Robots have been used in surgery since the late 1980s. Orthopaedic surgery began to incorporate robotic technology in 1992, with the introduction of ROBODOC, for the planning and performance of total hip replacement. The use of robotic systems has subsequently increased, with promising short-term radiological outcomes when compared with traditional orthopaedic procedures. Robotic systems can be classified into two categories: autonomous and haptic (or surgeon-guided). Passive surgery systems,

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... ich represent a third type of technology, have also been adopted recently by orthopaedic surgeons. While autonomous systems have fallen out of favour, tactile systems with technological improvements have become widely used. Specifically, the use of tactile and passive robotic systems in unicompartmental knee replacement (UKR) has addressed some of the historical mechanisms of failure of non-robotic UKR. These systems assist with increasing the accuracy of the alignment of the components and produce more consistent ligament balance. Short-term improvements in clinical and radiological outcomes have increased the popularity of robot-assisted UKR. Robot-assisted orthopaedic surgery has the potential for improving surgical outcomes. We discuss the different types of robotic systems available for use in orthopaedics and consider the indication, contraindications and limitations of these technologies. The term 'robot' is derived from the Polish word robota meaning forced labour, and describes a machine that carries out a variety of tasks automatically or with a minimum of external impulse, especially one that is programmable. 1 There are two main types of robotic surgery systems: haptic and autonomous. Haptic or tactile systems allow the surgeon to use or 'drive' the robot to perform the operation. This technology requires constant input by the surgeon for the procedure to proceed. In contrast, autonomous robotic systems require the surgeon to perform the approach and set up the machine, but once engaged, the robot completes the surgery without the surgeon's help. 2 The use of robotic technology has, in some cases, facilitated minimally invasive surgery, 2 which has gained popularity with some patients. In spinal surgery, robotics have been successfully used to increase the accuracy of placement of implants. 3 Furthermore, robotic technology can improve the radiological alignment of implants, 4 as predicted by the pre-operative plan. Haptic robotic systems The Robotic Arm Interactive Orthopedic System (RIO) (MAKO Surgical Corp., Fort Lauderdale, Florida) is an example of a commercially available, tactile robotic system that requires active participation of the surgeon to complete a unicompartmental knee replacement (UKR). It uses pre-operative CT scans to create a three-dimensional (3D) computerised model of the patient's knee. The surgeon uses this model pre-operatively to plan the sizing and placement of the components. Intra-operatively, the surgeon will reference the bony surfaces of the femur and tibia, allowing the pre-operative model to be 'merged' with the actual anatomy of the knee. After taking the knee through a range of movement, the flexion-extension gaps can be assessed and the operative plan finalised in terms of component placement, creating an exact cutting zone for the robot. The system's algorithm relies heavily on the pre-operative planning or templating process. During the resection of bone, the surgeon views the 3D model of the knee on a monitor while manipulating the burr. The robotic arm provides auditory as well as haptic feedback, limiting the force-controlled tip of the rotating burr to resect bone only within the confines of the pre-defined cutting zone. An additional safety feature automatically stops the burr if the surgeon goes outside the predetermined zone. This feature also engages if