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Do microprocessor-controlled knees work better?
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Journal o f Biomechanics 2006, Vol. 39 (Suppl 1)
netic resonance and video-fluoroscopic acquisitions. First, the elastic modulus was considered constant in the all fibres of both ligaments and equal to 175 MPa. Second, each ligament was divided into the two anatomical bundles using the nuclear magnetic resonance data-set, and the values of the elastic modulus were assigned to all fibres of each bundle. The mechanical model was implemented in ADAMS/View 2005, and the drawer test consisted into a tibial antero-posterior translation of ± 1 0 mm. The antero-posterior forces estimated with the two modelling conditions were quite similar for little values of translation, whereas increasing the translation the forces became more different. The global stiffness opposed from the whole joint was always bigger when the cruciate were modelled using two different bundles. The Anterior and the Posterior Terminal Stiffness were always estimated into the two standard deviations considering the measurements reported by Markolf (1976). The Laxity was a more critical parameter, but acceptable comparisons were reached all the same. 5926 Tu, 08:45-09:00 (P15) The relationship between the knee adduction torque and medial contact force during gait D. Zhao 1, S.A. Banks 1,2,3, K. Mitchell 3, D. D'Lima 4, C. Colwell Jr. 4, B.J. Fregly 1,2. 1Department of Mechanical & Aerospace Engineering, University of Florida, Gainesville, USA, 2Department of Biomedical Engineering, University of Florida, Gainesville, USA, 3 The Biomotion Foundation, Palm Beach, USA, 4Shiley Center for Orthopaedic Research & Education at Scripps Clinic, La Jolla, USA Adverse mechanical loading of the knee, and in particular high medial contact force, is believed to contribute to the development of knee osteoarthritis. Noninvasive in vive measurement of medial compartment contact force is not yet available. Consequently, the peak external knee adduction torque during gait has been identified as the best candidate to serve as surrogates for internal medial compartment contact force. This paper investigates the relationship between the knee adduction torque and in vive medial contact force and medial to total contact force ratio during gait. The adduction torque curve of a subject during overground gait was obtained with a motion capture system. The corresponding internal contact forces were calculated from data provided by an instrumented knee implant capable of measuring total axial force. An equation for partitioning total force into medial and lateral contact forces was determined using fluoroscopic data collected from the same subject performing treadmill gait. During overground gait, the peak measured axial load was 2.45 BW with a corresponding peak predicted medial compartment load of 1.51 BW. The peak knee adduction torque was 2.53%BW H. The medial contact force and adduction torque curves exhibited similar trends. Statistically significant correlations were found between the adduction torque and both the medial contact force and the ratio of medial to total contact force. The Pearson correlation coefficient of adduction torque vs. medial force was 0.85 and for adduction torque vs. medial to total force ratio 0.87. The results showed that knee adduction torque measured externally is an accurate predictor for internal medial compartment contact force and a strong correlation also exists between adduction torque and medial to total force ratio. 5943 Tu, 09:00-09:15 (P15) Do microprocessor-controlled knees work better? K.R. Kaufman 1, B. Iverson 1, D. Padgett 1, R.H. Brey 2, J.A. Levine 3, M.J. Joyner 4. 1Biomechanics/Motion Analysis Laboratory, 2Vestibular Laboratory, 3Endocrine Research Laboratory, 4Anesthesia Research, Mayo Clinic, Rochester, MN, USA Introduction: Microprocessor controlled knee joints have appeared on the market recently and have little data regarding their function. Therefore, the purpose of this study was to quantify the functional characteristics of active transfemoral amputees using a microprocessor controlled knee compared to the most prescribed mechanical knee joint. Methods: Thirteen subjects were studied (mean age 43±9 years). All subjects were long-term prosthesis users (19±11 years). A crossover design was used. Only the knee component was changed. Each subject was tested using a mechanical knee prosthesis (Mauch SNS or CaTech) and retested eight weeks after receiving a microprocessor controlled knee joint (OttoBock C-leg). A multifactor analysis was employed. Objective gait measurements were collected. Subjects' balance was tested on the Equitest TM Posturography System. Energy consumption measurements were made at 3 walking speeds (0.45, 0.9, and 1.3m/s) using a respiratory mass spectrometer. Total daily energy expenditure was quantified for 10 days using doubly-labeled water. Activity levels were quantified over the same time period using a Step Watch TM . The Prosthetic Evaluation Questionnaire (PEQ) was used to gather subjective feedback. Statistical comparisons were made using a paired t-test or the Wilcoxon signed-rank test. Results: Subjects demonstrated significantly improved gait and balance characteristics after receiving the microprocessor controlled prosthetic knee joint
