Analysis of three-dimensional in vivo knee kinematics using dynamic magnetic resonance imaging

Analysis of Three-Dimensional In Vivo Knee Kinematics Using Dynamic Magnetic Resonance Imaging C. Benjamin Ma, MD, Keh-yang Lee, PhD, Mark A. Schrumpf, BA, and Sharmila Majumdar, PhD Patients continue to develop premature arthritis despite good subjective and objective evaluations of anterior cruciate ligament (ACL) reconstructed knees. Current objective evaluations have been limited to muscle strength examination, radiographic imaging, and laxity measurements. Anterior–posterior laxity measurements were originally developed to diagnose ACL insufficiencies; however, their application has been broadened to evaluate the success of ACL reconstructions. Although we recognize the importance of the meniscal function in preventing osteoarthritis, we do not have any means to evaluate meniscal kinematics after ACL injuries and reconstruction. In this article, we will highlight the importance of developing new methods in evaluating in vivo tibiofemoral and meniscal kinematics under dynamic conditions. We will also present our recent work on magnetic resonance analysis of knee kinematics under simulated weight-bearing conditions. We hope that we can extend this technique in dynamic evaluation of cruciate ligament injured knees. With better quantification of three-dimensional tibiofemoral and meniscal kinematics, we hope that we can improve our ability to diagnose, treat and critically evaluate our reconstructions for the cruciate ligament injured patients. Oper Tech Orthop 15:57-63 © 2005 Elsevier Inc. All rights reserved. KEYWORDS knee, anterior cruciate ligament, meniscus, magnetic resonance imaging

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hort-term follow-up studies of anterior cruciate ligament (ACL) reconstructions have documented high success rates; however, long-term follow-up studies have been less encouraging. ACL reconstructions can still lead to premature osteoarthritis despite good objective stability measurements. The clinical experience clearly demonstrates a lack of understanding and basic science knowledge regarding knee kinematics after ACL deficiency and reconstruction. Currently, clinicians rely mostly on stability examinations on evaluating ACL-deficient knees. There are no current means that allow dynamic testing of the knee during various motions when the patients are symptomatic. The lack of detection severely hampered our ability to stratify patients after

Department of Orthopaedic Surgery, University of California San Francisco, San Francisco, CA Supported in part by NIH-RO1AR1776, and AOSSM Young Investigator’s Award. Address reprint requests to C. Benjamin Ma, MD, Assistant Professor in Residence, University of California, San Francisco, Department of Orthopaedic Surgery, 500 Parnassus Avenue, MU 320W, San Francisco, CA 94143-0728. E-mail: [email protected]

1048-6666/05/$-see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1053/j.oto.2004.10.013

ACL deficiency. Moreover, all our treatment modalities, such as bracing, primary repair, and reconstructions are evaluated based on examinations such as radiographs, muscle strength, and laxity measurements. These are not “dynamic” tests that can detect pathology or symptoms that are usually present during activities. All our current stability measurements have been on tibiofemoral translations. Although we know the importance of the meniscus in preventing premature osteoarthritis and the interdependence between the medial meniscus and ACL, we have failed to focus on the significance of changes in meniscus kinematics after ACL injuries.

Three-Dimensional Knee Kinematics Various techniques have been used to quantify the motion that occurs at the knee joint. These include the use of goniometers, 6-degrees-of-freedom linkage systems, optical tracking systems, the application of roentgen-stereophotogrammetry, and robotic technology. Goniometers have been 57

