Eur Spine J DOI 10.1007/s00586-014-3340-9
ORIGINAL ARTICLE
Restoration of thoracic kyphosis by simultaneous translation on two rods for adolescent idiopathic scoliosis Jean-Luc Clement • Edouard Chau Anne Geoffray • Georges Suisse
•
Received: 19 April 2014 / Revised: 24 April 2014 / Accepted: 24 April 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Introduction Sagittal and axial corrections of the threedimensional deformity characteristic of scoliosis remain challenging. Materials and Method The author developed a new technique for scoliosis correction consisting of the translation of vertebrae simultaneously towards two rods, which are pre-bent to the correct sagittal profile. Using two rods ensures both reduction and stabilization of the curve. The system includes stable anchorages with polyaxial-threaded extensions that connect to the rods. Deformity reduction is done by tightening nuts simultaneously and progressively on the two rods. Results demonstrate the efficiency of this technique to achieve normal thoracic kyphosis ([20°) in all 99 patients, with a mean gain of 19° of thoracic kyphosis in hypokyphotic cases. Coronal correction was 70-80 % with a vertebral rotation gain of 40 % where derotation connectors were used. Conclusions In a large consecutive series of patients, this new technique allows to achieve a good 3D correction of the scoliosis.
J.-L. Clement (&) E. Chau Department of Paediatric Orthopaedic Surgery and Scoliosis Surgery, Hoˆpital Pe´diatrique Nice CHU Lenval, 57 avenue de la Californie, 06200 Nice, France e-mail: [email protected]; [email protected] A. Geoffray Department of Paediatric Radiology, Hoˆpital Pe´diatrique Nice CHU Lenval, Nice, France G. Suisse Department of Electrophysiology, Hoˆpital Pe´diatrique Nice CHU Lenval, Nice, France
Keywords Adolescent idiopathic scoliosis Hypokyphosis Simultaneous translation on two rods Pedicle screws
Introduction Three-dimensional deformity correction is one of the main objectives of the surgical treatment of idiopathic scoliosis. In the coronal plane, recent publications reported an average coronal correction between 65 and 74 % with screws [1, 2], and between 61 and 64 % with hybrid constructs [3, 4]. The use of pedicle screw only or hybrid constructs allows better correction than hook-only constructs [1, 5]. Publications regarding the sagittal plane are more inconclusive. Several authors showed an increase of thoracic kyphosis with screw, hook, and hybrid constructs [6– 8] but gains were moderate. Other authors observed no change or a decrease of thoracic kyphosis with the same types of instrumentation. The restoration of a normal sagittal profile remains challenging. Nevertheless, sagittal restoration is important for longterm spinal health. Preservation of thoracic kyphosis is critical to maintain lumbar lordosis [9]. Emami [10] reported that sagittally decompensated patients had significantly more pain than well-balanced patients. Dekutoski [11] showed that a loss of sagittal balance is correlated with higher pseudarthrosis rate and fixation failures. Kim et al. reported a 27 % incidence of proximal junctional kyphosis (PJK) [12], and that a postoperative decrease of T5-T12 sagittal Cobb angle was correlated significantly with PJK. Sagittal impairment may also influence the cervical sagittal alignment. Several publications have demonstrated correlation between thoracic hypokyphosis and cervical
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kyphosis in AIS and the influence of scoliosis surgery on cervical sagittal alignment [13, 14] Cervical kyphosis is responsible for cervical pain in adults [15], and 57 % of patients surgically treated for scoliosis had cervical pains at 26 years follow-up [16]. Recent international communications indicate that restoration of kyphosis can depend on the technique, rod diameter, and rod material used [17, 18]. In a previous study, we compared results of two reduction methods for correction of thoracic hypokyphosis in AIS [19]; significantly better correction of hypokyphosis was achieved with simultaneous translation on two rods compared to sequential approximation. In fact, the reduction technique used may be the main reason for poor results in sagittal correction. In the axial plane, using screw-only constructs allows the development of derotation specific techniques [20, 21]. However, vertebral derotation seems detrimental to correction of thoracic kyphosis [22, 23]. In 2000, after trying different reduction systems, we developed a new technique for correction of scoliosis: Simultaneous Translation on Two Rods (ST2R). This technique consists of translating the vertebrae simultaneously towards two rods, which were previously bent to the desired sagittal profile. Dual rods ensure both reduction and stabilization of the deformity. The purpose of this paper is to detail the concept, surgical technique, and results of ST2R focusing on the restoration of the thoracic kyphosis in AIS patients.
