The robotic arm used in the MAKO system is based on one developed in the 1990s in MIT’s artificial intelligence lab. “It was one of the first robotic arms developed to work specifically with people,” says Rony Abovitz, chief technology officer at MAKO. Originally, MIT researchers had it throwing and catching baseballs. The arm is controlled by tension cables and low-friction bearings instead of gears. “This allows the arm to work in a humanlike way,” says Abovitz. The arm is very sensitive to force and torque applied by the surgeon, and it feels weightless.

There are two other robotic surgery systems in use in the United States today, both for soft-tissue surgeries. The da Vinci robot, made by Intuitive Surgical, of Sunnyvale, CA, is controlled by a surgeon at a distance. It’s designed for laparoscopic surgeries such as prostate removal. Another system, for placing catheters in the heart, is also operated from a remote console.

The MAKO system is unusual in that the surgery is performed collaboratively. “The surgeon’s hands are on the robot, moving the arm,” says Abovitz. Domenico Savatta, chief of minimally invasive and robotic adult urologic surgery at the Newark Beth Israel Medical Center, says that the MAKO system appears to offer “robotic assistance in a true sense” because it actually restricts the surgeon’s movements. Savatta uses the da Vinci system in the operating room, and he says that it doesn’t give the same level of feedback as the MAKO system. But the da Vinci robot isn’t as specialized as the MAKO system, which is currently only approved for partial knee-replacement surgeries.

As of the end of 2007, 181 procedures have been performed using the MAKO guidance system. The company has patients who’ve been monitored for up to 20 months after surgery, with good results.

Maurice Ferré, CEO and president of MAKO, says that the company does hope to expand the range of surgeries that can be performed with its guidance system, but it’s currently sticking with knees. Right now, MAKO’s system is approved for replacing only one of the three compartments of the knee joint. The company is currently developing systems for surgeries to replace two compartments at once.