The results of frontal and sagittal plane radiography at baseline, post-operatively and at the most recent follow up are shown at table 1. There was no direct or indirect operative mortality, and there were also no permanent neurological complications. According to the medical files, 7 revisions had to be performed (Table 2): Re-instrumentation had to be performed in 2 patients because of radiological evidence of pseudarthrosis with loosening of the implant and loss of correction. In these two patients the implant is still in situ at the time of follow up. Complete implant removal was undertaken in only one patient because of persistent back pain in the region of the instrumentation (late operative site pain). Intra-operatively there was slight metallosis and there was no evidence of infection or pseudarthrosis. We also recorded the following complications, which did not require revision: 8 patients had an asymptomatic hook dislocation, in each case in the distal region of the instrumentation. In 2 further patients there was dislocation of the vertical rod and in 4 further patients the last radiological follow up showed an asymptomatic fracture of the vertical rod without significant distraction of the fracture site as possible evidence of pseudarthrosis. There was no case of pedicle screw fatigue fracture or fracture of a transverse connector rod. The cumulative rate of re-operation was 14.0%. It must be emphasized that we did not see a late deep infection in any patient, and only one implant had been completely removed at the time of follow up. In the SRS questionnaire, the total score averaged 95.8 ± 8.8 points out of maximum of 120 points (range 60 – 110 points) at the final follow up. In the questionnaire, 48 of 49 patients (98%) were highly or fairly satisfied with the result of the back treatment; only one female patient was somewhat dissatisfied – however we saw no objective (e.g. loss of correction) signs concerning this result. 42 of 49 patients (86%) reported to suffer never or rarely from back pain at rest. Overall 44 of 49 patients (90%) would definitely or probably undergo the same treatment again. The SRS scores did not depend significantly (p > 0.05) on the scoliosis classification or gender, either (Figure 2A–2D).

	baseline	postop	correction rate	follow up	correction rate
Thoracic curve (°)	62.4 ± 14.1	26.9 ± 9.8	56.9%	31.0 ± 11.2	50.3%
Lumbar curve (°)	43.5 ± 14.9	16.3 ± 9.9	62.5%	21.3 ± 13.3	51.0%
Apical translation (mm)	51.7 ± 26.2	18.7 ± 14.7	63.8%	25.3 ± 11.9	51.1%
Frontal balance (mm)	15.4 ± 12.4	13.8 ± 1.5		10.8 ± 9.7
Thoracic kyphosis angle curve (°)	19.1 ± 14.5	22.1 ± 11.1		25.8 ± 12.3
Lumbar lordosis angle curve (°)	56.1 ± 12.8	55.9 ± 10.2		57.9 ± 9.9

complications	number of patients	operative revision after...
Neurologic complication	1	1 day
acute infection	1	3 weeks
implant failure	1	3 weeks
loss of correction	1	22 months
late operative site pain (LOSP)	1	43 months
pseudarthrosis	2	73 and 102 months
late deep infection	0	-
reoperation for all reasons	7/50 (14%)

Surgical correction of AIS in general can be regarded as a safe and proven procedure yielding favorable long-term results superior to those of a brace treatment [10]. However, the existing and evolving multitude of methods and systems [11, 12] underlines that there is no established and internationally accepted standard for the surgical procedure. Although the Harrington rod (developed originally for patients with poliomyelitis) was used most frequently throughout the world for operative correction of AIS for over 40 years, overall long-term results are scarcely examined and often refer only to specific questions [13], This might be due to the fact that many of these implants were removed after only a few years, routinely or because of complications [14]. For the implants with pedicle screws and hooks fixation very few long-term results have been published too, although these systems has been available as an implant for over 20 years: Helenius et al. [15] investigated 57 patients with AIS and CD instrumentation a mean of 13.0 years post-operatively. Pre-operatively the average frontal thoracic Cobb angle had been 55°. Upon follow up, the average thoracic curve was 32°, resulting in a 42% correction. The frontal lumbar curve showed an average correction of 32% at the time of follow up. The documented complications were one case of acute (1.7%) and three cases (5.3%) of late deep infection, but prophylactic antibiotics (single shot) had not been administered. Clinically, the average SRS score was 97 points, and 6 patients (10.5%) reported back pain often or very often. Cook et al. [16] investigated 49 patients a mean of 105 months post-operatively with the isolated question of the revision rate. 12 of 49 patients (24.5%) had to undergo revision surgery. The indications were late operative site pain (LOSP) (12.2%), prominence or improperly placed implant, pseudarthrosis and late deep infection. Clark and Shufflebarger [17] investigated 917 patients with a CD implant retrospectively for late deep infection. A total of 21 patients (2.3%) were documented. In all cases complete implant removal was performed. The initial symptom had been development of a fistula or a fluctuant swelling below the skin an average of 3.1 years post-operatively. Bago et al. [18] presented a survivorship analysis of CD instrumentation in the surgical treatment of idiopathic scoliosis. Re-operation, usually implant removal, had to be performed in 23 of 113 patients (20.3%). The reason for the majority of re-operations was late infection, followed by mechanical failure, LOSP and acute infection. We also have had observed a much higher revision rate with CD implants previously used in our department before the introduction of titanium 1993 [19]. Hahn et al. [20] showed an incidence of late infection of 7.5% for AIS, treated with universal spine system (USS). Remes et al. [21] reported 3 out of 55 patients (7.3%) with late deep infection after correction of AIS with USS, and Richards [5] reported 10 patients (6.7%) who had late drainage at a mean of 25 months after placement of Texas Scottish Rite Hospital (TSRH) instrumentation to correct AIS. Therefore, the titanium implant in this study seems to be favorable in particular with respect to loss of correction, revision surgery for late deep infection or LOSP. The cause of LOSP has not so far been confirmed; mechanical irritation caused by the implant itself is suggested in particular, and also pseudarthrosis, implant loosening, bursa formation or subclinical infections. In our study, late deep infection was not observed in any of the patients, which is in contrast to most of the published series with late deep infection rates typically between 2% and 9% (Table 3). The reasons for this difference, should it be systematic, remain unclear, because the systems differ both in material and design. However, titanium alloy itself is corrosion-resistant, biocompatible and bioadhesive in vitro and in vivo and demonstrates a markedly low adherence for bacteria [22–24].

Authors	implant system	Patients	reoperation rate
Richards S. [5]	TSHR	10 out of 149	6.7%
Clark CE. [17]	CD	21 out of 917	2.3%
Helenius I. [15]	CD	3 out of 57	5.3%
Bago J. [18]	CD	10 out of 113	8.8%
Remes V. [21]	CD	3 out of 57	5.3%
Remes V. [21]	USS	4 out of 55	7.3%
Hahn F. [20]	USS	5 out of 67	7.5%