Medical Surgery with FDA-Approved Haptics

The Barrett WAM™ arm

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Small titanium knee implants have been rapidly replacing more-traumatic total-knee replacements by limiting surgery to only the diseased part of the bone.  However, these surgeries require an array of complex implant shapes to cover the variety of disease patterns and bone geometries.  Pockets are created manually for implants with a high-speed hand-held Anspach burr cutter.  It is important to note that, while lacking the precision of a robot, the feel of the cutting progress gives the surgeon a wealth of intuitive information about the diseased bone that is not available from pre-operative X-rays.

In 1998, Barrett licensed several patents underlying the original WAM™ arm to MAKO Surgical, Inc. parent, Z-KAT, Inc., to improve knee-implant surgery.  In 2006, the United States Federal, Drug, and Food Administration (FDA) cleared MAKO/Z-KAT to use WAM™-based technologies that combine the best of a surgeon’s intuition and a robot’s precision through active haptics (touch sensing). 

The job of the WAM™ arm is to improve precision of the finished implant pockets while remaining transparent to the surgeon’s feel of the bone condition.  Matching pocket and implant geometries minimizes trauma, ensures secure implant retention, and optimizes resulting joint functionality. 

In the MAKO/Z-KAT Haptic Guidance System™ (HGS™) the hand-held cutting tool is fastened to the end of a WAM™ arm allowing the robot and the surgeon to share the tool as the surgeon guides it through the surgery.  Initially, the WAM merely applies its Zero-G function, in which the weight of the tool is electronically counterbalanced.  Removing the tool’s weight enhances fidelity of the surgeon’s feel. 

The WAM does nothing else unless the surgeon attempts to move the spinning-burr cutting head beyond an invisible, virtual barrier that exactly matches the selected implant shape at a precise location relative to the patient’s knee.  At that barrier the WAM projects a perpendicular virtual force field that the surgeon feels and, depending on the circumstances, chooses to avoid, use as a guide to slide along, or consciously override simply by shoving through it. Fiducials on the knee report small shifts in knee position, enabling software to update the position and orientation of the virtual barrier in realtime.

In the manual-only method a long incision is made to retract layers of skin, muscle, and tendons well off the knee area so that the surgeon may mark and guide the cut visually.  In the WAM™ assisted version, only a key-slot-sized incision is needed to allow the burr cutter tip to slip under the skin.  All position information is provided by the force field and screens showing realtime simulations of the progress.

The nature of this system enables training via simulated surgeries.  It also allows all aspects (force & positions) of the surgery to be saved for later feedback to the surgeon.

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The New Barrett WAM Arm.