Explain the Kocher prediction rule to a family with an irritable hip — OSCE

The parents of a five-year-old boy are in the emergency department after he woke with a fever of 39 degrees and refused to walk, holding his right leg still. The registrar suspects septic arthritis based on a high Kocher score and has arranged a hip ultrasound and orthopaedic review. The parents are frightened, they think the limp is from the fall he had at the playground yesterday, and they do not understand why their child needs a needle in his hip and possibly an operation. Counsel them.