Dwyer instrumentation in the treatment of adolescent idiopathic scoliosis

Identifying risks factors in thoracolumbar anterior fusion surgery through predictive analytics in a nationally representative inpatient sample

PURPOSE

Anterior thoracolumbar (TL) surgical approaches provide more direct trajectories compared to posterior approaches. Proper patient selection is key in identifying populations that may benefit from anterior TL fusion. Here, we utilize predictive analytics to identify risk factors in anterior TL fusion in patients with trauma and deformity.

METHODS

In this retrospective cohort study of patients receiving anterior TL fusion (between and including T12/L1), population-based regression models were developed to identify risk factors using the National Readmission Database 2016-2017. Readmissions were analyzed at 30- and 90-day intervals. Risk factors included hypertension, obesity, malnutrition, smoking, alcohol use, long-term opioid use, and frailty. Multivariate regression models were developed to determine the influence of each risk factor on complication rates.

RESULTS

A total of 265 and 375 patients were identified for the scoliosis and burst fracture cohorts, respectively. In patients with scoliosis, alcohol use was found to increase the length of stay (LOS) (p = 0.00061) and all-payer inpatient cost following surgery (p = 0.014), and frailty was found to increase the inpatient LOS (p = 0.0045). In patients with burst fractures, malnutrition was found to increase the LOS (p < 0.0001) and all-payer cost (p < 0.0001), obesity was found to increase the all-payer cost (p = 0.012), and frailty was found to increase the all-payer cost (p = 0.031) and LOS (p < 0.0001).

DISCUSSION

Patient-specific risk factors in anterior TL fusion surgery significantly influence complication rates. An understanding of relevant risk factors before surgery may facilitate preoperative patient selection and postoperative patient triage and risk categorization.

Reducing the kyphosis effect of anterior short thoracolumbar/lumbar scoliosis correction with an autograft fulcrum effect

Background

Anterior scoliosis correction is a powerful technique with the disadvantage of a kyphotic effect on lumbar and thoracolumbar curves. We aimed to investigate whether a cognizant interposition of a rib graft anteriorly and at the concave side of the scoliotic curve causes significant fulcrum effect to enforce scoliosis correction and to reduce interfusional kyphosis in anterior scoliosis corrections.

Methods

Twenty otherwise comparable patients with lumbar and thoracolumbar adolescent idiopathic scoliosis (AIS) curves undergoing anterior short scoliosis correction with (n = 10) or without (n = 10, matched for age, gender and degree of deformity) fulcrum effect were retrospectively compared by means of radiographic measurements (sagittal and coronal profile, Cobb angles and intersegmental deformity correction angles) to evaluate the effect of this modified surgical technique.

Results

The overall amount of scoliosis correction was similar with 74 and 60% of initial curves of 57° and 53° in the case and control group respectively with a mean of 3 fused segments (4 screws).

Statistically relevant differences were found for intersegmental coronal cobb angles at the apex of 20° to 3° and 17° to 9° with and without fulcrum, respectively (p < 0.05). Creation of kyphosis in the fused segments was reduced with an interfusional kyphotic sagittal cobb angle of 15° pre-operatively vs. 3° post-operatively compared to the control group (13° pre-operatively vs. 18° post-operatively), (p < 0.05).

Conclusions

Interfusional hyperkyphosis associated with anterior scoliosis correction for thoracolumbar/lumbar curves can be reduced with cognizant positioning of the bone autograft at the antero-lateral (concave) site in the intervertebral region to create a fulcrum effect.

Trial registration

Registered at swissethics: BASEC No.: 2018–00180.

Anterior instrumented fusion for adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional deformity of the spine consisting of a lateral curvature, apical vertebral rotation, and an impairment of the sagittal profile. Surgical options include anterior and posterior approaches. Anterior instrumented fusion is suitable in Lenke type 1 and 5 curves. It supplies excellent results in coronal plane correction and is superior in the restoration of the sagittal profile and apical derotation. Fusion is shorter compared to posterior correction, and the complication rate is low. Pulmonary function is impaired postoperatively but recovers within a few years.

Biomechanical Analysis of Wide Posterior Releases Compared With Inferior Facetectomy and Discectomy in the Thoracolumbar and Lumbar Spine

STUDY DESIGN

In vitro biomechanical analysis.

OBJECTIVES

Compare the destabilizing effects of anterior discectomy to posterior spinal releases.

SUMMARY OF BACKGROUND DATA

Posterior release and pedicle screw fixation has become the accepted form of treatment for lumbar and thoracolumbar pediatric scoliotic spinal deformity. A biomechanical evaluation of posterior releases with comparison to traditional anterior releases has not been reported in the lumbar spine.

METHODS

Eleven fresh-frozen human thoracolumbar specimens (T9-L5) were tested by a robotic manipulator (Staubli RX90; moment target of 5.0 Nm, force target of 50 N) in axial rotation (AR), plus lateral and anterior translation (LT and AT). Specimens underwent either sequential anterior release (partial and full discectomy) or posterior release (inferior facetectomy and wide posterior release) from T10 to L4. Partial discectomy retained the posterior 50% of disc and posterior longitudinal ligament, whereas full discectomy removed all of the disc and PLL. Wide posterior release included total facetectomy plus ligamentum flavum and spinous process resection.

