Robotic Hip Replacement: How It Works and Why It Differs From Traditional Surgery

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What is robotic hip replacement?

Robotic hip replacement is a total hip replacement in which a robotic arm helps me carry out a surgical plan built from a CT scan of your own hip. The implants are the same proven parts used in a traditional hip replacement. What changes is how precisely they are placed.

In my practice at the Bone and Joint Institute of Tennessee in Franklin, I use the Mako® SmartRobotics™ system from Stryker® across more than 700 hip and knee replacements a year. I also serve as a consultant to Stryker on the platform, and I mention that up front so you know where I stand.

Here’s what I tell my patients: the robot does not replace my judgment or my hands. It gives me measurements I could only estimate before, and it holds my instruments to the plan.

How is robotic hip replacement different from traditional hip replacement?

The difference comes down to three things: how the surgery is planned, how the bone is prepared, and what the surgeon can measure during the operation. The incision, anesthesia, and implants are essentially the same either way.

Planning: a 3D model instead of a 2D X-ray

Traditional planning uses a flat X-ray with plastic templates laid over it. It works well most of the time, but an X-ray flattens a three-dimensional joint, and the magnification is never exact.

With robotic hip replacement, a CT scan is turned into a 3D model of your pelvis and thigh bone. On that model I choose implant sizes, set the socket angles, and see the expected leg length and offset (the sideways distance from pelvis to thigh bone, which affects your stride) before we enter the operating room.

During surgery: a boundary instead of freehand

Preparing the hip socket means using a rounded reamer to shape the bone so the new cup fits. Done freehand, it depends on the surgeon’s eye. The robotic arm turns the plan into a physical boundary: I can move the reamer freely inside the planned zone, but it will not let me go deeper or drift off angle.

Stryker calls this AccuStop™ haptic technology. I think of it as bumper rails: I still do the reaming, and the rails keep it where we planned.

Measurement: numbers instead of estimates

Before the final implants go in, the screen shows me socket angle, leg length change, and offset change in millimeters. In traditional surgery, those are judgment calls.

How is a robotic hip replacement done, step by step?

A robotic hip replacement follows five steps: a CT scan, a 3D surgical plan, registration of your bone in the operating room, robotic-guided socket preparation, and a final check of leg length and stability before closing.

Step 1: The CT scan

A few weeks before surgery, you have a painless CT scan of your pelvis and knees. That scan becomes the 3D model we plan on.

Step 2: The 3D plan

I review your model and set the plan: cup size, cup angle, stem size, and target leg length and offset. I compare the planned hip to your other hip so the two match. This happens before surgery day, not during it.

Step 3: Registration in the operating room

After the incision, I touch a series of points on your pelvis and thigh bone with a tracked probe. The system matches those points to your CT model. If the match is off by more than half a millimeter, it makes me repeat it.

I perform nearly all of my hip replacements through the anterior approach, which goes between muscles rather than through them. Combining that approach with the robot gives patients a muscle-sparing incision and a precisely placed implant.

Step 4: Preparing the socket and placing the implants

With the robotic arm guiding the reamer, I prepare the socket to the planned depth and angle; the screen turns green when the bone matches the plan. The cup is pressed in at that angle, then I prepare the thigh bone and place the stem and ball.

Step 5: The final check

Before closing, I move the hip through its range of motion while the system reports leg length, offset, and stability. If a number is off, I change the ball size or neck length and check again.

Does the robot perform the hip replacement?

No. The robot never makes a decision or moves on its own. I hold the instruments, I make every cut, and I can adjust the plan at any point. The robotic arm is a guide for my hands and a measuring tool for the result.

What are the proven benefits of robotic hip replacement?

The best-supported benefits of robotic hip replacement are more accurate socket placement, more consistent leg length and offset, lower dislocation rates, and less bone removed. These come from published comparisons of robotic and manual technique, listed at the end of this article.

• Accurate socket placement. In a matched-pair study, 100 percent of robotic cups landed in the classic safe zone, compared with 80 percent of manual cups. Cup angle is the biggest surgical factor in dislocation and wear.
• Leg length you can trust. In a series of 534 robotic anterior hip replacements, more than 95 percent finished with neutral leg length.
• Restored hip center. Robotic planning more reliably puts the new joint’s center of rotation where your original one was, so the hip feels natural.
• Less bone removed. Because the reamer stops at the planned depth, the cup can often be a size closer to your own ball size.
• Lower dislocation rates. Comparative studies report fewer dislocations after robotic hip replacement than after manual technique.

