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- Tendon Mechanobiology: Experimental Models Require Mathematical Underpinning. [JOURNAL ARTICLE]
- Bull Math Biol 2013 May 17.
Mathematical and computational modeling is in demand to help address current challenges in mechanobiology of musculoskeletal tissues. In particular for tendon, the high clinical importance of the tissue, the huge mechanical demands placed on it and its ability to adapt to these demands, require coupled, multiscale models incorporating complex geometrical and microstructural information as well as time-based descriptions of cellular activity and response.This review introduces the information sources required to develop such multiscale models. It covers tissue structure and biomechanics, cell biomechanics, the current understanding of tendon's ability in health and disease to update its properties and structure and the few already existing multiscale mechanobiological models of the tissue. Finally, a sketch is provided of what such models could achieve ideally, pointing out where experimental data and knowledge are still missing.
- Biocomposites reinforced by fibers or tubes, as scaffolds for tissue engineering or regenerative medicine. [JOURNAL ARTICLE]
- J Biomed Mater Res A 2013 May 16.
As a dynamic and hierarchically organized composite, native extracellular matrix (ECM) not only supplies mechanical support which the embedded cells needs but also regulates the functions of various cellular through interaction with them. Based on the ECM-mimetic principle, good biocompatibility and appropriate mechanical properties are the two basic requirements that the ideal scaffolds for the tissue engineering or regenerative medicine need. Some fibers and tubes have been shown effective to reinforce scaffolds for tissue engineering or regenerative medicine. In this review, three parts, namely properties affected by the addition of fibers or tubes, scaffolds reinforced by fibers or tubes for soft tissue repair and scaffolds reinforced by fibers or tubes for hard tissue repair, are stated, which shows that tissue repair or regeneration efficacy was enhanced significantly by fiber or tube reinforcement. Also, it indicates that these reinforcing agents can improve the biocompatibility and biodegradation of the scaffolds in most cases. However, there are still some concerns, such as the homogeneousness in structure or composition throughout the reinforced scaffolds, the adhesive strength between the matrix and the fibers or tubes, cytotoxicity of nanoscaled reinforcing agents, etc., which were also discussed in the conclusion and perspectives part.
- Anterior Release Generates More Thoracic Rotation than Posterior Osteotomy: A Biomechanical Study of Human Cadaver Spines. [JOURNAL ARTICLE]
- Spine (Phila Pa 1976) 2013 May 15.
Study Design. Biomechanical testing of human cadaveric spines
Objective.To determine the effect of anterior and posterior anatomic structures on the rotational stability of the thoracic spineSummary of Background Data. Historically, large and/or stiff spinal deformities were treated with anterior release to facilitate correction. However, anterior release increases risks and requires a two-part procedure. Recently, large or rigid deformities have been treated with a single posterior procedure using pedicle screws and spinal osteotomies. No study has yet evaluated the effect of anterior release or posterior osteotomy on thoracic spinal column rotation.Methods. Thoracolumbar spines were obtained from cadavers and segmented into upper, middle, and lower specimens. Specimens were cyclically loaded with a ±5Nm moment in axial rotation for 10 cycles. Specimens were tested intact and then retested after sectioning or removal of each structure to simulate those removed during anterior release and posterior osteotomy. The total increases in axial rotation after posterior and anterior resections were calculated using a 3D motion capture camera system. For each ligament resection, the absolute and percent change in degrees of rotation was calculated from comparison to the intact specimen. The median data points were compared to account for outliers.
Results.Resection of anterior structures was more efficacious than resection of posterior structures. An 8.8 to 71.9% increase in the amount of axial rotation was achieved by a posterior release, while resection of anterior structures led to a 141 to 288% increase in rotation. The differences between the anterior and posterior resections at all levels tested (T2-3, T6-7, and T10-11) were significant (p < 0.05).
Conclusion.Anterior release generated significantly more thoracic rotation than posterior osteotomy in biomechanical testing of human cadaver spines.
- Scheimpflug imaging for laser refractive surgery. [JOURNAL ARTICLE]
- Curr Opin Ophthalmol 2013 May 15.
PURPOSE OF REVIEW:To review the principles and clinical applications of Scheimpflug corneal and anterior segment imaging with special relevance for laser refractive surgery.