RESULTS

Inferior facetectomy produced an average increase of 1.5° ± 1.0° (p = .0625), 1.0 ± 0.8 mm (p = .0313), and 0.2 ± 0.3 mm (p = .156) in AR, LT, and AT, respectively. Compared with partial facetectomy, wide posterior release produced an average additional increase of 8.1° ± 4.0° (p = .0312), 2.0 ± 2.2 mm (p = .4062), and 1.1 ± 1.0 mm (p = .0625) in AR, LT, and AT, respectively. Full discectomy produced 201%, 161%, and 153% of the motion relative to wide posterior release in AR, LT, and AT, respectively (p = .0043, .0087, and .0173). Partial discectomy and wide posterior release proved statistically equivalent.

CONCLUSIONS

Wide posterior release of the thoracolumbar spine allows significant correction and may be superior to inferior facetectomy in axial rotation. Although complete discectomy with PLL resection would likely allow greater correction, a more clinically realistic partial discectomy confers similar corrective potential in vitro compared with wide posterior release.

LEVEL OF EVIDENCE

Not applicable.

Evolution of Surgery for Adolescent Idiopathic Scoliosis Over 20 Years: Have Outcomes Improved?

STUDY DESIGN

Retrospective review of a prospective adolescent idiopathic scoliosis (AIS) registry.

OBJECTIVE

To study the evolution of the operative approach, outcomes, and complication rates in AIS surgery over the past 20 years.

SUMMARY OF BACKGROUND DATA

Surgical techniques in AIS surgery have evolved considerably over the past 20 years. We study the trends in the operative management of AIS over this period and their impact on perioperative outcomes.

METHODS

A total of 1819 AIS patients (1995-2013) with 2-year F/U were studied. Operative approach, perioperative parameters, major complication rates, and SRS outcomes were assessed. Linear regression was used to assess the trend of changes over 5-year quartiles.

RESULTS

Mean age at surgery was 14.6 ± 2.1 years, 80.2% were females, and this remained consistent throughout. Operative time, EBL/level, and LOS decreased over the 20 years (P < 0.0001). The use of antifibrinolytic (AF) increased from 6.7% to 68.8% in the past 10 years (P < 0.0001). Number of levels fused increased and LIV was more distal (in relation to stable vertebrae) over time in Lenke 1 and 2 curves (levels fused 7.97-9.94, P < 0.0001 and 9.8-11.0, P=0.0134, respectively). Anterior spinal fusion (ASF) in Lenke 1 curves decreased from 81% in the first quartile to 0% in the last (P = 0.0429). ASF for Lenke 5 curves evolved from 78% in the second quartile to 0 in the last. Thoracoplasty performance decreased from 76% to 20.3% (P = 0.1632). All screw constructs in PSF cases increased from 0% to 98.4% (P = 0.0095). Two-year major complication rates decreased over time (18.7%-5.1%; P = 0.0173). Increased improvement in SRS scores were observed in pain, image, function, and total domains.

CONCLUSION

Evolution of surgical technique in AIS over the past 20 years has resulted in a cessation of anterior only surgery, increasing use of all screw constructs, less blood loss, greater use of AF, shorter operative times and LOS, lower major complications rates, and greater improvements in SRS scores.

LEVEL OF EVIDENCE

2.

Spontaneous Thoracic Curve Correction After Selective Posterior Fusion of Thoracolumbar/Lumbar Curves in Lenke 5C Adolescent Idiopathic Scoliosis

Selective fusion of the thoracolumbar/lumbar (TL/L) curve is an effective method for the treatment of Lenke type 5C curves. Several studies have demonstrated that spontaneous correction of the thoracic curve does indeed occur. However, how this correction occurs after isolated posterior segmental instrumentation of the structural lumbar curve has not been well described. The aim of this study was to evaluate the response of the thoracic curve to selective TL/L curve fusion in patients with Lenke type 5C adolescent idiopathic scoliosis (AIS) and assess the correlative clinical outcomes. Thirty-four consecutive patients with Lenke type 5C AIS were included in this study. All patients underwent selective TL/L curve instrumentation and fusion via the posterior approach. Coronal and sagittal radiographs were analyzed before surgery, at 1 week after surgery and at least 2 years after surgery. The preoperative coronal Cobb angle of the major TL/L curve was 45.4° ± 7.0°, and that of the minor thoracic curve was 25.4° ± 8.8°. The major TL/L and minor thoracic curves were corrected to postoperative angles of 9.5° ± 5.0° and 11.2° ± 5.2°, respectively, and measured 10.5° ± 6.0° and 13.4° ± 7.5° at the follow-up, respectively. The supine side-bending average Cobb angle of the thoracic curve was 9.9°. These results demonstrate satisfactory improvements because of coronal and sagittal restoration. Significant correlations were found between the preoperative and early postoperative conditions and the Cobb angle changes of the minor thoracic curve and the major TL/L curves (r = 0.42, P = 0.01). Significant correlations were also observed between the early and final follow-up postoperative conditions and the Cobb angle changes of the minor thoracic curve and the major TL/L curves (r = 0.57, P < 0.001). Significant correlations were observed between increased thoracic kyphosis (TK) and increased lumbar lordosis (LL) in the preoperative and early postoperative conditions (r = 0.36, P = 0.035) and between increased TK and increased LL in the preoperative and final follow-up postoperative conditions (r = 0.51, P = 0.002). Spontaneous correction of the thoracic curve is a reflection of the TL/L curve correction in Lenke 5C AIS patients. Supine side-bending radiographs are an effective method of predicting the spontaneous correction of thoracic curves. The correction of LL is important for maintaining spinal sagittal alignment.

