At a glance
- Planning: 3D model of your hip from a computed tomography scan (CT)
- Precision: the socket sits at the planned angle, usually deviating by only a few degrees
- Control: leg length and hip geometry are measured to the millimetre in the operating theatre
- Safety: the robotic arm works only within the planned boundaries
- Your surgeon operates: the robot guides, it does not operate on its own
- Muscle-sparing: the procedure is also possible through the front approach
What the robotic arm actually does
Measuring your hip completely before the operation
The CT produces a 3D model of your pelvis and thigh bone. On that model we determine:
- the size of the socket and the stem – before the operation rather than only during it
- the centre of rotation of your hip joint
- bone quality and bone thickness in the socket floor and along the socket rim
- the rotation (torsion) of the thigh bone, which differs from person to person
- the difference in leg length and the distance of the thigh bone from the pelvis (offset), which sets the tension of the hip muscles
This is how we decide before the operation where and at which angle the prosthesis should sit. The plan is matched to your anatomy, not to an average value.
Preparing the bone exactly to plan
When milling the socket, your surgeon guides the robotic arm by hand. The arm allows the bone to be worked on only at the planned depth and in the planned direction. If the milling cutter deviates, the arm brakes it. This way we remove only as much bone as necessary. Healthy bone is preserved – which matters should a revision ever become necessary.
Inserting the socket at the planned angle
While the socket is being tapped in, the robotic arm holds exactly the planned inclination and opening angle. This is precisely the moment when the socket can tilt unnoticed in the freehand technique. With the robotic arm we see the values on the screen throughout the whole process.
Checking leg length and hip geometry in real time
After the trial implants are inserted, the system measures leg length and offset to the millimetre. If anything deviates from the plan, we correct it immediately, before the final prosthesis is inserted.
Matching socket and stem to each other
The robotic arm measures the rotation in which the prosthetic stem actually sits in the thigh bone. We align the position of the socket to that value. Surgeons call this the combined anteversion. It largely determines how stable the joint is and how freely it can move without prosthetic parts striking each other.
Robotic arm or freehand – what is the difference?
In the classical operation by hand, experienced surgeons place the prosthesis using judgement, feel and X-ray control. In most cases this works very well. However, during the operation the surgeon sees only a section of the pelvis, and the patient's position on the table changes the perception of angles. That is why, even in very experienced hands, the socket lies outside the intended range in some patients.
| Robotic arm or freehand – what is the difference? | Freehand | With robotic arm |
|---|---|---|
| Planning | 2D X-ray | 3D model from CT |
| Implant size | determined during the operation | planned in advance |
| Socket angle | by judgement and experience | measured, usually deviating by only a few degrees |
| Socket within the target range | not in every patient | in studies almost always |
| Leg length | estimated and felt | measured to the millimetre |
| Bone preparation | by feel | within fixed boundaries |
Planning
- Freehand
- 2D X-ray
- With robotic arm
- 3D model from CT
Implant size
- Freehand
- determined during the operation
- With robotic arm
- planned in advance
Socket angle
- Freehand
- by judgement and experience
- With robotic arm
- measured, usually deviating by only a few degrees
Socket within the target range
- Freehand
- not in every patient
- With robotic arm
- in studies almost always
Leg length
- Freehand
- estimated and felt
- With robotic arm
- measured to the millimetre
Bone preparation
- Freehand
- by feel
- With robotic arm
- within fixed boundaries
What advantages do the studies show?
The position of the socket is one of the most important factors for a stable and long-lasting hip joint. Large study reviews show:
- More accurate socket position: with the robotic arm the socket sits in the optimal angle range considerably more often than in the operation by hand. The deviation from the plan is usually only a few degrees.
- More accurate leg length: noticeable leg-length differences after the operation are less frequent.
- More natural hip geometry: the centre of rotation of the joint is restored more accurately.
- Fewer complications: in a review of 38 studies with more than 10,000 patients, complications occurred less often after robotically assisted surgery – in particular dislocation of the prosthesis.
- A good feeling in everyday life: patients “forget” their artificial joint somewhat more often in everyday life.
Honestly: where pain and mobility are concerned, the results are on average as good as after a prosthesis carefully placed by hand. Whether the higher precision also makes the prosthesis last longer cannot yet be said with certainty, because the follow-up periods are still too short. The greatest gain lies in precision and predictability – and these count most in difficult hips.
Where the robotic arm makes the difference
We are convinced users of robotics but use them selectively. We see the greatest benefit where the anatomy is unusual and experience alone reaches its limits.
Osteoarthritis with hip dysplasia
In a congenital malformation the socket is flat, often shifted upwards, and the bone is thin at the edges. Here it has to be decided to the millimetre where the new socket will find secure hold without breaching the socket floor. At the same time the centre of rotation should sit as close to its natural position as possible. On the 3D model we see in advance where enough bone is present. The robotic arm then places the socket exactly there. The often rotated thigh bone can be compensated in the same way.
After previous surgery on the pelvis or thigh bone
After a pelvic osteotomy (PAO), a corrective osteotomy of the thigh bone or a pelvic fracture, the usual orientation points the surgeon uses in the freehand technique are missing. The 3D model shows the actual shape and replaces that orientation.
Limited mobility of the spine
After a spinal fusion or with severe wear, the pelvis no longer tilts as usual when sitting down and standing up. This changes the effective position of the socket and clearly increases the risk of dislocation. In these cases we include X-rays taken standing and sitting in the planning and align the socket accordingly.
Other situations
- A clear leg-length difference before the operation
- A very deep socket (protrusio) or an unusual shape of the thigh bone
- Marked obesity, where orientation points are hard to identify during the operation
- Very young and active patients in whom as much of their own bone as possible should be preserved
Whether a robotic-arm-assisted operation makes sense for you is something we discuss in the consultation.
We also use the robotic arm in the knee – for the knee prosthesis, the partial replacement (inlay) and the replacement of the patellofemoral joint.
Are there disadvantages?
- An additional computed tomography scan is needed for the planning – with a low radiation dose.
- The operation takes somewhat longer than without a robotic arm.
- For revision operations on prostheses that are already in place, the robotic arm is usually not used.
- The general risks of a hip prosthesis remain: infection, thrombosis, bleeding after the operation, rarely a dislocation or a bone fracture. Overall, however, they occur less often.
After the operation
Aftercare is no different from a hip prosthesis without a robotic arm. You may bear weight on the leg immediately and get up with assistance on the day of the operation or the day after.
Frequently asked questions
+Does the robot operate on its own?
No. Your surgeon performs every step. The robotic arm makes sure that the planned path is followed.
+Is the prosthesis a different one?
No. We use established implants – only placed more precisely.
+How exact is “to the millimetre”?
In studies the socket angle and leg length usually deviate from the plan by only a few degrees or a few millimetres. Differences of that size cannot be reliably recognised with the naked eye during an operation.
+Does my health insurance pay for it?
Yes. The hip prosthesis is an insurance benefit, even when we place it with the robotic arm.