- Email: [email protected]
Knee loading is lower during mindful walking compared to regular walking: a preliminary study
Abstracts / Osteoarthritis and Cartilage 25 (2017) S76eS444
thought to contribute to greater joint loading and thus may be a factor in exercise induced pain flares. Methods: Prior to participation in study activities, participants first completed an IRB approved informed consent document and then the Physical Activity Readiness Questionnaire and Knee Osteoarthritis Outcome Score (KOOS) to assess risk factors for exercise participation and knee symptom severity. Exercise protocol. Participants completed a 20 treadmill walk (20MTW) at preferred walking pace. Perceived pain was evaluated on an 11 point verbal numeric pain rating scale (vNRS) in the first and final 2 minutes of each 20MTW. A change in pain 1 in response to the 20MTW was considered clinically significant. Electromyography (EMG) was collected during the first and last minutes of the 20MTW. Electrodes were placed over the rectus femoris, vastus lateralis, vastus medialis, and biceps femoris and semitendinosus, according to SENIAM guidelines. The co-contraction between the knee extensors and flexors was determined using a modified co-contraction index (CCI) for terminal swing (last 15% of swing), loading response, mid-stance, and terminal stance. Statistics. Paired t-tests (a ¼ 0.05) were used to test for differences in CCI from the beginning to the end of the 20MTW. One -tailed un-paired t-tests were used to test for group differences in CCI at both the beginning and end of 20MTW. Results: There were small but not significant CCI increases for terminal swing and early stance and CCI decreases for mid and late stance in response to the 20MTW for all knee OA. When participants were divided into the pain flare and no pain flare groups there was a trend for a greater increase (þ6.8%) in CCI for the pain flare as compared to the no pain flare group (-3.7%) in terminal swing (p ¼ 0.096). There were no differences in the CCI between the pain flare and no pain flare group at baseline. Conclusions: In the literature, individuals with knee pain are hypothesized to adopt neuromuscular strategies to increase knee joint stiffness and decrease joint movement (e.g., joint angle excursion), theoretically to control the tissue loads and thus limit pain. In agreement with this hypothesis, there was a trend for a greater increase in CCI for patients who experienced a significant exercise induced pain flare. Increases in CCI may be an attempt to constrain joint motion and control the pain flare during gait, however it may also contribute to pain flares in gait. In either senario, increased CCI may produce greater joint loads and have a negative impact on joint health.
Table 1 Subject characteristics. KOOS pain scores were significantly worse for the pain flare group N (F)
Age
BMI
Treadmill KOOS Pain Speed(m/s) Score
All 16 (10) 62.7 ± 6.1 25.8 ± 3.7 0.96 ± 0.28 No Pain 8 (7) 63.3 ± 7.0 25.7 ± 3.4 1.00 ± 0.19 Pain 8 (3) 62.1 ± 5.4 25.9 ± 4.2 0.92 ± 0.36
Pain Change
64.6 ± 18.0 0.6 ± 1.0 70.3 ± 13.8 -0.1 ± 0.4 58.8 ± 20.8 1.4 ± 0.7
S133
184 THE EFFECTS OF GAIT MODIFICATION VIA REAL-TIME KNEE ADDUCTION MOMENT FEEDBACK ON KNEE LOADING DURING WALKING e A PILOT FEASIBILITY STUDY B. Jackson, K.E. Gordon, A.H. Chang. Northwestern Univ., Chicago, IL, USA Purpose: The external knee adduction moment (KAM) during gait is an important loading variable in medial tibiofemoral osteoarthritis (OA). Efforts have been directed toward developing and testing non-pharmacological interventions to reduce KAM and ultimately slow disease course in medial OA. Recent studies have shown that knee flexion moment (KFM) and KAM impulse also play a role in medial joint loading and disease process. We evaluated the effects of gait modification, using real-time first peak KAM visual feedback, on the first peak KAM, KAM impulse during stance phase, and peak KFM; and whether participants could maintain the KAM-reducing gait after feedback removal. Methods: Eleven healthy individuals (age ¼ 26 ± 4.7 years, height ¼ 1.68 ± 0.09 m, weight ¼ 64.6 ± 16.3 kg, 73% women) performed a series of walking trials on a split-belt instrumented treadmill (Motekforcelink, Amsterdam, Netherlands) under 4 conditions of