Computer Assisted Surgery in Total Knee Replacement – Align to survive!

What do you know about Osteoarthritis?

One-tenth of the population over 55 years is affected with osteoarthritis of knee. Though it is a common problem in older people but a major concern of pain and disability. Apart from osteoarthritis, conditions like rheumatoid arthritis, seronegative arthritis, posttraumatic arthritis and malignant tumour conditions of the knee joint also cause severe morbidity to patients.

Currently, approximately 2% of the population of 55 years age and above are so disabled that they need TKR. This procedure increases the life expectancies and public expectations, thereby improving the quality of life and mobility in later years. The estimated prevalence of osteoarthritis in women is nearly twice as high in men. 

Why is Total Knee Replacement (TKR) necessary?

Most patients are able to manage their symptoms with medical treatment and conservative methods, despite that several patients are referred to joint replacement specialists for further management.

TKR is indicated for:

• Pain relief
• Functional improvement in severe knee joint degeneration
• Arthritis
• Stability of knee
• Adequate alignment of prosthesis components and limb
• Allow sufficient range of motion

When is it required?

Total knee replacement (TKR) is considered necessary when your knee is damaged beyond repair. Doctors can make this out by performing special knee x-rays. If your knees are damaged and it is restricting your movement, then you are the right candidate for TKR.

In TKR, the parameters that decide longevity are reproducible surgical technique and alignment of implants. Surgical technique is the most critical factor in deciding the success of TKR, among other factors like appropriate soft-tissue balance, accurate axial alignment whether viewed from front or sides ( i.e in both coronal and sagittal planes ), and symmetrical rectangles of flexion and extension gaps. 

Which technique is used?

Computer navigation is a technique which aids the surgeon during surgery to achieve perfect alignment.

Note: In this operation, the whole knee is not replaced but rather an artificial implant is fixed over the worn out ends of the bones. The knee specialists perform this surgery using the latest technique of computer navigation. It is a step by step operation. If one step goes wrong it affects the next and the next, and so on. With computer assistance, the surgeon can plan the steps of surgery on the computer generated model, before executing them on the patient. This implies that a surgeon can know what effect a particular surgery will have. If some action does not appear okay on the model knee, the surgeon has a choice to make changes. Also, with computer navigation, the surgeon can check the accuracy of each step before going on to the next. All these checks and balances require sophisticated computer equipment and time, but what comes out at the end is perfect fitting.

Conventionally, mechanical jigs were used for this surgery. The use of these jigs involved certain amount of judgment, so called “eye-balling” on the part of the surgeon. Ironically, sometimes even when the case is in best hands, the judgment can be incorrect in 30% of cases. The reason for this is that human anatomy is variable, and it is not always possible to predict the variation in surgical technique required to match a particular patient. In other words, a ‘cook book’ approach does not work all the time.

It is important to realize that conventional techniques in TKR surgery have resulted in high prosthesis survival rate lasting up to 15–20 years. As the CAS has survived its infancy, it is therefore important that functional and clinical outcomes be collected on a regular basis in order to elucidate the role of it.

Few Pros and Cons of CAS!

Navigation was first introduced experimentally in the 1980s and clinically in the 1990s, but has only entered mainstream orthopedics in the last 7 years. CAS is developing rapidly and undergoing drastic evolution. It is being used in orthopedics with a multiple applications, ranging from knee and hip arthroplasties to pedicle screw placement. The current optical systems are likely to be replaced by electromagnetic or other types of registration and tracking systems.

The Computer-assisted systems (CAS) are active (surgical robots) or passive i.e. systems that do not perform any part of the knee replacement surgery, but assist in the positioning of the surgical instruments.

There are several advantages of the CAS:

- Dynamic assessment of deformity at any angle of flexion with patella in situ as opposed to conventional TKR where tensioning devices can be used in zero and 90° only.

- Calculation of soft tissue tension to give a perfectly balanced knee.

- Accurate restoration of mechanical limb axis.

- Reduced blood loss.

- Decrease in incidence of fat embolism due to extra-medullary instrumentation.

- Accuracy of data on soft tissue tensions even in 1 mm and 1°. Surgeon is given control, feedback, ability to correct errors and documentation needed by CAS.

But there are some disadvantages:

• Prolonged operative time.
• Certain learning curves.
• Significant cost implication for purchase and maintenance of the system.
• Lack of adequate evidence of the long-term benefits of CAS over conventional surgery in terms of implant survivorship and patient benefits for TKA.

There has been renewed enthusiasm in the issue of alignment since the introduction of computer navigation. Computer assisted surgery in TKR is aimed at achieving alignment with a neutral mechanical axis. Advances will continue and our goal of achieving perfection and outlasting longevity still lie at the horizon.