Surgery Section - Computer Assisted Navigation for Orthopedic Procedures of the Pelvis and Appendicular Skeleton

IMPORTANT REMINDER

This Medical Policy has been developed through consideration of medical necessity, generally accepted standards of medical practice, and review of medical literature and government approval status.

Benefit determinations should be based in all cases on the applicable contract language. To the extent there are any conflicts between these guidelines and the contract language, the contract language will control.

The purpose of medical policy is to provide a guide to coverage. Medical Policy is not intended to dictate to providers how to practice medicine. Providers are expected to exercise their medical judgment in providing the most appropriate care.

Description

The term “computer assisted musculoskeletal surgical navigational orthopedic procedure” describes navigation systems that provide additional information during a procedure that attempt to further integrate preoperative planning with intraoperative execution.

The goal of computer-assisted navigation (CAN) is to increase surgical accuracy and reduce the chance of malposition of implants. For total knee arthroplasty (TKA), malalignment is commonly defined as a variation of greater than 3 degrees from the targeted position. Proper implant alignment is believed to be an important factor for minimizing long-term wear, risk of osteolysis, and loosening of the prosthesis. In addition to reducing the risk of substantial malalignment, CAN may improve soft tissue balance and patellar tracking. CAN is also being investigated for operations with limited visibility such as placement of the acetabular cup in total hip arthroplasty (THA) and for minimally invasive orthopedic procedures. (Minimally invasive orthopedic surgery is discussed separately in policy No. 7.01.98.) Other potential uses of CAN for surgical procedures of the appendicular skeleton include screw placement for fixation of femoral neck fractures and tunnel alignment during reconstruction of the anterior cruciate ligament (ACL).

CAN devices may be image-based or non-image based. Image-based devices use preoperative computed tomography (CT) scans and operative fluoroscopy to direct implant positioning. Newer non-image based devices use information obtained in the operating room, typically with infrared probes. For TKA, specific anatomic reference points are made by fixing signaling transducers with pins into the femur and tibia. Signal emitting cameras (e.g., infrared) detect the reflected signals and transmit the data to a dedicated computer. During the surgical procedure multiple surface points are taken from the distal femoral surfaces, tibial plateaus, and medial and lateral epicondyles. The femoral head center is typically calculated by kinematic methods that involve movement of the thigh through a series of circular arcs, with the computer producing a three-dimensional model that includes the mechanical, transepicondylar and tibial rotational axes. CAN systems direct the positioning of the cutting blocks and placement of the prosthetic implants based on the digitized surface points and model of the bones in space. The accuracy of each step of the operation (cutting block placement, saw cut accuracy, seating of the implants) can be verified, thereby allowing adjustments to be made during surgery.

Navigation involves the three steps described below:

1. Data Acquisition

   Data can be acquired in three different ways: fluoroscopic, CT/MRI guided, or via imageless systems. This data is then used for registration and tracking, described below. Image guided systems are somewhat self explanatory. The image-less systems rely on other information such as centers of rotation of the hip, knee or ankle, or visual information like anatomical landmarks.

2. Registration

   Registration refers to relating images (e.g., x-rays, CT, MRI or patients’ 3-D anatomy) to the anatomical position in the surgical field. Early registration techniques required the placement of pins or “fiduciary markers” in the target bone. This required an additional surgical procedure. More recently, a surface matching technique is used in which the shapes of the bone surface model generated from preoperative images are matched to surface data points collected during surgery.

3. Tracking

   Tracking refers to the sensors and measurement devices that can provide feedback during surgery regarding the orientation and relative position of tools to bone anatomy. For example, optical or electromagnetic trackers can be attached to regular surgical tools which can then provide real time information related to the position and orientation of the tools’ alignment with respect to the bony anatomy of interest.

With respect to orthopedic procedures, computer assisted navigation is most commonly performed as an adjunct to fixation of pelvic, acetabular or femoral fractures, and as an adjunct to hip and knee arthroplasty procedures.

Surgical navigation systems require FDA clearance, but generally are subject only to 510(k) clearance since computer assisted surgery is considered analogous to a surgical information system in which the surgeon is only acting on the information that is provided by the navigation system. As such, the FDA does not require data documenting the intermediate or final health outcomes associated with computer assisted surgery. (In contrast, robotic procedures, in which the actual surgery is robotically performed, are subject to the more rigorous requirement of the PMA process.) A variety of surgical navigation procedures have received FDA clearance through the 510(k) process, and in general, the labeled indications are very broad. Below is one example.

