Accuracy of anterior cruciate ligament tunnel placement with an active robotic system: a cadaveric study

Editorial Commentary: Computer-Assisted Surgery Has Already Arrived in Sports Medicine, and Robots Are Next

Robot-assisted surgery (RAS) is a procedure in which a computerized system actively interacts with surgical instruments to perform specific tasks independent of the human surgeon. This is distinguished from computer-aided navigation (CAN) by the independence of the computer system. Navigation tells the surgeon what to do, whereas RAS does (some of) it. Both RAS and CAN are simply two subcomponents of computer-assisted surgery (CAS). CAS is the application of digital technology to improve surgical precision through improved training/education, surgical planning, anatomic alteration, and/or implant placement. Everything from arthroscopic simulators (and eventually, virtual reality) used to train residents, to patient-specific implants (for knee osteotomies), to augmented reality headsets to guide minimally invasive procedures, to RAS and CAN, fall under the umbrella of CAS. The eventual adoption of robot-assisted surgery for orthopaedic sports medicine and arthroscopy procedures is inevitable and will dramatically improve the precision with which we perform surgery.

The 45° and 60° of sagittal femoral tunnel placement in anterior cruciate ligament reconstruction provide similar knee stability

PURPOSE

The aim of the present study was to compare 45° and 60° of sagittal femoral tunnel angles in terms of anterior tibial translation (ATT), valgus angle and graft in situ force following anterior cruciate ligament reconstruction (ACLR).

METHODS

Ten porcine knees were subjected to the following loading conditions: (1) 89 N anterior tibial load at 35° (full extension), 60° and 90° of knee flexion and (2) 5 N m valgus tibial moment at 35° and 45° of knee flexion. ATT and graft in situ force of the intact anterior cruciate ligament (ACL) and ACLR were collected using a robotic universal force/moment sensor (UFS) testing system for (1) ACL intact, (2) ACL-deficient (ACLD) and (3) two different ACLR using different sagittal femoral tunnel angles (coronal 45°/sagittal 45° and coronal 45°/sagittal 60°).

RESULTS

During the anterior tibial load, the femoral tunnel angle of ACLR knees at coronal 45°/sagittal 45° and 60° had significantly higher ATT than that of the ACL-intact knees at 60° of knee flexion (p < 0.05). The femoral tunnel angle of ACLR knees at coronal 45°/sagittal 60° had significantly lower graft in situ force than that of the ACL-intact knees at 60° and 90° of knee flexion (p < 0.05). During the valgus tibial moment, the femoral tunnel angle of ACLR knees at coronal 45°/sagittal 45° and 60° had significantly lower graft in situ force than that of the ACL-intact knees at all knee flexions (p < 0.05).

CONCLUSIONS

The femoral tunnel angle of ACLR knees at coronal 45°/sagittal 45° provided similar ATT, valgus angle and graft in situ force to that of ACLR knees at coronal 45°/sagittal 60°. Therefore, both femoral tunnel angles could be used in ACLR, as the sagittal femoral tunnel angle does not appear to be relevant in post-operative knee stability.

LEVEL OF EVIDENCE

Not applicable.

Radiological evaluation of tunnel position in single bundle anterior cruciate ligament reconstruction in the Indian population and their clinical correlation

BACKGROUND

Proper positioning of osseous tunnels during single bundle arthroscopic ACL reconstruction, which gives reproducibly good clinical outcome, is a matter of concern. Little evidence is there correlating tunnel position in arthroscopic ACL reconstruction with their clinical outcome in Indian population. Our aim in this study was to examine if the radiological tunnel-positions were significantly associated to the clinical outcomes.

METHODS

ACL reconstruction was performed in 147 young patients with an isolated ACL tear. They were followed up prospectively for the next two years. Clinical assessment of each patient was done using the International Knee Documentation Committee (IKDC) evaluation form before surgery and at two years later the surgery. At the same time, the radiological assessment was done on standard digital radiographs.

