Toshinori Tsukanishi

Bone Regeneration and Remodeling within a Unidirectional Porous Hydroxyapatite Bone Substitute at a Cortical Bone Defect Site: Histological Analysis at One and Two Years after Implantation

Unidirectional porous hydroxyapatite (UDPHAp) is an artificial bone substitute with a unique microstructure consisting of 100–300-µm oval pores that present the material unidirectionally. UDPHAp has a compression strength of 14 MPa and a porosity of 75%, which promotes cell migration and capillary formation within the material. Despite these advantageous properties, bone remodeling and bone formation with UDPHAp remain unclear. To examine long-term remodeling and differences in bone formation based on the defect site, trapezoidal prism-shaped UDPHAp blocks were implanted into rectangular-shaped cortical bone defects in the proximal tibia of Japanese white rabbits. Histological analysis performed at 52 and 104 weeks after implantation revealed that bone and capillaries had formed within the implanted UDPHAp material. Bone formed within the UDPHAp implanted in the cortical defect of rabbit tibia and remodel up to two years. The percentage of new bone area within UDPHAp was larger in cortical lesions than that in medullary lesions. These findings suggest that UDPHAp is a promising material for the repair of non-critical-sized cortical bone defects.

Denosumab for Treatment of a Recurrent Cervical Giant-Cell Tumor

A 43-year-old male patient with C5 giant cell tumor (GCT) underwent tumor resection and anterior bone fusion of C4–C6. The tumor recurred locally 9 months after surgery with the patient complaining of neck and shoulder pain similar to his preoperative symptoms. Denosumab was administered and his pain disappeared after a two-month administration, with a sclerotic rim formation seen at the tumor site on computed tomography. He has been followed for 18 months with no evidence of tumor recurrence. Complete resection is generally recommended, but is not easy for many patients with cervical GCT because of the existence of neurovascular structures. Some patients suffer from recurrence and treatment becomes more difficult. As such, denosumab may be an efficacious option for treatment of recurrent GCT of the cervical spine, although long-term follow-up is required to monitor for presence or absence of recurrence.

Tumor-selective near-infrared photodynamic therapy with novel indocyanine green-loaded nanocarrier delays paralysis in rats with spinal metastasis

BACKGROUND Although recent advances in surgery have improved the quality of life of patients with spinal metastasis, local recurrence is still relatively common. Therefore, there is an urgent need for new surgical treatment options for metastatic spinal cancer. We previously described a novel nanocarrier loaded with indocyanine green (ICG), ICG-lactosome which exhibits tumor selectivity and is a potential near-infrared (NIR) fluorescence imaging agent for the diagnosis of spinal metastasis. The purpose of this study was to investigate the therapeutic effects of tumor-selective photodynamic therapy (PDT) with ICG-lactosome and NIR light irradiation in a rat model of spinal metastasis. METHODS Twenty-one Fischer 344 rats each with a single spinal metastasis in the L6 vertebral body were divided into 3 treatment groups: PDT with a low-concentration ICG-lactosome injection (6 rats), PDT with high-concentration ICG-lactosome injection (7 rats), and a group without ICG-lactosome injection (8 rats). All the animals received local NIR light irradiation with a total energy of 5 J (0.5 W for 10s). RESULTS Both the PDT groups injected with ICG-lactosome showed delayed deterioration of hind-limb paralysis compared with the group without ICG-lactosome. CONCLUSION This modified PDT procedure could be an effective local treatment for spinal metastasis.

A Novel Unidirectional Porous Hydroxyapatite Cylinder Implanted in the Dorsal Muscles of Dogs Promotes Fibrous Tissue Vascularization and Invasion

We recently synthesized a novel unidirectional porous hydroxyapatite (UDPHAp) material with a microstructure consisting of cross-sectional oval pores (diameter, 100-300 μm) . The unidirectional pores of UDPHAp are expected to facilitate the ingrowth of new tissues at sites of implantation. Here, we estimated the osteoinductive capacity of UDPHAp following its implantation in the dorsal muscles of dogs, and also investigated the affinity of UDPHAp for muscle and connective tissues. As a reference material, the HAp porous ceramic product Apaceram® (HOYA, Tokyo, Japan), which is commercially available in Japan and has a different microstructure from UDPHAp, was also used. A cylinder-shaped UDPHAp block was implanted in the dorsal muscles of two beagle dogs. At 1 and 2 years post-implantation, muscle and connective tissues had directly attached to UDPHAp at the upper and lower perforated surfaces. Histological assessment, revealed the direct invasion of fibrous tissues and small capillaries into the unidirectional pores of UDPHAp. Notably, no osseous tissue had formed within UDPHAp. Our findings suggest that the unidirectional pores of UDPHAp are advantageous for the vascularization and invasion of fibrous tissues. However, this unique structure does not contribute to osteoinductive capacity.

