Ching-Lung Tai

Pullout strength for cannulated pedicle screws with bone cement augmentation in severely osteoporotic bone: Influences of radial hole and pilot hole tapping

BACKGROUND Pedicle screw fixation in a severely osteoporotic spine remains a challenge for orthopedic surgeons. The previous literature does not adequately address the effects of radial holes for cannulated screws with cement injection and pilot hole tapping on the bone/screw interfacial strength. METHODS Specially designed cannulated pedicle screws, with or without radial holes, were installed in tapped and untapped pilot holes and then injected with cement. A uniform synthetic bone (test block) was used to provide a platform for each screw design. Specimens with inserted screws were then tested for axial pullout failure. FINDINGS (1) Cannulated screws with cement augmentation significantly increased the pullout strength in comparison to solid screws. Additionally, the amount of cement exuded from the cannulated screws increased with an increasing number of radial holes, leading to an increase in the average ultimate pullout strength for cannulated screws with a large number of radial holes. (2) Radiological examination indicated that the cement was exuded from the most proximal holes at the very beginning of its flow path, whereas no cement exudation was found at the remaining distal holes. (3) Cement exudation from the holes of cannulated screws into the open cell of the test block led to a composite (cement/bone) structure at the area of cement exudation. Observations of the failed specimens indicated that failure occurred at the composite/bone interface, while the composite was well bonded to the screws. This implies that the screw/composite interfacial strength was much higher than the composite/bone interfacial strength. (4) Tapping pilot holes decreased the pullout strength of the screws. Generally, larger standard deviations were found for the tapped cases, implying that untapped cases results are more repeatable than tapped cases results. INTERPRETATION Cannulated pedicle screws with radial holes combined with PMMA cement augmentation but without tapping may be a viable clinical option for achieving fixation in severely osteoporotic bone.

The healing of critical-sized femoral segmental bone defects in rabbits using baculovirus-engineered mesenchymal stem cells

Management of massive segmental bone defects remains a challenging clinical problem and bone marrow-derived mesenchymal stem cells (BMSCs) hold promise for bone regeneration. To explore whether BMSCs engineered by baculovirus (an emerging gene delivery vector) can heal large bone defects, New Zealand White (NZW) rabbit BMSCs were transduced with the BMP2-expressing baculovirus or VEGF-expressing baculovirus, and co-implanted into critical-sized (10mm) femoral segmental defects in NZW rabbits. X-ray analysis revealed that the baculovirus-engineered BMSCs not only bridged the defects at as early as week 2, but also healed the defects in 100% of rabbits (13/13) at week 4. The osteogenic metabolism, as monitored by positron emission tomography (PET) also suggested the completion of bone healing at week 8. When compared with other control groups, the BMP2/VEGF-expressing BMSCs remarkably enhanced the segmental bone repair and mechanical properties, as evidenced by micro-computed tomography (microCT), histochemical staining and biomechanical testing. The ameliorated bone healing concurred with the augmented angiogenesis. These data demonstrated, that BMSCs engineered to express BMP2 and VEGF accelerate the repair of large femoral bone defects and improve the quality of the regenerated bone, which paves an avenue to utilizing baculovirus as a vector for BMSCs modification and regenerative medicine.

Biomechanical comparison of lumbar spine instability between laminectomy and bilateral laminotomy for spinal stenosis syndrome - an experimental study in porcine model.

BackgroundThe association of lumbar spine instability between laminectomy and laminotomy has been clinically studied, but the corresponding in vitro biomechanical studies have not been reported. We investigated the hypothesis that the integrity of the posterior complex (spinous process-interspinous ligament-spinous process) plays an important role on the postoperative spinal stability in decompressive surgery.MethodsEight porcine lumbar spine specimens were studied. Each specimen was tested intact and after two decompression procedures. All posterior components were preserved in Group A (Intact). In Group B (Bilateral laminotomy), the inferior margin of L4 lamina and superior margin of L5 lamina were removed, but the L4–L5 supraspinous ligament was preserved. Fenestrations were made on both sides. In Group C (Laminectomy) the lamina and spinous processes of lower L4 and upper L5 were removed. Ligamentum flavum and supraspinous ligament of L4–L5 were removed. A hydraulic testing machine was used to generate an increasing moment up to 8400 N-mm in flexion and extension. Intervertebral displacement at decompressive level L4–L5 was measured by extensometerResultsThe results indicated that, under extension motion, intervertebral displacement between the specimen in intact form and at two different decompression levels did not significantly differ (P > 0.05). However, under flexion motion, intervertebral displacement of the laminectomy specimens at decompression level L4–L5 was statistically greater than in intact or bilateral laminotomy specimens (P = 0.0000963 and P = 0.000418, respectively). No difference was found between intact and bilateral laminotomy groups. (P > 0.05).ConclusionWe concluded that a lumbar spine with posterior complex integrity is less likely to develop segment instability than a lumbar spine with a destroyed anchoring point for supraspinous ligament.

