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Fatigue of acrylic bone cement—The influence of strain range and mean strain
284
Abstracts
an extension peak after heel-off. The flexion moment peak at toe-strike was greater than normal for both adjustments of the orthosis. In normal gait, the total knee moment is minimized; but any factor, including adjustment of an ankle-foot orthosis can increase the knee moment, creating knee instability and increasing the muscular effort needed during ambulation. A DETAILED STUDY OF THE EFFECTS OF LONG TERM USE ON A TOTAL KNEE PROSTHESIS E. H. COALE, S. A. GOLDSTEIN, R. R. RESCHLY,and L. S. MATTHEWS,(Orthopaedic Biomechanics Laboratory, University of Michigan, Ann Arbor, MI, U.S.A.) The first patient treated with Spherocentric arthroplasty at our institution donated her knee for research at her death. She was seventy years old at the time of arthroplasty for degenerative arthritis. No special cement techniques were used. Her arthroplasty was a clinical success for the 6.5 years until her death. The knee joint was carefully removed preserving the bone-cement interface, surrounding soft tissue and the supporting trabecular bone. The tissue was examined using standard light, phase contrast and polarized microscopy. The trabecular bone was examined for remodeling response and viability. Special thin ground specimens were examined for interdigitation of cement membrane formation and tissue viability. The polyethylene components were evaluated for wear and/or deformation by utilizing a computer actuated precision x-y table and a LVDT gage head along a z-axis. PMMA REINFORCED
BY HYDROXY + APATITE CRYSTALS PRELIMINARY RESULTS: CREEP ANALYSIS
A. CASTALDINI,A. CAVALLINI(Physics Institute of the University of Bologna) A. MORONI, R. OLMI and L. RANIERI (III Orthopedic Clinic of the Rizzoli Orthopedic Institute, University of Bologna, Italy) The importance of the use of acrylic cements in prosthetic surgery has induced study of the behavior of compound cements for strengthening of the prosthetic implant. The authors have, therefore, seen it opportune to add synthetic hydroxy-apatite crystals to a PMMA base commercial cement (Surgical Simplex) keeping in mind, besides normal criteria (e.g. non-toxicity), its affinity with the great quantity of crystalline units of hydroxy-apatite present in the bone. A study was therefore carried out to determine deformation in the reinforced cement using various percentages of hydroxy-apatite. In order to examine the variation of the plastic deformability from the moment of mixing, creep tests were subsequently made from the polymerization moment. FATIGUE OF ACRYLIC BONE CEMENT-THE INFLUENCE AND MEAN STRAIN
OF STRAIN RANGE
E. I. GATES, D. R. CARTERand W. H. HARRIS(Orthopaedic Research Laboratories, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, U.S.A.) Fatigue tests were conducted of wet acrylic bone cement specimens at 37°C with zero-tension and tension-compression loading. Testing was conducted in strain control at a physiologic strain rate of 0.02 s- i. The number of cycles to fatigue failure was more strongly governed by cyclic strain than cyclic stress. The fatigue date, when plotted on a modified Goodman diagram, lay below the Goodman line, with an n value less than one, indicating that the critical parameter in determining fatigue failure is the maximum cyclic tensile strain rather than cyclic strain range. Specimen porosity distribution played a major role in determining the fatigue strength. Weibull analysis was used to quantify the degree of data scatter, and may be useful in developing design criteria for the surgical use of bone cement. MUSCULAR POWER ACROSS THE KNEE JOINT DURING THE PULL IN OLYMPIC WEIGHTLIFTING R. M. ENOKA (Department
of Physical Education, University of Arizona, Tucson, AZ, U.S.A.)