RESULTS

Considering the anterior and posterior-most points on the Blumensaat's line as 0% and 100% respectively the average position of the femoral tunnel was at 84.8%. Similarly, the tibial tunnel was at 46.8% along the tibial plateau. On the coronal plane the average position of the tibial tunnel was at 45.6% point along the tibial plateau (measured from the medial-most point towards laterally). The mean position of the femoral tunnel in the coronal plane was at 43.2% along the broadest part of the distal femur (measured from the lateral extent). The average inclination angle of the graft measured 19.6° (along the coronal plane).

CONCLUSION

Ideal clinical outcome was significantly associated with the placement of the femoral tunnel along the sagittal plane. Placement of the femoral tunnel should not be beyond the 85% mark along the Blumensaat's line from the anterior-most point. No correlation was established between clinical results and any of the remaining radiological parameters described above.

Three dimensionalCT analysis of femoral tunnel position after ACL reconstruction. A prospective study of one hundred and thirty five cases

BACKGROUND

One of the principal causes for failure of anterior cruciate ligament reconstruction (ACL) is femoral tunnel mal-position. Several studies compare the position of femoral tunnels achieved with various techniques, with small series and using a quadrant assessment method.

QUESTIONS

(1) What is the incidence of anatomical positioning of the intra-articular femoral tunnel aperture in primary ACL reconstruction in a university knee surgery? (2) What are the main errors in positioning?

METHODS

3D-CT scans were performed after primary ACL reconstruction in 135 consecutive cases. The intra-articular position of the femoral tunnel aperture was analyzed using the Magnussen classification.

RESULTS

The intra-articular tunnel position was deemed anatomical in 77%, intermediate in 20.8%, and non-anatomical in 2.2%. Among the mal-positioned tunnels, 54.8% were vertical, 29% were anteriorly positioned, and 16.1% were both.

CONCLUSIONS

The intra articular femoral tunnel aperture was well positioned using an outside-in technique. The main error of tunnel positioning was a tunnel too vertical.

LEVEL OF EVIDENCE

Level III, prospective study (case series).

Basic biomechanic principles of knee instability

Motion at the knee joint is a complex mechanical phenomenon. Stability is provided by a combination of static and dynamic structures that work in concert to prevent excessive movement or instability that is inherent in various knee injuries. The anterior cruciate ligament (ACL) is a main stabilizer of the knee, providing both translational and rotatory constraint. Despite the high volume of research directed at native ACL function, pathogenesis and surgical reconstruction of this structure, a gold standard for objective quantification of injury and subsequent repair, has not been demonstrated. Furthermore, recent studies have suggested that novel anatomic structures may play a significant role in knee stability. The use of biomechanical principles and testing techniques provides essential objective/quantitative information on the function of bone, ligaments, joint capsule, and other contributing soft tissues in response to various loading conditions. This review discusses the principles of biomechanics in relation to knee stability, with a focus on the objective quantification of knee stability, the individual contributions of specific knee structures to stability, and the most recent technological advances in the biomechanical evaluation of the knee joint.

Accuracy of a computer-assisted planning and placement system for anatomical femoral tunnel positioning in anterior cruciate ligament reconstruction

BACKGROUND

Femoral tunnel positioning is a difficult, but important factor in successful anterior cruciate ligament (ACL) reconstruction. Computer navigation can improve the anatomical planning procedure besides the tunnel placement procedure.

METHODS

The accuracy of the computer-assisted femoral tunnel positioning method for anatomical double bundle ACL-reconstruction with a three-dimensional template was determined with respect to both aspects for AM and PL bundles in 12 cadaveric knees.

RESULTS

The accuracy of the total tunnel positioning procedure was 2.7 mm (AM) and 3.2 mm (PL). These values consisted of the accuracies for planning (AM:2.9 mm; PL:3.2 mm) and for placement (about 0.4 mm). The template showed a systematic bias for the PL-position.

CONCLUSIONS

The computer-assisted templating method showed high accuracy for tunnel placement and has promising capacity for application in anatomical tunnel planning. Improvement of the template will result in an accurate and robust navigation system for femoral tunnel positioning in ACL-reconstruction.

