Does Computer-Assisted Surgery Improve Outcomes of TKA?
A review of the evidence for using computer-assisted navigation, handheld navigation, robotic surgery, and patient-specific instrumentation in total knee arthroplasty.
Jonathan Vigdorchik, MD, and John Buza, MD
The authors have no disclosures relevant to this article.
The past decade has seen tremendous growth in the number of computer-assisted technologies available to surgeons who perform total knee arthroplasty (TKA). Although these technologies aim to improve the precision and accuracy of TKA, research on the clinical benefits is still in its early stages. In addition, the capabilities, advantages, and drawbacks of each type of computer-assisted technology are poorly understood.
This article serves to introduce the 4 major types of computer-assisted technology used in TKA – computer-assisted navigation, handheld navigation, robotic surgery, and patient-specific instrumentation – and to present the best available evidence regarding their use.
Computer-assisted navigation generates a 3-dimensional model of the patient’s knee intraoperatively and then correlates this model with the surgeon’s instruments to allow for precise cutting and implantation. The 3-dimensional model is based on either intraoperative (fluoroscopy-assisted) images or preoperative (CT scan or MRI) images.
Numerous studies and meta-analyses have shown that computer-assisted navigation improves component alignment and restores the mechanical axis during TKA. [1-5]
Thienpont et al  aggregated 10 meta-analyses and compared the results of 28,763 patients who had undergone either conventional TKA or TKA with computer-assisted navigation. They found a significantly lower likelihood of mechanical axis outliers (defined as more than 2°) with the use of computer-assisted navigation than with conventional arthroplasty (P<0.05). 
Although most studies indicate that computer-assisted navigation improves alignment, additional clinical benefits have not been clearly shown. No difference in functional or clinical outcomes has been found at up to 10 years after TKA when comparing computer-assisted navigation with conventional TKA. [6-10]
In a randomized controlled trial of 71 patients with a minimum 2-year follow-up, Spencer et al  found no significant difference in functional outcome scores between patients who underwent TKA with computer-assisted navigation and those who underwent conventional TKA.
However, in a meta-analysis of 21 studies including 1713 knees that underwent either computer-assisted (n=869) or conventional (n=844) TKA, Rebal et al  found that in addition to improving alignment, computer-assisted navigation was associated with significantly greater increases in Knee Society Score at 3 and 12 months after surgery (P<0.03).
Potential Drawbacks and Limitations
There are a number of potential drawbacks to the use of computer-assisted navigation:
- Many navigation systems rely on the anatomic registration of various points intraoperatively, which, if marked incorrectly, may lead to component malposition. 
- Component malposition may also occur when markers that are drilled into the femur or tibia move during the course of surgery.
- Fractures have been reported at the drilling site of the marker. [12-13]
With the miniaturization of electronics in the last decade, interest in the use of smartphone-based technology in orthopaedic surgery has grown. The 2 primary technologies that enable this use are accelerometers and sensors:
- Accelerometers are small devices that measure the position of an object relative to a given axis and then use this information to calculate the mechanical axis of the femur and tibia to assist in performing the femoral and tibial cuts.
- Sensors are small transducers that measure the mechanical force, or contact load, in the medial and lateral compartment of the knee.
These technologies do not require preoperative imaging, increased operative time, additional incisions, or a high capital expenditure for the equipment. [14-17] In addition, handheld devices are typically compatible with multiple implant systems.
A randomized controlled trial by Nam et al  compared the use of extramedullary guides versus accelerometer-based navigation for tibial alignment in 100 TKA patients. Accelerometer-based navigation led to significant improvements in the coronal alignment (95.7% vs. 68.1% within 2° of perpendicular to the tibial mechanical axis; P<0.001) and the posterior slope (95.0% vs. 72.1% within 2° of a 3° posterior slope; P=0.007). 
Other authors, however, have found no significant difference in implant alignment, mechanical axis, or clinical outcomes at 6 months postoperatively when using accelerometer-based technology. 
Sensor-assisted surgery is designed to improve soft tissue balancing. Gustke et al  evaluated the use of intraoperative sensors in 135 patients undergoing TKA. Eighteen patients (13%) were unbalanced, defined as an intercompartmental pressure of greater than 15 pounds of pressure.  At 1 year after surgery, a significantly higher percentage of patients in the balanced group were satisfied or very satisfied compared with patients in the unbalanced group (96.7% vs. 82.1%; P=0.043). 