Baseline, Feedback, No Feedback Early, and No Feedback Late. Participants received real-time visual feedback of the first peak KAM of the right limb (feedback limb) displayed on a monitor in front of the treadmill. Participants walked at their preferred walking speed and were instructed to modify their gait patterns to lower KAM by 20%. No KAM feedback of the left limb was provided. Participants were encouraged to experiment with various strategies, but avoid adjustments that felt unnatural or unsustainable in daily ambulation. Bilateral joint kinematics and kinetics during each walking condition were recorded by a 12-camera motion capture system and the instrumented treadmill and processed using Visual 3D software (C-Motion, Germantown, Maryland). Change in each knee loading parameter (first peak KAM, KAM impulse, and peak KFM) in both limbs across conditions was assessed using one-way repeated measures analysis of variance and Bonferroni-corrected pairwise comparisons. Results: The modified gait significantly reduced the first peak KAM of the right limb in all conditions (p < 0.01), with a mean (±SD) reduction of 23.4 ± 19.8% in the Feedback, 21.3 ± 19.6% in the No Feedback Early, and 23.7 ± 20.1% in the No Feedback Late conditions. Similar reductions were found in KAM impulse of the right limb (p < 0.05): 21.2 ± 27.3% in the Feedback, 23.7 ± 28% in the No Feedback Early, and 13.2 ± 19.5% in the No Feedback Late conditions. KAM parameters of the left limb (nonfeedback) were also reduced during the Feedback condition, but to a lesser extent. Figure 1 summarizes the median and quartiles of percent changes in the first peak KAM and KAM impulse in the Feedback, No Feedback Early, and No Feedback Late conditions for the right (feedback limb) and the left (non-feedback limb) respectively. No statistically significant peak KFM increase was observed in the Feedback, and No Feedback Early conditions for either limb. Ten different gait modification strategies were reported. The altered gait patterns for lowering KAM were participant-specific and multi-modal; each participant reported a combination of 2e3 gait modification strategies used for KAM reduction. Conclusions: Successful 20% reductions in KAM and KAM impulse were achieved without concomitant deleterious increases in KFM. The findings support the real-time KAM visual feedback as a tool for individualized gait modification to reduce knee load. Future studies to evaluate its effectiveness in participants with confirmed medial knee OA or at risk for knee OA development is warranted. 185 KNEE LOADING IS LOWER DURING MINDFUL WALKING COMPARED TO REGULAR WALKING: A PRELIMINARY STUDY D. Kumar. Boston Univ., Boston, MA, USA Purpose: To compare gait biomechanics during mindful walking and regular walking. Methods: We studied four expert mindful walking (ChiWalking®) instructors (age>40 years, BMI < 25 kg/m2, 3 men, 1 woman) in this study. The instructors walked over-ground at their self-selected walking speed while 3-D biomechanics data were collected using motion capture cameras and in-ground force platforms. All instructors performed mindful walking and regular walking trials at matched speeds and the order of the condition was randomized. Peak kinematic and kinetic
S134
Abstracts / Osteoarthritis and Cartilage 25 (2017) S76eS444
variables during the stance phase of walking were calculated. We used paired t-tests to compare the gait variables between mindful walking and regular walking conditions. Results: The results are shown in Table 1. We observed lower peak adduction and flexion moments, and lower adduction and flexion moment impulses during mindful walking compared to regular walking. Additionally, the breaking, propulsive, and vertical ground reaction force (GRF) impulses were lower during mindful walking. The instructors reduced the time their feet were in contact with the ground during mindful walking and reduced the flexion range of motion during loading response. Conclusions: In this proof of concept preliminary study, we observed a reduction in measures of knee loading with a mindful walking activity compared to regular walking. A reduction in the knee adduction moment by itself may not be sufficient to reduce knee loading unless accompanied by a reduction in knee flexion moment. With