This article is more than 5 years old. Information may no longer be current.

Navigated Anterior Cruciate Ligament Reconstruction: Correlation Between Computer Data and Radiographic Measurements

Add topic to email alerts

Receive an email when new articles are posted on

Please provide your email address to receive an email when new articles are posted on .

Subscribe

Added to email alerts

You've successfully added to your alerts. You will receive an email when new content is published.

Click Here to Manage Email Alerts

You've successfully added to your alerts. You will receive an email when new content is published.

Click Here to Manage Email Alerts

Back to Healio

We were unable to process your request. Please try again later. If you continue to have this issue please contact customerservice@slackinc.com.

Back to Healio

Abstract

The goal of this study was to prove the reliability of computer-aided navigation for the surgical reconstruction of the anterior cruciate ligament (ACL) using an arthroscopic procedure. The study involved 50 patients preceded by a learning curve period. Computer-recorded data were compared with specific radiography measurements of the frontal and anteroposterior views. The radiographs were used to measure the position of the tibial tunnel in the frontal and sagittal plane, the angulation of the tibial tunnel in the frontal and sagittal plane, and the position of the femoral tunnel in the lateral condyle.

Navigation was introduced in knee surgery more than 10 years ago and has been used in anterior cruciate ligament (ACL) reconstruction.^1,2 Navigation allows surgeons to check the correlation between intraoperative data recorded with a computer-aided navigation system as well as review data from postoperative radiography measurements. The goal of this study was to establish the reliability of the navigated ACL surgery and to make suggestions to improve this reliability. The authors also compared the accuracy of a traditional femoral aiming device (Phusis, Saint Ismier, France) with the navigated technique. This prospective study began with 50 patients after an initial period with >100 patients.

Materials and Methods

The study included 50 randomly selected patients who suffered from ACL rupture. Twenty-three (46%) patients were female and 27 (54%) were male.

For 2 years, the authors used a kinematics, image-free navigation system (OrthoPilot, B. Braun Aesculap, Tuttlingen, Germany), with ACL software version 2.0, for tibial and femoral tunnel placement during ACL reconstruction. The system consisted of a computer linked to an optoelectronic infrared camera. Transmitters were fixed on the tibia and the medial femoral condyle of the patient. Another passive transmitter performed palpations with special pointers and tibial and femoral aiming devices.

Strict frontal and lateral radiography measurements were taken. The width and depth of the tibia plateau were measured, as well as the position of the medial tibia eminence with reference to the anterior edge of the tibia plateau in the sagittal plane. Finally, the length of the Blumensaat line was measured. All radiography was carried out using the same scale factor, and the operation was performed arthroscopically. The goal was to replace the ACL using the middle third of the patellar tendon as a graft.

Transmitters were placed on the medial side of the tibia and on the medial condyle of the femur, using two short (2.5 mm) pins. This was followed by extra-articular palpations of the anterior tibial tuberosity, the tibial crest at the lower third, and the medial and lateral edges of the tibia plateau with a very rigid ceramic pointer. Knee kinematics were recorded from full extension to 90° of flexion, and the anterior drawer was measured using the Lachman test. Arthroscopic procedure began with knee exploration to treat potential meniscal lesions and clean the intercondylar notch to expose the internal side of the lateral condyle and to make accurate internal palpations.

Internal palpations were performed on the tibial medial eminence, anterior arch of the intercondylar notch, internal side of the lateral condyle, anterior notch and point of the Blumensaat line, and the posterior edge of the condyle. The following two palpations were carried out with a ceramic hook pointer, because previous experience shows that errors occur because of pointers bending under force.

Following these palpations, the tibia tunnel position and orientation were located using a navigated aiming device equipped with a passive sensor. The computer displayed a cartographic axial view of the tibia plateau, with the current position of the center of the aiming device and its placement in the sagittal plane and in the frontal plane (Figure 1). A displayed projection of the intercondylar notch on the tibial plateau enabled the surgeon to locate the potential areas of conflict. Hence, before drilling the tunnel with a 2.5-mm pin, a surgeon can change the position of the aiming device until it appears to be in the correct position. Finally, the tunnel was drilled with cannulated drills slid over the pin.

The next step was to prepare the femoral tunnel. At this stage, traditional aiming devices were used to drill the tunnel from the outside to the inside of the femur. Once the pin was in place and slightly protruding beyond the internal side of the lateral condyle, the pin position was recorded with the navigated femur guide equipped with a passive sensor that was directly placed on the pin extremity. The computer recorded the distance from the pin to the over-the-top position, which corresponded to the most posterior edge of the internal side of the lateral condyle (Figure 2). The surgery continued by positioning and fixating the graft. All computer data were stored on the hard drive and separated into one file per patient. Strict frontal and profile radiographs were taken 48 hours after surgery in the standing position, with the scale factor checked.

