Biomechanics of the unilateral posterosuperior, unipedicular, and bipedicular approaches for treatment by percutaneous vertebroplasty: a comparative study.

Percutaneous vertebroplasty (PVP) via the unilateral posterosuperior approach has achieved good clinical results for the treatment of osteoporotic vertebral compression fractures. This study compared the biomechanical performance of a single vertebral body after PVP by the unilateral posterosuperior, unipedicular, and bipedicular approaches. Twenty-one vertebral bodies from the osteoporotic spine segments (T11-L1) of seven older female cadavers were randomly assigned to the unipedicular (group A), bipedicular (group B), or unilateral posterosuperior approach group (group C). After constructing the fracture compression model, PVP was performed by the different approaches. CT scans showed symmetrical, evenly distributed bone cement in groups B and C and unilaterally distributed cement in group A. The recovery rates of the anterior vertebral body height in groups B and C were significantly higher than those in group A after PVP (P<0.05). The left curvature elastic moduli after PVP were significantly higher in group A than in groups B and C; however, the right curvature moduli in group A were lower than in the other groups (P<0.05). The flexion, extension, and vertical compression elastic moduli were lowest in group B (P<0.05). After PVP, failure strength and stiffness in groups B and C were comparable (P>0.05) and higher than those in group A (P<0.05). PVP through the unilateral posterosuperior approach was superior to the unipedicular approach and comparable to the bipedicular approach based on the biomechanical performance of a single vertebral body. Due to its safety, simplicity, and efficacy, the unilateral posterosuperior approach is recommended for clinical application.

Pullout strength of reinserted pedicle screws using the previous entry point and trajectory.

PURPOSE: This study compared the biomechanics of reinserted pedicle screws using the previous entry point and trajectory with those of correctly inserted pedicle screws. METHODS: The study used 18 lumbar vertebrae (L1-6) from three fresh calf spines to insert 6.5 × 40-mm pedicle screws. A control screw was inserted correctly along the axis of one pedicle, while an experimental screw was reinserted completely using the previous entry point and trajectory in the other pedicle. The experimental screw was removed after being completely inserted in group A and after 80% of the total trajectory inserted in group B. And the experimental screw was removed after 60% of the total trajectory was reached in group C. The biomechanical values of the pedicle screws were measured. RESULTS: There were no significant differences in pedicle screw axial pullout strength between reinserted screws and correct screws in the 3 groups (PA = 0.463, PB = 0.753, PC = 0.753). Stiffness measurement increased for the reinserted screw compared with that of the control screw. Fracturing was observed between the vertebral body and pedicle. CONCLUSION: Theoretically, a surgeon can remove the pedicle screw when necessary, inspect the trajectory, and reinsert the screw using the previous entry point and trajectory.

Risk of vertical transmission of hepatitis B after amniocentesis in HBs antigen-positive mothers.

BACKGROUND & AIMS: Despite appropriate immunoprophylaxis, HBV vertical transmission (VT) occurs in 5-10% of infants born to HBs-antigen (HBsAg)+ mothers. We investigated whether amniocentesis increases the risk of transmission. METHODS: We performed a case-control study on infants who were born to HBsAg+ mothers without antiviral exposure and completed appropriate immunization. Infants born to mothers with amniocentesis were compared to those without amniocentesis to assess VT rates, which were defined by the percentage of infants with HBsAg positivity when they were 7-12 months old. RESULTS: Of the 642 consecutive infants enrolled, 63 infants with amniocentesis were compared with 198 matched infants selected from the remaining 579 infants without amniocentesis. There was a higher VT rate in infants with amniocentesis than in those without amniocentesis (6.35% vs. 2.53%; p=0.226). Maternal HBV DNA levels before amniocentesis were further stratified to <500 copies/ml, 500-6.99 log10 copies/ml, and ⩾ 7 log10 copies/ml for subset analyses. There were no significant differences in the VT rates between the amniocentesis group and the control group if the maternal HBV DNA levels were <6.99 log10 copies/ml. However, a significantly higher VT rate was observed in the amniocentesis group vs. the control group if the maternal HBV DNA levels were ⩾ 7 log10 copies/ml (50% vs. 4.5%, respectively, p=0.006). According to baseline value risk analyses, performing amniocentesis on highly viremic mothers was a risk factor for HBV transmission (OR=21.3, 95% CI: 2.960-153.775). CONCLUSIONS: Amniocentesis performed on HBsAg+ mothers with HBV DNA ⩾ 7 log10 copies/ml significantly increased the frequency of VT. HBsAg+ women who plan to have amniocentesis should be evaluated for the risk of VT and stratified according to their HBV DNA levels. Further prospective studies are warranted to verify our findings.

Biomechanical analysis of the impact of fibular osteotomies at tibiotalar joint: A cadaveric study.

BACKGROUND: Osteotomy of the fibula is a common orthopedic procedure performed for various indications, including harvesting fibula for grafting purposes. The effect of fibular osteotomy and need for tibiofibular syndesmotic fixation fusion at different levels on tibiotalar joint is matter of debate. We performed a biomechanical analysis of the impact of fibular osteotomies at different levels and whether the fixation of distal tibiofibular joint mitigates instability caused by the osteotomy. MATERIALS AND METHODS: Six lower limb specimens from fresh adult cadavers were used to prepare leg-foot models. The specimens were assigned to six status according to the level of osteotomy and whether fixation of distal tibiofibular joint was performed or not. Each specimen was then loaded axially to 700 N by the material testing machine, and the tibiotalar joint contact area and peak pressure were measured using an electronic pressure sensor. RESULTS: The contact area and the pressure of tibiotalar joint showed significant changes when compared to the normal specimen. All osteotomy specimens had a decreased tibiotalar contact area and an increased peak pressure. This positively correlated with proximity of level of osteotomy to the lateral malleolus. CONCLUSIONS: Through this study, we found that fibular osteotomy had an adverse effect in terms of decreasing the contact surface of tibiotalar joint that led to increased peak pressure in the joint. However, bone fusion and screw fixation of the distal tibiofibular joint reduced these adverse effects.

