QUT Digital Repository: //eprints.qut.edu.au/25879/1/c25879.pdf · 2010. 6. 9. · 156 though in one case T4 was instrumented. The most common distal instrumented levels were T11

QUT Digital Repository: http://eprints.qut.edu.au/

Hay, Douglas and Izatt, Maree T. and Adam, Clayton J. and Labrom, Robert D. and Askin, Geoffrey N. (2009) Radiographic outcomes over time after endoscopic anterior scoliosis correction. Spine, 34(11). pp. 1176-1184.

© Copyright 2009 Lippincott Williams & Wilkins

Radiographic outcomes over time after endoscopic scoliosis correction

1

1 2

Radiographic outcomes over time following endoscopic anterior scoliosis correction: A 3 prospective series of 106 patients 4

5 6

7 Douglas Hay (FRCS), Maree T Izatt (BPhty), Clayton J Adam (PhD), Robert D Labrom (MSc, 8

FRACS), Geoffrey N Askin (FRACS) 9

10

Paediatric Spine Research Group, Queensland University of Technology and Mater Health Services 11

Brisbane Ltd, Queensland, Australia 12

13

14

Name and Address for Correspondence 15

Associate Professor Clayton Adam 16

Paediatric Spine Research Group 17

Level 2, Mater Children’s Hospital 18

Raymond Terrace, South Brisbane, Qld, 4101, Australia 19

Phone: +61 7 3163 6162 20

Mobile: 0405 148 686 21

Fax: +61 7 3163 1744 22

Email: [email protected] 23

24

25

Sources of Support 26

No financial support was received for this study. 27

28

29


2

Keywords 30

anterior scoliosis surgery, endoscopic anterior scoliosis correction, anterior thoracoscopic 31

instrumentation, major Cobb angle, instrumented Cobb angle, curve decompensation 32

33

Introduction 34

Since the use of a thoracoscope to access the spine anteriorly was first reported in 1993,1 35

minimally invasive approaches for scoliosis correction have become an alternative to open 36

surgical techniques for selected cases.2-14 Endoscopic anterior scoliosis correction has been used 37

for the past decade, with reported benefits of less fused levels, sagittal profile restoration, 38

reduced pain and chest wall morbidity, shorter hospital stay, faster recovery of lung function, 39

better cosmesis, and lower infection rates, blood loss and lower incidence of neurological 40

complications.6-16 41

42

However, the technique is technically demanding with a substantial surgical learning 43

curve.12,17,18 Due to the level-sparing approach, any potential for decompensation following 44

endoscopic anterior surgery is of considerable clinical interest. Several studies have reported on 45

Cobb angle correction at a single time point after surgery,6,12,14,17-19 but to our knowledge only 46

one paper has reported correction at more than one time point post-operatively.20 However, this 47

paper did not perform statistical analysis of loss of correction versus time after surgery. In 48

addition, the two most commonly reported instrumentation related complications following 49

endoscopic scoliosis surgery are rod breakage and screw loosening, and it is important to qualify 50

whether these two occurrences are associated with greater decompensation following surgery. 51

52

Accordingly, the aim of this study was to prospectively analyse how key radiological parameters 53

and rib hump change during the two years following endoscopic anterior scoliosis correction 54


3

surgery. The effects of instrumentation related complications on these changes are also 55

investigated. 56

57

Materials and Methods 58

Study Cohort. Between April 2000 and June 2006, a total of 106 patients underwent endoscopic 59

anterior instrumented fusion using a single rod technique to correct progressive scoliosis. The 60

study data was gathered prospectively for all cases. The option to undergo an endoscopic 61

procedure was presented to each patient after clinical and radiologic assessment by the senior 62

authors to assess suitability. Patients and/or their parents were given the option of either open 63

posterior or endoscopic anterior surgery, and the benefits, risks, and potential complications 64

associated with each approach were presented. 65

66

Deformity Details. The 99 idiopathic curves were classified according to the Lenke classification 67

with the majority (88 of 99 = 89%) Lenke Type 1 curves, and eight Type 2, one Type 3 and two 68

