Surgical treatment of adolescent severe stiff idiopathic scoliosis with combined anterior and posterior approach – a prospective cohort study

Ketan Khurjekar, A.K. Shyam, Vivek Sharma, K. Keskar, P. K. Sancheti

Sancheti Institute of Orthopaedics and Rehabilitation, 16 Shivaji Nagar, Pune 411 005 Maharashtra, India.

Address for Correspondence:

A.K. Shyam
Sancheti Institute of Orthopaedics and Rehabilitation,
16 Shivaji Nagar,
Pune 411 005,
Maharashtra, India.
Phone:  020 25536666, 91 9833110366,
Fax    :  020 25533233
E-mail: drashokshyam@yahoo.co.uk

Abstract:

Background: The main purpose of this study was to assess the results of surgical treatment of severe and stiff adolescent idiopathic scoliosis with combined anterior-posterior approach in terms of correction of deformity radiologically in coronal and sagittal plane, clinically with SRS scoring and associated complications.

Materials and methods: A prospective study of clinical and radiological outcome of 32 patients with adolescent idiopathic scoliosis, treated surgically during February 2006 to June 2008 with combined approach (anterior release and posterior instrumentation) was performed. Preoperative evaluation in the form of plain anterior, posterior and lateral bending films and MRI spine to rule out any congenital anomaly were performed. All of these patients had Cobb’s angle > 60 with average being 73°± 13.4º and stiff scoliosis. Single stage surgery was performed in all these patients with anterior release, deformity correction and posterior instrumentation in form of either a hybrid system with proximal hooks and distal pedicle screws or total pedicle screw construct. Multiple radiographic assessments on preoperative, immediate postoperative and final postoperative radiographs and scoring according to SRS-22 scoring system were performed. The data was analysed using paired t test with p value <0.05 taken as significant.

Results: The patients were followed up for regular interval up to mean 1.5 ± 0.6 years (range 1 year to 3 years). Coronal balance improved significantly from 80.7º pre op to 26.7º post op. The average immediate post operative correction achieved was 65% in coronal view and the loss of correction over the period of 2 years was 7%. The sagittal balance was very well taken care off with average post operative sagittal curve being 25° in hypokyphotic spine and 35° in hyperkyphotic spine. These were both significantly improved over pre operative vaules.SRS scores were significantly improved post operatively. Final fusion involved 8.6 vertebrae on an average as compared to 9.91 levels from the pre operative radiographs. This indicated significant number of levels preserved by the combined approach. We had 3 superficial infection, 1 deep infection and 2 implant removal in our series.

Conclusions: The anterior release and posterior instrumentation is a good method of treatment of adolescent idiopathic scoliosis with acceptable correction in coronal and sagittal alignment, has less number of fused levels and acceptable rate of complications.

J.Orthopaedics 2009;6(4)e6

Keywords:

adolescent scoliosis; anterior release and posterior instrumentation; severe stiff idiopathic scoliosis

Introduction:

The posterior instrumentation has been the mode of treatment of scoliosis since it was first introduced by Harrington¹ in 1960 in the form of distraction rods and hooks. The development of Posterior segmental spinal instrumentation systems^1,2,3 with third generation Cotrel- Dubousset (CD) implants which provides multiple points of fixation to the spine and apply compression, distraction, and rotation forces through the same rod; better coronal plane correction and better control in the sagittal plane could be achieved^2,3. With these multiple segmental fixation the complications associated with the Harrington rods in form of loss of corrections, suboptimal fixation, implant failure and lumbar kyphosis were eliminated^2,3. Even though the correction achieved with these posterior instrumentation with pedicle screw and hook system was satisfactory the long term results were high as it had longer fusion level, screw breakage, increased tortional forces, crank shaft phenomenon and flatback syndrome were commonly associated in these patients^2,3.

