Keya Mao

Application of intraoperative computed tomography with or without navigation system in surgical correction of spinal deformity: a preliminary result of 59 consecutive human cases.

Study Design. A retrospective analysis of patients undergoing spinal deformity correction surgery by the assistance of intraoperative computed tomography (iCT) with or without navigation system. Objective. To share our preliminary experience and analysis of the iCT navigation system applied to spinal deformity surgery. Summary of Background Data. The iCT navigation system has been shown to improve accuracy and safety in posterior instrumentation. It not only decreased the operation time but also prevented excessive radiation exposure to the medical staff. To date, there are only few reports about the application of the iCT navigation system in spinal deformity surgery. Methods. From April 2009 to September 2010, 59 patients who had a diagnosis of scoliosis, kyphosis, or scoliokyphosis and underwent iCT-assisted surgical correction were included. Without randomization, 28 patients were operated with the iCT-navigation system, and the other 31 patients were operated with standard procedure under iCT assistance. The detailed procedures, preoperative and intraoperative images were illustrated. The accuracy of screw placement, time for screw insertion, postoperative correction rate, and iCT scanning data were analyzed. Results. There were significant differences between 2 groups in (1) the preoperative Cobb angle (76.2° and 62.6° in the navigation and non-navigation groups), (2) the accuracy and the revision rate of thoracic pedicle screws and total pedicle screws, and (3) the average screw insertion time. The breach rate and the revision rate of thoracic pedicle screws and total pedicle screws were significantly lower and the average screw insertion time was significantly lesser in the navigation group than in the non-navigation group. There were no statistically significant difference in (1) the breach rate and the revision rate of lumbar pedicle screws, (2) the mean iCT scanning time and time-out, (3) the mean number of fusion segments, (4) the mean number of iCT scans, and (5) the postoperative correction rate. Complications were encountered in 2 patients in the non-navigation group but none in the navigation group. There was no reoperation due to implant malposition in both groups. Conclusion. The iCT navigation system provides desirable accuracy of posterior spinal instrumentation for patients during surgical correction of spinal deformity without radiation exposure to the medical staff, especially in thoracic spine instrumentation. Meanwhile, the iCT in itself is an effective means of assessing complex instrumentation of the spinal deformity.

A new method for calculating the exact angle required for spinal osteotomy.

Study Design. Prospective study. Objective. To assess a new method for determining the exact angle required for spinal osteotomy in patients with ankylosing spondylitis (AS). Summary of Background Data. The ideal method for maintaining sagittal balance is to shift the center of gravity of the trunk over the hip axis when pelvic and lower extremity joints are in the neutral position. For patients with AS, various methods have been explored to calculate the required corrective angle. However, these methods carry some limitations. Methods. Twenty patients with AS who underwent spinal osteotomy for correcting kyphotic deformity were studied. Pre- and postoperative full-length freestanding radiographs of the whole spine and pelvis were obtained for all patients. We calculated the ideal postoperative pelvic tilt according to pelvic incidence, and chose the plumbline of the hilus pulmonis rather than C7 as gravity axis of the trunk. Then, the necessary angular correction at the level of osteotomy was calculated. Pre- and postoperative radiological parameters, including Cobb T1–S1, pelvic incidence, pelvic tilt, sacral slope, and sagittal vertical axis were measured. Health related quality of life, including Oswestry Disability Index and Scoliosis Research Society outcomes instrument-22, were administered before surgery and at 6-month follow-up. Results. The preoperative and postoperative Cobb T1–S1 were 52° and 3°, respectively (P < 0.001). All patients demonstrated changes in preoperative to postoperative radiographical parameters including decreased pelvic tilt (from 30° to 11°, P < 0.001) and sagittal vertical axis (from 18 cm to 7 cm), increased sacral slope (from 16° to 35°, P < 0.001), but no significant change in pelvic incidence. Health related quality of life scores at 6-month follow-up had significantly improved compared with those before surgery. Conclusion. This method provides an accurate and reproducible calculation for AS correction. Level of Evidence: 2

Investigation of the histology and interfacial bonding between carbonated hydroxyapatite cement and bone