Materials and methods Materials The instrumentation used was a top-loading, side connection system including stable vertebral anchors linked to rods by connectors. Vertebral anchors included pedicle screws with different lengths and diameters that allowed use in both thoracic and lumbar vertebrae. Different types of claws were also available: pediculo-transverse or pediculo-laminar for thoracic claws, and lamino-laminar for the lumbar claws. These self-stabilizing claws were composed of a main hook and a counter hook, and were as stable as pedicle screws. This system also had a sacral plate fixation with one screw in the pedicle of S1 and the other in the wing of the sacrum, which could be reinforced by an iliac screw. Each anchorage was made with a polyaxial-threaded extension that enabled connection to the rods. Different connectors were available to allow surgeons to adapt to any situation; this includes standard, derotation, realignment, off-set, angled, and open connectors.
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Rods were made of titanium alloy-TiAl6 V or Co–Cr with a diameter of 5.5 or 6.0 mm to allow a balance between flexibility and strength. Methods Operative technique Instrumentation was performed in two operative phases: (1) placing the vertebral anchorages and (2) setting the rods and correcting the deformity. Vertebral anchorages Upon surgeon preference, the construct could be either a screw-only construct or a hybrid construct with screws and claws. Usually, we used mainly thoracic and lumbar pedicle screws with claws at the cephalad end of the construct. Claws or ligament fixation systems (LigaPASSTM) were used when the pedicle was too narrow for screw placement, or too difficult to find, like in the concavity of the curve. Lumbar and thoracic pedicle screws The technique described is a ‘‘free-hand’’ screw fixation technique developed by the author [19]. When the pedicle was difficult to find, the funnel technique for the cervical spine could be used. This technique consisted of removing all cancellous bone with a curette and visualizing the inside of the pedicle. Sometimes the entry point of the pedicle was hidden by the articular cortex, which was then removed with a rongeur. Once the pedicle was visualized, it was enlarged and the screw was inserted. However, in some cases, the pedicle could not be found, and it was not possible to insert a screw. In the case of infraction, the faulty direction was easily detected by feeling for the breach in the pedicle wall using the probe. It was possible to correct the direction of the drilling. This was necessary due to the risk in initially setting up the screw wrong; a screw with poor anchorage was like to be misplaced and removed. Thoracic spinal claw The claw consisted of a main polyaxial pedicle hook and a counter hook, facing each other. The counter hook closed the claw. First, the base of the transverse process of the underlying vertebra was partially resected using a rongeur to facilitate pedicle hook placement. The articular process, transverse process, and lamina were prepared with their respective hook starters. Second, the transverse or lamina counter hook was placed using the hook inserter. The pedicle hook, with its
Eur Spine J
Fig. 1 Simultaneous translation on two rods (ST2R) technique. a Both rods, previously bent according to the sagittal curvature, are dropped over flexible guides placed onto the threaded extensions of
each anchorage. b Nuts are loaded onto each of the threaded extension. The nuts are tightened only at the top of the threaded extension to maintain the mobility of the rods
Fig. 2 a, b The two rods are oriented in the sagittal plane without reduction of the deformity, thanks to the polyaxial-threaded extensions. c The two nuts on the upper anchorage are tightened to lock the rotation of the rods (arrow)
threaded extension, was then placed onto the connection axis and implemented under the articular process. The claw was initially closed using its compressor forceps, and then locked by the final tightening of the threaded extension. When all the anchorages were fixed, a radiographic control was performed to verify the vertebral level, length, and position of the screws. Rod and connector insertion and reduction of the deformity After selecting the rod length, the rod was contoured according to the desired sagittal curvature. The connectors were slid onto the rod, matching the number of anchorages. In most cases, the rods were placed on the median line. Derotation connectors could be loaded onto both rods for four or five vertebrae at the apex of the thoracic deformity. Standard connectors could be used at the other anchorages.
