A customized modular reference array clamp for navigated spine surgery

A customized modular reference array clamp for navigated spine surgery
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  Arch Orthop Trauma Surg (2010) 130:1475–1480DOI 10.1007/s00402-010-1060-0  1 3 ORTHOPAEDIC SURGERY A customized modular reference array clamp for navigated spine surgery Padhraig F. O’Loughlin · Dorothea Daentzer · Tobias Hüfner · Nesrin Uksul · Mustafa Citak · Jonas Haentjes · Christian Krettek · Musa Citak Received: 9 November 2009 / Published online: 30 January 2010 󰂩  Springer-Verlag 2010 Abstract  Introduction The current authors have developed a modu-lar system of reference array W xation which is tailored spe-ci W cally to the spinal level being operated upon. Theybelieve that this system may further increase the precisionand accuracy of pedicle screw placement.  Materials and methods Two formalin- W xed whole bodycadavers were used for this study. For cervical spine evalu-ation of the reference clamp, four odontoid screws (two percadaver) for C1/C2-fusion and four lateral mass screws(two per cadaver) were implanted. Following navigatedscrew placement with 2D and 3D X uoroscopic veri W cation,insertion of two lateral mass screws was performed. In thesame way, lumbar and thoracic pedicle screws wereimplanted. Two pedicle screws were placed at two levels of the lumbar and two levels of the thoracic areas giving anoverall of 16 screws implanted (8 cervical, 4 thoracic, and 4lumbar). Postoperative evaluation involved comparison of postoperative 3D scans and preoperative planning images.A simple classi W cation system was used for evaluation of any deviation from the planned trajectory.  Results All pedicle screw placements were performed asplanned without any technical problems. The referencearray clamps remained in position at all the spinal levels atwhich they were employed with no loosening or displace-ment and no secondary damage to any of the spinousprocesses. Manual manipulation was performed but nodisplacement or slippage was observed. Image artefactscaused by the reference clamp were not signi W cant as toobscure the area of interest. Both imaging modalities (Iso-C3D and Vario 3D) generated su Y ciently precise 3D images.There was no substantial di V  erence in quality when thosetwo systems were compared.  Discussion Insu Y cient W xation of the reference clampcan lead to failure and complications. To date, no referenceclamp systems have been developed speci W cally for navi-gated spine surgery. Conclusions Stable reference array W xation is a criticalstep in navigated surgery. To date, the same referenceclamps have been applied to the spinal anatomy as havebeen developed srcinally for the appendicular skeleton.The current investigators have developed a novel modularclamp and have demonstrated its e Y cacy in a cadavericmodel. Keywords Computer-assisted surgery · Reference marker clamps · Registration · Navigated spinal surgery · Spinal fracture · Pedicle screw placement Introduction Since the introduction, by Roy-Camille [23], of instru-mented internal W xation within the spine, transpedicularscrews have been used with increasing frequency in spinalfusion procedures. The application of pedicle screws hasresulted in superior fusion rates [8, 27], mainly due to the biomechanical advantage conferred in comparison to other P. F. O’Loughlin · T. Hüfner · Mustafa Citak · Musa Citak ( & )Department of Orthopaedic Surgery, Hospital for Special Surgery, Computer Assisted Surgery Center, 535 East 70th Street, New York, NY 10021, USAe-mail:; citak.musa@mh-hannover.deD. DaentzerOrthopedic Department, Hannover Medical School, Hannover, GermanyT. Hüfner · N. Uksul · J. Haentjes · C. Krettek · Musa Citak Trauma Department, Hannover Medical School, Hannover, Germany  1476Arch Orthop Trauma Surg (2010) 130:1475–1480  1 3 methods of stabilization [17, 26]. The main challenge, how- ever, with transpedicular W xation is accuracy in placementgive the close proximity of the spinal cord [25] particularlywithin the thoracic spine and to the lumbar nerve roots [9]within the lumbar spine. The incidence of neurologicalcomplications associated with pedicle screw misplacementmay