“The OEC FlurorTrak™ 9800 Plus provides the physician with fluoroscopic imaging during diagnostic, surgical and interventional procedures. The surgical navigation feature is intended as an aid to the surgeon for locating anatomical structures anywhere on the human body during either open or percutaneous procedures. It is indicated for any medical condition that may benefit from the use of stereotactic surgery and which provides a reference to rigid anatomical structures such as sinus, skull, long bone or vertebra visibile on fluoroscopic images.”

Several navigation systems (e.g., PiGalileo™ Computer-Assisted Orthopedic Surgery System, PLUS Orthopedics; OrthoPilot® Navigation System, Braun; Navitrack® Navigation System, ORTHOsoft) have received FDA clearance specifically for TKA. FDA-cleared indications for the PiGalileo system are representative. This system “is intended to be used in computer-assisted orthopedic surgery to aid the surgeon with bone cuts and implant positioning during joint replacement. It provides information to the surgeon that is used to place surgical instruments during surgery using anatomical landmarks and other data specifically obtained intra-operatively (e.g., ligament tension, limb alignment). Examples of some surgical procedures include but are not limited to:

• Total knee replacement supporting both bone referencing and ligament balancing techniques
• Minimally invasive total knee replacement"

Policy/Criteria

Computer assisted navigation for orthopedic procedures involving the pelvis and appendicular skeleton is considered investigational.

Scientific Background

Trauma or Fracture

Computer assisted surgery has been described as an adjunct to pelvic, acetabular or femoral fractures. For example, fixation of these fractures typically requires percutaneous placement of screws or guide wires. Conventional fluoroscopic guidance (i.e. C-arm fluoroscopy) provides imaging in only one plane. Therefore, the surgeon must position the implant in one plane, and then get additional images in other planes in a trial and error fashion to ensure that the device has been properly placed. This process adds significant operating time and radiation exposure. It is hoped the computer assisted navigation would allow for minimally invasive fixation and provide more versatile screw trajectories with less radiation exposure. Therefore, computed assisted navigation is considered an alternative to the existing image guidance using C-arm fluoroscopy.

In order to determine whether or not computer assisted surgery results in improved health outcomes, controlled trials are needed, comparing the operating time, the radiation exposure and long term outcomes of those whose surgery was conventionally guided using C-arm versus image-guided using computer assisted surgery. While several in vitro and review studies have been published (2-4), a literature search through June 27, 2006 identified only one clinical trial of computer assisted surgery in trauma or fracture cases. Suhm and colleagues reported on a case series of 27 patients with femoral fractures who underwent implantation of a femoral nail. (5) Outcomes included precision of interlocking, exposure time and OR time. However, without a control or comparison group, it is not possible to determine the impact of the computer assistance on final health outcomes.

CAN for internal fixation of femoral neck fractures has been described in a retrospective analysis consisting of two cohorts of consecutive patients (20 each, performed from 2001 to 2003 at two different campuses of a medical center) who underwent internal fixation with three screws for a femoral neck fracture. (6) Three of five measurements of parallelism and neck coverage were significantly improved by CAN; these included a larger relative neck area held by the screws (32% vs. 23%) and less deviation on the lateral projection for both the shaft (1.7 vs. 5.2 degrees) and the fracture (1.7 vs. 5.5 degrees) screw angles. Slight improvements in anteroposterior screw angles (1.3 vs. 2.1 and 1.3 vs. 2.4 degrees) did not reach statistical significance. There were two reoperations in the CAN group and 6 in the conventional group. Complications (collapse, subtrochanteric fracture, head penetration, osteonecrosis) were lower in the CAN group (3 vs. 11). Additional controlled studies are needed.