Both rods were dropped over flexible guides, which were placed onto the threaded extensions of the screw heads, and nuts were loaded onto each of the threaded extension (Fig. 1). The nuts were tightened only at the top of the threaded extension to maintain the mobility of the rods. The rods were then oriented in the sagittal plane without deformity reduction. For single thoracic curves, the nuts on the two cephalad anchorages were tightened to lock the rotation of the rods (Fig. 2). For double curves (thoracic and lumbar), we preferred to lock the rod rotation on the neutral intermediate anchorages between the two curves. For thoracic curves, reduction was achieved through progressive and alternating tightening of the nuts on both rods, allowing the vertebrae to gradually approach the rods (Fig. 3). In case of a derotation maneuver, the concave derotation connectors were aligned parallel to the coronal plane and their position on the concave rod was locked
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Fig. 3 a2c Reduction is achieved through a progressive and alternative tightening of the nuts on the two rods allowing the vertebrae to gradually approach the rods with a medial and posterior
translation. d Once reduction was fully achieved, the nuts are torqued and sheared off and the threaded extensions broken
with a set screw. The convex derotation connectors were left free to allow the vertebrae to rotate around the convex rod. The derotation effect was obtained by supplementary translation on the concave side when the convex translation was finished. For thoracolumbar or lumbar curves, we used derotation connectors at each level. The reduction was done in three steps: translation, compression on the convex side, and derotation on the concave side. First, we performed the translation maneuver on the convex rod by progressively tightening the convex nuts. Then, we gradually compressed the convex anchorages and locked the connectors by tightening the set screws. To allow derotation around the convex rod, we unlocked the intermediate convex set screws and kept the connectors of the extremities of the compressed convex zone locked to maintain the compression previously applied. Then, we oriented the concave derotation connectors parallel to the coronal plane and locked the concave set screws. By progressively tightening
the concave nuts, we achieved vertebral derotation (Fig. 1c, d). At the end of the procedure, we re-tightened the convex derotation connector set screws. With both curves types, once reduction was fully achieved, the nuts were torqued and sheared off and the threaded extensions were broken.
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Patients Between June 2000 and December 2009, 137 consecutive AIS patients were surgically treated with ST2R at a single institution by one orthopedic surgeon (JLC). Ninety-nine patients had completed preoperative and postoperative (1 month, 1 year, and 2 years or more) data sets and were included in the analysis. Standard standing anteroposterior (AP) and lateral radiographs of the spine were taken preoperatively at 1-month, 1-, 2-, 3-, and 5-year follow-ups. AP radiographs in supine lateral bending positions were also taken before
Eur Spine J
Fig. 4 a2c 13.8-year-old girl with a right thoracic idiopathic scoliosis of 57° with thoracic hypokyphosis and non-structural proximal thoracic and distal lumbar curves (Lenke 1A). d, e
Instrumentation with screws and two proximal pediculo-transverse claws from T3 to L1 with the goal to take all the thoracic kyphosis in the instrumentation
surgery to evaluate the flexibility of the curve. Computed tomography (CT) scans of the apical vertebra of the main curve were also obtained at pre- and immediate postoperative visits. Cobb angles of the main curve and proximal and distal counter curves were evaluated on coronal radiographs. Using lateral radiographs, thoracic kyphosis (TK) was measured from the superior endplate of the T4 vertebra to the inferior endplate of the T12 vertebra, and lumbar lordosis was measured from the superior endplate of L1 vertebra to the superior endplate of S1 vertebra. Axial rotation was evaluated with CT scans using the Aaro method [24].
In the sagittal plane, the average global thoracic kyphosis angle increased from 23° to 34° at the last follow-up (p \ 0.0001) (Figs. 4, 5). For hypokyphotic patients (n = 42), the average thoracic kyphosis angle was increased from 8° to 28° at 1 month and was maintained until last visit at 30° (p \ 0.0001).The mean gain was 22°. For patients with normal kyphosis (n = 43), the mean angle was 29° preoperatively improved to 34° at 1 month and to 36° at last follow-up (p \ 0.0001). For preoperative hyperkyphosis cases (n = 14), the angle was reduced from 47° to 39° postoperatively and was 41° at last follow-up (p \ 0.05). For the average global lordotic angle, there was no change in the global cohort. Nevertheless, in patients with preoperative hypokyphosis, the lordosis was improved from 42° to 50° at last follow-up (p \ 0.0001) (mean gain of 8°). In the axial plane, no reduction of the vertebral rotation was observed in the 41 patients who had undergone preand postoperative CT scan of the apical vertebra. In the most recent cases, the patients with derotation connectors (n = 12) obtained a derotation of the apical vertebra of 40 %.