Evaluation of idiopathic scoliosis by anterior and posterior arthrodesis

<sec><title>OBJECTIVE:</title><p> To evaluate comparatively surgical treatment of adolescent idiopathic scoliosis type 5CN by anterior and posterior approach.</p></sec><sec><title>METHODS:</title><p> The study consists of a comparative retrospective study of two groups of patients with the thoracolumbar spine arthrodesis technique by anterior and posterior approach. Twenty and two patients were sequentially selected, 11 operated by anterior approach - called Group I - and 11 by posterior approach - Group II. Anamnesis and physical examination were performed, as well as length of hospital stay and ICU stay, degree of correction, comorbidities and pre and postoperative radiographic images data were gathered.</p></sec><sec><title>RESULTS:</title><p> The mean age was 13.7 years in Group I and 14 years in Group II. The average hospital stay was 5.81 days for Group I and 5 for Group II. The average ICU stay was 2.81 and 2 days, respectively. Considering the operated levels, Group I presented an average of 4.81 vertebrae (4-6 levels), and Group II presented an average of 6.36 vertebrae (5-11 levels). Complications did not show statistically significant difference.</p></sec><sec><title>CONCLUSION:</title><p> Despite the limited number of patients in groups, it was demonstrated that the posterior approach reduces the number of days of hospitalization and ICU stay. However, it was found increased levels included in the arthrodesis.</p></sec>

Determination of the distal fusion level in the management of thoracolumbar and lumbar adolescent idiopathic scoliosis using pedicle screw instrumentation

Study Design

A retrospective study.

Purpose

To determine the exact distal fusion level in the management of thoracolumbar/lumbar adolescent idiopathic scoliosis (TL/L AIS) using pedicle screw instrumentation (PSI).

Overview of Literature

The selection of distal fusion level remains controversial in TL/L AIS.

Methods

Radiographic parameters of 66 TL/L AIS patients were analyzed. The patients were grouped according to the distal fusion level; L3 group (fusion to L3, n=58) and L4 group (fusion to L4, n=8). The L3 group was subdivided into L3A (L3 crosses the mid-sacral line with rotation of less than grade II, n=33) and L3B (L3 does not cross the mid-sacral line or rotation is grade II or more, n=25) based on both bending radiographs. All of the patients in the L4 group had the same location and rotation of L3 in bending films as that of patients in the L3B group. An unsatisfactory result was defined as a lowest instrumented vertebral tilt (LIVT) of more than 10° or coronal balance of more than 15 mm.

Results

Among the 3 groups, there was a significantly lesser correction in the TL/L curve and LIVT in the L3B group. Unsatisfactory results were obtained in 3 patients (9.1%) of the L3A group, in 15 patients (68.2%) of the L3B group, and in 1 patient (12.5%) of the L4 group with a significant difference.

Conclusions

In TL/L AIS treatment with PSI, the curve can be fused to L3 with favorable radiographic outcomes when L3 crosses the mid-sacral line with rotation of less than grade II in bending films. Otherwise, fusion has to be extended to L4.

Adolescent scoliosis classification and treatment

Adolescent idiopathic scoliosis (AIS) affects up to 3% of the population. It can be stratified by curve type according to the Lenke classification. This classification system incorporates curve magnitude, flexibility, the lumbar modifier, and the sagittal plane. The Lenke classification serves as a guide for selection of levels for surgical treatment of AIS. Surgical treatment of AIS includes anterior and posterior approaches; most AIS is treated through a posterior approach. Surgical goals include maximizing correction in the coronal, sagittal, and axial planes.

Posterior pedicle screws combined with shortening and release techniques for lumbar and thoracolumbar adolescent idiopathic scoliosis

OBJECTIVE

To prospectively evaluate the clinical and radiographic effects of posterior surgery with wide posterior shortening release and segmental pedicle screws techniques in a consecutive group of patients with thoracolumbar /lumbar adolescent idiopathic scoliosis.

METHODS

Between April 2002 and July 2005, 114 patients (86 women and 28 men) were enrolled in this study. There were 72 Lenke type 5, 32 Lenke type 6, and 10 Lenke type 3C curves. Radiographic parameters such as coronal plane Cobb angle; lordosis angle; lowest instrumented vertebrae (LIV) angulation; and the distances from the central sacral vertical line (CSVL) to the LIV, to the apical vertebra and to the C7 plumb line, were analyzed. Complication rates were also recorded during follow-up.