The anterior instrumentation first introduced by Dwyer and supported by Zielke ^{4, 5}, Kaneda⁶ and Hopf⁷ advocated that better correction could be achieved by placing instrumentation in the vertebral bodies after anterior release and discectomy. 90% of the rotational stability of the spine has been shown to exist in the anterior two-thirds of the vertebral body and disc, which is why an anterior release is such an effective manoeuvre prior to fusion⁴. The anterior instrumentation systems by Dwyer, Zielke, Kaneda have been used with anterior release with or without posterior instrumentation especially in lumbar or thoracolumbar curves.

The correction of scoliosis requires release of the tethering structures such as rib heads, facet joints, intervertebral discs, anterior longitudinal ligaments. This can be addressed only with the combined anterior and posterior approaches so that all the tethering structures can be released in order to make it more flexible. There has been a recent interest in the posterior only approach for scoliosis correction which relies on pedicle screws at every level and correction obtained with rod rotation and plastic deformation of stiff soft tissue structures. However the posterior de-rotation manoeuvre may transmit torsional forces to adjacent spinal segments, which can result in decompensation, and may paradoxically increase the cosmetic deformity in some cases and also the inability of posterior segmental constructs to reliably provide de-rotation and restore normal kyphosis in patients with hypokyphosis or lordosis^8,9. The use of anterior release in these cases along with posterior instrumentation will avoid these complications and will also decrease the number of fused levels.

In the current study, we have attempted to assess the results of combined approach to posterior only approach in terms of the amount of correction, SRS scores and shorter fusion length.

Materials and Methods:

We had a total of 32 patients in our study (22 girls and 10 boys). The average age was 13.9 years (range, 10.7 to 18.2 years). 75% of the cases were in the age group of 12 to 16 years.

Inclusion criteria:

1.     Adolescent idiopathic scoliosis curves more than 60 degrees of Cobb’s angle which are stiff on side bending views (correction < 25 deg.).

Exclusion criteria:

1.     congenital/ neuromuscular scoliosis

2.     curves less than 60 degrees

The pre operative evaluation was done in the form of plain anteroposterior, lateral, side bending and traction radiograph using long cassette (36”). The coronal measurement was taken with the help of Cobb’s method^10,11  and the sagittal measurement was taken with the help of sagittal vertebral axis which is a plumb line drawn from the centre of C7 vertebrae body. Flexibility of the curves was measured by side bending radiographs. MRI spine taken in all these patients was to rule out any congenital anomaly.

The Lenke’s classification system for AIS was used in our study ¹². According to Lenke’s classification the maximum numbers of the cases in our study were of type I (15.6%) and V (28.1%) (Table 1).

Table 1: Curve distribution

The single stage surgery was performed in these patients by one surgeon. Anterior release was done either by open thoracotomy or retroperitoneal approach in lateral decubitus position. Anterior release included diskectomies and release of anterior longitudinal ligament and was followed by posterior instrumentation. Posterior segmental instrumentation with hybrid fixation using hooks in proximal segments and pedicle screws in distal segments was used in 22 patients while in 10 patients total pedicle screw construct was used. The choice of hooks or screws was made based on surgeon’s preference and size of the pedicle. Pedicle screws were placed parallel to superior end plates under the vision of image intensifier using specific anatomical landmarks and various confirmatory tests used to ensure intraosseus placement. Drill holes were undertapped by 1mm for better hold. The posterior facet fusion was done after decorticating the laminae, posterior elements and the facet joints.

The radiographic evaluation was done preoperatively, immediate postoperatively and at the time of last follow up. In pre operative radiographs we counted the levels of vertebrae fused till the lowest stable vertebrae as recommended by the posterior only fusion techniques¹³ . In post operative radiographs we counted the number of levels actually released and fused to achieve maximum correction. This difference gave us the number of motion segments preserved by this technique as compared to posterior only approach. Immediate post operative radiographs were compared with the preoperative radiographs to measure the correction achieved intraoperatively. Final radiographs taken at the end of 2 years were compared with postoperative radiographs to measure the loss of correction which is due to dynamic nature of the curve and settling of the implant.

