Radiographic results of arthrodesis with Cotrel-Dubousset instrumentation for the treatment of adolescent idiopathic scoliosis. A five to ten-year follow-up study

Trends in Medical Costs for Adolescent Idiopathic Scoliosis Surgery in Japan

STUDY DESIGN

A retrospective review of clinical data and costs was performed for surgeries for adolescent idiopathic scoliosis (AIS) conducted from 2008 to 2017.

OBJECTIVE

Cost containment and healthcare value have become focal points in Japanese health care policy. The purpose of the study was to investigate trends over time in medical costs for surgery for AIS.

METHODS

A total of 83 patients underwent surgery for AIS from 2008 to 2017 at our hospital. Clinical data and length of stay were collected, and medical costs for surgery, local bone grafting, fees per day, and surgical instruments were evaluated.

RESULTS

There were slight year-by-year decreases in fees per day and decreases in costs of surgical instruments. The average length of stay was 16.4 days and gradually decreased over time. In contrast, scoliosis surgery costs increased about 1.6 times in 10 years from $9515 to $15 130.

CONCLUSION

The trends for decreases in fees per day and prices for surgical instruments reflect recent government medical cost control policies. The cost for scoliosis surgery is also defined by the government, and the increase over 10 years may reflect the perspective of valuing effective and advanced surgeries. This study of cost trends of operative spinal intervention provides an assessment of surgical benefit and is likely to influence health care costs.

What are normal radiographic spine and shoulder balance parameters among adolescent patients?

STUDY DESIGN

Retrospective.

OBJECTIVES

To define normal values and distributions for sagittal, coronal, and shoulder balance among healthy adolescents, both for traditional radiographs and biplanar radiography. Our understanding of spine balance, especially in the sagittal plane, has expanded rapidly in recent years. Additionally, there has been growing use of simultaneous biplanar radiography which requires slightly different patient positioning. However, the normal ranges of several commonly used parameters have not yet been defined, either in traditional or biplanar radiography.

METHODS

Radiographs were retrospectively reviewed of 273 patients aged 10-18 years seen in spine clinics at two high-volume centers and not diagnosed with any spine pathology. One center utilized traditional radiography and the other biplanar radiography. Coronal, sagittal, and shoulder balance were measured for each patient. Intra-observer reliability and normal values with distributions were reported for each parameter.

RESULTS

Intra-observer reliability was excellent (intra-class correlation coefficients ≥ 0.98). Each parameter was normally distributed at each institution based on Kolmogorov-Smirnov testing. Sagittal balance was more negative at the institution using traditional radiographs (- 3.4 ± 4.2 vs. 0.3 ± 2.2, p < 0.001). Coronal balance was statistically, but not clinically, significantly more negative at this institution (- 0.6 ± 1.4 vs. - 0.2 ± 1.0, p = 0.007). Shoulder balance was not different between institutions. The "normal" ranges (mean ± 2 standard deviations, i.e., expected to include 95% of patients) were - 2.8 to 2.0 cm for coronal balance, - 9.0 to 6.1 cm for sagittal balance, and - 1.5-2.4 cm for shoulder balance.

CONCLUSIONS

In adolescents without known spine pathology, the mean coronal, sagittal, and shoulder balance is near neutral, but each parameter varies over a large range; so the average patient deviates from neutral by 1.0 ± 0.7 cm, 3.1 ± 2.6 cm, and 0.9 ± 0.7 cm, respectively. The most important difference between biplanar and traditional radiographs was a significantly more negative sagittal balance in the biplanar group which may be attributable to arm positioning.

LEVEL OF EVIDENCE

Level III.

SRS-22r Scores in Nonoperated Adolescent Idiopathic Scoliosis Patients With Curves Greater Than Forty Degrees

STUDY DESIGN

Case control comparative series.

OBJECTIVE

Describe surgical range adolescent idiopathic scoliosis (AIS) patients electing to forgo surgery and compare health-related quality-of-life outcomes to a similar cohort of operated AIS patients by the same single surgeon.

SUMMARY OF BACKGROUND DATA

No data have been published either documenting SRS-22r scores of nonoperated patients with curves ≥40° or comparing these scores to a demographically similar operated cohort.