RESULTS

The average coronal correction was from 61° to 13° (78.6%). In the sagittal plane, lumbar lordosis was normalized from 36° with a wide range (23°-67°) to 42° with a normal range (34°-55°). The LIV had 79% correction of coronal angulations. The center sacral line to LIV was improved from 2.3 cm to 0.5 cm, apex to center sacral line from 5.0 cm to 1.6 cm, and CSVL from 2.7 cm to 0.8 cm. A total of 1460 pedicle screws were placed safely, average 9.6 levels (5-14) were fused. The patients were followed up for an average of 30 months (range, 12-50). There was excellent maintenance of correction at final follow-up.

CONCLUSION

Wide posterior release and segmental pedicle screw instrumentation has excellent radiographic and clinical results with minimal complications.

Long-term outcomes of anterior spinal fusion with instrumentation for thoracolumbar and lumbar curves in adolescent idiopathic scoliosis

STUDY DESIGN

A retrospective review of the long-term clinical and radiographic outcomes of anterior spinal fusion with instrumentation for thoracolumbar and lumbar curves in adolescent idiopathic scoliosis (AIS).

OBJECTIVE

To evaluate a group of patients based on Scoliosis Research Society (SRS)-30 and Oswestry data as well as radiographic and magnetic resonance imaging (MRI) and report the results of long-term follow-up of this surgical treatment for this particular curve pattern in AIS.

SUMMARY OF BACKGROUND DATA

Anterior spinal fusion with instrumentation has been used for many years in the treatment of thoracolumbar and lumbar curves in AIS. However, the long-term radiographic and functional outcomes of this procedure are not well known.

METHODS

During 1984 to 1995, 31 patients with the diagnosis of AIS underwent anterior spinal instrumentation and fusion for thoracolumbar or lumbar scoliosis at our institution. A retrospective review of this patient group was performed to evaluate patient satisfaction, functional outcome, curve progression, implant failure, and disc degeneration. Radiographs and lumbar MRIs were obtained along with SRS-30 Questionnaire and Oswestry Disability Index data.

RESULTS

Eighteen patients were available for review. Average follow-up for this study was 16.97 years. Based on SRS-30 and the Oswestry Disability Index data, most patients had good function scores and acceptable pain levels. Radiographs demonstrated no progression of the thoracolumbar or thoracic curves. Implant failure was identified in 2 patients. Radiographic changes of early degenerative disc disease were identified in most patients but had no correlation with SRS or Oswestry data. These degenerative changes were evident on both radiographs and MRI.

CONCLUSION

The anterior approach in the treatment of thoracolumbar and lumbar curves in AIS offers good long-term functional outcomes for patients. Despite expected degenerative changes, patients scored well on the SRS and Oswestry tests, and were able to pursue careers and family activities.

Comparison of surgical treatment in Lenke 5C adolescent idiopathic scoliosis: anterior dual rod versus posterior pedicle fixation surgery: a comparison of two practices

STUDY DESIGN

Multicenter analysis of 2 groups of patients surgically treated for Lenke 5C adolescent idiopathic scoliosis (AIS).

OBJECTIVE

Compare patients with Lenke 5C scoliosis surgically treated with anterior spinal fusion with dual rod instrumentation and anterior column support with patients surgically treated with posterior release and pedicle screw instrumentation.

SUMMARY OF BACKGROUND DATA

Treatment of single, structural, lumbar, and thoracolumbar curves in patients with AIS has been the subject of some debate. Advocates of the anterior approach assert that their technique spares posterior musculature and may save distal fusion levels, and that with dual rods and anterior column support the issues with nonunion and kyphosis have been obviated. Advocates of the posterior approach assert that with the change to posterior pedicle screw based instrumentation that correction and levels are equivalent, and the posterior approach avoids the issues with nonunion and kyphosis. This report directly compares the results of posterior versus anterior instrumented fusions in the operative treatment of adolescent idiopathic Lenke 5C curves.

METHODS

We analyzed 62 patients with Lenke 5C based on radiographic and clinical data at 2 institutions: 31 patients treated with posterior, pedicle-screw instrumented fusions at 1 institution (group PSF); and 31 patients with anterior, dual-rod instrumented fusions at another institution (group ASF). Multiple clinical and radiographic parameters were evaluated and compared.