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58 used in the past; however, these are fairly imprecise and difficult to characterize motion that has 6° of freedom.1,2 The accuracy depends highly on the interface between the skin and the linkage itself.3 Modifications have include cortical pins that enable fixation of the linkage system to bone; however, this modification is only applicable to cadaveric specimens.4-6 Optical tracking systems have evolved significantly over the years and have been used extensively to study knee kinematics in those patients who have ACL-deficient knees and in those who have undergone total knee-replacement surgery. They are versatile systems that allow the investigation of knee kinematics throughout various knee motions, such as stair-climbing, gait analysis, and cutting motion.7-9 Roentgen-stereophotogrammetry has been used to characterize knee motion by determining the amount of translation between bony landmarks. Biplanar photography has to been used to characterize the complex 6-degree-of-freedome knee motion.10-12 This method is more time-consuming and requires long exposure to radiation. Robotic technology is an innovative methodology that has been used to study kinematics in cadaveric knees.13-16 Combining the robotic manipulator, a highly accurate spatial linkage device, with a force moment sensor, the system consists of a feedback loop between knee kinematics and force vector measurement. Extensive research has been performed using robotic technology to study variables in ACL and posterior cruciate ligament (PCL) reconstructions, in situ forces in ligament grafts,17,18 and the significance of multiligament injuries.19,20 However, this current technology has been limited to the use in only cadaveric specimens. All the above systems have allowed accurate measurements of knee kinematics; however, these methods are limited to measuring kinematics of the whole knee joint, namely the relative position between the femur and the tibia. Until recently, there has been no existing device that allows measurement of in vivo kinematics of intra-articular structures. Determining in vivo kinematics of intraarticular structures is difficult and challenging secondary to their inaccessibility within the knee. Magnetic resonance imaging (MRI) has revolutionized the field of radiology. It provided a noninvasive method in evaluating soft tissue structures. Its application in the field of orthopaedics has changed the management of various common orthopaedic ailments. Injuries to intraarticular structures, such as the menisci, cruciate ligament, and collateral ligaments, can be accurately identified preoperatively using MRI.21-24 Menisci motion in the cadaveric knee has been evaluated using MRI.25,26 Even though this study was performed in cadaveric specimens, it was one of the early studies on kinematic MRI of the knee joint in evaluating motion of an intraarticular structure. Dynamic imaging can provide insights on injury mechanisms as well as treatment protocols. Currently, limited dynamic or kinematic MRI has been used in the analysis of patellofemoral joint mechanics, ligament insufficiencies and shoulder instability.27-30 Logan and coworkers30 examined tibiofemoral kinematics in ACL-deficient knees by using an open MRI system under weight-bearing conditions and found anterior subluxation of

the lateral tibial plateau. Scarvell and coworkers31 compared tibiofemoral contact with movement of the femoral condylar centers in ACL-deficient knees by using a closed MR scanner under weight-bearing conditions. Both studies have shown that MRI can be used to study tibiofemoral kinematics. Although the open MR scanners used in some of the previous studies allow for greater knee flexibility, they are generally limited by lower magnetic field strength and poorer image quality. Moreover, to investigate the knee stability and the risk of injury in meniscus after rupture of the ACL, a simultaneous analysis of tibiofemoral and meniscal kinematics under weight-bearing conditions is necessary.

ACL Reconstructions ACL reconstructions are now routinely performed after ACL injuries. The results of ACL reconstructions have improved tremendously with the evolution of a more anatomic and functional reconstruction. Reconstruction of the ACL using biologic grafts is now considered the “gold standard” for ACL reconstructions. Many studies have reported 85% to 95% success rate in short-term follow-up studies.32-50 Even though most of the patients can return to their previous sporting activities, there are still a high number of re-ruptures, persistent pain, and early arthritis recorded in longterm follow-up studies.51,52 A bone scan of the ACL reconstructed knee shows abnormalities even years after the reconstruction.53,54 These reports have stimulated researchers to improve their reconstructive techniques and also search for means of better evaluating the ACL reconstructed knee. ACL-reconstructed knees are currently being evaluated using subjective criteria, such as the patients’ symptoms with daily activities and functional tests. Objective evaluations focus mainly on laxity examinations, quadriceps strength, and radiographic findings.55,56 These information are useful; however, they do not address the direct question on whether the ACL-reconstructed knee can restore the normal biomechanics of the knee joint itself. As mentioned earlier, laxity measurements only address anterior–posterior translations but do not account for rotational stability. Although the ACL is a primary restraint for anterior translation, it is also plays a key role in rotatory stability of the knee. Currently, there have been no studies on whether ACL reconstruction can restore in vivo kinematics of the menisci and cruciate ligaments and normal tibiofemoral kinematics during motion. Despite having high subjective knee scores and stable laxity measurements after ACL reconstructions, some patients can still develop premature arthritis. A more comprehensive and detail objective evaluation of the knee is crucial to determine the success of current treatment of ACL insufficiencies. ACL reconstructions have traditionally been reconstructed using the “single-bundle” technique, with one femoral and one tibial tunnel. The intact ACL consists of 2 bundles, namely the anteromedial and posterolateral bundle, which tightens and loosens at various flexion angles.57,58 Concerns have been voiced on whether a “single-bundle” ACL reconstruction is able to duplicate the complex biomechanical be-