Effect of shock‐wave therapy on patellar tendinopathy in a rabbit model

This study investigated the effect of shock‐wave therapy (SWT) on collagenase induced tendinopathy in the rabbit patellar tendon. Eighteen rabbits were treated by ultrasonography‐guided injection of 0.025 ml collagenase into the patellar tendon in both knees. After tendinopathy was confirmed at 3 weeks post‐treatment by the histological examination, SWT was initiated to the right patellar tendon involving 1500 cycles at 0.29 mJ/mm2 in two separated weekly courses from 4 weeks post‐treatment. The rabbits were randomly divided into two groups, which were sacrificed at the 4th and 16th week after SWT, respectively. The histological examination, the mechanical and biochemical tests then were performed. The ultimate tensile load in the SWT tendon increased 7.03% at 4 week and 10.34% at 16 week after treatment as compared to the sham group. Hydroxyproline concentrations increased in the SWT tendons over both the 4 and 16 weeks after treatment. Moreover, the pyridinoline concentration increased at the 4th week but decreased at 16th week as compared to the sham group. The histological examination demonstrated increased blast‐like tenocyte at the 4th week, while more mature tenocyte with neovasculization at the 16th week. The result obtained here validates the effectiveness of the SWT in the established tendinopathy. SWT may increase collagen synthesis and collagen crosslink formation during early healing process.

Pullout strength of pedicle screws with cement augmentation in severe osteoporosis: A comparative study between cannulated screws with cement injection and solid screws with cement pre-filling

BackgroundPedicle screws with PMMA cement augmentation have been shown to significantly improve the fixation strength in a severely osteoporotic spine. However, the efficacy of screw fixation for different cement augmentation techniques, namely solid screws with retrograde cement pre-filling versus cannulated screws with cement injection through perforation, remains unknown. This study aimed to determine the difference in pullout strength between conical and cylindrical screws based on the aforementioned cement augmentation techniques. The potential loss of fixation upon partial screw removal after screw insertion was also examined.MethodThe Taguchi method with an L8 array was employed to determine the significance of design factors. Conical and cylindrical pedicle screws with solid or cannulated designs were installed using two different screw augmentation techniques: solid screws with retrograde cement pre-filling and cannulated screws with cement injection through perforation. Uniform synthetic bones (test block) simulating severe osteoporosis were used to provide a platform for each screw design and cement augmentation technique. Pedicle screws at full insertion and after a 360-degree back-out from full insertion were then tested for axial pullout failure using a mechanical testing machine.ResultsThe results revealed the following 1) Regardless of the screw outer geometry (conical or cylindrical), solid screws with retrograde cement pre-filling exhibited significantly higher pullout strength than did cannulated screws with cement injection through perforation (p = 0.0129 for conical screws; p = 0.005 for cylindrical screws). 2) For a given cement augmentation technique (screws without cement augmentation, cannulated screws with cement injection or solid screws with cement pre-filling), no significant difference in pullout strength was found between conical and cylindrical screws (p > 0.05). 3) Cement infiltration into the open cell of the test block led to the formation of a cement/bone composite structure. Observations of the failed specimens indicated that failure occurred at the composite/bone interface, whereas the composite remained well bonded to the screws. This result implies that the screw/composite interfacial strength was much higher than the composite/bone interfacial strength. 4) The back-out of the screw by 360 degrees from full insertion did not decrease the pullout strength in any of the studied cases. 5) Generally, larger standard deviations were found for the screw back-out cases, implying that the results of full insertion cases are more repeatable than those of the back-out cases.ConclusionsSolid screws with retrograde cement pre-filling offer improved initial fixation strength when compared to that of cannulated screws with cement injection through perforation for both the conically and cylindrically shaped screw. Our results also suggest that the fixation screws can be backed out by 360 degrees for intra-operative adjustment without the loss of fixation strength.