Type 5 curves. The remaining seven cases had a small associated syrinx or dilated central canal 69

found by magnetic resonance imaging, despite having presented with an idiopathic type curve. 70

104 patients had right sided thoracic major curves and two had left sided thoracolumbar curves. 71

All patients had either a normal thoracic kyphosis or hypokyphosis (three patients had a thoracic 72

lordosis) with a mean (± SD) of 18.4±9.8° (range -13 to 40). Mean preoperative rib hump 73

measurement was 16.5±4.4° (range 10 to 30). 74

75

Surgical Technique. The procedures were performed by the two senior authors (GNA and 76

RDL) at the Mater Children's Hospital in Brisbane, Australia. The surgical technique has been 77

reported previously.11,12 Briefly, the disc spaces of the levels to be instrumented are cleared and 78

the intervertebral spaces packed with either femoral head allograft (62 cases) or mulched 79


4

autograft (rib heads for 38 cases, iliac crest for 6 cases). Allograft is supplied through the 80

Queensland Bone Bank (either cadaveric donation or femoral head donation at time of hip 81

replacement). Bone banking in Australia is well established & tightly regulated by health 82

authorities. Donors are screened using stringent protocols employed for organ donation. The 83

bone is irradiated & stored at temperatures in the vicinity of -70 Celsius. Autograft was used 84

early in the series but due to donor site pain and the inadequate volume of bone available, an 85

alternative was sought to achieve what our surgeons consider to be optimum conditions for bony 86

fusion. If instrumentation extended beyond T12, an interbody spacer cage packed with graft 87

material was placed between T12-L1 to assist the spine’s transition into lordosis. A single 88

4.5mm diameter rod was used for the first 78 procedures and a 5.5mm diameter rod was used for 89

all subsequent cases. The Eclipse (98 cases) or Legacy (8 cases) Instrumentation systems 90

(Medtronic Sofamor Danek, Memphis, TN) were used to achieve curve correction using a 91

standard compression technique with x-ray monitoring. The Legacy system assists the surgeon to 92

avoid cross threading of the screw head which may result in loosening of the nut and is now 93

standard practice, differing only in the design of the screw-rod interface. 94

95

Radiographic Evaluation. All patients had a standardised postero-anterior and lateral standing 96

radiograph using a long 36 inch plate with a grid, prior to surgery, and at 2, 6, 12 and 24 months 97

postoperatively. The use of postero-anterior radiographs has been shown to reduce breast 98

irradiation by 92%, and by >99% when combined with shielding and filtration21. Radiographic 99

parameters were measured using the Cobb method at all review appointments by experienced 100

spinal orthopaedic surgeons, according to Scoliosis Research Society definitions (SRS Revised 101

Glossary of Terms). 102

103


5

The following radiological parameters were investigated; the Cobb angles of the major curve, the 104

distal compensatory curve, the instrumented curve and T5-T12 sagittal kyphosis, shoulder 105

balance, and coronal spinal balance (distance of midpoint of C7 body from the central sacral line 106

on a posteroanterior radiograph). Sagittal spinal balance (distance of midpoint of the C7 body to 107

a vertical line through the posterior superior corner of the sacrum on lateral radiograph) was not 108

analysed as erratic results due to variations in patient trunk and arm positioning raised doubts as 109

to the reliability of the results. Proximal compensatory curves were present and measured in too 110

few patients to analyse, as the patient group that suits the surgical technique typically do not 111

exhibit this curve to any degree. 112

113

After surgery, there is a distinction made between the major Cobb angle and the instrumented 114

