Implant and spinal mobility influence on the spinal curvature correction in adolescent idiopathic Lenke I type scoliosis

1 Vilnius University, Faculty of Medicine, Gastroenterology, Nephrourology and Surgery Clinic, Santariškių Str. 2, LT-08661 Vilnius, Lithuania 2 Vilnius University, Faculty of Medicine, M. K. Čiurlionio Str. 21, LT-03101 Vilnius, Lithuania E-mail: giedrius.bernotavicius@vuvl.lt 1 Vilniaus universiteto Medicinos fakulteto Gastroenterologijos, nefrourologijos ir chirurgijos klinika, Santariškių g. 2, LT-08661 Vilnius 2 Vilniaus universiteto Medicinos fakultetas, M. K. Čiurlionio g. 21, LT-03101 Vilnius El. paštas: giedrius.bernotavicius@vuvl.lt


Background and objective
There are still a few researches accomplished to evaluate the advantages and disadvantages of screw, hybrid, and hook techniques in the treatment of adolescent idiopathic scoliosis.As the results are controversial, researchers still look for optimally safe, least traumatizing and economically reasonable methods to treat spinal deformities.The aim of this study is to analyze postoperative spine deformity correction results for Lenke type 1 dependent on fixation type and preoperative bending films.Patients and methods A retrospective study was performed.Patients admitted to the Children's Hospital, Affiliate of Vilnius University Hospital Santariskiu Klinikos Orthopedic Department in the period of 1994-2013 were included; 74 cases were analyzed.Three groups according to spine implants were generated.The first included patients treated with pedicle screw fixation, the secondhybrid, and the third -hook fixation.Inclusion criteria: the adolescent age group (10)(11)(12)(13)(14)(15)(16)(17)(18), idiopathic scoliosis Lenke I type who undergone posterior spinal fusion with pedicle screws; hybrid fixation and hook application were evaluated in order to compare curve correction dependence on fixation type and curve flexibility.Thoracic and lumbar curve measurements on the coronal plane were performed using the Cobb technique applied on anterior posterior radiographs taken before and two days after surgery.Also, to measure curve flexibility, preoperative passive standing bending films were analyzed.Curve degrees in preoperative passive bending films were compared with the remaining postoperative spinal curves in groups separately.The remaining postoperative curves were compared respectively.

Introduction
Spinal implant constructs have developed over years from in situ fusion and cast stabilization to non-segmental rods, to segmental wire fixation, to segmental hook fixation, to segmental screw fixation and to segmental hook and screw fixation [1].Each improvement has to be estimated, and it is important to find out which surgical technique gives the best clinical benefits to the patient.
The use of pedicle screw in lumbar curves improved the correction and stabilization of various spinal deformities, and some studies supported the advantages of lumbar pedicle screws versus hook instrumentation [2,3].However, the use of pedicle screws in the thoracic spine was not as widely adopted in AIS because of the confined anatomic dimensions and morphologic distortion of scoliotic pedicles, the close proximity of the spinal cord to the concave pedicle, and the subsequent risk to the spinal cord and visceral structures with screw malposition.Nevertheless, the application of pedicular screws expands the potential of spinal deformity correction in three dimensions, requires better correction results, shorter fixation length and reduces the usage of thoracoplasty procedures as well as postoperative correction loss.
There were a few researches accomplished to evaluate the advantages and disadvantages of screw, hybrid, and hook techniques [1,4,5].As the results are controver-sial, researchers still look for optimally safe, least traumatizing and economically reasonable methods to treat spinal deformities.Therefore, the aim of this research is to evaluate the lateral bending radiographs and to compare them with the remaining curves, fixation length after operation, applying different surgical techniques in the Lenke I type scoliosis.Thoracic and lumbar curve measurements on the coronal plane were performed using the Cobb technique applied on posterior-anterior radiographs taken immediately before and two days after the operation.Also, to measure curve flexibility, preoperative passive  standing bending films were analyzed (Figure 4).These views were obtained upright with the patient leaning maximally to one side or the other.The bending film Cobb angle was compared with the neutral position.

