Septic Arthritis an Overview

Acute septic arthritis affects all age groups.

It is caused by haematogenous spread of a bacterial organism, or by a penetrating injury. The joint is swollen and painful to move. Treatment is by arthrotomy and irrigation, appropriate antibiotic therapy, splints and physiotherapy.

SUMMARY

Septic arthritis is usually a monoarthritis. It is a febrile condition;
joints affected have painful motion and an effusion.
The most usual causative organism is Staphylococcus areus,
but the intracellular cocci such as pneumo or gonococcus are common. In neonates and infants younger than 6 months, S aureus and gram-negative anaerobes comprise the majority of infections.
Treatment is by antibiotics and effective irrigation of the joint
by open arthrotomy. Postoperative physiotherapy and mobilisation of the joint
is necessary, while splinting prevents contractures.
Early treatment may prevent severe complications such as dislocation,
acvascular necrosis and late osteoarthritis.

Etiology: Most septic arthritis cases are caused by Staphylococcus aureus and streptococci. In neonates and infants younger than 6 months, S aureus and gram-negative anaerobes comprise the majority of infections. Haemophilus influenzae is commonly seen in neonates and children up to 2 years age (in South Africa, although in many developed lands the incidence due to this organism, has dramatically decreased due to widespread use of the vaccine). After 2 years S Aureus (as in the case of acute osteomyelitis)is the main causative organism. In the sexually active patient, Neisseria gonorhoeae is a common culprit.

DIAGNOSIS and MANAGEMENT PROTOCOL

The patient complains of spontaneous onset of pain in a joint. Episodes of penetrating trauma e.g. knife wound or thorn must be enquired about, as well as previous febrile illnesses, osteomyelitis and sexually transmitted diseases.
The patient is systemically ill. Superficial joints have an obvious effusion and are warm. The is painful on movement with pain on less than 5 degrees joint movement being characteristic. Children usually present with an acute febrile illness and a swollen painful joint. The exception is the immunologically suppressed patient, the elderly, and neonates, who may produce minimal clinical signs. In the neonate (especially when in a temperature controlled environment, such as an incubator) Pseudo paralysis or failure to spontaneously move a limb, is often the only clue to septic arthritis.

Special Investigations:

X-rays - may show widening of the joint space, indicating an effusion.

This X-ray shows an effusion
- widening of the right joint space

Haematology - ESR and white cell count raised
Blood culture - recommended in children who present with a septicaemia-

(80% Specificity)

Joint aspiration - (may be done as a diagnostic test, but is not an effective treatment modality. It only recommended for superficial joints,
where diagnosis is in doubt)

Aspiration of knee for suspected septic arthritis Aspiration of knee. Observe aseptic precautions - insert a needle into the joint by placing it under the patella, either medially, or laterally.

Appearance of synovial fluid in septic arthritis. Pus colored fluid (yellow or green), with WBC count of >100 000 cells /mm^3,
The other condition that gives high white cell counts is crystal synovitis
(do polarised microscopy, and check the serum uric acid for elevated levels, if gout is suspected)

Synoial glucose level: Low synovial glucose level (40 mg/dl or less than half the serum level) is suspicious of a pyogenic joint infection.

Prevention:

Explore and debride all deep wounds in the region of a joint.
Neglect of this principle, with mere suture of a penetrating wound near any joint will likely to result in septic arthritis. Wounds particularly at risk are those near the knee and the knuckles. (street fighter ,with tooth penetrating. MP joint).

