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Mechanical Loading Keynote Address
Journal of Biomechanics 34 (2001) S29
Mechanical Loading Keynote Address Experimental and theoretical investigations in osteoarthritis research W. Herzoga, J. Z. Wub, A. Clarka a
Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada b NIOSH, Morgantown, WV, USA
1. Introduction
3. Results
Osteoarthritis (OA) affects almost four out of five Canadians past the age of 65. In most cases, OA is idiopathic, and at present, there appears to be no accepted approach for the prevention of OA, nor are there established treatment modalities that could stop or even reverse OA. Osteoarthritis is typically considered a disease of articular cartilage, and studies on OA have focused on the changes in material properties of articular cartilage in experimental models of OA. Furthermore, OA is produced in animal models by a disruption of the normal joint mechanics (anterior cruciate ligament (ACL) transection, meniscectomy, etc.). Articular cartilage material properties are primarily determined in explants loaded in vitro. Joint loading in animal models of OA is typically determined using the joint kinematics and the external ground reaction forces. Our approach to OA research has differed somewhat from the mainstream approach, in that we have attempted (i) to first establish a bonafide model of OA; (ii) to quantify the internal, in vivo joint loading in this OA model, (iii) to consider the whole joint in the disease process, and (iv) to model the internal loading of the joint by appropriate multi-phasic, dynamic, structural, continuum mechanics models of articular contact. The purpose of the presentation at Biomechanica will be to introduce our experimental model of OA, to demonstrate how we quantified some aspects of the in vivo internal joint loading, and to present the corresponding theoretical results.
We observed bona fide, endstage OA in 10 experimental animals at 18–74 months following ACL transection. Three primary results emerged: (i) The external ground reaction forces and hindlimb joint kinematics returned to normal levels after approximately one year following intervention. nevertheless, joint degeneration continued. (ii) Joint degeneration was systematic across animals and was location dependent. For example, the retropatellar articular cartilage at endstage OA was thickened, had round chondrocytes in the surface layer, was soft, and showed great loss of proteoglycans. In contrast, the femoral groove articular cartilage looked and behaved perfectly normal. (iii) There appeared to be spontaneous regeneration of full cartilage focal lesions on the femoral condyles.
4. Discussion Despite a return to normal external locomotor kinematics within about 1 year, knee degeneration in the ACL-transected cats continued. This result demonstrates that normal external loading conditions do not guarantee successful control of joint degeneration. The great differences in local joint degeneration suggest that the internal, local mechanical loading might differ greatly from one articular surface to the next, or that structural and material properties might differ to produce heterogeneous joint degeneration. Finally, it appears that local regeneration of articular cartilage might be possible at distinct positions of the joint. These areas of regeneration should be carefully studied to elucidate how spontaneous repair might occur.
2. Methods We produced OA in the cat knee by transection of the ACL and evaluated a total of 26 animals from 4 weeks to 74 months following surgery. Internal muscular forces were measured using standard buckle-type transducers or implantable tendon force transducers. Electromyographical signals were evaluated using chronically implanted, bipolar, fine wire electrodes. In vitro, in situ, and in vivo pressure distribution measurements were performed using Fuji pressensor film. Cartilage mechanical properties were determined using stress-relaxation testing with an indentor or in an in situ joint contact configuration. Physiological deformation of the external surface of articular cartilage were measured by laser scanning, and internal structural changes of loaded articular cartilage was established using histology. Standard biochemical testing for proteoglycan and water content and external kinetic and kinematic measurements supplemented the above procedures.
PII: S 0 0 2 1 - 9 2 9 0 ( 0 1 ) 0 0 1 2 2 - 1
5. Conclusions Knee degeneration in the ACL transected cat is local, suggesting that local loading and/or local structural properties vastly differ across the articulating joint surfaces. It will be one of our priorities to systematically study the in vivo, internal, local loading of joints and to determine the corresponding functional properties of the articular cartilage surfaces.
Acknowledgements CIHR Canada, The Arthritis Society of Canada, AHFMR, NSERC.
