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The influence of anatomy (normal versus scoliosis) on the free-hand placement of pedicle screws: Is misplacement more frequent in patients with anatomical deformity?

ABSTRACT: STUDY DESIGN: Retrospective prognostic study. OBJECTIVE: To evaluate whether patients with anatomical deformity due to scoliosis have a higher frequency of inaccurate pedicle screw insertion and related complications using the free-hand technique compared with those whose normal anatomy had been impacted by trauma. METHODS: Consecutively treated trauma patients with otherwise normal anatomy (48 patients instrumented with 291 screws, group A) and scoliosis patients (24 patients instrumented with 287 screws, group B) were evaluated. Screw position on CT was evaluated using the classification by Gertzbein and Robbins with modification by Karagoz Guzey. (See web appendix at www.aospine.org/ebsj for complete classification description.) Images were examined by two fellows and one junior staff member none of whom participated in patient management. Screw position was determined by consensus. RESULTS: In group A, five (1.7%) out of 289 screws were severely misplaced and 26 (9%) screws caused either medial (3.8%) or lateral (5.2%) cortical breeches. The other 258 (89.3%) screws were fully contained within the cortical boundaries of the pedicle. In group B, seven (2.8%) out of 256 screws were severely misplaced. Thirty-three (13%) screws caused cortical breeches, either medial (9%), lateral (2%), or anterior (2%), and 216 (84.3%) screws were fully contained within the cortical boundaries of the pedicle and the vertebra. Neurological complications were reported in one patient with scoliosis. No vascular complications were reported in either group. CONCLUSIONS: The percentage of incorrectly placed screws was similar in both groups, trauma and deformity patients. The presence of vertebral anatomical changes related to adult scoliosis was not associated with an increase in the screw-related neurological or vascular complications. [Table: see text] The definiton of the different classes of evidence is available on page 73.

SUBMITTER: Gruenberg M

PROVIDER: S-EPMC3623099 | biostudies-other | 2010 Aug

REPOSITORIES: biostudies-other

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Project description:The three-dimensional correction of severe rigid scoliosis has been improved by segmental pedicle screw instrumentation. However, there can be significant difficulty related to the use of a rigid rod, especially in the apex region of severe scoliosis. This study is a retrospective matched cohort study to evaluate the advantages of Nitinol shape memory alloy (SMA) rod-based correction by comparing the clinical and radiographic results obtained from using a temporary SMA rod and those from a standard rod in the correction of severe scoliosis. From May 2004 to September 2006, patients with matched curve type, ages at surgery, operative methods and fusion levels in our institute and instrumented with either SMA rods (n = 14) or traditional correction techniques (n = 16) were reviewed. In SMA group, the SMA rods served as a temporary intraoperative tool for deformity correction and were replaced by standard rods. The blood loss at surgery averaged 778 +/- 285 ml in the traditional group and 585 +/- 188 ml in the SMA group (P < 0.05). Operative time averaged 284 +/- 53 min in the SMA group and 324 +/- 41 min in the traditional group (P < 0.05). In the SMA group, the preoperative major curve was 92.6 degrees +/- 13.7 degrees with a flexibility of 25.5 +/- 7.3% was corrected to 29.4 degrees +/- 5.7 degrees demonstrating a 68.4% immediate postoperative correction. In the traditional group, the preoperative major curve was 88.6 degrees +/- 14.6 degrees with a flexibility of 29.3 +/- 6.6% was corrected to 37.2 degrees +/- 7.3 degrees demonstrating a 57.8% immediate postoperative correction. There was a statistic difference between the SMA group and traditional group in correction rate of the major thoracic curve. In the SMA group, one case suffered from deep infection 2 months postoperatively. In the traditional group, 6 of 16 cases suffered pedicle screw pull out or loosening during placement of the standard rod at the apex vertebrae on the concave side. In three cases, the mono-axial pedicle screws near the apex were abandoned and in five cases replaced with poly-axial pedicle screws. This study shows that the temporary use of SMA rod may reduce the operative time, blood loss, while improve the correction of the coronal plane when compared with standard techniques.