be as high as 7% [10]. The extent of hardware mis-placement, where an obvious risk of compromising neuro-logical structures exists, is said to range from >2mm [11,25] to >6mm [12, 24] for medial misplacement. Taking these points into consideration along with a pub-lished rate of pedicle screw misplacement of up to 39.9%amongst all such screws and 28.5% of medially misplacedpedicle screws [12], it is important to seek ways to improveaccuracy. Therefore, it is logical that one of the W rst goalsof computer-assisted surgery has been to target this realmof orthopaedic surgery in an e V  ort to improve the accuracyand precision of pedicle screw placement [18]. Severalstudies have established an improvement in the rate of opti-mally placed pedicle screws within the cervical, thoracic,and lumbar spine with the use of computer-assisted tech-niques [1, 13, 14, 21]. In tandem with the evolution of more sophisticated com-puter software and hardware, there has been gradual develop-ment of newer navigation instruments and in particular,reference arrays [5, 6, 19]. A problem with these tools, which are typically applied in an intraosseous fashion to the regionof interest so as to allow registration of the subject’s anat-omy, is their universal mode of attachment. What may bee V  ective and practical in the femur for example does not nec-essarily function well within the spine especially given theunique anatomy of the various groups of vertebrae. Cur-rently, the orthopeadic surgeon is forced to utilize just onereference marker W xation system for all sections of the spine.The purpose of this study was to develop a novel modu-lar spine reference array. Its modularity facilitates modi W -cation for di V  erent vertebral levels in order to improve themechanical stability. The second goal of this manuscriptwas to evaluate the new clamp in an experimental study intwo full specimens. Materials and methods Development of the modular clampThe clamp is composed of two units. The proximal unit ismade up of the mechanical device for clamping, and fur-thermore, the reference marker array (Fig.1). Dependingon the height necessary for the procedure in question, thedistal unit can be changed to conform to the local anatomy.Thus, the portion can be adjusted to be speci W c to the cervi-cal, thoracic and lumbar anatomy (Fig.2a–c). Fig.1 The proximal unit of the modular clamp: 1  connector for cali-bration spheres, 2  clamp tightening mechanism, 3  plug-in points for thedistal unit (which varies in shape depending on the vertebral levelbeing operated upon) Fig.2a  Y-shaped clamping apparatus designed for the lumbar spine( left  ) with close-up view ( right  ), b  thoracic spine clamp (L-shaped,given the elongated and horizontally oriented spinous processes at thislevel), and c  cervical spine clamp  Arch Orthop Trauma Surg (2010) 130:1475–14801477  1 3 Navigation system and imagingThe navigation system utilized was the Cappa Spine 3Dsystem (CAS Innovations, A Siemens Company, Erlangen,Germany). Two 3D X uoroscopes were utilized for imaging:the Iso-C 3D (Siemens, Erlangen, Germany) and Vario 3D(Ziehm, Nürnberg, Germany). Cappa Spine 3D is referredto as a passive navigation system employing sphericalmarkers that re X ect the infrared light of the camera. A min-imum of three calibration spheres are required to determinethe instrument location. In this way, the instrument posi-tions can be detected and tracked continuously throughoutthe operation and visualized on a display unit. Followingattachment of the reference star at the desired height 3Ddata are acquired by the Iso-C 3D system and transferredvia power cable to the navigation system. Once the lengthand diameter of the screws being used have been selected,virtual drill paths may be generated and adjusted to opti-mize placement. The screws are navigated speci W callyusing a navigated drill sleeve (CAS Innovations, A Sie-mens Company, Erlangen, Germany).Cadaver testing Cervical spine For evaluation of the reference clamp in the cervical spine,four odontoid screws (two per cadaver) for C1/C2-fusion andfour lateral mass screws (two per cadaver) were implantedunder navigated guidance. Two formalin- W xed whole bodycadavers were used. Once