New fluoroscopic imaging technique for investigation of 6DOF knee kinematics during treadmill gait
© Li et al; licensee BioMed Central Ltd. 2009
Received: 14 November 2008
Accepted: 13 March 2009
Published: 13 March 2009
This report presents a new imaging technique for non-invasive study of six degrees of freedom (DOF) knee kinematics during treadmill gait.
Materials and methods
A treadmill was integrated into a dual fluoroscopic imaging system (DFIS) to formulate a gait analysis system. To demonstrate the application of the system, a healthy subject walked on the treadmill at four different speeds (1.5, 2.0, 2.5 and 3.0 MPH) while the DFIS captured the knee motion during three strides under each speed. Characters of knee joint motion were analyzed in 6DOF during the treadmill walking.
The speed of the knee motion was lower than that of the treadmill. Flexion amplitudes increased with increasing walking speed. Motion patterns in other DOF were not affected by increase in walking speed. The motion character was repeatable under each treadmill speed.
The presented technique can be used to accurately measure the 6DOF knee kinematics at normal walking speeds.
Accurate data of six degrees-of-freedom (6DOF) knee kinematics is instrumental for investigation of biomechanical mechanisms of knee pathology such as osteoarthritis, ligamentous injuries and total knee arthroplasty. Traditional gait analysis used multiple video cameras to track the three-dimensional (3D) motions of reflective markers fixed to the skin, which was limited to reveal relative motion of the femoral and tibial bones. Invasive methods, such as using reflective markers directly fixed to bone using a thin rod or opaque markers embedded within the bones, [3–7] were applied to detect bony motion in order to eliminate the effect of skin motion and enhance the accuracy of motion data. In another way, a point-cluster technique, which is noninvasive, has also been proposed to improve the traditional gait analysis method in order to reduce the effect of relative motion of the skin and bones.
Recently, fluoroscopic imaging technique, due to its relative accessibility, easiness to operate, and low radiation dosage compared to traditional X-rays, has been used for the analysis of knee joint motion during gait [9–11]. However, the use of just a single image might not detect knee joint motion in the out-of-plane degrees-of-freedom in the same accuracy as compared to the accuracy in in-plane motion[12, 13]. In our laboratory, we validated the method using the cine function of two fluoroscopes to simultaneously capture dynamic knee joint motion. This study presents how to use this technique to determine 6DOF knee joint motion during treadmill gait with different speeds.
The diameter of the image intensifier of the fluoroscopes is ~310 mm. In general, given the size of the image intensifier of the fluoroscopes might be difficult to capture the entire range of knee motion during the treadmill gait. Therefore, the two fluoroscopes are positioned so that their intensifiers form an angle between 120 and 130° (Fig. 1). In this setup, the dual fluoroscopic system has a common field of view with a length of ~450 mm. Therefore, the entire knee motion could be captured by both fluoroscopes during the gait cycle.
To demonstrate the methodology of treadmill gait analysis, one healthy subject (male, 45 years old) performed gait on the treadmill at different speeds: 1.5, 2.0, 2.5 and 3.0 mile/hour MPH (or 0.67, 0.89, 1.12 and 1.34 m/s, respectively). Two laser-positioning devices were attached to the two fluoroscopes to help the subject align the target knee (left) within the field of view of the fluoroscopes during gait with the assistance of a technician. The knee was then imaged from heel strike to toe-off during three consecutive strides after about 30 seconds of practice. The subject took 5 minute rest after testing for each speed.
Reproduction of in-vivo knee kinematics
The anatomic model of the target knee, including the bony geometry of the tibia and femur, was reconstructed by tracing the bony contours on sagittal plane magnetic resonance (MR) images of the knee in solid modeling software (Rhinoceros®, Robert McNeal & Associates, Seattle, WA). The MR images were obtained using a 3.0 Tesla MR scanner (MAGNETOM® Trio, Siemens, Erlangen, Germany) while the subject was lying supine with the knee in a relaxed, extended position. The MR scanner employed a 3D double echo water excitation sequence and the following parameters: field-of-view = 160 × 160 × 120 mm, voxel resolution = 0.31 × 0.31 × 1.00 mm, time of repetition (TR) = 24 ms, time of echo (TE) = 6.5 ms, and flip angle = 25°. A joint coordinate system described previously (Fig. 1B) was adopted to determine the 6DOF knee joint kinematics .
The model and the dual fluoroscopic images were placed into a virtual DFIS environment where the in-vivo positions of knee were reproduced by matching projections of the models to their outlines on the fluoroscopic images . The knee positions during three strides at each treadmill speed were reproduced. For each stride, the knee position was analyzed at each 10% of the stance phase from heel strike to toe-off.
The average speed of the knee during stance phase was calculated by dividing the maximal traveling distance by the corresponding traveling time. The data on 6DOF knee kinematics, including knee flexion, internal-external tibial rotation, as well as medial-lateral translation and varus-valgus rotation, were analyzed. The repeatability of the treadmill gait was determined by the standard deviation of the three strides of each treadmill speed.
