Background/Aims

Bisphosphonates play an important role in the treatment of catabolic bone diseases such as osteoporosis. In addition to their anti-resorptive activity exerted by their proapoptotic effect on osteoclasts, recent data suggest that nitrogen-containing bisphosphonates (N-BP) may also promote osteogenic differentiation by an unknown mechanism. Similar bone-anabolic effects have been attributed to cholesterol-lowering statins, which represent another class of mevalonate pathway inhibitors besides N-BP, suggesting a common mode of action. In vascular endothelial cells statins were recently shown to activate the Mek5/Erk5 mitogen-activated protein kinase cascade, which plays an important role in cellular differentiation, apoptosis or inflammatory processes. Here we evaluated whether N-BPs may also target the Mek5/Erk5 pathway and analysed the consequence of Erk5 activation on bone-relevant gene expression, calcification and osteoblast differentiation.

The relationship between radiologic union and clinical outcome in thoracoscopic scoliosis surgery is not clear, as apparent non-union does not always correspond to a poor clinical result. Our aim was to evaluate CT fusion rates 2yrs after thoracoscopic surgery, and explore the relationship between fusion scores and; (i) rod diameter, (ii) graft type, (iii) fusion level, (iv) implant failure, and (v) lateral position in disc space.

Between 2000 and 2006 a cohort of 44 patients had thoracoscopic scoliosis correction. Discectomies were performed and defect was packed with either autograft (n=14) or allograft (n=30). Instrumentation consisted of either 4.5mm (n=24) or 5.5mm (n=20) single titanium anterior rod and vertebral body screws. Fusion quality and implant integrity were evaluated 2yr following surgery using low-dose CT. At each disc space, left, right and mid-sagittal CT reconstructions were generated and graded using the Sucato 4-point scale (Sucato, 2004) which is based on calculated percentage of fusion across disc space.

Fusion scores were measured for 259 disc spaces in 44 patients. Rod diameter had a strong effect on fusion score, with a mean score of 2.12±0.74 for 4.5mm Ti rod, decreasing to 1.41+0.55 for 5.5mm Ti rod, and to 1.09+0.36 for 5.5mm Ti-alloy rod. Mean fusion scores for autograft and allograft subgroups were 2.13±0.72 and 2.14±0.74 respectively. Fusion scores were highest in the middle of implant construct, dropping off by 20–30% toward the ends. Fusion scores adjacent to the rod (2.19±0.72) were significantly higher than on the contralateral side of the disc (1.24±0.85). Levels where rod fracture occurred (n=11) had lower fusion scores than those without fracture (1.09±0.67 vs 1.76±0.80). Levels where top screw pullout occurred (n=6) had lower CT fusion scores than those without (1.25±0.60 vs 1.83±0.76).

Rod diameter (larger), intervertebral level (proximal or distal), lateral position in disc (further from rod) and rod fracture or screw pullout all reduce fusion scores, while graft type does not affect scores. The assumed link between higher fusion score and better clinical outcome must be treated with caution, because rod fractures did not necessarily occur in patients with lower fusion scores. It is possible that with a stiffer rod, less bony fusion mass is required for a stable construct. We propose that moderate fusion scores secure successful clinical outcomes in thoracoscopic scoliosis surgery.

Introduction

Luk (Luk et al. Spine vol 23(21) 2303-2307 1998) has shown that in posterior surgery, the correction achieved can be predicted by fulcrum bending films. The relevance to anterior correction has been disputed, as this commonly involves shortening the spine by the removal of intervertebral discs. The aim of the study was to see whether the pre-operative bending angle reflected the degree of correction achieved.

Purpose

1. To evaluate how radiological parameters change during the first 3 years following anterior endoscopic surgery. 2. To report complications encountered in this period.

Introduction

Radiographic parameters have been shown to have a poor correlation with clinical outcome after open scoliosis procedures. However this has not been previously addressed after endoscopic surgery. The purpose of our study was to examine prospectively the relationship between curve correction and clinical outcome for endoscopic scoliosis surgery.