a mindful walking technique, we observed reductions in both adduction and flexion moments, and adduction and flexion moment impulses, suggesting that the knee contact forces are likely reduced with mindful walking. The reductions in breaking, propulsive, and vertical GRF further suggest that impact forces on the body, and knee loading are reduced with a mindful walking technique. These changes are likely related to a reduction in stance time along with a decrease in step length and increase in cadence as is the goal of the mindful walking technique. Therefore, an investigation into the use of this mindful walking technique to reduce knee loading in people with knee osteoarthritis is warranted. Table 1 Gait variables (Mean and Standard Deviation) during regular walking and mindful walking Gait Variables Sagittal
Flexion Moment (Nm) Flexion Impulse (Nm*s) Flexion Excursion (Degrees) Extension Excursion (Degrees) Frontal Adduction Moment (Nm) Adduction Impulse (Nm*s) Frontal Excursion (Degrees) GRF Vertical Impulse (N*s) Breaking Impulse (N*s) Propulsive Impulse (N*s) Stance Time (s)
Regular Walking
Mindful Walking
P-value
57.99 (12.74) 7.57 (2.58) 18.9 (2.0)
40.83 (9.65) 4.55 (2.06) 12.9 (1.4)
0.042 0.023 0.015
19.9 (7.7)
17.7 (3.1)
0.250
37.73 (5.44) 6.41 (0.28)
31.61 (4.29) 4.90 (1.23)
0.006 0.033
6.3 (2.7)
5.8 (2.0)
0.296
310.12 (34.76) 22.27 (3.75) -20.97 (2.99) 0.59 (0.04)
272.01 (38.00) 15.74 (3.99) -14.36 (3.04) 0.52 (0.06)
0.020 0.045 0.017 0.017
hamstrings, of a 11-year old boy were used for this analysis. From these images, we established the three-dimensional (3D) models in each position. Finite element model: These 3D images were imported into the Abaqus software (ver. 6.11-1, Dassault Systemes, Paris, France) for processing the FE model in each position. The element size was 1.0 mm each and there were 307,027 elements with 118,884 nodes. The thickness of the cortical bone was set as 2.5 mm based on the CT data and triangular prism elements (C3D6). This cortical bone area was divided into 4 layers from the surface to the border of cancellous bone. The cancellous bone was filled with tetrahedron elements (C3D4). Material property of the PCL and conditioning of femoral footprint: The PCL footprints at femur and tibia were decided from the MR images. We illustrated the PCL as a single bundle ligament. The diameter of femoral and tibial footprints of the PCL was set as 7 mm from the MR images. The center of each footprint was connected by single non-linear cable element representing as the PCL ligament. The elastic module of the PCL was set as 131.5 MPa. The stress-strain relationship of nonlinear ligament elements was described following previous report. Boundary and loading condition: We fixed the femur and the tibia was forced to 110 flexed position of the knee. In this motion, the stress alternation upon femur due to distalization of femoral footprint of the PCL was evaluated. For distalization of the femoral footprint of the PCL, we made a 50% offset of the center, i.e. 3.5 mm distalization of center of footprint along the Z-axis, as a distalized model. Results: From the distalization of the femoral footprint of the PCL, the distance from the center of femoral footprint to the tibial side increased from 30.99 mm to 33.63 mm in 110 -flexed position, the difference was 2.64 mm. The stress at femoral footprint was similar in pre and postdistalization, 3.0 MPa each. And this stress was observed from the cortical to cancellous bone layers and also this stress was similar in preand post-distalization models, 1.5 and 1.6 MPa, respectively. However, its distribution was altered in post-distalization model. The layer in cortical bone was evaluated in each layer and we found slightly higher stress existed in all layers in the distalized model, this difference was 0.25 MPa though (Figure 1). Conclusions: In this study, we demonstrated that the distalization of femoral footprint of the PCL alter stress distribution in MFC from FE analysis. And interestingly, this stress distribution was exactly matched with MFC OCD lesion that we frequently observe fissure, fibrillation, and detachment of subchondral bone at arthroscopy. To our knowledge, this is the first report to unveil the etiology of OCD using the mathematical method.
