Computer Navigation for Hip Replacement Surgery

Computer navigation for hip replacement surgery involves the use of a computer with an optical camera, and optical trackers on our surgical instruments to increase the accuracy of implant placement during hip replacement surgery.

Hip replacement surgery done with current mechanical instruments is a very successful procedure, however, still areas of concern.

When we perform hip replacement surgery, there is a risk that the ball of the joint can pop out or dislocate from the socket. One of the reasons that this can happen is due to malposition of the implants. We also know that wear of the implants is directly related to implant position. Over the past decade, several new materials have been used for hip replacements to minimize wear. Although these materials are promising in reducing wear when implanted correctly, they are also proving to be less forgiving to malposition.

Review of the literature shows that greater than 20% of hip replacements are put in with implants not in the ideal position. This number can be reduced to less than 5% with computerized guidance.

During hip replacement surgery the length of the leg can be altered. Most patients develop some shortening of their leg with loss of cartilage in the hip joint. This can be corrected with hip replacement surgery. Computerized guides have the potential to be more accurate in correcting leg length inequalities.

How does computer navigation work for hip replacement surgery?

A computer with a optical camera is set up in the operating room.

Using a probe with reflective arrays, points are taken from the patient’s pelvis in order to tell the computer where the patient’s pelvis is in a three dimensional coordinate system.

The same probe is used to identify the patient’s acetabulum (hip socket) for the computer during the surgical procedure. When we are ready to insert the acetabular component of the hip replacement, the handle that we use to put the component in place also can be seen by the computer. Because the computer knows the precise location of the pelvis and the component in 3 dimensional space, we get real time analysis of the position of the implant. This avoids any guess work in the operating room and increases accuracy.

Points are then taken on the femur or thigh bone in order to measure length of the leg. When putting the implant in the femur we can reassess these points in order to ensure that we are appropriately correcting the length of the leg.

Computer navigation technology still relies on the skill and accuracy of the surgeon using it. The accuracy in the operating room is dependant on the surgeon picking accurate points during the registration process.

Outcomes of hip replacement surgery depend on many factors including a hospital with a low infection rate, specialized anesthesia, appropriate soft tissue management, accurate implant positioning, good post operative pain control, and skilled rehabilitation and a motivated patient.

Dr. Mayman would be happy to discuss the details of computer navigated hip replacement surgery with you in more detail at the time of your office visit.

Computer Navigation for Knee Replacement Surgery

Computer navigation for knee replacement surgery has been a developing technology over the past decade.

The goals of computer navigated surgery are to use computerized guides to make knee replacement surgery more precise and reproducible.

Knee replacement surgery is a very effective procedure that alleviates pain and allows return to activity for hundreds of thousands of patients every year.  We have seen a great increase in the number of patients presenting for knee replacement surgery.  We have also seen younger patients presenting with severe arthritis of their knees.  Although the results of knee replacement surgery have been excellent when performed in the appropriate setting, long term survivorship of the implants has always been of concern. 

Over the years we have learned that the alignment of the implants is critically important for this long term survivorship.  In simple terms, tires on a car with malaligned wheels wear faster than tires on a car with well aligned wheels.  The same phenomenon occurs with knee replacements.  When loads go up in knee replacements due to patient weight or activity levels, these alignment issues can become more important.

Computer navigation systems are basically GPS systems for the operating room.  They consist of an optical camera attached to a computer along with optical trackers on the instruments used in the operating room.

Most modern systems are relatively small and unobtrusive in the operating room.

The procedure is done in the same fashion as a standard knee replacement.

Reflective arrays are placed on the femur and the tibia so that the camera and computer always knows the three dimensional position of the bones.

Once the arrays are set up on the knee, multiple points on the leg are registered to calibrate the computer.

At this time the computer now knows the starting alignment of the leg as well as the size of the bones.

We can then proceed with surgery to correct both the bony alignment and the tension in the appropriate ligaments.

The computer allows me to set the cutting guides to remove precise amounts of bone with accuracy that is more reproducible than standard mechanical guides.

The system that I am now using utilizes a robotic cutting block for the femoral cuts.  The computer is set up to make cuts for the appropriate size implant with accurate three dimensional alignment.  This is done in real time on the computer with the surgeon controlling the computer with a hand and foot control.  The position of the robot can be adjusted in all three planes.

Trial implants are always used prior to putting in the final implants.  This allows us to check alignment and sizing. At this point, adjustments can be made if necessary.  The knee can be taken through a range of motion and alignment can be tested through this range of motion.

When performing knee replacement surgery we are attempting to make the alignment of the leg perfectly straight from the center of the hip, through the center of the knee and then to the center of the ankle.  We know from years of scientific data, that with modern day mechanical guides we get this right within 3 degrees approximately 80% of the time.

Twenty percent of knees done today with mechanical guides have errors of 4 degrees or more.  The majority of the literature looking at alignment using computerized guides show that we can improve this number to approximately 95%.

Computer navigation addresses one of many factors that go into obtaining an optimal result in knee replacement surgery.  This needs to be combined with appropriate soft tissue management, good post-operative pain management and rehabilitation in order to maximize the function and life span of knee replacements.