Introduction: Compared with open instrumented anterior spinal fusion for adolescent idiopathic scoliosis (AIS), endoscopic surgery offers clinical benefits that include reduced pulmonary morbidity and improved cosmesis. However, quantitative data on the radiological improvement of vertebral rotation using this method is limited. The aim of this study was to measure pre-operative and postoperative axial vertebral rotational deformity at the curve apex in endoscopic anterior instrumented scoliosis surgery patients using computed tomography (CT), and assess the relevance of these findings to clinically measured chest wall rib hump deformity correction.

Methods: Between November 2002 and August 2005, twenty patients with right-sided thoracic curves underwent endoscopic single-rod anterior instrumented fusion. Pre and post surgical axial vertebral rotation was measured at the curve apex on preoperative and two-year postoperative CT using Aaro and Dahlborn’s method. Rib hump deformity correction was retrieved from a surgical database and correlated to the CT findings. Linear regression was used to investigate the correlation between apical vertebral rotation measured on CT and rib hump measured using a scoliometer.

Results: The mean angle of correction achieved in axial vertebral body derotation at the apical vertebra as measured by CT was 7.9°. This equated to a 43% improvement (range 20–90%). The preoperative and postoperative clinical measurements i.e. rib hump deformity correction, correlated significantly with CT measurements using regression analysis (p=0.03) and the mean improvement in rib hump deformity was 55%.

Conclusion: To our knowledge, this is the first quantitative CT study to confirm that endoscopic anterior instrumented fusion for AIS substantially improves the axial vertebral body rotational deformity at the apex of the curve. The margin of correction of 43% compares favourably historically published figures for all-hook-rod constructs in posterior spinal fusion. In addition, the CT measurements obtained significantly correlated to the clinical outcome of rib hump deformity correction.

Study Aims: This study’s objectives were to measure pre-operative and postoperative axial vertebral rotational deformity at the curve apex in endoscopically-treated anterior-instrumented scoliosis patients using CT, and assess the relevance of these findings to clinically measured chest wall rib hump deformity correction.

Introduction: Thoracoscopic instrumented anterior spinal fusion for adolescent idiopathic scoliosis (AIS) has clinical benefits that include reduced pulmonary morbidity, postoperative pain, and improved cosmesis. However, quantitative data on radiological improvement of vertebral rotation using this method is lacking.

Methods: Between November 2002 and August 2005, 20 AIS patients with right-sided thoracic major curves underwent endoscopic single-rod anterior fusion. Preoperative and two-year postoperative CT was performed to assess axial vertebral rotation at the curve apex. Correlation between apical vertebral rotation measured on CT and rib hump measured using a scoliometer was assessed.

Results: The mean angle of correction achieved in axial vertebral body derotation at the apical vertebra measured by CT was 7.9° and equated to 43% improvement. Preoperative and postoperative rib hump deformity correction correlated significantly with CT measurements using regression analysis (p=0.03). The mean improvement in rib hump deformity was 55%. Conclusion: We believe this is the first quantitative CT study to confirm that endoscopic anterior instrumented fusion for AIS substantially improves axial vertebral body rotational deformity at the apex of the curve. The margin of correction of 43% compares favourably with historically published figures of 24% for patients with posterior all-hook-rod constructs. CT measurements correlated significantly to the clinical outcome of rib hump deformity correction.

Ethics: local committee approval

Statement of Interest: none

Introduction: The use of anterior vertebral staples in the fusionless correction of scoliosis has received increased attention in recent literature. Several animal studies have shown stapling to be effective in modulating vertebral growth. In 2005 Betz (1) published the only clinical series to date. Despite the increasing volume of literature suggesting the efficacy of this treatment, little is known about it’s biomechanical consequences. In 2007 Puttlitz (2) measured the change in spinal range of motion after staple insertion in a bovine model. They found a small but statistically significant decrease in range of motion in axial rotation and lateral bending. The clinical significance of this is questionable as the differences were only a few degrees over three vertebral levels. A well designed biomechanical evaluation of the effects of staple insertion on spinal stability is needed. The aim of this study was to evaluate the effect of insertion of a laterally placed anterior vertebral staple on the stiffness characteristics of a single motion segment.

Methods: Four-pronged shape memory alloy staples were inserted into fourteen individual bovine thoracic motion segments. A displacement controlled six degree-of-freedom robotic facility was used to test control and staple constructs through a pre-determined range of motion in flexion, extension, lateral bending, and axial rotation. All data were synchronised with robot position data and filtered using moving average methods. The stiffness in each condition was calculated in units of Nm/degree of rotation. Paired t-tests were used to compare results.

