Bone and joint infection is an extremely common emergency procedure in paediatric orthopaedics. An arthrotomy is a surgical exploration of a joint and is commonly needed to be performed for septic arthritis on an emergency basis. Although there is an increasing trend towards arthroscopic irrigation and washout, open arthrotomy is still an important tool for orthopaedic surgeons. It also has other therapeutic purposes, and these include: debridement/removal of loose bodies, ligament reconstruction, fracture fixation, disarticulation, joint replacement and tumour excision. We describe the most commonly used approaches to perform arthrotomy in the hip, knee, ankle, shoulder, elbow, wrist, hand and fingers. Orthopaedic surgeons must be aware of common pitfalls and neurovascular structures present when performing an arthrotomy of common joints. This article provides an illustrative overview to approach each joint and will be a quick-reference guide especially for junior orthopaedic surgeons.