Posterior thoracic fixation has been used worldwide

Transcription

1 J Neurosurg Spine 19: , 2013 AANS, 2013 Multistep pedicle screw insertion procedure with patient-specific lamina fit-and-lock templates for the thoracic spine Clinical article Taku Sugawara, M.D., 1 Naoki Higashiyama, M.D., 1 Shuichi Kaneyama, M.D., 2 Masato Takabatake, M.D., 2 Naoko Watanabe, 1 Fujio Uchida, D.Eng., 3 Masatoshi Sumi, M.D., 2 and Kazuo Mizoi, M.D. 1 1 Department of Neurosurgery, Akita University School of Medicine; 3 Akita Industrial Technology Center, Akita; and 2 Department of Orthopedic Surgery, Kobe Rosai Hospital, Kobe, Japan Object. Pedicle screw fixation is a standard procedure of spinal instrumentation, but accurate screw placement is essential to avoid injury to the adjacent structures, such as the vessels, nerves, and viscera. The authors recently developed an intraoperative screw guiding method in which patient-specific laminar templates were used, and verified the accuracy of the multistep procedure in the thoracic spine. Methods. Preoperative bone images of the CT scans were analyzed using 3D/multiplanar imaging software and the trajectories of the screws were planned. Plastic templates with screw guiding structures were created for each lamina by using 3D design and printing technology. Three types of templates were made for precise multistep guidance, and all templates were specially designed to fit and lock on the lamina during the procedure. Plastic vertebra models were also generated and preoperative screw insertion simulation was performed. Surgery was performed using this patient-specific screw guide template system, and the placement of screws was postoperatively evaluated using CT scanning. Results. Ten patients with thoracic or cervicothoracic pathological entities were selected to verify this novel procedure. Fifty-eight pedicle screws were placed using the screw guide template system. Preoperatively, each template was found to fit exactly and to lock on the lamina of the vertebra models, and screw insertion simulation was successfully performed. Intraoperatively the templates also fit and locked on the patient lamina, and screw insertion was completed successfully. Postoperative CT scans confirmed that no screws violated the cortex of the pedicles, and the mean deviation of the screws from the planned trajectories was 0.87 ± 0.34 mm at the coronal midpoint section of the pedicles. Conclusions. The multistep, patient-specific screw guide template system is useful for intraoperative pedicle screw navigation in the thoracic spine. This simple and economical method can improve the accuracy of pedicle screw insertion and reduce the operating time and radiation exposure of spinal fixation surgery. ( Key Words posterior fixation thoracic spine pedicle screw screw guide template fit-and-lock template Posterior thoracic fixation has been used worldwide for the treatment of spinal injury, segmental instability, kyphosis, scoliosis, infections, and tumors. 2,11 Pedicle screw fixation can provide immediate rigid intervertebral fixation, 10 but carries a potential risk for injury to the arteries, nerve roots, and dural sac. 20,24 Freehand thoracic pedicle screw insertion is associated with cortical perforation of the pedicles in 25% 43% of cases, 3,11,24 but cadaver anatomical studies and an individualized pedicle screw guiding technique based on CT measurements have reduced the failure rate to 15% 16%. 5,25 Recently, more Abbreviation used in this paper: OPLL = ossification of the posterior longitudinal ligament. J Neurosurg: Spine / Volume 19 / August 2013 advanced preoperative image-based or CT-based computer navigation systems have been introduced to guide insertion of the pedicle screws, but the accuracy of the systems is less than expected and the failure rate is still 8.5% 11%. 8,26 Patient-specific drill guide templates have been developed as an inexpensive, accurate alternative to guide pedicle screw insertion. Most studies using patient-specific drill guide templates use computer software to generate a plastic drill guide based on the individual CT scans, but deviation can occur in as many as 16% of screw insertions. 4,12 15,19,22 The inaccuracy of the template-assisted pedicle screw placement may be derived from insecure fixation of the template to the lamina and absence of con- 185