186 FINITE ELEMENT ANALYSIS FOR INVESTIGATION OF THE ETIOLOGY OF OSTEOCHONDRITIS DISSECANS IN MEDIAL FEMORAL CONDYLE M. Ishikawa, A. Nakamae, T. Nakasa, Y. Sumida, N. Adachi. Hiroshima Univ., Hiroshima, Japan Purpose: Osteochondritis dissecans (OCD) was reported by Franz €enig in 1888. So far, repetitive microtrauma is a favorable and the Ko most accepted etiology because patients with OCD are usually involved in high athletic activity and the increase of the patient population associated with increasing sports participation. Recently we introduced a unique anatomic feature of the femoral footprint of posterior cruciate ligament (PCL) in the patients with MFC OCD lesions. In the previous study, it was demonstrated that the femoral footprint of the PCL in patients with MFC OCD was located significantly distal position compared to the patients with non-OCD lesions. However, the mechanism predisposing to lesions due to this anatomic factor still remains unsolved. The purpose of this study was to investigate the alteration of in situ stress on the MFC due to distalized femoral footprint of PCL at knee flexion using finite element (FE) model. Methods: This study was approved by the Ethical Committee of Hiroshima University (Approval number: E-14). Establishment of threedimensional models: The CT images of the left knee joint, taken at full extension and 110 flexion without an applied load on the quadriceps or
187 ASSOCIATION BETWEEN ULTRASONOGRAPHY MEASUREMENTS OF TALAR CARTILAGE THICKNESS AND LOADING DURING GAIT IN INDIVIDUALS WITH CHRONIC ANKLE INSTABILITY K. Song, B.G. Pietrosimone, E.A. Wikstrom. UNC Chapel Hill, Chapel Hill, NC, USA Purpose: Individuals with chronic ankle instability (CAI) tend to develop post-traumatic ankle osteoarthritis (PTAOA), potentially due to altered mechanical loading of articular cartilage associated with aberrant gait biomechanics. The overall magnitude (peak vertical ground reaction force [vGRF]) and rate of loading (vGRF_LR) are higher in those
thought to contribute to greater joint loading and thus may be a factor in exercise induced pain flares. Methods: Prior to participation in study activities, participants first completed an IRB approved informed consent document and then the Physical Activity Readiness Questionnaire and Knee Osteoarthritis Outcome Score (KOOS) to assess risk factors for exercise participation and knee symptom severity. Exercise protocol. Participants completed a 20 treadmill walk (20MTW) at preferred walking pace. Perceived pain was evaluated on an 11 point verbal numeric pain rating scale (vNRS) in the first and final 2 minutes of each 20MTW. A change in pain 1 in response to the 20MTW was considered clinically significant. Electromyography (EMG) was collected during the first and last minutes of the 20MTW. Electrodes were placed over the rectus femoris, vastus lateralis, vastus medialis, and biceps femoris and semitendinosus, according to SENIAM guidelines. The co-contraction between the knee extensors and flexors was determined using a modified co-contraction index (CCI) for terminal swing (last 15% of swing), loading response, mid-stance, and terminal stance. Statistics. Paired t-tests (a ¼ 0.05) were used to test for differences in CCI from the beginning to the end of the 20MTW. One -tailed un-paired t-tests were used to test for group differences in CCI at both the beginning and end of 20MTW. Results: There were small but not significant CCI increases for terminal swing and early stance and CCI decreases for mid and late stance in response to the 20MTW for all knee OA. When participants were divided into the pain flare and no pain flare groups there was a trend for a greater increase (þ6.8%) in CCI for the pain flare as compared to the no pain flare group (-3.7%) in terminal swing (p ¼ 0.096). There were no differences in the CCI between the pain flare and no pain flare group at baseline. Conclusions: In the literature, individuals with knee pain are hypothesized to adopt neuromuscular strategies to increase knee joint stiffness and decrease joint movement (e.g., joint angle excursion), theoretically to control the tissue loads and thus limit pain. In agreement with this hypothesis, there was a trend for a greater increase in CCI for patients who experienced a significant exercise induced pain flare. Increases in CCI may be an attempt to constrain joint motion and control the pain flare during gait, however it may also contribute to pain flares in gait. In either senario, increased CCI may produce greater joint loads and have a negative impact on joint health.