An ideal bone implant should facilitate the formation of a new bone layer as an osteo-integrated interface between bone and the implanted biomaterials. In the present work, the interface between carbonated hydroxyapatite (CHA) cement and bone was evaluated by interfacial bonding strength measurements and histological characterizations. CHA cement was implanted into a mongrel dogs femoral supracondylar and below the tibial plateau area, and was then tested ex vivo by, respectively, detaching and pullout experiments. Polymethylmethacrylate (PMMA) was used as a control. CHA cement could be directly injected and solidified in situ to repair bone defects. Histology results showed that CHA bonded with bone through gradual remodeling and was replaced by new bone tissue, which is an attribute for excellent biocompatibility. The interfacial bonding strength increased with implantation time. After 16 weeks implantation, the measured detaching force and the pullout force between CHA and bone were 281 +/- 16 N and 512.5 +/- 14.5 N, respectively. These values were several times higher compared to 5 days implantation. In contrast, the control showed a fibrous microstructure between PMMA and bone, and the detaching force and the pullout force decreased with implantation time. The results strongly suggest that CHA can form a better osteo-integrated interface compared to PMMA, and could be used as an ideal biomaterial for bone defect repair.

Two-level spinal osteotomy for severe thoracolumbar kyphosis in ankylosing spondylitis. Experience with 48 patients.

Study Design. A retrospective study. Objective. To report surgical results for severe thoracolumbar kyphosis secondary to ankylosing spondylitis (AS) corrected with 2-level spinal osteotomy. Summary of Background Data. Transpedicular osteotomy in the lumbar spine is the major approach to correct kyphosis in AS. Most surgical procedures were performed at 1 level and only few literature report 2-level osteotomy in 1 patient. Methods. From January 2003 to June 2011, we reviewed 48 patients experiencing AS with severe thoracolumbar kyphosis who underwent stage 2-level spinal osteotomy in our hospital. The osteotomies were performed at T12 and L2 or L1 and L3, according to the apex of kyphosis. Preoperative and postoperative height, chin-brow vertical angle, sagittal balance, and the sagittal Cobb angle of the vertebral osteotomy segment were documented. Intraoperative, postoperative, and general complications were recorded. Results. The chin-brow vertical angle improved from 65.0° ± 28.0° to 5.0°± 10.0° (P = 0.000) and the sagittal imbalance distance improved from 26.9 ± 10.4 cm to 10.6 ± 5.6 cm (P = 0.000). The mean amount of correction was 24.9° at the superior site of the osteotomy and 38.1° at the inferior site of the osteotomy. Postoperatively, all patients could walk with horizontal vision and lie on their backs. No major acute complications such as death or complete paralysis occurred. Five patients experienced complications such as infections (n = 1) and cerebrospinal fluid leaks (n = 4). Both Oswestry Disability Index and Scoliosis Research Society scores improved largely. Fusion at the osteotomy site was achieved in each patient, and no implant failures were noted. Conclusion. Single-stage 2-level osteotomy can effectively and safely correct kyphotic deformities of the thoracolumbar spine caused by AS. Level of Evidence: 3

Multilevel 3D Printing Implant for Reconstructing Cervical Spine With Metastatic Papillary Thyroid Carcinoma

Study Design. A unique case report. Objective. A three-dimensional (3D) printing technology is proposed for reconstructing multilevel cervical spine (C2–C4) after resection of metastatic papillary thyroid carcinoma in a middle-age female patient. Summary of Background Data. Papillary thyroid carcinoma is a malignant neoplasm with a relatively favorable prognosis. A metastatic lesion in multilevel cervical spine (C2–C4) destroys neurological functions and causes local instability. Radical excision of the metastasis and reconstruction of the cervical vertebrae sequence conforms with therapeutic principles, whereas the special-shaped multilevel upper-cervical spine requires personalized implants. 3D printing is an additive manufacturing technology that produces personalized products by accurately layering material under digital model control via a computer. Reporting of this recent technology for reconstructing multilevel cervical spine (C2–C4) is rare in the literature. Methods. Anterior-posterior surgery was performed in one stage. Radical resection of the metastatic lesion (C2–C4) and thyroid gland, along with insertion of a personalized implant manufactured by 3D printing technology, were performed to rebuild the cervical spine sequences. The porous implant was printed in Ti6AL4V with perfect physicochemical properties and biological performance, such as biocompatibility and osteogenic activity. Finally, lateral mass screw fixation was performed via a posterior approach. Results. Patient neurological function gradually improved after the surgery. The patient received 11/17 on the Japanese Orthopedic Association scale and ambulated with a personalized skull-neck-thorax orthosis on postoperative day 11. She received radioiodine I131 therapy. The plane x-rays and computed tomography revealed no implant displacement or subsidence at the 12-month follow-up mark. Conclusion. The presented case substantiates the use of 3D printing technology, which enables the personalization of products to solve unconventional problems in spinal surgery. Level of Evidence: 5