Results The mean age of the 99 AIS patients was 14.8 years (11.7-21.5 years). According to Lenke classification [25], thoracic curves (Lenke types 1-3) were mainly instrumented (72 %). In the coronal plane, the average main curve was reduced from 55° to 16° at 1 month and maintained at the last visit (p \ 0.0001) (Figs. 2a-c, 3a-c). The mean correction was 70 % with a bending flexibility of 51 %.There was no significant difference between correction of thoracic scoliosis (69 %) and thoracolumbar/lumbar scoliosis (72 %). However, using derotation connectors significantly increased the coronal correction (80 vs. 72 %, p \ 0.05).
Discussion The translation technique was first introduced by Luque and then improved in the following years. The objective was to pull back the vertebrae toward the rods and to obtain
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Fig. 5 a2c 14-year-old boy with a right thoracic idiopathic scoliosis of 95° with hypokyphosis and structural proximal thoracic and distal lumbar curves (Lenke 4B). d, e Instrumentation from T2 to L4 with screws and two proximal pediculo-transverse claws
a compromise between the stiffness of the spine and the rigidity of the rods. This technique requires stable anchorages to be effective. The ISOLA instrumentation consisting of a multiple anchors system uses this vertebral translation with interesting results as reported by Asher [4], with a thoracic kyphosis gain of 10° for the hypokyphotic patients. ST2R is a translation technique. There is no need for rod rotation, sequential approximation, in situ bending, or direct vertebral rotation. The threaded extension allows the rods to connect to all of the anchorages, even when located at some distance from the rod. It leaves the rod very mobile and so that rods can be oriented in the sagittal plane before any reduction maneuvers are performed. The reduction maneuver is obtained simply by progressively tightening all nuts on both rods, which ensures medial and posterior vertebral translation. Using two rods this way ensures the correction of the scoliosis, contrary to other techniques that use one rod to reduce and another to stabilize. It is possible to combine this translation maneuver to a compression and/or derotation maneuver. ST2R never uses a distraction maneuver, which we consider associated to a neurologic risk. The stresses are also shared across all of the anchorages. Results from this series are similar to results previously reported [19, 26, 27]. In comparison with other reduction techniques, our results in the coronal plane are comparable to all screw constructs (64-74 %) [1, 2, 5, 28] and superior to hybrid constructs (61-64 %) [3, 4, 29]. Kim and Lowenstein demonstrated the superiority of all screw
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constructs against hybrid or all hook constructs [1, 2, 5]. To our knowledge, the gain of 22° in the sagittal plane for hypokyphotic patients is the best outcome ever reported in literature. Whereas ST2R achieved gain in thoracic kyphosis, other techniques presented postoperative loss [1, 2, 5, 30–32]. It is even more challenging to reduce axial rotational deformity while simultaneously restoring sagittal balance through techniques such as direct vertebral rotation (DVR) [30], in situ contouring (ISC)[33], and vertebral coplanar alignment (VCA) [34]. Although effective in reducing the rib hump [30], pushing down on the convex side to achieve axial rotation flattens the thoracic segment. Our data regarding derotation connectors are not sufficient for a conclusion. However, derotation connectors seem to be effective in the most recent cases. They allow for partial correction of the vertebral rotation, increased coronal correction (80 %), and reduction of hypokyphosis that can be maintained.
Conclusion The restoration of normal kyphosis in AIS patients is a challenge. Simultaneous Translation on Two Rods, which allows the rod to remotely connect to the anchorages, reduces the deformity by translating the vertebrae simultaneously towards both rods. This is an effective and simple method for treating scoliosis, especially in achieving sagittal correction of thoracic hypokyphosis.
Eur Spine J Conflict of interest Jean-Luc Clement has a consulting agreement with Medicrea International. 16.