2 T. Sugawara et al. firmation steps for location of entry points, drilling screw holes, and placing screws. Here we describe our fit-and-lock templates and multistep screw insertion technique for more accurate screw placement, including details of design of the templates and surgical procedures. This system resulted in no incidences of perforation of the pedicle in the insertion of 58 thoracic pedicle screws, and the mean deviation of the screws from the center of the pedicle was less than 1 mm. Methods This study included 10 patients (5 men and 5 women, age range years) with thoracic or cervicothoracic spinal pathological entities. Five patients had OPLL, 3 had spinal tumors, and 2 had spondylosis. A high-accuracy 3D CT scanner (Lightspeed VCT; GE Healthcare [or similar machines]) with a slice thickness of mm was used to obtain preoperative images of the thoracic spine. The images were exported in the DI- COM format to 3D/multiplanar imaging software (Ziostation; Ziosoft [or other]). Reconstructed bone images were viewed on several optional planes and safe trajectories of the screws were planned. The trajectories were planned to penetrate the center of the pedicles, approximately parallel to the upper endplate of the vertebra. The location of the screw tip was planned at least 5 mm posterior from the anterior cortex of the vertebral body. The coordinates of the bone entry points and the tip of the screws were determined (Fig. 1). Finally the diameter and length of the screws were selected based on the computer simulation. Three templates were produced for accurate guidance of the pedicle screw insertion. Location templates with 3-mm-diameter holes were made to mark the screw entry points on the lamina. Drill guide templates with 3- to 4-mm-diameter cylindrical structures (depending on the diameter of the drilling tool) were created to control the screw trajectory before screw insertion. Screw guide templates with 13- to 15-mm-diameter cylindrical structures (depending on the diameter of the screw driver) and 30-mm length were made to control screw insertion. Small windows were made in the cylindrical structures of the drill guide templates to confirm that drilling was performed exactly through the entry points marked with the location template. Small windows were also made in the screw guide templates to confirm that the screw was placed through the drill hole. The procedures and templates are shown in Figs. 1 and 2. Bone data were extracted from the DICOM data by using image processing software (VG Studio Max; Volume Graphics GmbH or Mimics; Materialize), and transferred to 3D modeling software (Freeform; Data Design) to design laminar templates and 3D models of thoracic vertebrae. The templates were specially designed to fit and lock onto the patient-specific 3D shape of the lamina. Therefore, the templates covered part of the right, left, upper, and lower sides of the lamina and the base of the spinous process to avoid slipping during the procedure (Fig. 2). The patient-specific templates and patient-specific bone models were made of nonsoluble acrylate with the aid of a 3D printing system (Connex 500; Objet Ltd.). Fitting of the templates to the laminae was evaluated and screw insertion simulation was performed before surgery. Preoperatively, screw insertion simulation was performed with the vertebra models and templates. Screws, rods, and instruments (Synapse system; Synthes, Inc. or CD Horizon Legacy spinal system; Medtronic, Inc.) were prepared and the simulation was performed using the same procedures as an actual surgery. The screws that were placed were confirmed not to violate the cortical wall of the pedicle and vertebra by visual inspection. The accuracy of the screw insertion simulation was confirmed by CT scans in some cases. An example of T-3 pedicle screw insertion is shown in Fig. 3. The templates were then sterilized with a plasma sterilizer and used for intraoperative navigation. During surgery, screw navigation was carried out with the template system and C-arm fluoroscope. The placement of the screws was examined on postoperative CT scans. Deviation of the screws was determined by measurement of the distance from the planned trajectory to the center of the screw on the middle coronal plane of the pedicles by using the 3D/multiplanar imaging software described above (Fig. 4). Results This method was used to insert a total of 58 thoracic pedicle screws (T1 4, 40 screws; T5 8, 10 screws; T9 12, 8 screws). The mean surgery time was minutes (range minutes). Preoperatively, the patient-specific templates were fitted and locked on the laminae of the vertebra models. The following simulation was then performed (Video 1); marking the entry points using the location templates, drilling the screw trajectory using the drill guide templates, and screw insertion. Video 1. Clip showing procedures in which the templates were used to control entry point, drilling trajectory, and screw insertion in a plastic spinal model. Click here to view with Media Player. Click here to view with Quicktime. None of the screws were found to violate the cortex of the pedicles of the vertebra models. Intraoperatively, the templates