METHODS

Individuals with curves ≥40°, age ≥18 years, and electing to forgo surgery were identified. All patients completed an SRS-22r questionnaire. This nonoperated cohort's SRS-22r scores were compared to those of a large demographically similar cohort operated by the same surgeon. Group differences between the SRS-22r scores were evaluated by comparing these to published Minimal Clinically Important Differences (MCID) for the SRS-22r.

RESULTS

One hundred ninety subjects with nonoperated curves were compared to 166 individuals who underwent surgery. The nonoperated cohort averaged 23.5 years of age, averaged 7.7 years since curve reached 40°, and had an average 50° Cobb angle at last follow-up. No statistical significant differences were found between the groups on the Pain, Function, or Mental Health domains of the SRS-22r. Statistically significant differences in favor of the operative cohort were found for self-image, satisfaction, and total score. The observed group differences did not meet the established thresholds for minimal clinically important differences in any of the domain scores, the average total score, or raw scores.

CONCLUSION

There are no meaningful clinically significant differences in SRS-22r scores at average 8-year follow-up between AIS patients with curves ≥40° treated with or without surgery. These data in conjunction with an absence of long-term evidence of serious medical consequences with nonsurgical management of curves ≥40° should encourage surgeons to reevaluate the benefits of routine surgical care.

LEVEL OF EVIDENCE

3.

Selection of the Lowest Level for Fusion in Adolescent Idiopathic Scoliosis-A Systematic Review and Meta-Analysis

STUDY DESIGN

A systematic review of studies reporting pain as a long-term outcome after spinal fusion surgery for treatment of adolescent idiopathic scoliosis.

OBJECTIVE

To identify studies that report pain after spinal fusion surgery for scoliosis based on the distal extent of fusion and to combine results to determine if there is an increased incidence of back pain in patients treated with fusion to the lower lumbar spine.

SUMMARY OF BACKGROUND DATA

The methods and results of existing studies are inconsistent and only occasionally reach statistical significance. No thorough review of the available information has been published.

METHODS

An electronic literature search was performed to identify studies that met predetermined eligibility criteria. Data extracted included number of cases fused to L3 or above, to L4 or L5, and the number of those cases experiencing pain. Further, when possible, the pain variable was stratified into severe or mild categories to allow a more specific subanalysis.

RESULTS

Eight studies met inclusion criteria. The meta-analysis for occurrence of pain, the primary outcome, resulted in a final odds ratio of 1.29 (95% CI 0.91-1.82, n = 1,155). When pain was stratified according to severity and only those cases in the severe category considered for meta-analysis, the resulting odds ratio was 1.43 (95% CI 0.72-2.82, n = 900). Neither analysis reached statistical significance.

CONCLUSIONS

Although there was a trend toward increased pain in patients whose fusion extended to L4 or L5, there was no statistically significant association between the distal level of fusion and incidence of subsequent back pain, both with and without stratification according to severity of back pain. Because of the limitations of published research, the effect of fusion into the lower lumbar spine on back pain is unknown. Higher quality studies with long-term follow-up and consistent reporting of outcomes are needed.

Predicting operative blood loss during spinal fusion for adolescent idiopathic scoliosis

BACKGROUND

Patient and surgical factors are known to influence operative blood loss in spinal fusion for adolescent idiopathic scoliosis (AIS), but have only been loosely identified. To date, there are no established recommendations to guide decisions to predonate autologous blood, and the current practice is based primarily on surgeon preference. This study is designed to determine which patient and surgical factors are correlated with, and predictive of, blood loss during spinal fusion for AIS.

METHODS

Retrospective analysis of 340 (81 males, 259 females; mean age, 15.2 y) consecutive AIS patients treated by a single surgeon from 2000 to 2008. Demographic (sex, age, height, weight, and associated comorbidities), laboratory (hematocrit, platelet, PT/PTT/INR), standard radiographic, and perioperative data including complications were analyzed with a linear stepwise regression to develop a predictive model of blood loss.