RESULTS

The mean age, preoperative major curve magnitude, and preoperative lowest instrumented vertebral (LIV) tilt were similar in both groups (age: PSF = 15.5 years, ASF = 15.6 years; curve size: PSF = 50.3 degrees +/- 7.0 degrees , ASF = 49.0 degrees +/- 6.6 degrees ; LIV tilt: PSF = 27.5 degrees +/- 6.5 degrees , ASF = 27.8 degrees +/- 6.2 degrees ). After surgery, the major curve corrected to an average of 6.3 degrees +/- 3.2 degrees (87.6% +/- 5.8%) in the PSF group, compared with 12.1 degrees +/- 7.4 degrees (75.7% +/- 14.8%) in the ASF group (P < 0.01). At final follow-up, the major curve measured 8.0 degrees +/- 3.0 degrees (84.2% +/- 5.8% correction) in the PSF group, compared with 15.9 degrees +/- 9.0 degrees (66.6% +/- 17.9%) in the ASF group (P = 0.01). This represented a loss of correction of 1.7 degrees +/- 1.9 degrees (3.4% +/- 3.7%) in the PSF group, and 3.8 degrees +/- 4.2 degrees (9.4% +/- 10.7%) in the ASF group (P = 0.028). The LIV tilt decreased to 4.1 degrees +/- 3.4 degrees after surgery in the PSF group, and 4.5 degrees +/- 3.7 degrees in the ASF group. At final follow-up, the LIV tilt was 5.1 degrees +/- 3.5 degrees in the PSF group, and 4.5 degrees +/- 3.7 degrees in the ASF group. EBL was identical in both groups, and length of hospital stay was significantly (P < 0.01) shorter in the PSF group (4.8 vs. 6.1 days). There were no complications in either group which extended hospital stay or required an unplanned second surgery.

CONCLUSION

At a minimum of 2-year follow-up, adolescents with Lenke 5C curves demonstrated statistically significantly better curve correction, less loss of correction over time, and shorter hospital stays when treated with a posterior release with pedicle screw instrumented fusion compared with an anterior instrumented fusion with dual rods for similar patient populations.

Anterior arthrodesis with instrumentation for thoracolumbar scoliosis: comparison of efficacy in adults and adolescents

STUDY DESIGN

A retrospective review was performed of adult and adolescent patients who underwent anterior spinal fusion for thoracolumbar idiopathic scoliosis; radiographic and clinical outcomes were compared.

OBJECTIVE

The objective of this study was to compare the efficacy of anterior instrumentation to treat thoracolumbar scoliosis in adults and adolescents by evaluating radiographic and clinical outcomes.

SUMMARY OF BACKGROUND DATA

Anterior spinal arthrodesis is an effective treatment for idiopathic scoliosis. Deformity characteristics and clinical outcomes of adults versus adolescents have not been compared.

METHODS

A retrospective review of patients undergoing anterior fusion for thoracolumbar scoliosis was performed. Clinical outcomes were assessed using SRS-22. Preoperative and postoperative long films were evaluated independently. Flexibility, curve correction, and clinical outcomes were compared between adult and adolescents.

RESULTS

Fifteen adults and 15 adolescents who underwent anterior spinal fusion and instrumentation were evaluated. Mean follow-up was 47 and 46 months, respectively. Flexibility of the major curve in adults (63%) was less than in adolescents (79%) (P < 0.05). Mean preoperative, major curve Cobb angles were 51 degrees and 49 degrees for adults and adolescents, respectively. Mean postoperative Cobb angles improved less for adults (17 degrees ) than for adolescents (10 degrees ) (P < 0.05). The SRS-22 questionnaire revealed no statistical difference between populations.

CONCLUSION

Anterior spinal fusion is an option for both adults and adolescents with flexible, moderate thoracolumbar/lumbar curves. Flexibility significantly decreased with increased age and curve magnitude. This significantly affected curve correction. Adult patients may develop early degeneration at primary curve and compensatory curves. Careful patient selection is critical with this technique.

Blood loss in pediatric spine surgery

This article reviews the extent of blood loss in spine surgery for scoliosis corrections in the pediatric age group. An extensive literature review presents blood loss values in surgery for adolescent idiopathic scoliosis, cerebral palsy, Duchenne muscular dystrophy, spinal muscular atrophy, and myelomeningocoele. The underlying disorder plays a major role in determining the extent of blood loss. Blood loss is considerably higher in those patients with a neuromuscular scoliosis compared with adolescent idiopathic scoliosis. Within the neuromuscular group those with Duchenne muscular dystrophy demonstrate the highest mean levels of blood loss. Blood loss is also shown to be progressively greater with increasing numbers of vertebral levels incorporated into the fusion, with posterior fusions compared to anterior fusions, and in those patients having both anterior and posterior fusions.

The posterior approach for lumbar and thoracolumbar adolescent idiopathic scoliosis: posterior shortening and pedicle screws

STUDY DESIGN

Prospective clinical case series.

BACKGROUND DATA

Lumbar and thoracolumbar adolescent idiopathic scoliosis has traditionally been treated with an anterior approach and instrumentation. This anterior method often has had problems with kyphosis, pseudarthrosis, and loss of correction. The senior author has had good results treating these same lumbar and thoracolumbar curves posteriorly with wide posterior release and segmental instrumentation. In this series of his evolving technique, he adds pedicle screws as the sole anchor in the thoracolumbar/lumbar curves.

OBJECTIVES

To prospectively evaluate outcomes, coronal and sagittal radiographic results, balance parameters, complications, and reoperations in a group of consecutive patients with lumbar and thoracolumbar adolescent idiopathic scoliosis. These patients were surgically treated with wide posterior release and segmental posterior screw instrumentation with 2-year minimum follow-up (range 26-47 months).