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34. Vallespir GP, Flores JB, Trigueros IS, Sierra EH, Ferna´ndez PD, Olaverri JCR, Alonso MG, Galea RR, Francisco AP, de Rodrı´guez Paz B, Carbonell PG, Thomas JV, Lo´pez JLG, Paulino JIM, Pitarque CB, Garcı´a OR (2008) Vertebral coplanar alignment: a standardized technique for three dimensional correction in scoliosis surgery: technical description and preliminary results in Lenke type 1 curves. Spine 33(14):1588
ORIGINAL ARTICLE
Restoration of thoracic kyphosis by simultaneous translation on two rods for adolescent idiopathic scoliosis Jean-Luc Clement • Edouard Chau Anne Geoffray • Georges Suisse
•
Received: 19 April 2014 / Revised: 24 April 2014 / Accepted: 24 April 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Introduction Sagittal and axial corrections of the threedimensional deformity characteristic of scoliosis remain challenging. Materials and Method The author developed a new technique for scoliosis correction consisting of the translation of vertebrae simultaneously towards two rods, which are pre-bent to the correct sagittal profile. Using two rods ensures both reduction and stabilization of the curve. The system includes stable anchorages with polyaxial-threaded extensions that connect to the rods. Deformity reduction is done by tightening nuts simultaneously and progressively on the two rods. Results demonstrate the efficiency of this technique to achieve normal thoracic kyphosis ([20°) in all 99 patients, with a mean gain of 19° of thoracic kyphosis in hypokyphotic cases. Coronal correction was 70-80 % with a vertebral rotation gain of 40 % where derotation connectors were used. Conclusions In a large consecutive series of patients, this new technique allows to achieve a good 3D correction of the scoliosis.
J.-L. Clement (&) E. Chau Department of Paediatric Orthopaedic Surgery and Scoliosis Surgery, Hoˆpital Pe´diatrique Nice CHU Lenval, 57 avenue de la Californie, 06200 Nice, France e-mail: [email protected]; [email protected] A. Geoffray Department of Paediatric Radiology, Hoˆpital Pe´diatrique Nice CHU Lenval, Nice, France G. Suisse Department of Electrophysiology, Hoˆpital Pe´diatrique Nice CHU Lenval, Nice, France
Keywords Adolescent idiopathic scoliosis Hypokyphosis Simultaneous translation on two rods Pedicle screws
Introduction Three-dimensional deformity correction is one of the main objectives of the surgical treatment of idiopathic scoliosis. In the coronal plane, recent publications reported an average coronal correction between 65 and 74 % with screws [1, 2], and between 61 and 64 % with hybrid constructs [3, 4]. The use of pedicle screw only or hybrid constructs allows better correction than hook-only constructs [1, 5]. Publications regarding the sagittal plane are more inconclusive. Several authors showed an increase of thoracic kyphosis with screw, hook, and hybrid constructs [6– 8] but gains were moderate. Other authors observed no change or a decrease of thoracic kyphosis with the same types of instrumentation. The restoration of a normal sagittal profile remains challenging. Nevertheless, sagittal restoration is important for longterm spinal health. Preservation of thoracic kyphosis is critical to maintain lumbar lordosis [9]. Emami [10] reported that sagittally decompensated patients had significantly more pain than well-balanced patients. Dekutoski [11] showed that a loss of sagittal balance is correlated with higher pseudarthrosis rate and fixation failures. Kim et al. reported a 27 % incidence of proximal junctional kyphosis (PJK) [12], and that a postoperative decrease of T5-T12 sagittal Cobb angle was correlated significantly with PJK. Sagittal impairment may also influence the cervical sagittal alignment. Several publications have demonstrated correlation between thoracic hypokyphosis and cervical
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kyphosis in AIS and the influence of scoliosis surgery on cervical sagittal alignment [13, 14] Cervical kyphosis is responsible for cervical pain in adults [15], and 57 % of patients surgically treated for scoliosis had cervical pains at 26 years follow-up [16]. Recent international communications indicate that restoration of kyphosis can depend on the technique, rod diameter, and rod material used [17, 18]. In a previous study, we compared results of two reduction methods for correction of thoracic hypokyphosis in AIS [19]; significantly better correction of hypokyphosis was achieved with simultaneous translation on two rods compared to sequential approximation. In fact, the reduction technique used may be the main reason for poor results in sagittal correction. In the axial plane, using screw-only constructs allows the development of derotation specific techniques [20, 21]. However, vertebral derotation seems detrimental to correction of thoracic kyphosis [22, 23]. In 2000, after trying different reduction systems, we developed a new technique for correction of scoliosis: Simultaneous Translation on Two Rods (ST2R). This technique consists of translating the vertebrae simultaneously towards two rods, which were previously bent to the desired sagittal profile. Dual rods ensure both reduction and stabilization of the deformity. The purpose of this paper is to detail the concept, surgical technique, and results of ST2R focusing on the restoration of the thoracic kyphosis in AIS patients.