Table 1 Subject characteristics. KOOS pain scores were significantly worse for the pain flare group N (F)
Age
BMI
Treadmill KOOS Pain Speed(m/s) Score
All 16 (10) 62.7 ± 6.1 25.8 ± 3.7 0.96 ± 0.28 No Pain 8 (7) 63.3 ± 7.0 25.7 ± 3.4 1.00 ± 0.19 Pain 8 (3) 62.1 ± 5.4 25.9 ± 4.2 0.92 ± 0.36
Pain Change
64.6 ± 18.0 0.6 ± 1.0 70.3 ± 13.8 -0.1 ± 0.4 58.8 ± 20.8 1.4 ± 0.7
S133
184 THE EFFECTS OF GAIT MODIFICATION VIA REAL-TIME KNEE ADDUCTION MOMENT FEEDBACK ON KNEE LOADING DURING WALKING e A PILOT FEASIBILITY STUDY B. Jackson, K.E. Gordon, A.H. Chang. Northwestern Univ., Chicago, IL, USA Purpose: The external knee adduction moment (KAM) during gait is an important loading variable in medial tibiofemoral osteoarthritis (OA). Efforts have been directed toward developing and testing non-pharmacological interventions to reduce KAM and ultimately slow disease course in medial OA. Recent studies have shown that knee flexion moment (KFM) and KAM impulse also play a role in medial joint loading and disease process. We evaluated the effects of gait modification, using real-time first peak KAM visual feedback, on the first peak KAM, KAM impulse during stance phase, and peak KFM; and whether participants could maintain the KAM-reducing gait after feedback removal. Methods: Eleven healthy individuals (age ¼ 26 ± 4.7 years, height ¼ 1.68 ± 0.09 m, weight ¼ 64.6 ± 16.3 kg, 73% women) performed a series of walking trials on a split-belt instrumented treadmill (Motekforcelink, Amsterdam, Netherlands) under 4 conditions of Baseline, Feedback, No Feedback Early, and No Feedback Late. Participants received real-time visual feedback of the first peak KAM of the right limb (feedback limb) displayed on a monitor in front of the treadmill. Participants walked at their preferred walking speed and were instructed to modify their gait patterns to lower KAM by 20%. No KAM feedback of the left limb was provided. Participants were encouraged to experiment with various strategies, but avoid adjustments that felt unnatural or unsustainable in daily ambulation. Bilateral joint kinematics and kinetics during each walking condition were recorded by a 12-camera motion capture system and the instrumented treadmill and processed using Visual 3D software (C-Motion, Germantown, Maryland). Change in each knee loading parameter (first peak KAM, KAM impulse, and peak KFM) in both limbs across conditions was assessed using one-way repeated measures analysis of variance and Bonferroni-corrected pairwise comparisons. Results: The modified gait significantly reduced the first peak KAM of the right limb in all conditions (p < 0.01), with a mean (±SD) reduction of 23.4 ± 19.8% in the Feedback, 21.3 ± 19.6% in the No Feedback Early, and 23.7 ± 20.1% in the No Feedback Late conditions. Similar reductions were found in KAM impulse of the right limb (p < 0.05): 21.2 ± 27.3% in the Feedback, 23.7 ± 28% in the No Feedback Early, and 13.2 ± 19.5% in the No Feedback Late conditions. KAM parameters of the left limb (nonfeedback) were also reduced during the Feedback condition, but to a lesser extent. Figure 1 summarizes the median and quartiles of percent changes in the first peak KAM and KAM impulse in the Feedback, No Feedback Early, and No Feedback Late conditions for the right (feedback limb) and the left (non-feedback limb) respectively. No statistically significant peak KFM increase was observed in the Feedback, and No Feedback Early conditions for either limb. Ten different gait modification strategies were reported. The altered gait patterns for lowering KAM were participant-specific and multi-modal; each participant reported a combination of 2e3 gait modification strategies used for KAM reduction. Conclusions: Successful 20% reductions in KAM and KAM impulse were achieved without concomitant deleterious increases in KFM. The findings support the real-time KAM visual feedback as a tool for individualized gait modification to reduce knee load. Future studies to evaluate its effectiveness in participants with confirmed medial knee OA or at risk for knee OA development is warranted. 