Results: Stiffness measurements in the control condition correlated with previously published measures (3). A significant decrease in stiffness (p< 0.05) following staple insertion was found in flexion, extension, lateral bending away from the staple, and axial rotation away from the staple. Stiffness for axial rotation towards the stapled side was significantly greater than for away. A near significant increase in lateral bend stiffness away from the staple compared with towards was also seen.

Discussion: These results suggest that staple insertion consistently decreased stiffness in all directions of motion. This is contrary to the results of Puttlitz (2), which reported a reduced range of motion (i.e. increased stiffness) for some motions using moment-controlled testing. This decrease in stiffness could not be explained by changes in anatomy or tissue properties between specimens, as each stapled motion segment was compared with its own intact state. Addition of the staple would intuitively be expected to increase motion segment stiffness, however we suggest that the staple prongs may cause sufficient disruption to the vertebral bodies and endplates to slightly reduce overall stiffness. Hence, growth modulation may be achieved through physical disruption of the endplate, rather than static mechanical stress. Further research is planned to investigate the proportion of load carried by the staple during spinal movement and the anatomical effect of the staple on the physis. In conclusion, anterior vertebral stapling causes a slight but significant decrease in the stiffness of treated motion segments.

Introduction: Pre-operative coronal curve flexibility assessment is of key importance in the surgical planning process for scoliosis correction. The fulcrum bending radiograph is one flexibility assessment technique which has been shown to be highly predictive of potential curve correction using posterior surgery, however little is known about the extent to which soft tissue structures govern spinal flexibility. The aim of this study was to explore how the mechanical properties of spinal ligaments and intervertebral discs affect coronal curve flexibility in the fulcrum bending test. To this end a biomechanical analysis of a scoliotic thoracolumbar spine and ribcage was carried out using a three dimensional finite element model.

Methods: CT-derived spinal anatomy for a 14 year old female adolescent idiopathic scoliosis patient was used to develop the 3D finite element model. Physiological loading conditions representing the gravitational body weight forces acting on the spine when the patient lies on their side over the fulcrum bolster were simulated. Initial mechanical properties for the spinal soft tissues were derived from existing literature. In six separate analyses, the disc collagen fibre and ligament stiffness values were reduced by 10%, 25% and 40% respectively, and the effects of reduced tissue stiffness on fulcrum flexibility were assessed by comparison with the initial model. Finally, the effect of discectomy on fulcrum flexibility was simulated for thoracic levels T5 to T12.

Results: Reducing disc collagen fibre stiffness resulted in a greater change in segmental rotations in the fulcrum bending test than reducing ligament stiffness. However, reductions of up to 40% in disc collagen fibre stiffness and ligament stiffness produced no clinically measurable increase in fulcrum flexibility (increase of 1.2%). By contrast, following removal of the discs, the simulated fulcrum flexibility increased by more than 80% compared to the initial case.

Discussion: Disc collagen fibre and ligament stiffness both have minimal influence on scoliotic curve flexibility. However, discectomy simulation shows that the intervertebral discs are of critical importance in determining spinal flexibility.

Introduction: The occurrence of non-union following instrumented scoliosis correction may predispose to pseudarthrosis and subsequent implant failure. Although non-union is often multifactorial, it is widely accepted that bone graft of adequate quality and quantity is fundamental to achieve solid fusion. Conventionally, autologous rib graft or iliac crest harvest has been utilised for endoscopic anterior instrumented scoliosis surgery. However, these techniques increase the operative duration and cause donor site morbidity, both of which may lengthen hospital stay. Alternatives such as allograft bone and bone morphogenetic proteins have gained more widespread use and may improve fusion rates although this remains controversial. The aim of this study was to compare two-year postoperative fusion rates for a series of patients who underwent endoscopic anterior instrumentation for thoracic scoliosis utilising various bone graft types.