Femoral translations during gait at different speeds showed similar patterns (Figs. 3D and 3E). The femur translated anteriorly during loading response and early midstance and moved posteriorly thereafter until terminal stance when it shifted anteriorly again. In medial-lateral direction, the femur moved laterally during early stance and medially towards toe-off.
This paper introduced the technique of using the DFIS for measurement of 6DOF in-vivo knee kinematics during treadmill gait. The data showed that this technique is feasible to analyze the dynamic knee motion during a wide range of treadmill speeds (up to 3 MPH). Since this technique reproduced the knee positions using 3D anatomic models of the knee, 6DOF tibiofemoral joint kinematics during gait can be obtained.
Few studies have utilized fluoroscopes to investigate human knee motion during gait . For example, Zihlmann et al.  moved a fluoroscope to follow the knee motion to overcome the limited field of view of the image intensifier. They estimated an accuracy of 0.2 mm for in-plane translation and of 3.25 mm for out-plane translation and an accuracy of 1.57° for rotation in a knee after total joint arthroplasty during level walking. To overcome the limitation of the image intensifier size in the DFIS set up, the two fluoroscopes are positioned so that their common image zone covers the knee motion during the complete gait cycle on a treadmill .
The DFIS has been recently validated to measure dynamic knee motion . Using standard geometry, the sphere positions could be determined with a SD below 0.2 mm when sphere moved at a speed up to 0.5 m/second. The dynamic validation using cadaveric knees, demonstrated that the DFIS on average has an accuracy of less than 0.15 mm and 0.1 mm/s in determining translation and velocity, respectively. Varadarajan et al.  demonstrated that the DFIS can measure translation in knee after total joint arthroplasty with an accuracy of less than 0.4 mm at a speed of 0.5 m/s. The accuracy of the DFIS depends on the speed of the moving joint.
The data of this paper revealed that the knee traveling speed is lower than the treadmill speed (Fig. 2). At the treadmill speed of 2.5 MPH, the knee speed during stance phase is less than 0.4 m/second, while at treadmill speed of 3.0 MPH, the knee speed is about 0.8 m/second. Our data also showed that with increasing speed, the amplitude of knee flexion during stance phase increases. This finding is in agreement with other studies in the literature [18–21]. Treadmill gait was also shown to be repeatable across the multiple strides as indicated by the standard deviation calculated from three strides at each treadmill speed.
The pulse imaging character of the fluoroscopes is an important factor for analyzing treadmill gait. In a pulsed fluoroscopic system such as the one used in our set up, the pulse width and frame rate are decoupled parameters. The inverse of frame rate corresponds to time difference between two consecutive images, whereas pulse width corresponds to excitation time for each image. If the rate at which pulses are generated is matched to the rate of acquisition then each image corresponds to a pulse. In this case, pulse width limits the image quality for a given frame rate. Theoretically, the maximal pulse rate (and matched frame rate) is limited by the pulse width. Therefore, a pulse width of 8 ms has a maximum frame rate of 125 frames/second, which is higher than the recommended minimal frame rate of 60 frames/second for gait analysis. However, a reduced rate of image capture (e.g. 15 or 30 pulses/second and matched frame rates) can be employed to limit unnecessary radiation exposure and data processing without adversely affecting image quality. This is because the image quality is actually related to pulse width even though fewer images are taken. Therefore, we could chose to use 15 or 30 pulses/second in our application, depending on the moving speed of the joint.
In summary, this paper introduced the DFIS technique for measurement of 6DOF in-vivo knee kinematics during treadmill gait. The technique showed feasibility to analyze the dynamic knee motion during wide range of walking speeds (up to 3 MPH). The fluoroscopic system has a low radiation dosage, is non-invasive, and can be constructed using any pair of readily available fluoroscopes. Since this technique reproduced the knee positions during gait using 3D anatomic models of the knee, 6DOF tibiofemoral joint kinematics can be accurately obtained. This technique can be used as an alternative option for treadmill gait analysis in healthy, injured, and surgically treated knees.
The technical assistance of Angela Moynihan, Jong Keun Seon, Bijoy Thomas and Kartik Mangudi Varadarajan is greatly appreciated. This work was supported by National Institute of Health (R01 AR052408 and R21 AR051078).