Oral Presentations (p < 0.05). There were no significant differences in the metabolic cost of walking (p > 0.5). Most importantly, the improvements in gait and balance translated into increased activity levels. The subjects increased their steps per day by 18% along with a significant increase in total daily energy expenditure. When using the microprocessor controlled knee, the subjects displayed a strong trend toward increased satisfaction in their lives (p = 0.06). Discussion: Although the first commercially available micro-processor controlled knee joint was introduced over a decade ago, few studies have evaluated these devices. Given the paucity of studies, it is difficult for third-party payers to develop an appropriate medical policy regarding coverage for microprocessorcontrolled knees. The data from this study demonstrates that individuals using a microprocessor-controlled knee have improvements in gait and balance which translate into increased activity in the users' daily life. 6995 Tu, 09:15-09:30 (P16) Mediation o f knee strength by a psychosocial factor to affect walking performance in knee osteoarthritis M.R. Maly 1, IRA. Costigan 2, S.J. Olney 3. 1School ef Physical Therapy, The University of Western Ontario, London, Ontario, Canada, 2School of Physical & Health Education and CSchool of Rehabilitation Therapy, Queen's University, Kingston, Ontario, Canada Confidence to complete physical tasks, self-efficacy, explains 50% of walking performance [1]. Hamstrings strength relates to self-efficacy in knee osteoarthritis (OA) [2]. We examined whether self-efficacy mediated the effect of hamstrings strength on walking performance in knee OA. A mediator is a variable representing a mechanism through which an independent variable influences the dependent variable of interest [3]. Method: Participants had radiographic medial knee OA (n =54, age 68.3±8.7). Walking performance was assessed with the Six Minute Walk (SMW), which records self-paced indoor walking distance. Self-Efficacy was assessed using the Functional Self-Efficacy subscale (FSE) of the Arthritis Self-Efficacy Scale. Hamstrings strength was the mean peak flexor torque (HAMS) of 5 maximumeffort 60°/s trials on an isokinetic dynamometer. Mediation criteria included relationships (HAMS*FSE, FSE*SMW, HAMS*FSE) and a linear regression to explain variance in the SMW with HAMS, controlling for FSE. Partial mediation was assessed with a standard equation, called the Sobel equation [4]. Results & Discussion: HAMS explained 14% of the variance in FSE (P = 0.004). FSE explained 50.6% of the variance in SMW (P < 0.001). HAMS explained 21% of the variance in SMW (P < 0.001 ). Controlling for FSE did not remove all of the effect of HAMS on SMW, suggesting that HAMS was not fully mediated by FSE. For HAMS, the Sobel equation calculated a z value of 2.81; because this value is >1.96, the effect of HAMS on SMW was partially mediated by FSE. HAMS represents capability of the motor control system and is likely perceived to determine self-efficacy for walking performance. Strength may also interact with other unknown variables to influence performance in people with knee OA. Canadian Institutes for Health Research (#99034), Natural Sciences & Engineering Research Council, Toronto Rehabilitation Institute. References [1] Maly. Phys Ther. 2005; 85: 1318-1328. [2] Maly. Arthritis Care Res., in press. [3] Baron J. Person Social Psych. 1986; 51:1173-1182. [4] MacKinnon Psychol Methods 2002; 7: 83-104. 5049 Tu, 09:30-09:45 (P16) Application o f functional data analysis techniques to study knee biomechanics in patients with degenerative arthritis before and after total knee replacement C. Avila, A. Page, C. Atienza, A. Oltra, A. G6mez, A. L6pez, P. Vera, J. Prat. Institute de Biomec~nica de Valencia, Universidad Polit~cnica de Valencia, Valencia, Spain The aim of this study is to characterize knee biomechanics in osteoarthritic patients who undergo a total knee replacement (TKR) and relate it to their clinical situation by means of analyzing the kinematics and dynamics of different types of movement. Most of the published biomechanical studies about patients with knee osteoarthritis are based on gait analysis and on the statistical analysis of scalar variables resulting from the parameterization of the movement curves like angular rotations or forces across the knee joint. This approach does not consider the dynamic aspects of movement, therefore limiting the scope of results. Actually, there is no agreement about the best method clarify differences between different grades of pathology or to evaluate patients' clinical situation in an objective way. We propose a new approach for the biomechanical analysis of patients suffering knee degenerative arthritis based on the evaluation of other activities more demanding than gait and the use of functional data analysis techniques