185 KNEE LOADING IS LOWER DURING MINDFUL WALKING COMPARED TO REGULAR WALKING: A PRELIMINARY STUDY D. Kumar. Boston Univ., Boston, MA, USA Purpose: To compare gait biomechanics during mindful walking and regular walking. Methods: We studied four expert mindful walking (ChiWalking®) instructors (age>40 years, BMI < 25 kg/m2, 3 men, 1 woman) in this study. The instructors walked over-ground at their self-selected walking speed while 3-D biomechanics data were collected using motion capture cameras and in-ground force platforms. All instructors performed mindful walking and regular walking trials at matched speeds and the order of the condition was randomized. Peak kinematic and kinetic
S134
Abstracts / Osteoarthritis and Cartilage 25 (2017) S76eS444
variables during the stance phase of walking were calculated. We used paired t-tests to compare the gait variables between mindful walking and regular walking conditions. Results: The results are shown in Table 1. We observed lower peak adduction and flexion moments, and lower adduction and flexion moment impulses during mindful walking compared to regular walking. Additionally, the breaking, propulsive, and vertical ground reaction force (GRF) impulses were lower during mindful walking. The instructors reduced the time their feet were in contact with the ground during mindful walking and reduced the flexion range of motion during loading response. Conclusions: In this proof of concept preliminary study, we observed a reduction in measures of knee loading with a mindful walking activity compared to regular walking. A reduction in the knee adduction moment by itself may not be sufficient to reduce knee loading unless accompanied by a reduction in knee flexion moment. With a mindful walking technique, we observed reductions in both adduction and flexion moments, and adduction and flexion moment impulses, suggesting that the knee contact forces are likely reduced with mindful walking. The reductions in breaking, propulsive, and vertical GRF further suggest that impact forces on the body, and knee loading are reduced with a mindful walking technique. These changes are likely related to a reduction in stance time along with a decrease in step length and increase in cadence as is the goal of the mindful walking technique. Therefore, an investigation into the use of this mindful walking technique to reduce knee loading in people with knee osteoarthritis is warranted. Table 1 Gait variables (Mean and Standard Deviation) during regular walking and mindful walking Gait Variables Sagittal
Flexion Moment (Nm) Flexion Impulse (Nm*s) Flexion Excursion (Degrees) Extension Excursion (Degrees) Frontal Adduction Moment (Nm) Adduction Impulse (Nm*s) Frontal Excursion (Degrees) GRF Vertical Impulse (N*s) Breaking Impulse (N*s) Propulsive Impulse (N*s) Stance Time (s)
Regular Walking
Mindful Walking
P-value
57.99 (12.74) 7.57 (2.58) 18.9 (2.0)
40.83 (9.65) 4.55 (2.06) 12.9 (1.4)
0.042 0.023 0.015
19.9 (7.7)
17.7 (3.1)
0.250
37.73 (5.44) 6.41 (0.28)
31.61 (4.29) 4.90 (1.23)
0.006 0.033
6.3 (2.7)
5.8 (2.0)
0.296
310.12 (34.76) 22.27 (3.75) -20.97 (2.99) 0.59 (0.04)
272.01 (38.00) 15.74 (3.99) -14.36 (3.04) 0.52 (0.06)
0.020 0.045 0.017 0.017
hamstrings, of a 11-year old boy were used for this analysis. From these images, we established the three-dimensional (3D) models in each position. Finite element model: These 3D images were imported into the Abaqus software (ver. 6.11-1, Dassault Systemes, Paris, France) for processing the FE model in each position. The element size was 1.0 mm each and there were 307,027 elements with 118,884 nodes. The thickness of the cortical bone was set as 2.5 mm based on the CT data and triangular prism elements (C3D6). This cortical bone area was divided into 4 layers from the surface to the border of cancellous bone. The cancellous bone was filled with tetrahedron elements (C3D4). Material property of the PCL and conditioning of femoral footprint: The PCL footprints at femur and