IMPACT EXPERIMENTS IN ORTHOPAEDIC BIOMECHANICS

A better understanding of the fracture mechanism, kinematics of the anatomic structure and tissue tolerances can improve clinical prognosis and design of anthropomorphic test devices. An impact apparatus was designed to do experiments in vitro in the areas of orthopaedic biomechanics, either in hard tissue or soft tissue. METHODS: The specimens were subjected to high-speed trauma produced by an impact apparatus. This testing setup is a falling weight system which can do axial and eccentric impacts for different objectives of the orthopaedic studies. A special design was installed to assure only one impact on the specimen for biomechanical analysis. A high-speed camera was placed in front of the specimen to record the trauma event. In this study, the specimens included porcine vertebras, rabbit achilles tendons and human leg cadavers. Observations were also made to get more details by X-ray and/or by CT scan. RESULTS: Spinal fractures similar to those found clinically were successfully produced in porcine spines by impact testing. The deformations of the discs and the kinematical stability of the spinal experimental segments were also found. For the experiment on the achilles tendon, the high speed traction mechanism could produce strain injury to the specimen and get the immediate tensile force in the traction process. For the study on internal fixation for calcaneal fractures, clinically-relevant fractures under high speed impact were produced. The specimens with both longitudinal and transverse primary fracture lines were selected for simulated open reduction and internal fixation. All mechanical failures of the reconstructed calcanens occurred through the transverse primary fracture line. CONCLUSION: Impact experiment is a useful method to do fundamental research in orthopaedic biomechanics. The results in the animal model offer useful insight into bone fractures in human. The repeatability and reproducibility of animal tests offer a great opportunity to evaluate spinal fracture mechanics. The test on the achilles tendon injury was just a pilot study, and a well-designed protocol is needed to improve the results. The study on calcaneal fractures resulted in adding a longitudinal. Transfixing screw is recommended to enhance the strength of internal fixation in the presence of a transverse primary fracture line. From the above three studies, it was concluded that the impact method is an excellent experiment to produce tissue failure and/or fractures for further orthopaedic research

Mini-open anterior spine surgery for anterior lumbar diseases

Minimally invasive surgeries including endoscopic surgery and mini-open surgery are current trend of spine surgery, and its main advantages are shorter recovery time and cosmetic benefits, etc. However, mini-open surgery is easier and less technique demanding than endoscopic surgery. Besides, anterior spinal fusion is better than posterior spinal fusion while considering the physiological loading, back muscle function, etc. Therefore, we aimed to introduce the modified “mini-open anterior spine surgery” (MOASS) and to evaluate the feasibility, effectiveness and safety in the treatment of various anterior lumbar diseases with this technique. A total of 61 consecutive patients (46 female, 15 male; mean age 58.2 years) from 1997 to 2004 were included in this study, with an average follow-up of 24–52 (mean 43) months. The disease entities included vertebral fracture (20), failed back surgery (13), segmental instability or spondylolisthesis (10), infection (8), herniated disc (5), undetermined lesion for biopsy (4), and hemivertebra (1). Lesions involved 13 cases at T12–L1, 18 at L1–L2, 18 at L2–L3, 22 at L3–L4 and 11 at L4–L5 levels. All patients received a single stage anterior-only procedure for their anterior lumbar disease. We used the subjective clinical results, Oswestry disability index, fusion rate, and complications to evaluate our clinical outcome. Most patients (91.8%) were subjectively satisfied with the surgery and had good-to-excellent outcomes. Mean operation time was 85 (62–124) minutes, and mean blood loss was 136 (minimal-250) ml in the past 6 years. Hospital stay ranged from 4–26 (mean 10.6) days. Nearly all cases had improved back pain (87%), physical function (90%) and life quality (85%). Most cases (95%) achieved solid or probable solid bony fusion. There were no major complications. Therefore, MOASS is feasible, effective and safe for patients with various anterior lumbar diseases

Biomechanical effects of polyaxial pedicle screw fixation on the lumbosacral segments with an anterior interbody cage support