Cobb angle. The major Cobb angle is a true measure according to the definition of Cobb,22 i.e., 115

between the most inclined endplates at the proximal and distal ends of the postoperative major 116

curve. The instrumented Cobb angle is measured only for the instrumented vertebral levels, and 117

therefore does not always encapsulate the full extent of the postoperative major curve. This 118

distinction is illustrated in Figure 1. The curve correction or correction rate is defined as the 119

difference in Cobb angle after surgery divided by the preoperative Cobb angle and is expressed 120

as a percentage of the preoperative major Cobb angle. 121

122

Rib Hump Correction. The rib hump or rotational distortion of the torso was assessed at each 123

medical review using an inclinometer (Scoliometer, Scoliosis Research Society, Milwaukee, WI) 124

with the standing patient in the forward flexed position, with knees locked, arms hanging and 125

palms opposed. 126

127


6

Statistical Analysis. The mean and standard deviation of each radiographic parameter as well as 128

the rib hump were calculated preoperatively, and at 2, 6, 12 and 24 months after surgery. To 129

determine whether postoperative changes in radiographic parameters and rib hump were 130

statistically significant for the entire patient group, paired t-tests were used to compare values at 131

each review with the values at the subsequent review (ie preoperative vs 2 months, 2 vs 6 132

months, 6 vs 12 months, and 12 vs 24 months). The entire group was then divided into three 133

subgroups; subgroup 1 contained those patients with no mechanical complications over the 24 134

month postoperative period, subgroup 2 contained those patients in which a rod fracture occurred 135

in the 24 month postoperative period, and subgroup 3 contained those patients who experienced 136

screw-related complications (screw pullout or loosening) in the 24 month postoperative period. 137

Due to the smaller patient numbers in subgroups 2 and 3, non-parametric Wilcoxon signed ranks 138

tests were used to assess the significance of any changes between the review intervals. 139

140

Results 141

Patient Cohort. 106 patients (95 females, 11 males) were included in the study and all 142

underwent endoscopic anterior scoliosis correction. Data for all patients was available from the 143

two month review, 105 patients at 6 months, 103 patients at 1 year and 99 patients at two years. 144

Of the seven patients with incomplete follow-up at 24 months, two were from the screw-related 145

complication sub-group, and the remaining five were from the ‘no mechanical complications’ 146

subgroup. All seven patients with incomplete datasets are considered to be either lost to follow-147

up or unable to return for review due to geographical isolation. The mean age at surgery was 148

16.1 years (range 10-46), with 11 patients aged over 18 years who demonstrated sufficient major 149

and compensatory curve flexibility to be considered suitable for this selective anterior fusion 150

procedure. Figure 2 shows preoperative coronal, lateral and fulcrum bending radiographs and 151

postoperative coronal and lateral views for two representative patients from the series. 152


7

153

Intrumentation Levels. The mean number of levels instrumented was 6.8 (range 5 to 9). The 154

most common proximal extension of the instrumentation was to T5 (n=41) and T6 (n=49), 155

though in one case T4 was instrumented. The most common distal instrumented levels were T11 156

(n=33) and T12 (n=51). Ten patients were instrumented to L1 and three to L2. 157

158

Mechanical Complications 159

There were 12 cases where the rod fractured (11.3%) and all occurred after the 12 month review, 160

being found on the 24 month radiographs despite the patients being asymptomatic. In another 12 161

cases there were screw related complications including eight with top screw partial pullout, two 162

with the bottom nut separated from the screw head, one with top screw plough, and one where 163

the top screw moved partially off the end of the rod. The screw related complications all 164

occurred early in the postoperative recovery period and were either found prior to discharge from 165

the hospital or on the two month radiograph. 166

167

Radiographic Results 168

The radiographic results for the entire patient series at all follow-up intervals are presented in 169

Table 1, including the correction rates for the major Cobb angle, the instrumented Cobb angle 170

and rib hump, and the distal compensatory curve. Table 2 gives the minimum, maximum, and 171

