What Is Role of Computer Navigation in Hip and Knee Arthroplasty?

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Chapter 90 What Is Role of Computer Navigation in Hip and Knee Arthroplasty?

RAJIV. GANDHI, MD, FRCSC, NIZAR N. MAHOMED, MD, SCD, FRCSC

Achieving the correct rotation and alignment of the implant components is critical for the short- and long-term survival of hip and knee arthroplasty. In total hip arthroplasty (THA), wear,^1,² range of motion,³ and stability⁴ are all affected by component orientation. In total knee arthroplasty (TKA), authors have shown that knee implants malpositioned by more than 3 degrees had a 24% loosening rate by 3 years after surgery as compared with 3% for correctly aligned implants.^5,⁶

The correct placement of implants is guided by preoperative radiographs and templating, intraoperative anatomic landmarks, and mechanical alignment guides on the instrumentation sets. However, patient positioning on the table is variable, anatomic landmarks are often difficult to reliably identify in arthritic joints, and mechanical alignment guides have not improved accuracy of acetabular positioning.^7,⁸

Computer-assisted surgery (CAS) has the potential to improve surgical accuracy through less invasive techniques and to improve clinical outcomes for patients. Computer-based tools allow for preoperative templating with three-dimensional imaging and intraoperative real-time positional information on tracking tools and bony structures. The clinical utility of these tools as compared with conventional techniques is being investigated in total joint arthroplasty.

BACKGROUND

Picard and colleagues ⁹ have classified CAS into active robotic systems, semiactive robotic systems, and passive systems. Active robotic systems are those in which a robot performs some surgical tasks such as drilling and reaming without the direct intervention of the surgeon. Many systems use a preoperative computed tomographic (CT) scan to plan the surgery. These systems are costly and involve complex equipment in the operating room, and thus have not been widely used.

Semiactive robots do not perform surgical tasks directly but rather direct placement of surgical tools in space. With this system, the surgeon first indicates the desired position and orientation of the implant on a three-dimensional template. The robot then positions the saw and drill guides so that the surgeon can make the necessary cuts. Passive systems include CT-based, fluoroscopy-based, or imageless navigation.

CT-based systems require a preoperative CT scan that is used to construct a three-dimensional model of the joint including the mechanical, transepicondylar, and tibial rotation axis. Surface landmarks of the joint are then acquired intraoperatively by touching the bony points with a tracking probe. Fluoroscopy-based navigation uses two or more intraoperative fluoroscopic views that are entered into the computer, thereby calculating the required anatomic references. A third method requires no images be obtained before or during surgery, but rather relies on the computer system having a database of prescanned CT images to calculate reference axes. The surgeon inputs multiple bony reference points into the computer that are compared with the database to define a three-dimensional model of the patient’s anatomy.

Regardless of the type of computerized navigation system, the main goal is to increase surgical accuracy and reduce the chance of malposition of the implants. The potential downsides of navigation are the increased cost, exposure to radiation, and increased surgical time.

CLINICAL RESULTS

Total Hip Arthroplasty

Achieving the correct abduction and anteversion of the acetabular component could potentially improve the longevity of a THR, improve the range of motion,³ and decrease the dislocation rate.¹⁰^–¹² Lewinnek and coauthors¹³ recommend an abduction angle of 40 ± 10 degrees and an anteversion angle of 15 ± 10 degrees as the safe zone for cup orientation. Many studies have investigated whether CAS can help improve accuracy in cup placement.

Kalteis and investigators,¹⁴ in a prospective, randomized trial, examined CT-based navigation versus imageless navigation versus conventional techniques for positioning of the acetabulum. The data showed that the incidence of component malposition was 53% in the freehand group, 17% in the CT-based group, and 7% with imageless navigation. The authors conclude that navigation significantly improved component alignment (P = 0.003), and there was no difference between CT-based and imageless navigation (P = 0.23). In comparing the mean abduction and anteversion angles between the groups, navigation was significantly better than conventional techniques with no difference between the CT-based versus imageless navigation. Surgical time was increased 8 minutes with imageless navigation and 17 minutes with CT-based navigation with no difference in blood loss among the three groups.

Parratte and Argenson ¹⁵ compared image-free navigation and freehand techniques for cup placement in a prospective randomized study of 60 patients. They found that 57% of the cups in the freehand group were malpositioned outside the acceptable range as compared with 20% in the navigation group (P = 0.002). When they compared the mean cup angles for both abduction and anteversion between the two groups, there was no significant difference. The mean surgical time was 12 minutes greater for the navigation group.

Leenders and researchers ¹⁶ undertook a prospective, randomized trial comparing CT-based navigation and freehand techniques for positioning of the acetabular component. CAS surgery led to a significantly improved accuracy for placing the cup within the safe zone of 45 to 55 degrees as compared with traditional methods (P < 0.001). The authors found that only 2 of the 50 patients in the CAS group had abduction angles of cup outside the safe zone.

Other authors have concluded similar findings that navigation helped improve alignment in cup position and reduce the number of outliers from the acceptable range.^17,¹⁸ Many of these studies are short-term follow-up, and it would be prudent to follow these patients long term to see whether the improved component alignment leads to an improved outcome and survival of the implant. Overall, there is no reported increase in complication rate associated with CAS.

A further advancement has been the use of active systems and a robot that serves as a delivery tool for a surgical procedure planned before surgery on a computer. The surgeon positions a robot by means of a referencing procedure and then can supervise the robot throughout the process.

A prospective, randomized study from Germany by Schwieger and colleagues ¹⁹ compared robotic insertion (ROBODOC) and conventional techniques for total hip replacement. After 24 months of follow-up, the authors conclude that limb-length equality and varus/valgus alignment of the femoral component was improved with the robot (P < 0.001). Recurrent dislocations and subsequently the revision rate was greater in the robotic group (P < 0.001), and the duration of surgery was increased in the robotic group (P < 0.001). No difference was found at 2 years in the Harris hip, Merle d’Aubigné, and the Mayo clinical scores between the two groups. The authors conclude that the 18% dislocation rate in the robot group was due to the abductor muscle deficiencies either from the wide surgical approach needed for the robot or the damage it caused to the tendon during the reaming process, but not from malposition of the components. Furthermore, the authors suggest this technology needs some further development before it can be considered for routine use in THA.

The stability of the femoral implant inserted with ROBODOC was evaluated by Nogler and researchers ²⁰ in a prospective, randomized cadaveric study. The authors conclude that there was no difference in femoral component micromotion at the time of insertion; therefore, the robot system did not enhance stability as compared with manual insertion techniques (Table 90-1 and Fig. 90-1).

TABLE 90-1 Summary of Best Evidence for Navigation and Hip Arthroplasty

FIGURE 90-1 Navigation in total hip replacement. A, Intraoperative tracking of landmarks. B, Real-time feedback on acetabular positioning.

(Courtesy Smith & Nephew, Memphis, TN)

Total Knee Arthroplasty

Minor implant malpositioning can lead to early wear and loosening, and poorer clinical results. Ritter and coworkers ²¹ have proposed that implants should be aligned in a neutral mechanical axis ±3 degrees varus or valgus for better survivorship. Ten percent of knees lie outside of this range using standard instrumentation. Rotational malpositioning can affect patellar tracking and cause subluxation.²²

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