RESULTS

Estimated blood loss was 907±775 mL for posterior spinal fusion (PSF, n=188), 323±171 mL for anterior spinal fusion (ASF, n=124), and 1277±821 mL for combined procedures (n=28). For patients undergoing PSF, stepwise analysis identified sex, preoperative kyphosis, and operative time to be the most important predictors of increased blood loss (P<0.05). For ASF, the mean arterial pressure at incision and the operative time were predictive (P<0.05). The following formula was developed to estimate blood loss in PSF: blood loss (mL)=C+Op-time (min)×(6.4)-pre-op T2-T12 kyphosis (degrees)×(8.7), C=233 if male and -270 if female.

CONCLUSION

We find sex, operative time, and preoperative kyphosis to be the most important predictors of increased blood loss in PSF for AIS. Mean arterial pressure and operative time were predictive of estimated blood loss in ASF. For posterior fusions, we also present a model that estimates blood loss preoperatively and can be used to guide decisions regarding predonation of blood and the use of antifibrinolytic agents.

LEVEL OF EVIDENCE

Retrospective study: Level II.

Outcomes Following Posterior Fusion for Adolescent Idiopathic Scoliosis With and Without Autogenous Iliac Crest Bone Graft Harvesting

STUDY DESIGN

Retrospective.

SUMMARY OF BACKGROUND DATA

There is continued controversy regarding the morbidity associated with harvesting iliac crest bone graft (ICBG). More important, its effect on clinical outcomes is poorly understood.

OBJECTIVES

The purpose of this study was to determine whether harvesting ICBG affects clinical outcomes after posterior instrumented fusion in patients with adolescent idiopathic scoliosis (AIS).

METHODS

We identified patients enrolled in a prospective, multicenter database of patients with AIS who had posterior instrumented fusion with complete preoperative and 2-year postoperative Scoliosis Research Society (SRS)-22R data. Patients who had a previous fusion, thoracoplasty, or anterior surgery were excluded. We classified patients into 2 groups: those who underwent ICBG harvest (ICBG group) and those who did not (non-ICBG group).

RESULTS

We included 342 patients in the ICBG group versus 563 in the non-ICBG group. There were no significant differences in preoperative age (14.9 vs. 14.8; p = .178), major Cobb angle (51.3 vs. 51.8; p = .782), minor Cobb angle (34.8 vs. 35.1; p = .846), or Pain (4.11 vs. 4.11; p = .912), Appearance (3.29 vs. 3.33; p = .384), Activity (4.15 vs. 4.14; p = .847); Mental (3.95 vs. 4.00; p = .313), or Total (3.86 vs. 3.87; p = .603) SRS-22R scores. The average operative time was slightly longer in the ICBG group (293.55 vs. 276.21 minutes; p = .002). Estimated blood loss was greater in the ICBG group (939.47 vs. 723.63 mL; p = .000; 12.2% vs. 9.2% estimated blood volume; p = .000). The average number of levels fused was similar between groups (10.6 vs. 10.3; p = .137). There were no significant differences in any of the postoperative SRS-22R domains: Pain (4.30 vs. 4.34; p = .373), Appearance (4.23 vs. 4.19; p = .310), Activity (4.31 vs. 4.33; p = .509), Mental (4.20 vs. 4.23; p = .532), Satisfaction (4.42 vs. 4.43; p = .870), or Total Score (4.27 vs. 4.29; p = .674). By 2-year follow-up, there was 1 nonunion reported in the ICBG group and none in the non-ICBG group.

CONCLUSIONS

After posterior instrumented fusion surgery for AIS, ICBG harvesting was associated with longer operative times and increased blood loss, but did not influence 2-year outcomes, which included pain and appearance scores.

Cotrel-dubousset instrumentation for the correction of adolescent idiopathic scoliosis. Long-term results with an unexpected high revision rate

Background

For many years, the CD instrumentation has been regarded as the standard device for the surgical correction of adolescent idiopathic scoliosis (AIS). Nevertheless, scientific long-term results on this procedure are rare. Therefore, we conducted a retrospective follow-up study of patients treated for AIS with CD instrumentation and spondylodesis.

Methods

A total of 40 patients with AIS underwent CD instrumentation in our department within 3 years and between 1990 and 1992. For the retrospective analysis, first all the patient documents were reviewed, and pre-/postoperative X-ray images as well as those at the latest follow-up were analysed. Furthermore, it was attempted to conduct a clinical survey using the SRS-24 questionnaire, which was sent to the patients after a preceding announcement on the phone.