Ex vivo gene therapy in autologous critical-size craniofacial bone regeneration.

In therapeutic bone repairs, autologous bone grafts, conventional or vascularized allografts, and biocompatible artificial bone substitutes all have their shortcomings. The bone formed from peptides [recombinant human bone morphogenetic proteins (BMPs)], demineralized bone powder, or a combination of both is small in size. Tissue engineering may be an alternative for cranial bone repair. In this study, the authors developed an animal model to test the hypothesis that replication-defective, adenovirus-mediated human BMP-2 gene transfer to bone marrow stromal cells enhances the autologous bone formation for repairing a critical-size craniofacial defect. The mesenchymal stromal cells of miniature swine were separated from the iliac crest aspirate and expanded in monolayer culture 1 month before implantation. The cultured mesenchymal stromal cells were infected with recombinant, replication-defective human adenovirus BMP-2, 7 days before implantation. Bilateral 2 × 5-cm2 cranial defects were created, leaving no osteogenic periosteum and dura behind. Mesenchymal stromal cells at 5 × 107/ml were mixed with collagen type I to form mesenchymal stromal cell/polymer constructs. Mesenchymal stromal cells used for the control site were infected with adenovirus &bgr;-Gal under the same conditions. After 6 weeks and 3 months, 10 miniature swine were euthanized and the cranium repair was examined. Near-complete repair of the critical-size cranial defect by tissue-engineered mesenchymal stromal cell/collagen type I construct was observed. The new bone formation area (in square centimeters) measured by three-dimensional computed tomography demonstrated that the improvement from 6 weeks to 3 months was significantly greater on the experimental side than on the control side (2.15 cm2 versus 0.54 cm2, p < 0.001) and significantly greater at 3 months than at 6 weeks (2.13 cm2 versus 0.52 cm2, p < 0.001). The difference between the experimental and control groups was significant at 3 months (mean difference, 2.13 cm2; p < 0.001). The maximal compressive strength of the new bone was similar to that of the normal cranial bone when evaluated by biomechanical testing (cranium bone versus tissue-engineered bone, 88.646 ± 5.121 MPa versus 80.536 ± 19.302 MPa; p = 0.227). Adenovirus was absent from all constructs by immunochemical staining at 6 weeks and 3 months after implantation. The successful repair of cranial defects in this experiment demonstrates the efficacy of the integration of the autologous stem cell concept, gene medicine, and polymers in producing tissue-engineered bone.

Effect of intermittent cigarette smoke inhalation on tibial lengthening : Experimental study on rabbits

We investigated the effect of intermittent cigarette smoke inhalation on the bone healing of tibial lengthening in rabbits. Thirty-eight male rabbits were divided into two groups of 19 animals each. The first group went through intermittent cigarette smoke inhalation, and the second group did not go through intermittent cigarette smoke inhalation. Each animals right tibia was lengthened 5 mm using an uniplanar lengthening device. Five animals of each group were killed at 4, 6, and 8 weeks postoperatively for biomechanical testing, and one animal of each group was killed at 2, 4, 6, and 8 weeks postoperatively for histologic study. Using the contralateral nonoperated tibia as an internal control, we found that torsional strength of the lengthened tibia of the smoke inhalation group was decreased significantly compared with the non-smoke inhalation group. The mean percent of maximal torque at 4, 6, and 8 weeks were 22.0, 66.3, and 78.6%, respectively, in the smoke inhalation group, whereas the mean percent of maximal torque were 48.0, 84.1, and 90.8% %, respectively, in non-smoke inhalation group (one-tailed t test, p < 0.01, p < 0.01, and p < 0.05 at 4, 6, and 8 weeks, respectively). Our histologic observations revealed that the granulation tissue resorption, bone formation, and remodeling were delayed in smoke inhalation group. The results of this study suggest that intermittent inhalation of cigarette smoke delays, but does not prevent, the bone healing in tibial lengthening.