were fitted and locked on the patient laminae and screw insertion was performed as planned. Soft tissues on the laminae needed to be removed as far as possible to ensure the fit and lock of the templates. Postoperative CT scans confirmed that no screws violated the cortex of the pedicles, and the mean deviation of the actual screw trajectory from the planned screw trajectory on the coronal plane at the midpoint of the pedicle was 0.87 ± 0.34 mm. Representative pre- and postoperative CT scans of a patient with OPLL are shown in Fig. 5. The cost of the screw guide templates and a vertebra model for 1 thoracic spine (for 2 pedicle screws) was approximately $8 and $17, respectively. For 10 levels of fixation (20 pedicle screws), the total cost of screw guide templates and a spine model was $250. Discussion During the development of the thoracic pedicle screw insertion technique, many anatomical studies of the struc- 186 J Neurosurg: Spine / Volume 19 / August 2013

3 Screw guide templates Fig. 1. Schematic drawings showing the multistep thoracic pedicle screw insertion guidance system. tures of the thoracic spine were conducted and methods to plan safe trajectories were proposed. 9,27 The entry points for thoracic pedicle screw insertion have been recommended at the junction between the midlines of the facet joint and transverse process, 21 or at the junction of the lateral margin of the facet and the midline of the transverse process in the lower thoracic levels. 16 More recent studies have demonstrated that the safe entry points are different at each thoracic vertebra level. For example, the safe entry points are approximately 7 8 mm medial to the lateral edge of the superior facet and 3 4 mm superior to the midline of the transverse process for T1 2, and 4 5 mm medial to the lateral margin of the facet and 5 8 mm superior to the midline of the transverse process for T The ideal angle of pedicle screw insertion is also controversial. The transverse angle of the pedicle axis was found to be Fig. 2. Three types of templates. Location templates mark the screw entry points on the lamina, drill guide templates control the screw trajectory before screw insertion, and screw guide templates control screw insertion. J Neurosurg: Spine / Volume 19 / August

4 T. Sugawara et al. Fig. 3. Postprocedure CT scans of the plastic vertebra models after T2 4 screw insertion simulation. Scans include a 3D image (A), axial view at the T-3 level (B), and coronal view at the midpoint of the pedicles (C). Fig. 4. Measurement of screw deviation. Distance from the planned trajectory to the center of the placed screw was measured on 3D/multiplanar software at T1 2, at T3 11, and 10 at T However, even using the results from these detailed anatomical studies, thoracic pedicle screws can violate the cortex of the pedicles. Freehand thoracic pedicle screw insertion resulted in a 25% 43% rate of cortical perforation of the pedicles, even by experienced surgeons. 3,11,24 Detailed anatomical studies to find the specific insertion point based on morphological data from cadaveric studies resulted in a 16% failure rate, 5 and individualized pedicle screw guidance based on CT measurements resulted in a 15.9% failure rate. 25 Preoperative image-based or CT-based computer navigation systems have been introduced to guide the insertion of pedicle screws in spine surgery, but the accuracy of the system is questionable and the failure rate is still high (8.5% 11%). 8,26 These failures are largely attributable to individual anatomical variations of the thoracic spine, so screw insertion should be individually planned. Recent developments in intraoperative imaging equipment have introduced CT navigation procedures. The accuracy of pedicle screw insertion by CT-based computer navigation has been well studied. In a large cohort study of 220 consecutive patients undergoing pedicle screw insertion, the overall pedicle breach rate was reported as 7.5% overall and 9% in the thoracic spine. 17 A meta-analysis of perforation risk for computer-navigated pedicle screw insertion estimated the overall risk as 6%. 23 Recently developed intraoperative CT-based navigation (isocentric C-arm or O-arm) is thought to improve this accuracy, because preoperative CT navigation is based on images obtained with the patients in the supine position, whereas the patients undergo surgery in the prone position. However, even with this advanced method, thoracolumbar and sacral pedicle perforation rates are 3.2% 4.8%. 