Review Article

Correction maneuvers in scoliosis surgery - an overview Ameer S Theruvath1, Rajat Mahajan2, Gururaj M3, Chhabra HS4, Vikas Tandon5, Ankur Nanda6 www.kjoonline.org Indian Spinal Injuries Centre, New Delhi, India

1,2

Fellow in Spine Surgery

3,5,6

4

Consultant Spine Surgeon

Chief of Spine services

Correspondence should be sent to: [email protected]

Abstract Scoliosis surgery is one of the most challenging procedures in the surgical world. Many procedues are described for the correction of the spinal deformities. The authors review the different posterior surgical maneuvers used in correction of scoliosis. The methods like distraction-compression, single and double rod rotation, rod translation, direct vertebral rotation, cantilever bending technique and vertebral co-planar realignment are reviewed in detail. For any given curve, multiple maneuvers or a combination of these tactics would work out best. An individual surgeon may be comfortable with a specific method or methods. Nevertheless it is important for all surgeons treating scoliosis to be familiar with multiple correction strategies and to be aware of the evolution and scientific principles of the maneuvers employed.

Key words: Scoliosis, Surgical correction maneuvers, Posterior instrumentation

Introduction Scoliosis surgery is one of the most demanding surgical procedures in spine surgery in terms such as patient selection, planning, operative skills, surgical expertise as well as post operative care and rehabilitation. Of these, surgical decision making and planning are the most crucial and tricky arenas which have been exhaustively covered in existing literature eventhough there are no universal consensus in many issues such as surgical goals, selection of fusion levels and selective fusion of certain curve types. Available online at www.kjoonline.org Quick response code

Kerala Journal of Orthopaedics 2012;25:73-77 © Kerala Journal of Orthopaedics

There has been a gradual shift of surgical goal from attaining maximal curve correction to achieving the best possible global coronal and sagittal balance with optimal curve correction in the recent times. The surgical maneuvers involved in curve correction has not been a subject of debate at least in the initial two or three decades of scoliosis surgery when the instrumentation system of Dr. Paul Harrington was the name of the game. Nobody cared to question the simple logic of straightening a curve by distracting it on one side and compressing at the other. Moreover the surgical results of this system was, to say the least, outstanding at that times. But with thorough

Kerala Journal Of Orthopaedics Volume 25 | Issue 2 | July 2012

understanding of the pathoanatomy of the disease and evolution of improved mechanical efficiency of instrumentation systems the situation began to change. The literature is now rich with this issue and there are many studies comparing the efficiency of one method over the other. But the data is largely scattered among letters and compilations are sparse. We review the evolution, philosophy and current trends of these maneuvers in the backdrop of a classical disease which bears the flag of the fraternity of orthopedics. The manevers described are for the posterior spinal instrumented fusions. The anterior surgical maneuvers are not included in this review since the principles and strategies for anterior instrumented fusion are radically different from posterior surgeries. The various methods reviewed here largely pertain to adolescent idiopathic scoliosis because the premises of correction of other curves such as in infantile scoliosis and neuromuscular curves tend to differ in certain terms. Spine surgery is one of the most challenging affairs in the modern surgical world. Inspite of the spectacular advances in the field of scoliosis surgery,neurological as well 73

Review Article Ameer et al.:Correction maneuvers in scoliosis surgery - an overview