BACKGROUND: Lumbosacral fusion is a relatively common procedure that is used in the management of an unstable spine. The anterior interbody cage has been involved to enhance the stability of a pedicle screw construct used at the lumbosacral junction. Biomechanical differences between polyaxial and monoaxial pedicle screws linked with various rod contours were investigated to analyze the respective effects on overall construct stiffness, cage strain, rod strain, and contact ratios at the vertebra-cage junction. METHODS: A synthetic model composed of two ultrahigh molecular weight polyethylene blocks was used with four titanium pedicle screws (two in each block) and two rods fixation to build the spinal construct along with an anterior interbody cage support. For each pair of the construct fixed with polyaxial or monoaxial screws, the linked rods were set at four configurations to simulate 0°, 7°, 14°, and 21° lordosis on the sagittal plane, and a compressive load of 300 N was applied. Strain gauges were attached to the posterior surface of the cage and to the central area of the left connecting rod. Also, the contact area between the block and the cage was measured using prescale Fuji super low pressure film for compression, flexion, lateral bending and torsion tests. RESULTS: Our main findings in the experiments with an anterior interbody cage support are as follows: 1) large segmental lordosis can decrease the stiffness of monoaxial pedicle screws constructs; 2) polyaxial screws rather than monoaxial screws combined with the cage fixation provide higher compression and flexion stiffness in 21° segmental lordosis; 3) polyaxial screws enhance the contact surface of the cage in 21° segmental lordosis. CONCLUSION: Polyaxial screws system used in conjunction with anterior cage support yields higher contact ratio, compression and flexion stiffness of spinal constructs than monoaxial screws system does in the same model when the spinal segment is set at large lordotic angles. Polyaxial pedicle screw fixation performs nearly equal percentages of vertebra-cage contact among all constructs with different sagittal alignments, therefore enhances the stabilization effect of interbody cages in the lumbosacral area

Biomechanical analysis of the lumbar spine on facet joint force and intradiscal pressure - a finite element study

<p>Abstract</p> <p>Background</p> <p>Finite element analysis results will show significant differences if the model used is performed under various material properties, geometries, loading modes or other conditions. This study adopted an FE model, taking into account the possible asymmetry inherently existing in the spine with respect to the sagittal plane, with a more geometrically realistic outline to analyze and compare the biomechanical behaviour of the lumbar spine with regard to the facet force and intradiscal pressure, which are associated with low back pain symptoms and other spinal disorders. Dealing carefully with the contact surfaces of the facet joints at various levels of the lumbar spine can potentially help us further ascertain physiological behaviour concerning the frictional effects of facet joints under separate loadings or the responses to the compressive loads in the discs.</p> <p>Methods</p> <p>A lumbar spine model was constructed from processes including smoothing the bony outline of each scan image, stacking the boundary lines into a smooth surface model, and subsequent further processing in order to conform with the purpose of effective finite element analysis performance. For simplicity, most spinal components were modelled as isotropic and linear materials with the exception of spinal ligaments (bilinear). The contact behaviour of the facet joints and changes of the intradiscal pressure with different postures were analyzed.</p> <p>Results</p> <p>The results revealed that asymmetric responses of the facet joint forces exist in various postures and that such effect is amplified with larger loadings. In axial rotation, the facet joint forces were relatively larger in the contralateral facet joints than in the ipsilateral ones at the same level. Although the effect of the preloads on facet joint forces was not apparent, intradiscal pressure did increase with preload, and its magnitude increased more markedly in flexion than in extension and axial rotation.</p> <p>Conclusions</p> <p>Disc pressures showed a significant increase with preload and changed more noticeably in flexion than in extension or in axial rotation. Compared with the applied preloads, the postures played a more important role, especially in axial rotation; the facet joint forces were increased in the contralateral facet joints as compared to the ipsilateral ones at the same level of the lumbar spine.</p

