Trauma with direct inoculation
Microbiology
"Clean trauma" - skin flora
Diabetes mellitus, bites - Polymicrobial (gram -, anerobes)
Puncture from plants - Fungal (sporotrichosis)
Hematogenous spread
Microbiology
Gonorrhea
Look for vesiculopustular skin lesion, polyarthralgia
Mycobacteria
Contiguous spread
Infectious tenosynovitis
Calcaneal bursitis
Calcific tendinitis
Septic bursitis
Olecranon bursitis 
Flexor tenosynovitis
Prepatellar bursitis 
Pes anserine bursitis