A distal femoral supra-condylar plate: biomechanical comparison with condylar plate and first clinical application for treatment of supracondylar fracture.

PURPOSE: An anatomical supra-condylar plate is designed and analysed by biomechanical testing. METHODS: The biomechanical properties of the supra-condylar and condylar plate were compared in six matched pairs of cadaveric femurs. A transverse osteotomy gap was created to simulate an OTA/AO type A3 supracondylar fracture. The left and right specimens were fitted with supra-condylar and condylar plate, respectively. Nondestructive axial compression, three-point bending and torsion tests were performed, and the peak load of the bone-implant construction was measured. The fracture site suitable for supra-condylar plate application and its correlation with femoral length were calculated. The gender influence on it was also discussed. RESULTS: The difference of stiffness between the supra-condylar and condyle groups were not significant (P > 0.05) at 363.4 and 362.5 N/mm for compression, 229.5 and 237.6 N/mm in the sagittal plane and 195.5 and 188.4 N/mm in the coronal plane for three-point bending, and 7.5 and 7.9 Nm/deg for axial torsion, respectively. The peak load was 4438 ± 136.15 N and 5215 ± 174.33 N, respectively, for the two groups. The average extent of the fracture site suitable for the application of the supra-condylar plate was 70.86 ± 4.61 mm. The femoral length and gender showed no influence on it. CONCLUSION: Despite the limited bone contact area provided by the supra-condylar plate, its construct stiffness is comparable to the condylar plate. The supra-condylar plate can be used to treat carefully-selected extra-articular supracondylar fractures.

[Biomechanical evaluation of TiNi shape-memory sawtooth-arm embracing plate and its effect on fracture healing].

OBJECTIVE: To investigate the detailed biomechanics of TiNi shape-memory sawtooth-arm embracing plate (TiNi SMA) by comparing with limited-contact dynamic compression plate (LC-DCP) and static interlocking intramedullary nail (SIiN), so as to provide theoretical evidence for clinical application. METHODS: Eight paired cadaveric femurs immersed in formaldehyde were harvested from eight specimens of adults. After making X-ray films and modeling midpiece transverse fracture, one side randomly was fixed by TiNi SMA (group A) and SIiN (group C) orderly, the other side was fixed by LC-DCP (group B). The axial compression, three-point bending (pressed from plate side and opposite side both of group A and group B, from inside of group C), and torsion were tested, and the stress shielding rate was compared. RESULTS: At every classified axial compression load, the strains of group A were greater than those of group B and group C (P < 0.05), the displacements of group A were greater than those of group B and group C (P < 0.05) except 100 N. At every classified three-point bending moment, the displacement of group A were greater than those of group B and group C pressed both from two sides, but there was no difference when pressing from two sides under the same load of group A (P > 0.05). At every torsion moment, the torsion angels of group A were greater than those of group B (P < 0.05), but equal to those of group C (P > 0.05). At 600 N of axial compression load, the stress shielding rates of groups A, B, C were 48.30% +/- 22.99%, 89.21% +/- 8.97%, 95.00% +/- 3.15%, respectively, group A was significantly less than group B and group C (P < 0.01). CONCLUSION: The anti-bending ability of TiNi SMA is weaker than LC-DCP and SIiN; the anti-torsion ability of TiNi SMA is weaker than SIiN, but TiNi SMA is a center-type internal fixation, the superior stress shielding rate and micromovement promote the stress stimulation of fracture, which makes it an ideal internal fixation device.

Biomechanical evaluation of stability and three-dimensional movements of the atlantoaxial joint after artificial atlanto-odontoid joint arthroplasty.

OBJECTIVE: To investigate the stability and three-dimensional movements of the atlantoaxial joint after artificial atlanto-odontoid joint (AAOJ) arthroplasty. METHOD: Ten sets of AAOJ implanted in bony specimens from 10 adults were used to test the pull-out strength of the atlas-axis components with a MTS858 Mini Bionix machine. Another twelve human cadaveric specimens including C(0)-C(4) were used to evaluate the three-dimensional movements of C(1)-C(2) under five different conditions in sequence, that is, the complete specimen, anterior decompression, posterior transarticular screws fixation, AAOJ arthroplasty and fatigue test. RESULT: There were significant differences between atlas and axis components in the maximum pull-out strength and trajectory length, however the yield length was not significantly different. The maximum pull-out strength of the atlas and axis was positively correlated with trajectory length (r(1)= 0.880, P < 0.05) and yield length (r(2)= 0.606, P < 0.05), respectively. After AAOJ arthroplasty, the range of movement (ROM) with respect to rotation and the neutral zone of the atlantoaxial joint were close to normal (P > 0.05), but the ROM in flexion-extension and lateral bending was significantly smaller compared with the specimens which underwent anterior decompression (P < 0.05). No abrasion and abnormal mobilization were observed after 2000 cycles of flexion, extension, lateral bending and axial rotation in the fatigue test. CONCLUSIONS: The self-designed AAOJ has excellent biomechanical performance, and AAOJ arthroplasty can restore excellent instant stability and preserve the movement of the atlantoaxial joint.