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MRI MODEL-BASED KNEE JOINT SURFACE MOTION ANALYSIS
Presentation 0800, Imaging. 16:45, Room 101B
S156
MRI MODEL-BASED KNEE JOINT SURFACE MOTION ANALYSIS B Gao, S Subramanian, N Zheng University of Florida, Gainesville, Florida USA, Email: [email protected], web: www.ortho.ufl.edu/BMAL INTRODUCTION In the past decade, knee joint motion analysis has been advanced from a 2-D segmental level to a 3-D joint-surface level by using Roentgen stereophotogrammetric analysis, single and biplane fluoroscopy. However, these radiographic techniques involve radiation and only offer small motion capture volume thus are not suitable for large subject population and daily activity research. By combining optical stereophotogrammetry and subject-specific MRI model, this work explored the feasibility of a radiation-free approach to animate and analyze 3-D knee joint surface movement. METHODS Two researchers were tested as subjects after signing a consent form approved by IRB. Nineteen contrast-enhanced sphere markers, which were visible by both MRI and optical stereophotogrammetry system, were attached to the right thigh and shank close to the knee joint. The MR scans were performed using the Siemens 1.5T MAGNETOM Symphony MR scanner with a 3D FLASH sequence (Fig.1 a). After the scanning, 90 more reflective markers were attached to thigh and shank and major joints (Fig.1 b). With all these regular and contrast-enhanced markers, a static trial was captured using a motion analysis system (MAC, Santa Rosa, CA) with the subject in a supine posture similar to the pose during MRI scanning. After the static trial, data from ten trials of level waking were collected.
Fig.1 MRI based motion analysis. An open-source software (www.slicer.org) was used to segment MRI images and construct the 3-D models for femur, tibia and each double-purpose marker (Fig.1 c). To improve accuracy, a custom-made Matlab program was developed to segment the cartilage model. Each contrast-enhanced marker’s position relative to the underlying bone was determined based on the MRI models. Because regular markers’ positions relative to the double-purpose markers had been determined based on the static trial, their positions in the bone coordinate systems were also established. Femur and tibia movement during level walking was calculated as previously described [1-2]. Finally, using the motion data and the geometry of the bone and cartilage models, joint surface kinematics was analyzed. RESULTS AND DISCUSSION Generally, the animation presented smooth and reasonable knee joint movement during the whole gait cycle. Even without any constrains applied between tibia and
Journal of Biomechanics 40(S2)
femur during the calculation procedure, overlap or lift-off between the two bones was small (Fig. 2).
Fig.2 Animation of femur movement relative to the tibia during level walking. Figure 3 illustrates three directional velocity distribution on the femoral cartilage surface relative to the tibia at heel strike (HS) and toe off (TO). At the HS instant, the whole cartilage moved to the anterior and medial relative to the tibia, with small flexion velocity, appearing as a “sliding” motion. At the TO instant, the contacting portion of the cartilage moved slower in both AP and ML directions, but the flexion velocity became much higher, more like “rolling” motion.
