Knee Kinematics & Robotics Lab

Mechanobiology Lab | Tissue Mechanics Lab | Shoulder Biomechanics Lab

• Savio L-Y. Woo, PhD, DSc - Director
• Steven Abramowitch, PhD - Associate Director
• Matthew Fisher
• Chris Richards
• Giovanni Zamarra
• Xiaoyan Zhang
• Noah Lorang

The overall goal of this research team is the detailed elucidation of the contribution of the anterior cruciate ligament (ACL) to the intact knee and the evaluation of ACL replacement grafts. Projects performed by this research team are supported by Dr. Woo's NIH grant entitled "In Situ forces in the ACL and its Replacements" that has been ongoing for almost a decade. Several studies are being performed using the robotic/UFS testing system - which combines a 6-DOF manipulator equipped with a universal force-moment sensor. Together, this system can apply various combinations of external loads to the intact knee and record the resulting joint motion. These loads can be simple, such as anterior loading, or more complex, such as combined rotatory loading, simulating clinically relevant situations.

Perhaps more important, however, is that information about the intact ACL can subsequently be utilized to evaluate the success of various techniques of surgical reconstruction of the ACL. In the laboratory, once the ACL is removed from a knee specimen, various reconstructive procedures can be attempted within the same knee specimen. The role of these replacement grafts can then be determined as was done for the intact ACL, and the results compared to the intact ACL to assess the relative success of the reconstruction. Recent progress is further described in these areas: 1) Evaluating ACL replacement grafts, 2) Determination of in-vivo external loads and force in the ACL, and 3) Computational modeling of the knee.

1) All-Inside ACL Reconstruction
ACL reconstruction using hamstrings tendons has recently received much attention. However, use of the hamstrings graft also presents other concerns such as loss of active knee flexion at deeper flexion angles and lower internal tibial torque as well as muscular weakness. The latter directly impacts knee function and stability, as the strength of the hamstring muscles was found to decrease at 9 months after surgery. Further, the semitendinous tendon helps to limit excessive anterior tibial translation when the knee is near full extension. Therefore, it has become known that it may be desirable to preserve as much of the hamstrings tendon as possible during ACL reconstruction, particularly for young and active patients.
Recently, an alternative surgical approach, namely the "All-inside" technique, has been used for ACL reconstruction. In this technique, the femoral and tibial tunnels are only drilled manually halfway through the bone making the length of the graft significantly shorter than traditional methods. As a result, only one hamstrings tendon (semitendinosus or gracilis) folded in triple or quadruple strands is needed as a replacement graft. In a clinical follow-up study (average 29 months), the overall patient satisfaction was good as they could have a rapid return to previous activity, with good muscle function and knee stability. However, it is necessary to validate the clinical findings with quantitative data in terms of restoring knee kinematics in a controlled laboratory study.
Thus, in this project, in collaboration with Let People Move in Perugia-Italy and Innovazione Medica, we wish to determine if the use of one hamstring tendon (semitendinosus or gracilis) graft in the "All-inside" technique for ACL reconstruction could restore normal knee kinematics and in-situ force of the ACL to the level of an intact knee. To do this, we will apply anterior tibial and combined rotatory loads using a robotic/UFS testing system between full extension and 120° of knee flexion, and measured and compared the resulting 5 degrees of freedom (DOF) kinematics and in situ forces of the ACL of the intact knee, as well as those of the ACL reconstructed knees.


A high payload robot
     
A)                                B)
Schematics of the "All-inside Technique" showing A) manual drill inserted through tibial bone tunnel, and B) the "drill-wings" turned out such that the bone tunnel can be manually drilled from the inside of the knee joint.

