20 consecutive patients with adolescent idiopathic scoliosis irrespective of sex were operated in the Spine surgery division of Dept of Orthopaedics, in Calicut Medical College south India during the year 2001 to 2006 were reviewed.  Only thoracic curves between the level of T4 to T11 were selected for the study.  The inclusion criteria were adolescent idiopathic scoliosis less than 19 years of age, single rigid rod anterior spinal instrumentation with fusion, thoracic curves, and minimum follow up of one year.  Average age was 14.5.  All patients were treated with stand alone single rigid anterior rod fixation without tetra-spikes.  Thoracic curves are selected with at least 60% flexibility of secondary curves were selected. All patients had thoracic major curves.  King classification was followed in this study (15). 

Radiographic evaluation was done pre operative  post operative and follow up. Standing AP, Lat stress views,stretch views and rib hump views were taken in all patients. The radiographic measurements involved frontal (Major Thoracic, Major T-L, Compensatory TL and lumbar) Sagital cobb’s angle T2 –T12 for thoracic kyphosis,L1 –L5 for lumbar lordosis,

T-L junction alignment was measured fromT10-L3.Coronal and sagital trunk translation was measured radio- graphically by measuring the distance from the central sacral line and from the middle of the C7 body respectively

Stagnara views were taken in all patients to asses the rotational element. Rib hump views were taken in all patients to assess the torso rotation. All x-rays were taken preoperatively and post operatively.

Selection of fusion levels was done in neutral standing and bolster view in lying down position,(it is taken in the lateral decubitus position with a bolster under the convex side and AP view of the spine is taken). Fusion was done from end vertebra to end vertebra. The distal end vertebra was saved in some patients based on horizontalization of distal end vertebra on a stretch film, which normally would have been instrumented in a posterior approach. In major thoracic curves the TL or L curves were taken as compensatory curves. In major TL curve Thoracic curve is taken as compensatory which were not included in the current study.

Surgery was done with patient in lateral decubitus position with convex side up through a thoracotomy and in some cases by double thoracotomy. The preoperatively selected rib was excised. The rib selected is one rib above the uppermost instrumented vertebra or at the level of uppermost instrumented vertebra. The thoracic cavity is open through the rib bed of the excised rib by cutting the parietal pleura, after protecting the intercostal neurovascular bundle. A double thoracotomy is performed in large curves by removing two ribs at different levels wherever needed. Intervertebral disc ,the annulus  resected and end plates of adjacent vertebra removed. The rib heads were  removed in the span of instrumented vertebra to facilitate derotation. 

Fully threaded self tapping vertebral screws were used without tetra spikes.  Rods were contoured and placed over the screw heads.  Care was taken to maintain the sagital balance also.  Autografts were used  in the prepared disc spaces within the span of instrumented vertebra.  Patients were mobilized on a modified Knight Tailors brace for a period of 3 to 6 months.  Brace is used to control the secondary curves, as well as an external support.  Double thorocotomy was used in 6 patients.  14 patients had single thorocotomy.  The incision is modified in the thoracic curve such that damage to the breast is avoided.  After derotation and correction of deformity, adjacent screws were compressed with bone graft in situ.  This prevented excess kyphosis.  This series involved majority of children with small vertebra, hence two screws could not be applied to one vertebra. But the author believes that two rods two screw system is biomechanically more stable. 

A 12 years old girl with king type II curve with a progressive deformity.The curve is structural ,with reasonable amount of flexibility on stress films with a huge rib hump despite 40 degree curve in stress film. To achieve anterior fusion and to prevent any possibility of crank shaft phenomenon occurring and to avoid damaging the lumbar extensor mechanism selective fusion of the lower thoracic curve was performed. The upper thoracic curve showed 5 degree decompensation but the overall sagital and coronal correction was excellent in the post operative radiogram. The rib hump was reduced drastically. The decompensation of upper thoracic curve disappeared   on follow up.

Observation and Results: 

20 children with adolescent idiopathic scoliosis underwent anterior spinal fusion with single solid rigid rod anterior instrumentation.  All were available for follow up.  The average follow up was 2 years, ranged from half year to 4.5 years.  The deformity was progressive in all patients preoperatively, and documented radiologically.  The average major thoracic curve was 70°, with range of 55-85°, which was corrected to 12° post operatively, with the correction rate of 83%. The average secondary thoracolumbar scoliosis was 40° (20-60°), corrected to 10° post operatively, with 75% correction. The overall correction was 80%.The average pre operative compensatory curves in the thoracolumbar region 30° (range 20-40°).  The lumbar secondary curve in thoracic major curve is 37° (range 20-44°).  After correction it was 15° and 17° respectively.  In one patient there was decompensation of secondary thoraco-lumbar curve to 15° compared to the preoperative film.  It was treated with brace and on follow up the curve improved to 8°.  The flexibility of the primary thoracic curve was 68% on stress film in by Cobbs method. The flexibility of thoracolumbar curve was 80%, in thoracic primary curves.  In seven patients distal end vertebra could be saved by pre operative evaluation using stress films.  The sagital alignment preoperatively in the thoracic region was thoracic kyphosis of 0-18° preoperatively, which improved to 12° postoperatively.  The lumbar lordosis was 52° preoperatively (range 24-75°) improved to 43° post operatively.  The thoracic and lumbar sagital alignment improved in all patients post operatively.  The average coronal plane lateral trunk shift was 15 mm (range 0-30 mm), improved to 7 mm after surgery.  On follow up, the trunk shift was 7.5 mm.  One patient had a coronal plane decompensation in thoracolumbar spine by 5 mm. Sagital plane trunk offset improved from 20mm (range 0-40 mm) before surgery to 8 mm (range 0-16 mm) in follow up.  There was no sagital plane decompensation in any patient. 

