Xiaobang Hu

What Is the Learning Curve for Robotic-assisted Pedicle Screw Placement in Spine Surgery?

BackgroundSome early studies with robotic-assisted pedicle screw implantation have suggested these systems increase accuracy of screw placement. However, the relationship between the success rate of screw placement and the learning curve of this new technique has not been evaluated.Questions/purposesWe determined whether, as a function of surgeon experience, (1) the success rate of robotic-assisted pedicle screw placement improved, (2) the frequency of conversion from robotic to manual screw placement decreased, and (3) the frequency of malpositioned screws decreased.MethodsBetween June 2010 and August 2012, the senior surgeon (IHL) performed 174 posterior spinal procedures using pedicle screws, 162 of which were attempted with robotic assistance. The use of the robotic system was aborted in 12 of the 162 procedures due to technical issues (registration failure, software crash, etc). The robotic system was successfully used in the remaining 150 procedures. These were the first procedures performed with the robot by the senior surgeon, and in this study, we divided the early learning curve into five groups: Group 1 (Patients 1–30), Group 2 (Patients 31–60), Group 3 (Patients 61–90), Group 4 (Patients 91–120), and Group 5 (Patients 121–150). One hundred twelve patients (75%) had spinal deformity and 80 patients (53%) had previous spine surgery. The accuracy of screw placement in the groups was assessed based on intraoperative biplanar fluoroscopy and postoperative radiographs. The results from these five groups were compared to determine the effect on the learning curve. The numbers of attempted pedicle screw placements were 359, 312, 349, 359, and 320 in Groups 1 to 5, respectively.ResultsThe rates of successfully placed screws using robotic guidance were 82%, 93%, 91%, 95%, and 93% in Groups 1 to 5. The rates of screws converted to manual placement were 17%, 7%, 8%, 4%, and 7%. Of the robotically placed screws, the screw malposition rates were 0.8%, 0.3%, 1.4%, 0.8%, and 0%.ConclusionsThe rate of successfully placed pedicle screws improved with increasing experience. The rate of the screws that were converted to manual placement decreased with increasing experience. The frequency of screw malposition was similar over the learning curve at 0% to 1.4%. Future studies will need to determine whether this finding is generalizable to others.Level of EvidenceLevel III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

Robotic assisted surgeries for the treatment of spine tumors.

Background Surgery plays an important role in the treatment of patients with metastatic or primary spine tumors. In recent years, various new techniques, such as robotic assisted spine surgery have been developed which has shown some promising results by improving the accuracy of spinal instrumentation and reducing potential complications. The purpose of this study was to evaluate our early experience using robotic guidance in the treatment of spinal tumors. Methods Data were collected from medical records for each surgery in which the robotic system was used to assist with biopsy, pedicle screw placement and/or vertebral augmentation in the treatment of spinal tumors. Patients age, gender, diagnosis and surgical procedure were documented. The surgical time, estimated blood loss, peri-operative and post-operative complications were obtained. The visual analog scale (VAS) for back pain and leg pain were also recorded. Results A total of 9 consecutive patients (7 female, 2 male) were included in this study, beginning with the first case experience. The mean age of the patients was 60 years (range 47-69). All patients presented with thoracic or lumbar vertebral collapse and/or myelopathy. Robotic assisted posterior instrumentation was successfully performed in all patients. Robotic assisted vertebral augmentation was performed in 4 patients. The average number of levels instrumented was 5. The average surgery time (skin to skin) was 4 hours and 24 minutes and the mean blood loss was 319 ml. There were no complications perioperatively or through the latest follow-up. Seven of the 9 patients reported improved back pain and/or leg pain at the latest follow-up and the data were not available in two patients. Conclusions The published complication rates of spinal tumor surgeries range between 5.3% and 19%. With robotic assistance, the surgical complication rate appears improved over the historical figures. Our study shows that the robotic system was safe and performed as desired in the treatment of metastatic and primary spine tumors. These results support that further evaluation in a larger series of patients.

Two novel high performing composite PMMA-CaP cements for vertebroplasty: An ex vivo animal study.

There is a growing body of the literature on new cement formulations that address the shortcomings of PMMA bone cements approved for use in vertebroplasty (VP) and balloon kyphoplasty (BKP). The present study is a contribution to these efforts by further characterization of two pre-mixed CaP filler-reinforced PMMA bone cements intended for VP; namely, PMMA-HA and PMMA-brushite cements. Each of these cements showed acceptable levels of various properties determined in porcine vertebral bodies. These properties included radiographic contrast, maximum exotherm temperature setting time, cement extravasation, stiffness change after fatigue loading, change of VB height after fracture following fatigue loading, and interdigitation. Each property value was comparable to or better than that for a PMMA bone cement approved for use in BKP. Thus, the results for the composite bone cements are promising.