METHODS

Sixty-two consecutive patients with thoracolumbar and lumbar adolescent idiopathic scoliosis were treated with a wide posterior release and segmental pedicle screw instrumentation limited to the curve defined by the Cobb measurement. The patients were evaluated clinically and radiographically at intervals up to 36 months. There was 2-year minimum follow-up.

RESULTS

One patient was lost to follow-up. Of the remaining 61 patients, there were 51 Lenke 5 Type curves, 7 Lenke Type 3C curves, and 3 Lenke Type 6 curves. Only the curve defined by the Cobb measurement was fused. A total of 613 pedicle screws were placed safely. Average coronal correction of the thoracolumbar/lumbar curves was from 52 degrees to 10 degrees (80%). In the sagittal plane, lumbar lordosis was normalized from 41 degrees with a wide range (20 degrees -70 degrees ) to 42 degrees with a normal range (34 degrees -47 degrees ). There were no pseudoarthroses, no reoperations, no infections, no problems with screw placement, and excellent maintenance of correction at last follow-up. The lowest instrumented vertebrae had 81% correction of coronal angulation, center sacral line to lowest instrumented vertebrae was improved from 2.4 cm to 0.7 cm, and apex to center sacral line was improved from 5.2 cm to 1.5 cm. The C7 plumb line to center sacral line was also improved from 2.5 cm to 0.6 cm, illustrating the centering of the trunk.

CONCLUSIONS

Wide posterior release and segmental pedicle screw instrumentation has excellent radiographic and clinical results with minimal complications. There were no pseudoarthroses and no reoperations.

Anterior single rod instrumentation for thoracolumbar adolescent idiopathic scoliosis with and without the use of structural interbody support

STUDY DESIGN

A radiographic and clinical outcomes analysis of 41 patients treated for thoracolumbar adolescent idiopathic scoliosis utilizing a single anterior rigid rod construct.

OBJECTIVES

To evaluate the necessity of structural interbody support to improve primary curve correction and preserve or augment lordosis when used in conjunction with a single anterior rigid rod construct, to identify parameters that predict horizontalization of the lowest instrumented vertebra, adjacent disc angulation, and distal uninstrumented vertebrae, and to assess patient satisfaction following surgery.

BACKGROUND DATA

Instrumentation-induced kyphosis has been a concern with nonrigid anterior systems used in the past for the treatment of scoliosis. Interbody structural support has been recommended to maintain appropriate sagittal profile when anterior systems are utilized. It has also been suggested that the use of structural interbody support creates a fulcrum to increase curve correction when compression is applied to the convexity of the deformity. However, the necessity of interbody structural support when used in conjunction with a rigid anterior system has not been previously evaluated in patients with adolescent idiopathic scoliosis.

MATERIALS AND METHODS

Forty-one patients mean age 15.9 years (range 12.1-18.6 years) with thoracolumbar adolescent idiopathic scoliosis underwent anterior spinal fusion using a single 6.0 to 6.5 mm solid rod construct between June 1995 and August 1999 performed by the senior author (T.G.L.). Four additional patients with thoracolumbar curves with similar anterior instrumentation over the same time period were lost to follow-up or had incomplete records and were not included in the study. Structural interbody support was used in 21 patients and packed morselized autograft alone was used in 20 patients. The patients in the group with packed morselized bone alone generally underwent surgery earlier in the series before the author began using structural interbody support on a regular basis. Each patient had a minimum follow-up of 3 years. Preoperative, initial, and most recent (>3 years) follow-up radiographs were reviewed to determine in each group Cobb angle measurements, flexibility of primary, secondary, and fractional curves, apical and end vertebral translation, lowest instrumented vertebral and caudal disc angulation, global coronal and sagittal balance, and sagittal Cobb measurements in both instrumented levels as well as lumbar lordosis (T12-S1). In addition, the SRS outcomes instrument was completed by 38 of 41 patients.

RESULTS

The mean preoperative primary curve in patients with structural support was 47 degrees (Group II) and 45 degrees in patients without structural support (Group I). Mean curve correction was to 13 degrees in Groups I and II. One patient in Group II became slightly more unbalanced at final follow-up; otherwise all were improved after surgery. Sagittal measurements over instrumented segments as well as total lumbar lordosis (T12-S1) was maintained between preoperative and final postoperative values in both groups. Similarly, in both groups, when horizontalization of the distal end instrumented vertebra was achieved on the preoperative reverse side-bending radiograph, more normal relationships were achieved between instrumented and distal noninstrumented segments (adjacent disc angulation and fractional lumbar curve) at final follow-up (P <or= 0.01). Patients in both groups were equally pleased with their clinical outcomes based on the SRS outcomes instrument.

CONCLUSIONS

The use of interbody structural support does not appear to be necessary to maintain an appropriate sagittal profile or to maximize coronal curve correction when a rigid rod construct with packed morselized bone is used for the treatment of thoracolumbar adolescent idiopathic scoliosis. Parameters predicting horizontalization of the lower instrumented vertebra and uninstrumented segments below the construct were identified, which, if achieved, should predict an optimal long-term outcome. Clinical outcomes were very good in both groups.