Materials and methods Materials The instrumentation used was a top-loading, side connection system including stable vertebral anchors linked to rods by connectors. Vertebral anchors included pedicle screws with different lengths and diameters that allowed use in both thoracic and lumbar vertebrae. Different types of claws were also available: pediculo-transverse or pediculo-laminar for thoracic claws, and lamino-laminar for the lumbar claws. These self-stabilizing claws were composed of a main hook and a counter hook, and were as stable as pedicle screws. This system also had a sacral plate fixation with one screw in the pedicle of S1 and the other in the wing of the sacrum, which could be reinforced by an iliac screw. Each anchorage was made with a polyaxial-threaded extension that enabled connection to the rods. Different connectors were available to allow surgeons to adapt to any situation; this includes standard, derotation, realignment, off-set, angled, and open connectors.
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Rods were made of titanium alloy-TiAl6 V or Co–Cr with a diameter of 5.5 or 6.0 mm to allow a balance between flexibility and strength. Methods Operative technique Instrumentation was performed in two operative phases: (1) placing the vertebral anchorages and (2) setting the rods and correcting the deformity. Vertebral anchorages Upon surgeon preference, the construct could be either a screw-only construct or a hybrid construct with screws and claws. Usually, we used mainly thoracic and lumbar pedicle screws with claws at the cephalad end of the construct. Claws or ligament fixation systems (LigaPASSTM) were used when the pedicle was too narrow for screw placement, or too difficult to find, like in the concavity of the curve. Lumbar and thoracic pedicle screws The technique described is a ‘‘free-hand’’ screw fixation technique developed by the author [19]. When the pedicle was difficult to find, the funnel technique for the cervical spine could be used. This technique consisted of removing all cancellous bone with a curette and visualizing the inside of the pedicle. Sometimes the entry point of the pedicle was hidden by the articular cortex, which was then removed with a rongeur. Once the pedicle was visualized, it was enlarged and the screw was inserted. However, in some cases, the pedicle could not be found, and it was not possible to insert a screw. In the case of infraction, the faulty direction was easily detected by feeling for the breach in the pedicle wall using the probe. It was possible to correct the direction of the drilling. This was necessary due to the risk in initially setting up the screw wrong; a screw with poor anchorage was like to be misplaced and removed. Thoracic spinal claw The claw consisted of a main polyaxial pedicle hook and a counter hook, facing each other. The counter hook closed the claw. First, the base of the transverse process of the underlying vertebra was partially resected using a rongeur to facilitate pedicle hook placement. The articular process, transverse process, and lamina were prepared with their respective hook starters. Second, the transverse or lamina counter hook was placed using the hook inserter. The pedicle hook, with its
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Fig. 1 Simultaneous translation on two rods (ST2R) technique. a Both rods, previously bent according to the sagittal curvature, are dropped over flexible guides placed onto the threaded extensions of
each anchorage. b Nuts are loaded onto each of the threaded extension. The nuts are tightened only at the top of the threaded extension to maintain the mobility of the rods
Fig. 2 a, b The two rods are oriented in the sagittal plane without reduction of the deformity, thanks to the polyaxial-threaded extensions. c The two nuts on the upper anchorage are tightened to lock the rotation of the rods (arrow)
threaded extension, was then placed onto the connection axis and implemented under the articular process. The claw was initially closed using its compressor forceps, and then locked by the final tightening of the threaded extension. When all the anchorages were fixed, a radiographic control was performed to verify the vertebral level, length, and position of the screws. Rod and connector insertion and reduction of the deformity After selecting the rod length, the rod was contoured according to the desired sagittal curvature. The connectors were slid onto the rod, matching the number of anchorages. In most cases, the rods were placed on the median line. Derotation connectors could be loaded onto both rods for four or five vertebrae at the apex of the thoracic deformity. Standard connectors could be used at the other anchorages.
