Thoracoscopic Anterior Instrumentation For Scoliosis

David H. Clements, M.D.
Rohinton K. Balsara, M.D.

Introduction
Posterior spinal fusion (PSF) with spinal instrumentation has been the mainstay of surgical treatment since the late 1960s. In 1991, we began a prospective study to evaluate the safety and efficacy of a selective anterior thoracic fusion using thoracic segmental instrumentation performed through an open thoracotomy. Our study indicated that the procedure was safe, with coronal and sagittal correction comparable to posterior instrumentation and fusion [1]. In addition, due to the selective fusion, fewer vertebrae in the lumbar spine required incorporation into the fusion (average levels saved equals 2.5) compared to PSF. Thus the scoliosis could be corrected and fused while leaving the lower back flexible and relatively well aligned.

Fig. 1A 15–year–old female with a 42 degree right thoracic curve, a 21 degree upper thoracic curve, and a 37 degree lumbar curve. She has a large rib prominence.

Fig. 1B The sagittal profile shows 18 degree of kyphosis from T5 to T12.

Fig. 1C The left supine bend film shows the upper thoracic curve to reduce to 14 degree and the left lumbar curve to reduce to 10 degree. The first disc space to reverse is L3 on L4, with approximately 15% of residual rotation. Therefore, posterior instrumentation would need to go to L3. This curve would be classified as a King 2–1/2 or a Lenke, et al. Type 1B–.

Fig. 1D This patient had an anterior spinal fusion with the thoracoscopic technique of the vertebrae of the Cobb angle from T5 to T12 performed via thoracoscope along with internal thoracoplasty. If this patient had been fused posteriorly, the instrumentation would have had to have been extended to L3 based on the criteria of Cotrel and Dubousset. For this patient, we were able to save three distal fusion levels. Residual curvature in the thoracic spine is 10 degree, the upper thoracic curve is 7 degree, and the lumbar curve 22 degree. It is anticipated that the lumbar curve will continue to improve over time.

Fig. 1E The sagittal profile is restored to 25 degree.

Thoracoscopic anterior release and fusion is a technique for obtaining additional flexibility of the thoracic spine as an aid in correction of the spinal deformity [2,3,4,5]. Instead of a long open thoracotomy to obtain exposure of the anterior spine, small incisions are made to allow introduction of a thoracoscope and working instruments. The advantages are less postoperative pain in the chest wall, better long–term cosmesis, and equal release when compared to open discectomy [5].

Combining a selective anterior thoracic instrumentation and fusion with a thoracoscopic approach creates a novel treatment for thoracic adolescent idiopathic scoliosis.

Indications
Our inclusion criteria for patients who are candidates for this procedure were developed from our experience utilizing anterior thoracic instrumentation.

A thoracic idiopathic curve (Lenke, et al. Type 1 [6]), which measures between 40 and 70º by the Cobb method is the primary indication. The age group of patients with adolescent idiopathic scoliosis between 10 and 21 years of age ensures that the vertebrae will be fully formed and that the spine should be flexible. The lumbar curve should be flexible enough on the bending films to correct to less than 25º. There should be minimal clinical lumbar asymmetry in the prone position on the exam table.

Thoracic kyphosis should be measured from T5 to T12. Due to the kyphosing nature of the anterior instrumentation, 40º or less of kyphosis should be present preoperatively so as not to cause hyperkyphosis. A patient who is hypokyphotic (less than 20º) would be an ideal candidate for this procedure, as their kyphosis will fall into the normal range postoperatively. Junctional kyphosis at the thoracolumbar area is not a contraindication.

The ability of the patient to tolerate one lung anesthesia is crucial. The lung in the chest cavity entered by the thoracoscope must be kept completely collapsed for the entire procedure, which may last 6 to 8 hours. Preoperative assessment by pulmonary function tests and by an anesthesiologist is necessary for the procedure to succeed. Prior surgical procedures in the chest cavity to be entered, or a history of pleural adhesions or scarring, are a contraindication to the procedure due to the subsequent inability to completely collapse the lung. An anesthesiologist experienced in utilizing one lung ventilation techniques is also required for the success of the procedure.