Anterior cruciate ligament reconstruction: can anatomic femoral placement be achieved with a transtibial technique?

BACKGROUND

Recent reports have suggested that a traditional transtibial technique cannot practically accomplish an anatomic anterior cruciate ligament (ACL) reconstruction.

HYPOTHESIS

The degree to which a transtibial technique can anatomically position both tibial and femoral tunnels is highly dependent on tibial tunnel starting position.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Eight fresh-frozen adult knee specimens were fixed at 90° of flexion and then dissected to expose the femoral and tibial ACL footprints. After the central third patellar tendon length was measured for each specimen, computer-assisted navigation was used to identify 2 idealized tibial tunnel starting points, optimizing alignment with the native ligament in the coronal plane but distal enough on the tibia to provide manageable bone-tendon-bone autograft-tibial tunnel mismatch (point A = 10-mm mismatch; point B = 0-mm mismatch). Tibial tunnels were then reamed to the center of the tibial insertion using point A in half of the knees and point B in the other half. Guide pin positioning on the femoral side was then assessed before and after tibial tunnel reaming, after beveling the posterolateral tibial tunnel rim, and after performing a standard notchplasty. After the femoral tunnel was reamed, the digitized contours of the native insertions were compared with those of both tibial and femoral tunnels to calculate percentage overlap.

RESULTS

Starting points A and B occurred 15.9 ± 4.5 mm and 33.0 ± 3.3 mm distal to the joint line, respectively, and 9.8 ± 2.4 mm and 8.3 ± 4.0 mm from the medial edge of the tibial tubercle, respectively. The anterior and posterior aspects of both tibial tunnels' intra-articular exits were within a few millimeters of the native insertion's respective boundaries. After the tibial tunnel was reamed from the more proximal point A, a transtibial guide pin was positioned within 2.1 ± 1.6 mm of the femoral insertion's center (vs 9.3 ± 1.9 mm for point B; P = .02). After beveling a mean 2.6 mm from the back of the point A tibial tunnels, positioning improved to within 0.3 ± 0.7 mm from the center of the femoral insertion (vs 4.2 ± 1.1 mm for the point B tibial tunnels; P = .008). Compared with the more distal starting point, use of point A provided significantly greater insertional overlap (tibial: 97.9% ± 1.4% vs 71.1% ± 15.1%, P = .03; femoral: 87.9% ± 9.2% overlap vs 59.6% ± 8.5%, P = .008). No significant posterior femoral or tibial plateau breakthrough occurred in any specimen.

CONCLUSION

Tibial and femoral tunnels can be positioned in a highly anatomic manner using a transtibial technique but require careful choice of a proximal tibial starting position and a resulting tibial tunnel that is at the limits of practical. Traditional tibial tunnel starting points will likely result in less anatomic femoral tunnels.

CLINICAL RELEVANCE

A transtibial single-bundle technique can accomplish a highly anatomic reconstruction but does require meticulous positioning of the tibial tunnel with little margin for error and some degree of graft-tunnel mismatch.

Development of a femoral template for computer-assisted tunnel placement in anatomical double-bundle ACL reconstruction

Femoral graft placement is an important factor in the success of anterior cruciate ligament (ACL) reconstruction. In addition to improving the accuracy of femoral tunnel placement, Computer Assisted Surgery (CAS) can be used to determine the anatomic location. This is achieved by using a 3D femoral template which indicates the position of the anatomical ACL center based on endoscopically measurable landmarks. This study describes the development and application of this method. The template is generated through statistical shape analysis of the ACL insertion, with respect to the anteromedial (AM) and posterolateral (PL) bundles. The ligament insertion data, together with the osteocartilage edge on the lateral notch, were mapped onto a cylinder fitted to the intercondylar notch surface (n = 33). Anatomic variation, in terms of standard variation of the positions of the ligament centers in the template, was within 2.2 mm. The resulting template was programmed in a computer-assisted navigation system for ACL replacement and its accuracy and precision were determined on 31 femora. It was found that with the navigation system the AM and PL tunnels could be positioned with an accuracy of 2.5 mm relative to the anatomic insertion centers; the precision was 2.4 mm. This system consists of a template that can easily be implemented in 3D computer navigation software. Requiring no preoperative images and planning, the system provides adequate accuracy and precision to position the entrance of the femoral tunnels for anatomical single- or double-bundle ACL reconstruction.