The rate of mechanical energy flowing into or out of muscles, power absorption and production respectively, is often thought to limit human performance, especially if the event is of short duration (e.g. Wilkie, 1960). The intent of this investigation was to evaluate the relevance of this premise to Olympic weightlifting by examining the influence of skill and load on the muscular power produced by experienced weightlifters. Muscular power across the knee joint was determined with respect to the mass of the leg as the product of the resultant muscle torque,
Abstracts
an extension peak after heel-off. The flexion moment peak at toe-strike was greater than normal for both adjustments of the orthosis. In normal gait, the total knee moment is minimized; but any factor, including adjustment of an ankle-foot orthosis can increase the knee moment, creating knee instability and increasing the muscular effort needed during ambulation. A DETAILED STUDY OF THE EFFECTS OF LONG TERM USE ON A TOTAL KNEE PROSTHESIS E. H. COALE, S. A. GOLDSTEIN, R. R. RESCHLY,and L. S. MATTHEWS,(Orthopaedic Biomechanics Laboratory, University of Michigan, Ann Arbor, MI, U.S.A.) The first patient treated with Spherocentric arthroplasty at our institution donated her knee for research at her death. She was seventy years old at the time of arthroplasty for degenerative arthritis. No special cement techniques were used. Her arthroplasty was a clinical success for the 6.5 years until her death. The knee joint was carefully removed preserving the bone-cement interface, surrounding soft tissue and the supporting trabecular bone. The tissue was examined using standard light, phase contrast and polarized microscopy. The trabecular bone was examined for remodeling response and viability. Special thin ground specimens were examined for interdigitation of cement membrane formation and tissue viability. The polyethylene components were evaluated for wear and/or deformation by utilizing a computer actuated precision x-y table and a LVDT gage head along a z-axis. PMMA REINFORCED
BY HYDROXY + APATITE CRYSTALS PRELIMINARY RESULTS: CREEP ANALYSIS
A. CASTALDINI,A. CAVALLINI(Physics Institute of the University of Bologna) A. MORONI, R. OLMI and L. RANIERI (III Orthopedic Clinic of the Rizzoli Orthopedic Institute, University of Bologna, Italy) The importance of the use of acrylic cements in prosthetic surgery has induced study of the behavior of compound cements for strengthening of the prosthetic implant. The authors have, therefore, seen it opportune to add synthetic hydroxy-apatite crystals to a PMMA base commercial cement (Surgical Simplex) keeping in mind, besides normal criteria (e.g. non-toxicity), its affinity with the great quantity of crystalline units of hydroxy-apatite present in the bone. A study was therefore carried out to determine deformation in the reinforced cement using various percentages of hydroxy-apatite. In order to examine the variation of the plastic deformability from the moment of mixing, creep tests were subsequently made from the polymerization moment. FATIGUE OF ACRYLIC BONE CEMENT-THE INFLUENCE AND MEAN STRAIN
OF STRAIN RANGE
E. I. GATES, D. R. CARTERand W. H. HARRIS(Orthopaedic Research Laboratories, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, U.S.A.) Fatigue tests were conducted of wet acrylic bone cement specimens at 37°C with zero-tension and tension-compression loading. Testing was conducted in strain control at a physiologic strain rate of 0.02 s- i. The number of cycles to fatigue failure was more strongly governed by cyclic strain than cyclic stress. The fatigue date, when plotted on a modified Goodman diagram, lay below the Goodman line, with an n value less than one, indicating that the critical parameter in determining fatigue failure is the maximum cyclic tensile strain rather than cyclic strain range. Specimen porosity distribution played a major role in determining the fatigue strength. Weibull analysis was used to quantify the degree of data scatter, and may be useful in developing design criteria for the surgical use of bone cement. MUSCULAR POWER ACROSS THE KNEE JOINT DURING THE PULL IN OLYMPIC WEIGHTLIFTING R. M. ENOKA (Department
of Physical Education, University of Arizona, Tucson, AZ, U.S.A.)
The rate of mechanical energy flowing into or out of muscles, power absorption and production respectively, is often thought to limit human performance, especially if the event is of short duration (e.g. Wilkie, 1960). The intent of this investigation was to evaluate the relevance of this premise to Olympic weightlifting by examining the influence of skill and load on the muscular power produced by experienced weightlifters. Muscular power across the knee joint was determined with respect to the mass of the leg as the product of the resultant muscle torque,