3D In vivo knee kinematics using dynamic MRI havior of the ACL. More specifically, there have been concerns with rotatory stability after single-bundle ACL reconstructions. Biomechanical studies have demonstrated that double-bundle ACL reconstruction can better restore rotational control in the ACL deficient knees.59 The theory behind the double-bundle reconstruction is the anatomic restoration of the 2-bundle intact ACL.60,61 Although in cadaveric evaluations anatomic ACL reconstructions can have better rotational stability, it has yet to be demonstrated clinically.59 This novel reconstruction still lack long-term clinical follow-up. Current objective measurements do not allow us to determine the efficacy of rotational control of surgical reconstructions, better objective evaluations are required to assess the success of surgical treatments. The objective of this work is to determine the changes in knee kinematics after ACL insufficiency and reconstructions and, more importantly, to better quantify 3-dimensional tibiofemoral kinematics and in vivo meniscal kinematics. In this article, we will present some of our preliminary work on the effect of simulated squat in the ACL deficient and intact knee using MRI. In this study, we used an axial loading apparatus to determine the changes in meniscal and tibiofemoral kinematics using a weight-bearing MRI. By using a weight-bearing MRI, we aim to (1) establish an in vivo analytical method for meniscal and tibiofemoral kinematics using high-field MRI and (2) study the changes in in vivo meniscal and tibiofemoral kinematics in ACL insufficient knees.

Materials and Methods Dynamic MRI MRI scans are acquired with a Signa 1.5-T echo-speed system (GE Medical Systems, Waukesha, WI) and a dual phasedarray coil (USA Instruments, Cleveland, OH). For each subject, sagittal images of both the ACL-deficient and contralateral intact knees were obtained using a fast spin echo sequence with TR of 3000 ms, TE of 9.1 ms, a 512 ⫻ 256 matrix, 16 echo train length, 16-cm field of view, and 1.5-mm thick sections with zero spacing. The receiver bandwidth was 64 kHz.

Tibiofemoral Kinematics After image acquisition, a 3-dimensional image registration program written in Java was used to determine kinematic measurements based on an anatomical-landmark-matching algorithm. The algorithm translates, rotates, and scales images and matches corresponding anatomical landmarks by minimizing the least squared errors of the residual distances between corresponding landmarks. Figure 1 represents the method of landmark matching. A knee is illustrated at extension (Fig. 1A) and flexion (Fig. 1B), and the black markers are examples of anatomical landmarks. By matching corresponding landmarks, one image can be transformed to register with the other. The yellow tibia in the superimposed image (Fig. 1C) shows the overlap of the tibia at extension and flexion, and the green and red femur shows the relative femoral positions. After registration, 3 kinematic measurements;

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Figure 1 The landmark matching registration technique. A knee is illustrated at extension (A) and flexion (B) and the black markers are examples of anatomical landmarks. By matching the corresponding landmarks, one image can be transformed to register with the other. The yellow tibia in the superimposed image (C) shows the overlap of the tibia at extension and flexion. The green and red femur shows the relative femoral positions with respect to the tibia at extension and flexion.

anterior tibial translation (ATT), medial tibial translation (MTT), and internal tibial rotation (ITR) can be calculated.

Meniscal Kinematics For each image, menisci and tibiofemoral contact areas are segmented. By using the registrations obtained previously, the menisci and contact areas at extension and flexion of the knee are reconstructed on the tibial plateau. The centroids of contact areas are also calculated and displayed. Two sagittal planes are selected at the medial and lateral contact area centroids. Meniscal positions on each plane, including the anterior and posterior points of the anterior and posterior horns, at extension and flexion are registered; 8 positions are registered for each meniscus (4 for flexion and 4 for extension). To quantitate meniscal kinematics, meniscal positions are reconstructed and recorded as a percentage with respect to the anteroposteior width of the tibia. Figure 2 illustrates the meniscal positions of an ACL-deficient and a PCL-deficient patient. The meniscal positions are reconstructed on the tibial plateau. For the ACL-deficient patient, the menisci are translated posteriorly, especially in extension and the posterior horn of the lateral meniscus when compared with contralateral intact knee. For the PCL-deficient patient, the menisci are translated anteriorly, most notably in flexion and the lateral meniscus. There also is a significant anterior shift of the centroid of the lateral compartment.