Anterior cruciate ligament tibial guide pin accuracy and surgical precision: comparing 3.0-mm and 2.4-mm guide pins

PURPOSE

The purpose of this study was to evaluate the accuracy of a 3.0-mm-diameter anterior cruciate ligament (ACL) tibial guide pin versus a standard, 2.4-mm drill-tipped guide pin. A secondary purpose was to evaluate surgeon precision in identifying the true (anatomic) center of the ACL tibial footprint using arthroscopic visualization.

METHODS

Five matched pairs of cadaveric knees were disarticulated, leaving a well-defined footprint of the ACL on the tibial plateau. The tibial footprint was digitally recorded by a bioengineer, and the true center of the footprint was calculated. Next, using arthroscopic visualization, a surgeon identified and marked his estimation of the true center of the ACL tibial footprint. This mark was then digitally recorded by the bioengineer and compared with the calculated center, allowing quantification of surgeon anatomic precision. Finally, under arthroscopic visualization, the surgeon was given 1 attempt to aim and drill the guide pin to his mark. Pin position was digitally recorded; the distance of the drill pin from the mark quantifies drill pin placement accuracy.

RESULTS

Mean accuracy for the 3.0-mm guide pin was 2.87 +/- 1.19 mm versus 6.98 +/- 1.29 mm for the 2.4-mm pin. The difference was significant (P = .005). Surgeon anatomic precision was 3.32 +/- 2.10 mm.

CONCLUSIONS

Our results show that a 3-mm ACL tibial guide pin is significantly more accurate than a 2.4-mm-diameter pin. The 3-mm pin accuracy is within the range of surgeon precision; the 2.4-mm pin accuracy is not.

CLINICAL RELEVANCE

Pin accuracy and surgeon precision are clinically relevant measures because anatomic tunnel placement is a determinant of ACL reconstruction outcome.

Functional outcomes and health-related quality of life after robot-assisted anterior cruciate ligament reconstruction with patellar tendon grafts

During a short period of time, surgical robots had been propagated for automated tunnel placement in anterior cruciate ligament (ACL) reconstruction. Clinical outcome data are currently unavailable. Between 2000 and 2003, 152 patients underwent ACL replacement with the assistance of the Computer Assisted Surgical Planning and Robotics system (CASPAR, OrtoMaquet, Germany) at our hospital. After minimal invasive pin placement in both the tibia and femur, computed tomography was used to register anatomical landmarks and to plan graft tunnel alignment. The robot was used to drill tibial and femoral tunnels in an outside-in fashion according to pre-operative planning. There was one procedure-specific Serious Adverse Event (i.e., an intraoperative transection of the posterior cruciate ligament). After IRB approval, all patients were invited for a follow-up examination. Data from 100 patients (35 women, 65 men, mean age 35 [SD 11] years, median follow-up 61 [range 42-77] months) form the basis of this report. Side-to-side differences in anterior laxity were measured with the KT-1000 arthrometer. Patient-centered outcomes included the Lysholm-Score, the lower extremity functional scale (LEFS), and the Short Form 36 (SF36). The mean KT-1000 side-to-side difference was 0.89 [95% confidence interval (CI) 0.52-1.26] mm. Eight and five patients had a positive Lachman and pivot shift test, respectively. The Lysholm-Score averaged 86 (95% CI 83-89) points. Excellent, good, fair, and poor outcomes were reported by 38, 32, 20, and 10 patients. The LEFS averaged 85 (95% CI 82-88) points. The mean SF36 Physical Component Score was 48.4 (95% CI 46.5-50.3), indicating residual deficits compared to the population norm. All tibial graft tunnels did not cross the Blumensaat line, but were placed slightly anterior to the optimal center of 42% reported in previous studies. Compared to literature data, robot-assisted ACL reconstruction with BTB grafts may lead to higher knee stability, but poorer functional outcomes. The immense additional efforts with the procedure did not pay off in a benefit to patients.

