I'm sure you've searched the internet already, but if not, this is a good up to date link :- http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001466/
I'm not a GP, as you know, but I doubt GPs have much experience of septic arthritis as it's not common.
It should be considered in any acutely inflamed joint, as it can indeed destroy it in a day or two.
Risk factors are pre-existing joint disease, especially rheumatoid arthritis, diabetes, immunosuppression, kidney disease, and joint replacements.
Urgent joint aspiration by needle
for microscopy and culture are the key investigation. Plain X Rays can appear normal. Blood culture can help for guiding antibiotic choice later.
A key question is - how did the bug get there ? Is there another focus of infection, like pneumonia ?
If in doubt, start " empirical " ( best guess ) antibiotics until the type of bug and sensitivity is known.
An orthopaedic specialist may be needed for arthroscopy ( examination of the joint and possible biopsy for microscopy ).
Splinting and hospitalization may be needed, and ( later ) physiotherapy.
As always I'm well aware that all this may be expensive. Septic arthritis - if that's the diagnosis - is a serious condition, but treatable.