Results
Since December 1996 we have prospectively studied 30 patients who have undergone thoracoscopic anterior fusion and instrumentation for adolescent idiopathic scoliosis. We have performed the procedure on two males and 28 females. The age at the time of surgery was a mean of 14.7 years, with a range of 12 to 18 years. The number of vertebral levels fused was a mean of 8 (range, 6 to 9). The preoperative thoracic curve averaged 47.6º (range, 40.0 to 58.0º). The first erect postoperative film of the primary thoracic coronal curve averaged 15.4º (range 5.0 to 44.0º) (60% correction). Kyphosis measured preoperatively from T5 to T12 measured an average of 22.0º (range 6 to 38º). The first erect kyphosis measurement averaged 22.5º (range 3 to 63º).

Neurologic complications consisted of two peroneal palsies in the down leg, which resolved by three months. These were not present at the end of the procedure but developed over the subsequent 24 hours postoperatively. Somatosensory evoked potential monitoring and wake–up tests were both normal in these patients. A change in leg position has obviated any further neurologic complications. Three patients developed a postoperative pleural effusion, which resolved without reinsertion of a chest tube.

Three patients sustained a broken rod postoperatively. One was revised through a posterior approach with instrumentation, and the two remaining were painless and are being followed. These occurred prior to the use of anterior intervertebral body structural support in addition to the rod, which is now standard procedure.

Conclusion
If untreated, thoracic adolescent idiopathic scoliosis of 40º or greater may progress after the end of skeletal growth. In the adolescent patients with idiopathic scoliosis, however, the concerns are usually with the deformity of the trunk. A procedure, which can correct and fuse this deformity in a minimally invasive fashion is extremely attractive to patients, families, and surgeons. The preponderance of female patients presenting for operative scoliosis treatment only increases the desirability of a procedure that effectively corrects the deformity while creating minimally visible surface scarring. The added benefit of a mobile, minimally deformed lumbar spine for these patients as they age is also immeasurable.

References
1. Betz RR, Harms J, Clements DH, Lenke LG , Lowe TG, Shufflebarger HL, Jeszenszky D, Beele B: Comparison of anterior and posterior instrumentation for correction of adolescent thoracic idiopathic scoliosis. Spine 24:225–239, 1999.

2. Cunningham BW, Kotani Y, McNulty PS, Cappuccino A, Kanayama M, Fedder IL , McAfee PC: Video–assisted thoracoscopic surgery versus open thoracotomy for anterior thoracic spinal fusion. A comparative radiographic, biomechanical, and histologic analysis in a sheep model. Spine 23:1333–1340, 1998.

3. Mack MJ, Regan JJ, McAfee PC, Picetti GD III, Ben–Yishay A, Acuff TE: Video–assisted thoracic surgery for the anterior approach to the thoracic spine. Annals of Thoracic Surgery 59:1100–1106, 1995.

4. McAfee PC, Regan JJ, Zdeblick T, Zuckerman J, Picetti GD III, Heim S, Geis WP, Fedder IL: The incidence of complications in endoscopic anterior thoracolumbar spinal reconstructive surgery. A prospective multicenter study comprising the first 100 consecutive cases. Spine 20:1624–1632, 1995.

5. Newton PO, Wenger DR, Mubarak SJ, Meyer RS: Anterior release and fusion in pediatric spinal deformity. A comparison of early outcome and cost of thoracoscopic and open thoracotomy approaches. Spine 22:1398–1406, 1997.

6. Lenke LG, Betz RR, Harms J, Clements DH, Lowe TG, Bridwell KH: A new and comprehensive classification system of adolescent idiopathic scoliosis. Spine in press: 2001.

7. Lenke LG, Betz RR, Harms J, Bridwell KH, Clements DH, Lowe TG: Spontaneous lumbar curve correction following selective anterior or posterior thoracic fusion in adolescent idiopathic scoliosis. Spine 24:1663–1671, 1999.