Histological Analysis of Bone Bonding and Ingrowth into Connected Porous Hydroxyapatite Spacers in Spinal Surgery

To evaluate the osteoconductive potential of connected porous hydroxyapatite (HAp), we histologically analyzed the newly formed bone inside unidirectional porous HAp (Regenos®, Kuraray, Japan; 75% porosity, n=17) and interconnected porous HAp (Neobone®, Covalent Materials, Japan; 75% porosity, n=10) 26 weeks after their implantation as bone spacers between the split lumbar laminae of goats. As a control, non-connected porous HAp spacers (Apaceram®, Pentax, Japan; 50% porosity, n=5) were used. After staining non-decalcified samples with Villanueva Goldner, changes in pore shape were evaluated microscopically and new bone formation in HAp spacers was quantitatively analyzed. In addition, blood vessel distribution was evaluated by hematoxylin and eosin staining. Changes in pore shape were observed in 76% of the Regenos® spacers and 90% of the Neobone® spacers but were not detected in the Apaceram® spacers. Only limited new bone formation was observed in the Regenos® and Neobone® spacers, whereas vascular-like structures were detected in 82% of the Regenos®, 70% of the Neobone®, and 80% of the Apaceram® spacers. The changes in pore shape were thought to have resulted from the low initial compression strength of the connected porous HAp, which may have limited the inherent osteoconductive potential of connected HAp. Our findings suggest that the maintenance of pore shape is required for promoting new bone formation in connected porous HAp when used as lamina spacers in spinal surgery.

Unidirectional Porous β-Tricalcium Phosphate Bone Substitute: Examination of Balance between New Bone Formation and Absorption

In the present study, we have newly developed an artificial bone substitute, which is unidirectional porous β-tricalcium phosphate (UDPTCP). The objective of this study was to examine the effects of high and low porosity substitutes on the balance between new bone formation and β-TCP absorption. Materials and MethodsSix male Japanese white rabbits (weight 3.1–3.5 kg, approximately 18– 21 weeks old) were used for this study. Intra-venous injection of pent barbiturate was administered and the both medial and lateral femoral condyle were exposed. A hole of 5 mm diameter was drilled to a depth of 12 mm in the metaphysis, perpendicular to the long axis of the femur. (Figure 1) Figure 1. Operation procedureIn the next step, a cylindrical UDPTCP test piece measuring 4.8 × 11 mm was implanted in the holes. Within the bone substitute, unidirectional pores ranging from 100 to 300 μm in diameter were made. This unique architecture fostered transmission of fluids and cells into the piece. In this case, the test piece was implanted into the bone perpendicular to the long axis of the femur, and the orientation of uni-directional pore was parallel to the long axis of femur. We prepared two different test pieces having low (69%) and high (74%) porosities. Half of the animals were sacrificed at 3 weeks after the operation and the remaining half at 6 weeks. After removal of the femoral condyle, the specimen was fixed in formalin and demineralized. Specimens were obtained from the central axis of the cylindrical piece as well as from the lateral or medial surfaces at a distance of 4 mm from midline. The histological samples were prepared for H&E and TRAP staining. Results and Discussion 　At 3 weeks interval, woven bone, which was formed along the wall of the substitute, could be observed by H&E staining in both low and high porosity substitutes (Figure 2a, 2b). In addition, there were osteoblast-like cells lining the newly formed bone surface with extensive capillary formation (Figure 3). At 6 weeks, the β-TCP walls had thinned and bone had matured in both the groups (Figure 4a, 4b). However, in the high-porosity group, β-TCP absorption tended to be more prominent (Figure 4). In addition, it was observed that at the center of the piece, β-TCP absorption was more prominent than that in the 4 mm-area obtained from the lateral or medial surfaces. At 3 and 6 weeks interval, activities of osteoclast-like multinuclear cells were seen on the surface of the pore wall as observed by TRAP staining. Figure 2a. Low porosity (69%) Figure 2b. High porosity (74%) Fig.2a and Fig.2b H&E staining (×12.5) after 3 weeks (center of the specimen)Figure 3. Formation of woven bone with osteoblast-like cells lining the low porosity specimen at 3 weeks. (H&E staining ×400) Figure 4a. Low porosity Figure 4b. High porosityFig.4a and Fig. 4b H&E staining at 6 weeks after implantation. In high porosity, dense-pink staining areas are located at peripheral in the field.Figure 5. TRAP-positive multinuclear cells (black arrow) were seen on the wall and in the capillaries.Conclusions　The UDPTCP implanted in the medullar canal of the femur was absorbed by multinuclear cells and quickly replaced by the newly formed bone. Our results are consistent with those of other studies using porous β-TCP [1]. In our preparation, porosity had certain effects on the balance between bone formation and　β-TCP absorption. Because of the unique architecture of unidirectional pores within the β-TCP specimen as well as easy formation of capillary network and access to osteoclasts may have accelerated absorption of the substitute. UDPTCP is very promising scaffolding material for bone regeneration. However, optimization of the porosity of UDPTCP in accordance with its application site is necessary before its clinical use. Reference[1] Naoki Kondo, Akira Ogose, Kunihiko Tokunaga, Tomoyuki Ito, Katsumitsu Arai, Naoko Kudo, Hikaru Inoue, Hiroyuki Irie, Naoto Endo: Bone formation and resorption of highly purified β-tricalcium phosphate in the rat femoral condyle. Biomaterials 26: 5600-5608, October 2005.

