Robotic Knee Replacement

Robotic knee replacement is more precisely called robot-assisted total knee replacement: the surgeon performs the operation and a robotic arm, guided by a CT-based plan, helps place each bone cut within millimetres and degrees. It improves alignment and reduces soft tissue trauma and blood loss, but at ten years its functional results match conventional surgery, and it adds roughly 1,000 to 1,200 US dollars to the bill.

Dr. Rakesh Mahajan, Vice Chairman & HOD - Orthopedics, BLK-Max Super Speciality Hospital, New Delhi, India, uses a robotic system in his own practice and is notably candid about its limits. His account of the technology is neither promotional nor dismissive. Robotics, in his view, solves a real problem in a defined group of knees, offers modest short-term advantages in the rest, and is spreading partly because of market forces. This guide sets out that view: what the robot actually does, which patients genuinely need it, what it costs, and where the technology is heading.

Two companion articles go deeper. One explains how robot-assisted knee replacement works and how it compares with conventional surgery, from the alignment problem that created the field to the trial evidence. The other covers recovery after knee replacement, infection prevention, implant lifespan and protecting the knees.

Robot-assisted, not robotic: who performs the surgery

The name matters. Dr. Mahajan insists on "robot-assisted total knee replacement" rather than "robotic knee replacement", because the robot does not perform the operation. The surgeon exposes the joint, makes the decisions and remains in control throughout; the robot assists, chiefly by executing a pre-planned bone cut at the intended angle and depth.

In practice, that assistance has three components:

1. Planning. A CT scan of the lower limb is converted into a three-dimensional digital model of the patient's knee, which maps the exact anatomy and sizes the implant before the operation.
2. Balancing. During surgery, the soft tissues are balanced virtually in both flexion and extension, and the plan is checked dynamically through the full range of motion.
3. Execution. A robotic arm with haptic feedback (a physical resistance that stops the cutting tool at the boundary of the plan) restricts each cut to the planned bone.

The full workflow, including how sensors are fixed to the femur and tibia and how the robot equalises the flexion and extension gaps, is described in the companion article on how robot-assisted knee replacement works.

Why robotics entered knee replacement

The case for robotics is a case about alignment. Studies of the first-generation implants used from the late 1980s attributed many failures to outliers: knees whose post-operative alignment fell outside the target range. A knee aligned more than about 3 degrees away from neutral wears faster and is prone to aseptic loosening, the gradual loosening of an implant without infection, which shortens its life. Manual instruments alone could not reliably keep every knee inside the target. Computer navigation was the first answer and went through three generations; robotic assistance is the latest, and it enhances the surgical procedure, implant alignment and soft tissue balancing.

Who needs robotic knee replacement?

Robotic assistance earns its place in three groups of knees: those with an old fracture, those with retained hardware and those with a significant valgus deformity. From the patient's side, every candidate for knee replacement is eligible for the robot-assisted technique. From the surgeon's side, Dr. Mahajan is clear that many patients do not need it, and that an honest surgeon will say so. He names the clear indications:

• An old fracture around the knee. A healed fracture at the distal end of the femur or the proximal end of the tibia that has left an angular deformity.
• Hardware in the bone. Plates and screws from earlier trauma surgery. Conventional surgery aligns the femoral cut using a rod passed inside the femur (intramedullary alignment), which retained hardware makes impossible.
• A significant valgus knee. A knock-kneed deformity, in which the lower leg angles outwards from the knee, of more than about 7, 10 or 12 degrees, which he describes as a definite indication.

Dr. Mahajan regards old fractures and retained hardware as "sure-shot" cases for robotic alignment. A knee with a small or moderate deformity, by contrast, can be done very well with conventional mechanical alignment, the standard technique that sets every knee to a neutral, straight limb axis. For a referring doctor, this is the practical filter: the robot earns its place where the anatomy defeats the conventional instruments.

Can a robotic knee operation be converted to open surgery?