Both rods were dropped over flexible guides, which were placed onto the threaded extensions of the screw heads, and nuts were loaded onto each of the threaded extension (Fig. 1). The nuts were tightened only at the top of the threaded extension to maintain the mobility of the rods. The rods were then oriented in the sagittal plane without deformity reduction. For single thoracic curves, the nuts on the two cephalad anchorages were tightened to lock the rotation of the rods (Fig. 2). For double curves (thoracic and lumbar), we preferred to lock the rod rotation on the neutral intermediate anchorages between the two curves. For thoracic curves, reduction was achieved through progressive and alternating tightening of the nuts on both rods, allowing the vertebrae to gradually approach the rods (Fig. 3). In case of a derotation maneuver, the concave derotation connectors were aligned parallel to the coronal plane and their position on the concave rod was locked
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Fig. 3 a2c Reduction is achieved through a progressive and alternative tightening of the nuts on the two rods allowing the vertebrae to gradually approach the rods with a medial and posterior
translation. d Once reduction was fully achieved, the nuts are torqued and sheared off and the threaded extensions broken
with a set screw. The convex derotation connectors were left free to allow the vertebrae to rotate around the convex rod. The derotation effect was obtained by supplementary translation on the concave side when the convex translation was finished. For thoracolumbar or lumbar curves, we used derotation connectors at each level. The reduction was done in three steps: translation, compression on the convex side, and derotation on the concave side. First, we performed the translation maneuver on the convex rod by progressively tightening the convex nuts. Then, we gradually compressed the convex anchorages and locked the connectors by tightening the set screws. To allow derotation around the convex rod, we unlocked the intermediate convex set screws and kept the connectors of the extremities of the compressed convex zone locked to maintain the compression previously applied. Then, we oriented the concave derotation connectors parallel to the coronal plane and locked the concave set screws. By progressively tightening
the concave nuts, we achieved vertebral derotation (Fig. 1c, d). At the end of the procedure, we re-tightened the convex derotation connector set screws. With both curves types, once reduction was fully achieved, the nuts were torqued and sheared off and the threaded extensions were broken.
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Patients Between June 2000 and December 2009, 137 consecutive AIS patients were surgically treated with ST2R at a single institution by one orthopedic surgeon (JLC). Ninety-nine patients had completed preoperative and postoperative (1 month, 1 year, and 2 years or more) data sets and were included in the analysis. Standard standing anteroposterior (AP) and lateral radiographs of the spine were taken preoperatively at 1-month, 1-, 2-, 3-, and 5-year follow-ups. AP radiographs in supine lateral bending positions were also taken before
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Fig. 4 a2c 13.8-year-old girl with a right thoracic idiopathic scoliosis of 57° with thoracic hypokyphosis and non-structural proximal thoracic and distal lumbar curves (Lenke 1A). d, e
Instrumentation with screws and two proximal pediculo-transverse claws from T3 to L1 with the goal to take all the thoracic kyphosis in the instrumentation
surgery to evaluate the flexibility of the curve. Computed tomography (CT) scans of the apical vertebra of the main curve were also obtained at pre- and immediate postoperative visits. Cobb angles of the main curve and proximal and distal counter curves were evaluated on coronal radiographs. Using lateral radiographs, thoracic kyphosis (TK) was measured from the superior endplate of the T4 vertebra to the inferior endplate of the T12 vertebra, and lumbar lordosis was measured from the superior endplate of L1 vertebra to the superior endplate of S1 vertebra. Axial rotation was evaluated with CT scans using the Aaro method [24].
In the sagittal plane, the average global thoracic kyphosis angle increased from 23° to 34° at the last follow-up (p \ 0.0001) (Figs. 4, 5). For hypokyphotic patients (n = 42), the average thoracic kyphosis angle was increased from 8° to 28° at 1 month and was maintained until last visit at 30° (p \ 0.0001).The mean gain was 22°. For patients with normal kyphosis (n = 43), the mean angle was 29° preoperatively improved to 34° at 1 month and to 36° at last follow-up (p \ 0.0001). For preoperative hyperkyphosis cases (n = 14), the angle was reduced from 47° to 39° postoperatively and was 41° at last follow-up (p \ 0.05). For the average global lordotic angle, there was no change in the global cohort. Nevertheless, in patients with preoperative hypokyphosis, the lordosis was improved from 42° to 50° at last follow-up (p \ 0.0001) (mean gain of 8°). In the axial plane, no reduction of the vertebral rotation was observed in the 41 patients who had undergone preand postoperative CT scan of the apical vertebra. In the most recent cases, the patients with derotation connectors (n = 12) obtained a derotation of the apical vertebra of 40 %.