Dynamic Computed Tomography Myelography including the Prone Position as a Reliable Preoperative Imaging Method for Osteoporotic Vertebral Fracture with Neurological Deficits: A Preliminary Report of Three Cases

Aims: Delayed paralysis after osteoporotic vertebral fracture (OVF) in the elderly is caused by severe compression on the spinal cord or the cauda equina from the collapsed vertebral fragment that is retropulsed into the spinal canal. Patients with retropulsion of the vertebral fragment that occupies approximately 40% or more of the spinal canal likely develop delayed paralysis, suggesting that narrowing of 40% is the critical point. However, whether or not a neural decompression procedure during posterior instrumentation surgery, such as laminectomy should be performed during the surgery is still controversial. We performed dynamic computed tomography myelography (CTM) including the prone (surgical) position with OVF to investigate if the severity of spinal cord and cauda equina compression during the surgery could be estimated in advance. Materials and methods: The CTM was examined in 3 OVF patients (1 man and 2 women; mean age, 84 years) with neurological deficit in the supine and prone (surgical) positions to accurately estimate the necessity of decompression during surgery. Results: The spinal narrowing was 50% or higher in the supine position, but was less than 40% in the prone position in two patients (fracture at the T11 and L1 vertebrae), indicating that decompression was not necessary. Decompression was required in one patient (fracture at the L2 vertebra) with a high narrowing rate of 57% in the supine position and 56% in the prone position. Conclusion: Diagnostic imaging in the supine position alone will not help estimate the severity of intraoperative spinal cord or cauda equina compression because the degree of vertebral instability varies in each patient with OVF. ORIGINAL ARTICLE 1,4,5Assistant Professor, 2,3,6-8Spine Surgeon, 9Associate Professor, 10Professor 1,4-10Department of Orthopedic Surgery, University of Tsukuba Tsukuba, Ibaraki, Japan 2Department of Orthopedic Surgery, Kenpoku Medical Center Takahagi Kyodo Hospital, Takahagi, Ibaraki, Japan 3Department of Orthopedic Surgery, Ichihara Hospital, Tsukuba Ibaraki, Japan Corresponding Author: Toru Funayama, Assistant Professor Department of Orthopedic Surgery, University of Tsukuba Tsukuba, Ibaraki, Japan, Phone: +81298533219, e-mail: funatoru3 @gmail.com 10.5005/jp-journals-10039-1171

Risk Factors for Proximal Junctional Fracture following Fusion Surgery for Osteoporotic Vertebral Collapse with Delayed Neurological Deficits: A Retrospective Cohort Study of 403 Patients