The following measurements must be in accordance with the computed navigation data: the position of the tibial tunnel in the frontal plane; the distance from the center of the tibial tunnel to the medial edge of the tibia plateau in relation to the width of the tibia plateau (Figure 3); the position of the tibial tunnel in the sagittal plane; the distance from the center of the tibial tunnel to the anterior edge of the tibia plateau in relation to the depth of the tibia plateau (Figure 4); the angulation of the tibial tunnel in the frontal plane; the angle formed by the axis of the tibial tunnel and the axis of the tibial crest in the frontal plane; the angulation of the tibial tunnel in the sagittal plane; the angle formed by the axis of the tibial tunnel and the sagittal axis of the tibial crest; and the distance from the center of the femoral tunnel to the posterior edge of the lateral condyle in the sagittal plane, over the top.

Each measurement was recorded in an Excel spreadsheet, and statistical processing was carried out by Stat View with the t test.

Results

The position of the tibial tunnel was measured from its center in relation to the width of the frontal plane. On the radiographs, the position of the center of the tunnel was 45.02% of the width of the tibia plateau on average, with a maximum of 60% and a minimum of 40%. The SD value was 3.57%. In the navigation procedure, the center of the pin of the tibial aiming device was used as a reference to determine the tunnel position, and the external palpations of the tibia plateau (medial and lateral) served to measure width. The average result for the center of the tunnel was 45.97%, with a maximum of 62% and a minimum of 34%. The SD value was 4.87%. The different statistical tests showed a strong correlation between both measurements. The F test value was 0.03. The t test results showed no difference between both measurements case by case, with t=1.13 and P=.26.

The position of the tibial tunnel was measured from its center and expressed as a percentage of the depth in the sagittal plane. The radiographic result showed the tunnel center position as 37.31% of the depth of the tibia plateau on average, with a maximum of 48% and a minimum of 25%. The SD value was 5.95%.

During the navigation, the authors used the center of the pin of the tibial guide as a reference to locate the tunnel. The depth of the tibia plateau was assessed by palpation of the anterior tibial tunnel and additionally through measurements taken on preoperative radiography. The result for the tunnel center was 38.27%, with a maximum of 56%, a minimum of 12%, and an SD value of 9.32%. The different statistical tests showed a strong correlation between both measurements, with a slightly larger dispersion than the measurement in the frontal plane.

The F test value was 0.002. The t test results showed no difference between both measurements case by case, with t=0.557 and P=.5802.

The angulation of the tibial tunnel axis was measured in relation to the mechanical axis of the tibia. This measurement was carried out on radiography excluding the ankle. Two points located at least 10 cm away enabled the surgeons to define the tibial axis. The angle measurement yielded an average of 13.77°, with a maximum of 27°, a minimum of 2°, and an SD value of 5.15°. With the computer-aided system, the angle was recorded with the axis of the pin of the tibial tunnel and the axis formed by the palpation of the anterior tibial tuberosity and the tibial crest, at 10 cm under the articular joint line as reference. The angle was 8.64°, with a maximum of 20° and a minimum of 0°. The F test value was 0.96. The existence of a relationship was displayed but with a weak correlation. The t test results showed a statistical difference between both measurements case by case, with t=6.287 and P<.0001.

Likewise, the angle of the tibial tunnel was measured in relation to the tibia axis, which was easily measured by the axis formed by the center of the anterior tibial tuberosity and the tibial crest 10 cm under the articular joint line. The average result for this angle was 44.52°, with a maximum of 56°, a minimum of 33°, and an SD value of 5.22°. The computer record displayed an average angle of 51.10°, with a maximum of 59°, a minimum of 32°, and an SD value of 5.51°. The F test value was 0.70. A relationship existed between both measurements, but again, with a weak correlation. The t test result showed a statistical difference between the measurements, case by case, with t= 5.73 and P<.0001.

The position from the center of the femoral tunnel was assessed in millimeters. Radiography recorded an average position of the center of the femoral pin at 5.29 mm from the most posterior part of the lateral condyle, with a maximum of 8 mm, a minimum of 2 mm, and an SD value of 1.41 mm. The computer recorded an angle of 4.96 mm, with a maximum of 13 mm, a minimum of 0 mm, and an SD value of 2.43 mm. The F test value was 0.0003, which proves the strong correlation between both measurements. The t test result showed no difference between both measurements case by case, with t=1.453 and P=.1528.

Discussion

The goal of this study was to establish the reliability of a computer-aided procedure by comparing highly accurate computer-recorded data with radiography data, which were widely used but associated with accuracy problems.