2) Determination of in-vivo external loads and force in the ACL
Each year, approximately 1 in 3000 people in the United States alone rupture their ACL. Among a younger population (age 15 to 45 years old), the incidence of ACL injury is even higher, elevated to one in 1,750. Furthermore, women are at a two to eight times greater risk for ACL injury than men while participating in the same sports. This high incidence in females, coupled with the increasing number of female participants in sports, has led many people to consider this an epidemic. Thus, the subject has drawn increasing attention from investigators. However, the intraarticular position of the ACL poses significant challenges for studying its in vivo function.
With our collaborators at the Steadman-Hawkins Research Foundation, we have recently been able to develop a novel method for determining the in vivo ACL forces resulting from a dynamic jump landing. Kinematic data from subjects landing from a jump will be collected at our collaborator's lab using a biplane fluoroscopy system. The system tracks the movements of the tibia and femur at 1000 Hz with high precision and accuracy during the dynamic jump landing. This data can then be input into our high payload robot and replayed on cadaveric knees in our lab. By the principle of superposition, we can then determine the in vivo force in the ACL resulting from dynamic jump landing.

      
A rendering (left) of our dual fluoroscopy system imaging the knee (right). The system is capable of imaging from the the ankle to the neck and can be adjusted for different subject heights or landing platforms.


Example of the tracking analysis of one frame during a dynamic jump landing. Bone geometries reconstructed from CT scans are automatically matched onto calibrated fluoroscopy images after their contours are detected semi-automatically.

3) Computational modeling of the knee
Finite element (FE) modeling has been demonstrated as a powerful tool to study the biomechanical function of biological tissues. It can provide information otherwise difficult to obtain from experiments, such as stress and strain distribution, to help to understand the mechanisms of injury, design optimal reconstruction and rehabilitation protocols, and understand the environment of ACL remodeling. However, the reliability of the model strongly depends on an appropriate geometrical reconstruction and accurate mathematical descriptions of the behavior of the tissues. Thus, the objective of this study was to build a subject-specific FE model of the ACL to analyze its stress and strain distribution under an 134 N anterior tibial load at full extension, 30° and 60° flexion, as well as under combined rotatory loads at 15° and 30° flexion. Compared to previous models, this model considered the irregular hourglass shape of ACL as well as the spiral orientation of its fiber bundles, which was incorporated into a transversely isotropic constitutive model. We hypothesize that under the anterior tibial load, when the knee joint moves to higher flexion angles, the peak stress will shift from the posterior portion of the ACL to the anterior portion of the ACL. Under the combined rotatory loads, we further hypothesize that the peak stress will be located in the posterior portion of the ACL. The resultant force predicted by the model will be validated by comparing to the experimental forces determined using the robotic/UFS testing system.
   
A)                        B)
A)ACL digitization to get its geometry B)Reconstructed ACL geometry and its fiber orientation.

