Mini Bone-Attached Robot System | Sensor Based Planning Laboratory

Mini Bone-Attached Robotic System


Original Cad Model	Rapid Prototype	Functional Prototype

People:

Brad Lisien
Nathan Abraham
Alon Wolf
Howie Choset
Branislav Jaramaz
Anthony DiGioia III

Description:

A study based on the National Hospital Discharge Survey (1996-1999), indicates that there will be over 474,000 Total Knee Arthroplasty procedures performed in 2030. Current techniques for performing these procedures generally and unfortunately involve invasive surgery. By definition, performing any procedure less invasively results in less soft tissue disruption, with the positive effects of reduced pain, faster healing and recovery, and fewer complications. Correct alignment of a joint implant is critical for the joint to function properly and to minimize wear which ensures longevity of the implant.

This research seeks to develop a novel computer assisted and robotic tool that will enable less and minimally invasive surgical techniques for orthopaedic surgery while at the same time provide more precise bone shaping. The clinical focus will be on Joint Arthroplasty i.e., total knee and hip replacement procedures. The Miniature Bone Attached Robotic System (MBARS) is a miniature parallel robotic device that is attached to the operated bone and actively shapes it according to a patient specific pre-operative plan to fit an implant. As MBARS is rigidly attached to the operated bone, the two become a one rigid body eliminating the need to compute relative motions from individually tracked entities, which results in greater precision. After a one time registration of the robot.s location to the patient specific computer bone model, the robot actively mills the bone (just like a CNC machine) resulting in a precise bone surface to which the implant may be attached. Additionally, with the aid of a computer, more intricate designs that integrate more effectively with the anatomy can be implanted.

MBARS Non-Image Patellofemoral Methodology

The 6 degree of freedom parallel structure design of MBARS allows for the sensing of an arbitrary surface in addition to active positioning of a tool. This functionality enables the system to operate without the use of expensive, time consuming, and radiation intensive CAT scan surface models. The surgeon would pilot the robot equipped with a force sensor along the patellar tracking line on the femur. The robot would then automatically trace the surface of the bone with its force sensor to build a model of the articular surface. From a library of patellofemoral implants, the system would choose an appropriate implant and then optimally place it on the surface model of the bone. Once this location is determined, the system would plan a complete coverage path which would result in the shape of the implant being cut into the bone. The robot is then outfitted with a cutting tool and the cutting path is downloaded to the robot's onboard electronics which then guide the cutting tool through its planned trajectory.

The robot was designed to have all of the electronics necessary to control the robot on-board. There are six separate micro-controllers located in the base of the robot attached to the knee, one for each of the actuators. Each micro-controller is a small computer that controls the motion of one actuator to guide the robot along the planned path. Communication about the path to follow is handled over a small, 4-wire cable to a notebook computer thus there are only two, easily managed cables exiting the robot, one for communication and one for power.

It is important to note that the patellofemoral procedure is only an example of what the MBARS is capable of doing. We are also developing methodologies for other orthpaedic procedures such as uni-condylar implants and hip replacements.

Pictures and movies:


Front view of robot mounted to femur.	Top view	Bottom view


Close up of actuators	Resulting milled surface	Milled surface with mock-up implant


Motion control electronics in the base plate	Close-up movie of external contour (mpeg) small(727k) large(12.2M)	Pulled-back movie of external contour (mpeg) small(751k) large(11.6M)