Introduction Approximately 3% of osteoporotic vertebral fractures develop osteoporotic vertebral collapse (OVC) with neurological deficits, and such patients are recommended to be treated surgically. However, a proximal junctional fracture (PJFr) following surgery for OVC can be a serious concern. Therefore, the aim of this study is to identify the incidence and risk factors of PJFr following fusion surgery for OVC. Methods This study retrospectively analyzed registry data collected from facilities belonging to the Japan Association of Spine Surgeons with Ambition (JASA) in 2016. We retrospectively analyzed 403 patients who suffered neurological deficits due to OVC below T10 and underwent corrective surgery; only those followed up for　≥2 years were included. Potential risk factors related to the PJFr and their cut-off values were calculated using multivariate logistic regression analysis and receiver operating characteristic (ROC) analysis. Results Sixty-three patients (15.6%) suffered PJFr during the follow-up (mean 45.7 months). In multivariate analysis, the grade of osteoporosis (grade 2, 3: adjusted odds ratio (aOR) 2.92; p=0.001) and lower instrumented vertebra (LIV) level (sacrum: aOR 6.75; p=0.003) were independent factors. ROC analysis demonstrated that lumbar bone mineral density (BMD) was a predictive factor (area under curve: 0.72, p=0.035) with optimal cut-off value of 0.61 g/cm2 (sensitivity, 76.5%; specificity, 58.3%), but that of the hip was not (p=0.228). Conclusions PJFr was found in 16% cases within 4 years after surgery; independent risk factors were severe osteoporosis and extended fusion to the sacrum. The lumbar BMD with cut-off value 0.61 g/cm2 may potentially predict PJFr. Our findings can help surgeons select perioperative adjuvant therapy, as well as a surgical strategy to prevent PJFr following surgery.

Formation of osteon-like structures in unidirectional porous hydroxyapatite substitute: UNIDIRECTIONAL POROUS HYDROXYAPATITE SUBSTITUTE

Abstract Unidirectional porous hydroxyapatite (UDPHAp) bone substitute comprises a microstructure of cross‐sectionally oval pores with diameters ranging from 30 to 300 µm. Bone remodeling within the UDPHAp is expected upon implantation into bone; however, the mechanism and factors influencing this bone growth remain unclear. The objectives of the present study were to assess the vasculature and microstructure of newly formed bone and to determine how bone formation is affected by load transfer and UDPHAp pore size. Formation of osteon‐like structures, defined by the presence of lacunae, canaliculi and a central lumen containing capillaries, was observed within the implanted UDPHAp material in all animals after six weeks. The number of osteocytes and osteon‐like structures in areas adjacent to the cortex of recipient bone was significantly higher than in areas next to the medullary cavity throughout the recovery period. Notably, osteon‐like structures tended to form in smaller diameter pores. Continuous bone remodeling might be promoted by the rapid formation of unidirectional capillaries and the osteocyte lacunae‐canalicular system. Load transfer and smaller pore size could positively affect cortical bone regeneration.

Prediction of Treatment Resistance in Conservative Treatment of Osteoporotic Vertebral Fractures Using Lateral Plain Dynamic Loading Radiographs

Purpose: To elucidate the association between computed tomography (CT)/magnetic resonance imaging (MRI) and radiographic findings of fractured vertebral body instability in patients with osteoporotic vertebral fractures and to clarify whether resistance to conservative treatment can be evaluated on the basis of dynamic loading radiography.Methods: Seventy-eight patients aged ≥ 65 years who underwent conservative treatment for osteoporotic single vertebral fractures of the thoracolumbar junction were divided into the conservative treatment-resistant group (18 patients) and control group (60 patients). We evaluated the accuracy of the prediction of resistance to conservative treatment on the basis of the CT/MRI findings and the difference in compression rates between standing and supine positions at the time of the first visit. The differences in compression rates (%) were compared between the two groups. In addition, a receiver operating characteristics (ROC) curve was drawn to evaluate the accuracy of the prediction of resistance to conservative treatment.Results: In patients without (47 cases) and with CT findings (31 cases), the mean differences in compression rates (%) was 8.9% and 19.1%, respectively (p=0.0029). The mean differences in compression rates (%) of patients without (60 cases) and with MRI findings (18 cases) was 9.7% and 24.0%, respectively (p=0.0043). The mean differences in compression rates (%) in the conservative treatment-resistant group was 26.3%, while that in the control group was 9.0 (p=0.0066). In addition, according to the ROC curve of the difference in compression rate was 0.93 (95% confidence interval: 0.87–1), and when a 20% difference in compression rate was considered as the threshold value.Conclusion: Dynamic loading radiography is useful for the evaluation of resistance to conservative treatment in patients with osteoporotic vertebral fractures, and that a compression rate difference of ≥ 20% predicts resistance to conservative treatment.