At 2 years follow up, there was a loss of correction of 0.5°.  End vertebra and stable vertebra tilt improved  by 85% and 88% respectively.  The tangential rib hump angle was corrected by 75% (overall).  Apical vertebra rotation was corrected by 68% by derotation maneuver after rib hump resection.  Only autogenic bone grafts were used in this study.  Average blood loss in this study was 1200ml.  The average operation time was 210 Minutes.  No neurological or vascular complications were noted intra operatively or post operatively.  Stagnara wake up test was done in all patients after instrumentation.  Fusion could be achieved at all levels in the latest follow up.  No implant failure was present till the latest follow up.  Minor complications like UTI in 5 patients, paralytic ileus in 10 patients, excess chest drainage in 1 patient was noted.  Intercoastal chest drainage was used in all patients for 48 patients.  In the patient in whom, there was thoracolumbar decompensation, the trunk shift was minimal.  This decompensation was due to very high degree of correction of the primary curve.  This was treated by post operative bracing and on follow up, the curve improved.   

Scoliosis research society instrument (16­) questionnaire was done in all patients.  All patients were available for follow up.  Average satisfactory score was 4.3/5.  Self image score  was 4.4/5.  Functional score was 4.5/5.  Mental health score was 4.2/5.  Overall total score was 84%.  All patients were satisfied with the results.     

A 13 years old girl with type 2 king curve showing fairly good flexibility in stress films was treated with anterior instrumentation and fusion with excellent post operative post operative correction in both sagital and coronal plane

Discussion:

The introduction of anterior scoliosis surgery by Dwyer et all (1) provided a powerful innovative method of deformity correction in the spine.  Anterior correction of scoliosis in adolescent idiopathic scoliosis group in the thoraco lumbar and lumbar spine has already been reported with good results(17,18,19,20) with less implant problems, more rapid healing and lower pseudoarthrosis rate than posterior instrumentation and fusion, even with vertebral screws.  Kaneda et all reported Kaneda Anterior Spinal Stabilization System (KASS), to correct the deformity with a rod rotation maneuver (10,11). The fusion segments were in the area of Cobbs angle.  Number of segments fused was less than that of Posterior fusion.  Even though thoracic curves are severe, reports of thoraco-lumbar and lumbar curves treated by anterior instrumentation is prevalent in literature.(11)  We could find only scanty reference in English literature regarding correction by anterior instrumentation in adolescent idiopathic scoliosis (10). 

Thoracic spine is connected to the ribs by the costo transverse and rib  head articulation of the vertebra.  This forms a rigid anatomical structure compared to thoraco lumbar or lumabar spine.  The thoracic scoliosis is more rigid than thoracolumbar or lumbar curves for the same reasons (21).  Rib head resection with rod rotation maneouver makes the thoracic spine less rigid (10).  Oda  et all (22) reported biomechanical role of costo vertebral articulation and the rib cages in the stability of thoracic spine and concluded that these were the significant stabilizers in lateral bending and axial rotation.  Anterior release and rib head resection makes the curve less rigid(10).  So a high rate of correction can be obtained with shorter segment fusion, compared to posterior procedure, by rib head resection, derotation after anterior release.  Dickson et all (23) stressed that the axial plane rotational deformity has got its own importance when attempting sagital and coronal plane correction.  Theoretically 3 D correction should solve all the problems in scoliosis, but clinically the unsightly rib hump causes the major cosmetic concern.  Anterior thoracoplasty is a useful adjunct to anterior instrumentation.  Kaneda et all reported good results  without any incidence of implant failure, with no evidence of pseudo arthrosis even with single screw single rod system (10,11).  Twin et all reported good results in another study with single rod anterior instrumentation (24).  One of the main points assessed in this manuscript is to address the sagital plane effect of adolescent idiopathic scoliosis in thoracic spine.  The authors have noted, the maintenance of normal thoracic kyphosis and lumbar lordosis on follow up.  Adolescent idiopathic scoliosis is mainly a hypo kyphotic scoliosis and kyphogenic effect of thoracic anterior instrumentation has resulted in normal kyphosis in the thoracic spine.  Also maintenance of normal thoracic kyphosis has resulted in maintenance of normal lumbar lordosis. Since  only thoracic major curves were selected for this study the sagital plane correct ion in span of instrumented curve is to be stressed.   