Preparation of combined β-TCP/α-CSH artificial bone graft and its performance in a spinal fusion model

To evaluate α-calcium sulfate hemihydrate (α-CSH)/β-tricalcium phosphate (β-TCP) combined artificial bone graft (COB) in an animal model of posterolateral spinal fusion, α-CSH and β-TCP were combined in a 3 : 7 weight ratio. A rabbit model of posterolateral spinal fusion was produced (N = 36); one side was implanted with the COB, and the other with local autogenous bone. Rabbits were killed on the 4th, 8th, or 12th week after surgery and fusion, COB degradation, mineralization, and new bone formation were evaluated. Scanning electron microscopy revealed that the COB retained the porous spatial structure of β-TCP and α-CSH crystals were adhered to the surface and pores of β-TCP. At the 12th week after surgery, the fusion rate was 75.0% on the 12th week after the operation, which was higher than the fusion rate of 54.4% the autogenous bone side (p = 0.073). Bone volume fraction of the COB was 0.49 ± 0.08 for the 4th week and 0.16 ± 0.05 for the 12th week after surgery. The mineralization rate of the new bone was greater on the side implanted with autogenous bone than on the side implanted with COB at all the three time points after surgery. At each time point after surgery, the difference in mineralization rate between the autogenous bone side and the COB side was statistically significant (p < 0.001); α-CSH/β-TCP in a 3 : 7 weight ratio was as effective as local autogenous bone in producing spinal fusion in a rabbit model. Used in this ratio, the speed of material degradation and new bone formation are relatively equivalent, and the rate of new bone mineralization is similar to that of autogenous bone graft.

Lung Volume Change After Pedicle Subtraction Osteotomy in Patients With Ankylosing Spondylitis With Thoracolumbar Kyphosis

Study Design. A retrospective clinical study. Objective. To investigate the lung volume (LV) change in patients with ankylosing spondylitis (AS) with thoracolumbar kyphosis after the pedicle subtraction osteotomy procedure. Summary of Background Data. Thoracolumbar kyphosis with respiratory impairment is the consequence of most untreated AS patients. Restrictive pulmonary function is prevalent in these patients. The ideal evidence for restrictive pulmonary function impairment is to investigate the LV. A computed tomography (CT)-based method can help to obtain accurate LV change during the osteotomy. Method. Twenty-eight patients with AS with thoracolumbar kyphosis were included. All of these patients underwent pedicle subtraction osteotomy to correct their sagittal deformity. Pre- and postoperative full-length radiographs and CT scans were reviewed. The sagittal correction of the spine was measured. CT scans were used to estimate the pre- and postoperative LV with software. The relationship between the sagittal correction and the LV change was investigated. All the patients were followed up for 2 years at least. Results. The pedicle subtraction osteotomy procedure was performed safely on each patient without serious complications. The average preoperative T1–S1 Cobb was 67.7° (42° ∼ 88°) and the postoperative was 7.6° (−11° ∼ 21°). T1–S1 Cobb change was 60.0° in average (P < 0.05). The LV increased by 396 mL in average. Significant correlation was found between the percentage of LV change and T1–S1 Cobb change (r = 0.7219, P < 0.05). The location we selected for pedicle subtraction osteotomy varied from T12 to L3. No relationship was found between the osteotomy location and the LV change. Conclusion. The pedicle subtraction osteotomy effectively corrected the sagittal deformity of patients with AS. LV increased significantly after the osteotomy. Level of Evidence: 4

Effect and Strategy of One-stage Interrupted Two-level Transpedicular Wedge Osteotomy for Correcting Severe Kyphotic Deformities in Ankylosing Spondylitis.