Journal o f Biomechanics 2006, Vol. 39 (Suppl 1)
netic resonance and video-fluoroscopic acquisitions. First, the elastic modulus was considered constant in the all fibres of both ligaments and equal to 175 MPa. Second, each ligament was divided into the two anatomical bundles using the nuclear magnetic resonance data-set, and the values of the elastic modulus were assigned to all fibres of each bundle. The mechanical model was implemented in ADAMS/View 2005, and the drawer test consisted into a tibial antero-posterior translation of ± 1 0 mm. The antero-posterior forces estimated with the two modelling conditions were quite similar for little values of translation, whereas increasing the translation the forces became more different. The global stiffness opposed from the whole joint was always bigger when the cruciate were modelled using two different bundles. The Anterior and the Posterior Terminal Stiffness were always estimated into the two standard deviations considering the measurements reported by Markolf (1976). The Laxity was a more critical parameter, but acceptable comparisons were reached all the same. 5926 Tu, 08:45-09:00 (P15) The relationship between the knee adduction torque and medial contact force during gait D. Zhao 1, S.A. Banks 1,2,3, K. Mitchell 3, D. D'Lima 4, C. Colwell Jr. 4, B.J. Fregly 1,2. 1Department of Mechanical & Aerospace Engineering, University of Florida, Gainesville, USA, 2Department of Biomedical Engineering, University of Florida, Gainesville, USA, 3 The Biomotion Foundation, Palm Beach, USA, 4Shiley Center for Orthopaedic Research & Education at Scripps Clinic, La Jolla, USA Adverse mechanical loading of the knee, and in particular high medial contact force, is believed to contribute to the development of knee osteoarthritis. Noninvasive in vive measurement of medial compartment contact force is not yet available. Consequently, the peak external knee adduction torque during gait has been identified as the best candidate to serve as surrogates for internal medial compartment contact force. This paper investigates the relationship between the knee adduction torque and in vive medial contact force and medial to total contact force ratio during gait. The adduction torque curve of a subject during overground gait was obtained with a motion capture system. The corresponding internal contact forces were calculated from data provided by an instrumented knee implant capable of measuring total axial force. An equation for partitioning total force into medial and lateral contact forces was determined using fluoroscopic data collected from the same subject performing treadmill gait. During overground gait, the peak measured axial load was 2.45 BW with a corresponding peak predicted medial compartment load of 1.51 BW. The peak knee adduction torque was 2.53%BW H. The medial contact force and adduction torque curves exhibited similar trends. Statistically significant correlations were found between the adduction torque and both the medial contact force and the ratio of medial to total contact force. The Pearson correlation coefficient of adduction torque vs. medial force was 0.85 and for adduction torque vs. medial to total force ratio 0.87. The results showed that knee adduction torque measured externally is an accurate predictor for internal medial compartment contact force and a strong correlation also exists between adduction torque and medial to total force ratio. 5943 Tu, 09:00-09:15 (P15) Do microprocessor-controlled knees work better? K.R. Kaufman 1, B. Iverson 1, D. Padgett 1, R.H. Brey 2, J.A. Levine 3, M.J. Joyner 4. 1Biomechanics/Motion Analysis Laboratory, 2Vestibular Laboratory, 3Endocrine Research Laboratory, 4Anesthesia Research, Mayo Clinic, Rochester, MN, USA Introduction: Microprocessor controlled knee joints have appeared on the market recently and have little data regarding their function. Therefore, the purpose of this study was to quantify the functional characteristics of active transfemoral amputees using a microprocessor controlled knee compared to the most prescribed mechanical knee joint. Methods: Thirteen subjects were studied (mean age 43±9 years). All subjects were long-term prosthesis users (19±11 years). A crossover design was used. Only the knee component was changed. Each subject was tested using a mechanical knee prosthesis (Mauch SNS or CaTech) and retested eight weeks after receiving a microprocessor controlled knee joint (OttoBock C-leg). A multifactor analysis was employed. Objective gait measurements were collected. Subjects' balance was tested on the Equitest TM Posturography System. Energy consumption measurements were made at 3 walking speeds (0.45, 0.9, and 1.3m/s) using a respiratory mass spectrometer. Total daily energy expenditure was quantified for 10 days using doubly-labeled water. Activity levels were quantified over the same time period using a Step Watch TM . The Prosthetic Evaluation Questionnaire (PEQ) was used to gather subjective feedback. Statistical comparisons were made using a paired t-test or the Wilcoxon signed-rank test. Results: Subjects demonstrated significantly improved gait and balance characteristics after receiving the microprocessor controlled prosthetic knee joint