as other complications like post operative decompensation are still met with. Transmission of a fraction of the force applied around it to the spinal cord can result in devastating neurological consequences. The following are the methods reviewed in chronological order: 1. Distraction-compression 2. Simple Rod rotation 3. Simultaneous double rod rotation (SDRR) 4. Rod Translation 5. Direct vertebral rotation (DVR) 6. Cantilever bending technique (CBT) 7. Vertebral co-planar alignment (VCA) Distraction The Harrington instrumentation system, since its inception in 1962 remained the state of the art technique for scoliosis correction for around a decade and a half. It was primarily designed to apply distraction to the spine. 50-60% of curve correction could be achieved using these rods and the results were considered excellent 1 given the limited surgical armamentarium available at those times. The rate of neurological injury were remarkably low. Though the instrumentation system is out of flavour in current times, it marked the beginning of the great era of corrective scoliosis surgery and provided the only means of obtaining significant curve correction for a long time. The following were the major pitfalls of the system: 1. Limited amount of correction 2. Iatrogenic flatback if fusion extends to lumbar region 3. Do not address rotational deformity 4. Lamina fracture if excessive corrective forces are applied 5. Inadequate rib cage correction 6. Post operative immobilization required Simple Rod rotation With the advent of posterior segmental spinal instrumentation systems multiple points of fixation were available and in addition to distraction-compression forces rotational forces could also be exerted over the curves. Dr. Jean Cotrel and Dr. Yves Dubousset2 from France introduced the most widely accepted multihook segmental instrumentation system which is considered by many as a revolution in the field of scoliosis surgery. The technology originally named as Universal instrumentation and later came to be called CD instrumentation in honour of its inventors was based on the realization of the three dimensional nature of the deformity. The premises of curve correction was now shifted to derotation of the curve by 74

rotating the rod. With the advent of pedicle screws and the modification of instrumentation systems, more powerful corrective forces could be utilised. It was believed that the rod rotation brought about the correction by truly derotating the curve along the transverse axis. But intense research and biomechanical simulation studies proved that this concept is not completely correct. Mechanism of curve correction by rod rotation: A contoured rod is applied to the concavity (in case of a thoracic curve) of the curve after appropriate releases. Plugs are applied to the anchor points i. e. between screw/hook and the rod but not tightened. The rod is now rotated towards the concavity of the curve. This exerts a powerful postero medialisation pull on the apical (mainly) as well as the juxta apical vertebrae which are translated rather than rotated toward the midline as well as posteriorly. At the same time at least in theory it also indirectly de rotates the apical vertebra in the transverse plane thereby affecting some rotational correction also. But for this rotational correction to happen friction must be absent / negligible at the screw-rod interface and the screw should be freely gliding in the rod. This ideal situation occurs only in smaller, less rigid curves. Friction is almost always present in the junctions and if it is considerable, it actually increases the rotational deformity and the resultant rib hump. Clinically ,the effect of rod rotation on rotational correction of scoliosis is negligible. Nevertheless, a very good amount of coronal as well as sagital correction is still obtained with this manoeuvre. To understand the mechanism of sagittal correction obtained one must also appreciate movement of the upper and lower instrumented levels. During the 900 rod rotation the upper instrumented vertebra is shifted anteriorly as well as it is flexed in the sagittal plane . Likewise the lower instrumented vertebra is shifted anteriorly and extended in the sagittal plane. These movements helps recreate the sagittal profile during derogation. One should also realise that the rotational and translational influence of the manoeuvre is also transmitted to the segments outside the confines of the instrumentation. This becomes especially significant in the selective fusion of thoracic curves in major thoracic-compensatory lumbar curves where excess derotation can detrimentally influence the spontaneous correction of the compensatory lumbar curve. In the lumbar spine the rod should be applied to the convexity of the curve and rotated clockwise as seen from the caudal end to recreate the lumbar lordosis. The important difference in rod rotation on the curve in the lumbar and thoracic regions is that in the lumbar region, rod rotation does not increase the rotational deformity of the apical vertebra but tend to reduce it since the direction of rotation is opposite to that in thoracic region. The spinous processes which are shifted to the concavity of the curve are pulled towards the midline in the process of Kerala Journal of Orthopaedics Volume 25 | Issue 2 | July 2012

Review Article Ameer et al.:Correction maneuvers in scoliosis surgery - an overview

