Robot-assisted knee replacement: what are the benefits compared with conventional surgery?

The pain caused by advanced osteoarthritis of the knee does not always set in suddenly. It often develops gradually: at first, it makes long walks difficult; then it forces you to avoid stairs; and, over time, it can interfere with your rest, your independence and activities that were previously part of your daily life.

When conservative treatments no longer provide sufficient relief, a knee replacement may become an option for reducing pain and regaining mobility. It is at this point that many patients ask themselves a new question: what is the difference between a prosthesis implanted using conventional surgery and a robot-assisted procedure?

The main benefit of robotic assistance is that it enables the surgeon to take precise measurements during the operation, analyse how the joint behaves and check the position of the prosthesis in greater detail before completing the procedure.

The robot does not operate autonomously nor does it replace the specialist’s expertise. It is a tool that expands the information available to plan and carry out the surgery in a more personalised way.

As Dr Carlos Encinas Ullán, head of the Knee Unit at the Publio Cordón Memorial Hospital, explains:

“The robot’s main benefit is not that it operates for us, but that it allows us to gain a very precise understanding of the knee we are treating. During the operation, we can study its alignment, assess how the ligaments are responding and anticipate the effect each adjustment would have on the position of the prosthesis. The decision still rests with the surgeon, but we have more information to help us make it.”

Before we talk about the robot: when is a knee replacement indicated?

Knee osteoarthritis causes progressive deterioration of the cartilage that protects the joint surfaces. As it progresses, pain, stiffness, inflammation, loss of mobility and even progressive deformity of the limb may occur.

However, the presence of osteoarthritis on an X-ray does not necessarily mean that surgery is required.

Two people with seemingly similar X-ray findings may experience very different levels of pain and limitation. For this reason, the decision to operate must take into account the actual impact of the condition: how far the patient can walk, whether the pain also occurs at rest or during the night, which activities they have stopped doing, and to what extent they have lost their independence.

“We do not recommend a knee replacement simply because there is evidence of advanced osteoarthritis on an X-ray,” says Dr Encinas. “We need to understand how that knee affects the patient’s life: how far they can walk, which activities they have stopped doing, and whether conservative treatments still allow them to maintain an acceptable quality of life. Surgery makes sense when there is a clear link between the deterioration of the joint and significant functional limitation.”

Before considering a knee replacement, measures such as therapeutic exercise, physiotherapy, weight management where indicated, drug treatment or certain injections are usually assessed.

Surgery is considered when joint damage is severe, these alternatives are no longer sufficient, and the deterioration significantly impairs daily life.

The availability of advanced technology should not rush a procedure that is not yet indicated. First, it must be determined whether a prosthesis is the appropriate solution and whether the time is right to proceed. Only then does it make sense to decide which approach to planning will provide the greatest benefit to that patient.

Each knee presents different decisions

Although people usually talk about ‘replacing the knee’, a total knee replacement does not replace the entire joint.

During the operation, the damaged surfaces of the femur and tibia are prepared and the prosthetic components are fitted onto them. A piece of durable material is inserted between the two, facilitating smooth movement and enabling the restoration of stable motion.

But the outcome does not depend solely on the quality of the implant.

The surgeon must decide on its size, position and orientation. They also need to assess the tension in the ligaments that stabilise the joint when the knee is straightened and bent.

These decisions must be tailored to the individual, as not all knees have the same anatomy nor have they developed osteoarthritis in the same way. Leg alignment, the distribution of wear and tear, the shape of the bones, ligament stability and previous range of motion vary from person to person.

“Knee replacement surgery should not be seen as applying a one-size-fits-all approach to every knee,” explains Dr Encinas. “We work within very clearly defined safety parameters, but each patient has a different anatomy, deformity and ligament balance. Robotic assistance helps us to understand these specific characteristics and to decide what correction that joint actually needs.”

Tailoring the procedure does not mean abandoning the established principles of prosthetic surgery. It means applying them with more information about the specific patient and avoiding, where possible, unnecessary alterations to their anatomy.

How does the ROSA system assist during surgery?

The ROSA system — which stands for Robotic Orthopaedic Surgical Assistant — is a platform designed to assist the specialist during the implantation of a knee prosthesis.

At the start of the procedure, the equipment records various anatomical landmarks. Using these, the system generates a digital representation of the joint and provides information on the position of the femur, the tibia and the limb axis.