Study Design Eight ACL-deficient patients and 10 normal volunteers with no major knee injuries were included in the study. The inclusion criteria for patient recruitment were isolated ACL deficiency, no other associated ligament injuries, no meniscal pathology and contralateral uninjured knee. Sagittal images of both knees were obtained in full extension and flexion (45°), as the subjects lay supine on a custom-made, MRcompatible, weight-bearing apparatus with 124.7 N of axial loading (Fig. 3). This axial loading device allows us to study

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Figure 2 Reconstructed meniscal positions on the tibial plateau. Meniscal positions in extension are represented in red while in flexion are represented in blue. The centroids of the contact area for the medial and lateral compartments are also illustrated by the red (extension) and blue (flexion) dots on the respective tibial plateau. (A) Meniscal positions for an ACL deficient patient. (B) Meniscal positions for a PCL-deficient patient.

knee kinematics in the simulated squat position. To help reduce knee motion during the scan, a separate knee holder was designed to guide the knee laterally and axially. Additionally, the foot position is controlled to have a neutral alignment.

Results Tibiofemoral Kinematics Among the 3 bilateral measures of tibiofemoral kinematics, significant differences between ACL-deficient group and the normal group were seen in ATT. In the normal group, average difference in ATTs of ⫺0.5 ⫾ 1.2 (mean ⫾ SD) and ⫺0.5 ⫾ 1.3 mm were recorded at extension and flexion, respectively. In the ACL-deficient group, average difference in ATTs between the intact and ACL-deficient knees were 3.0 ⫾ 1.1 and 1.3 ⫾ 0.8 mm at extension and flexion, respectively. The average difference in ATTs of the normal group were significantly less than those of the ACL-deficient patients. When ATT for the medial and lateral compartments were consid-

Figure 3 Picture of a custom-made, weight-bearing apparatus in the MR scanner. The subject lays supine on the MR scanner, the knee is supported between the two plates of a custom-knee holder (solid black arrow). The axial load is applied through the foot via a foot plate that is connected to weights hanging behind the patient (white arrow).

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Table 1 Meniscal Positions at Extension and Flexion At Extension

At Flexion

Position

Intact

ACL-Def

C. Int

Intact

ACL-Def

C. Int

AAM PAM APM PPM AAL APL PAL PPL

ⴚ7.9 ⴞ 2.4 9.8 ⴞ 4.3 60.7 ⴞ 3.6 91.9 ⴞ 4.4 18.4 ⴞ 5.6 41.6 ⴞ 3.8 74.2 ⴞ 3.8 95.3 ⴞ 3.6

ⴚ4.7 ⴞ 3.3 14.3 ⴞ 2.4* 64.6 ⴞ 3.3 93.1 ⴞ 5.8 20.8 ⴞ 6.4 45.0 ⴞ 3.6* 79.6 ⴞ 3.8* 100.6 ⴞ 4.4*

ⴚ5.5 ⴞ 2.2 11.9 ⴞ 2.8 63.1 ⴞ 3.7 93.7 ⴞ 3.7 17.4 ⴞ 3.3 40.0 ⴞ 2.3 75.1 ⴞ 3.2 95.7 ⴞ 3.4

1.1 ⴞ 7.3 25.0 ⴞ 9.1 69.2 ⴞ 6.8 98.1 ⴞ 5.9 29.3 ⴞ 6.3 49.6 ⴞ 5.5 77.7 ⴞ 5.2 97.3 ⴞ 4.4

1.3 ⴞ 6.2 20.9 ⴞ 4.1 68.4 ⴞ 4.1 94.5 ⴞ 6.0 29.5 ⴞ 4.2 47.1 ⴞ 5.2 79.3 ⴞ 3.9 98.8 ⴞ 4.0

ⴚ1.9 ⴞ 3.2 19.8 ⴞ 5.0 68.8 ⴞ 4.5 96.2 ⴞ 2.3 26.3 ⴞ 5.0 45.5 ⴞ 4.3 76.3 ⴞ 3.2 97.1 ⴞ 4.1