Anterior thoracolumbar instrumentation: stiffness and load sharing characteristics of plate and rod systems

STUDY DESIGN

An in vitro biomechanical study using a thoracolumbar corpectomy model to compare load sharing capabilities and stiffnesses of six different anterior instrumentation systems (three rod styles and three plate styles) for stabilizing the thoracic and lumbar spine.

OBJECTIVES

To evaluate the axial load sharing capabilities of the instrumentation in a thoracolumbar corpectomy model and to measure the bending stiffness of the anterior instrumentation systems for the axes of flexion-extension, lateral bending, and axial rotation with and without an anterior column graft in place.

SUMMARY OF BACKGROUND DATA

Prior publications have analyzed biomechanical characteristics of many spinal instrumentation systems. These reports have compared anterior instrumentation systems with posterior instrumentation systems, in situ fusion techniques, intervertebral spacers, structural allograft and instrumentation, and combined anterior and posterior instrumentation. Other reports have published data on the biomechanical characteristics of typical anterior and posterior spinal instrumentation systems. However, there are no published reports that specifically compare the characteristics of anterior plate-style with anterior rod-style systems, or examining load sharing capabilities.

METHODS

Six constructs of each of six instrumentation systems were mounted on simulated vertebral bodies. A custom four-axis spine simulator was used to apply independent flexion-extension, lateral bending, and axial rotation moments as well as axial compressive loads. Axial load sharing was measured through a range of applied axial loads from 50 N to 500 N with rotational moments maintained at 0 Nm. The bending stiffness of each construct was calculated in response to +/-5.0 Nm moments about each axis of rotation with a 50 N compressive axial load with a full-length corpectomy graft in place, simulating reconstruction of the anterior column, and with no graft in place, simulating catastrophic graft failure. Statistical significance was determined using an analysis of variance and Fisher PLSD post hoc test with an alpha <or= 0.05.

RESULTS

Load sharing results ranged from 63% to 89%. There was an inverse relationship between load sharing and stiffness. No correlation was found between load sharing and implant style (rod vs. plate). With the graft in place, stiffness result varied by instrumentation system rather than by plate/rod style. Without the graft, the stiffness of the constructs decreased approximately one-third in flexion-extension, two-thirds in lateral bending, and one-fifth in axial rotation, underlying the importance of the graft in overall construct stiffness.

CONCLUSIONS

For both load sharing and stiffness, there is more influence from the design of the instrumentation system, than whether it is a plate or rod style system. The graft contributed to overall construct stiffness, particularly in lateral bending.

Dual-rod correction and instrumentation of idiopathic scoliosis with the Halm-Zielke instrumentation

STUDY DESIGN

A prospective clinical and radiographic evaluation of 45 consecutive patients with idiopathic adolescent and adult scoliosis treated with anterior dual-rod Halm-Zielke instrumentation.

OBJECTIVES

Clinical and radiographic evaluation with a minimum follow-up of 2 years.

SUMMARY OF BACKGROUND DATA

Halm-Zielke instrumentation was developed to eliminate the disadvantages of Zielke instrumentation in terms of lack of primary stability and a kyphogenic effect.

METHODS

All patients underwent an identical anterior surgical technique with the Halm-Zielke instrumentation of the primary curve. The system is composed of a lid-plate, which is fixed to the lateral aspect of the vertebral body with two screws: a sunk screw anteriorly and a ventral derotation spondylodesis (VDS) screw posteriorly. The lid-plate design provides the lowest possible implant profile. The longitudinal components consist of a threaded rod and a solid, fluted rod. Correction is performed with both the threaded and the solid rod. The solid rod allows derotation and correction of the sagittal plane and provides primary stability.

RESULTS

Preoperative curves ranged from 35 degrees to 92 degrees Cobb angle. Final correction of the frontal plane averaged 67% within the instrumented levels and 59% for the total primary curve. The apical vertebral rotation of the primary curve was corrected by 52% on average without loss of correction during follow-up. Thoracolumbar kyphosis was present in 11 patients and corrected in all cases from an average of 20 degrees to 2 degrees after surgery and to 8 degrees at follow-up. We observed two cases of implant failure with one resulting in a pseudarthrosis.

CONCLUSION

Halm-Zielke instrumentation proved to be a major improvement of the original VDS-Zielke. It eliminates the kyphogenic effect and provides primary stability.

Selective anterior fusion of thoracolumbar/lumbar curves in adolescents: when can the associated thoracic curve be left unfused?

STUDY DESIGN

A retrospective multicenter study was conducted to investigate patients with a major thoracolumbar/lumbar adolescent idiopathic scoliosis and an associated minor thoracic curve treated with an anterior instrumentation and fusion of the lower curve.

OBJECTIVE

To establish criteria for determining when such curves can be successfully treated by an anterior only procedure of the lower curve with acceptable spinal balance and residual thoracic curve.

SUMMARY OF BACKGROUND DATA

Anterior spinal instrumentation techniques have been proved effective for the management of isolated thoracolumbar/lumbar scoliosis with small compensatory thoracic curves. The success of a selective anterior fusion when the associated thoracic curve had some structural changes in a small preliminary study was variable and was the stimulus for this study.