A novel methodology to reproduce previously recorded six-degree of freedom kinematics on the same diarthrodial joint

The objective of this study was to develop a novel method to more accurately reproduce previously recorded 6-DOF kinematics of the tibia with respect to the femur using robotic technology. Furthermore, the effect of performing only a single or multiple registrations and the effect of robot joint configuration were investigated. A single registration consisted of registering the tibia and femur with respect to the robot at full extension and reproducing all kinematics while multiple registrations consisted of registering the bones at each flexion angle and reproducing only the kinematics of the corresponding flexion angle. Kinematics of the knee in response to an anterior (134 N) and combined internal/external (+/-10 N m) and varus/valgus (+/-5 N m) loads were collected at 0 degrees , 15 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion. A six axes, serial-articulated robotic manipulator (PUMA Model 762) was calibrated and the working volume was reduced to improve the robot's accuracy. The effect of the robot joint configuration was determined by performing single and multiple registrations for three selected configurations. For each robot joint configuration, the accuracy in position of the reproduced kinematics improved after multiple registrations (0.7+/-0.3, 1.2+/-0.5, and 0.9+/-0.2 mm, respectively) when compared to only a single registration (1.3+/-0.9, 2.0+/-1.0, and 1.5+/-0.7 mm, respectively) (p<0.05). The accuracy in position of each robot joint configuration was unique as significant differences were detected between each of the configurations. These data demonstrate that the number of registrations and the robot joint configuration both affect the accuracy of the reproduced kinematics. Therefore, when using robotic technology to reproduce previously recorded kinematics, it may be necessary to perform these analyses for each individual robotic system and for each diarthrodial joint, as different joints will require the robot to be placed in different robot joint configurations.

Varying femoral tunnels between the anatomical footprint and isometric positions: effect on kinematics of the anterior cruciate ligament-reconstructed knee

BACKGROUND

Knee kinematics and in situ forces resulting from anterior cruciate ligament reconstructions with 2 femoral tunnel positions were evaluated.

HYPOTHESIS

A graft placed inside the anatomical footprint of the anterior cruciate ligament will restore knee function better than a graft placed at a position for best graft isometry.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ten cadaveric knees were tested in response to a 134-N anterior load and a combined 10-N.m valgus and 5-N.m internal rotation load. A robotic universal force-moment sensor testing system was used to apply loads, and resulting kinematics were recorded. An active surgical robot system was used for positioning tunnels in 2 locations in the femoral notch: inside the anatomical footprint of the anterior cruciate ligament and a position for best graft isometry. The same quadrupled hamstring tendon graft was used for both tunnel positions. The 2 loading conditions were applied.

RESULTS

At 30 degrees of knee flexion, anterior tibial translation in response to the anterior load for the intact knee was 9.8 +/- 3.1 mm. Both femoral tunnel positions resulted in significantly higher anterior tibial translation (position 1: 13.8 +/- 4.6 mm; position 2: 16.6 +/- 3.7 mm; P < .05). There was a significant difference between the 2 tunnel positions. At the same flexion angle, the anterior tibial translation in response to the combined load for the intact knee was 7.7 +/- 4.0 mm. Both femoral tunnel positions resulted in significantly higher anterior tibial translation (position 1: 10.4 +/- 5.5 mm; position 2: 12.0 +/- 5.2 mm; P < .05), with a significant difference between the tunnel positions.

CONCLUSION

Neither femoral tunnel position restores normal kinematics of the intact knee. A femoral tunnel position inside the anatomical footprint of the anterior cruciate ligament results in knee kinematics closer to the intact knee than does a tunnel position located for best graft isometry.

CLINICAL RELEVANCE

Anatomical femoral tunnel position is important in reproducing function of the anterior cruciate ligament.