Restoration of Cervical Alignment is Associated with Improved Clinical Outcome after One and Two Level Anterior Cervical Discectomy and Fusion

Background Anterior cervical discectomy and fusion (ACDF) remains the standard of care for patients with cervical radiculopathy who are unresponsive to conservative care. However, the maintenance and restoration of cervical alignment as a predictive factor for outcome has not yet been fully evaluated. The purpose of this study was to evaluate the impact of maintaining or restoring cervical alignment on one and two level ACDF patients’ outcome. Methods Data were collected from 104 patients who underwent one and two level ACDF. Cervical alignment was measured preoperatively and at follow-up visits. The patients were classified into three groups based on the postoperative change of their cervical alignment. Neck pain, arm pain, and Neck Disability Index (NDI) scores were obtained preoperatively and at the latest follow-up visit. Incidences of adjacent segment degeneration (ASD) and reoperations because of ASD were recorded. Results There were 64 patients in the Maintained group, 17 patients in the Restored group and 23 patients in the Kyphotic group. Pre-operatively, the neck pain scores, arm pain scores and NDI scores were not statistically different among the three groups (p>0.05). On average at 12 months follow-up, the neck pain scores improved by 2.7, 4.2, and 2.7 points respectively in the three groups (p>0.05). The patients’ arm pain scores improved by 2.1, 2.4, and 2.8 points respectively (p>0.05). NDI scores improved by 12, 31 and 13.7 points respectively (p<0.05). The incidences of ASD and reoperations because of ASD were 16%, 12% and 35% respectively (p>0.05). Conclusions The patients with restored cervical alignment had significantly greater NDI improvement and relatively better neck pain improvement. There was a trend for patients who had unchanged cervical kyphosis to have a higher incidence of ASD. Our study suggests that restoration of cervical alignment will contribute to improved clinical outcome in the patients who have one and two level ACDF surgeries. Level of Evidence This is a level III study.

Proximal instrumented vertebral body chance fracture after pedicle screw instrumentation in a thoracic kyphosis patient with osteoporosis.

Study Design: We present a case of proximal vertebral body chance fracture after pedicle screw instrumentation and fusion in a 67-year-old woman with osteoporosis and thoracic kyphosis. Objective: To report the rare and unique complication of proximal vertebral body chance fracture after pedicle screw instrumentation and fusion in a kyphosis patient. Summary of Background Data: Pedicle screw instrumentation has been associated with complications not limited to neurological or vascular injury, loss of curve correction, intraoperative pedicle fracture or loosening, dural laceration, deep infection, and pseudarthrosis. To the best of our knowledge, there are no previous reports describing a chance-type fracture generated by a pedicle screw fixation at the proximal end of a construct. Methods: A 67-year-old woman suffered from progressive thoracic kyphosis and mid thoracic pain presented 2 weeks after pedicle screw instrumentation and correction. She developed a vertebral body fracture at the proximal end of the instrumentation construct. Surgical intervention, including removal of the screws in the fractured vertebrae and extension of the instrumented fusion across the cervicothoracic junction, effectively restored the physiological sagittal alignment. Results: Postoperatively, at 12-month follow-up, the patient is doing exceptionally well with near-complete relief of back pain and an excellent maintenance of correction. Conclusions: Chance fracture in osteoporotic bone at the proximal end of a construct due to a pedicle screw is a rare complication but it may result in catastrophic consequences. Early recognition of this complication, reduction of the fraction-dislocation, and an extension of the instrumentation can be utilized for realignment and long-term stabilization.

Thoracic and lumbar vertebrae morphology in Lenke type 1 female adolescent idiopathic scoliosis patients.

Background Pedicle screws are widely used in adolescent idiopathic scoliosis (AIS) surgeries. Pedicle screw malposition may lead to serious vascular and neurologic complications. Knowledge of the morphometric anatomy of the thoracic and lumbar vertebrae is essential for the surgeon while implanting pedicle screws. It has been reported that there is a reduction of pedicle width at the concavity of the curve in AIS patients. However, it is unclear if gender plays a role in this pedicle width pattern. The goal of this study is to assess the vertebrae morphology in a more homogeneous group of AIS patients - female patients with Lenke type 1 curve. Methods The thoracic and lumbar vertebra and pedicle morphometry of 17 consecutive Lenke type 1 female AIS patients was analyzed based on 1mm fine cut CT scans. Morphometric anatomy of 539 pedicles from T1 to L5 was studied. Measurements included pedicle length, chord length, transverse pedicle width, transverse pedicle angle and vertebral rotation angle. Results The mean age of the patients was 14 years old (range 12-18). The mean Cobb angle was 56° (range 43° -88°) and the mean angle of vertebral rotation varied between 4-13.8°. The apical vertebra was between T7 and T11. The transverse pedicle width was significantly smaller (p < 0.05) on the concave side in the apical region of the thoracic spine (T7 and T8), measuring between 2.1-2.2 mm on the concave side and 2.7-3.1 mm on the convex side. Meanwhile, in some upper thoracic vertebrae (T3, T4, T5), the width was significantly bigger (p < 0.05) on the concave side than on the convex side, measuring between 2.8-4 mm on the concave side and 1.8-2.4 mm on the convex side. In the lumbar spine, the width varied between 4.1-9.9 mm without significant differences between the concave and convex sides (p > 0.05). The pedicle length varied between 15.4-28.7 mm and was significantly smaller (p < 0.05) on the concave side at T4, T5 and L2. The chord length was shortest at T1, measuring 32.4 mm and increased gradually to 54.3 mm at L3 but no statistical difference was found between the concave and convex sides. The transverse pedicle angle varied between 11.8° and 35° and was significantly bigger on the concave side at T7 and on the convex side at L1 (p < 0.05). Conclusions The vertebrae morphology in Lenke type 1 female AIS patients is substantially different from the vertebrae in normal spines especially at the apex and in the upper thoracic region. This is consistent with some previous reports which did not distinguish between male and female patients. Our findings suggest that gender does not play a major role in the vertebrae morphology pattern of AIS patients. Furthermore, recognizing this pattern is critical in order to optimize pedicle screw instrumentation and may allow for some leeway adjustments in the pedicle screw trajectory regardless of the methods of implantation.