After more than twenty years and thousands of hip replacements, the biggest change I see is consistency: more cases land exactly where I planned.

Is recovery faster after robotic hip replacement?

Recovery after robotic hip replacement follows the same timeline as a well-done traditional hip replacement: walking the day of surgery, home the same day or the next, and daily activities within about three to six weeks. The robot does not speed up how tissue heals.

What shapes early recovery is the surgical approach. The anterior approach spares muscle, which is why many of my patients skip the old hip precautions. The robot helps later: a hip with matched leg length and a well-placed socket is less likely to limp or dislocate. Read more in my article on hip replacement restrictions.

Like any joint replacement, robotic hip replacement carries risks, including infection, blood clots, fracture, nerve irritation, and implant wear over many years. I review these with every patient, and I do not promise a specific outcome.

Who is a good candidate for robotic hip replacement in Middle Tennessee?

You may be a candidate for robotic hip replacement if you have hip arthritis, avascular necrosis, hip dysplasia, or post-injury arthritis that no longer responds to medication, injections, or physical therapy. The decision is the same as for any total hip replacement; the robot is a tool I add once we agree surgery is right.

I see patients from Franklin, Brentwood, Nashville, Columbia, Spring Hill, Murfreesboro, and across Middle Tennessee at the Bone and Joint Institute of Tennessee, 3000 Edward Curd Lane, Franklin, TN 37067. Learn more on our robotic joint replacement page or in our hip and knee FAQ.

If hip pain is limiting your life, schedule a consultation with Dr. Calendine or call (615) 791-2630. No referral is required. We will look at your X-rays together and decide whether robotic hip replacement is the right next step.

Disclosure: Dr. Calendine serves as a paid consultant to Stryker Corporation for the Mako robotic platform. The opinions in this article are his own. Mako, SmartRobotics, AccuStop, and Stryker are trademarks of Stryker Corporation; their mention does not imply sponsorship or endorsement.

Medical disclaimer: This article is for educational purposes only and is not a substitute for personal medical advice from a qualified orthopaedic surgeon. Individual results vary. Always discuss your specific condition, risks, and treatment options with your physician.

References

1. Domb BG, El Bitar YF, Sadik AY, Stake CE, Botser IB. Comparison of robotic-assisted and conventional acetabular cup placement in THA: a matched-pair controlled study. Clin Orthop Relat Res. 2014;472(1):329-336. doi:10.1007/s11999-013-3253-7
2. Perazzini P, Trevisan M, Sembenini P, et al. The Mako robotic arm-assisted total hip arthroplasty using direct anterior approach: surgical technique, skills and pitfalls. Acta Biomed. 2020;91(Suppl 4):21-30. doi:10.23750/abm.v91i4-S.9659
3. Foissey C, Batailler C, Coulomb R, et al. Image-based robotic-assisted total hip arthroplasty through direct anterior approach allows a better orientation of the acetabular cup and a better restitution of the centre of rotation than a conventional procedure. Int Orthop. 2023;47(3):691-699. doi:10.1007/s00264-022-05624-6
4. Suarez-Ahedo C, Gui C, Martin TJ, Chandrasekaran S, Lodhia P, Domb BG. Robotic-arm assisted total hip arthroplasty results in smaller acetabular cup size in relation to the femoral head size: a matched-pair controlled study. Hip Int. 2017;27(2):147-152. doi:10.5301/hipint.5000418
5. Bukowski BR, Anderson P, Khlopas A, Chughtai M, Mont MA, Illgen RL. Improved functional outcomes with robotic compared with manual total hip arthroplasty. Surg Technol Int. 2016;29:303-308. PubMed
6. Caba M, Gains C, Nessler J, et al. Physical and mental demand during direct anterior total hip arthroplasty: comparison of robotic-assisted and conventional techniques. J Orthop. 2024;62:126-132. doi:10.1016/j.jor.2024.07.001