Anterior Cruciate Ligament (ACL) Reconstruction

Several studies reported the use of CAN for ACL reconstruction. One of the studies randomized 60 patients to either manual or computer-assisted guidance for tunnel placement with follow-up at 1, 3, 6, 12, 18, and 24 months. (7) There were no differences between the groups in measurements of laxity. However, there was less variability in side-to-side anterior laxity in the navigated group (e.g., 97% were within 2 mm of laxity in the navigated group versus 83% in the conventional group at an applied force of 150 Newtons). There was a significant difference in the sagittal position of the tibial tunnel (distance from the Blumensaat line of 0.4 vs. -1.2 mm), suggesting possible impingement in extension for the conventional group. At the final follow-up (24 months) all knees had normal function, with no differences observed between the groups. Another study randomized 53 patients to manual or computer-assisted ACL reconstruction by 3 experienced surgeons (at least 1,000 cruciate ligament operations). (8) Tunnel placement and range variance were similar for the 2 groups; the authors concluded that experienced surgeons can achieve essentially the same positioning as CAN. Hart and colleagues compared biomechanical radiographic and functional results in patients randomized to ACL reconstruction using CAN (n=40) or the standard manual targeting technique (n=40). (9) Blinded evaluation found more exact bone tunnel placement with CAN, but no overall difference in biomechanical stability or function between the groups. The authors concluded that “the scientific evidence does not yet support definitive relations between long-term outcomes and repeatability of positioning or the superiority of one ideal location versus another.”

Arthroplasty (Total hip [THA] and total knee [TKA])

Unlike fractures, for which the surgery is typically image-guided using C-arm fluoroscopy, routine arthroplasties are conventionally done without image guidance. Therefore, in this setting computer assisted surgery is not considered an alternative to C-arm fluoroscopy, but a novel approach.

For both total hip and knee arthroplasties, optimal alignment is considered an important aspect of long term success.  Malalignment of arthroplasty components is one of the leading causes of instability and reoperation.  In THA, orientation of the acetabular component of the THA is considered critical.  For TKA, alignment of the femoral and tibial components as well as ligament balancing are considered important factors in determining success.  The alignment of the knee prosthesis can be measured along several different axes, including the mechanical axis and the frontal and sagittal axes of both the femur and tibia.  It is proposed that computer assisted surgery improves the alignment of the various components of THA and TKA.

A search of the MEDLINE database concentrated on identifying controlled trials comparing stability and reoperation rates between conventional THA and computer assisted surgery. Intermediate outcomes include the percentage of implants which achieve a predetermined level of acceptable alignment. Paratte and Argenson randomized patients to CAN for THA (n=30) or freehand cup positioning (n=30) by an experienced surgeon. (10) The mean additional time for the computer-assisted procedure was 12 minutes. There was no difference between the computer-assisted group and the freehand-placement group with regard to the mean abduction or anteversion angles measured by CT. A smaller variation in the positioning of the acetabular component was observed in the CAN group; 20% of cup placements were considered to be outliers in the CAN group compared with 57% in the freehand-placement group. Another study randomly assigned 36 patients with symptomatic adult dysplastic hip to either CT-based navigation or the conventional technique for periacetabular osteotomy. (11) An average of 0.6 intraoperative radiographs were taken in the navigated group compared with 4.4 in the conventional group, resulting in a total operative time that was 21 minutes shorter for CAN. There were no differences between the groups for correction in femoral head coverage or for functional outcomes (pain, walking, range of motion) at 24 months.

It has been proposed that CAN may overcome the difficulties of reduced visibility of the surgical area associated with minimally invasive procedures. A 2007 review by Ulrich and colleagues summarized studies that compared outcomes from minimally invasive THA-CAN and standard THA. (12) Seventeen studies were described in this evidence-based review, including nine prospective comparisons, seven retrospective comparisons, and one large (n=100) case series. The authors concluded that alignment with minimally invasive CAN appears to be at least as good as standard THA, although the more consistent alignment must be balanced against the current expense of the computer systems and increased surgical time. Improved health outcomes have not yet been demonstrated with CAN or minimally invasive THA, either alone or in combination.

A 2007 TEC Assessment evaluated CAN for TKA. (13) Nine studies from seven randomized controlled trials (RCTs) were reviewed. Criteria for the RCTs included having at least 25 patients per group and comparing limb alignment and surgical or functional outcomes following TKA with CAN or conventional methods. Also reviewed were cohort and case series that evaluated long-term associations between malalignment of prosthetic components and poor outcomes. In the largest of the cohort studies, which included over 2,000 patients (3,000 knees) with an average of 5-year follow-up, 41 revisions for tibial component failure (1.3% of the cohort) were identified. The risk ratio for age was estimated at 8.3, with a greater risk observed in younger, more active patients. For malalignment (defined as >3 degrees varus or valgus), the risk ratio was estimated to be 17.3.