converting the lumbar scoliosis into lumbar lordosis. Hence presence of friction at rod-tulip interface is not a concern as in reality it exerts a derotational influence in the apical and juxta apical vertebrae. One should always remember that rotation of rod should always be carried out toward the direction where it is applied, that is, towards the concavity in thoracic and towards the convexity in the lumbar. This is because of the fact that the medial wall of the pedicle is at least 300% stronger than the lateral wall. If rotation is attempted in the same direction by applying rod on the opposite side that is for example a convex rod applying posteromedial pull at the apex, the chance of pedicle screw breaching the weaker lateral wall is high. Simultaneous double rod rotation technique. Manabu3 and workers developed a variation in the rod rotation technique to overcome some limitations of simple rod rotation technique. Many a times the rotating rod i e concave rod in thoracic curve tends to flatten out during the rotation maneouver. This is especially true with the the modern titanium rods that are much less stiff than the previously employed stainless steel rods. This straightening out directly translates into loss of optimum sagittal profile that leads to less satisfactory outcome. Developers of this technique claim that rods when they are introduced on both sides of the curve and simultaneously rotated, brings about synchronous correction of the coronal as well as the sagittal profiles without any one of the longitudinal members being flattened out. They also point out that this technique has a positive influence on rotational deformity correction. This is because,in this method, the concave rod in a typical thoracic curve is bent more sharply than the convex rod which necessitates the concave rod to negotiate a larger distance than its convex counterpart. This coupling of forces create a rotational moment at the apical vertebra which tend to derotate it. The major correcting force applied to the spine by this method is synchronous upward-pushing in the posteromedial direction. Rod Translation manoeuvre More recently certain instrumentation systems have been developed in which a translational technique4,5 is used for obtaining reduction rather than a rotation maneuver. In this the instrumented vertebrae are gradually translated towards the rod with the help of specialized instruments such as the “persuader”(universal spine system-Synthes) or with pedicle screw/hook extensions as in the Colorado instrumentation (Sofamor-Danek) Direct vertebral rotation(DVR) Eventhough the CD system and rod rotation maneouver was a huge leap in the history of scoliosis surgery, the basic pathoanatomy of scoliosis namely the rotational deformity Kerala Journal Of Orthopaedics Volume 25 | Issue 2 | July 2012

continued to evade surgical correction. Suk and associates in 1999 introduced the concept called Direct Vertebral Rotation,6,7 which could effectively correct a substantial amount of rotational malalignment in scoliosis. After the CD this was yet another landmark in evolution of scoliosis surgery. Suk introduced the DVR as a procedure done along with the rod rotation maneouver and thereafter a lot of refinements were made in this technique by various workers across the globe. The concept of direct vertebral rotation is to correct vertebral rotation by application of a posterior force in the direction opposite to that of the deformity. After pedicle screws are applied and rod rotation is done to correct the coronal and sagittal deformity, torque is applied to the pedicle screws using long screw derotators on both concave and convex sides of the curve. Since spinous process always rotate to the concavity in scoliosis, DVR must always be done towadrs the convexity of the curve at the apical and juxtaapical vertebrae. On the lowermost one or two screws, however, the direction of DVR depends on the rotation of vertebra in the compensatory lumbar curve. If the compensatory lumbar curve is large enough to cross the central sacral line,then the lowermost two levels must be rotated in the direction opposite to that of thoracic DVR in order to reduce the rotational deformity of the lumbar curve. On the other hand if the curve is a single thoracic scoliosis(eg., Lenke Type IA, IB) there is no need to perform DVR on the lowermost screws because lumbar rotation is spontaneously corrected during the thoracic DVR. As mentioned earlier DVR is now performed by a number of methods other than with concomittant rod rotation, out of which the most notable and widely accepted method is the bilateral apical vertebral derotation (BAVD) method with the aid of vertebral column manipulation (VCM) set. In the original DVR technique of Suk, rotational forces are applied on the individual vertebra through a single pedicle either concave or convex (unipedicular grip). The tendency to screw ploughing can be reduced here by applying derotation to apical and juxtaapical screws together in the required direction. In BAVD, the chances of screw pullout is further reduced manytimes by applying forces through a bipedicular grip combined with a triangulation technique. The vertebral column manipulator (VCM-Medtronic) is a versatile apparatus which when assembled resemble an external fixator. In this, pedicle screws are introduced in the routine manner. The tulip of the screws used allows connection of derotator implant holder on its medial tab without hindering the placement of rod. The advantage is that the rods can be applied after the corrective maneouver, while the VCM apparatus is still in place. The derotator implant holders are attached to both sides of the vertebrare planned for derotation. Now the concave and convex 75

