Crystal arthropathy is the most common cause of acute arthritis but clinicians should also be aware of the possibility of concomitant infection, according to new research.

A retrospective review of 172 patients with acute arthritis who underwent a joint aspiration (mostly of the knee) at the Westmead and Auburn Hospitals, found more than half (52%) had crystals including uric acid and calcium pyrophosphate dihydrate.

Predictive factors were older age, higher urate level and total mononuclears on synovial fluid.

About 14% of joint aspirations were positive for bacteria, mostly Staph aureus, and almost 19% of the patients who had blood cultures taken were positive. Almost 5% of joint aspirations were positive for both bacteria and crystals.

Predictive factors for bacteria were features of sepsis such as temperature, sweats and chills, along with restricted range of motion, elevated CRP and total leukocyte count in synovial fluid.

A majority of all patients received antibiotics (56%) with high proportion (43%) receiving them before their joint aspiration.

Dr Katrina Pavic, an advanced rheumatology trainee at Westmead Hospital, told the limbic early antibiotic use was reasonable for patients presenting to the ED with features of sepsis.

“But in those circumstances where a patient isn’t particularly unwell, when there is time available for us or the orthopedic surgeons to come and have a look or to do an aspiration, then it would be preferable to do that before commencing antibiotics.”

“Generally speaking, you wouldn’t rush in with antibiotics, you would try to isolate the problem first and foremost and then if necessary, treat for septic arthritis.”

She said it was worth being vigilant for the possibility that septic arthritis could arise even in patients who seem to have an alternative explanation for their symptoms.

“For example, in patients with a history of RA which flares up from time to time with multiple joints becoming active, if all of a sudden they develop just one acutely inflamed joint… then you shouldn’t just attribute that to their RA, but consider the possibility of septic arthritis.”

The study found a high proportion of patients with septic arthritis had previously undergone a joint surgical intervention.

“If someone comes into hospital with an acute joint issue on a background of previous joint replacement, there is a role to engage the orthopaedic surgeons as soon as possible,” Dr Pavic said.