Vercillo, F., Noorani, S., Dede, O., Woo, S.L-Y.: Determination of a Safe Range of Knee Flexion Angles for Fixation of Grafts in Double Bundle ACL Reconstruction: A Human Cadaveric Study. Am. J. of Sports Medicine, 35(9):1513-1520, 2007. Giffin, J.R., Stabile, K.J., Zantop, T., Vogrin, T.M., Woo, S.L-Y., Harner, C.D.: Importance of Tibial Slope for Stability of the PCL Deficient Knee. Am. J. of Sports Medicine, 35(9):1443-1449, 2007. Darcy, S.P., Kilger, R.H.P., Woo, S.L-Y., Debski, R.E.: Estimation of ACL Forces by Reproducing Kinematics Between Sets of Knees: A Novel Non-Invasive Methodology. J. of Biomechanics, 39(13):2371-2377, 2006. Moore, S., Thomas, M., Woo, S.L-Y., Gabriel, M., Kilger, R., Debski, R.: A Novel Methodology to Reproduce Previously Recorded Six-Degree of Freedom Kinematics on the Same Diarthrodial Joint. J. of Biomechanics, 39(10):1914-1923, 2006. Kilger, H.P., Stehle, J., Fisk, J.A., Thomas, M., Miura, K. Woo, S.L-Y.: Anatomic Double Bundle Reconstruction after Valgus High Tibial Osteotomy: A Biomechanical Study. Am. J. of Sports Medicine, 34(6):961-967, 2006. Yamamoto, Y., Hsu, W.H., Fisk, J.A., Van Scyoc, A.H., Miura, K., Woo, S.L-Y.: The Effect of the Iliotibial Band on Knee Biomechanics during a Simulated Pivot Shift Test. J. of Orthopaedic Research, 24(5):811-819, 2006. Hsu, W.H., Fisk, J. A., Yamamoto, Y., Debski, R.E., Woo, S.L-Y.: Differences in Torsional Joint Stiffness of the Knee Between Genders - A Human Cadaveric Study. Am. J. of Sports Medicine, 34(5):765-770, 2006. Miura, K., Woo, S.L-Y., Brinkley, R., Fu, Y.C., Noorani, S.: Effects of Knee Flexion Angles for Graft Fixation on Its Force Distribution in Double Bundle Anterior Cruciate Ligament Reconstruction. Am. J. of Sports Medicine, 34(4):577-585, 2006. Margheritini, F., Rihn, J.A., Mauro, C.S., Stabile, K.J., Woo, S.L-Y., Harner, C.D.: Biomechanics of Initial Tibial Fixation in Posterior Cruciate Ligament Reconstruction. Arthroscopy, 21(10):1164-1171, 2005. Kilger, R., Thomas, M., Hanford, S., Alaseirlis, D., Pässler, H., and Woo, S.L-Y.: The Effectiveness of Reconstruction of the Anterior Cruciate Ligament Using the Novel Knot/ Pressfit Technique: A Cadaveric Study. Am. J. of Sports Medicine, 33(6):856-863, 2005. Yamamoto Y, Hsu WH, Woo SL-Y, VanScyoc A, Takakura Y, Debski R. Knee Stability and Graft Function Following ACL Reconstruction: A Comparision of a Lateral and an Anatomic Femoral Tunnel Placement. Am. J. of Sports Medicine, 32(8):1825-1832, 2004 Song, Y, Debski, RE, Musahl, V, Thomas, M, Woo, SL-Y. A three-dimensional finite element model of the human anterior cruciate ligament: a computational analysis with experimental validation. J Biomech. 2004 March 37(3): 383-90 Gabriel MT, Wong EK, Woo SL-Y, Yagi M, Debski RE. Distribution of in situ forces in the anterior cruciate ligament in response to rotatory loads. J Orthop Res. 2004 Jan;22(1):85-9. Gao F, Li S, Li ZM, Latash ML, Zatsiorsky VM. Matrix analyses of interaction among fingers in static force production tasks. Biol Cybern. 2003 Dec;89(6):407-14. Fukuda Y, Woo SL-Y, Loh JC, Tsuda E, Tang P, McMahon PJ, Debski RE. A quantitative analysis of valgus torque on the ACL: a human cadaveric study. J Orthop Res. 2003 Nov;21(6):1107-12. Kanamori A, Lee JM, Haemmerle MJ, Vogrin TM, Harner CD. A biomechanical analysis of two reconstructive approaches to the posterolateral corner of the knee. Knee Surg Sports Traumatol Arthrosc. 2003 Sep;11(5):312-7. Musahl V, Burkart A, Debski RE, Van Scyoc A, Fu FH, Woo SL-Y. Anterior cruciate ligament tunnel placement: Comparison of insertion site anatomy with the guidelines of a computer-assisted surgical system. Arthroscopy 19:154-60, 2003. Loh JC, Fukuda Y, Tsuda E, Steadman RJ, Fu FH, Woo SL-Y. Knee stability and graft function following anterior cruciate ligament reconstruction: Comparison between 11 o'clock and 10 o'clock femoral tunnel placement. Arthroscopy 19:297-304, 2003. Musahl V, Abramowitch SD, Gabriel MT, Debski RE, Hertel P, Fu FH, Woo SL-Y. Tensile properties of an anterior cruciate ligament graft after bone-patellar tendon-bone press-fit fixation. Knee Surg Sports Traumatol Arthrosc 11:68-74, 2003.