10th, 25th, 50th, 75th, 90th percentiles for progression of each radiographic parameter between 2 172

and 24 months after surgery. 173

174

Figure 3 displays the change in Cobb angle with time following surgery for the (i) major, (ii) 175

instrumented, (iii) distal compensatory, and (iv) T5-12 kyphosis curves as well as the changes in 176

rib hump over the same intervals. For the entire patient cohort, there were statistically significant 177


8

increases in major and instrumented Cobb angle over each follow-up interval. There was a 178

statistically significant increase in rib hump (from 6.4 to 7.3 degrees) between 2 and 6 months 179

post-surgery. There were no other statistically significant changes between 2 and 24 months at 180

the P=0.05 level. Figure 4 illustrates the variation in major Cobb angle over time with the patient 181

cohort divided into the three subgroups described earlier (no mechanical complications, rod 182

fractures and screw related complications). Subgroup 1 (no complications) showed statistically 183

significant increases in major Cobb angle between 2 and 6 months, 6 and 12 months, and 12 and 184

24 months. Subgroup 2 (rod fractures) showed a significant increase in major Cobb angle 185

between 6 and 12 months (ie before the rod fractures occurred) but did not show a statistically 186

significant increase between 12 and 24 months despite this interval being where the rod fractures 187

occurred. Subgroup 3 (screw-related complications) only showed a statistically significant 188

increase between the 2 and 6 month review. Figures 5 - 8 present the results (using the same 189

three subgroups as in Figure 4) for instrumented Cobb angle, distal compensatory curve, T5-T12 190

sagittal kyphosis and rib hump values over time for the same three subgroups. In Figure 5, 191

subgroup 1 (no complications) showed statistically significant increases in instrumented Cobb 192

angle between 2 and 6 months, and between 12 and 24 months. Subgroup 2 (rod fractures) 193

showed a statistically significant increase between 2 and 6 months. In Figure 6, there were no 194

statistically significant changes in distal compensatory curve magnitude from 2 to 24 months. In 195

Figure 7, the only statistically significant increase in T5-T12 sagittal kyphosis was for subgroup 196

1 (no complications) between 2 and 6 months post-surgery. In Figure 8, there was a statistically 197

significant increase in rib hump for subgroups 1 and 2 from 6 to 12 months, and for subgroup 2 198

(rod fractures) from 12 to 24 months. 199

200

Examination of shoulder balance revealed that the mean shoulder height deviation for subgroup 201

1 (no mechanical complications) and subgroup 2 (rod fracture) was almost zero (


9

surgery. At the 2 month radiograph, subgroups 1 and 2 had mean shoulder height differences of 203

7 and 10mm respectively, and by 24 months these had reduced to between 2.5 and 4.1mm. 204

Subgroup 3 (screw-related complications) had a mean preoperative shoulder height difference of 205

8.6±13mm, which reduced to almost level by the 2 month review (2.5± 11mm) and thereafter 206

remained stable. Table 1 gives mean values for shoulder height balance at all reviews for the 207

entire cohort. 208

209

Coronal spinal balance measurements revealed the mean deviation of the C7 vertebral body from 210

the central sacral vertical line before surgery to be between 0 and 3.2mm for subgroups 1 and 3, 211

and 5.4 ± 13mm for subgroup 2, the rod fracture group. Interestingly, all groups were deviated to 212

the left of the central sacral vertical line at all time intervals after surgery with a trend over time 213

decreasing the distance away from the central sacral vertical line. At the 12 month follow-up all 214

subgroup means were in the range of 4.2 to 5.5mm, and by 24 months remained deviated to the 215

left between 2.1 to 5.4 mm. Table 1 gives mean (±SD) values for coronal spinal balance at all 216

review time points for the entire cohort. 217

218

Discussion 219

The objectives of surgery in adolescent idiopathic scoliosis are to halt progression, permanently 220

correct the deformity in three dimensions, improve trunk appearance and keep short and long-221

term complications to a minimum.23 Excellent results have been published for clinical outcome, 222

coronal correction, and in some cases sagittal correction using multi-segmental dual rod 223

posterior systems.24-26 Against this benchmark, similar coronal correction has been reported for 224

anterior approaches with a reduced number of fused levels, and anterior approaches have also 225

been credited with superior kyphotic restoration.13,27-29 The endoscopic anterior approach is our 226

method of choice for selected single thoracic curves, and we have previously reported on 227