Bone healing of tibial lengthening is enhanced by hyperbaric oxygen therapy: a study of bone mineral density and torsional strength on rabbits.

We investigated the effect of intermittent hyperbaric oxygen (HBO) therapy on the bone healing of tibial lengthening in rabbits. Twelve male rabbits were divided into two groups of six animals each. The first group went through 2.5 atmospheres absolute of hyperbaric oxygenation for 2 hours daily, and the second group did not go through hyperbaric oxygenation. Each animals right tibia was lengthened 5 mm using an uniplanar lengthening device. Bone mineral density (BMD) study was performed for all of the animals at 1 day before operation and at 3, 4, 5, and 6 weeks after operation. All of the animals were killed at 6 weeks postoperatively for biomechanical testing. Using the preoperative BMD as an internal control, we found that the BMD of the HBO group was increased significantly compared with the non HBO group. The mean %BMD at 3, 4, 5, and 6 weeks were 69.5%, 80.1%, 87.8%, and 96.9%, respectively, in HBO group, whereas the mean %BMD were 51.6%, 67.7%, 70.5%, and 79.2%, respectively, in non-HBO group (two tailed t test, p < 0.01, p < 0.01, p < 0.01, and p < 0.01 at 3, 4, 5, and 6 weeks, respectively). Using the contralateral nonoperated tibia as an internal control, we found that torsional strength of lengthened tibia of the HBO group was increased significantly compared with the non-HBO group. The mean percent of maximal torque was 88.6% in HBO group at 6 weeks, whereas the mean percent of maximal torque was 76.0% in non-HBO group (two-tailed t test, p < 0.01). The results of this study suggest that the bone healing of tibial lengthening is enhanced by intermittent hyperbaric oxygen therapy.

Patellar tension band wiring: a revised technique.

Abstract Using a modified AO tension band wiring technique to treat a patellar fracture has become popular and has achieved a high success rate. However, the technique of Kirschner wire insertion has not been considered in detail, which may migrate and consequently introduce fragments loss of reduction. A revised technique involving bending both ends of the Kirschner wires was prospectively studied. Sixty-eight consecutive patients were so treated, and 62 patients were followed-up for at least 2 years (range 2–6 years). All fractures healed with a union rate of 100% (62/62) and a union period of 2.5 ± 0.5 months. Skin irritation was noted in 2 patients (3%). All patients achieved a satisfactory result. We therefore recommend this revised technique to treat all patellar fractures because of its high union rate and low complication rate.

Treatment of femoral neck nonunions with a sliding compression screw: comparison with and without subtrochanteric valgus osteotomy.

BACKGROUND The aim of this prospective study was to investigate and compare the results of treatment of femoral neck nonunions using a sliding compression screw (SCS) with and without subtrochanteric valgus osteotomy (SVO). METHODS Thirty-two consecutive patients with femoral neck nonunions, which sustained no osteonecrosis of the femoral head based on bone scan study, were prospectively treated with SCS with (21 patients) or without (11 patients) SVO. The indication for SCS with SVO was a femoral neck nonunion with leg shortening of more than 1.5 cm. SCS without SVO was for leg shortening of less than 1.5 cm. RESULTS Seventeen patients with osteotomy and nine patients without osteotomy were followed for at least 2 years (range, 2-8 years). All femoral neck fractures healed, with a union period of 4.6+/-1.0 months (95% confidence interval, 4.1-5.1 months) for osteotomy cases and 4.6+/-1.1 months (95% confidence interval, 3.8-5.4 months) for nonosteotomy cases (p = 0.83). However, in the osteotomy group, two patients sustained osteonecrosis of the femoral head, and nonunion remained in 1 patient at the osteotomy site (complication rate, 18%; 3 of 17 patients). There were no complications in the nonosteotomy group (p = 0.26). The average lengthening achieved from osteotomy was 1.0 to 1.5 cm (p < 0.001). CONCLUSION Using SCS without SVO to treat femoral neck nonunions can result in a very satisfactory outcome. It is thus preferred for indicated patients. SCS without SVO, however, cannot concomitantly correct a femoral neck shortening; furthermore, shortening may deteriorate because of a telescoping effect. For patients with evident shortening, therefore, combined SVO with SCS is more suitable.