The future of knee replacement: robots, custom guides and new surgical techniques

The problem technology is trying to solve

Knee replacement works well for most people. Implants routinely last 20 years or more. But a meaningful share of patients, often quoted at 10% to 20%, still have pain, stiffness or a knee that never feels natural.¹ Technology companies have pitched their tools as a fix for that group. The theory: if the implant is placed more exactly, the knee should feel better.

That theory is now being tested properly, in large randomized trials and national registries.

Robotic surgery: more precise, not yet better for patients

Robotic systems don't operate on their own. They help the surgeon plan the cuts from imaging or measurements taken during surgery, then guide or limit the saw so the bone is cut where the plan says.

RACER-Knee, published in The Lancet in August 2026, is the most rigorous test so far.¹ It randomized 339 patients at 10 UK hospitals to Mako robotic-arm surgery or conventional instruments. Patients didn't know which they got.

• The robot was more precise. On average, the final leg alignment landed 2.0 degrees from the plan with the robot and 2.8 degrees with conventional instruments.
• Patients didn't notice a difference. At 12 months, the main score for how "natural" the knee felt was 49.2 with the robot and 50.2 without. Pain, function, opioid use and time to discharge were also similar.
• The robot added about 10.5 minutes of operating time and roughly £950 per case. Serious complications were equal in both groups.

The RASKAL trial in Australia compared robotic surgery with computer navigation in 303 patients and found no significant difference in patient-reported outcomes.² Registry data point the same way. A 2026 BMJ study of UK registry data, including more than 22,000 robotic knee replacements, found no difference in revision risk at an average of about 2.5 years.³ An Australian registry analysis likewise found no revision benefit across the whole group.⁴

Two caveats matter. These are early results, and implants fail slowly, so a difference in long-term survival could still appear. RACER-Knee plans to follow patients for 10 years.¹ And the trials mostly tested one robot and one implant in skilled hands. A robot may help a less experienced or lower-volume surgeon more than it helps a specialist who already does this every day.

Adoption keeps climbing anyway. Zimmer Biomet estimates that about 80% of US orthopedic surgeons still don't use robotics, which is why every major company is racing to sell smaller, cheaper systems.¹¹ Stryker's US orthopedic technology sales, led by its Mako robot, grew about 18% in the third quarter of 2026.¹²

Patient-specific instrumentation: a quiet plateau

Patient-specific instrumentation (PSI) uses a CT or MRI scan taken before surgery to make plastic cutting guides that fit only your bone. The idea is to get robot-like planning without buying a robot.

The evidence has been consistent for years. A meta-analysis of randomized trials found PSI improved alignment by fractions of a degree, around 0.3 degrees on the main leg axis. It didn't reduce outliers in a clinically meaningful way or improve early patient-reported outcomes.⁵ A 2025 update found CT-based and MRI-based guides performed about the same.⁶ A 2026 review of partial knee replacement reached a similar conclusion: no better function with PSI.⁷

Where PSI still earns a place is in specific situations: unusual anatomy, hardware already in the bone, deformities that make standard rods hard to use, or a hospital that wants personalized planning without the cost of a robot. For a typical patient, it isn't a reason to choose one surgeon over another.

Alignment: the debate that may matter more than the tool

For decades the goal was a perfectly straight leg, called mechanical alignment. But many people's legs were never straight, even before arthritis. Newer approaches, called kinematic, restricted kinematic or functional alignment, place the implant closer to each person's natural anatomy and ligament tension.

This is where robots and planning software may finally prove useful: not by cutting more precisely in the old position, but by making a personalized plan practical.

• A randomized trial of 109 knees found that, after the initial bone cuts, 61% of kinematically aligned knees were balanced through the full range of motion, compared with 12% of mechanically aligned knees. The mechanically aligned knees needed more soft-tissue releases.⁹
• A double-blinded randomized trial of 100 robotic knee replacements, which won the Rand Award at the 2026 AAHKS meeting, found better scores on some patient-reported measures at 1 and 2 years with functional alignment.⁸
• But a pooled analysis of patient-level data from several trials found kinematic alignment using patient-specific guides produced outcomes similar to mechanical alignment overall, with a small edge in pain scores.¹⁰

If you want the details on each approach, our robotics and alignment page explains the options in plain language.

So the signal is promising but not settled. More trials are under way. My read: if any technology changes how patients feel, it will be through smarter choices about where to put the implant, not through another fraction of a degree of accuracy.