RECENT FINDINGS:Computerized Scheimpflug imaging has been used for corneal and anterior segment tomography (CASTm) in different commercially available instruments. Such approach computes the three-dimensional image of the cornea and anterior segment, enabling the characterization of elevation and curvature of the front and back surfaces of the cornea, pachymetric mapping, calculation of the total corneal refractive power and anterior segment biometry. CASTm represents a major evolution for corneal and anterior segment analysis, beyond front surface corneal topography and single point central corneal thickness measurements. This approach enhances the diagnostic abilities for screening ectasia risk as well as for planning, evaluating the results, managing complications of refractive procedures, and selecting intraocular lens power, type, and design. In addition, dynamic Scheimpflug imaging has been recently introduced for in-vivo corneal biomechanical measurements and has also been used for anterior segment imaging of femtocataract surgery.
SUMMARY:Scheimpflug imaging has an important role for laser refractive surgery with different applications, which continuously improve due to advances in technology.
- An FE investigation simulating intra-operative corrective forces applied to correct scoliosis deformity. [JOURNAL ARTICLE]
- Scoliosis 2013 May 16; 8(1):9.
BACKGROUND:Adolescent idiopathic scoliosis (AIS) is a deformity of the spine, which may require surgical correction by attaching a rod to the patient's spine using screws implanted in the vertebral bodies. Surgeons achieve an intra-operative reduction in the deformity by applying compressive forces across the intervertebral disc spaces while they secure the rod to the vertebra. We were interested to understand how the deformity correction is influenced by increasing magnitudes of surgical corrective forces and what tissue level stresses are predicted at the vertebral endplates due to the surgical correction.
METHODS:Patient-specific finite element models of the osseoligamentous spine and ribcage of eight AIS patients who underwent single rod anterior scoliosis surgery were created using pre-operative computed tomography (CT) scans. The surgically altered spine, including titanium rod and vertebral screws, was simulated. The models were analysed using data for intra-operatively measured compressive forces -- three load profiles representing the mean and upper and lower standard deviation of this data were analysed. Data for the clinically observed deformity correction (Cobb angle) were compared with the model-predicted correction and the model results investigated to better understand the influence of increased compressive forces on the biomechanics of the instrumented joints.
RESULTS:The predicted corrected Cobb angle for seven of the eight FE models were within the 5[degree sign] clinical Cobb measurement variability for at least one of the force profiles. The largest portion of overall correction was predicted at or near the apical intervertebral disc for all load profiles. Model predictions for four of the eight patients showed endplate-to-endplate contact was occurring on adjacent endplates of one or more intervertebral disc spaces in the instrumented curve following the surgical loading steps.
CONCLUSION:This study demonstrated there is a direct relationship between intra-operative joint compressive forces and the degree of deformity correction achieved. The majority of the deformity correction will occur at or in adjacent spinal levels to the apex of the deformity. This study highlighted the importance of the intervertebral disc space anatomy in governing the coronal plane deformity correction and the limit of this correction will be when bone-to-bone contact of the opposing vertebral endplates occurs.
- Quantitative evaluation of mechanical properties in tissue-engineered auricular cartilage. [JOURNAL ARTICLE]
- Tissue Eng Part B Rev 2013 May 16.
Tissue-engineering (TE) efforts for ear-reconstruction often fail due to mechanical incompetency. It is therefore key for successful auricular cartilage TE to ensure functional competency, i.e. to mimic the mechanical properties of the native ear tissue. A review of past attempts to engineer auricular cartilage shows unsatisfactory functional outcomes with various cell-seeded biodegradable polymeric scaffolds in immunocompetent animal models. However, promising improvements to construct stability were reported with either mechanically-reinforced scaffolds or novel two-stage implantation techniques. Nonetheless, quantitative mechanical evaluation of the constructs is usually overlooked, and such an evaluation of TE constructs alongside a benchmark of native auricular cartilage would allow real-time monitoring and improve functional outcomes of auricular TE strategies. Although quantitative mechanical evaluation techniques are readily available for cartilage, these techniques are designed to characterize the main functional components of hyaline and fibrous cartilage such as the collagen matrix or the glycosaminoglycan (GAG) network, but they overlook the functional role of elastin, which is a major constituent of auricular cartilage. Hence for monitoring auricular cartilage TE, novel evaluation techniques need to be designed. These should include a characterization of the specific composition and architecture of auricular cartilage, as well as mechanical evaluation of all functional components. Therefore, this paper reviews the existing literature on auricular cartilage TE as well as cartilage mechanical evaluation and proposes recommendations for designing a mechanical evaluation protocol specific for auricular cartilage, and establishing a benchmark for native auricular cartilage to be used for quantitative evaluation of TE auricular cartilage.