Methods: 19 patients who had undergone endoscopic anterior instrumented scoliosis correction using identical instrumentation (4.5mm diameter titanium anterior rod and vertebral body screws, Eclipse, Medtronic) between May 2000 and August 2005 were identified from a surgical database of 132 consecutively treated individuals. All patients received bone graft to supplement thoracic fusion. Discectomy was performed at the levels to be instrumented and intervertebral spaces were packed with autologous rib heads (8 patients), iliac crest (1 patient), or mulched femoral head allograft (10 patients). The quality of thoracic fusion and implant integrity were evaluated two years following scoliosis correction using low-dose CT performed in accordance with local ethical approval. The intervertebral fusion was assessed using a modified Sucato method (1). Each level was graded using a 4-point scale based on calculated percentage of fusion across the disc space. 0 points indicated no fusion; 1 point, fusion < 25%; 2 points, fusion between 25 and 50%; 3 points, fusion between 50 and 75%; 4 points > 75% or complete fusion. The fusion was considered solid with a score of 3 points or more. Data was analysed with non-parametric tests using a significance level of 0.05.

Results: Of the cohort, nine had evidence of implant failure with rod fracture. All implant failures occurred in the group who received either rib head or iliac crest graft. No rod fractures were identified in the femoral allograft group. The mean fusion grade in the autologous bone graft group was 1.91 whereas in the allograft group this was 3.30 (95% confidence intervals 1.38–2.44 and 2.99–3.61 respectively) with a statistically significant difference in fusion rates between these two groups (p=0.001).

Discussion: This study demonstrated significantly better rates of thoracic fusion in endoscopic anterior instrumented scoliosis correction using mulched femoral allograft compared with autologous rib heads and iliac crest graft. This could be partly explained by the difficulty obtaining sufficient quantities of autologous graft. The lower fusion rate seen in the autologous graft group appears to predispose to rod fracture although the longer-term clinical consequence of implant failure in this group is not clear and warrants further study.

Introduction: Open instrumented anterior spinal fusion for adolescent idiopathic scoliosis (AIS) is a proven technique for vertebral derotation that, compared with posterior spinal fusion procedures, invariably requires fewer distal fusion levels to be performed. With the advent and evolution of endoscopic anterior instrumentation, further clinical benefits are possible such as reduced pulmonary morbidity, improved cosmesis and less postoperative pain. However, quantitative data on the radiological improvement of vertebral rotation using this method is limited. The aim of this study was to measure preoperative and postoperative axial vertebral rotational deformity at the apex of the curve in endoscopic anterior instrumented scoliosis surgery patients using computed tomography (CT), and assess the relevance of these findings to clinically measured chest wall rib hump deformity correction.

Methods: Between November 2002 and August 2005, adolescent idiopathic scoliosis patients with right-sided thoracic major curves were selected for endoscopic single-rod anterior fusion by the senior authors. Low-dose pre-operative CT was performed as described previously (1) and two-year postoperative CT was also performed on consenting patients in accordance with local ethical committee approval. The pre and post surgical axial vertebral rotation was measured at the curve apex using Aaro and Dahlborn’s method (2). Intraobserver and interobserver variability was assessed. Additional clinical information such as rib hump deformity correction and change in the Cobb angle was retrieved from a surgical database and correlated to the CT findings. Least squares linear regression was used to investigate the correlation between apical vertebral rotation measured on CT and rib hump measured using a scoliometer.

Results: Twenty patients were included in the study. The mean angle of correction achieved in axial vertebral body derotation at the apical vertebra measured by CT was 7.9° (median preoperative angle 17.3° [range 12.5° to 27.3°] and median postoperative angle 10.3° [range 1.8° to 18.1°]. This equated to a 43% improvement (range 20–90%). The preoperative and postoperative clinical measurements i.e. rib hump deformity correction, correlated significantly with CT measurements using regression analysis (p=0.03) and the mean improvement in rib hump deformity was 55% (median preoperative 15.0° [range 10° to 30°] and median postoperative 7.0° [range 4° to 10°]). 95% confidence intervals for intraobserver and interobserver validity were within the ranges ±4.5° to ±6.4°.

Discussion: We believe this is the first quantitative CT study to confirm that endoscopic anterior instrumented fusion for AIS substantially improves the axial vertebral body rotational deformity at the apex of the curve. The margin of correction of 43% compares more favourably than the historically published figure of 24% in a cohort of patients with all-hook-rod constructs used for posterior spinal fusion (3). Patient age and gender demographics, curve magnitude and curve types in the historical study were similar to our group, and an identical CT protocol for measuring vertebral derotation was utilised. In addition, the CT measurements obtained significantly correlated to the clinical outcome of rib hump deformity correction.