Discectemy with end plate removal and bone graft has resulted in 100% fusion.  It has been reported that (11) dual rod system with two screws are more rigid than single rod system.  However all dual rod systems require placement of 2 screws in each segment.  This many be impossible in smaller thoracic vertebrae in a child.  There is increased risk of canal penetration in 2 screw systems against in 1 screw system.  In 2 screw system, staple is usually a must, which needs ligation of segmental vessel at every level.  In single screw system, selected segmental vessels may be saved from ligation.  This avoids the danger of ischemic cord necrosis, especially when the vessel to be ligated is the artery of Adam Kewicz, which gives the major blood supply to the spinal cord.  The present study has shown 100% fusion rate with single solid rigid rod anterior instrumentation and the correction is good as dual rod system with disc excision and fusion.  The present study also shows that the technique when compared to standard posterior fusion techniques has led to selection of less fusion segments (the distal most vertebra can be saved).  This may allow normal function of the spine with mobility.  The options in adolescent idiopathic scoliosis are stand alone anterior procedure with fusion, stand alone posterior procedure or combined procedure.  Anterior surgery is a viable option, but the case selection should be accurate.  The compensatory curve should be flexible.   

In a study by Brodner et all (25) the patient group with thoracolumbar anterior correction for the average 40 ° curve, the segments fused were 5.6.  This resulted in half the levels to be fused when compared to posterior fusion. In this study the average segments fused was 5 for an average curve of 70 degrees. This is probably because of additional derotation facilitated by rib head resection in this study. The current study also showed sagital correction of thoracic curve from 9 degrees of kyphosis to 12 degress of kyphosis. The lubmbar lordosis improved from 52 degrees to 43 degrees. The average  coronal plane curve correction was by 83% in the current study. Harrington rod with posterior instrumentation needs fusion of more segments with ensuing back pain due to degeneration (26).  This can be prevented by anterior surgery.  In the reported series of anterior instrumentation, the correction rate was 47%(11), 58%(18)(20) and 71%.  Another series (27) included 6.8 segments in the thoracic spine.  Average 6 ° loss of correction in the frontal and 8 ° correction in the sagital plane has been reported in single rod system (28).  Kaneda et all reported 1.2 ° coronal and 1 ° saggital plane loss of correction in the thoracic spine (10).  (But was with dual rod system in the lower thoracic and lumbar region)  The correction loss in our patient was loss of  1° in the coronal and 0.5° in the sagital plane(in to hypokyphosis) respectively.  This is probably due to newer segmental single rod systems used in this study.  This may confirm the usefulness of single screw single rod system in the thoracic spine anteriorly.  Suggestion of athletic activity after scoliosis surgery is a matter of debate (29).  The authors believe that the anterior surgery offers the best chance of return to athletic activities because of more biologic nature of the procedure with minimum segments fused, correction at the site of deformity with preservation of mobility.  Even at this point of writing this paper we are following up these patients and a longer term follow up may probably tell us the further functional benefits of anterior short segment correction in thoracic scoliosis.   

In this study sub periosteal rib head resection and rod rotation has been done in 20 patients.  In these patients the correction rate of apical vertebral rotation was 62%.  Pre operative sagital deformity ranged from 5° lordosis to 30° kyphosis.  Post operatively it is corrected to 12° kyphosis, which stresses the effectiveness of anterior procedure in maintaining sagital plane alignment.  External support with Knight Tailors brace was used until fusion.  This is especially useful to control the secondary curves.  This study included 4 patients with Type II curves.  One patient had thoracolumbar trunk shift as a part of decompensation, which was managed with brace and later improved.  Bridewell et all studied 82 patients with adolescent idiopathic scoliosis (right thoracic scoliosis) treated by CD instrumentation using posterior derotation maneuver (30).  They found 8 patients with gross decompensation on follow up.  Majority were type II curves.  They stated that in type II curves, too much correction of the primary thoracic curve beyond the flexibility of the lumbar curve may produce decompensation.  Schilenzke (31) et all compared the radiographic outcome of Harrington rod and  CD instrumentation.  They stated that rotation was unchanged in Harrington group.  But  rotation was increased in CD group in comparison to pre operative assessment.  This indicates that derotation maneuver transfers the rotation to the un instrumented lumbar curve.  In anterior correction of scoliosis also the same principle applies.  So it could cause decompensation if the lumbar compensatory curve if it has rotary elements or if the thoracic curve is too rigid in stress films.  Over correction of thoracic curve should be prevented so that decompensation will not occur.  In type III and IV curves, thoracic correction is enough for overall curve correction.

Conclusion:

Anterior correction of thoracic curve in adolescent idiopathic scoliosis leads to excellent curve correction in the frontal and saggital plane, by fusing the thoracic major curve.  There is no incidence of excess kyphosis, implant failure or gross loss of correction or pseudoarthrosis on follow up.  Over correction of the type II curves may lead to decompensation.  Rib head resection facilitates derotation maneuver.  Anterior thoracoplasty is a usual adjunct in anterior scoliosis surgery.  Spontaneous correction of the compensatory curves can occur.  This procedure is not kyphogenic – sagital plane correction was excellent.  Usefulness of this more physiological procedure is stressed in the current study, even though there are only scanty reports available in English literature. 

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