In several specialties, a robotic or minimally invasive operation sometimes has to be converted to open surgery. Dr. Mahajan's answer for robotic knee replacement is no. Robot-assisted knee replacement is itself performed through a standard open incision, so there is no keyhole procedure to abandon. The only scenario he described is a failure of the machine itself, which he put at one in a million; in that event, the surgeon simply completes the operation with the conventional technique.

Does an experienced surgeon need a robot?

Asked whether a surgeon with decades of precise operating experience really needs robotics, Dr. Mahajan agreed with the premise. Some surgeons of his age and experience, he said, still prefer mechanical alignment. He was equally direct about why robotics is spreading regardless: certain things are market-driven, and over time market forces take over from conventional methods, as is happening in every field. In time, he suggested, robotics may become much stronger than conventional surgery.

This is a useful corrective for patients choosing between hospitals on the strength of a robot. The device improves the consistency of alignment, which matters most when the anatomy is distorted; it does not substitute for the judgement of the surgeon using it.

How much does robotic knee replacement cost?

Robot-assisted knee replacement adds roughly 1,000 to 1,200 US dollars over a conventional mechanically aligned replacement, in Dr. Mahajan's figure. He identified cost as one of the two main limitations of the technique: robots are expensive to install and expensive to maintain, and that cost reaches the patient.

For the base cost of the operation itself, see the cost of total knee replacement. The second limitation, a longer operating time while a surgeon climbs the learning curve, is covered in the companion article on how the technique compares.

Robotic knee replacement results: what the evidence says

Robotic knee replacement delivers real short-term advantages, but its ten-year results match conventional surgery. The short-term gains are less soft tissue damage, less blood loss, less early pain, faster early recovery, lower use of opioid painkillers and a shorter hospital stay. Initial patient satisfaction is also higher. Over the long term, implant survival and functional scores at ten years are similar to those of conventional techniques. Dr. Mahajan described a study in which each patient had one knee replaced robotically and the other conventionally; at five years, patients could no longer tell which knee was which.

His summary is measured. The ability to execute a pre-operative plan precisely produces better alignment, but randomised controlled trials confirming a long-term clinical advantage are still lacking. The detail behind each of these findings is in the comparison of robotic and conventional knee replacement.

Remote surgery and the future of robotic knee replacement

Remote robotic surgery is not yet part of knee replacement. Reports of surgery performed remotely by robot appear regularly in the news, but Dr. Mahajan was clear that telesurgery has not been tried in knee or hip replacement, because the necessary software is not usually available; it may come in the future, but it is not present today.

He sees three forces shaping the next phase:

• Smaller, portable robots. The first robots were expensive. Manufacturers are now introducing smaller and portable systems, and costs are falling.
• AI-generated alignment. He expects artificial intelligence to generate the alignment of the robotic arm in future.
• Market forces. Adoption is market-driven, and he expects that pressure to keep widening the use of robots.

What this means for patients and referring doctors

Dr. Mahajan's position translates into a simple set of principles for anyone weighing the operation:

• The decision to replace the knee comes first. Robotics is a way of performing a knee replacement, not a reason to have one.
• The robot matters most in distorted anatomy. Old fractures, retained hardware and marked valgus deformity are where it offers a clear technical advantage.
• For a typical arthritic knee, both techniques work. A small or moderate deformity can be corrected very well conventionally, with long-term results that match robotic surgery.
• Preparation matters as much as technique. Control of blood sugar, treatment of urinary infection and strong quadriceps muscles shape the outcome whichever method is used, as the guide to recovery and infection prevention explains.

The questions put to Dr. Mahajan during the session, including questions from a doctor in Tanzania, are collected in the Live Discussion for this masterclass. His earlier masterclasses take the same pragmatic approach to other joints: complex total hip arthroplasty and joint pain in the younger population. Other Jivo Masterclass series approach the arthritic knee from different angles: Dr. Ramkinkar Jha's guide to hip and knee replacement surgery covers implants and revision, and Dr. Rohit Lamba's article on knee arthritis causes and diagnosis covers the condition that leads to surgery. For the wider orthopaedic context, see the orthopaedics specialty hub.