tibia were decided from the MR images. We illustrated the PCL as a single bundle ligament. The diameter of femoral and tibial footprints of the PCL was set as 7 mm from the MR images. The center of each footprint was connected by single non-linear cable element representing as the PCL ligament. The elastic module of the PCL was set as 131.5 MPa. The stress-strain relationship of nonlinear ligament elements was described following previous report. Boundary and loading condition: We fixed the femur and the tibia was forced to 110 flexed position of the knee. In this motion, the stress alternation upon femur due to distalization of femoral footprint of the PCL was evaluated. For distalization of the femoral footprint of the PCL, we made a 50% offset of the center, i.e. 3.5 mm distalization of center of footprint along the Z-axis, as a distalized model. Results: From the distalization of the femoral footprint of the PCL, the distance from the center of femoral footprint to the tibial side increased from 30.99 mm to 33.63 mm in 110 -flexed position, the difference was 2.64 mm. The stress at femoral footprint was similar in pre and postdistalization, 3.0 MPa each. And this stress was observed from the cortical to cancellous bone layers and also this stress was similar in preand post-distalization models, 1.5 and 1.6 MPa, respectively. However, its distribution was altered in post-distalization model. The layer in cortical bone was evaluated in each layer and we found slightly higher stress existed in all layers in the distalized model, this difference was 0.25 MPa though (Figure 1). Conclusions: In this study, we demonstrated that the distalization of femoral footprint of the PCL alter stress distribution in MFC from FE analysis. And interestingly, this stress distribution was exactly matched with MFC OCD lesion that we frequently observe fissure, fibrillation, and detachment of subchondral bone at arthroscopy. To our knowledge, this is the first report to unveil the etiology of OCD using the mathematical method.
186 FINITE ELEMENT ANALYSIS FOR INVESTIGATION OF THE ETIOLOGY OF OSTEOCHONDRITIS DISSECANS IN MEDIAL FEMORAL CONDYLE M. Ishikawa, A. Nakamae, T. Nakasa, Y. Sumida, N. Adachi. Hiroshima Univ., Hiroshima, Japan Purpose: Osteochondritis dissecans (OCD) was reported by Franz €enig in 1888. So far, repetitive microtrauma is a favorable and the Ko most accepted etiology because patients with OCD are usually involved in high athletic activity and the increase of the patient population associated with increasing sports participation. Recently we introduced a unique anatomic feature of the femoral footprint of posterior cruciate ligament (PCL) in the patients with MFC OCD lesions. In the previous study, it was demonstrated that the femoral footprint of the PCL in patients with MFC OCD was located significantly distal position compared to the patients with non-OCD lesions. However, the mechanism predisposing to lesions due to this anatomic factor still remains unsolved. The purpose of this study was to investigate the alteration of in situ stress on the MFC due to distalized femoral footprint of PCL at knee flexion using finite element (FE) model. Methods: This study was approved by the Ethical Committee of Hiroshima University (Approval number: E-14). Establishment of threedimensional models: The CT images of the left knee joint, taken at full extension and 110 flexion without an applied load on the quadriceps or
187 ASSOCIATION BETWEEN ULTRASONOGRAPHY MEASUREMENTS OF TALAR CARTILAGE THICKNESS AND LOADING DURING GAIT IN INDIVIDUALS WITH CHRONIC ANKLE INSTABILITY K. Song, B.G. Pietrosimone, E.A. Wikstrom. UNC Chapel Hill, Chapel Hill, NC, USA Purpose: Individuals with chronic ankle instability (CAI) tend to develop post-traumatic ankle osteoarthritis (PTAOA), potentially due to altered mechanical loading of articular cartilage associated with aberrant gait biomechanics. The overall magnitude (peak vertical ground reaction force [vGRF]) and rate of loading (vGRF_LR) are higher in those