2.

The morphology of the pedicle, such as shape and pedicle axis angle, differed over the lumbar levels, our measurements demonstrated similar data excluding the diameter of the trajectory. There were no significant differences between each level of the lateral and cephalad angles.

OBJECT Cortical bone trajectory (CBT) maximizes thread contact with the cortical bone surface and provides increased fixation strength. Even though the superior stability of axial screw fixation has been demonstrated, little is known about the biomechanical stiffness against multidirectional loading or its characteristics within a unit construct. The purpose of the present study was to quantitatively evaluate the anchorage performance of CBT by the finite element (FE) method. METHODS Thirty FE models of L-4 vertebrae from human spines (mean age [± SD] 60.9 ± 18.7 years, 14 men and 16 women) were computationally created and pedicle screws were placed using the traditional trajectory (TT) and CBT. The TT screw was 6.5 mm in diameter and 40 mm in length, and the CBT screw was 5.5 mm in diameter and 35 mm in length. To make a valid comparison, the same shape of screw was inserted into the same pedicle in each subject. First, the fixation strength of a single pedicle screw was compared by axial pullout and multidirectional loading tests. Next, vertebral fixation strength within a construct was examined by simulating the motions of flexion, extension, lateral bending, and axial rotation. RESULTS CBT demonstrated a 26.4% greater mean pullout strength (POS; p = 0.003) than TT, and also showed a mean 27.8% stronger stiffness (p < 0.05) during cephalocaudal loading and 140.2% stronger stiffness (p < 0.001) during mediolateral loading. The CBT construct had superior resistance to flexion and extension loading and inferior resistance to lateral bending and axial rotation. The vertebral fixation strength of the construct was significantly correlated with bone mineral density of the femoral neck and the POS of a single screw. CONCLUSIONS CBT demonstrated superior fixation strength for each individual screw and sufficient stiffness in flexion and extension within a construct. The TT construct was superior to the CBT construct during lateral bending and axial rotation.

Human adipose tissue, obtained by liposuction, was processed to obtain a fibroblast-like population of cells or adipose tissue-derived stromal cells (ATSCs). The ATSCs, as well as bone marrow-derived mesenchymal stem cells (BMSCs), have the capacity for renewal and the potential to differentiate into multiple lineages of mesenchymal tissues. These cells are capable of forming bone when implanted ectopically in an appropriate scaffold. The aim of this study was to evaluate a beta-tricalcium phosphate (beta-TCP) as a scaffold and to compare the potential of osteogenic differentiation of ATSCs with BMSCs. Both cell types were loaded into beta-TCP disk and cultured in an osteogenic induction medium. Optimal osteogenic differentiation in ATSCs in vitro, as determined by secretion of osteocalcin, scanning electron microscope, and histology, were obtained in the culturing with the beta-TCP disk. Furthermore, bone formation in vivo was examined by using the ATSC- or BMSC-loaded scaffolds in nude mice. The present results show that ATSCs have a similar ability to differentiate into osteoblasts and to synthesize bone in beta-TCP disk as have BMSCs.