Comparison of Rod Thickness in VATS Table 4. Other Operative Data No. of levels fused* Operation time (hr)* Transfusion rate (%) Blood loss (mL)* Thin rod group 6.2 ± 0.8 (5 - 8) 6.2 ± 1.3 (4 - 9) 21 311 ± 117 (140 - 680) Thick rod group 5.9 ± 1.2 (5 - 8) 6.3 ± 1.6 (4 - 10) 16 287 ± 105 (134 - 610) p value 0.19 0.13 0.75 0.38 *The data are given as the mean and the standard deviation, with the range in parentheses. Operative parameters Table 4 shows the various operative parameters measured which showed no significant difference between the 2 groups. Complications In the thick rod group, there were a total of three complica- tions (12%) These included 2 cases of perioperative saddle extension breakage of the poly-axial reduction screw and 1 case of intercostal neuralgia. The saddle extension break- age of the poly-axial reduction screw occurred in two early cases while trying to break off the long extensions of the reduction screw head after the fixation and correction was completed. This problem was solved in the subsequent cases by devising a custom-made instrument for this in- tended purpose. The patient with intercostal neuralgia recovered after 2 weeks with appropriate medication. In the thin rod group, there were three complications (12.5%). These included 1 case of cap loosening, 1 case of deep wound infection with proximal screw loosening, and 1 case of intercostal neuralgia. The cap loosening was noticed in one of the screws at 2 weeks post-op and was managed with a new cap by using the same thoracoscopic portals. The case of the deep wound infection was noticed at the most superior portal with some signs of loosening of the screw on radiographs. The patient was successfully intravenously treated followed by oral antibiotics and recovered uneventfully. The patient with intercostal neu- ralgia was similarly treated as the previous case and also recovered uneventfully. SRS-22 outcome scores The mean total SRS-22 scores improved in both groups when compared with the pre-operative values. The mean total scores at the final follow-up were 4.47 for the thick rod group and 4.23 for the thin rod group. Neither the total scores nor the individual scores for each domain showed any statistical difference between both groups. DISCUSSION VATS on adolescent idiopathic scoliosis has the advantages of an open anterior surgery while offering the potential of decreased impact on pulmonary function, improved visu- alization of the spine with enhanced access to the extremes of the curve, decreased post-operative pain, and improved cosmesis as a result of the use of small incisions.3-5,13-15 Re- cently, indications for VATS has been extended to thoraco- lumbar junction scoliosis16 or even thoracoplasty.1 The suc- cess of VATS has generally been attributed to the develop- ment and availability of specific surgical instruments and implants. Crawford, et al.7 pointed out that the future capa- bilities for this procedure in the management of spinal deformities will be dependent on the development of cor- rective implants or instrument devices. In the past, many authors have reported a high incidence of the loss of correction, pseudoarthrosis, and rod break- age in open thoracotomy when a thin flexible rod was used.9,10,17,18 Also, different results have been reported according to rod diameter in open thoracotomy anterior fusion. One animal study reported that a 5.0 mm diameter rod had significantly more stiffness compared to a 4.0 mm diameter rod.19 Modifications in rod diameter and material properties have also been considered. As stiffness varies in proportion to the fourth power of the radius of the rod, the trade-off between stiffness and ease of insertion was traditionally managed by varying rod diameter.20 Yoon, et al.21 reported on the use of 4.0-mm stainless steel versus 4.75-mm titanium alloy single-rod and showed improved maintenance of deformity correction at 2-years post-op and a lower incidence of instrumentation-related compli- cations (pseudarthrosis, rod breakage, and surgical revi- sions) compared to the 4.0-mm stainless steel construct. Therefore, we hypothesize that a 5.5 mm thick rod would result in a stronger and more rigid construct than the 4.5 mm thin rod, resulting to a greater maintenance of defor- mity correction and the lesser incidence of instrumentation- related complications. In the present series, a significant difference was noted in the coronal plane correction between the two groups. A comparable correction was achieved in both groups pre- operatively, which may be attributed to either the supine position, state of anesthesia, and similar release discecto- mies carried out by the single surgeon in all cases. How- ever, the actual coronal plane correction measured on the standing post-operative radiographs taken at the end of the two weeks showed a lesser correction for the thin rod group. Yonsei Med J http://www.eymj.org Volume 51 Number 5 September 2010 757