Technology in Total Joint Replacement Surgery

Within the field of orthopedic surgery, total hip and knee replacement surgeries remain some

of the most common and successful procedures performed. A tremendous amount of research

and development has occurred over decades in the effort to improve patient’s satisfaction and

clinical success. One aspect of that development has centered on ways to improve the accuracy

and precision of the surgical steps themselves. During the surgery, several bone preparation

steps need to be completed prior to placing the implants in the hip or knee. Those steps

require the surgeon to accurately identify anatomic landmarks in the patient and use those to

begin the process of replacing the joint. In addition, the surgeon must account for differences

from one patient to the next and adapt the plan to meet the unique characteristics of that

particular joint replacement. Today’s blog will focus on the development of technological

advancements that are designed to improve the accuracy and precision of carrying out those

steps in both total knee and total hip replacement surgery. More specifically, we will discuss

computer-assisted and robotic-assisted surgery below.

Total Knee Replacement

As discussed in last month’s blog, total knee replacement surgery has evolved considerably over

time. Traditionally, surgeons have used special cutting guides to assist with the alignment of

the implants during the procedure. While these can be used very accurately and precisely by

skilled surgeons in the majority of cases, studies have shown that patient anatomy, surgeon

error, and other factors can result in outlier cases where the implants do not get placed in the

exact orientation that the surgeon intended. These outliers have been the main target of new

technology aimed at reducing those cases. While this field continues to advance quite rapidly

and incorporate new types of systems, most systems fall into one of two categories, computer-

assisted surgery (aka navigation) or robotic-assisted surgery.

Computer-assisted Surgery

With this type of system, cutting guides are still used for making the bone cuts, but the surgeon

aligns them on the patient using computer assistance. Special devices are firmly placed in the

bone on the femur and tibia which communicate with the computer system and provide

reference points for alignment. These allow the surgeon to teach the computer about the

patient’s knee by either showing the computer where specific anatomic landmarks are located

or by drawing out the surface of the bones within the knee.

Once the computer knows the anatomy, shape, and alignment of the joint, the cutting guides

can be placed on the bones using the computer to verify their placement. After the guides are

placed, the remainder of the surgery is performed in the same way as with traditional manual

surgeries. However, the computer system can also be used to verify that the bone cuts are

accurate along the way, which provides the surgeon additional information and the ability to

make adjustments as needed.

Robotic-assisted Surgery

Taking the technological advancement one step further, robotic-assisted surgery not only uses

computerized systems to plan the surgery but also incorporates an additional layer of control

with a robotic arm. Many different companies have now developed robotic systems for use in

knee replacement and each have unique advantages and disadvantages. Some systems use

pre-operative images, such as a CT scan, to plan out the surgery and use that as a reference

during the procedure. The surgeon uses a tool to map out the knee during surgery, which then

allows the robot to know where the knee is in three-dimensional space and link that with the

CT scan. Other robotic systems are called “imageless” because no pre-operative imaging

studies are required. Instead, these systems require the surgeon to teach the robot about the

anatomy and shape of the knee for planning purposes. Some robotic systems also allow the

surgeon to teach the computer about the soft tissue balance of the knee, which was also

discussed in last month’s blog. Once all of this data is given to the system, the surgeon has the

ability to manipulate the bone cuts to best suit the patient’s knee.

While these initial steps are very similar to computer-assisted surgery, the difference lies in

how the surgical plan is carried out. With robotic-assisted surgery, the device carrying out the

bone cuts is controlled by the robot to some degree. Most systems lock in the direction that

each bone cut should be made and limits the path of the saw blade to the correct orientation.

These systems also allow the surgeon to check each cut and ensure its accuracy.

Outcomes

The main goals of computer- and robotic-assisted total knee replacements are to accurately

place the implants and ultimately to improve the patient’s function after surgery. Many studies

have evaluated these systems to determine whether these goals have been met. One large

study that reviewed 23 clinical trials showed that the use of computer assistance resulted in

significantly lower risk of malalignment. 1 This finding has been confirmed with a number of

others as well, including a study in 2008 that showed only 0.55% of robotic-assisted knee

replacements had malalignment as compared to 26.4% of traditional knee replacements. 2

Other studies have focused on patient functional outcomes. Some data has suggested that

patients experience less pain, need less narcotics, and have a shorter hospital stay after robotic-

assisted surgery. 3 Despite these differences, however, no study has shown improved long-term

function when comparing these techniques. 4 Many researchers would suggest that this may

change over time as the robotic techniques continue to be perfected, but only time will tell.

