High correlation between mechanical properties and bone mineral parameters in embalmed femurs after long-term storage

Angle-stable interlocking nailing in a canine critical-sized femoral defect model for bone regeneration studies: In pursuit of the principle of the 3R’s

Introduction: Critical-sized long bone defects represent a major therapeutic challenge and current treatment strategies are not without complication. Tissue engineering holds much promise for these debilitating injuries; however, these strategies often fail to successfully translate from rodent studies to the clinical setting. The dog represents a strong model for translational orthopedic studies, however such studies should be optimized in pursuit of the Principle of the 3R’s of animal research (replace, reduce, refine). The objective of this study was to refine a canine critical-sized femoral defect model using an angle-stable interlocking nail (AS-ILN) and reduce total animal numbers by performing imaging, biomechanics, and histology on the same cohort of dogs.

Methods: Six skeletally mature hounds underwent a 4 cm mid-diaphyseal femoral ostectomy followed by stabilization with an AS-ILN. Dogs were assigned to autograft (n = 3) or negative control (n = 3) treatment groups. At 6, 12, and 18 weeks, healing was quantified by ordinal radiographic scoring and quantified CT. After euthanasia, femurs from the autograft group were mechanically evaluated using an established torsional loading protocol. Femurs were subsequently assessed histologically.

Results: Surgery was performed without complication and the AS-ILN provided appropriate fixation for the duration of the study. Dogs assigned to the autograft group achieved radiographic union by 12 weeks, whereas the negative control group experienced non-union. At 18 weeks, median bone and soft tissue callus volume were 9,001 mm³ (range: 4,939–10,061) for the autograft group and 3,469 mm³ (range: 3,085–3,854) for the negative control group. Median torsional stiffness for the operated, autograft treatment group was 0.19 Nm/° (range: 0.19–1.67) and torque at failure was 12.0 Nm (range: 1.7–14.0). Histologically, callus formation and associated endochondral ossification were identified in the autograft treatment group, whereas fibrovascular tissue occupied the critical-sized defect in negative controls.

Conclusion: In a canine critical-sized defect model, the AS-ILN and described outcome measures allowed refinement and reduction consistent with the Principle of the 3R’s of ethical animal research. This model is well-suited for future canine translational bone tissue engineering studies.

Characterization of the mechanical properties of human parietal bones preserved in modified larssen solution, formalin and as fresh frozen

PURPOSE

Although the fresh frozen (FF) cadaver is preferred for surgical applications, it is limited due to short usage time, unsuitable for reuse and the risk of infection. Due to its limited use, FF cadavers, which are covered by import in countries with insufficient body donation cause low-cost effectiveness. With the increase of real human tissue specimen necessities for surgical training, long-term preservation of the cadavers is crucial due to changes in mechanical properties. Therefore, studies on embalming solutions have increased in recent years.

METHODS

We quantify the biomechanical properties of human parietal bones preserved via modified larssen solution (MLS) and compare the results with the specimens preserved as FF and fixed with 10% formalin-based solution (F10). The rectangular samples of 24 parietal bones of male individuals were resected from MLS-embalmed, F10-embalmed and FF cadavers to form three groups each containing eight samples. These specimens were tested longitudinally to identify mechanical properties.

RESULTS

The tensile test results showed that there is not a significant difference between the groups in terms of stiffness, elastic modulus, strain at ultimate stress, failure strain and effective plastic strain. However, the yield stress, ultimate stress, yield strain, failure stress and total energy and post-yield properties are significantly lower in F10 than MLS and FF groups.

CONCLUSION

It is observed that the mechanical properties of MLS preserved and FF parietal bones have almost similar properties. Thus, it can be concluded that MLS is a suitable fixative solution for bone studies and bone-related surgical anatomy training applications.

Cervical spinal instability causes vertebral microarchitecture change and vertebral endplate lesion in rats

Background

The vertebral endplate (VEP) was damaged after spinal instability induced by cervical muscle section (CMS). Whether CMS induces bone formation and mechanical loading change in the vertebra is still obscure. This study was aimed to explore mechanical loading change and endplate damage after CMS.

Methods

Forty-eight rats were randomly divided into the CMS group and the sham group. The C6/7 segments were harvested at 4, 8, and 12 weeks after surgery. The microarchitectures of the C6 vertebra ​and the vertebral endplate lesions and intervertebral disc height of C6/7 were measured by micro-computed tomography. Micro-finite element analysis was used to evaluate biomechanical properties of the C6 vertebra. Bone remodelling of the C6 vertebra ​and the endplate ​sclerosis and intervertebral disc degeneration of C6/7 were evaluated by histological and immunohistochemical analyses.

Results

CMS significantly induced bone formation of the C6 ventral vertebra ​and increased the biomechanical properties of mainly the ventral side at 4 weeks, which was gradually rebalanced throughout the rest of the study. CMS also significantly increased protein expression of transforming growth factor-β1 (TGF-β1) and phosphorylated small mothers against decapentaplegic (pSmad)2/3 ​at 4 weeks. Moreover, tartrate-resistant acid phosphatase staining showed that osteoclast-positive cells were slightly in number decreased at 4 weeks, but were obviously increased at 8 weeks. The VEP of the ventral side was abraded earlier followed by calcification in situ later after CMS, consistent with the biomechanical enhancements observed. The degree of endplate degeneration was aggravated with time. Finally, CMS decreased intervertebral disc height and increased disc degeneration scores with time.

Conclusions

Spinal instability induced by CMS increases bone mass and biomechanical loading of the ventral side of vertebra in the early stage, which might initiate VEP damage and cause intervertebral disc degeneration.

The translational potential of this article

Our study indicates that vertebral trabecular changes may involve in intervertebral disc degeneration induced by spinal instability. This may help to elucidate the mechanisms by which disc degeneration occur.

Real time monitoring of screw insertion using acoustic emission can predict screw stripping in human cancellous bone

BACKGROUND

To develop experience, orthopaedic surgeons train their own proprioception to detect torque during screw insertion. This experience is acquired over time and when implanting conventional/non-locked screws in osteopenic cancellous bone the experienced surgeon still strips between 38 and 45%. Technology needs to be investigated to reduce stripping rates. Acoustic-Emission technology has the ability to detect stress wave energy transmitted through a screw during insertion into synthetic bone. Our hypothesis is Acoustic-Emission waves can be detected through standard orthopaedic screwdrivers while advancing screws through purchase and overtightening in cancellous human bone with different bone mineral densities replicating the clinical state.

METHODS

77 non-locking 4 mm and 6.5 mm diameter cancellous bone screws were inserted through to stripping into the lateral condylar area of 6 pairs of embalmed distal femurs. Specimens had varying degrees of bone mineral density determined by quantitative CT. Acoustic-Emission energy and axial force were detected for each test.

RESULTS

The tests showed a significant high correlation between bone mineral density and Acoustic-Emission energy with R = 0.74. A linear regression model with the mean stripping load as the dependent variable and mean Acoustic-Emission energy, bone mineral densities and screw size as the independent variables resulted in r² = 0.94.

INTERPRETATION

This experiment succeeded in testing real time Acoustic-Emission monitoring of screw purchase and overtightening in human bone. Acoustic-Emission energy and axial compressive force have positive high correlation to bone mineral density. The purpose is to develop a known technology and apply it to improve the bone-metal construct strength by reducing human error of screw overtightening.