Results

Radiologically, the frontal main curvature was improved from a preoperative angle of 69.2° to a postoperative angle of 35.4°, and the secondary curvature was improved from a preoperative angle of 42.6° to a postoperative angle of 20.5°. The latest radiological follow-up at average 57.4 months post surgery showed an average loss of correction of 9.6° (main curvature) and 4.6° (secondary curvature), respectively.

Within the first 30 days post surgery, 3 out of 40 patients (7.5%) received early operative revision for the dislocation of hooks or rods.

At an average of 45.7 months (range 11 to 142 months), 19 out of 40 patients (47.5%; including 2 patients with early revision) received late operative revisions: The reasons were late infection (10 out of 40 patients; 25%) with the development of fistulae (7 cases) or putrid secretion (3 cases), which was resolved with the complete removal of instrumentation after all. The average time until revision was 35.5 months (range 14 to 56 months) after CD instrumentation. Furthermore, complete implant removal was necessary in 8 out of 40 patients (20%) for late operate site pain (LOSP). The average time until removal of instrumentation was 62.7 months (range 18 to 146 months) post surgery; and one patient received partial device removal for prominent instrumentation 11 months post surgery. Altogether, only 22 out of 40 CD instrumentations (55%) were still in situ.

After an average period of 14.3 years post surgery, it was possible to follow-up 14 out of 40 patients (35%) using the SRS-24 questionnaire. The average score was 93 points, without showing significant differences between patients with or without their instrumentation in situ.

Conclusions

Retrospectively, we documented for the first time a very high revisions rate in patients with AIS and treated by CD instrumentation. Nearly half of the instrumentation had to be removed due to late infection and LOSP. The reasons for the high rate of late infections with or without fistulae and for LOSP were analysed and discussed in detail.

Unanticipated revision surgery in adolescent idiopathic scoliosis

STUDY DESIGN

Retrospective case series.

OBJECTIVE

The objective of this study was to share our experience in the surgical treatment of adolescent idiopathic scoliosis (AIS), specifically the rate of revision surgeries and their indications.

SUMMARY OF BACKGROUND DATA

Minimizing AIS surgical morbidity includes prevention of short- and long-term complications that could require an unanticipated revision. There have been an increasing number of reports about revision rates and their causes in AIS. This study summarizes the experience of a large patient population treated by a single surgeon in a single institution.

METHODS

All patients who underwent surgical treatment for AIS between 10 and 20 years of age during 1983 to 2005 were reviewed. All revision surgeries performed during the same period were searched. The indications for revision and type of procedure performed were recorded.

RESULTS

A total of 502 patients with AIS underwent spinal fusion with instrumentation at an average age of 14.3 years at initial surgery. In 485 patients, the surgery consisted of posterior-only spinal fusion. A total of 24 revision surgeries were performed for 23 patients (4.9%; cumulative probability of revision = 8%). The primary indications for revision were residual rib deformity (n = 8), instrumentation dislodgement (n = 4), compensatory curve progression (n = 3), junctional kyphosis (n = 3), and symptomatic implants (n = 3). One patient had a late infection. There was 1 case of pseudoarthrosis. One patient requested scar revision. There were no cases of neurological deficit.

CONCLUSION

In this single-surgeon series, revision after the index spinal fusion was required for a relatively low proportion of patients. The main indications for revision were residual rib deformity, hook dislodgment, and progression of the unfused compensatory curve.

Long-term magnetic resonance imaging follow-up demonstrates minimal transitional level lumbar disc degeneration after posterior spine fusion for adolescent idiopathic scoliosis

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To describe long-term clinical and imaging results focusing on the uninstrumented lumbar spine after posterior spinal fusion for adolescent idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

Although previous studies found rates of low back pain after long fusion for adolescent idiopathic scoliosis which are comparable to rates found in the general population, many surgeons believe that the long lever arm associated with the fusion mass will result in increased stress at uninstrumented caudal intervertebral discs and accelerated degenerative changes.

