The organisms reach the joint by one of the following routes:

- Haematogenous: This is the commonest route. There may be a primary focus of infection in the form of pyoderma, throat infection, septicaemia.

- Secondary to nearby oseomyelitis: This is a particularly common route in joints with intra articular metaphysis eg the hip shoulder etc

- Penetrating wounds: the knee, being a superficial joint is often affected via this route

- Iatrogenic: This may occur following intra articular steroid injections in different arthritis and during femoral artery punctures for blood collection

-Umbilical cord sepsis: in infants can travel to joints

As the organism reaches the joint by one of the above routes, there begins in inflammatory response in the synovium resukting in the exudation of fluid within the joint. Joint cartilage is destroyed by inflammatory granulation tissue and lysosomal enzymes in the joint exudate. Outcome, varies from complete healing to total destruction of the joint. The latter may result in a complete loss of joint movement (ankylosis).

Diagnosis

Mainly clinical
Usually a child
Knee is the commonest joint affected limb
In its subacute form, the parents may notice that the child is not allowing anybody to touch the joint.  He may not be moving it properly. In the lower limbs a paindul limp may be the first thing to draw attention. It may be associated with low grade fever.

On examination: 

The child is generally severely toxic with high temperature and tachycardia. The affected joint is swollen and held in position of ease. Palpation reveals increased temperature, tenderness and effusion
There is severe limitation in the joint movements in all directions. Any attempts at either passive or active movements causes severe pain and muscle spasms.  In subacute forms, some amount of movement is possible.

Investigations

Radiological Examination:
Dx in early stage is crucial.
Xrays are usually normal
A careful look at the Xray may reveal increased joint space and a soft tissue shadow corresponding to the distended capsule due to the swelling of the joint. Ultrasound examination is useful in detecting collection in deep joints such as the hip and shoulder. If found, one could aspirate the fluid and send for culturing the organism responsible for infection

In the later stagem the joint space is narrowed. There may be irregularity of the joint margins. Occasionally there may be a subluxation or dislocation of the joint.

Blood shows neutrophilic leucocytosis.
ESR in markedly elevated. A blood culture may grow the causative organisms

Joint aspiration is the quickest and the best method of diagnosing septic arthritis. The fluid may show features of acute septic inflammation. Gram staining provides a clue to the type of organism, till one gets the culture type of organism till one gets the culture report.





Differential Diagnosis

Acute osteomyelitis
Acute lymphadenitis
Acute bursitis

- mimic an arthritis because in some of these conditions, the joint is kept in a deformed position. Also there may be pain and muscle with attempted movements, but these signs are basically becasue the body is trying to prevent any because the body is trying to prevent any motion in the vicinity of the inflamed part. Careful examination reveals that reasonably pain free movements are presents  at the joint, and the movements are limited in every direction. The swelling may also be localised to one side of the joint.


Other causes of acute arthritis:

An acute septic arthritis should also be differentiated from other causes of arthritis as discussed:

Rheumatic arthritis: commonly a migratory polyarthritis, but may present with only one joint affected. The subsequent fleeting character of the arthritis, high C reactive protein levels in the serum and joint aspiration helps n its diagnosis.

Haemophilia: A past history of a bleeding disorder especially in a boy with an acute painful joint, would suggest the diagnosis. Abnormal bleeding and clotting times are helpful for confirmation.

Tubercular arthritis: It may sometimes present in a rather acute form. A past or family history of tuberculosis may be present. Joint aspiration and AFB examination may be help in its diagnosis.

Treatment

Diagnose and treat asap
Confirm or rule out diagnosis by joint aspiration
Parenteral broad spectrum antibiotics.

A combination of Ceftriaxone and cloxacillin in appropriate dises is usually given. These are subsequently changed to specific antibiotics as per aspirate cultrue and sensitivity reports. The joint must be put to rest in a splint or in traction

Whenever pus is aspirated the joint should be opened up (arthrotomy), washed and closed with a suction drain. THe same can be now done arthroscopically, As the inflammation is brought under control general condition of the patient improves, fever and local signs of inflammation subside, the joint is then gradually mobilised. Antibiotics are continued for 6 weeks.

In late cases: with radiological destruction of the joint margins movement. In such cases after an arthrotomy  and extensivedebridement of the joint. It is immobilised in the position of optimum function, so that as the disease heals, ankylosis occurs in that position.

Complications

Deformity
Stiffness
Pathological dislocation: as the joint gets filled with inflammatory exudate, the supporting ligaments and joint capsule get stretched. Muscle spasm associated with the disease may result in pathological dislocation of the joint. Posterior dislocation of the hip and triple displacement of the knee occur.

Osteoarthritis: Even if septic arthritis has been treated rather early some permanent changes in the articular cartilage occur, and give ise to early osteoarthritis a few years later.