Spinal Myeloid Sarcoma “Chloroma” Presenting as Cervical Radiculopathy: Case Report

Study Design Case report. Objective Myeloid sarcoma (also known as chloroma) is a rare, extramedullary tumor composed of immature granulocytic cells. It may occur early in the course of acute or chronic leukemia or myeloproliferative disorders. Spinal cord invasion by myeloid sarcoma is rare. The authors report a rare case of spinal myeloid sarcoma presenting as cervical radiculopathy. Methods A previously healthy 43-year-old man presented with progressive neck, right shoulder, and arm pain. Cervical magnetic resonance imaging (MRI) revealed a very large enhancing extradural soft tissue mass extending from C7 through T1, with severe narrowing of the thecal sac at the T1 level. The patient underwent posterior cervical open biopsy, laminectomy, and decompression. Histologic examination of the surgical specimen confirmed the diagnosis of myeloid sarcoma. Postoperatively, a bone marrow biopsy was done, which showed myeloproliferative neoplasm with eosinophilia. The patient then received systemic chemotherapy and radiotherapy. Results At the 10-month follow-up, the patient reported complete relief of arm pain and neck pain. X-rays showed that the overall cervical alignment was intact and there was no evidence of a recurrent lesion. MRI showed no evidence of compressive or remnant lesion. Conclusions Spinal myeloid sarcoma presenting as cervical radiculopathy is rare, and it may be easily misdiagnosed. Knowledge of its clinical presentation, imaging, and histologic characterization can lead to early diagnosis and appropriate treatment.

Biomechanical behavior of novel composite PMMA-CaP bone cements in an anatomically accurate cadaveric vertebroplasty model

Vertebral compression fractures are caused by many factors including trauma and osteoporosis. Osteoporosis induced fractures are a result of loss in bone mass and quality that weaken the vertebral body. Vertebroplasty and kyphoplasty, involving cement augmentation of fractured vertebrae, show promise in restoring vertebral mechanical properties. Some complications however, are reported due to the performance characteristics of commercially available bone cements. In this study, the biomechanical performance characteristics of two novel composite (PMMA‐CaP) bone cements were studied using an anatomically accurate human cadaveric vertebroplasty model. The study involves mechanical testing on two functional cadaveric spinal unit (2FSU) segments which include monotonic compression and cyclical fatigue tests, treatment by direct cement injection, and microscopic visualization of sectioned vertebrae. The 2FSU segments were fractured, treated, and mechanically tested to investigate the stability provided by two novel bone cements; using readily available commercial acrylic cement as a control. Segment height and stiffness were tracked during the study to establish biomechanical performance. The 2FSU segments were successfully stabilized with all three cement groups. Stiffness values were restored to initial levels following fatigue loading. Cement interdigitation was observed with all cement groups. This study demonstrates efficient reinforcement of the fractured vertebrae through stiffness restoration. The pre‐mixed composite cements were comparable to the commercial cement in their performance and interdigitative ability, thus holding promise for future clinical use.

Robotic-Assisted Spine Surgery

Spine surgery is challenging especially in patients with deformity or those who require complex revision surgeries. Robotic-assisted spine surgery systems have shown some promising initial results by increasing the accuracy of spinal instrumentation and thereby reducing potential complications, decreasing operative time, and reducing radiation exposure. The currently available robotic systems may show particular benefit in minimally invasive approaches and complex cases. Further experience and rigorous studies will be required before the full potential of robotic-assisted systems can be realized in the spine surgery field.

Minimally Invasive Facet Screw Fixation

Facet screw fixation is a relatively simple and effective technique for short-segment fusion in the spine. By placing screws directly across the articulating facet joint to immobilize a motion segment, one reduces the surgical exposure and hardware use compared to contemporary pedicle screw fixation. Other advantages include a shorter operating time, less cost, low complication rate, and potentially quicker postoperative recovery compared to pedicle screw fixation. Biomechanical and clinical studies have proven that overall facet screw fixation is a safe and stable method of posterior stabilization with high fusion rate if it is used properly for the right indication. In this chapter, we discuss the indications, contraindications, surgical technique, and clinical results of this technique.