Treatment:

The joint needs to be thoroughly irrigated and appropriate antibiotic therapy started. Aspiration of a superficial joint is acceptable for diagnostic purposes, but will not rid a joint of all pus. Deep joints such as the hip are difficult to aspirate and failure to obtain pus may simply be because of faulty technique.
An open arthrotomy is recommended in most cases. Arthroscopy is also an effective method of thoroughly rinsing out a joint.
It allows, usually inaccessible regions of the joint, to be reached for lavage. High volume irrigation is possible through the arthroscope, allowing inaccessible parts of the joint can be visualised. Repeated needle aspirations and irrigation, is another modality, but is not as effective as the above methods, and should be reserved for superficial joints, in patients with high anaesthetic risk. A single aspiration will not be effective in draining a joint of thick pus and the procedure needs to be repeated daily.
Preoperative preparation will include an intravenous drip and adequate rehydration. Blood transfusion may be needed, especially cases of Staphylococcal septicaemia ( haemolysin). The patient may have other concomitant infections such as bronchopneumonia, meningitis (meningococcus) or osteomyelitis. These will also have to be addressed as they affect the anaesthetic risk. Under full or regional anesthesia, the joint is opened via an appropriate incision that gives good exposure to the joint.
After incision of the capsule pus swabs are taken of the synovial fluid for microscopy and culture. The joint is irrigated via a syringe and all pus is washed out. If the infection seems chronic, or the symptoms atypical, a synovial biopsy is taken. (Histology, MC&S for possible Tuberculosis). In children symptoms and signs of acute osteomyelitis are very similar.
Because of the possibility of concomitant, or misdiagnosed acute septic osteomyelitis a drill hole in the adjacent metaphysis maybe warranted in patients with open physes, especially if the joint does not contain obvious pus.
The synovuim is sutured. If significant pus was found , the wound is left open for later secondary suture,
otherwise, use a suction drain and close the wound.

Postoperative Care:

Antibiotics are given intravenously until the temperature is normal, followed by oral antibiotics. Organisms responsible are Staphylococcus
(especially in children), The intracellular cocci
e.g. Meningococcus and Gonococcus, in sexually active patients are not infrequent.
In the immune compromised patient, atypical organisms, such as fungal may be encountered. Clinical judgment as to appropriate antibiotic therapy,
must be used in view of the above variety of causative organisms.
E.g. a child. will probably have a Staphylococcal infection and Cloxacillin and Erythromycin would give good cover before pus swab results could give better guidance.
Physiotherapy - most joints need motion rather than immobilisation.
If the cartilage seems still viable, mobilise the joint with a continuous passive motion machine, if available, or regular active and passive physiotherapy. To prevent contractures , apply traction or splints while the patient is not exercising. Appropriate for the hip would be skin traction and for the ankle a plaster back slab.

In advanced or neglected septic arthritis there may be little hope of later joint function. It is then appropriate to permanently immobilise the joint in a functional position, so that the joint can ankylose.
Here a spicka cast for a hip or full length cast for a knee may be applied.

Prevention and management of complications:
Advanced arthritis can result in many serious complications. If the effusion recurs repeated explorations and debridements of the joint might be necessary. Suspect tuberculosis if the arthritis

does not respond to this regime and take a biopsy.
E.g. Arthritis of a child's hip can result in:

Complications of Septic Arthritis Hip in a child

(a) Dislocation
Is often seen in the hip due to the overdistended capsule. Traumatic dislocation of a child's hip is rare, consider sepsis as one of the causes if a hip dislocation is seen in the young child.

(b) Osteomyelitis of the femur
(c) Avascular necrosis femur head
(d) Ankylosis
(e) Late osteoarthritis

Late result of Septic Arthritis The photo shows the late complications
of septic arthritis.
Note the chronic osteomyelitis of the femur shaft. The femoral neck has fractured and the femoral head is loose and avascular. There is widening of the joint space. The effect of the absent growth plate will be measured in later years as the femur progressively shortens relative to the normal side.

Postoperative Course

The ESR should return to normal within a few weeks.

A septic joint may need more than one trip to theater for irrigation.
If the arthritis does not clear up rapidly on the above treatment,
suspect tuberculosis. Take synovial specimens for histology in all acute
arthritides, which do not respond to antibiotics.
TB is one of the few causes of arthritis that can be diagnosed on light microscopy.

Septic Arthritis