Materials and Methods
All cases were subdivided into three groups according to the Lenke type 1 classification for idiopathic scoliosis A, B, and C modifier.These three modifier types were differentiated according to the curve apex deviation from the central line.
Curve degrees in preoperative passive bending films were compared with the remaining postoperative spinal curves in three groups separately.To compare the preoperative stiffness of the curves, the flexibility % was calculated as Flexibility % = preoperative curve -lateral bending curve × 100 preoperative curve

Correction % was calculated as
Correction % = preoperative curve -lateral bending curve × 100 preoperative curve The remaining postoperative curves and the correction % were compared among the groups.Various SAS procedures were applied to non-parametrical criteria for dependent and independent samples to perform the statistical analysis.Statistical significance was established at the P < 0.05 level.and 30.19º (±8.29) in the hook group.Figure 3

Results
Among 74 patients with AIS who were operated on at the VUVL pediatric orthopedics and traumatology center, 67 (90.50%) were female and 7 (9.50%)male.The radiographic results are shown in   2).Consequently, the thoracic curve tends to recover more than the curve remaining in the lateral bending film, and only screw fixation is able to correct the lumbar curve as it is expected in the remaining lateral bending curve.
The mean correction of the thoracic curve was 68.87% in the screw group, 58.76% in the hybrid and 50.27% in the hook group.The mean correction % of the lumbar curve was 75.58% in the screw group, 66.27% in the hybrid and 53.53% in the hook group.Therefore, the thoracic and lumbar deformity using screw fixation recovers on the average by 20% more than hook and by 10% more than hybrid application (Table 3).ing adolescent idiopathic scoliosis (AIS) was reported by Suk et al. in 1995 andLiljenquvist et al. in 1997.The technology has changed, but the goals of surgery for AIS remain the same: to halt curve progression and to correct deformity, maintain a balanced spine in the coronal and sagittal planes, preserve as many mobile spinal segments as possible, and prevent surgical complications such as junctional kyphosis, adding-on, and revision surgery [1,[4][5][6][7][8][9][10][11][12].The pedicular screw construct is able to correct the thoracic curve no matter how severe it is (A, B or C); however, lumbar curve correction drops when the modifier type is B or C. The other operative methods are less effective to correct both thoracic and lumbar curves despite the modifier type and also tend to lose correction % for type 1B or 1C.The pedicular screw construct is able to correct the thoracic curve no matter how severe it is (A, B or C); however, the lumbar curve correction decreases when the modifier type is B or C. The other operative methods are less effective to correct both thoracic and lumbar curves despite the modifier type and also tend to lose the correction % for types 1B or 1C.
The thoracic curve correction and fixation level comparison among the groups according to the Lenke I type in the group with the screw instrumentation fixation level was Th4-L1, and in the hybrid and hook group it was Th3-L3.

