The longevity and ultimately the success of knee and hip replacement surgery depends on the surgeon’s ability to place the implants accurately and to restore soft-tissue balance. Traditionally this is achieved by the skill of the surgeon, who translates the information contained in the pre-operative plan into practice during surgery. CAS is a machine’s capability coupled with a human’s judgement to perform a task better than either machine or human could do alone.

What is CAS: The principle of CAS is straightforward. A similarity can be drawn between CAS to assist with surgery and GPS to assist with route planning. Both provide a means for getting to the next stage, ie analytical and process-based assistance to provide information that allows better decision-making. There is a GPRS system (similar to a GPRS satellite) that tracks the entire limb and bone via optical sensors that the surgeon places on the bone. The GPRS system sends the observed information to a Computer that can then accurately plan the surgical procedure. In CAS, a digital model is produced that serves as a map for each particular procedure. The image is then made available to surgeons to guide them through the operation. Dedicated surgical instruments can be incorporated into the map so that their position, attitude and progress can be controlled and monitored to within a fraction of a millimetre or degree. CAS benefits surgeons by allowing them to make informed decisions at the right time during surgery, enabling use of minimally invasive surgery (MIS) and ensuring accurate positioning of knee and hip replacement components.

	Assist with pre-operative planning
	Allow modification of the plan during the surgical procedure according to intra-operative findings
	Ensure surgical accuracy and consistency
	Shorten the time taken to perform procedures
	Decrease trauma to the patient, leading to quicker recovery
	Decrease long-term costs of treatment