The positions of the tibial tunnel in the sagittal plane and in the frontal plane are in full agreement with the literature on the tibial insertion position of the ACL.^3-6 This is an important point because it enables surgeons to state that the navigation of the tibial tunnel is reliable for this type of procedure.⁷ In comparison with radiography data, the two positions showed little differences with regard to the frontal plane. The agreement is easily explained by the simplicity of taking radiography measurements on the frontal plane with the conventional method and external palpations of the medial and lateral edges of the tibia plateau with the computer-aided method. The risk of error may be low, except in obese patients, which would tend to increase the measured width of the tibia plateau. The use of an extremely rigid ceramic hook made the procedure even more reliable than when using other hooks. A larger risk of error in the sagittal plane exists because of the lack of palpation of the posterior edge of the tibia plateau during the procedure. The computer then relies on the radiography measurement of the depth of the tibia plateau measured on preoperative radiography, explaining the slight discrepancy observed in this series. The reliability of the method can be improved by adding an additional palpation to the procedure.

The comparisons of the angular measurements were problematic. Again, it must be noted that abnormal angulation of the tibial tunnel was neither in the sagittal plane nor in the frontal plane with regard to the conventional technique observed. A discrepancy between the radiography measurements and the computer measurements exists, however, although both measurements evolve in the same direction. It is difficult to conclude if the axis measured on a frontal or sagittal radiograph and the axis determined by the external palpations are exactly the same. The use of slightly different anatomic references in the radiographic measurements important because, although representing the axis of the tunnel is simple, representing the tibial axis particularly on a radiograph without showing the ankle, is quite difficult. Measurement differences result from the inaccuracy of the radiographic measurements, not from the computer or palpations. Finally, the measurement of the position of the femoral tunnel demonstrates the reliability of the computer procedure and the ability to reproduce the surgery using the conventional aiming device. An excellent correlation between the computer data and the radiography measurements is observed. The correlation does not surprise the authors because locating landmarks on a strict profile radiography, and a conventional femur guide (Phusis), was used to place in the pin of the femoral tunnel. The position of the center of this pin was recorded, and the position is in full agreement with the relevant literature.⁸ For a successful, highly accurate navigation, obtaining accurate palpation data is essential. The quality of the palpations depends on the rigidity of the pointer and the accuracy of the points to be palpated. The authors noticed particularly that the palpation of the medial tibia eminence is subject to random variations because its surface is extended in the sagittal plane. Hence, the point is difficult to use. Palpation using the hook of the posterior part of the Blumensaat line is particularly accurate, however.

An effective radiology department capable of reproducing radiography images with consistent enlargement, meeting all criteria to obtain highest-quality frontal and profile views was essential.

Conclusion

The study demonstrated the reliability of the computer-aided procedure in ACL graft surgery under arthroscopy. The study also showed the difficulty of comparing certain computer data with radiography measurement data, particularly angular data. Finally, the evaluation confirmed the reliability of the conventional drill guide compared with the computer aiming device in locating the femoral tunnel.

At the end of the study, the authors confirm the interest of navigation in ACL surgery. Navigation can provide valuable information on potential conflicts with the roof of the notch or the lateral condyle that surgeons might neglect. Also, navigation is a learning tool for less experienced surgeons to learn to avoid errors when placing the tunnels. By continuing this study, the authors are aiming for better accuracy of the palpations, an essential step in making navigation more reliable.

References

1. Panisset J-C, Saragaglia D. Place de la navigation dans la chirurgie du ligament croisé antérieur. Cahiers d’enseignement de la SOFCOT. Ligaments Croisés du Genou. Vol. 86:42-48.
2. Jalliard R, Lavallee S, Dessenne V. Computer-assisted reconstruction of the anterior cruciate ligament. Clin Orthop Relat Res. 1998; 354:57-64.
3. Picard F, Digioia AM, Moody J, et al. Accuracy in tunnel placement for ACL reconstruction. Comparison of traditional arthroscopic and computer assisted navigation techniques. Comput Aided Surg. 2001; 6:279-289.
4. Klos TV, Habets RJ, Banks AZ, et al.. Computer assistance in arthroscopic anterior cruciate ligament reconstruction. Clin Orthop Relat Res. 1998; 5:65-69.
5. Howell SM. Principles for placing the tibial tunnel and avoiding roof impingement during reconstruction of a torn anterior cruciate ligament. Knee Surg Sports Traumatol Arthrosc. 1998;6:S49-S55.
6. Howell SM, Taylor MA. Failure of reconstruction of the anterior cruciate ligament due to impingement by the intercondylar roof. J Bone Joint Surg Am. 1993; 75:1044-1055.
7. Cuomo P, Edwards A, Giron F, et al. Validation of the 65 degrees Howell guide for anterior cruciate ligament reconstruction. Arthroscopy. 2006; 22:70-75.
8. Jackson DW, Gasser SI. Tibial tunnel placement in ACL reconstruction. Arthroscopy. 1994; 10:124-131.
9. Morgan CD, Kalmam VR, Grawl DM. Definitive landmarks for reproducible tibial tunnel placement in anterior cruciate ligament reconstruction. Arthroscopy. 1995; 11:275-288.

Authors

Drs Panisset and Boux de Casson are from the Clinique des Cèdres, Grenoble, France.