Septic arthritis is the inflammation sequency that comes after a pathogenic agent enters the steril cavity of the joint.
It is a TRUE medical urgency.
We must understand the chain of events to bring the best treatment to each patient.
The profanation of the joint
The agent enters the joint space (usually bacteria, but it can be a virus, fungus or even tuberculosis).
The ways of contamination are
- Hematogenous, from blood stream (most frequent)
- Direct inoculation (knee infiltration, aspiration, surgery, etc)
- Contiguous, an adjacent infection.
The inflammation events
The host’s immune system activates every mechanism aviable to rapidly destroy the invader. Synovial cells use IL-6 and 1-β, C Reactive Protein comes then to opsonize bacteria (targets them), and complement comes to scene.
Later, polymorphonuclear leukocytes and macrophages migrate into the joint and phagocyte (eat) the bacteriae producing more inflammatory cytokines, TNF- α and IL-8. And lastly come the type T lymphocytes.
All that complex process, usually, results in the efficient destruction of bacteriae.
The destruction of the joint structure
Now that the causin organisms, or most of them, are dead… many enzymes (metalloproteinase/collagenase, peroxidase) remain in the joint space and start destroyin the cartilage.
If this is not stopped in less than a couple of days, the destruction is non-reversible. That is why, septic arthritis must be treated as soon as suspected, to avoid severy disfunction.
Diagnosis
Early diagnosis is mandatory to avoid permanent disfunction or even dead.
Risk factors
The very first step is to identify those patients who might be at risk of presenting with a setic arthritis, and it is very useful when we have limited access to specific laboratory tests.
- Age
- Diabetes
- Osteoarthritis
- Rheumatic diseases
- Autoimmune diseases
- Malnutrition
- Invasive procedures (aspiration, injection, surgery)
- Recent trauma
- Meds: steroids, chemotherapy.
- Intravenous drug abuse
- Cancer
- Skin damage
- Recent or actual infection in othe part of the body
Symptoms
Despite many symptoms that can or cannot be present, PAIN is certainly the cardinal symptom, the most important above all.
Other symtpoms include:
- Joint swelling: Even though the effusion of the knee is pretty obvious, in contrast, in the shoulder hip it is not so notorious.
- Function limitation: Range of motion is particularly affected because of intense pain.
- Hyperthermia: As a result of the inflammatory process, we percieve surrounding skin with a higher temperature.
- Hyperemia: we might observe a reddish skin due to vascular flow augmentation.
- Fever: not all patients present fever, so that the lack of it does not rule the diagnosis of septic arthritis out.
Lab Test
Without doubt there is a lot of information everywhere about lab tests for septic arthritis diagnosis.
Firstly I enlist the two principal tests:
C – Reactive Protein (serum): very useful. Basically its a blood substance that increases in few hours when inflammation is present. It is of special use to follow the patient recovery and test if the treatment is correct.
Leukocyte count (synovial): Synovial, not serum (blood) leukocyte count, by JOINT ASPIRATION, gets high. And here is whet discussion starts. Many texts theorize numbers of >20,000 />40,000/>60,000.
Insted the real diagnostic number is not a solid landmark. In order to stablish a reference point we must talk about sensitivity and specificity.
The synovial leukocytes discussion
Sensitivity is the chance a test has to detect all sick people.
Specificity is the chance a test has to detect all healthy people.
A lab test, ideally, must be 100% sensible and specific, this means, all labeled patients as healthy are actually healty, and all diagnosed with the disease are sick.
If we use the 50,000 synovial leukocyte limit, it means that we can have a sick patient with a lab test result of 38,000, labeled as healthy, and consequently would not recieve early treatment.
Contrarily, if we stablish a value as low as 2,000 it means we will diagnose sickness in lots of healthy people and give unnecessary and potentially dangerous treatments.
So the value is around 16,000 to 17,000 aprox. Why? Because many authors found this is the value where specificity and sensibility meet each other. And as an exception to this site intention, we do present bibliography for this specific value.
S F Li, C Cassidy, C Chang, S Gharib, J Torres. Diagnostic utility of laboratory tests in septic arthritis. Emerg Med J 2007;24:75-77.
So the important thing is, not to take any value as absolute. Take a decission based on clinical findings and lab tests all together. Even synovial fluid physical appaearence is of good use.
Remember: if you suspect of septic arthritis… perform a joint aspiration. Even if it is negative and a septic arthritis is highly suspected, perform an arthrotomy/arthroscopy and a joint lavage.
Other lab tests
Serum leukocytes: we can observe a normal value at the very start of symptoms. Otherwise they are usually high (12,000 or more).
Sedimentation rate: takes longer than CRP to be detected, but it becomes high after some time.
Procalcitonin: elevated in bacterial infections. For example, would not be high in gout arthritis, and then helps us to stablish diferential diagnosis.
Treatment – surgical
As we have seen, the cartilage is the main target of enzymes, so the treatment is to avoid that.
Surgeon must evacuate and irrigate the joint. No matter if tis by an open arthrtotomy or by arthroscopy. The purpose is to dilute and evacuate the inflammatory liquids away.
We use a penrose drain for 2 days to inspect the characteristics of joint fluid.
Antibiotics must cover broad spectrum since admissión, contrary to chronic osteomyelitis, there is no time to waste.
Samples of tissue and fluid go to lab, and we adjust the treatment when results are aviable. Although, almost half of the time cultures are negative with no bacteria isolation and empirical antibiotics should be used.
***When the surgeon observes white rice-like material, he should rule out tuberculosis.
Treatment – Medical
Short steroid doses improve prognosis. We use 3 dexametasone doses, each one every 12 hours.
In non-risk patients for bad-bugs (methicilin resistant S. aureus or E. coli ESBL, for example), a first or second generation cephalosporin (cephalothin) + an aminoglycoside (gentamicin/amikacin) is a good option.
For risk patients Vancomicyn/amikacin stills a good combination. Clindamicyn is an alternative to vancomicyn when allergy is present.
Anyway, antibiotics should be adjusted as soon as culture results are aviable, as well as an antibiogram.
Quinolones: We have detected in a 10-year inside study, a resistance to quinolones in up to 70% of biopsies (different septic bone and joint diseases). So quinolones are only used when antibiogram strongly suggests it.
We use CPR as reference to discontinue antibiotics, which usually takes weeks. We also follow up kidney and liver function closely, as well as nutrition and other comorbidities as diabetes.
Weight bearing is allowed when CPR decreases.
Shoulder Septic Arthritis
Special attention to this. Since we won’t find severe movement limitation, shoulder has very wide range of motion in any direction. Pain is bearable until it is too late.
Shoulder septic arthritis is dangerous, patient might die. So, if your patient meets risk factors (old, ostearthritis, acute pain, CPR elevated, diabetic, etc) it is always a good idea to aspirate the joint.
We use the anterior approach as used for the anterior arthroscopic protal, to get a sample from gleno-humeral space, with a 14 or 16 gauge periphereal catheter.
Non resolving septic arthritis
If joint fluids comming from drain, are not red clear, but instead they are mucoid/darkbrown/fetid, or CPR does not decreases, patient might have a bigger undetected problem, like a deep abscess or a disecant infection.
Magnetic Resonance Imaging comes to big utility here.
If a second joint is compromised, a distant septic focus might be hidden, like endocarditis, urologic or gynecologic infections or even sistemeic tuberculosis.