Discussion
Segmental instrumentation in spinal surgery was first introduced by Luque in 1982 when he combined the rods with sublaminar wires.The next significant development was the segmental hook-rod system designed by Cotrel-Dubousset.The use of pedicle screws in treat-As to the analysis of what is the best implants to use, the debate extends from the mid-1990s.Discussions were held on the biomechanics of the operation and the safety of the complications, a three-dimensional deformity correction, improvement in clinical outcomes, and cost [1].Authors argue whether the fixation with screws is more efcient than fixation with hooks.According to some studies, using screw fixation the possibility of mechanical deformation of the spine to correct three planes and between the two segments is higher than using hook fixation [2,4,[13][14][15].Yilmaz et al. [4] have discovered that pedicle screw and hybrid instrumentations provide a significantly greater spinal deformity correction than hook fixation in every radiographic measure and maintenance of the correction in the coronal and sagittal planes.HS An et al. [14] compared the stability of posterior hook-rod and pedicle screw configuration in an unstable burst-fracture model and have found that pedicle screw constructs are more stable than hook-rod systems.
For a long time, the use of screws in the thoracic and especially convex side was debatable.Morphological changes in the vertebrae, the spinal cord, aorta infringement are limited by the frequent use of screws in thoracic spinal curvature correction.The experience and tapping screws' precision and control of growth are influenced by the increasing use of spinal screws in the treatment of deformities [2,7,16].In literature, there are few scientific studies to look at the different fixation methods on the results of the correction.One of the first studies was done by Kim colleagues [17] who compared the use of hooks and screws adjusting spinal deformities.The authors' postoperative correction was better in the screw group as compared with the hooks.The correction was 76% and 50%.Our result is 74% and 49%, which validates the data.Suk and colleagues [18] presented data which compare the fixation screws and hooks with respect to all three planes of correction and a statistically significant difference.From these data, the screw fixation is much more effective.However, Karatoprak and colleagues state that the difference is not great, especially when using the hybrid sistem (hooks and screws) [19].The correction of spinal deformity was 70.3% and 67.7%, respectively.Di Silverstre and colleagues [5] reported that using the screws, especially for large deformations of the spine, provides a greater correction in both planes, less post-operative correction of fixed spinal degrees of loss, and less revision surgery.Using only the screw fixation of the spine, the fixed number of segments is lower [2,4].The literature and our results confirm that the screw fixation of thoracic curvature recover the average of 25%, and this is by 20% more than with hook fixation (p < 0.05) [4,17,20,21].
Rose and colleagues compared the minimum 2-year follow-up results of adult idiopathic scoliosis patients instrumented with pedicle screw and hybrid constructs with 34 patients in each group.Patients with pedicle screws had a significantly higher curve correction rate (55.6% vs. 40.1%),and the correction was maintained in both groups.However, coronal balance and blood loss were similar in both groups and so were the SRS outcome scores.What is more, patients in the hook / hybrid group had a better sagittal alignment in the last follow-up.[22].
Jaquith and colleagues made an interesting study [1] which compared the cost of spinal implants -hook and hybrid constructs and pedicle screw constructs in the posterior spinal fusion in AIS.Pedicle screw instrumentation was more expensive overall, per fused level, and per the degree of correction.Also, more implants were used, but more levels were fused in the pedicle screw group than in the hook-hybrid group.Nevertheless, pedicle screws provided a significantly better correction of the major spinal curve.
According to our data, the postoperative deformity correction was much higher than expected from lateral bending radiographs.This can be explained by the fact that we use the lateral bending maneuver without mechanical action.Using the mechanical effects of X-rays to bend the larger planned correction and postoperative results are virtually identical [23].We consider that using the mechanical action to perform the lateral bending radiographs before surgery is not as accurate as using a simple passing maneuver in order to determine fixation length and location.Summarizing the discussion, the spinal fixation with pedicle screws provided a better correction after surgery, and it is a safe technique but much more expensive than hook fixation.The preoperative assessment of spinal mobility must be carried out in order to plan the method of fixation and the size of the spinal fusion.

Conclusions
Thoracic curve tends to recover more than the curve remaining in the lateral bending film.Only fixation with pedicle screws is able to correct the lumbar curve for the Lenke type 1 as it is expected in the remaining lateral bending curve.Thoracic and lumbar deformity using screw fixation recovers on the average by 20% more than the hook and by 10% more than the hybrid application.Segmental pedicle screw instrumentation offers a significantly better curve correction as compared with the hybrid and hook instrumentation and has a shorter fusion level.

Statement of conflict of interests
The authors state no conflict of interests.

A
retrospective chart review was done in the spine service of the Vilnius University Children's Hospital.All patients with operative AIS were analyzed from a single institutional database.Data collection was carried out prospectively ant retrospectively in the screw group and retrospectively in the hybrid and hook groups.Inclusion criteria: children at the age of 10 to 18 with the Lenke type 1 were involved.Patients with congenital scoliosis were excluded from the analysis.The included 74 patients were analyzed and underwent posterior spinal fusion with pedicle screws (27) in 2012-2013, hybrid (16) in 2010-2011, and hook application (31) in the period 1994-2005.

Figure 1 .
Figure 1.A-D, preoperative spine X-rays of a patient with screw instrumentation

Figure 2 .Figure 3 .
Figure 2. Preoperativespine X-rays of a patient with hooks instrumentation

Table 1 .
Measurement and calculation results

Table 2 .
The p significance between spine mobility and correction inside each group

Table 3 .
The p significance for correction % among the groups