The surgeon can also move the knee to assess how the ligaments behave at different degrees of flexion. This provides information not only on the shape of the bones, but also on the stability of the joint.

Using this data, the surgeon can plan:

• The orientation of the prosthesis components.

• The amount of bone to be prepared.

• The correction of the leg’s alignment.

• The tension that the ligaments will retain.

• The balance of the knee when straightening and bending it.

One of the main benefits of this process is the ability to simulate modifications before making the bone cuts.

“We can make small virtual adjustments to the planned position of the prosthesis and see how they would affect the stability of the knee,” explains Dr Encinas. “For example, we can assess whether a difference of a few degrees in the orientation of a component improves the balance between the inner and outer sides of the joint. This ability to anticipate helps us choose the most appropriate option before making any cuts to the bone.”

Once the plan has been finalised, the system helps guide the instruments used to prepare the bone. The specialist retains control of the procedure and can modify the plan whenever they deem it necessary.

How does it differ from conventional surgery?

Conventional knee replacement surgery is a well-established technique that can deliver excellent results when the indication is correct and the procedure is carried out by an experienced team.

In this procedure, the specialist uses anatomical landmarks, mechanical guides and specific instruments to make the cuts and position the components.

Robot-assisted surgery does not replace these fundamentals. It adds digital measurements and a greater ability to check during the operation whether the plan is being accurately replicated.

Therefore, they should not be viewed as two completely opposing procedures. Robotic surgery builds on the knowledge and experience developed over decades in conventional arthroplasty.

Nor does the difference necessarily lie in the size of the incision or in the fact that a machine places the prosthesis on its own. It lies in the way the joint is assessed, the effect of each decision is anticipated, and the execution of the surgical plan is monitored.

What advantages can robotic assistance offer?

More personalised planning

The technology allows the anatomy of the knee and its behaviour during movement to be assessed. This can be particularly relevant where there is a pronounced deformity, uneven wear across different areas of the joint, or significant alterations in ligament tension.

The aim is not to fit every prosthesis in a completely different way, but to understand what correction that particular knee requires and to find a stable position within safe clinical parameters.

Greater precision in executing the plan

Robotic assistance allows surgeons to check whether the cuts and the position of the components match the plan. Small variations in orientation can alter the distribution of loads, the stability or the movement of the joint.

Having measurements available during the procedure helps the specialist to detect any potential deviations and correct them before the prosthesis is finally implanted.

More information on ligaments

The knee does not function solely through the relationship between its bones. Ligaments guide and stabilise movement.

The system allows the gap between the articular surfaces and the tension in the ligaments to be assessed as the knee is straightened and bent. With this information, the surgeon can adjust the planning to ensure the joint maintains the correct balance throughout the range of motion.

“The knee isn’t just bone,” explains Dr Encinas. “We can position the components correctly from a radiological point of view and yet still need to make a finer adjustment to ensure the ligaments maintain the right tension when the joint is straightened and bent. The system helps us to integrate these two dimensions: the position of the prosthesis and the behaviour of the tissues that stabilise it.”

Verification before completing the procedure

Once the joint has been prepared, the team can compare the result achieved with the planned procedure. This final check does not eliminate the complexity of the surgery, but it provides an additional layer of control and allows adjustments to be made before the operation is completed.

What has research shown so far?

The advantage that emerges most consistently in the scientific literature is greater precision in component positioning across all planes (coronal, sagittal and rotational); robotic surgery reduces the rates of deviation from the pre-planned alignment and position. However, the clinical-radiological paradox persists: the improvement in precision has not yet translated into demonstrated superiority in functional outcomes or revision rates at the available follow-up time points.

 A systematic review and meta-analysis of randomised clinical trials published in 2023 in *Acta Orthopaedica* analysed the outcomes of robot-assisted total knee replacement compared with conventional surgery. The researchers observed improvements in various radiological parameters and some favourable functional differences. However, they noted that several of these differences were small and did not always reach a level of clinical significance clearly perceptible to the patient.

Another meta-analysis of randomised clinical trials, published in 2024, found better results in terms of anatomical and mechanical alignment with robotic surgery, whilst clinical outcomes, function and complication rates were similar to those of conventional surgery.

These studies encompass various robotic platforms and are not limited to the ROSA system. Their findings help to understand the general trends in robotic surgery, but should not be attributed entirely to a single technology.