Total Hip Replacement

Hip replacement surgery differs significantly as compared to total knee replacement with

regard to the surgical technique. Hip replacement requires surgeons to accurately grind away a

small bowl-shaped area in the pelvis for the socket side of the joint and to create enough space

in the top of the femur for placement of an implant containing the ball side of the joint. While

the mechanics of replacing the joint are quite different for the surgeon as compared to knee

replacements, the steps involved can still benefit from the use of computer or robotic

assistance.

Computer- vs. Robotic-assisted

Similar to the procedures performed with knee replacement, computer and robotic-assisted hip

replacements start with teaching the computerized system where the hip is in 3-dimensional

space. Special guides are placed firmly in the bones of the hip and are used as reference points

for the remainder of the surgery. These computerized and robotic systems can be image-

based, with pre-operative images obtained before surgery, or can be imageless where the

surgeon maps out all of the anatomy during the surgery.

Just like in knee replacements, taking an extra step of using a robotic arm to help with the

surgery is the difference between computer-assisted and robotic-assisted surgery. In this case,

the robotic arm typically aligns devices called reamers that grind away the bowl-shaped socket

in the pelvis and then holds the socket in the correct orientation as the surgeon impacts it in

place. On the ball side of the joint, both types of systems can assist the surgeon by ensuring

that the hip replacement is further aligned properly with regard to the patient’s leg lengths and

other measurements important in making the hip replacement as stable as possible.

Outcomes

As more computer- and robotic-assisted hip replacement systems have been approved, so have

the number of clinical studies looking at their effectiveness. Most studies have focused on the

accuracy and precision of placing the socket side of the joint. The bowl-shaped implant must be

placed accurately within the pelvis to reduce the chance of the hip dislocating after surgery. A

large amount of research has been performed to define the best location for the socket and it is

clear that relatively small errors in implant placement can make the entire joint unstable. As a

result, this has been the main focus in clinical studies, which have shown that computer- and

robotic-assisted systems result in more accurate placement of the socket and with fewer

outliers. 5 The improvements in accuracy and precision have resulted in lower rates of hip

dislocation in clinical studies as well. 6

Texas Hip and Knee Center

The use of technological advances as described above continues to rise in joint replacement

surgery over the last several decades. At Texas Hip and Knee, both computer-assisted and

robotic-assisted technologies are available and utilized by the surgeons in the practice. If you

are a patient and the advantages of these technologies appeal to you, please discuss whether

you would be a good candidate for this type of surgery with your surgeon. It should be noted

that a few disadvantages to the use of this technology do exist. As mentioned above, the

placement of special guides is needed to carry out these surgeries. While they are removed at

the conclusion of the surgery, they can result in additional sites of pain and have rarely been

associated with infections. In addition, if an image-based technique is used, patients must

realize that there may be some added cost, a small amount of additional radiation exposure,

and the inconvenience of getting the imaging study completed. Many surgeons and patients

agree that the advantages of these systems outweigh their limitations, but a careful discussion

with your surgeon is always needed prior to choosing this type of surgery.

1 Hetaimish BM, et al. Meta-analysis of navigation vs. conventional total knee arthroplasty. J Arthroplasty 2012;

27:1177-1182.

2 Mannan A, et al. Increased precision of coronal plan outcomes in robotic-assisted total knee arthroplasty: A

systematic review and meta-analysis. Surgeon 2018;16(4):237-244.

3 Kayani B, et al. Robotic-arm assisted total knee arthroplasty is associated with improved early functional recovery

and reduced time to hospital discharge compared with conventional jig-based total knee arthroplasty. Bone Joint J

2018;100-B(7):930-937.

4 Cho KJ, et al. Robotic versus conventional primary total knee arthroplasty: Clinical and radiological long-term

results with a minimum follow-up of ten years. Int Orthop 2019;43(6):1345-1354

5 Kayani B, et al. Assuring the long-term total joint arthroplasty: A triad of variables. Bone Joint J 2019;101-B(1

suppl A):11-18.

6 Illgen RL, et al. Robotic-assisted total hip arthroplasty: Outcomes at minimum two-year follow-up. Surg Technol

Int 2017;30:365-372.