6,18 The inaccuracy of pedicle screw insertion performed using intraoperative CT may result from changes in the spinal alignment, such as torsion during drilling and screw placement. This issue seems difficult to solve, because image-based navigation is not real-time navigation. Patient-specific drill guide templates have been developed as an inexpensive, accurate method to guide spinal fixation screws. Most previous studies used the DICOM data of CT images and computer software to generate plastic drill guide templates, but misplacement occurred in as many as 16% of pedicle screw insertions. 1,4,12,14,19,22 Most drill guide templates were designed to fit on the patient laminae, but were not secured on the laminae, which might have been one reason for the inaccuracy of the procedure. Therefore, we designed the templates to cover the 3D shape of the laminae, and accordingly the templates can be fixed to the laminae. This 3D shape of the templates assures that the procedure cannot be affected by spinal alignment change, such as torsion during drilling and screw placement. In addition, a multistep procedure was used to avoid technical errors. First, location templates were used to identify and mark the entry point on the laminae. Second, drill guide templates were used to drill holes for the screw, and the windows in the cylindrical templates were used to confirm that drilling was performed exactly through the marked entry points. Third, screw guide templates were used to guide the screw insertion to the planned screw tip points. We believe that this multistep screw insertion technique with fit-and-lock templates is the key to accurate screw placement. This system resulted in no incidents of perforation of the pedicle in the insertion of 58 thoracic pedicle screws, and the mean deviation of the screws from the center of the pedicle was 0.9 mm, suggesting higher accuracy than obtained by previous methods. 1,4,12,14,19,22 Our novel multistep screw guide template system, which uses lamina-anchoring templates, is an inexpensive, accurate, and practical method for spinal screw insertion. This system does not require expensive equipment, such as an intraoperative computer navigation system or 188 J Neurosurg: Spine / Volume 19 / August 2013

5 Screw guide templates Fig. 5. Preoperative (A C) and postoperative (D F) CT scans obtained in a patient with OPLL. Axial views (A and D) at the T-3 level, sagittal views of the screw trajectory (B and E), and coronal views at the midpoint of the pedicles (C and F) show accurate screw insertion. intraoperative CT scanner, and can reduce radiation exposure of both the patients and the operators. This method is especially useful for patients with small pedicles or severe spinal malalignment. Nevertheless, there are some limitations. In our methods, the templates were designed to cover the upper part of the laminae, and therefore the interspinous ligament at the proximal end of the fused segments had to be removed. However, the templates can be designed to cover different parts of the lamina; for example one side or the lower half, not to disrupt the tension band. The design of the templates can be refined for that purpose in future studies. The other limitation is that the technique requires 2 3 days to produce the templates: 1 2 days for the design and 1 day for printing. Consequently, this method cannot be used for emergency surgery. Further progress in computer technology to speed these steps is awaited. Conclusions The multistep, patient-specific screw guide template system is useful for intraoperative pedicle screw navigation in the thoracic spine. This simple and economical method can improve the accuracy of pedicle screw insertion and reduce the operating time and radiation exposure of spinal fixation surgery. Disclosure The authors report no conflict of interest concerning the materials and methods used in this study or the findings specified in the pa per. Author contributions to the study and manuscript preparation in clude the following. Conception and design: Sugawara. Acquisition J Neurosurg: Spine / Volume 19 / August 2013 of data: Sugawara, Higashiyama, Kaneyama, Takabatake, Uchida, Su mi. Analysis and interpretation of data: Sugawara. Drafting the article: Sugawara. Critically revising the article: all authors. Re viewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Sugawara. Ad ministrative/technical/material support: Watanabe. References 1. Abul-Kasim K, Söderberg M, Selariu E, Gunnarsson M, Kherad M, Ohlin A: Optimization of radiation exposure and image quality of the cone-beam O-arm intraoperative imaging system in spinal surgery. J Spinal Disord Tech 25:52 58, Abumi K, Kaneda K: Pedicle screw fixation for nontraumatic lesions of the cervical spine. Spine (Phila Pa 1976) 22: , Belmont PJ Jr, Klemme WR, Dhawan A, Polly DW Jr: In vivo accuracy of thoracic pedicle screws. Spine (Phila Pa 1976) 26: , Berry E, Cuppone M, Porada S, Millner PA, Rao A, Chiverton N, et al: Personalised image-based templates for intra-operative