Introduction: Vertebral rotation is an important aspect of spinal deformity in scoliosis, associated with ribcage deformity (rib hump). Although both lateral curvature and axial rotation appear to increase together in progressive scoliosis, the mechanisms driving vertebral rotation are not clearly established and it is not known whether lateral curvature precedes rotation, or vice versa. This study investigates the hypothesis that intravertebral (within the bone) rotation in idiopathic scoliosis is caused by growth in the presence of gravity-induced torsions, the twisting moments generated by gravitational forces acting on the scoliotic spine.

Methods: The twisting moment Tp acting at an arbitrary point P on a three-dimensional spinal curve is given by Tp=Mp·â, where Mp=r¥F is the total moment due to gravity force F acting at (vector) distance r, and â is the tangent to the spinal curve at P (Figure One). Standing radiographs for five idiopathic scoliosis patients were used to define three-dimensional curves representing the approximate axes of rotation of each spine, running along the anterior edge of the neural canal from T1 to S1. The equilibrium equations above were then solved to calculate gravity-induced torsions exerted by head and torso weight about the spinal axes for each patient. Intravertebral rotations were measured for the same patients using Aaro & Dahlborn’s technique with reformatted computed tomography images in the plane of superior and inferior endplates of each vertebra. The gravity-induced torsion curves were compared with intravertebral rotation measurements to see whether gravity-induced torsion is a likely contributor to intravertebral rotation.

Results: Gravity-induced torques as high as 4 Nm act on the spines of idiopathic scoliosis patients due to static body weight in the standing position. Maximum intravertebral rotations (for a single vertebra) were approximately 78. There appears to be general agreement between the measured intravertebral rotations and profiles of gravity-induced torsion along the length of the spine (Figure 2). Rotation measurements confirm the finding of previous authors that maximum intravertebral rotations occur at the ends of a scoliotic curve (with little relative rotation at the apex), and this finding is consistent with the gravity-induced torsion profiles calculated.

Conclusion: Gravity-induced torsion is a potential cause of vertebral rotation in idiopathic scoliosis. Since the spine must be curved in three-dimensions (out of plane) to produce such torques, vertebral rotation would be expected to occur subsequent to an initial lateral deviation, suggesting that coronal curvature ‘drives’ axial rotation during scoliosis progression.

Introduction It is important to understand the mechanics of the lumbar spine, as it has been shown that much low back pain is attributable to mechanical factors. One important aspect of spinal mechanics is the neutral zone, defined as a region of little or no resistance to motion on either side of the neutral position for a motion segment. If the neutral zone is a significant feature of intervertebral joint mechanics then the spinal joints will have little intrinsic stability and rely on muscles to control their movement around the neutral position. This has significant implications for our understanding of how degenerative changes to the spinal joints might destabilise the spine. This study was performed to characterise the size of the neutral zone and the effect of axial preload for different spinal motions.

Methods Using a 6 degree-of-freedom (DOF) ABB industrial robot incorporating a 6-DOF JR3 force sensor, six isolated ovine lumbar joint segments were subjected to 5 repetitive movements in 3 directions (6° extension / 15° flexion, +/− 7° lateral bend, +/− 3° axial twist) with 4 different preloads (0, 150, 300, 450N) under 2 conditions (facet joints intact and facets removed). For each direction, the fixed axis about which the joint would rotate with a minimal motion-opposing moment was determined in advance. In accordance with a previous study by this group, the neutral zone was defined as the region where absolute rotational stiffness is less than 0.05 Nm/°.

Results When moving from 6° of extension to −15° (flexion) a neutral zone was usually observed starting around 0° and continuing as far as −8 or −9°. The neutral zone was in the same region when moving in the opposite direction, except when the specimen showed a considerable amount of hysteresis, in which case the neutral zone could start as early as −11° or −12° and usually continued to −2°or −3°. Increasing preload usually made the joint stiffer in the regions outside the neutral zone, but did not affect the neutral zone itself. If present without preload, hysteresis usually increased with increasing preload. In lateral bend and axial twist no neutral zone was generally observed. In lateral bend the stiffness gradually increased with rotation, whereas in axial twist the stiffness was usually constant over the range of movement. For all movements, the only effect of facet removal was a constant reduction in stiffness over the whole movement. For lateral bend this meant that the stiffness around 0° usually would drop below the threshold of 0.05Nm/°, hence creating a neutral zone extending over a couple of degrees.