adequate exposure of the spinousprocesses had been achieved, the reference clamp wasattached (Fig.3a–c). Trajectories were planned after dataacquisition. Raw planning of the trajectory was accom-plished via pointer whereas the Vernier adjustment was car-ried out manually (Fig.4a). Once a universal navigationadapter (Cas Innovations, Erlangen, Germany) had beeninstalled and calibrated, a special drill guide (Synthes, Ober-dorf, Switzerland) was used (Fig.4b, c). Satisfactory drillingwas veri W ed by X uoroscopy (Fig.4d). The two odontoidscrews were implanted using navigation as well utilizing aspecial navigated screwdriver (Synthes, Oberdorf, Switzer-land) (Fig.5a). Following navigated screw placement(Fig.5b) with 2D and 3D X uoroscopic veri W cation (Fig.5c,d), insertion of two lateral mass screws was performed. Thoracic and lumbar spine In the same way, lumbar and thoracic pedicle screws wereimplanted. Two pedicle screws were placed at two levels of the lumbar and two levels of the thoracic areas giving anoverall total of 16 screws implanted (8 cervical, 4 thoracic,and 4 lumbar).Postoperative evaluation followed, with comparison of postoperative 3D scans and preoperative planning images.A simple classi W cation system was used for evaluation:Grade 1, deviation of the executed trajectory from theplanned trajectory by<2mm; Grade 2, deviation>2mmwithout cortical breach; Grade 3, cortical breach withoutspinal canal compression; Grade 4, spinal canal compres-sion. Furthermore, the stability of the reference clamp wascontrolled manually after each screw insertion. Results All of the pedicle screw placements were performed asplanned without any technical problems. The referencearray clamps remained in position at all the spinal levels atwhich they were employed with no loosening or displace-ment and no secondary damage to any of the spinous pro-cesses. The reference clamp was easy to adjust and adapteditself well to the spinal anatomy enabling a solid W xation.In order to check its stability, some manual manipulationwas performed but no displacement or slippage wasobserved. During placement of the 16 screws, four acciden-tal collisions with the clamp occurred without any signi W -cant displacement of the clamp. To verify this, scans weretaken which showed no deviation greater than 1mm. Imageartefacts caused by the reference clamp were not signi W cant Fig.3a  Cervical spine clamp in situ, b  2D image of C-spine, and c , d  image of C-spine  1478Arch Orthop Trauma Surg (2010) 130:1475–1480  1 3 Fig.4a  Virtual trajectory generation ( green arrow ) and b  screenshot post-drilling. The green arrow  (trajectory) and navigated drill (  yellow arrow ) are seen to be exactly overlying each other. Both circles  ( green  and blue ) at the bottom of the screenshot aid navigation. c  Drilling without drill calibration. d  A 2D X uoroscopic lateral view post-drilling Fig.5a  Screw calibration, b  navigated screw insertion  Arch Orthop Trauma Surg (2010) 130:1475–14801479  1 3 as to obscure the area of interest. Both imaging modalities(Iso-C 3D and Vario 3D) generated su Y ciently precise 3Dimages. There was no substantial di V  erence in quality whenthose two systems were compared. All screws were placedsatisfactorily in cortical bone with no Grade 3 or Grade 4deviation recorded. In terms of deviation in classi W cation,of the cervical screws placed, six screws were of Grade 1and two screws were of Grade 2; at the thoracic level threescrews were of Grade 1 and another two were of Grade 2; atthe lumbar spine, four screws were of Grade 1 and onescrew was of Grade 2. Discussion Navigation systems have made a signi W cant contribution toimproving precision in orthopaedics and trauma surgery [3,20–22]. However to date, while computer navigation has been employed with success in the spine [1, 4, 13, 24], many of the tools used have been designed primarily forother areas of the body. This prompted the current investi-gators to develop reference array clamps not only unique tothe spinal column but adjustable such that they could bemodi W ed depending on the level of the spinal column beingaddressed. In the current study, the advantages of com-puter-assisted navigation with these customized