The steering knuckle is the pivot point of the steering system, which allows the wheels to turn. On cars with conventional suspension systems, the steering knuckle's spindle locates and supports the inner and outer wheel bearings.

The terms spindle and hub are sometimes used interchangeably with steering knuckle, but refer to different parts. The wheel and tire assembly attach to the hub or spindle of the knuckle where the tire/wheel rotates while being held in a stable plane of motion by the knuckle/suspension assembly.

A broken steering knuckle is unsafe to drive on at all. It needs immediate replacement. With the right tools and a comprehensive tutorial you should be able to replace it in a matter of two or three hours.