Results The mean age of the 99 AIS patients was 14.8 years (11.7-21.5 years). According to Lenke classification [25], thoracic curves (Lenke types 1-3) were mainly instrumented (72 %). In the coronal plane, the average main curve was reduced from 55° to 16° at 1 month and maintained at the last visit (p \ 0.0001) (Figs. 2a-c, 3a-c). The mean correction was 70 % with a bending flexibility of 51 %.There was no significant difference between correction of thoracic scoliosis (69 %) and thoracolumbar/lumbar scoliosis (72 %). However, using derotation connectors significantly increased the coronal correction (80 vs. 72 %, p \ 0.05).
Discussion The translation technique was first introduced by Luque and then improved in the following years. The objective was to pull back the vertebrae toward the rods and to obtain
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Fig. 5 a2c 14-year-old boy with a right thoracic idiopathic scoliosis of 95° with hypokyphosis and structural proximal thoracic and distal lumbar curves (Lenke 4B). d, e Instrumentation from T2 to L4 with screws and two proximal pediculo-transverse claws
a compromise between the stiffness of the spine and the rigidity of the rods. This technique requires stable anchorages to be effective. The ISOLA instrumentation consisting of a multiple anchors system uses this vertebral translation with interesting results as reported by Asher [4], with a thoracic kyphosis gain of 10° for the hypokyphotic patients. ST2R is a translation technique. There is no need for rod rotation, sequential approximation, in situ bending, or direct vertebral rotation. The threaded extension allows the rods to connect to all of the anchorages, even when located at some distance from the rod. It leaves the rod very mobile and so that rods can be oriented in the sagittal plane before any reduction maneuvers are performed. The reduction maneuver is obtained simply by progressively tightening all nuts on both rods, which ensures medial and posterior vertebral translation. Using two rods this way ensures the correction of the scoliosis, contrary to other techniques that use one rod to reduce and another to stabilize. It is possible to combine this translation maneuver to a compression and/or derotation maneuver. ST2R never uses a distraction maneuver, which we consider associated to a neurologic risk. The stresses are also shared across all of the anchorages. Results from this series are similar to results previously reported [19, 26, 27]. In comparison with other reduction techniques, our results in the coronal plane are comparable to all screw constructs (64-74 %) [1, 2, 5, 28] and superior to hybrid constructs (61-64 %) [3, 4, 29]. Kim and Lowenstein demonstrated the superiority of all screw
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constructs against hybrid or all hook constructs [1, 2, 5]. To our knowledge, the gain of 22° in the sagittal plane for hypokyphotic patients is the best outcome ever reported in literature. Whereas ST2R achieved gain in thoracic kyphosis, other techniques presented postoperative loss [1, 2, 5, 30–32]. It is even more challenging to reduce axial rotational deformity while simultaneously restoring sagittal balance through techniques such as direct vertebral rotation (DVR) [30], in situ contouring (ISC)[33], and vertebral coplanar alignment (VCA) [34]. Although effective in reducing the rib hump [30], pushing down on the convex side to achieve axial rotation flattens the thoracic segment. Our data regarding derotation connectors are not sufficient for a conclusion. However, derotation connectors seem to be effective in the most recent cases. They allow for partial correction of the vertebral rotation, increased coronal correction (80 %), and reduction of hypokyphosis that can be maintained.
Conclusion The restoration of normal kyphosis in AIS patients is a challenge. Simultaneous Translation on Two Rods, which allows the rod to remotely connect to the anchorages, reduces the deformity by translating the vertebrae simultaneously towards both rods. This is an effective and simple method for treating scoliosis, especially in achieving sagittal correction of thoracic hypokyphosis.
Eur Spine J Conflict of interest Jean-Luc Clement has a consulting agreement with Medicrea International. 16.
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