Adolescent idiopathic scoliosis (AIS) treated with arthrodesis and posterior titanium instrumentation: 8 to 12 years follow up without late infection
© Mueller and Gluch; licensee BioMed Central Ltd. 2009
Received: 5 July 2009
Accepted: 12 August 2009
Published: 12 August 2009
There are no data in the peer-reviewed literature regarding long term results in patients treated for AIS with a posterior titanium instrumentation. Therefore we assessed the outcome in 50 patients treated by titanium implant.
A total of 50 patients with a mean age of 16.6 years were treated. In all patients, titanium hooks and pedicle screws were used in combination. The demographic data and the pre- and post-operative radiographs of all 50 patients were re-examined, and 49 of the 50 patients (98%) attended a radiological and clinical follow up-examination on average 10.1 years post-operatively. The clinical results were recorded by means of the SRS 24 questionnaire.
In the frontal plane, the mean pre-operative thoracic and lumbar curve had been 62.4° and 43.5° respectively, post-operatively the curves were reduced to 26.9° and 16.3°, resulting in a correction rate of 56.9% for thoracic and 62.5% for lumbar curve. At the follow up-evaluation, the Cobb angle of the thoracic and lumbar curve was 31.0° and 21.3° respectively, giving a final correction rate of 50.3% for thoracic, and 51.0% for lumbar curve. 7 of the 50 patients (14.3%) had undergo revision surgery for complications, but complete implant removal was necessary in only one case. Analysis of the SRS 24 questionnaire showed an average score of 95.8 points.
Posterior titanium instrumentation is a safe and effective procedure in the surgical correction of AIS. In this retrospective study with small patient number, it shows favourable long-term results; in particular, the loss of correction is low, no late infection occurred and there was a very high survival rate of the implant itself.
Various anterior and posterior operative procedures are available for the treatment of adolescent idiopathic scoliosis (AIS). Among the posterior procedures, two different systems can be distinguished: With the development of the Harrington rod a long segment implant first became available and has established itself as the most frequently applied method for the operative treatment of the various forms of scoliosis . With this system, frontal correction is achieved primarily by distraction of the spine with elongation of the concave side of the curve. The procedure also requires post-operative stabilization of the trunk with an orthesis or plaster cast for several months in order to maintain the achieved correction. These disadvantages led to the development of the Cotrel-Dubousset (CD) double-rod technique , which achieves not only better sagittal and frontal correction but also avoids post-operative immobilization due to greater primary stability . Numerous modifications of the CD system followed [4, 5]; besides segmental hooks and sublaminar wires, transpedicle screws are now
also increasingly used for correction because they can improve the primary stability . In our department a double-rod system made of titanium has been used exclusively since 1993 for the operative correction of scoliosis which allows correction through segmental hooks and/or transpedicle screws by "over the top" loading (System WSI Titan, Peter Brehm Chirurgie Mechanik, 91084 Weisendorf, Germany). The aim of our study was therefore to examine the long term efficacy and safety of this titanium implant in AIS.
Materials and methods
Between January 1993 and March 1996 a total of 50 patients with AIS underwent operative correction with the titanium implant. The study sample consisted of 44 females and 6 males with an average age of 16 years (range 12 to 21 years) at the time of surgery. According to the SRS terminology there were 30 thoracic, 16 double, 3 thoracolumbar and 1 lumbar curves. According to the King classification  there were 2 patients with Type I, 25 patients with Type II, 9 patients with Type III, 7 patients with Type IV, and 3 patients with Type V curves. 4 patients could not be classified according to King (3× thoracolumbar, 1× left lumbar).
Initially the demographic data of all 50 patients was recorded from the medical files. From pre- and post-operative spinal radiographs in both planes (cassettes with 36 inches length) the following parameters were assessed: frontal main and secondary curves using the Cobb method ; sagittal thoracic kyphosis angle measured from T5 to T12 and lordosis angle from L1 to S1, also using the Cobb method; frontal balance, determined on the basis of horizontal distance from the center of the C7 vertebral body to the center of the sacrum; apical vertebral translation (distance between the plumbline and the mid portion of the vertebral body at the apex of the 7 curve). Attention was also paid to radiological complications such as rod fracture, pedicle screw fracture or hook dislocation.
Following evaluation of the demographic and radiological data between January 2005 and August 2005, the patients were invited by telephone to attend a follow up- examination. The mean follow up was 121.7 ± 14.1 months (range 101 to 151 months) respectively 10.1 years. 49 of the 50 patients (98%) accepted the invitation to follow up; only one patient had moved abroad and could not be contacted for the questionnaire, but the demographic data and the pre- and post-operative radiological results and those at the time of the last follow up were included. At follow up, the radiological examinations mentioned above were repeated and compared with the previous films. The patients were also given a questionnaire of the Scoliosis Research Society with 24 questions, which measures the quality of life of scoliosis patients. The SRS 24 questionnaire is a disease-specific, reliable and validated questionnaire used to assess outcomes in AIS . The questionnaire includes 24 questions, and the maximum possible score is 120 points, indicating that the patient is highly satisfied and asymptomatic.
SPSS Version 8 software for Window was used for the statistical analysis, part for frontal and sagittal balances of all patients pre-, postoperative and at final follow-up time and p values of ≤ 0.05 were considered significant. Descriptive statistics were used to determine means, standard deviations (SD) and ranges. Comparisons between variables were performed using Student's t test and the Kruskal-Wallis test.
The blood loss was 1980 ml on average (range 600 to 4500 ml), and the operation time was 270 min on average (range 140 to 410 min). Fusion with the implant included 10.0 (range 6 to 13) vertebrae on average. The average cephalic level of fusion was T 5.2 and the average caudal level of fusion was L 2.3. The two rods were fixed with a combination of hooks and pedicle screws only, with an average of 8.9 hooks and 4.2 screws per patient. A total of 424 hooks and 209 pedicle screws were inserted in 50 patients. The pedicle screws were inserted mainly in the lumbar region of the instrumentation.
Results of frontal and sagittal plane radiography at baseline, post-operatively and at the most recent follow up (mean ± standard deviation)
Thoracic curve (°)
62.4 ± 14.1
26.9 ± 9.8
31.0 ± 11.2
Lumbar curve (°)
43.5 ± 14.9
16.3 ± 9.9
21.3 ± 13.3
Apical translation (mm)
51.7 ± 26.2
18.7 ± 14.7
25.3 ± 11.9
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
Overall reoperation rate for WSI titanium instrumentation
number of patients
operative revision after...
loss of correction
late operative site pain (LOSP)
73 and 102 months
late deep infection
reoperation for all reasons
Reoperation rates for late infection: Comparison of published results
In summery, the study presents the first long- term results with a posterior titanium instrumentation for the treatment of adolescent idiopathic scoliosis. The results are encouraging: the implant is safe and effective with a high level of patients satisfaction; in particular, no late infection occurred and there was a very high survival rate of the implant itself. However the study design was retrospective and the patient number small.
Each author certifies that he has no commercial associations (e.g. consultancies, stock ownership, equity interests, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. All authors give their consent to publish this study and accompanying data.
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