The combined data from the prospective RCTs showed:

• A significant decrease in the percentage of limbs considered to be outliers (e.g., >3 degrees of varus or valgus from a neutral mechanical axis) with CAN. In the conventional group, 33% of patients had malalignment of the overall femoral/tibial axis. In the navigated group, 18% of patients were considered to have malalignment of the mechanical axis. For the combined data set there was a decrease in malalignment in 15% of patients, with an estimated number needed to treat (NNT) of 6.7 to avoid one case of malalignment.
• Surgical time increased by 10 to 20 minutes in all but 1 study. CAN-associated reduction in blood loss was less consistent, with only some of the studies showing a decrease in blood loss of 100 to 200 ml.
• RCTs that assessed function (up to two years follow-up) did not find evidence of improved health outcomes. However, the studies were not adequately powered to detect functional differences, and data on long-term follow-up are not available.

The report concluded that no direct evidence is currently available to support an improvement in clinical outcomes with CAN for TKA. As a result of deficiencies in the available evidence (e.g., potential for bias in observational studies and lack of long-term follow-up in the RCTs), it is not possible to determine whether the degree of improvement in alignment that has been reported in the RCTs leads to meaningful improvements in clinically relevant outcomes such as pain, function, or revision surgery.

A meta-analysis of CAN for TKA was conducted that included 33 studies and 3,423 patients. (14) The studies were of varying methodological quality and included 11 randomized trials. Although no significant difference in mechanical axes between the navigated and conventional surgery group was found, navigated surgery was found to result in a lower risk of malalignment. It was calculated that one of every five patients would avoid unfavorable component positioning (greater than three degrees) with CAS. The authors concluded that methodological weaknesses of the available trials limited the conclusions of the meta-analysis and no conclusive inferences could be reached for functional outcomes or complication rates.

Carter and colleagues compared outcomes from TKA in consecutive patients prior to and after acquisition of a CAN system in a community hospital. (15) Out of 310 consecutive surgeries, 200 patients (100 CAN and 100 conventional) consented to follow-up with a computed tomography (CT) scan. Results were considered good if alignment was 3 degrees or less from the surgical goal, fair if between 4 and 6 degrees, poor if between 7 and 9 degrees, and extremely poor if greater than 9 degrees from the surgical goal. Blinded evaluation rated sagittal alignment as good in 78% of CAN and 47% of conventional knees for the femoral component, and in 93% of CAN and 64% of conventional knees for the tibial component. Thirteen knees had poor or extremely poor sagittal-tibial alignment in the conventional group. Coronal alignment was not significantly different between the groups, although variance was greater in the conventional group. Tibial rotation was inconsistent in both groups. No learning curve was observed for the accuracy of alignment, although the initial cases required 12 to 20 minutes in additional time. By the end of the series the highest volume surgeon required less time for CAN than for the conventional approach. Learning curves were also addressed in a prospective controlled observational study from 13 European orthopedic centers. (16) Five of the centers were experienced CAN users and eight started using CAN for the study. The first 30 consecutive cases from each center were evaluated in an intention-to-treat manner, totaling 150 patients in the control group and 218 in the study group. The operations initially took 10 to 20 minutes longer in the study group, but after 30 procedures the mean difference was 7 minutes (overall average of 118 minutes vs. 107 minutes operating time for the conventional group). Three month follow-up indicated that alignment for the experienced and novice centers was similar and there were no differences in functional outcomes at a mean 24-month follow-up (9 to 37 months range). One complication was reported for the study group, consisting of a femoral fracture through the hole of the reference screw.

As noted above, it has been proposed that CAN may overcome the difficulties of reduced visibility associated with minimally invasive procedures. Dutton and colleagues randomized 108 consecutive patients to computer-assisted “minimally invasive” TKA or conventional TKA with standardized perioperative pain management for both groups. (17) An independent physical therapist performed the preoperative and postoperative patient assessments. Operative time was found to increase by an average 24 minutes with minimally invasive CAN, with a difference in incision length of 4 cm (9 cm vs. 13 cm). Alignment was at 3 degrees or less from target in 92% of patients for the coronal tibiofemoral angle 90% for the sagittal tibial component angle. This compared with 68% and 61%, respectively, for patients in the conventional TKA group. Three other measured angles were not significantly different. There was no difference in post-operative pain between the two groups. Hospital stay, based on standardized functional criteria for discharge, was an average 1.2 days shorter (3.3 vs. 4.5 days). Functional improvement was noted at one month post-operatively for the number of patients who could walk independently for 30 minutes (details not reported). At six months, functional outcomes were similar for the two groups.