Specific evidence regarding ROSA is also growing. A systematic review published in 2024 concluded that the system demonstrated high precision in component positioning and reduced certain deviations from the planned procedure. Some of the included studies observed better functional outcomes during the first year, although no differences were found in the overall complication rate compared with conventional surgery. The authors also highlighted the need for larger studies and longer-term follow-ups.

“The evidence allows us to state with a fair degree of certainty that robotic systems improve the accuracy with which we carry out planning,” says Dr Encinas. “What we cannot yet say is that all patients will experience less pain, a faster recovery or a more durable prosthesis simply because a robot is used. We must clearly distinguish between what has already been proven and what still requires further monitoring.”

This distinction is essential. Greater technical precision is a significant advantage, but it should not be presented as a guarantee of a better outcome for everyone.

Is recovery faster?

Some studies have observed favourable differences during the early stages of recovery, but the results are not consistent. Recovery following prosthetic surgery depends on numerous factors: previous mobility and muscle strength, the degree of deformity, biological age, weight, associated medical conditions, pain management and active participation in rehabilitation.

Patients do not recover solely from the placement of the implant. They must also regain the function they may have lost during months or years of pain and inactivity.

For this reason, surgical precision must be integrated into a broader care process, which includes pre-operative preparation, anaesthetic assessment, pain management, early mobilisation, physiotherapy and post-operative follow-up.

Many patients begin walking with assistance within the first few hours or the following day. From then on, work is done to gradually regain range of motion, strength and confidence when walking.

Improvement continues over several months and is not always linear. Swelling, stiffness and fatigue may vary from one week to the next whilst the joint adapts.

Does a robot-assisted prosthesis last longer?

The positioning of the components and the balance of the knee are key factors in how well the implant functions. It is therefore reasonable to investigate whether more precise placement might improve its long-term performance. However, there is not yet sufficient data to confirm that prostheses implanted using current robotic systems last longer in all patients.

Longevity also depends on the type of implant, bone quality, weight, activity level, the stability achieved and the clinical outcome for each individual. At present, the main proven advantage is the precision of planning and its execution. Its potential impact on prosthesis survival will need to be confirmed by research involving longer-term follow-ups.

Do all patients need robotic assistance?

No. Robotics is a surgical tool, not a medical indication.

It can offer particular value in cases of knee deformities (severe varus or valgus), complex anatomy, asymmetric wear, previous knee surgery (osteotomies and osteosynthesis for fractures) or situations where it is important to replicate a highly individualised surgical plan.

However, not everyone with advanced osteoarthritis needs a total knee replacement. Depending on the location of the wear and tear, the patient’s age, the condition of the ligaments and their functional needs, a partial knee replacement, joint-preserving procedures or other treatment options may be considered.

“The role of a specialist unit is not to apply the same solution to all patients,” concludes Dr Encinas. “We must assess which structures can be preserved, whether there is an alternative to total joint replacement, and which technology offers a specific benefit in each case. Personalisation begins long before the patient enters the operating theatre.”

Technology realises its full potential within a specialised team

The robot is probably the most visible element of the procedure, but it is not the only factor determining its outcome. The indication, the surgeon’s experience, planning, ligament management, the prevention of complications and the rehabilitation programme remain essential.

The measurements provided by ROSA must be interpreted taking into account the patient’s anatomy, tissue condition and functional needs. This integration remains a medical responsibility.

Therefore, when considering robot-assisted prosthetics, it is not enough simply to ask which system will be used. It is also important to understand why the surgery is being recommended, what alternatives have been considered, what experience the team has, and how the recovery will be organised.

A more tailored approach to surgery, not an automated one

Robotic assistance represents an evolution in the way knee replacement surgery is planned and performed. Its main benefit is that it allows the specialist to gain a better understanding of the joint during the operation, to anticipate the effects of different decisions and to verify precisely whether the result matches the chosen strategy.

It does not turn the operation into an automated procedure, nor does it in itself guarantee a better recovery. Its value becomes apparent when technological precision is combined with appropriate clinical judgement, surgical expertise and comprehensive patient care.

The ultimate aim is not to operate using more technology, but to use it when it can help achieve a stable and functional knee, whilst respecting each person’s anatomy and their actual mobility needs.

The information in this article is provided for general awareness and does not replace an individualised medical assessment.