Mechanical Loading Keynote Address Experimental and theoretical investigations in osteoarthritis research W. Herzoga, J. Z. Wub, A. Clarka a
Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada b NIOSH, Morgantown, WV, USA
1. Introduction
3. Results
Osteoarthritis (OA) affects almost four out of five Canadians past the age of 65. In most cases, OA is idiopathic, and at present, there appears to be no accepted approach for the prevention of OA, nor are there established treatment modalities that could stop or even reverse OA. Osteoarthritis is typically considered a disease of articular cartilage, and studies on OA have focused on the changes in material properties of articular cartilage in experimental models of OA. Furthermore, OA is produced in animal models by a disruption of the normal joint mechanics (anterior cruciate ligament (ACL) transection, meniscectomy, etc.). Articular cartilage material properties are primarily determined in explants loaded in vitro. Joint loading in animal models of OA is typically determined using the joint kinematics and the external ground reaction forces. Our approach to OA research has differed somewhat from the mainstream approach, in that we have attempted (i) to first establish a bonafide model of OA; (ii) to quantify the internal, in vivo joint loading in this OA model, (iii) to consider the whole joint in the disease process, and (iv) to model the internal loading of the joint by appropriate multi-phasic, dynamic, structural, continuum mechanics models of articular contact. The purpose of the presentation at Biomechanica will be to introduce our experimental model of OA, to demonstrate how we quantified some aspects of the in vivo internal joint loading, and to present the corresponding theoretical results.
We observed bona fide, endstage OA in 10 experimental animals at 18–74 months following ACL transection. Three primary results emerged: (i) The external ground reaction forces and hindlimb joint kinematics returned to normal levels after approximately one year following intervention. nevertheless, joint degeneration continued. (ii) Joint degeneration was systematic across animals and was location dependent. For example, the retropatellar articular cartilage at endstage OA was thickened, had round chondrocytes in the surface layer, was soft, and showed great loss of proteoglycans. In contrast, the femoral groove articular cartilage looked and behaved perfectly normal. (iii) There appeared to be spontaneous regeneration of full cartilage focal lesions on the femoral condyles.
4. Discussion Despite a return to normal external locomotor kinematics within about 1 year, knee degeneration in the ACL-transected cats continued. This result demonstrates that normal external loading conditions do not guarantee successful control of joint degeneration. The great differences in local joint degeneration suggest that the internal, local mechanical loading might differ greatly from one articular surface to the next, or that structural and material properties might differ to produce heterogeneous joint degeneration. Finally, it appears that local regeneration of articular cartilage might be possible at distinct positions of the joint. These areas of regeneration should be carefully studied to elucidate how spontaneous repair might occur.
2. Methods We produced OA in the cat knee by transection of the ACL and evaluated a total of 26 animals from 4 weeks to 74 months following surgery. Internal muscular forces were measured using standard buckle-type transducers or implantable tendon force transducers. Electromyographical signals were evaluated using chronically implanted, bipolar, fine wire electrodes. In vitro, in situ, and in vivo pressure distribution measurements were performed using Fuji pressensor film. Cartilage mechanical properties were determined using stress-relaxation testing with an indentor or in an in situ joint contact configuration. Physiological deformation of the external surface of articular cartilage were measured by laser scanning, and internal structural changes of loaded articular cartilage was established using histology. Standard biochemical testing for proteoglycan and water content and external kinetic and kinematic measurements supplemented the above procedures.
PII: S 0 0 2 1 - 9 2 9 0 ( 0 1 ) 0 0 1 2 2 - 1
5. Conclusions Knee degeneration in the ACL transected cat is local, suggesting that local loading and/or local structural properties vastly differ across the articulating joint surfaces. It will be one of our priorities to systematically study the in vivo, internal, local loading of joints and to determine the corresponding functional properties of the articular cartilage surfaces.
Acknowledgements CIHR Canada, The Arthritis Society of Canada, AHFMR, NSERC.