Review Article Ameer et al.:Correction maneuvers in scoliosis surgery - an overview

screws are connected to each other by preloaded bridge nuts at the cephalad ends of the implant holders completing the triangulation. In a very flexible curve, the necessary corrective forces can be applied through a single trianguled segment. But in larger or stiff curves, a quadrilateral frame is created by connecting the triangulated apical and juxtaapical vertebrae. This allows for tremendous dilution of forces at the individual screw bone interface at the same time allowing the application of immense derotational and translational forces safely. Forces are applied through handles. Superior handle is connected vertically up from the middle of the cross connector and convex handle attached horizontally on the convex side end of the cross connector. Once the assembly is in place, start introducing the concave side rod which is prebent to confirm to the normal sagittal profile. Start from the most cephalad screw and gradually bring it down and engage each segment by applying derotational forces through the handles. With continued derotational and translational forces all the segments are captured into the rod to recreate spinal alignment. This method might qualify to be described as the current ‘state of the art’ technique of scoliosis correction eventhough there may not be a universal consensus in this regard. Cantilever bending technique In this technique of surgical correction,8,9 six groups of pedicle screws were inserted on the upper, apical, and lower segments on both sides of a curve. After the pedicle screw was positioned, a prebent rod was locked to the pedicle screws on the convex side. As two lever arms in the coronal plane, two long in situ benders were secured to the convex side of the rod (above and below the attachment of the apical pedicle screws) in the coronal plane. Bringing the free ends of the lever arms closer to each other could generate a powerful corrective force to correct the curve in the coronal plane. If necessary, another two long in situ benders were secured to the rod above and below the attachment of apical pedicle screws in the sagittal plane and acted as two lever arms in the sagittal plane. These can correct deformity in the sagittal plane with separate application of corrective force by the cantilever bending technique. A rod prebent to conform to the corrected curve was secured to the screws on the concave side to support and maintain the corrected curvature. After connecting both rods by transverse links and finely adjusting the end vertebrae according to the intraoperative PA radiographs to balance the body, the lever arms were released.

pedicle screws and aligning them linearly. This is followed by restoration of kyphosis by descending a longitudinal member down the slots while keeping polythene spacers between the tips of the slotted tubes. This achieves posterior divergence of the spinous processes and hence physiological kyphosis of the now linearly arranged spinal segments. The advantage of this technique compared to DVR is not yet clear. But there are a few differences in the methodology of correction between the two. In VCA, the correction is done by the convex side screws. The apical vertebra is rotated laterally so that the stronger medial pedicle wall is stressed rather than the weaker lateral wall. This reduces the chances of pedicle screw breach. From the neurological safety standpoint,manipulating the spinal column from the convex side appear to be safer as the cord is always shifted to the concavity of the curve.11 The authors, also claim that attaining stable anchorage of screws is easier and more secure on the convex pedicles. Another advantage claimed is that the correction is achieved before rods are placed which according to the inventors reduces the demands on instrumentation. This is not completely true as it is always the motion at anchor points which is more of a concern due to potential screw loosening. This however makes the rod placement much easier than other methods.

Conclusion The surgical strategies employed for scoliosis correction are highly individualised among surgeons. Choice of approach, levels of fusion, choice of instrumentation and choice of bone grafts- all vary according to surgeons preferences which evolve through his training and experience. The most variable of these factors is the correction maneuvers employed. It actually constitutes the “art” of scoliosis surgery. For any given curve, multiple maneuvers would be suitable to achieve an optimal correction. In some curves a combination of these tactics would work out best. This oftentimes is achieved intraoperatively by trial and error. An individual surgeon may be comfortable with a specific method or methods. Nevertheless it is important for all surgeons treating scoliosis to be familiar with multiple correction strategies and to be aware of the evolution and scientific principles of the maneuvers employed.

Vertebral coplanar alignment Vallespir10 and coworkers from Madrid introduced the concept in which they claim simultaneous recreation of coronal and sagittal profile along with correction of rotational deformity is achieved by the use of slotted longitudinal tubes attached to 76

Kerala Journal of Orthopaedics Volume 25 | Issue 2 | July 2012

Review Article Ameer et al.:Correction maneuvers in scoliosis surgery - an overview