guidance. Proc Inst Mech Eng H 219: , Cinotti G, Gumina S, Ripani M, Postacchini F: Pedicle instrumentation in the thoracic spine: a morphometric and cadaveric study for placement of screws. Spine (Phila Pa 1976) 24: , Costa F, Cardia A, Ortolina A, Fabio G, Zerbi A, Fornari M: Spinal navigation: standard preoperative versus intraoperative computed tomography data set acquisition for computer-guidance system: radiological and clinical study in 100 consecutive patients. Spine (Phila Pa 1976) 36: , Ebraheim NA, Xu R, Ahmad M, Yeasting RA: Projection of the thoracic pedicle and its morphometric analysis. Spine (Phila Pa 1976) 22: , Gelalis ID, Paschos NK, Pakos EE, Politis AN, Arnaoutoglou CM, Karageorgos AC, et al: Accuracy of pedicle screw 189

6 T. Sugawara et al. placement: a systematic review of prospective in vivo studies comparing free hand, fluoroscopy guidance and navigation techniques. Eur Spine J 21: , Kothe R, O Holleran JD, Liu W, Panjabi MM: Internal architecture of the thoracic pedicle. An anatomic study. Spine (Phila Pa 1976) 21: , Liljenqvist U, Hackenberg L, Link T, Halm H: Pullout strength of pedicle screws versus pedicle and laminar hooks in the thoracic spine. Acta Orthop Belg 67: , Liljenqvist UR, Halm HF, Link TM: Pedicle screw instrumentation of the thoracic spine in idiopathic scoliosis. Spine (Phila Pa 1976) 22: , Lu S, Xu YQ, Chen GP, Zhang YZ, Lu D, Chen YB, et al: Efficacy and accuracy of a novel rapid prototyping drill template for cervical pedicle screw placement. Comput Aided Surg 16: , Lu S, Xu YQ, Lu WW, Ni GX, Li YB, Shi JH, et al: A novel patient-specific navigational template for cervical pedicle screw placement. Spine (Phila Pa 1976) 34:E959 E966, Lu S, Zhang YZ, Wang Z, Shi JH, Chen YB, Xu XM, et al: Accuracy and efficacy of thoracic pedicle screws in scoliosis with patient-specific drill template. Med Biol Eng Comput 50: , Ma T, Xu YQ, Cheng YB, Jiang MY, Xu XM, Xie L, et al: A novel computer-assisted drill guide template for thoracic pedicle screw placement: a cadaveric study. Arch Orthop Trau ma Surg 132:65 72, Magerl FP: Stabilization of the lower thoracic and lumbar spine with external skeletal fixation. Clin Orthop Relat Res (189): , Nottmeier EW, Seemer W, Young PM: Placement of thoracolumbar pedicle screws using three-dimensional image guidance: experience in a large patient cohort. Clinical article. J Neurosurg Spine 10:33 39, Oertel MF, Hobart J, Stein M, Schreiber V, Scharbrodt W: Clinical and methodological precision of spinal navigation assisted by 3D intraoperative O-arm radiographic imaging. Technical note. J Neurosurg Spine 14: , Owen BD, Christensen GE, Reinhardt JM, Ryken TC: Rapid prototype patient-specific drill template for cervical pedicle screw placement. Comput Aided Surg 12: , Papin P, Arlet V, Marchesi D, Rosenblatt B, Aebi M: Unusual presentation of spinal cord compression related to misplaced pedicle screws in thoracic scoliosis. Eur Spine J 8: , Roy-Camille R, Saillant G, Mazel C: Plating of thoracic, thoracolumbar, and lumbar injuries with pedicle screw plates. Orthop Clin North Am 17: , Ryken TC, Owen BD, Christensen GE, Reinhardt JM: Imagebased drill templates for cervical pedicle screw placement. Laboratory investigation. J Neurosurg Spine 10:21 26, Shin BJ, James AR, Njoku IU, Härtl R: Pedicle screw navigation: a systematic review and meta-analysis of perforation risk for computer-navigated versus freehand insertion. A review. J Neurosurg Spine 17: , Vaccaro AR, Rizzolo SJ, Balderston RA, Allardyce TJ, Garfin SR, Dolinskas C, et al: Placement of pedicle screws in the thoracic spine. Part II: An anatomical and radiographic assessment. J Bone Joint Surg Am 77: , Xu R, Ebraheim NA, Ou Y, Yeasting RA: Anatomic considerations of pedicle screw placement in the thoracic spine. Roy-Camille technique versus open-lamina technique. Spine (Phila Pa 1976) 23: , Youkilis AS, Quint DJ, McGillicuddy JE, Papadopoulos SM: Stereotactic navigation for placement of pedicle screws in the thoracic spine. Neurosurgery 48: , Zindrick MR, Wiltse LL, Doornik A, Widell EH, Knight GW, Patwardhan AG, et al: Analysis of the morphometric characteristics of the thoracic and lumbar pedicles. Spine (Phila Pa 1976) 12: , 1987 Manuscript submitted November 18, Accepted April 22, Supplemental online information: Video: akamai.com/21492/wm.digitalsource-na-regional/spine _ video_1.asx (Media Player). com/21492/qt.digitalsource-global/spine _video_1.mov (Quicktime). Please include this information when citing this paper: published online May 24, 2013; DOI: / SPINE Address correspondence to: Taku Sugawara, M.D., Department of Neurosurgery, Akita University School of Medicine, Hondo, Akita , Japan. taku@nsg.med.akita-u.ac.jp. 190 J Neurosurg: Spine / Volume 19 / August 2013