Discussion Ovine spinal joints have a region where there is little to no resistance to flexion/extension. This region can be in excess of 10°. This means in their neutral position, the individual spinal joints have virtually no stability and the spine depends on other measures such as muscle activation to maintain stability in the sagittal plane. For lateral bend there is a region of little resistance as well, but it is not nearly as profound as in flexion/extension.

Introduction The NIH estimates that 30–50% of women and 20–30% of men will develop a vertebral fracture in their lifetime. 700,000 vertebral fractures occur each year in the United States alone, 85% of which are associated with osteoporosis. Osteoporosis leads to reduced stiffness of vertebral cancellous bone and eventual loss of cortical wall thickness. This study aims to investigate the effects of cortical wall thickness and cancellous bone elastic modulus on vertebral strength and fracture patterns using synthetic vertebrae made from bone analogue materials.

Methods Synthetic vertebrae were created using rapid prototyping for the cortical shell and expanding polyurethane foam filler for the cancellous core. Dimensions were based on human L1 vertebra as specified in Panjabi et al. (1992). Silicone mouldings were used as intervertebral disk phantoms. The synthetic vertebrae were subjected to uniaxial compression at constant strain rate (5mm/min) using a Hounsfield testing machine. Force and displacement were logged until ultimate specimen failure, as well as video to record gross fracture patterns.

Results Post-failure examination indicated that successful filling of the synthetic shell by the expanding foam was achieved. Pilot results demonstrate the repeatability of the technique, with < 4% variation between specimens compared to mean initial fracture load and < 2.5% variation from mean ultimate load. Initial fracture occurred at approximately 67% of ultimate failure load. Initial fracture occurred consistently at the vertebral endplates which is similar to reported in vitro behaviour with cadaveric specimens. Investigation of the effects of cancellous foam elastic modulus is currently underway.

Discussion A synthetic L1 vertebra has been successfully developed, providing a highly repeatable analogue for investigation of the biomechanics of osteoporotic vertebral compression fractures. While the magnitude of the force obtained from the synthetic vertebrae differs from real human vertebrae due to differing material properties, comparative biomechanics between the synthetic and real vertebrae appear consistent, and fracture patterns are similar to those observed in cadaveric studies.

Introduction Endoscopic scoliosis surgery can be complicated by rod breakage. The aim of this study was to examine the effect of rod breakage on clinical outcome and to determine any predisposing factors.

Methods We studied 83 consecutive patients that had undergone endoscopic correction for scoliosis. Patients were assessed pre-operatively and at regular intervals for up to three years post-operatively. Those patients sustaining rod breakages were compared with those that did not. Clinical outcome was assessed using the Scoliosis Research Society outcome instrument (SRS-24). Radiological assessment included coronal Cobb angles and the angle between adjacent screws.

Results There were 13 (15.7%) patients sustaining 16 rod breaks at a mean time from operation of 21.5 months. No significant change in Cobb angle occurred after rod breakage (mean 18.3 vs 19.7 degrees), p> 0.05. Comparing patients with and without rod breaks we found no difference in SRS-24 scores for pain (4.30 vs 4.39), self image (3.50 vs 3.70), function (3.56 vs 3.35) or patient satisfaction (4.22 vs 4.58). There was no significant difference in screw angle for those patients that developed rod breakages (mean 3.2 vs 2.7 degrees). Significantly more breakages occurred with rib (11/40) and iliac crest (2/7) autograft compared with femoral allograft (0/36), p< 0.01.

Discussion Rod breakage can occur following endoscopic scoliosis surgery. Our study shows that this is not associated with any significant loss of curve correction and has no effect on clinical outcome. Since changing to femoral allograft and by increasing the rod diameter no further rod breakages have occurred.

Introduction Radiographic parameters have been shown to have a poor correlation with clinical outcome after open scoliosis procedures. However this has not been previously addressed after endoscopic surgery. The purpose of our study was to prospectively examine the relationship between curve correction and clinical outcome for endoscopic scoliosis surgery.