The Scoliosis Research Society (SRS-22) questionnaire was used as a quality-of-life instrument to assess patient outcomes after operative treatment of adolescent idiopathic scoliosis. The SRS score has 4 elements such as function, pain, self image and mental satisfaction. All the patients were evaluated with SRS scoring preoperatively, immediate post operatively and at regular interval at the time of follow up in out patient department.

Statistical analysis was done using paired t test with p value of <0.05 taken as significant.

Results :
The majority of our cases were of high grade (60-80degree) with the average being 73°. Female patients dominated our study consisting 65% of total cases. Results of curve correction are given in Table 2. The post op correction achieved in our study was 65% in coronal view measured by Cobb’s method which is better than 47.5% as quoted in similar studies^14,15,16. In addition, the sagittal balance could be well achieved as post op curve measured 25° in hypokyphotic spine and 35° in hyperkyphotic spine. There was significant correction achieved for all these angles as compared to the pre operative values (p <0.01). comparision of angular deformities achieved at immediate post surgery to the final follow up showed only a loss of correction in coronal alignment of 1.8º [7%] while there was no change in the sagittal balance.

p value is for paired t test.

Table 2: Table showing correction of angular deformities on pre operative and final post operative radiographs.

When number of fused levels were compared with number of  levels expected to be fused on pre- operative radiographs (using posterior only approach), we found that significantly less number of vertebral levels required fusion when combined approach was used (Table 3)

Table 3: comparison between pre operative and post operative levels fused

* Expected segments fused in derived from pre operative radiograph with respect to posterior only fusion

**actual segments fused are seen in post operative radiograph using a combined approach.

∞ p value is for paired t test.

Changes in SRS 22 Score in the follow up period:- Self-image was significantly improved at 3 months and maintained improvement through 24 months. Function was significantly decreased at 3 months, but returned to baseline by 6 months. Pain was significantly worse at 3 months, but was significantly less at 6, 12, and 24 months when compared to 3 months.

A- Pain

B- Self image                                                                                 

C- Function

D-Mental satisfaction

The pre operative and post operative SRS 22 parameters were measured pre operatively and post operatively and all were found to be significantly improved (Table 4).

p value is for paired t test

Table 4: Comparison between different SRS 22 parameters pre operatively and post operatively.

Illustrative Case Studies:

1. Master AYS 16/m: Thoraco lumbar scoliosis with right sided major curve where anterior release from D6 to D12 and post instrumentation moss Miami from D3 to Dl2.

2. Miss AR 13/f: Thoraco lumbar scoliosis with left sided major curve-post moss Miami instrumentation from D-2 to D-l2.

Complications: In our study we had 3 cases with superficial infection which was treated with antibiotic while 1 case with deep infection was debrided in Operation theatre. Implant was removed in this case and infection control was achieved with repeated debridements. This patient had loss of correction with poor results.  Hook pullout was present in 1 case and 1 patient had screw breakage. Both these cases had implants removed after bony fusion consolidated. Both these patient had fair results. None of the cases had pseudoarthrosis, neurological complication or death.

Table 5: Complications

Discussion :

The goals of the scoliosis surgery include adequate and safe correction of deformity, bony fusion to prevent further deformity and to preserve motion segments while achieving the above two goals. Patient satisfaction is one of the major factors that justify these extensive surgeries. Present study tries to analyse the results combined anterior release with posterior fusion with respect to the goals achieved and also the patient satisfaction in adolescent idiopathic scoliosis.