10

pulmonary function restoration11, perioperative surgical aspects12, quality of life questionnaire 228

outcomes30, and the predictive ability of fulcrum bending radiographs31 for this technique. 229

Herein we report on the behaviour of the deformity correction with time after surgery, in order to 230

provide clinicians with quantitative data on the level of decompensation to expect in the two 231

years following endoscopic anterior scoliosis surgery. 232

233

The correction rate of the major curve in this study was in keeping with previously published 234

results for both open anterior and posterior techniques.8,13,14,19,24,28 During the two years 235

following surgery, there was a small (4°) loss of correction in the major Cobb angle, which is the 236

same as the value in the one existing longitudinal study mentioned earlier.20 Although this loss of 237

correction was statistically significant, it is less than the universally accepted 5° measurement 238

error for the Cobb technique.32-39 As a result, any loss of correction reported is not of sufficient 239

magnitude to be clinically relevant to the patient or surgeon. This also applies to the 2.8° loss of 240

correction for the instrumented curve between 2 and 24 months. The technique also 241

demonstrated significant improvement in the distal compensatory curve which was maintained 242

over time. The stable correction of the distal compensatory curve provides evidence to support 243

its exclusion from the fusion in this type of procedure. 244

245

With reference to Table 1, the overall difference between major and instrumented Cobb angles 246

increases slightly from 2.2° at 2 months, to 3.5° at two years. For the subgroup of screw related 247

complications the difference changes from 1° at 2 months to 2.2° at two years. The rod fracture 248

group shows a larger overall difference but less creep over time with 4.2° difference at 2 months 249

and 4.7° at 2 years. We suggest that it is useful to analyse the major and instrumented curves 250

separately, as it provides information on where any loss of correction may have occurred. 251

Wedging of the discs adjacent to the fused segment at either end of the construct contributes to 252


11

the major Cobb angle. However, it is this commonly occurring wedging that allows for better 253

shoulder balance when the patient adjusts their posture after anterior fusion. Similarly, the rib 254

hump correction achieved during surgery is maintained over time. The rib hump demonstrated an 255

overall increase of only 1.5° degrees after surgery across the study period which is not of 256

sufficient size to be clinically relevant. 257

258

Mean T5-T12 kyphosis increased by 48% from 18 preoperatively to 27 at 2 months, and 259

further to 31 at 24 months, a 67% increase from the preoperative mean value, adding support to 260

the claim of sagittal profile improvement following anterior scoliosis correction surgery. 261

Although the rod fracture group had a significant increase in thoracic kyphosis between 12 and 262

24 months, the increase in kyphosis for the whole group was not just due to rod fractures, as 263

evidenced by the fact that the 24 month increase in kyphosis for subgroup 1 (no mechanical 264

complications), was also 67% relative to the mean preoperative value, the same as for the overall 265

group. 266

267

Anterior scoliosis correction using flexible rods has been associated with a higher complication 268

rate when compared with posterior segmental instrumented fusions.27, 40 Betz et al28 found a 31% 269

rod breakage rate compared with 1% for posterior instrumentation, but used smaller threaded 270

rods. Newton et al20 reported a 6% rod fracture rate for a group of 50 patients who had similar 271

procedures to the current study (11% incidence of rod fractures). In our series, only one patient 272

has required a revision procedure at 2 year follow-up. With reference to Figure 4, the increase in 273

mean major Cobb angle from 2 to 24 months for Subgroup 2 (rod fractures) was 21.4° to 26.9° 274

(5.5°), whereas for subgroup 1 (no mechanical complications) it was 20.5° to 24.2° (ie. 3.7°), 275

suggesting that rod fractures are associated with slightly more decompensation after surgery, 276

however we note that differences of a few degrees are neither clinically measurable nor 277