All numbers are in % with respect to the tibia AP width. 0% and 100% represent points aligned with the anterior and posterior aspect of the tibia, respectively. AAM, the anterior border of the anterior horn of medial meniscus; PAM, the posterior border of the anterior horn of medial meniscus; APM, the anterior border of the posterior horn of medial meniscus; PPM, the posterior border of the posterior horn of medial meniscus; AAL, the anterior border of the anterior horn of lateral meniscus; PAL, the posterior border of the anterior horn of lateral meniscus; APL, the anterior border of the posterior horn of lateral meniscus; PPL, the posterior border of the posterior horn of lateral meniscus; Intact, volunteer group; ACL-Def, the deficient knee in the ACL-deficient group; C. int, the contralateral intact knee in the ACL-deficient group; Intact, volunteer group; ACL-Def, the ACL-def knee; C. Int, contralateral intact knee in the ACL-deficient group. *Significantly displaced posteriorly when compared with the contralateral intact side (p < 0.05).

ered separately, the difference in ATT in the lateral compartment of the normal group (⫺2.0 ⫾ 2.4 mm at extension and ⫺1.6 ⫾ 2.0 mm at flexion) was significantly less than for the ACL-deficient group (4.5 ⫾ 3.5 mm at extension and 1.0 ⫾ 1.9 mm at flexion). In the ACL-deficient group, the ATT from extension to flexion in the ACL-deficient knee (0.9 ⫾ 3.0 mm) was significantly less than the contralateral intact side (2.4 ⫾ 2.9 mm) with paired t-test analysis (P ⬍ 0.001). When the compartments were considered separately, the ATT from extension to flexion in the lateral compartment of the ACL-deficient side (2.9 ⫾ 4.0 mm) was significantly more than the contralateral intact side (6.0 ⫾ 5.2 mm) whereas no significant translations were observed in the medial compartment. For ITR, the difference in ITR (1.0° ⫾ 4.6°) in the ACLdeficient group at extension was found to be significantly higher than the normal group (⫺2.3° ⫾ 2.6°). No significant differences were observed in MTT, although a difference in MTT of 0.8 ⫾ 1.2 mm was observed in the ACL-deficient group at flexion whereas all other difference in MTT measures were all less than 0.2 mm.

Meniscal Kinematics To evaluate meniscal kinematics, meniscal positions were reconstructed and recorded as a percentage with respect to the AP width of the tibia as listed in Table 1. Significant meniscal excursions were observed with ACL deficiency. In the ACL-deficient knee, there were significant posterior shifts on 4 of the measured meniscal positions. In Figure 4, the positions of the medial and lateral meniscus for the ACLdeficient and contralateral intact knees were illustrated in a diagrammatic fashion. The lateral meniscus of the ACL-deficient knees at extension had 4.5⬃5% posterior translation when compared with the contralateral intact knee. This is approximately or 2.0⬃2.2 mm given the average AP width of the lateral tibia was 45 mm. A significant posterior translation was noted for the anterior horn of medial meniscus; however,

the posterior horn of the medial meniscus did not show any significant translations. Moreover, when comparing meniscal translation from extension to flexion, the medial and lateral menisci in the contralateral intact knees had significant posterior translation; however, for the ACL-deficient knee, the posterior horn in the lateral meniscus had a paradoxical anterior translation of 1.8 mm when compared with ⫺1.4 mm translation in the contralateral intact knees.

Discussion In this article, we presented a 3-dimensional, MR-based technique to obtain in vivo meniscal and tibiofemoral kinematics under weight-bearing conditions. The accuracy and reproducibility of the registration technique has been established with our previous study. The intra- and interobserver reproducibility for using the method were less than 0.8 mm for tibial translation, and less than 1° for rotation. In addition to obtaining tibiofemoral kinematics of the entire joint, we were also able to isolate kinematics of each compartment. In the ACL-deficient patients, our results demonstrated that the lateral compartment has the most significant translations under simulated weight-bearing condition. Our results are consistent with the findings of previous studies, where most of the translations occur in the lateral compartment.30 The medial meniscus did not have significant change in position despite significant changes in tibiofemoral kinematics, demonstrating its importance as the primary restraint for anterior translation in the ACL deficient knee. This also may reflect the high incidence of medial meniscus tear with ACL insufficiency. These results reflect the importance of anterolateral rotatory control of the ACL on knee kinematics. One of the advantages of this technique is the quantitative analysis of both meniscal and tibiofemoral kinematics in the same patient under weight-bearing conditions. The current laxity measurements have all focused on tibiofemoral trans-

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velopment of a more accurate three-dimensional in vivo analysis of knee kinematics is vital to critically evaluate our current treatment and subsequently, improve the outcome following ligament injuries to the knee.