METHODS

This is a retrospective chart and imaging review of adolescent idiopathic scoliosis patients treated with posterior fusion and segmental instrumentation. Patients completed follow-up examination, outcome questionnaires, radiographs, and magnetic resonance (MR) imaging. MR images were scored for evidence of degeneration of lumbar discs below the level of the fusion.

RESULTS

Twenty patients participated in the study, providing 90 discs below fusions for evaluation. The average follow-up was 11.8 years. The distal level of fixation was at L1 on average. The major curve averaged 55° ± 11° before surgery and was corrected to 25° ± 10° at follow-up. Follow-up MR imaging demonstrated new disc pathology in 85% of patients enrolled. Only one patient demonstrated significant degenerative disc disease at the junctional level, whereas most pathology was seen at the L5-S1 disc. The average Pfirrmann grade at uninstrumented levels deteriorated from 1.1 before surgery to 1.8 at follow-up. The greatest degree of degeneration was seen at the L5-S1 disc space where average degenerative scores increased from 1.2 before surgery to 2.3 after surgery. Three patients with severe disc disease were taking nonsteroidal anti-inflammatory drugs for pain, but no narcotics. Only mild scoliosis research society (SRS) and Oswestry changes were noted in this severe degeneration group.

CONCLUSION

Despite demonstrating an accelerated rate of L5-S1 disc degeneration, our study group has good functional scores and maintenance of correction over 10 years postfusion. In this long-term MR imaging follow-up study, disc degeneration was found remote to the lowest instrumented vertebra.

Pediatric pedicle screws: comparative effectiveness and safety: a systematic literature review from the Scoliosis Research Society and the Pediatric Orthopaedic Society of North America task force

BACKGROUND

Pedicle screws are widely used in spinal surgery. There is extensive published literature concerning the use of pedicle screw instrumentation for spinal surgery in adults. Now there is a trend to use pedicle screws in pediatric patients, including the very young. A systematic review of the current English-language literature on the use of pedicle screw instrumentation in the pediatric age group was performed to specifically determine (1) the pedicle screw placement accuracy in patients with spine deformity and (2) the effect size of all-pedicle screw constructs compared with other methods of spinal instrumentation in terms of the percentage of scoliosis correction.

METHODS

English-language studies of pedicle screw use in pediatric patients (defined as those younger than eighteen years of age) were included. Descriptive statistics synthesized the accuracy of pedicle screw placement. Accuracy rates were compared between pediatric and adult patients. The effect of pedicle screw instrumentation on scoliosis correction was calculated with use of Cobb angle measurements.

RESULTS

On the basis of the literature search, 1181 articles were screened, 320 abstracts were examined, and ninety full-text articles representing 5761 patients were reviewed in detail. Seventeen studies met the inclusion criteria for the analysis of pedicle screw placement accuracy. A total of 13,536 pedicle screws were placed in 1353 pediatric patients. The overall placement accuracy rate in pediatric patients was 94.9%, which was higher than the rate of 91.5% reported for adults. The weighted, geometric, and 5% trimmed mean accuracy rates of pedicle screw placement were 91.9%, 88.5%, and 89.1%, respectively (standard deviation = 10%; interquartile range = 10%). Sixteen comparative studies met the inclusion criteria for the analysis of the effect of pedicle screw instrumentation on scoliosis correction. Pedicle screw constructs had a significantly larger percentage of Cobb angle correction compared with hooks (Cohen's d = 1.14) and hybrid constructs (Cohen's d = 0.49).

CONCLUSIONS

The accuracy of pedicle screw placement in the pediatric spine exceeds the accuracy rate reported in adults. Pedicle screw instrumentation constructs are significantly more effective for scoliosis correction, as determined on the basis of Cobb angle measurements, than are hook constructs and hybrid constructs.

Short segment bone-on-bone instrumentation for adolescent idiopathic scoliosis: a mean follow-up of six years

STUDY DESIGN

Prospective case series.

OBJECTIVE

To evaluate the clinical and radiologic outcomes of short segment anterior scoliosis surgery with bone-on-bone apposition using a dual screw, dual rod system.

SUMMARY OF BACKGROUND DATA

Posterior segmental fixation for correction of AIS involves instrumentation of all the vertebrae included in the major curve. Our short segment anterior technique produces similar results by fusion of fewer levels.