Methods We studied 50 consecutive patients that underwent endoscopic instrumentation, with a minimum follow-up of two years. All patients were assessed pre-operatively and at 24 months post-operatively. Radiological parameters were measured from plain standing radiographs including the coronal Cobb angle, sagittal alignment, coronal alignment and shoulder elevation. Clinical outcome was assessed using the Scoliosis Research Society Outcomes Instrument (SRS-24). Correlation between radiological parameters and SRS-24 scores were determined using the Pearson correlation coefficient.

Results There were 45 females and 5 males with a mean age of 16.4 years (range, 10 to 46). The pre-operative coronal Cobb angle was mean 51.7 ± 8.5 and the postoperative instrumented Cobb angle was mean 20.4 ± 7.8 corresponding to a mean curve correction of 60.7%.

There was a positive correlation between instrumented Cobb angle and total SRS-24 score (p=0.03, r2=0.085) and between curve correction and total SRS-24 score (p=0.04, r2=0.081). No correlation was found between coronal alignment, sagittal alignment, shoulder elevation or size of rib hump and the SRS-24 scores (p> 0.05).

Discussion Overall endoscopic scoliosis surgery was associated with a good clinical outcome for our series of patients. Using a validated assessment instrument, clinical outcome correlated well with the amount of curve correction achieved.

Introduction Endoscopic single rod anterior fusion surgery for the treatment of adolescent idiopathic scoliosis (AIS) offers the advantages of improved cosmetic results, the fusion of fewer segments and faster patient rehabilitation. The development of a patient-specific finite element model of the spine to be used to predict post-operative biomechanical outcomes of anterior AIS surgery will improve the pre-operative planning and performance of scoliosis instrumentation. This study aims to develop a methodology for validating the finite element modeling approach to scoliosis surgical planning by producing biomechanical data for movements of ovine lumbar spines both with and without anterior rod scoliosis instrumentation.

Methods Ovine lumbar spine specimens were CT scanned, dissected and instrumented across four levels (L2–L5) with a generic anterior single rod and screw implant for scoliosis correction. A displacement controlled 6 degree-of-freedom robotic facility was used to perform biomechanical testing on the spine segments for rotations of ±4 degrees in flexion/extension and lateral bending, and ±3 degrees in axial rotation. The tests were repeated with the rod removed. Resistive force and moment data was recorded using a force transducer and strain gauges on the surface of the rod yielded torsion and bending moment strain data, recorded on a data logger. All data was synchronized with the robot position data and filtered using moving average methods. The stiffness of the spines for each movement was calculated in units of Nm/degree of rotation.

Results As expected the results reflect the variability found in biological materials. The similarities of behaviour profiles however, support the use of this method for FE model validation. The addition of the rod caused an increase in stiffness for each movement. This increase was 17±7% and 23±10% for left and right axial rotation, 93±35% and 73±50% for left and right lateral bending, and 78±46% and 67±35% for flexion and extension respectively. Recorded strains on the rod surface did not exceed 400με.

Discussion The outcomes of this study have provided an experimental method for validating behaviour predicted by finite element models of the spine fitted with anterior scoliosis instrumentation. Using the CT scans of the ovine spines along with documentation of the experimental positioning of the specimens, the testing conditions can be simulated in a finite element model and the experimental and predicted biomechanical outcomes compared. The study also offers comparative information about the relative stiffness of the spine with and without scoliosis instrumentation.

Introduction Endoscopic instrumentation for scoliosis has several advantages compared with open procedures. The purpose of our study was to prospectively assess the clinical outcome of patients after endoscopic anterior instrumentation and to evaluate their responses over time.

Methods A total of 83 consecutive patients underwent endoscopic instrumentation performed at a single unit. Patients completed the SRS-24 Outcomes Instrument pre-operatively and at 3, 6, 12 and 24 months postoperatively. The seven domains of the SRS-24 score were compared between each of the follow-up intervals. The dataset contained 24 responses at 3 months, 65 responses at 6 months, 63 responses at 12 months and 49 responses at 24 months.

Results There were 74 females and nine males with a mean age of 16.4 years (range, 10 to 46 years). The mean Cobb angle improved from 52.8 degrees pre-operatively to 21.9 degrees post-operatively. Over the follow-up period there were significant improvements in the activity level (p< 0.05), function from back condition (p< 0.05) and post-operative function (p< 0.01) domains. Most of this improvement occurred during the first post-operative year and none of the domains improved further after this time interval. There was no significant change in the pain, self image and patient satisfaction domains.

