Axial loading can help with growth if the right stimulus is in place namely existing remodeling conditions.
Effects of mechanical loading on cortical defect repair using a novel mechanobiological model of bone healing.
“Mechanical loading is an important aspect of post-surgical fracture care. The timing of load application relative to the injury event may differentially regulate repair depending on the stage of healing. Here, we used a novel mechanobiological model of cortical defect repair that offers several advantages including its technical simplicity and spatially confined repair program, making effects of both physical and biological interventions more easily assessed. Using this model, we showed that daily loading (5N peak load, 2Hz, 60 cycles, 4 consecutive days) during hematoma consolidation and inflammation disrupted the injury site and activated cartilage formation on the periosteal surface adjacent to the defect. We also showed that daily loading during the matrix deposition phase enhanced both bone and cartilage formation at the defect site, while loading during the remodeling phase resulted in an enlarged woven bone regenerate. All loading regimens resulted in abundant cellular proliferation throughout the regenerate and fibrous tissue formation directly above the defect demonstrating that all phases of cortical defect healing are sensitive to physical stimulation. Stress was concentrated at the edges of the defect during exogenous loading, and finite element (FE)-modeled longitudinal strain (εzz) values along the anterior and posterior borders of the defect (~2200με) was an order of magnitude larger than strain values on the proximal and distal borders (~50-100με){2000 is within physiological microstrain}. It is concluded that loading during the early stages of repair may impede stabilization of the injury site important for early bone matrix deposition, whereas loading while matrix deposition and remodeling are ongoing may enhance stabilization through the formation of additional cartilage and bone.”
“Compressive axial loading (100 cycles/day, 1 Hz, 5 days per week for 2 weeks at 0.5 N, 1 N,
and 2 N peak load) was applied across the flexed knee and ankle immediately after fracture
or after a 4-day delay, which coincided with the hematoma and inflammation stages”<-This is axial loading in contrast to lateral loading.
” femoral segmental defects subjected to daily cyclic bending (900 cycles, 1Hz, 15 min/day for 5 consecutive days per week for 1, 2 or 4 weeks) beginning on post-surgical day 10, which coincided with a provisional matrix scaffold, led to formation of pseudarthrosis with enhanced cartilage formation”
“In sum, loading produces a strain field around the defect that is high on the anterior and posterior borders and low on the proximal and distal borders”
” Daily loading during the inflammatory phase (PSD 2 to 5) delays hematoma clearance and bone matrix deposition, stimulates cellular proliferation and osteoclast activity, and promotes cartilage formation.”
” Proliferating cells were observed within the defect at all time points
post-loading and within the elevated periosteum and surrounding cartilage nodules
suggesting that loading activated proliferation even when strains were relatively low (50-100
με). ”
“low stress and strain lead to direct intramembranous bone formation, compressive stress and
strain lead to chondrogenesis, and high tensile strain leads to fibrous tissue formation”
Functional in situ assessment of human articular cartilage using MRI: a whole-knee joint loading device.
“The response to loading of human articular cartilage as assessed by magnetic resonance imaging (MRI) remainstobedefinedinrelationtohistologyandbiomechanics.Therefore,anMRI-compatiblewhole-kneejointloading device for the functional in situ assessment of cartilage was developed and validated in this study. A formalin fixed human knee was scanned by computed tomography in its native configuration and digitally processed to create femoral and tibial bone models. The bone models were covered by artificial femoral and tibial articular cartilage layers in their native configuration using cartilage-mimicking polyvinyl siloxane. A standardized defect of 8 mm diameter was created within the artificial cartilage layer at the central medial femoral condyle, into which native cartilage samples of similar dimensions were placed.After describing its design and specifications, the comprehensive validation of the device was performed using a hydraulic force gauge and digital electronic pressure-sensitive sensors. Displacement controlled quasi-static uniaxial loading to 2.5 mm (δ2.5) and 5.0 mm (δ5.0) of the mobile tibia versus the immobile femur resulted in forces of 141±8N(δ2.5) and 906±38 N (δ5.0) (on the entire joint)andlocalpressuresof0.680±0.088MPa (δ2.5) and 1.050±0.100 MPa (δ5.0) (at the site of the cartilage sample). Upon confirming the MRI compatibility of the set-up, the response to loading of macroscopically intact human articular cartilage samples (n = 5) was assessed on a clinical 3.0-T MR imaging system using clinical standard proton-density turbo-spin echo sequences and T2-weighted multi-spinecho sequences. Serial imaging was performed at the unloaded state (δ0) and at consecutive loading positions (i.e. at δ2.5 and δ5.0). Biomechanical unconfined compression testing (Young’s modulus) and histological assessment (Mankinscore)servedasthestandardsofreference.Allsampleswerehistologicallyintact(Mankinscore,1.8±1.3)and biomechanically reasonably homogeneous (Young’s modulus, 0.42 ± 0.14 MPa). They could be visualized in their entirety by MRI and significant decreases in sample height [δ0:2 .86±0.25mm; δ2.5:2 .56±0.25mm; δ5.0:2 .02±0.16mm; p < 0.001 (repeated-measures ANOVA)] as well as pronounced T2 signal decay indicative of tissue pressurization were found as a function of compressive loading. In conclusion, our compression device has been validated for the noninvasive response-to-loading assessment of human articular cartilage by MRI in a close-to-physiological experimental setting. Thus, in a basic research context cartilage may be functionally evaluated beyond mere static analysis and in reference to histology and biomechanics”
“In terms of hydration, compressive loading most likely induced considerable water redistribution within and possibly out of the tissue.”