Summary

Overall, the literature supports a decrease in variability of alignment with computer-assisted navigation, particularly with respect to the number of outliers. Although some observational data suggest that malalignment may increase the probability of early failure, recent RCTs with short to mid-term follow-up have not shown improved health outcomes with CAN. Given the low short-term revision rates associated with conventional procedures and the inadequate power of available studies to detect changes in function, studies that assess health outcomes in a larger number of subjects with longer follow-up are needed. The most promising utilization of this procedure appears to be the ability to decrease incision length without loss of accuracy in component alignment. Although evidence at this time has not adequately demonstrated improved health outcomes with this more resource-intensive combination, continued technology development in this area is expected.

References

1. BlueCross BlueShield Association Medical Policy Reference Manual, Policy No. 7.01.96
2. Schep NW, Broeders IA, van der Werken C. Computer assisted orthopaedic and trauma surgery. State of the art and future perspectives. Injury 2003;34(4):299-306
3. Slomczykowski MA, Hofstetter R, Sati M et al. Novel computer-assisted fluoroscopy system for intraoperative guidance: feasibility study for distal locking of femoral nails. J Orthop Trauma 2001;15(2):122-31
4. Hofstetter R, Slomczykowski M, Krettek C et al. Computer-assisted fluoroscopy-based reduction of femoral fractures and antetorsion correction. Comput Aided Surg 2000;5(5):311-25
5. Suhm N, Jacob AL, Nolte LP et al. Surgical navigation based on fluoroscopy-clinical application for computerassisted distal locking of intramedullary implants. Comput Aided Surg 2000;5(6):391-400
6. Liebergall M, Ben-David D, Weil Y et al. Computerized navigation for the internal fixation of femoral neck fractures. J Bone Joint Surg Am 2006; 88(8):1748-54
7. Plaweski S, Cazal J, Rosell P et al. Anterior cruciate ligament reconstruction using navigation: a comparative study on 60 patients. Am J Sports Med 2006; 34(4):542-52
8. Mauch F, Apic G, Becker U, et al. Differences in the placement of the tibial tunnel during reconstruction of the anterior cruciate ligament with and without computer-assisted navigation. Am J Sports Med 2007; 35(11):1824-32
9. Hart R, Krejzla J, Sváb P et al. Outcomes after conventional versus computer-navigated anterior cruciate ligament reconstruction. Arthroscopy 2008; 24(5):569-78
10. Parratte S, Argenson JN. Validation and usefulness of a computer-assisted cup-positioning system in total hip arthroplasty. A prospective, randomized, controlled study. J Bone Joint Surg Am 2007; 89(3):494-9
11. Hsieh PH, Chang YH, Shih CH. Image-guided periacetabular osteotomy: computer-assisted navigation compared with the conventional technique: a randomized study of 36 patients followed for 2 years. Acta Orthop 2006; 77(4):591-7
12. Ulrich SD, Bonutti PM, Seyler TM et al. Outcomes-based evaluations supporting computer-assisted surgery and minimally invasive surgery for total hip arthroplasty. Expert Rev Med Devices 2007; 4(6):873-83
13. BlueCross BlueShield Association Technology Evaluation Center. Computer assisted navigation for total knee arthroplasty. 2007; Vol 22, Number 10
14. Bauwens K, Matthes G, Wich M et al. Navigated total knee replacement. A meta-analysis. J Bone Joint Surg Am 2007; 89(2):261-9
15. arter RE 3rd, Rush PF, Smid JA et al. Experience with computer-assisted navigation for total knee arthroplasty in a community setting. J Arthroplasty 2008; 23(5):707-13
16. Jenny JY, Miehlke RK, Giurea A. Learning curve in navigated total knee replacement. A multi-centre study comparing experienced and beginner centres. Knee 2008; 15(2):80-4
17. Dutton AQ, Yeo SJ, Yang KY et al. Computer-assisted minimally invasive total knee arthroplasty compared with standard total knee arthroplasty. A prospective, randomized study. J Bone Joint Surg Am 2008; 90(1):2-9

Cross References

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