Discussion Our results for endoscopic scoliosis correction are comparable with those reported for open procedures. The greatest improvement in SRS scores occurred between six and twelve months post-operatively. The SRS-24 scores at one year from surgery may provide a good indicator of patient outcome in the long-term.

Introduction The use of anterior techniques to address scoliosis is well established. The method employed is dependent on the curve type, degree and the institution. There are apparent immediate perioperative advantages of an endoscopic technique over an open thoracotomy. In addition, endoscopic instrumentation and fusion has become accepted as a reliable method to address thoracic scoliosis.

Methods 101 patients have undergone anterior endoscopic instrumented correction for scoliosis at the Mater Children’s Hospital, Brisbane between 2000 and 2005. In 2002, a case series study was established to assess perioperative aspects. The majority of patients were entered into a database prospectively. A total of 83 patients were included in the study at the point of data analysis for this paper. The perioperative factors considered were: Theatre times; Blood management; Mobility; and Complications.

Results The mean age was 16 years. 75 curves were adolescent idiopathic. Eight curves were in neuromuscular patients. The majority, 59 (79%) were Lenke Type 1 curves. Operating times were divided into anaesthetic, surgical and X-ray. There was a mean reduction in anaesthetic time between the first and last 20 cases of 22 minutes (p=0.20). For X-ray this was 73 seconds (p< 0.001). The mean surgical time was 288 minutes. The mean reduction in surgical time was 76 minutes (p< 0.001). A scatter plot was also performed of surgical time versus case number. The surgical time has an apparent plateau after approximately 30 cases. This may suggest a learning curve of this number. The mean intra-operative blood loss was 380mls with no allogenic transfusions. The mean length of stay was 5.8 days. There was an overall perioperative complication rate of 12%. There were six reinsertions of ICC, one conversion to an open thoracotomy, two postoperative chest infections and one patient requiring re-intubation in intensive care due to narcosis. There were no subsequent problems for these patients with perioperative complications.

Discussion The use of endoscopic techniques to address scoliosis is employed in centres specializing in spinal deformity. The results above are comparable to those previously reported for both open and endoscopic anterior techniques. The results outlined demonstrate this to be a safe method regarding the perioperative morbidity and complications associated with the procedure.

Introduction: Low back pain (LBP) is an ailment affecting a large portion of the population and may result from degeneration of the intervertebral discs. Degeneration of the discs may be characterized by a loss of hydration, a more granular texture in the disc components and the presence of anular lesions which are tears in the anulus fibrosus. Research to date has been lacking in defining a relationship between LBP and anular lesions. In this study a materially and geometrically accurate finite element model (FEM) of an L4/5 intervertebral disc was developed in order to study the effects of anular lesions on the disc mechanics.

Methods: An anatomically accurate transverse profile for the disc FEM was derived from transversely sectioned human cadaveric discs. The anulus fibrosus ground substance was represented as an incompressible material using an Ogden hyperelastic strain energy equation. Material parameters were derived from experimentation on sheep discs. In order to separately assess the effects of degeneration of the nucleus and of the entire disc, four models were analysed. A healthy disc was modelled as reference and the three degenerate models comprised a degenerate nucleus (no hydrostatic nucleus pressure) with either a healthy anulus, or with a radial or rim anular lesion. Loading conditions to simulate the extreme range of physiological motions about the 6 axes of rotation were applied to the models and the peak rotation moments compared.

Results: The reduction in peak moment between the Healthy Disc FEM and the Healthy Anulus FEM ranged from 24% under flexion to 86% under right lateral bending. When the lesions were simulated, the rim and radial lesion resulted in variations in peak moment from the Healthy Anulus FEM of 1–10% and 0–4%, respectively.

Conclusions: The analysis suggested that loss of the nucleus pulposus pressure had a much greater effect on the disc mechanics than the presence of anular lesions. This indicated that the development of anular lesions prior to the degeneration of the nucleus would have minimal effect on the disc mechanics. But the response of an entirely degenerate disc would show significantly different mechanics compared to a healthy disc. With the degeneration of the nucleus, the disc stiffness will reduce and the outer innervated anulus may become overloaded and painful.