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Mechanical properties of osteopetrotic bone
295
Abstracts MECHANICAL
PROPERTIES
OF OSTEOPETROTIC
BONE
R. P. ROBINSON (Section of Orthopedics, The Mason Clinic, Seattle, WA, U.S.A.) F. VOSBURGH (Rockefeller University, New York, NY, U.S.A.) A. H. BURSTEIN (Biomechanics Department, The Hospital for Special Surgery New York, NY, U.S.A.) Osteopetrosis is a rare inherited disorder of bone which is clinically associated with frequent transverse fractures resulting from low energy injuries. In order to more completely understand the mechanism of pathologic fractures in these patients, bone material property specimens were made from a patient with osteopetrosis. Specimens were tested to failure in compression. Ultimate stress and modulus of elasticity were lower than human cortical bone 58 x lo6 k 14 x lo6 Nme2 and 2.1 x lo9 + 0.7 x lo9 Nm-’ respectively (for longitudinal specimens). Apparent density was comparable to that of human cortical bone 1.80+0.09 gcme3. Elastic modulus was found to be isotropic while ultimate stress was not. Sections examined with a Zeiss MOP digitizer revealed that more area in transverse sections was occupied by skeletal tissue than in longitudinal sections 90.3 y, + 3.31 and 73.0”. f 4.48 respectively, p < 0.01. A vague longitudinal orientation of tissue was seen histologically. THE DISTRIBUTION OF TIBIAL TRABECULAR BONE PROPERTIES DETERMINED BY COMPUTER ASSISTED AXIAL TOMOGRAPHY
AS
S. A. GOLDSTEIN, L. S. MATTHEWS, E. M. BRAUNSTEIN, and B. W. MARKS, (Orthopaedic Biomechanics Laboratory and Department of Radiology, University of Michigan, Ann Arbor, MI, U.S.A.) A General Electric CT/T 8800 computer assisted tomographic scanner equipped with a high resolution detector array was utilized to determine the mechanical properties of human proximal tibia1 metaphyseal bone. A matrix of approximately 100 volume elements was defined on each tibia. The mean densities and standard deviations in CT numbers (- loo0 = air density; + 100 = cortical bone) were recorded for each volume element. Utilizing the volume densities and locations, a statistically significant relationship between the CT densities and previously reported mechanical properties was found. This study indicates that high resolution CT scanning can be used to estimate the mechanical properties of trabecular bone. ACOUSTIC
EMISSION: A NON-INVASIVE MONITORING TECHNIQUE TOTAL JOINT REPLACEMENT PATIENTS
FOR
T. M. WRIGHT, D. L. BARTEL and A. H. BURSTEIN (The Hospital for Special Surgery, Affiliated with New York Hospital-Cornell University Medical College) Total joint replacement of diseased and damaged joints is successful in relieving pain and restoring function. Complications do exist, however, and are often associated with mechanical damage (e.g., loosening and fracture). The need exists for a technique to detect such damage at its earliest stage. Acoustic emission (AE) is a proven method for nondestructive monitoring of loaded structures. It involves the detection of stress waves emanating from sources of mechanical damage. AE signals, together with knowledge of the applied loads, can be used to determine the onset of damage, the damage source location. and, in some cases, the damage mechanism itself. AE monitoring of total joint replacement patients provides a non-invasive method for detecting damage which is easy to perform and of minimum risk to the patient. Development of AE monitoring has involved work in three areas: in-viva monitoring of patients, determination of soft tissue attenuation characteristics of AE signals, and in-vitro experiments to identify the AE characteristics of specific damage mechanisms. In-oiuo monitoring has centered on total knee patients. To date, 125 total knee joints in 89 patients have been monitored using conventional AE equipment. The results have shown excellent agreement between the AE characteristics (measured while loading the joint) and the clinical diagnosis based on patient symptoms and radiographic findings. STUDY OF THE INTERACTION BETWEEN KNEE JOINT POSITION, LOADS, AND MUSCLE ACTIVITY AT THE KNEE
JOINT
T. P. ANDRIACCHI, G. B. J. ANDERSSON, R. ORTENGREN and R. MIKOSZ (RushPresbyterian-St. Luke’s Medical Center, Department of Orthopedic Surgery, 1753 West Congress Parkway, Chicago, IL 60612, U.S.A.) The knee joint relies on muscles to provide stability as well as movement.