Study Design: Prospective study. Objective: To investigate the safety, outcome, and strategy of the 1-stage interrupted 2-level transpedicular wedge osteotomy for correcting the severe kyphotic deformity in ankylosing spondylitis (AS). Summary of Background Data: There has been a large series in the literature reporting on results of osteotomy for the correction of kyphotic deformity secondary to AS. However, few articles have reported, in detail, the plan, design, strategy, and effect of 1-stage interrupted 2-level transpedicular wedge osteotomy for the correction of severe kyphotic deformity in AS. Materials and Methods: From May 2003 to February 2010, 24 consecutive patients, 17 males and 7 females, suffering from AS with severe spinal kyphosis, underwent 1-stage interrupted 2-level transpedicular wedge osteotomy in our hospital by the corresponding author. Improvements in relevant parameters were recorded and clinical results were evaluated. Results: The average operating time was 282±43 minutes, and the average blood loss was 2202±737 mL. All the global and regional spinal alignments improved to relatively normal status: the global thoracolumbar kyphosis angle improved from 101.5±10.8 to 24.8±5.8 degrees (P<0.001), the thoracolumbar kyphosis improved from 37.9±5.1 to 0.7±12.8 degrees (P<0.001), and the lumbar lordosis improved from 35.0±9.2 to −25.7±10.9 degrees (P<0.001). Meanwhile, the chin-brow vertical angle improved from 79.5±5.1 to 8.5±2.7 degrees (P<0.001), and the sagittal imbalance distance improved from 49.6±6.5 to 11.5±3.5 cm (P<0.001). All the patients could walk with horizontal vision and lie on their backs postoperatively, and scoliosis research society-22 scores improved from 1.6±0.2 preoperatively to 4.3±0.2 at the 2-year follow-up. The mean time of follow-up was 52±28 months. Fusion of the osteotomy was achieved in each patient and no instances of loss of correction or implant failure were noted. Conclusion: For correcting severe kyphosis in patients with AS, the 1-stage interrupted 2-level transpedicular wedge osteotomy is a safe and effective technique that significantly improves appearance and function.

Preparation and properties of α-calcium sulphate hemihydrate and β-tricalcium phosphate bone substitute

Autogenous bone graft carries the risk of complications. In contrast, artificial bone graft provides initial strength and allows new bone ingrowth. In this study, we examined methods of preparation of α-calcium sulphate hemihydrate (α-CSH) and β-tricalcium phosphate (β-TCP), and a composite of the two materials. Characterization of the materials was determined with X-ray diffraction, differential thermal analysis (DTA), scanning electron microscopy (SEM), and porosity analysis. β-TCP exhibited the spatial structure and porosity of normal bone with a macropore size of 50-400 μm and some 1 μm micropores. α-CSH exhibited a regular crystal structure. A combined material was prepared in a 1:1 weight ratio, and in a rabbit model, the rate of new bone mineralization was similar to that of autogenous bone graft. The combined material of β-TCP and α-CSH in this study may provide similar efficacy as autogenous bone graft.

How to Calculate the Exact Angle for Two-level Osteotomy in Ankylosing Spondylitis?

Study Design. A prospective case series study. Objective. To describe and assess a two-level osteotomy method for the management of severe thoracolumbar kyphosis (TLK) in patients with ankylosing spondylitis (AS). Summary of Background Data. To achieve better postoperative outcomes in these patients, a sophisticated preoperative surgical plan is required. Most deformities are managed using a one-level osteotomy and a two-level osteotomy is seldomly reported. Till date, no study has described a two-level osteotomy for these cases. Methods. From January 2011 to December 2012, 10 consecutive patients with ankylosing spondylitis who underwent two-level spinal osteotomy were studied. Pre- and postoperative full-length free-standing radiographs, including the whole spine and pelvis, were available for all patients. Pre- and postoperative radiological parameters, including T5-S1 Cobb angles, TLK, lumbar lordosis, pelvic incidence, pelvic tilt, sacral slope, and sagittal vertical axis were measured. Health related quality of life , including Oswestry Disability Index and Scoliosis Research Society-22 surveys were administered before surgery and at 1-year follow up. Results. The preoperative and postoperative T5-S1 Cobb angles was 51.3° and −7.1°, respectively (P < 0.001). All patients demonstrated changes in postoperative radiographic parameters including decreased pelvic tilt (from 37.1° to 14.3°, P < 0.001), TLK (from 36.9° to 12.6°, P < 0.001), and sagittal vertical axis (from 21.4 cm to 7.1 cm, P < 0.001), increased lumbar lordosis (from -5.1° to −47.1°, P < 0.001), sacral slope (from 13.4° to 37.7°, P < 0.001), but no significant change in pelvic incidence. Health related quality of life scores at 1-year follow up were significantly improved compared to those before surgery. Conclusion. This calculation of two-level osteotomy provides an accurate and reproducible method for ankylosing spondylitis correction. By which, we can obtain satisfactory radiological parameters and clinical outcomes. Level of Evidence: 4