C. elegans EIF-3.K Promotes Programmed Cell Death through CED-3 Caspase

Programmed cell death (apoptosis) is essential for the development and homeostasis of metazoans. The central step in the execution of programmed cell death is the activation of caspases. In C. elegans, the core cell death regulators EGL-1(a BH3 domain-containing protein), CED-9 (Bcl-2), and CED-4 (Apaf-1) act in an inhibitory cascade to activate the CED-3 caspase. Here we have identified an additional component eif-3.K (eukaryotic translation initiation factor 3 subunit k) that acts upstream of ced-3 to promote programmed cell death. The loss of eif-3.K reduced cell deaths in both somatic and germ cells, whereas the overexpression of eif-3.K resulted in a slight but significant increase in cell death. Using a cell-specific promoter, we show that eif-3.K promotes cell death in a cell-autonomous manner. In addition, the loss of eif-3.K significantly suppressed cell death-induced through the overexpression of ced-4, but not ced-3, indicating a distinct requirement for eif-3.K in apoptosis. Reciprocally, a loss of ced-3 suppressed cell death induced by the overexpression of eif-3.K. These results indicate that eif-3.K requires ced-3 to promote programmed cell death and that eif-3.K acts upstream of ced-3 to promote this process. The EIF-3.K protein is ubiquitously expressed in embryos and larvae and localizes to the cytoplasm. A structure-function analysis revealed that the 61 amino acid long WH domain of EIF-3.K, potentially involved in protein-DNA/RNA interactions, is both necessary and sufficient for the cell death-promoting activity of EIF-3.K. Because human eIF3k was able to partially substitute for C. elegans eif-3.K in the promotion of cell death, this WH domain-dependent EIF-3.K-mediated cell death process has potentially been conserved throughout evolution

Clinical Assessment of Customized 3D-Printed Wrist Orthoses

Plaster casting has been effective in fracture rehabilitation due to its immobility capability. Thermoplastic casting gains some efficiency and convenience from clinical processing but fitting and immobility are two major tradeoffs. Three-dimensional (3D)-printed braces have demonstrated improvements in innovation, customization, and appearance, but one may question their effectiveness in rehabilitation. Via a science-based data-centric approach, we evaluated the feasibility of customizing 3D-printed braces for wrist fractures after surgery. First, we established a framework for determining a proper timeframe for reliable pressure measurement for plaster casts, devised a method to evaluate the immobilization capability of the plaster casts and customized braces, and assessed changes in immobilization capability due to the clearance adjustment of customized braces. Second, we compared the customized wrist braces and plaster casts in immobilization capability and functional effectiveness in clinical trials. Thirty-three patients were recruited (9, control; 24, experimental). Both the Disability of Arm, Shoulder, and Head, and the Manual Ability Measure surveys showed significant differences between the control and experimental groups after brace wearing time frames of 2, 4, 8, and 12 weeks, and 6 and 12 months. We found that customized braces can match plaster casts in immobilization ability and can promote effective functional recovery

Adjacent disc and facet joint degeneration in young adults with low-grade spondylolytic spondylolisthesis: A magnetic resonance imaging study

Premature adjacent-level degeneration has been attributed to vertebral fusion, but spondylolisthesis has not been reported as a pathological factor responsible for the degeneration of adjacent disc and facet joint. We hypothesized that the degeneration of disc and facet joints in the adjacent levels is correlated with spondylolisthesis. Methods: Magnetic resonance images of 35 symptomatic young adults (16–29 years old) with low-grade L5–S1 spondylolytic spondylolisthesis (Meyerding Grade 1 or 2) and 50 symptomatic young referents (20–29 years old) with L5–S1 disc herniation without spondylolisthesis were recruited to compare the differences between disc and facet-joint degenerations at the olisthetic and adjacent levels using the Mantel extension test. Results: There were statistically significant degenerative changes of the discs and facet joints at the olisthetic and adjacent levels of patients with spondylolytic spondylolisthesis compared with the reference group. There is a trend that the disc and facet joints degenerate the most at the olisthetic level and become less affected at adjacent levels away from the lesion of pars defect. Conclusion: Low-grade spondylolytic spondylolisthesis was associated with significant degenerations of the disc and facet joints at olisthetic and adjacent levels in young adults

Intradural lumbar disc herniation: A case report and literature review

Study design and objection: Intradural disc herniation is a unusual disease associated with spinal surgery. The definitive diagnosis of intradural herniation depends on intraoperative findings. Summary of background data: We present the case of a 63-year-old woman with backache and left sciatica radiation for more than two months. The L2/3 laminectomy and discectomy were performed after magnetic resonance imaging (MRI) study; however, no disc rupture was noted during surgery. Follow-up lumbar spine MRI revealed one large, ruptured disc. The patient underwent revision surgery with durotomy. The large intradural disc was found and removed piece by piece. Methods, Results, and Conclusions: Intradural disc herniation, especially large herniation, is hard to diagnose specifically despite the progression of neuroradiologic imaging techniques. A durotomy procedure should be considered if there is a missing ruptured disc or a palpable intradural mass during surgery