Project description:Pedicles are often broken when screws are inserted into hard pedicles with small diameters or when the diameter of the screw itself is inadequate. However, there is a lack of biomechanical literature that addresses screw loosening as a result of broken pedicles or the resulting salvage of those screws. We performed a novel in vitro study to compare the pullout strength of screws between intact pedicles and two different types of broken pedicles; strategies to prevent screw loosening were also compared. Thirty L4 Sawbones were designed to represent intact pedicles, semi-pedicles, and nonpedicles and were prepared for screw insertion. Three sizes of polyaxial screws (diameter × length dimensions of 6.0 mm × 45 mm, 6.0 mm × 50 mm and 6.5 mm × 45 mm) were independently and randomly distributed into the intact-pedicle group (IP group, n = 30), the semi-pedicle group (SP group, n = 15), or the nonpedicle group (NP group, n = 15). The experiments were conducted across a minimum of five trials for each of the chosen screw sizes. We then analyzed the results of the imaging, pullout testing, and embedded bone volume. Any fractures or defects of the vertebrae caused by screw insertion were excluded from the study. The appropriate screw trajectory and insertional depth were confirmed using axial and sagittal X-ray imaging prior to screw pullout testing. A pullout strength of only 41% to 45% for the SP group and 29% to 39% for the NP group was retained following a broken pedicle. The use of longer or larger-diameter screws appears to be an effective salvaging procedure for the NP group (p < 0.05). The embedded bone volume percentage analysis indicated that, compared to the IP group, 68% to 76% of effective bone embedded into the screw threads in the SP group, and 58% to 65% in the NP group. There was no direct correlation between the pullout strength and the embedded bone volume; however, less effective embedded bone volume was associated with lower pullout strength. This study describes the evolution of the well-established screw pullout test being applied to the broken pedicle Sawbone testing model. The pedicle plays an important role in determining the pullout strength of a screw. However, a salvage procedure that utilizes a longer or larger-diameter screw might be a reliable clinical approach to address broken pedicles.

Project description:IntroductionTransforaminal lumbar interbody fusion (TLIF) has been widely used in the treatment of lumbar degenerative disc disorders and shows favourable clinical results. Recently, cortical bone trajectory (CBT) has become a new trajectory for screw insertion in the lumbar spine. Several biomechanical studies have demonstrated that the CBT technique achieves screw purchase and strength greater than the traditional method. Currently, the available data on the clinical effectiveness of the two performed surgeries, TLIF with CBT screws (CBT-TLIF) and TLIF with traditional pedicle screws (PS-TLIF), are insufficient. This is the first randomised study to compare CBT-TLIF against traditional PS fixation and will provide recommendations for treating patients with lumbar degenerative disc disorders.Methods and analysisA blinded randomised controlled trial (blinding for the patient and statistician, rather than for the clinician and researcher) will be conducted. A total of 254 participants with lumbar disc degenerative disease who are candidates for TLIF surgery will be randomly allocated to either the CBT-TLIF group or the PS-TLIF group at a ratio of 1:1. The primary clinical outcome measures are the incidence of adjacent cranial facet joint violation, fusion rate and the screw loosening rate. Secondary clinical outcome measures are Visual Analogue Scale (VAS) of back pain, VAS of leg pain, Oswestry Disability Index, operative time, intraoperative blood loss and complications. These parameters will be evaluated on day 3, and then at 1, 3, 6, 12 and 24 months postoperatively.Ethics and disseminationThis study has been reviewed and approved by the Institutional Review Board of the Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical University (batch: 2017-03). The results will be presented in peer-reviewed journals and an international spine-related meeting after completion of the study.Trial registration numberNCT03105167; Pre-results.

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The influence of anatomy (normal versus scoliosis) on the free-hand placement of pedicle screws: Is misplacement more frequent in patients with anatomical deformity?

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