12

significant in individual patients. When the rod fractures were identified early in the series, the 278

titanium rod diameter was increased from 4.5 to 5.5mm and the bone graft changed from 279

autograft (either rib head or iliac crest) to mulched femoral head allograft (typically 2 heads) 280

densely packed into well prepared disc spaces. Since these changes, there have been no further 281

rod fractures in the last sixty cases. Examination of Figures 4 to 7 shows that there were no 282

statistically significant increases in rib hump or in major, instrumented or compensatory Cobb 283

angles after the rod fractures occurred (ie between 12 and 24 months after surgery). 284

285

The other mechanical complication in our series was partial proximal screw pullout. These cases 286

were spread throughout the entire series and in most cases were noted in the first postoperative 287

(2 month) radiograph. Figures 4 to 6 suggest that although screw-related complications reduce 288

postoperative correction by a few degrees relative to patients without complications, the 289

subsequent decompensation from 2 to 24 months after surgery is no greater for screw-related 290

complications than for patients with no complications. None of the screw-related complications 291

have required revision surgery to date. 292

293

Endoscopic anterior instrumentation for adolescent idiopathic scoliosis is a safe and viable 294

surgical option. After the initial correction provided by the procedure there is a small loss of 295

coronal plane correction over time, but it is of subclinical magnitude and falls within the 296

accepted measurement error (5) for the Cobb technique. Fractured rods and partial proximal 297

screw pullout reduce correction by a few degrees relative to cases without complications, but do 298

not lead to clinically significant progression after the complication has occurred. In our patient 299

series, the incidence of rod fractures has been reduced to zero since the adoption of a pure 300

titanium 5.5mm rod and meticulous bone grafting technique utilizing allograft. 301

302


13

Table 1. Radiographic and rib hump measures for the entire patient group. Shoulder balance is 303 displayed as a negative figure if the left shoulder is higher than the right, and a positive figure if 304 right shoulder is higher than the left. Coronal spinal balance is the distance of the midpoint of C7 305 verterbal body from the central sacral line and is a negative value if C7 is deviated to the left and 306 a positive figure if it is deviated to the right. All numbers are mean ± standard deviation. 307 308 309

310 311 312 313 314 Table 2. Changes between the 2 and 24 month reviews for all radiographic parameters (degrees) 315 and rib hump (degrees) displayed according to their percentile rankings for the entire cohort. A 316 negative value indicates a decrease and a positive value indicates an increase between the 2 and 317 24 month reviews. 318 319 320

Percentile Major Cobb Angle Instrumented Cobb Angle

Minor Cobb

T5-T12 Kyphosis

Rib Hump

Maximum 12 11 12 23 12 90th 10 8.5 5 12 5 75th 7 5 2 7.5 2

50th (median) 4 2 0 3 1 25th 1 0 -4 0 0 10th -1 -2 -6.7 -4 -1

Minimum -5 -7 -13 -11 -3 321 322

Variable Preop. 2 months 6 months 12 months 24 months Major Cobb (°) 51.8 ±8.7 21.1 ±7.2 22.9 ±7.5 24.1 ±8.1 25.1 ±8.4 Instrumented Cobb (°) as above 18.8 ±7.6 20.3 ±7.6 21.1 ±7.8 21.6 ±8.4 Distal compensatory Cobb (°) 31.9 ±10.6 18.3 ±8.9 18.3 ±9.1 17.8 ±9.6 18.1 ±10.4 T5-T12 kyphosis (°) 18.3 ±9.8 27.0 ±7.8 27.5 ±8.5 29.4 ±8.9 30.6 ±9.3 Rib hump(°) 16.5 ±4.4 6.4 ±3.1 7.3 ±3.2 7.5 ±3.5 7.8 ±3.4 Shoulder balance (cm) 0.1 ±1.3 -0.9 ±1.2 -0.6 ±0.9 -0.4 ±1.0 -0.2 ±0.9 Coronal spinal balance (cm) 0.05 ±1.4 -0.3 ±1.3 -0.4 ±1.3 -0.5 ±1.1 -0.4 ±0.9