Oral Presentations (p < 0.05). There were no significant differences in the metabolic cost of walking (p > 0.5). Most importantly, the improvements in gait and balance translated into increased activity levels. The subjects increased their steps per day by 18% along with a significant increase in total daily energy expenditure. When using the microprocessor controlled knee, the subjects displayed a strong trend toward increased satisfaction in their lives (p = 0.06). Discussion: Although the first commercially available micro-processor controlled knee joint was introduced over a decade ago, few studies have evaluated these devices. Given the paucity of studies, it is difficult for third-party payers to develop an appropriate medical policy regarding coverage for microprocessorcontrolled knees. The data from this study demonstrates that individuals using a microprocessor-controlled knee have improvements in gait and balance which translate into increased activity in the users' daily life. 6995 Tu, 09:15-09:30 (P16) Mediation o f knee strength by a psychosocial factor to affect walking performance in knee osteoarthritis M.R. Maly 1, IRA. Costigan 2, S.J. Olney 3. 1School ef Physical Therapy, The University of Western Ontario, London, Ontario, Canada, 2School of Physical & Health Education and CSchool of Rehabilitation Therapy, Queen's University, Kingston, Ontario, Canada Confidence to complete physical tasks, self-efficacy, explains 50% of walking performance [1]. Hamstrings strength relates to self-efficacy in knee osteoarthritis (OA) [2]. We examined whether self-efficacy mediated the effect of hamstrings strength on walking performance in knee OA. A mediator is a variable representing a mechanism through which an independent variable influences the dependent variable of interest [3]. Method: Participants had radiographic medial knee OA (n =54, age 68.3±8.7). Walking performance was assessed with the Six Minute Walk (SMW), which records self-paced indoor walking distance. Self-Efficacy was assessed using the Functional Self-Efficacy subscale (FSE) of the Arthritis Self-Efficacy Scale. Hamstrings strength was the mean peak flexor torque (HAMS) of 5 maximumeffort 60°/s trials on an isokinetic dynamometer. Mediation criteria included relationships (HAMS*FSE, FSE*SMW, HAMS*FSE) and a linear regression to explain variance in the SMW with HAMS, controlling for FSE. Partial mediation was assessed with a standard equation, called the Sobel equation [4]. Results & Discussion: HAMS explained 14% of the variance in FSE (P = 0.004). FSE explained 50.6% of the variance in SMW (P < 0.001). HAMS explained 21% of the variance in SMW (P < 0.001 ). Controlling for FSE did not remove all of the effect of HAMS on SMW, suggesting that HAMS was not fully mediated by FSE. For HAMS, the Sobel equation calculated a z value of 2.81; because this value is >1.96, the effect of HAMS on SMW was partially mediated by FSE. HAMS represents capability of the motor control system and is likely perceived to determine self-efficacy for walking performance. Strength may also interact with other unknown variables to influence performance in people with knee OA. Canadian Institutes for Health Research (#99034), Natural Sciences & Engineering Research Council, Toronto Rehabilitation Institute. References [1] Maly. Phys Ther. 2005; 85: 1318-1328. [2] Maly. Arthritis Care Res., in press. [3] Baron J. Person Social Psych. 1986; 51:1173-1182. [4] MacKinnon Psychol Methods 2002; 7: 83-104. 5049 Tu, 09:30-09:45 (P16) Application o f functional data analysis techniques to study knee biomechanics in patients with degenerative arthritis before and after total knee replacement C. Avila, A. Page, C. Atienza, A. Oltra, A. G6mez, A. L6pez, P. Vera, J. Prat. Institute de Biomec~nica de Valencia, Universidad Polit~cnica de Valencia, Valencia, Spain The aim of this study is to characterize knee biomechanics in osteoarthritic patients who undergo a total knee replacement (TKR) and relate it to their clinical situation by means of analyzing the kinematics and dynamics of different types of movement. Most of the published biomechanical studies about patients with knee osteoarthritis are based on gait analysis and on the statistical analysis of scalar variables resulting from the parameterization of the movement curves like angular rotations or forces across the knee joint. This approach does not consider the dynamic aspects of movement, therefore limiting the scope of results. Actually, there is no agreement about the best method clarify differences between different grades of pathology or to evaluate patients' clinical situation in an objective way. We propose a new approach for the biomechanical analysis of patients suffering knee degenerative arthritis based on the evaluation of other activities more demanding than gait and the use of functional data analysis techniques