Yao-Hung Wang

Prophylactic vertebroplasty may reduce the risk of adjacent intact vertebra from fatigue injury: an ex vivo biomechanical study.

Study Design. In vitro biomechanical study using human spine specimens. Objective. To find the biomechanical consequences of prophylactic vertebroplasty post fatigue loading. Summary of Background Data. Percutaneous vertebroplasty man be an effective treatment for osteoporotic vertebral compression fracture. One frequently observed complication post surgery is the adjacent vertebral failure (AVF). The prophylactic vertebroplasty was proposed to prevent the AVF. The vertebroplasty is, nevertheless, an invasive intervention. More scientific proves are needed for the application of this surgery on a still intact vertebra. Methods. Fourteen 5-level fresh human cadaveric thoracic motion segments were divided into standard and prophylactic group. Both ends of the specimen were mounted, leaving the center 3 vertebrae free. The lower level of free vertebrae was artificially injured and cement augmented. The center level vertebra of standard group remained intact and nonaugmented. The center level vertebra of prophylactic group also remained intact, but augmented with bone cement. The specimen was applied with a 2-hour, 5-Hz, 630-N (mean) compressive fatigue loading. Impulse test and CT scanning were conducted both before and after fatigue loading to find the variance of strain compliance of cortical shell and height of vertebral body. Results. The strain compliance of cortical shell is generally not statistically significantly affected by the fatigue loading, cement augmentation and vertebral level (All P > 0.05). The only exception is that the cortical strain compliance of augmented vertebrae tentatively decreased post fatigue loading (P = 0.012 for tensile strain compliance, and P = 0.049 for compressive strain compliance). The height loss of intact vertebra adjacent to a 2-level augmented (or intact-augmented) vertebra is significantly lower than the one adjacent to a 1-level augmented (or injury-augmented) vertebra (P = 0.014). For an osteoporotic vertebra, neither cortical strain compliance nor vertebral height loss is connected with bone mineral density (all P > 0.05). Conclusion. The strain compliance of cortical shell is generally not a sensitive indicator to predict risk of fatigue injury if the fatigue loading is mild. The prophylactic augmentation strengthens the osteoporotic vertebrae, decreases the progression of vertebral height loss, reduces the anterior body shift, and hence protects the adjacent intact vertebra from elevated flexion bending. It can be cautiously suggested that if the vertebra is osteoporotic and adjacent level is located at pivot or lordotic level of spinal column, the prophylactic augmentation may be an option to prevent the AVF.

The leakage pathway and effect of needle gauge on degree of disc injury post anular puncture : A comparative study using aged human and adolescent porcine discs

Study Design. An in vitro biomechanical study using aged human and adolescent porcine discs. Objectives. To find the leakage pathway and effect of needle gauge on the degree of disc injury post anular puncture. Summary of Background Data. Spinal needles are widely used for minimal invasive disc surgeries and disc degeneration/regeneration research. Applications of anular puncture require different diameters of spinal needles. However, the effect of needle diameters on the disc injury has not been systematically studied yet. Methods. Four groups of experiments were conducted: 1) porcine thoracic disc, 2) human thoracic disc, 3) porcine thoracic disc with 200 N external loading, and 4) porcine lumbar discs. The disc was punctured consecutively with needles from smaller diameter to larger diameter. After each anular puncture, the quantitative discomanometry technique was conducted to quantify the disc rupture pressure and volume. The association between needle gauge and rupture pressure and volume was analyzed. Results. The degree of disc injury increased with the diameter of needle. For an aged human thoracic disc, the anulus fibrosus cannot hold pressure more than 2 MPa after a 21-gauge-needle-anular-puncture. The leakage pathway of injected saline was through the anular fissure but was through the endplate when the disc was next to an osteoporotic vertebrae. The pressure holding power of porcine disc is stronger than of human disc. The rupture pressure of porcine lumbar disc is higher than of porcine thoracic disc. The axial compressive external loading increased the disc rupture pressure. The rupture volumes were not affected by the dimension of injury fissure. The rupture volume was at level of 0.3 mL without external loading and at 0.2 mL with external loading. Conclusion. A spinal needle of ≤22 gauge and injection volume of ≤0.2 mL are recommended to prevent postsurgery leakage.

A miniature patient-mount navigation system for assisting needle placement in CT-guided intervention

CT‐guided intervention is routinely performed in an iterative fashion that often leads to lengthy operation and high X‐ray exposure to patients. To streamline the workflow, we develop a patient‐mount navigation system for assisting needle placement in CT‐guided interventions.

MECHANISM AND RISK FACTORS OF ADJACENT VERTEBRAL FAILURE POST PERCUTANEOUS VERTEBROPLASTY - A STRAIN ENERGY DENSITY APPROACH

Abstract Percutaneous vertebroplasty (PV) is an effective treatment procedure for compression fracture of osteoporotic vertebra; however, adjacent vertebral failure (AVF) is a frequently observed complication of PV. The mechanism and risk factors of AVF are not yet clear and this problem has attracted a lot of research effort in the medical community. The purpose of this study is to analyze the mechanism and risk factors of AVF post cement augmentation using a strain energy density (SED) approach. Fresh porcine spine specimens (L1‐L5) were used. The effect of cement augmentation on the SED of vertebral bodies (VB), including the damaged VB and both adjacent cranial and caudal VBs, was analyzed. The result showed that the SED of the adjacent VBs did not increase after cement augmentation; however, the accumulated energy in the VBs of the whole spine motion segment decreased significantly after cement augmentation. This globally reduced energy is speculated to be absorbed by the disc between VBs. It is reasonable to believe that AVF may be initiated from the stressed disc. This study also suggests that poor bone quality and flexion compression are the two risk factors for AVF.

Nighttime maintenance of the equatorial ionization by F‐region polarization field

Abstract The east‐west plasma drift produced by the F‐region dynamo which has been proposed by Rishbeth(16) is included in the continuity equation of electron density, together with other transport and photo‐chemical processes. The numerical solution of the equation reveals that the inclusion of zonal drift has an effect of increasing the maximum electron density Nm during the night, especially just before sunrise. The height hm of Nm is also increased but at earlier hours. The reasons for these effects are discussed briefly.