METHODS

A multicenter study involved 49 adolescent patients with a major thoracolumbar/lumbar curve in which the associated minor thoracic curve measured between 30 degrees and 55 degrees. In all the patients, the apical vertebra of the lower curve lay outside the midsacral line, and the thoracic apical vertebra fell outside a line dropped from the center of C7. Multiple radiographic parameters were evaluated. The Risser sign, height, weight, onset of menses, and closure of the triradiate cartilages were studied to access the patients' maturity. All the patients were observed at least 2 years. Patients were considered to have a satisfactory result if the thoracic curve at the final follow-up assessment measured 40 degrees or less, if balance and sagittal alignment were reasonable, and if additional procedures were not required.

RESULTS

At final follow-up assessment, two groups emerged. Group 1 (n = 43) had satisfactory results. The preoperative thoracic curve in this group averaged 40 degrees and 26 degrees after surgery. The lumbar curve averaged 56 degrees before surgery and 22 degrees after surgery. Group 2 (n = 6) had unsatisfactory results. The average thoracic curve was 49 degrees before surgery 54 degrees after surgery, whereas the lumbar curve averaged 59 degrees before surgery and 27 degrees after surgery. Three of these patients underwent posterior thoracic instrumentation and fusion.

CONCLUSIONS

Statistical analysis showed that a successful surgical outcome was dependent on both the structural changes in the thoracic curve and the patient's maturity. The thoracolumbar/lumbar-thoracic (TL/L:T) Cobb ratio in combination with the degree of the thoracic curve on lateral bending was the best predictor among the structural indexes. Of 44 patients with a TL/L:T Cobb ratio of 1.25 or greater and/or a thoracic curve, which bent out to 20 degrees or less, 42 had a satisfactory result. The best predictor among the maturity indexes was closure of the triradiate cartilages. Of 43 patients in whom the triradiate cartilages were closed, 42 had satisfactory results. When this data is combined, the outcome for the thoracic curve can be reasonably predicted.

Supplementation of autogenous bone graft with coralline hydroxyapatite in posterior spine fusion for idiopathic adolescent scoliosis

Twenty-seven consecutive patients with adolescent idiopathic scoliosis underwent posterior spinal fusion with pediatric Texas Scottish Rite Hospital instrumentation. Coralline hydroxyapatite (Interpore, Irvine, Calif) was mixed with limited autograft from posterior iliac crest (an approximate 70/30 ratio of coralline hydroxyapatite to autograft). Patient evaluation was based on clinical and radiographic findings. On initial radiographic evaluation, a "snowstorm" appearance consistent with the exoskeleton of the coralline hydroxyapatite was observed. After two years, the fusion mass had a "marble-like" appearance with distinct decreased visibility of the disk spaces in the fusion mass. This latter stage of "marbilization correlated with solid fusion clinically. All patients achieved solid fusion at an average follow-up of 27 months. Coralline hydroxyapatite is safe, biocompatible, and effective in augmenting autogenous bone graft in the treatment of idiopathic adolescent scoliosis with posterior spinal fusion. In addition to decreased donor site morbidity, this may be invaluable in cases where there is insufficient autograft available.

The use of interbody cage devices for spinal deformity: a biomechanical perspective

Spinal instrumentation has revolutionized the treatment of spinal deformities and offers a plethora of techniques and designs to surgically treat deformity conditions. The authors address the biomechanical properties afforded by various posterior and anterior spinal instrumentation mechanisms, with and without intervertebral reconstruction, and the principles associated with optimal reconstruction techniques. The integration of multiple strategies can improve anterior and posterior construct stiffness in the treatment of spinal deformities. Structural interbody support probably is the best method to minimize longitudinal rod and screw-bone interface strain. Moreover, anterior load-bearing structural grafts and interbody devices have been shown to increase construct stiffness, decrease the incidence posterior implant failure, permit the use of smaller diameter longitudinal rods, and may enhance the rate of successful spinal arthrodesis. From a biomechanical standpoint, treatment of medium to high-grade spondylolisthesis with stand-alone interbody or transvertebral cages, in the absence of supplemental posterior fixation, is contraindicated. Collectively, the included studies reinforce the principles of load sharing between the anterior and posterior spinal columns and affirm the biomechanical dominance of anterior column support in circumferential spinal arthrodesis.

Mesh cages in idiopathic scoliosis in adolescents

Since 1995, titanium mesh cages have been used in the thoracolumbar and lumbar spine for instrumented anterior spinal fusions in adolescents with idiopathic scoliosis. One hundred thirty patients had 451 fusion levels with cages. Radiographic results show acceptable coronal correction with maintained or improved thoracolumbar and lumbar lordotic sagittal alignment. The pseudarthrosis rate has been 3% per patient (four of 130 patients) and 0.08% per fusion level with a cage (four of 451 levels). The authors think that the use of titanium mesh cages anteriorly with single or dual rod anterior instrumentation systems provide for adequate lordotic sagittal alignment and an acceptable pseudarthrosis rate.