Rabbit knee joint biomechanics: Motion analysis and modeling of forces during hopping

Although mechanical loading is known to influence trabecular bone adaptation, the role of specific loading parameters requires further investigation. Previous studies demonstrated that the number of loading cycles and loading duration modulate the adaptive response of trabecular bone in a rabbit model of applied loading. In the current study, we investigated the influence of load magnitude on the adaptive response of trabecular bone using the rabbit model. Cyclic compressive loads, producing peak pressures of either 0.5 or 1.0 MPa, were applied daily (5 days/week) at 1 Hz and 50 cycles/day for 4 weeks post-operatively to the trabecular bone on the lateral side of the distal right femur, while the left side served as an nonloaded control. The adaptive response was characterized by microcomputed tomography and histomorphometry. Bone volume fraction, bone mineral content, tissue mineral density, and mineral apposition rate (MAR) increased in loaded limbs compared to the contralateral control limbs. No load magnitude dependent difference was observed, which may reflect the critical role of loading compared to the operated, nonloaded contralateral limb. The increased MAR suggests that loading stimulated new bone formation rather than just maintaining bone volume. The absence of a dose-dependent response of trabecular bone observed in this study suggests that a range of load magnitudes should be examined for biophysical therapies aimed at augmenting current treatments to enhance long-term fixation of orthopedic devices. Keywords: trabecular bone; bone adaptation; rabbit; microcomputed tomography; mechanical stimulation Mechanical loading plays a central role in skeletal development and maintenance via both modeling and remodeling processes. 1-3 Throughout life the skeleton adapts by changing bone mass and architecture to the functional demands placed on it by mechanical stimuli. In cortical bone, loading must be dynamic rather than static to elicit an anabolic response 4 and adaptive remodeling is preferentially responsive to short periods of strain change. 5 For example, high-magnitude strains, varied by regulating the applied load 6-8 and strain rate, 9 enhanced cortical bone mass.Age-related bone loss, disuse-related bone loss, bone healing, and osseointegration around implants are all intimately coupled with the mechanical loading environment in trabecular bone. Despite the importance of studies on cortical diaphyseal bone adaptation to mechanical loading, prevention and treatment of osteoporosis and osteoarthritis requires investigation of trabecular bone adaptation. In addition, important questions remain concerning trabecular bone functional adaptation to a variety of loading parameters.Well-controlled and minimally invasive experimental models of loading in trabecular bone have been difficult to develop. [10][11][12][13] In vivo intermittent compressive loading via a hydraulic bone chamber stimulated bone matrix synthesis in trabecular bone of the canine tibial and femoral metaphyses. 14 While clearl...

Section: Discussionsupporting

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Trabecular bone adaptation to loading in a rabbit model is not magnitude‐dependent

Yang¹,

Willie²,

Beach³

et al. 2013

“…muscular activity. The compression forces acting on the rabbit knee have been estimated to be about three times bodyweight when hopping, 29 implying a stress at the growth plate of about 0.5 MPa. The mean ultimate tensile stress of 5-month-old bovine growth plates was reported as 1.4 MPa.…”

Section: Discussionmentioning

confidence: 99%

Endochondral growth in growth plates of three species at two anatomical locations modulated by mechanical compression and tension

Stokes

Aronsson

Dimock

et al. 2006

136

158

Sustained mechanical loading alters longitudinal growth of bones, and this growth sensitivity to load has been implicated in progression of skeletal deformities during growth. The objective of this study was to quantify the relationship between altered growth and different magnitudes of sustained altered stress in a diverse set of nonhuman growth plates. The sensitivity of endochondral growth to differing magnitudes of sustained compression or distraction stress was measured in growth plates of three species of immature animals (rats, rabbits, calves) at two anatomical locations (caudal vertebra and proximal tibia) with two different ages of rats and rabbits. An external loading apparatus was applied for 8 days, and growth was measured as the distance between fluorescent markers administered 24 and 48 h prior to euthanasia. An apparently linear relationship between stress and percentage growth modulation (percent difference between loaded and control growth plates) was found, with distraction accelerating growth and compression slowing growth. The growth-rate sensitivity to stress was between 9.2 and 23.9% per 0.1 MPa for different growth plates and averaged 17.1% per 0.1 MPa. The growth-rate sensitivity to stress differed between vertebrae and the proximal tibia (15 and 18.6% per 0.1 MPa, respectively). The range of control growth rates of different growth plates was large (30 microns/day for rat vertebrae to 366 microns/day for rabbit proximal tibia). The relatively small differences in growth-rate sensitivity to stress for a diverse set of growth plates suggest that these results might be generalized to other growth plates, including human. These data may be applicable to planning the management of progressive deformities in patients having residual growth. ß

“…36 Stair climbing results in larger relative bending moments than walking, so animals with flexed joints might also have higher amounts of bending moments in their femora. One study characterized knee biomechanics in rabbits, 41 providing insight in the differences in relative forces and moments compared to larger animals. From that study it can be anticipated that there would be larger bending moments on the femora in small animals such as mice.…”

Section: Remodeling Of Fracture Callus In Micementioning

confidence: 99%

Remodeling of fracture callus in mice is consistent with mechanical loading and bone remodeling theory

Isaksson

Gröngröft

Wilson

et al. 2008

During the remodeling phase of fracture healing in mice, the callus gradually transforms into a double cortex, which thereafter merges into one cortex. In large animals, a double cortex normally does not form. We investigated whether these patterns of remodeling of the fracture callus in mice can be explained by mechanical loading. Morphologies of fractures after 21, 28, and 42 days of healing were determined from an in vivo mid-diaphyseal femoral osteotomy healing experiment in mice. Bone density distributions from microCT at 21 days were converted into adaptive finite element models. To assess the effect of loading mode on bone remodeling, a well-established remodeling algorithm was used to examine the effect of axial force or bending moment on bone structure. All simulations predicted that under axial loading, the callus remodeled to form a single cortex. When a bending moment was applied, dual concentric cortices developed in all simulations, corresponding well to the progression of remodeling observed experimentally and resulting in quantitatively comparable callus areas of woven and lamellar bone. Effects of biological differences between species or other reasons cannot be excluded, but this study demonstrates how a difference in loading mode could explain the differences between the remodeling phase in small rodents and larger mammals.