- Chao EY: Biomechanics of the human gait. Frontiers in Biomechanics. Edited by: Zweifach B. 1986, New York, NY: Springer-Verlag, 225-219.View ArticleGoogle Scholar
- Lafortune MA, Cavanagh PR, Sommer HJ, Kalenak A: Three-dimensional kinematics of the human knee during walking. J Biomech. 1992, 25 (4): 347-57. 10.1016/0021-9290(92)90254-X.View ArticlePubMedGoogle Scholar
- Bach BR, Mikosz RP, Andriacchi TP: The influence of changing femoral attachment positions on force displacement characteristics of the anterior cruciate ligament. Trans ORS. 1988, 13: 129-Google Scholar
- Blankevoort L, Huiskes R, de Lange A: The envelope of passive knee joint motion. J Biomech. 1988, 21 (9): 705-20. 10.1016/0021-9290(88)90280-1.View ArticlePubMedGoogle Scholar
- Karrholm J: Roentgen stereophotogrammetry. Review of orthopedic applications. Acta Orthop Scand. 1989, 60 (4): 491-503.View ArticlePubMedGoogle Scholar
- Selvik G: Roentgen stereophotogrammetry. A method for the study of the kinematics of the skeletal system. Acta Orthop Scand Suppl. 1989, 232: 1-51.View ArticlePubMedGoogle Scholar
- van Dijk R, Huiskes R, Selvik G: Roentgen stereophotogrammetric methods for the evaluation of the three dimensional kinematic behaviour and cruciate ligament length patterns of the human knee joint. J Biomech. 1979, 12 (9): 727-31. 10.1016/0021-9290(79)90021-6.View ArticlePubMedGoogle Scholar
- Andriacchi TP, Alexander EJ, Toney MK, Dyrby C, Sum J: A point cluster method for in vivo motion analysis: applied to a study of knee kinematics. J Biomech Eng. 1998, 120 (6): 743-9. 10.1115/1.2834888.View ArticlePubMedGoogle Scholar
- Li G, Suggs J, Hanson G, Durbhakula S, Johnson T, Freiberg A: Three-dimensional tibiofemoral articular contact kinematics of a cruciate-retaining total knee arthroplasty. J Bone Joint Surg Am. 2006, 88 (2): 395-402. 10.2106/JBJS.D.03028.View ArticlePubMedGoogle Scholar
- Banks SA, Hodge WA: Accurate measurement of three-dimensional knee replacement kinematics using single-plane fluoroscopy. IEEE Trans Biomed Eng. 1996, 43 (6): 638-49. 10.1109/10.495283.View ArticlePubMedGoogle Scholar
- Stiehl JB, Komistek RD, Dennis DA, Paxson RD, Hoff WA: Fluoroscopic analysis of kinematics after posterior-cruciate-retaining knee arthroplasty. J Bone Joint Surg Br. 1995, 77 (6): 884-9.PubMedGoogle Scholar
- Li G, Wuerz TH, DeFrate LE: Feasibility of using orthogonal fluoroscopic images to measure in vivo joint kinematics. J Biomech Eng. 2004, 126 (2): 314-8. 10.1115/1.1691448.View ArticlePubMedGoogle Scholar
- You BM, Siy P, Anderst W, Tashman S: In vivo measurement of 3-D skeletal kinematics from sequences of biplane radiographs: application to knee kinematics. IEEE Trans Med Imaging. 2001, 20 (6): 514-25. 10.1109/42.929617.View ArticlePubMedGoogle Scholar
- Li G, Velde Van de SK, Bingham JT: Validation of a non-invasive fluoroscopic imaging technique for the measurement of dynamic knee joint motion. J Biomech. 2008, 41 (7): 1616-22. 10.1016/j.jbiomech.2008.01.034.View ArticlePubMedGoogle Scholar
- Varadarajan KM, Moynihan AL, D'Lima D, Colwell CW, Li G: In vivo contact kinematics and contact forces of the knee after total knee arthroplasty during dynamic weight-bearing activities. J Biomech. 2008, 41 (10): 2159-68. 10.1016/j.jbiomech.2008.04.021.PubMed CentralView ArticlePubMedGoogle Scholar
- Defrate LE, Papannagari R, Gill TJ, Moses JM, Pathare NP, Li G: The 6 degrees of freedom kinematics of the knee after anterior cruciate ligament deficiency: an in vivo imaging analysis. Am J Sports Med. 2006, 34 (8): 1240-6. 10.1177/0363546506287299.View ArticlePubMedGoogle Scholar
- Zihlmann MS, Gerber H, Stacoff A, Burckhardt K, Szekely G, Stussi E: Three-dimensional kinematics and kinetics of total knee arthroplasty during level walking using single plane video-fluoroscopy and force plates: a pilot study. Gait Posture. 2006, 24 (4): 475-81. 10.1016/j.gaitpost.2005.12.012.View ArticlePubMedGoogle Scholar
- Bohannon RW: Comfortable and maximum walking speed of adults aged 20–79 years: reference values and determinants. Age Ageing. 1997, 26 (1): 15-9. 10.1093/ageing/26.1.15.View ArticlePubMedGoogle Scholar
- Lelas JL, Merriman GJ, Riley PO, Kerrigan DC: Predicting peak kinematic and kinetic parameters from gait speed. Gait Posture. 2003, 17 (2): 106-12. 10.1016/S0966-6362(02)00060-7.View ArticlePubMedGoogle Scholar
- Miyoshi T, Shirota T, Yamamoto S, Nakazawa K, Akai M: Effect of the walking speed to the lower limb joint angular displacements, joint moments and ground reaction forces during walking in water. Disabil Rehabil. 2004, 26 (12): 724-32. 10.1080/09638280410001704313.View ArticlePubMedGoogle Scholar
- Andriacchi TP, Ogle JA, Galante JO: Walking speed as a basis for normal and abnormal gait measurements. J Biomech. 1977, 10 (4): 261-8. 10.1016/0021-9290(77)90049-5.View ArticlePubMedGoogle Scholar
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