References

Figure 4 Illustration of medial (A) and lateral (B) meniscal positions at extension for the ACL deficient knee. The triangles represent meniscal sections. At each border of the menisci, the mean and standard deviation of the position are printed above the triangle and represented as error bars at the border. All numbers are reported as a percentage with respect to the AP width of the tibia. 0% and 100% represent points aligned with the anterior and posterior aspect of the tibia, respectively. The first row represents the ACL-deficient knees and the second row is the contralateral intact knees.

lations. With the improvement in MRI, we are able to quantitate in vivo meniscal kinematics under dynamic loading conditions. Our future work consist of expanding this technique to other loading conditions, such as rotational torque or combined internal rotational torque and valgus stress— the pivot shift test. We also are investigating the possibility of doing ‘cine’ and real-time motion analysis of knee kinematics. In conclusion, we have applied a 3-dimensional, MRbased method to analyze in vivo knee kinematics under weight-bearing conditions. This noninvasive method allows us to objectively evaluate in vivo meniscal kinematics, in addition to tibiofemoral kinematics. We believe that the de-

1. Chao EYS: Justification of a triaxial goniometer for the measurement of joint rotation. J Biomech 13:989-1006, 1980 2. Lewis JL, Margolis M, Loch D, et al: Error analysis for a knee motion goniometer. ASME Summer Biomechanics Symposium 133-135, 1987 3. Lewis JL, Lew WD, Schmidt J: Description and error evaluation of an in-vitro knee joint testing system. J Biomech Eng 110:238-248, 1988 4. Trent PS, Walker PS, Wolf P: Ligament length patterns, strength and rotational axes of the knee joint. Clin Orthop 117:263-270, 1976 5. Reuben JD, Rovick JS, Walker PS, et al: Three-dimensional kinematics of normal and cruciate deficient knees—A dynamic in-vitro experiment. Trans Orthopaedic Res Soc 11:385, 1986 6. Reuben JD, Rovick JS, Schrager RJ, et al: Three-dimensional dynamic motion analysis of the anterior cruciate ligament deficient knee joint. Am J Sports Med 17:463-471, 1989 7. Andriacchi TP, Hurwitz DE: Gait biomechanics and total knee arthroplasty. Am J Knee Surg 10:255-60, 1997 8. Andriacchi TP, Toney MK: A point cluster method for in-vivo measurement of limb segment movement. ASME Adv Bioeng BED 28:185-186, 1994 9. Andriacchi TP: Functional analysis of pre and post-knee surgery: Total knee arthroplasty and ACL reconstruction. J Biomech Eng 115:575581, 1993 10. Lange Ad, van Dijk R, Huiskies R, van Rens TJG: Three-dimensional experimental assessment of knee ligament length patterns in-vitro. Trans Orthopaedic Res Soc 8:10, 1983 11. Friden T, Sommerlath K, Egund N, et al: Instability after anterior cruciate ligament rupture. Measurements of sagittal laxity compared in 11 cases. Acta Orthop Scand 63:593-598, 1992 12. Jonsson H, Karrholm J, Elmqvist LG: Laxity after cruciate ligament injury in 94 cases. The KT-1000 arthrometer versus roentgen stereophotogrammetry. Acta Orthop Scand 64:567-570, 1993 13. Fujie H, Mabuchi K, Woo SL-Y, et al: The use of robotics technology to study human joint kinematics: A new methodology. J Biomech Eng 115:211-217, 1993 14. Ishibashi Y, Rudy TW, Livesay GA, et al: A robotic evaluation of the effect of ACL graft fixation site at the tibia on knee stability. J Arthroscopy Rel Surg 13:177-182, 1997 15. Rudy T, Livesay GA, Xerogeanes JW, et al: A combined robotics/UFS approach to measure knee kinematics and determine in-situ ACL forces. ASME Adv Bioeng BED-28:287-288, 1994 16. Woo SL-Y, Runco TJ, Morrow DA, et al: The use of robotic technology in knee ligament research4th China-Japan-US-Singapore Conference on Biomechanics, 1995 (vol 4) 17. Woo SL-Y, Fox RJ, Sakane M, et al: Force and force distribution in the anterior cruciate ligament and its clinical implications. SportorthopädieSporttraumatologie 13:37-48, 1997 18. Stone JD, Carlin GJ, Ishibashi Y, et al: Assessment of PCL graft performance using robotic technology. Am J Sports Med 24:824-8, 1996 19. Ma CB, Papageogiou CD, Debski RE, et al: Interaction between the ACL replacement graft and MCL in a combined ACL⫹MCL knee injury using a goal model. Acta Orthop Scand 71:387-393, 2000 20. Harner CD, Vogrin TM, Hoher J, et al: Biomechanical analysis of a posterior cruciate ligament reconstruction. Deficiency of the posterolateral structures as a cause of graft failure. Am J Sports Med 28:32-39, 2000 21. Irie K, Yamada T, Inoue K: A comparison of magnetic resonance imaging and arthroscopic evaluation of chondral lesions of the knee. Orthopedics 23:561-564, 2000 22. Berns GS, Howell SM, Farley TE: The accuracy of signal intensity measurements in magnetic resonance imaging as evaluated within the knee. Magn Reson Imaging 13:573-578, 1992 23. Howell SM, Clark JA, Farley TE: A rationale for predicting anterior