As such, the muscles contribute
a major
Abstracts MECHANICAL
PROPERTIES
OF OSTEOPETROTIC
BONE
R. P. ROBINSON (Section of Orthopedics, The Mason Clinic, Seattle, WA, U.S.A.) F. VOSBURGH (Rockefeller University, New York, NY, U.S.A.) A. H. BURSTEIN (Biomechanics Department, The Hospital for Special Surgery New York, NY, U.S.A.) Osteopetrosis is a rare inherited disorder of bone which is clinically associated with frequent transverse fractures resulting from low energy injuries. In order to more completely understand the mechanism of pathologic fractures in these patients, bone material property specimens were made from a patient with osteopetrosis. Specimens were tested to failure in compression. Ultimate stress and modulus of elasticity were lower than human cortical bone 58 x lo6 k 14 x lo6 Nme2 and 2.1 x lo9 + 0.7 x lo9 Nm-’ respectively (for longitudinal specimens). Apparent density was comparable to that of human cortical bone 1.80+0.09 gcme3. Elastic modulus was found to be isotropic while ultimate stress was not. Sections examined with a Zeiss MOP digitizer revealed that more area in transverse sections was occupied by skeletal tissue than in longitudinal sections 90.3 y, + 3.31 and 73.0”. f 4.48 respectively, p < 0.01. A vague longitudinal orientation of tissue was seen histologically. THE DISTRIBUTION OF TIBIAL TRABECULAR BONE PROPERTIES DETERMINED BY COMPUTER ASSISTED AXIAL TOMOGRAPHY
AS
S. A. GOLDSTEIN, L. S. MATTHEWS, E. M. BRAUNSTEIN, and B. W. MARKS, (Orthopaedic Biomechanics Laboratory and Department of Radiology, University of Michigan, Ann Arbor, MI, U.S.A.) A General Electric CT/T 8800 computer assisted tomographic scanner equipped with a high resolution detector array was utilized to determine the mechanical properties of human proximal tibia1 metaphyseal bone. A matrix of approximately 100 volume elements was defined on each tibia. The mean densities and standard deviations in CT numbers (- loo0 = air density; + 100 = cortical bone) were recorded for each volume element. Utilizing the volume densities and locations, a statistically significant relationship between the CT densities and previously reported mechanical properties was found. This study indicates that high resolution CT scanning can be used to estimate the mechanical properties of trabecular bone. ACOUSTIC
EMISSION: A NON-INVASIVE MONITORING TECHNIQUE TOTAL JOINT REPLACEMENT PATIENTS
FOR
T. M. WRIGHT, D. L. BARTEL and A. H. BURSTEIN (The Hospital for Special Surgery, Affiliated with New York Hospital-Cornell University Medical College) Total joint replacement of diseased and damaged joints is successful in relieving pain and restoring function. Complications do exist, however, and are often associated with mechanical damage (e.g., loosening and fracture). The need exists for a technique to detect such damage at its earliest stage. Acoustic emission (AE) is a proven method for nondestructive monitoring of loaded structures. It involves the detection of stress waves emanating from sources of mechanical damage. AE signals, together with knowledge of the applied loads, can be used to determine the onset of damage, the damage source location. and, in some cases, the damage mechanism itself. AE monitoring of total joint replacement patients provides a non-invasive method for detecting damage which is easy to perform and of minimum risk to the patient. Development of AE monitoring has involved work in three areas: in-viva monitoring of patients, determination of soft tissue attenuation characteristics of AE signals, and in-vitro experiments to identify the AE characteristics of specific damage mechanisms. In-oiuo monitoring has centered on total knee patients. To date, 125 total knee joints in 89 patients have been monitored using conventional AE equipment. The results have shown excellent agreement between the AE characteristics (measured while loading the joint) and the clinical diagnosis based on patient symptoms and radiographic findings. STUDY OF THE INTERACTION BETWEEN KNEE JOINT POSITION, LOADS, AND MUSCLE ACTIVITY AT THE KNEE
JOINT
T. P. ANDRIACCHI, G. B. J. ANDERSSON, R. ORTENGREN and R. MIKOSZ (RushPresbyterian-St. Luke’s Medical Center, Department of Orthopedic Surgery, 1753 West Congress Parkway, Chicago, IL 60612, U.S.A.) The knee joint relies on muscles to provide stability as well as movement.
As such, the muscles contribute
a major