clampswere demonstrated for cervical, lumbar, and thoracic screwinsertion.Reference clamp placement is an important step in com-puter-assisted surgery [16]. Insu Y cient W xation of the refer-ence clamp can lead to failure and complications. Thisproblem is most apparent for registration which may beinaccurate and require repetition of the steps should theclamp loosen or become dislodged [5]. It is not clearexactly how frequently reference array movement occurs inthe clinical setting but it is likely that all who have everused navigated technology have experienced it at one timeor another. Whether the array has indeed shifted can bereadily established using the pointer tool.There has not been widespread W nancial support fromindustry to fuel the advancement of navigation hardwareand thus the onus has been on solitary work groups to tryreact to surgeons’ demands [6, 19]. Minimally invasive techniques and W xation stability have been of particularinterest to orthopaedists. Studies analyzing the mechanicalfeatures of one-pin and two-pin W xations can be found inthe literature, but there is no study dealing with the stabilityof spinal reference array clamps [2, 5, 15]. The current study focused on the development and subsequent testingof a new generation of spine clamps, which are tailored tothe di V  erent levels of spine anatomy. The level-speci W cdesign optimizes W xation. The cadaver tests demonstratedease-of-use and stability. The results obtained by thesystem in this study are comparable to previous studies byother research groups [14, 21, 24]. However, this study contains a unique aspect in that the current investigatorshave endeavoured to develop and test spine-speci W c refer-ence clamps.Another signi W cant problem in this area has been theappearance of artefacts upon imaging due to metallic hard-ware. The presence of those metal artefacts does not onlycompromise image quality but can also a V  ect registrationprecision [7]. The authors feel that the next evolution of thespine clamps would be to reduce these troublesome arte-facts even further. Conclusion Stable reference array W xation is a critical step in navigatedsurgery. Spinal anatomy presents unique challenges andthese vary according to the vertebral level being addressed.To date, the same reference clamps have been applied tothe spinal anatomy as were developed srcinally for theappendicular skeleton. The current investigators havedeveloped a novel modular clamp that has demonstratedstability in the current cadaveric model. The clinical bene W tof this clamp lies in its speci W city to the varying anatomicalfeatures of the vertebral levels. Thus, the design is anat-omy-based and the stability of clamp W xation is improved.The Authors also believe that the anatomy- based W xationdecreases the fracture risk in vertebral spine navigation. Adrawback of this study lies in the small number of speci-mens employed. To de W nitively establish a bene W t in thecurrent investigators’ modular clamp system, further stud-ies are required with ultimately a clinical study necessaryfor validation. Con X ict of interest statement None of the authors have any W nan-cial or personal relationships with other people, or organizations, thatcould inappropriately in X uence (bias) their work, within 3years of thebeginning of this study. References 1.Amiot LP, Lang K, Putzier M etal (2000) Comparative results be-tween conventional and computer-assisted pedicle screw installa-tion in the thoracic, lumbar, and sacral spine. Spine 25:606–6142.Board TN, Kendo V   D, Citak M etal (2008) Soft tissue dissectionin placement of reference markers during computer aided total hiparthroplasty. Comput Aided Surg 13:218–2243.Bottros J, Klika AK, Lee HH etal (2008) The use of navigation intotal knee arthroplasty for patients with extra-articular deformity.J Arthroplasty 23:74–784.Castro WH, Halm H, Jerosch J etal (1996) Accuracy of pediclescrew placement in lumbar vertebrae. Spine 21:1320–13245.Citak M, Board TN, Sun Y etal (2007) Reference marker stabilityin computer aided orthopedic surgery: a biomechanical study inarti W cial bone and cadavers. Technol Health Care 15:407–414
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