- Peri-implant bone length changes and survival rates of implants penetrating the sinus membrane at the posterior maxilla in patients with limited vertical bone height. [Journal Article]
- J Periodontal Implant Sci 2013 Apr; 43(2):58-63.
The aim of this study was to measure the peri-implant bone length surrounding implants that penetrate the sinus membrane at the posterior maxilla and to evaluate the survival rate of these implants.Treatment records and orthopantomographs of 39 patients were reviewed and analyzed. The patients had partial edentulism at the posterior maxilla and limited vertical bone height below the maxillary sinus. Implants were inserted into the posterior maxilla, penetrating the sinus membrane. Four months after implant insertion, provisional resin restorations were temporarily cemented to the abutments and used for one month. Then, a final impression was taken at the abutment level, and final cement-retained restorations were delivered with mutually protected occlusion. The complications from the implant surgery were examined, the number of failed implants was counted, and the survival rate was calculated. The peri-implant bone lengths were measured using radiographs. The changes in initial and final peri-implant bone lengths were statistically analyzed.Nasal bleeding occurred after implant surgery in three patients. No other complications were found. There were no failures of the investigated implants, resulting in a survival rate of 100%. Significantly more bone gain around the implants (estimated difference=-0.6 mm, P=0.025) occurred when the initial residual bone height was less than 5 mm compared to the >5 mm groups. No significant change in peri-implant bone length was detected when the initial residual bone height was 5 mm or larger.This study suggests that implants penetrating the sinus membrane at the posterior maxilla in patients with limited vertical bone height may be safe and functional.
- Frontal Plane Running Biomechanics in Female Runners with Previous Iliotibial Band Syndrome. [JOURNAL ARTICLE]
- J Appl Biomech 2013 May 13.
Proximal factors such as excessive frontal plane pelvis and trunk motion have been postulated to be biomechanical risk factors associated with iliotibial band syndrome. Additionally, lateral core endurance deficiencies may be related to increased pelvis and trunk motion during running. The purpose of this cross-sectional investigation was to determine if differences in biomechanics during running, as well as lateral core endurance exist between female runners with previous iliotibial band syndrome and controls. Gait and lateral core endurance were assessed in 34 female runners (17 with previous iliotibial band syndrome). Multivariate analysis of variance was performed to assess between group difference in pelvis, trunk, hip, and knee variables of interest. Runners with previous iliotibial band syndrome exhibited similar peak: trunk lateral flexion, contralateral pelvic drop, hip adduction, and external knee adduction moment compared to controls. Additionally, trunk - pelvis \ coordination was similar between groups. Contrary to our hypotheses, both groups exhibited trunk ipsilateral flexion. Lateral core endurance was not different between groups. These findings provide the first frontal plane pelvis and trunk kinematic data set in female runners with previous iliotibial band syndrome. Frontal plane pelvis and trunk motion may not be associated with iliotibial band syndrome.
- That's Why We Call It BIOmechanics!: Commentary on an article by H. John Cooper, MD, et al.: "Adverse Local Tissue Reaction Arising from Corrosion at the Femoral Neck-Body Junction in a Dual-Taper Stem with a Cobalt-Chromium Modular Neck". [Journal Article]
- J Bone Joint Surg Am 2013 May 15; 95(10):e711-2.
- Snake velvet black: Hierarchical micro- and nanostructure enhances dark colouration in Bitis rhinoceros. [Journal Article]
- Sci Rep 2013 May 16.:1846.
The West African Gaboon viper (Bitis rhinoceros) is a master of camouflage due to its colouration pattern. Its skin is geometrically patterned and features black spots that purport an exceptional spatial depth due to their velvety surface texture. Our study shades light on micromorphology, optical characteristics and principles behind such a velvet black appearance. We revealed a unique hierarchical pattern of leaf-like microstructures striated with nanoridges on the snake scales that coincides with the distribution of black colouration. Velvet black sites demonstrate four times lower reflectance and higher absorbance than other scales in the UV - near IR spectral range. The combination of surface structures impeding reflectance and absorbing dark pigments, deposited in the skin material, provides reflecting less than 11% of the light reflected by a polytetrafluoroethylene diffuse reflectance standard in any direction. A view-angle independent black structural colour in snakes is reported here for the first time.