The world's top medical technology companies are turning to robots to help with complex knee surgery, promising quicker procedures and better results in operations that has often left patients dissatisfied.
Demand for artificial replacement joints is growing fast, as baby boomers' knees and hips wear out, but for the past 15 years rival firms have failed to deliver a technological advance to gain them a significant market share.
Now US-based Stryker and Britain's Smith & Nephew, believe that is about to change, as robots give them an edge.
Robots should mean less trauma to patients and faster recovery, although they still need to prove themselves in definitive clinical studies, which will not report results for a couple of years.
Fares Haddad, a consultant surgeon at University College London Hospitals, is one of the first in Britain to use the new robots and he has been impressed. However, he agrees healthcare providers need decisive data to prove they are worth an investment that can be as much as US million for each robot.
"The main reason for using a robotic system is to improve precision and to be able to hit very accurately a target that varies from patient to patient," he said. "It is particularly useful in knees because they are more problematic (than hips) and there are a chunk of patients that aren't as satisfied as we would like with their knee replacement."
Satisfaction rates are only around 65 percent for knee operations, against 95 percent for hips, according to industry surveys. The rival types of robots vary in cost and sophistication, assisting surgeons with precision image guidance for bone cutting and the insertion of artificial joints.
Orthopedic companies hope to emulate the success of Intuitive Surgical, an early pioneer of robots in hospitals, which now has more than 4,000 of its da Vinci machines installed around the world for procedures including prostate removal, hernia repair and hysterectomies.
In addition to selling into big Western markets, they also want to expand robot use in India, China and other emerging markets, where owning a prestigious high-tech system can be a marketing advantage for private hospitals.
Stryker is leading the charge with its MAKO robotic arm, a platform it acquired for US.65 billion in 2013 and which has pioneered robot-assisted whole-knee operations by determining optimal positioning and then helping with bone cutting.
But it has competition from smaller rival Smith & Nephew, which last week launched a cheaper product called Navio for total knee replacements in the United States. The British group bought the company behind Navio for US5 million in 2016.
That has kicked off the battle in earnest, since both companies are now able to do total knee replacements, which represents the vast majority of knee procedures.