References 1. Samuel Kadoury Æ Farida Cheriet Æ Marie Beause´jour Æ Ian A. Stokes Æ Stefan Parent Æ Hubert Labelle A three-dimensional retrospective analysis of the evolution of spinal instrumentation for the correction of adolescent idiopathic scoliosis Eur Spine J 2009. 2. Yoann Lafon, PhD, Virginie Lafage, PhD,Jean Dubousset, PhD,and Wafa Skalli, PhD Intraoperative Three-Dimensional Correction During Rod Rotation Technique SPINE Volume 34, Number 5, pp 512– 519 ,2009. 3. Manabu Ito, M. D. , Ph. D. , Kuniyoshi Abumi , M. D. , Ph. D. , Yoshihisa Kotani, M. D. , Ph. D. , Masahik o Takahata, M. D. , Ph. D. , Hid eki Sudo, M. D. , Ph. D. , Yoshihiro Hojo, M. D Simultaneous double-rod rotation technique in posterior instrumentation surgery for correction of adolescent idiopathic scoliosis Technical note Spine 12:293–300, 2010. 4. Se´bastien Delorme, MSc, Hubert Labelle, MD, CarlE´ric Aubin, PhD, Jacques A. de Guise, PhD, Charles H. Rivard, MD Intraoperative Comparison of Two Instrumentation Techniques for the Correction of Adolescent Idiopathic Scoliosis Rod Rotation and Translation SPINE Volume 24, Number 19, pp 2011–2018 1999. 5. Jean-Luc Clement, MD,Edouard Chau, MD, Anne Geoffray, MD, and Marie-José Vallade, MD Simultaneous Translation on Two Rods to Treat Adolescent Idiopathic Scoliosis Radiographic Results in Coronal, Sagittal, and Transverse Plane of a Series of 62 Patients With a Minimum Follow-up of Two Years SPINE Volume 37, Number 3, pp 184–192 2012.

Screw Fixation in Adolescent Idiopathic Scoliosis SPINE Volume 29, Number 3, pp 343–349,2004. 7. Michael S. Chang, MD, and Lawrence G. Lenke, MD . Vertebral Derotation in Adolescent Idiopathic Scoliosis Oper Tech Orthop 19:19-23, 2009. 8. Kao-Wha Chang, MD, Ku-I Chang, MD, and Chi-Ming Wu, MD Enhanced Capacity for Spontaneous Correction of Lumbar Curve in the Treatment of Major Thoracic–Compensatory C Modifier Lumbar Curve Pattern in Idiopathic Scoliosis SPINE Volume 32, Number 26, pp 3020–3029,2007. 9. Kao-Wha Chang, MD,Cantilever Bending Technique for Treatment of Large and Rigid Scoliosis SPINE Volume 28, Number 21, pp 2452–2458, 2003. 10. Gabriel Piza‘ Vallespir, MD, PhD, Jesu´s Burgos Flores, MD, PhD, Ignacio Sanpera Trigueros, MD, PhD, Eduardo Hevia Sierra, MD, Pedro Dome´nech Ferna´ndez, MD, PhD, Juan Carlos Rodrý´guez Olaverri, MD, PhD Vertebral Coplanar Alignment A Standardized Technique for Three Dimensional Correction in Scoliosis Surgery: Technical Description and Preliminary Results in Lenke Type 1 Curves SPINE Volume 33, Number 14, pp 1588–1597 2008. 11. Yong Qiu, MD, Feng Zhu, MD, Bin Wang, MD, Yang Yu, MD, Zezhang Zhu, MD, Bangpin Qian, MD. Comparison of Surgical Outcomes of Lenke Type 1 Idiopathic Scoliosis Vertebral Coplanar Alignment Versus Derotation Technique SPINE Volume 33, Number 14, pp 1588–1597 2008.

6. Sang-Min Lee, MD, PhD, Se-Il Suk, MD, PhD, and EwyRyong Chung, MD, PhD Direct Vertebral Rotation: A New Technique of Three-Dimensional Deformity Correction With Segmental Pedicle

Source of funding: Nil; Conflict of interest: Nil

Cite this article as: Ameer S Theruvath, Rajat Mahajan, Gururaj M, Chhabra HS, Vikas Tandon, Ankur Nanda. Correction maneuvers in scoliosis surgery - an overview. Kerala Journal of Orthopaedics 2012;25:73-77

Kerala Journal Of Orthopaedics Volume 25 | Issue 2 | July 2012

77