Correction Rates (%) Preop. 2 months 6 months 12 months 24 months Major curve 59.5 55.8 53.5 51.8 Instrumented curve 63.9 61.0 59.6 58.8 Distal compensatory curve 42.7 43.1 44.7 45.4 Rib hump 60.9 54.4 53.9 51.7


14

Figure Captions 323

324

Figure 1. Coronal plane radiograph of single rod anterior endoscopic construct showing the 325

difference between major and instrumented Cobb angles 326

Figure 2. Preoperative coronal, lateral and fulcrum bending radiographs and postoperative 327

coronal and lateral views for two representative patients from the series (patients 81 and 93) 328

Figure 3. Changes in radiograph parameters over time following surgery (preoperative, 2 329

months, 6 months, 12 months, 24 months). The radiographic parameters included are major 330

Cobb angle, instrumented Cobb angle, distal compensatory Cobb angle, rib hump, and T5-T12 331

kyphosis angle. Note that a bar on the graph has been included for preoperative instrumented 332

Cobb angle. The value of this bar is a repeat of the major Cobb angle. Error bars represent ±1 333

standard deviation. 334

Figure 4. Major Cobb angle versus time for (a) subgroup 1 - no mechanical complications, (b) 335

subgroup 2 – rod fractures, (c) subgroup 3 – screw-related complications. Error bars represent ±1 336

standard deviation. 337

Figure 5. Instrumented Cobb angle versus time for (a) subgroup 1 - no mechanical 338

complications, (b) subgroup 2 – rod fractures, (c) subgroup 3 – screw-related complications. 339

Error bars represent ±1 standard deviation. 340

Figure 6. Distal compensatory Cobb angle versus time for (a) subgroup 1 - no mechanical 341

complications, (b) subgroup 2 – rod fractures, (c) subgroup 3 – screw-related complications. 342

Error bars represent ±1 standard deviation. 343

Figure 7. Rib hump versus time for (a) subgroup 1 - no mechanical complications, (b) subgroup 344

2 – rod fractures, (c) subgroup 3 – screw-related complications. Error bars represent ±1 standard 345

deviation. 346


15

Figure 8. T5-T12 kyphosis angle versus time for (a) subgroup 1 - no mechanical complications, 347

(b) subgroup 2 – rod fractures, (c) subgroup 3 – screw-related complications. Error bars 348

represent ±1 standard deviation. 349

350

351

352

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20

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40. Segel MH, Betz RR, Bridwell KH, et al. A critical analysis comparing Zielke 480

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16:153-4. 483

484

485

486

Instrumented Cobb

MajorCobb

Figure 1.

#93

#81

Figure 2.

0

10

20

30

40

50

60

70

Pre-op 2 months 6 months 12 months 24 months

Ang

le (d

egre

es)

Major Cobb angleInstrumented Cobb angleDistal compensatory Cobb angleRib humpT5-T12 kyphosis angle

**

* *

*

*

* Denotes statistically significant difference (P

0

10

20

30

40

50

60

70


Ang

le (d

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No mechanical complications

Screw related complications

Rod fractures* Denotes statistically significant difference (P

0

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20

30

40

50

60

70


Ang

le (d

egre

es)



Rod Fractures

**

***

†


0

5

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15

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25

30

35

40

45

50


Ang

le (d

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Rod Fractures* Denotes statistically significant difference (P

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25


Ang

le (d

egre

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Rod fractures

** †*

*


0

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45


Ang

le (d

egre

es)



Rod Fractures

* *

*

*


QUT Digital Repository: //eprints.qut.edu.au/25879/1/c25879.pdf · 2010. 6. 9. · 156 though in one case T4 was instrumented. The most common distal instrumented levels were T11

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