3D In vivo knee kinematics using dynamic MRI

24.

25.

26. 27.

28. 29. 30.

31.

32.

33.

34.

35. 36. 37.

38.

39.

40.

41.

42.

43.

cruciate graft impingement by the intercondylar roof: An MRI study. Am J Sports Med 19:276-282, 1991 Rosen MA, Jackson DW, Berger PE: Occult osseus lesions documented by MRI associated with anterior cruciate ligament ruptures. Arthroscopy 7:45-51, 1991 Thompson WO, Thaete FL, Fu FH, et al: Tibial meniscal dynamics using three-dimensional reconstruction of magnetic resonance images. Am J Sports Med 19:210-216, 1991 Thompson W, Fu F: The meniscus in the cruciate-deficient knee. Clin Sports Med 12:771-796, 1993 Sheehan FT, Zajac FE, Drace JE: In vivo tracking of the human patella using cine phase contrast magnetic resonance imaging. J Biomech Eng 121:650-656, 1999 Sheehan FT, Drace JE: Human patellar tendon strain. A noninvasive, in vivo study. Clin Orthop 370:201-7, 2000 Friedman RJ, Bonutti PM, Genez B: Cine magnetic resonance imaging of the subcoracoid region. Orthopedics 21:545-8, 1998 Logan MC, Williams A, Lavelle J, et al: Tibiofemoral kinematics following anterior cruciate ligament reconstruction using dynamic multiple resonance imaging. Am J Sports Med 32:984-992, 2004 Scarvell JM, Smith PN, Refshauge KM, et al: Comparision of kinematic analysis by mapping tibiofemoral contact with movement of the femoral condylar centers in healthy and anterior cruciate ligament injured knees. J Orthop Res 22:955-962, 2004 Aglietti P, Buzzi R, D’Andria S, et al: Long-term study of anterior cruciate ligament reconstruction for chronic instability using the central one-third patellar tendon and a lateral extraarticular tenodesis. Am J Sports Med 20:38-45, 1992 Bach BJ, Tradonsky S, Bojchuk J, et al: Arthroscopically assisted anterior cruciate ligament reconstruction using patellar tendon autograft. Five- to nine- year follow-up evaluation. Am J Sports Med 26:20-29, 1998 Brown C, Steiner M, Carson E: The use of hamstring tendons for anterior cruciate ligament reconstruction: technique and results. Clin Sports Med 12:723-756, 1993 Cho KO: Reconstruction of the anterior cruciate ligament by semitendinosis tenodesis. Journal of Bone Joint Surg 57A:608-612, 1975 Clancy WGJ: Intra-articular reconstruction of the anterior cruciate ligament. Orthopaedic Clin North Am 16:181-188, 1985 Clark R, Olson R, Larson B, et al: Cross-pin femoral fixation: a new technique for hamstring anterior cruciate ligament reconstruction of the knee. Arthroscopy 14:258-267, 1998 Feagin JAj, Wills R, Lambert K, et al: Anterior cruciate ligament reconstruction. Bone-patellar tendon-bone versus semitendinosus anatomic reconstruction. Clin Orthop 341:69-72, 1997 Fu FH, Bennett CH, Lattermann C, et al: Current trends in anterior cruciate ligament reconstruction. Part 1: Biology and biomechanics of reconstruction. Am J Sports Med 27:821-830, 1999 Fu FH, Bennett CH, Ma CB, et al: Current trends in anterior cruciate ligament reconstruction. Part II: Operative procedures and clinical correlations. Am J Sports Med 28:124-130, 2000 Harner CD, Marks PH, Fu FH, et al: Anterior cruciate ligament reconstruction: Endoscopic versus two-incision technique. Arthroscopy 10: 503-512, 1994 Harter RA, Osterning LR, Singer KM, et al: Long-term evaluation of knee stability and function following surgical reconstruction for anterior cruciate ligament. Am J Sports Med 16:434-443, 1988 Jackson DW, Grood ES, Goldstein JD, et al: A comparison of patellar

63

44.