What else is coming

• Cementless implants that bone grows into are spreading fast. Zimmer Biomet says cementless designs make up almost 30% of its total knees.¹³ Smith+Nephew received FDA clearance for a cementless version of its new LANDMARK knee in 2026, designed to work with its CORI robot.¹⁴ Registry results for cementless knees have been mixed, so long-term data matter. See our implant designs page.
• Smart implants like Zimmer Biomet's Persona IQ contain sensors that record steps, walking speed and range of motion after surgery. A claims-based analysis presented at AAOS 2026 linked it to fewer revisions, but it couldn't show cause and effect.¹⁵ The company's own labeling says the data haven't been shown to provide a clinical benefit.¹⁶
• Smaller robots and AI planning are being built for surgery centers, where most healthy patients' knee replacements are heading. Zimmer Biomet has submitted the Monogram robot to the FDA and added automated alignment planning to its ROSA system.¹¹

What this means for you

A robot or a custom guide isn't a guarantee of a better result, and lacking one isn't a reason to worry. The tools that most reliably improve outcomes are less flashy: a surgeon who does a lot of knee replacements, a realistic plan for your recovery, good control of weight and blood sugar, and a physical therapy program you stick with.

Questions worth asking your surgeon:

1. Do you use a robot, navigation or patient-specific guides, and why for my knee?
2. What alignment approach do you use, and how do you balance the ligaments?
3. How many knee replacements do you do a year, and what are your complication rates?
4. Would a cemented or cementless implant fit my bone and age better?
5. Does the technology change my cost, surgery time or recovery?

This analysis reflects published studies and public company information as of the date above. It isn't medical advice, and it doesn't rank or recommend any company or product.

Sources

1. Parsons H, Metcalfe A, Griffin J, et al. Robotic-arm-assisted versus conventional total knee replacement (RACER-Knee): a pragmatic, multicentre, participant-masked and assessor-masked, superiority, randomised controlled trial. Lancet. 2026;408(10558):924-934. doi:10.1016/S0140-6736(26)00986-4. Summary: medicaldialogues.in
2. Robotic-assisted surgery and functional alignment in total knee arthroplasty: the RASKAL registry-nested 2 x 2 factorial randomized trial. Bone Joint J. 2026;108-B. boneandjoint.org.uk. Commentary: Meneghini M. J Orthop Exp Innov. 2026;7(1). doi:10.60118/001c.160810
3. Mohammad HR, Judge A, Griffin XL, Murray DW. Early national comparison of robotic versus conventional hip and knee replacements using National Joint Registry data: target trial emulation study. BMJ. 2026;394:e100709. Summary: medicaldialogues.in
4. Robotic TKA showed no revision benefit: Australian Orthopaedic Association National Joint Replacement Registry analysis. conexiant.com
5. Patient-specific instrumentation does not improve radiographic alignment or clinical outcomes after total knee arthroplasty: a meta-analysis. Acta Orthop. 2016. pmc.ncbi.nlm.nih.gov
6. Shao L, Wu X-D, Liu Y, et al. No difference between CT- and MRI-based patient-specific instrumentation for total knee arthroplasty: an updated systematic review and meta-analysis. Front Bioeng Biotechnol. 2025;13:1624600. doi:10.3389/fbioe.2025.1624600
7. Ruhle V, Rudran B, Leung B, et al. Functional outcomes of patient-specific instrumentation versus conventional instrumentation for unicompartmental knee replacement: a systematic review and meta-analysis. Knee. 2026;63:104608. doi:10.1016/j.knee.2026.104608
8. Fontalis A, Kayani B, Haddad FS, et al. Functionally aligned vs. mechanically aligned robotic TKA: a double-blinded randomized trial. Presented at the AAHKS Annual Meeting, November 2026. Coverage: consultant360.com
9. Barroso Rosa S, Ismailidis P, Doma K, et al. Influence of total knee arthroplasty alignment on soft-tissue balance and pivot patterns: a randomized controlled trial of kinematic versus mechanical alignment. J Arthroplasty. 2025;40(12):3155-3161. doi:10.1016/j.arth.2025.05.128
10. Woon JTK, Zeng ISL, Calliess T, et al. Outcome of kinematic alignment using patient-specific instrumentation versus mechanical alignment in TKA: a meta-analysis and subgroup analysis of randomised trials. 2025. ore.exeter.ac.uk
11. Orthopedic market midyear outlook. ORTHOWORLD. 2026. orthoworld.com; and Zimmer Biomet Q3 2026 earnings call coverage. stockstory.org
12. What explains Stryker posting $1.96 EPS alongside adjusted EPS of $3.52. Kalkine. October 2026. kalkine.ca
13. Zimmer Biomet third quarter call coverage. Ryan Orthopaedics. ryortho.com
14. Smith+Nephew Third Quarter 2026 Trading Update. November 4, 2026. investegate.co.uk
15. Zimmer Biomet shares smart knee data at AAOS. MedTech Dive, via Pulse. March 2026. pulse.bot
16. Zimmer Biomet to preview the next era of intelligent orthopedic surgery at AAHKS 2026 (product labeling statement). meddeviceguide.com