Below is listed the tests you may use in diagnosis, with a mnemonic to the right. Click on each item to see more information:
| Arthrocentesis | All |
| Swabs | Septic |
| CRP | Cartilage |
| FBC / U+E | Feels |
| Imaging | Incredibly |
| Blood Culture | Bad |
Septic arthritis requires an orthopaedic referral, specialist input is needed for the management of this urgent condition
Aspiration of the joint space, similar to bursitis by removing some of that pressure it may provide a bit of relief however due to the volume of infected material its unlikely to be curative. It also allows us to take swabs and cultures from the collected pus and by growing whatever was in the joint we can try and figure out what caused the condition or if there are any weird and wonderful things there that we might need to get infectious diseases involved with.
In younger patients its usually a good idea to do vaginal and Anorectal swabs for gonorrhoea (Given that they are sexually active) to rule out infection from that route. Obviously don't go an do an STI screen on every patient with septic arthritis however younger, sexually active patients presenting with septic arthritis should be at least offered an STI screen.
May or may not be raised, one of those easy tests you can bash out to add detail to the overall clinical feature. Also provides a good reference point, ie if CRP suddenly shoots up it may point to something more sinister going on such as secondary osteomyelitis.
More important for anaesthetists, if your patient does have septic arthritis they will need to go to theatre for a washout so building up the clinical picture of kidney function, liver function etc will help the anaesthetists and also help you figure out what treatments you can give post operatively.
Less important than the others and not really diagnostic, however if a patient says they've had really bad knee pain for 6 days and only now gone to ED it's a good idea as they likely have bony involvement in the infection too.
This is absolutely vital that you do this, a lot of the time it may come back negative however it again portrays more of a clinical picture. It is a lot easier to take a set of blood cultures from a well, hydrated patient in ED than a patient that's wildly septic and NEWS-ing 10 on the ward.