Fig.3 Joint surface velocity (mm/sec) distribution of the femoral cartilage surface in anterior-posterior (AP), medial-lateral (ML) and superior- inferior (SI) at heel strike (HS) and toe off (TO) positions. Using a fresh cadaver the accuracy of this technique has been validated for three-dimensional knee joint movement [1]. The errors were less than 2 mm for translations and 1 degree for rotations. For the joint surface kinematics a validation study is underway and will be reported in future. This work demonstrated the potential of combining MRI and stereophotogrammetry as a new approach for 3-D knee joint surface motion analysis, which is suitable for large volume motion analysis and may provide a radiation-free alternative for radiographic techniques. REFERENCES 1. Gao, B et al. ISB XXI Congress, Taipei, Taiwan, July 1-5, 2007, submitted. 2. Zheng, et al. ORS annul meeting, paper 164, Feb 11-14, San Diego, CA. 2007
XXI ISB Congress, Podium Sessions, Monday 2 July 2007
S156
MRI MODEL-BASED KNEE JOINT SURFACE MOTION ANALYSIS B Gao, S Subramanian, N Zheng University of Florida, Gainesville, Florida USA, Email: [email protected], web: www.ortho.ufl.edu/BMAL INTRODUCTION In the past decade, knee joint motion analysis has been advanced from a 2-D segmental level to a 3-D joint-surface level by using Roentgen stereophotogrammetric analysis, single and biplane fluoroscopy. However, these radiographic techniques involve radiation and only offer small motion capture volume thus are not suitable for large subject population and daily activity research. By combining optical stereophotogrammetry and subject-specific MRI model, this work explored the feasibility of a radiation-free approach to animate and analyze 3-D knee joint surface movement. METHODS Two researchers were tested as subjects after signing a consent form approved by IRB. Nineteen contrast-enhanced sphere markers, which were visible by both MRI and optical stereophotogrammetry system, were attached to the right thigh and shank close to the knee joint. The MR scans were performed using the Siemens 1.5T MAGNETOM Symphony MR scanner with a 3D FLASH sequence (Fig.1 a). After the scanning, 90 more reflective markers were attached to thigh and shank and major joints (Fig.1 b). With all these regular and contrast-enhanced markers, a static trial was captured using a motion analysis system (MAC, Santa Rosa, CA) with the subject in a supine posture similar to the pose during MRI scanning. After the static trial, data from ten trials of level waking were collected.
Fig.1 MRI based motion analysis. An open-source software (www.slicer.org) was used to segment MRI images and construct the 3-D models for femur, tibia and each double-purpose marker (Fig.1 c). To improve accuracy, a custom-made Matlab program was developed to segment the cartilage model. Each contrast-enhanced marker’s position relative to the underlying bone was determined based on the MRI models. Because regular markers’ positions relative to the double-purpose markers had been determined based on the static trial, their positions in the bone coordinate systems were also established. Femur and tibia movement during level walking was calculated as previously described [1-2]. Finally, using the motion data and the geometry of the bone and cartilage models, joint surface kinematics was analyzed. RESULTS AND DISCUSSION Generally, the animation presented smooth and reasonable knee joint movement during the whole gait cycle. Even without any constrains applied between tibia and
Journal of Biomechanics 40(S2)
femur during the calculation procedure, overlap or lift-off between the two bones was small (Fig. 2).
Fig.2 Animation of femur movement relative to the tibia during level walking. Figure 3 illustrates three directional velocity distribution on the femoral cartilage surface relative to the tibia at heel strike (HS) and toe off (TO). At the HS instant, the whole cartilage moved to the anterior and medial relative to the tibia, with small flexion velocity, appearing as a “sliding” motion. At the TO instant, the contacting portion of the cartilage moved slower in both AP and ML directions, but the flexion velocity became much higher, more like “rolling” motion.
Fig.3 Joint surface velocity (mm/sec) distribution of the femoral cartilage surface in anterior-posterior (AP), medial-lateral (ML) and superior- inferior (SI) at heel strike (HS) and toe off (TO) positions. Using a fresh cadaver the accuracy of this technique has been validated for three-dimensional knee joint movement [1]. The errors were less than 2 mm for translations and 1 degree for rotations. For the joint surface kinematics a validation study is underway and will be reported in future. This work demonstrated the potential of combining MRI and stereophotogrammetry as a new approach for 3-D knee joint surface motion analysis, which is suitable for large volume motion analysis and may provide a radiation-free alternative for radiographic techniques. REFERENCES 1. Gao, B et al. ISB XXI Congress, Taipei, Taiwan, July 1-5, 2007, submitted. 2. Zheng, et al. ORS annul meeting, paper 164, Feb 11-14, San Diego, CA. 2007
XXI ISB Congress, Podium Sessions, Monday 2 July 2007