45. 46. 47.

48. 49.

50.

51.

52.

53.

54.

55.

56. 57.

58.

59.

60.

61.

tendon autograft and allograft used for anterior cruciate ligament reconstruction in the goat model. Am J Sports Med 21:176-185, 1993 Noyes FR, Barber SD, Mangine RE: Bone-patellar ligament-bone and fascia lata allografts for reconstruction of the anterior cruciate ligament. J Bone Joint Surg 72A:1125-1136, 1990 Puddu G: Method for reconstruction of the anterior cruciate ligament using the semitendinosus tendon. Am J Sports Med 8:402-404, 1980 Rosenberg TD: Technique for endoscopic method of ACL reconstruction. Acufex Microsurgical 1993;Technical Bulletin Shelbourne K, Gray T: Anterior cruciate ligament reconstruction with autogenous patellar tendon graft followed by accelerated rehabilitation. A two- to nine- year followup. Am J Sports Med 25:786-795, 1997 Shelton W, Papendick L, Dukes A: Autograft versus allograft anterior cruciate ligament reconstruction. Arthroscopy 13:446-449, 1997 Shino K, Inoue M, Horibe S, et al: Reconstruction of the anterior cruciate ligament using allogenic tendon. Am J Sports Med 18:457-465, 1990 Yasuda K, Tsujino J, Tanabe Y, et al: Effects of initial graft tension on clinical outcome after anterior cruciate ligament reconstruction: Autogenous doubled hamstring tendons connected in series with polyester tapes. Am J Sports Med 25:99-106, 1997 Otto D, Pinczewski LA, Clingeleffer A, et al: Five-year results of singleincision arthroscopic anterior cruciate ligament reconstruction with patellar tendon autograft. Am J Sports Med 26:181-188, 1998 Jomha NM, Pinczewski LA, Clingeleffer A, et al: Arthroscopic reconstruction of the anterior cruciate ligament with patellar-tendon autograft and interference screw fixation. The results at seven years. J Bone Joint Surg Br 81:775-779, 1999 Daniel DM, Stone ML, Dobson BE, et al: Fate of the ACL-injured patient: A prospective outcome study. Am J Sports Med 22:632-644, 1994 Daniel DM, Fithian DC, Stone ML, et al: A ten-year prospective outcome study of the ACL-injured patient. Atlanta, GA: American Academy of Orthopaedic Surgeons, 1996 L’Insalata JC, Fu FH, Irrgang PT, et al: The International Knee Documentation Committee evaluation form for assessment of outcome following anterior cruciate ligament reconstruction. 7th Congress of the European Society of Sports Traumatology, Knee Surgery and Arthroscopy. Budapest, Hungary, 1996 (vol 1) Hefti F, Muller W: Current state of evaluation of knee ligament lesions. The new IKDC knee evaluation form. Orthopaedics 22:351-62, 1993 Sakane M, Fox RJ, Li G, Rudy TW, Fu FH, Woo SL-Y: Forces in the AM and PL bundle of the ACL in response to anterior tibial loading of an intact knee2nd World Congress on Sports Trauma/AOSSM 22nd Annual Meeting. Lake Buena Vista, FL 1996 Livesay GA, Fujie H, Kashiwaguchi S, et al: Determination of the in-situ forces and force distribution within the human anterior cruciate ligament. Ann Biomed Eng 23:467-474, 1995 Yagi M, Wong EK, Kanamori A, et al: Biomechanical analysis of an anatomic anterior cruciate ligament reconstruction. Am J Sports Med 30:660-666, 2002 Muneta T, Sekiya I, Yagishita K, et al: Two-bundle reconstruction of the anterior cruciate ligament using semitendinosus tendon with endobuttons: operative technique and preliminary results. Arthroscopy 15: 618-624, 1999 Marcacci M, Molgora AP, Zaffagnini S, et al: Anatomic double-bundle anterior cruciate ligament reconstruction with hamstrings. Arthroscopy 19:540-546, 2003