In a review of literature, Lenke et al.¹⁴ have studied the amount of correction obtained in either anterior or posterior fusion. An overall correction rate of 58% was achieved in the anterior group, whereas only a 38% correction rate was observed in the posterior group. In anterior-group patients better spontaneous correction of the lumbar curve was demonstrated than in posterior group patients (56% and 37%, respectively). Good correction rates by anterior surgeries is also reported by other authors^17,18.19. In our study too the average immediate post operative coronal correction achieved was 65%. Over the follow up of 2 years the loss of correction was 7%. The result of scoliosis correction in our study was 57% as compared to preoperative measurements. The achieved correction is very well comparable with the contemporary literature. The sagittal imbalance was well restored within the normal range. The average correction in patients with hyperkyphotic spine was 35° while in hypokyphotic spine was 25° to create a balanced sagittal curve.  Creating a stable spinal construct with sound fusion was the goal of surgery, which was achieved in 100% (32 cases). With the help of anterior release the spinal column was made more flexible and amenable to posterior correction.

Recent studies by Lenke^15,16 however supported isolated posterior approach as compared to his previous studies. He advocated that the same correction can be achieved by isolated posterior approach compared to anterior if pedicle screws are used rather than the hooks and at all levels rather than at apices and end vertebrae. This observation is also noted  by Geck²⁰, Lenke^15,16, Wang²¹, DiSilvestre²² , Pateder²³,Hee².

Although the correction achieved was similar with posterior only approach using pedicle screws, the combined approach has better correction and less number of fused levels. This has been reported by numerous studies like Li ^24,25 ,Hempfing²⁶ , Rauzzino²⁷.

The average number of vertebrae fused in our study was 8.6 while calculation on the pre operative radiograph indicated fusion of 9.91 indicating preservation of at least 1.3 segment per case. The anterior release done in these patients prior to posterior fusion and instrumentation saved these motion segments in the lumbar spine which resulted in shorter fused spine. This helped us to preserve more lumbar motion segments and prevent accelerated degeneration of the lumbar discs and the final height achieved by the patient with less possibility of disc degeneration and back pain in future²⁸. Also, there is a general concern about possible neurological injury during the pedicle screw insertion although the incidence is quite low and involves a definite learning curve. There is also a commercial element affecting all posterior implants surgery since more number of screws is required.                  Complications nevertheless were present in our study in the form of superficial infection in 3 cases and deep infection in 1 case and 2 cases of implant failure but no incidence of neurological complications. The cases with superficial infection healed with one debridement and antibiotics. The case with deep infection required debridement with implant removal and had a poor result. Both patients with implant breakage reported after the fusion of the segments was achieved and only implant removal was done in these cases. A long term follow up of these patients is essential.

The SRS 22 has been validated as a potent tool for patient satisfaction after scoliosis surgery²⁹ and most important among the parameters is the improvement of self image of the patient. In our study the self image and the mental health are the two factors that improved very significantly as compared to the pre operative values. Thus we have achieved comparable results to contemporary literature with special emphasis on better correction and saving of distal mobile levels.  According to our study the anterior release and posterior instrumentation is a safe and effective method of correction in adolescent idiopathic scoliosis which carries less chance of neurological complications, better safety, high fusion rate, lesser implant failure and manageable complication rate.

One of the limitations of the study is short follow up. Since we have presented our early results and will be following the cohort prospectively, we shall be presenting the mid term follow up of these patients to assess implant failure, loss of correction, mechanical back pain, adjacent level degeneration and other related complications. A second limitation is relative heterogeneity of the sample with respect to Lenke’s classification and small sample size. An adequately powered randomized controlled longitudinal trial will be needed to emphasize the results of combined anterior and posterior approach versus posterior alone surgeries in adolescent idiopathic scoliosis.

Conclusions: 

We conclude that the combined anterior and posterior method of scoliosis correction is an effective method of correction of scoliosis surgery in adolescent idiopathic curves in terms of the number of fused levels and the amount of correction. The anterior release certainly makes the idiopathic curve more flexible and more amenable to posterior correction using instrumentation.

Reference :

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This is a peer reviewed paper 

Please cite as: A.K. Shyam: Surgical treatment of adolescent severe stiff idiopathic scoliosis with combined anterior and posterior approach – a prospective cohort study.

J.Orthopaedics 2009;6(4)e6

URL: http://www.jortho.org/2009/6/4/e6

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