There are currently no randomized controlled trials demonstrating improved soft tissue balancing with the use of sensor-based technologies compared with conventional instrumentation.
Potential Drawbacks and Limitations
- Accelerometer-based technology is designed to allow the surgeon to accurately place the cutting guides for the distal femoral and tibial cuts. However, it does not assist with anterior or posterior femoral cuts or implant rotation.
- Sensor-based technology is used primarily for soft tissue balancing; it is not used to make the initial femoral or tibial resections.
Robotic-assisted surgery allows for 3-dimensional milling or cutting based on preoperative planning and tactile feedback from the surgeon. It requires the patient to undergo a preoperative CT scan, which the surgeon uses in planning the procedure to virtually implant the components.
Robotic-assisted TKA has been shown to restore mechanical alignment, especially femoral component rotation, to a greater degree than conventional surgeries. [19-22]
Park et al  randomized patients to either conventional TKA (n=30 patients) or robotic-assisted TKA (n=32 patients). At a mean follow-up of 4 years, significant differences were found in the coronal femoral component angle (mean 97.7° vs. 95.6°; P<0.01), the sagittal femoral angle (mean 0.2° vs. 4.2°; P< 0.01), and the sagittal tibial angles (mean 85.5° vs. 89.7°; P<0.01), all in favor of robotic-assisted surgery. 
They found no difference in the Knee Society score , tibio-femoral angle, or coronal tibial component angle.
Although most studies show an improvement in lower extremity alignment or component positioning, robotic-assisted TKA has not been proven to offer any clinical benefit for the patient.
Song et al  conducted a randomized controlled trial of 30 patients undergoing simultaneous bilateral TKA, with 1 knee undergoing robotic-assisted TKA and the other undergoing conventional TKA. They found no significant differences between knees in range of motion, Hospital for Special Surgery (HSS) scores, or Western Ontario and McMaster University (WOMAC) scores at 1 year after surgery (P>0.05). [24,25]
- Robotic-assisted surgery has been associated with additional time, cost, and radiation exposure related to obtaining a preoperative CT scan.
- Problems encountered with the use of markers drilled into the tibia and femur, including movement leading to component malposition and fracture, are uncommonly reported but are possible. [11-13]
- Robotic-assisted TKA is unable to perform soft tissue balancing, which is critical to the success of TKA.
- There is a high start-up cost (up to $800,000) and a learning curve associated with the use of any new technology, which may be prohibitive for many surgeons and hospital systems. 
Patient-specific instruments were designed to reap the benefits of computer-assisted navigation or robotic-assisted surgery while simplifying these operating room procedures. A preoperative CT scan or MRI is used to manufacture custom cutting guides that are sent directly to the hospital in a sterile instrument pack.
As with robotic-assisted surgery, few high-quality studies have been done to evaluate radiographic and functional outcomes when patient-specific instrumentation is used.
Ng et al  included 569 TKAs performed with patient-specific instruments and 155 TKAs performed with conventional instruments in a retrospective review. They found that patient-specific instrumentation led to improved alignment compared with conventional instrumentation (88% vs. 78%, respectively; P < 0.001). 
In a recent systematic review of 22 studies, however, Sassoon et al  found that most studies did not demonstrate improvement in overall limb alignment with the use of patient-specific instrumentation.
- The major disadvantage of patient-specific instrumentation is the cost associated with imaging and subsequent fabrication of single-use instruments.
- Planning during the preoperative period also requires substantial time of the patient, the surgeon, and the office staff.
Computer-assisted navigation and robotic-assisted surgery can significantly improve component alignment compared with conventional TKA. It is still unknown, however, if this improvement will lead to better patient outcomes or decreased revision rates.
Handheld navigation does not require additional incisions or substantial initial expense compared with other technologies, but it is still unproven compared with conventional instrumentation.
Patient-specific instrumentation has had less favorable early results, with only minor improvement in component alignment compared with conventional TKA.
Jonathan M. Vigdorchik, MD, is an Assistant Professor of Orthopaedic Surgery, Associate Fellowship Director in Adult Reconstruction, and Co-Director of Robotics in Orthopaedic Surgery at NYU Langone Medical Center’s Hospital for Joint Diseases, New York, New York. John Buza, MD, is a Resident in Orthopaedic Surgery at NYU Langone Hospital for Joint Diseases, New York, New York.
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