METHODS

Forty-five patients operated between 1996 and 2004. Twenty-eight thoracic (Lenke 1) and 17 thoracolumbar (Lenke 5). The mean age was 19 years, 87% were females, and the mean follow-up was 72 months (range 28-121 months). We operated on curves less than 85° with "total discectomy," bone-on-bone apposition, and dual-screw, dual-rod fixation.

RESULTS

A mean of five vertebrae (four discs) were instrumented, with a mean operative time of 360 minutes, blood loss of 877 mL and a hospital stay of 9.1 day. Lenke 1. The main preop thoracic curve was 52.5°, final postop curve 27.9°, by fusing five vertebrae, four discs. A spontaneous improvement of 47.5% of the lumbar compensatory curve was seen. The lower tilt angle corrected from 20.9° to 11°. Lenke 5. The preoperative thoracolumbar major curve corrected from 50.5° to 18.3° (final) with fusion of four vertebrae, three discs. A spontaneous improvement of 37.4% occurred in the thoracic compensatory curve. The preop tilt angle improved from 27.7° to 8.3°.The sagittal and coronal balance was restored in all the patients. There were no neurologic, vascular, pulmonary, or implant-related complications. Union occurred within 3 months. All the patients returned to an unrestricted lifestyle within 4 months.

CONCLUSION

We report good results after surgical correction using our short segment bone-on-bone technique. Improvements were noted and maintained, over a 6-year period.

Intraoperative techniques to reduce the potential of set-screw loosening in long spinal constructs: a static and fatigue biomechanical investigation

STUDY DESIGN

The purpose of this study was to investigate the effects of implant selection and set-screw tightening technique on the loosening torques in long scoliosis constructs after long-term biaxial fatigue loading.

SUMMARY OF BACKGROUND DATA

Expanded use of pedicle screws in the correction of long scoliotic curves and the mechanical demands on segmental fixation systems requires surgeon awareness of revisiting set screws to ensure full screw/rod engagement and minimize the potential of set-screw loosening and/or rod slippage postoperatively.

METHODS

Biomechanical tests were performed to evaluate the effect of set-screw tightening techniques and rod approximation on screw/rod interface strength.

RESULTS

Rod reduction test shows the force required to approximate a rod to a pedicle screw is statistically lower with uniplanar or polyaxial screws, when compared with monoaxial screws. This ease of approximation in both polyaxial and uniplanar screws directly correlate to improvement in the axial slippage resistance. In the simulated spinal model construct, rod/screw securement can vary based on the number of tightening torques applied to the system.

CONCLUSIONS

Sequential revisiting of sets crews in long scoliosis constructs resulted in a statistically significant increase in loosening torque for monoaxial and polyaxial screw systems. Intraoperative securement assessment of set screws is recommended. The use of polyaxial and uniplanar screws at the distal ends in long constructs is recommended to increase the screw/rod interface strength.

Comparação entre dois métodos de posicionamento para realização do raio X e sua repercussão na avaliação da cifose torácica utilizando o método de Cobb e no equilíbrio sagital

INTRODUÇÃO: o tratamento da cifose torácica é baseado na aferição da magnitude da curva baseada em mensurações radiográficas, e proporcionar o correto equilíbrio sagital pela correção cirúrgica de uma gibosidade é de importância fundamental. OBJETIVO: análise radiográfica prospectiva do efeito da variação da posição dos braços sobre a aferição da cifose torácica e do equilíbrio sagital entre pacientes com idades pré-estabelecidas. MÉTODOS: foram realizadas radiografias na posição lateral da coluna vertebral utilizando-se dois métodos posicionais: posição 1, em que o paciente permanecia de pé, com os joelhos juntos, pés alinhados com os ombros, cabeça reta direcionada para a frente, braços estendidos a 90º em relação ao tronco, mantendo os membros superiores estendidos e paralelos ao chão; uma segunda radiografia foi obtida com o paciente de pé, com os joelhos juntos, pés alinhados com os ombros, cabeça reta direcionada para a frente, com os cotovelos fletidos e os dedos repousando sobre a fossa supraclavicular bilateralmente. Os braços devem formar um ângulo de aproximadamente 45º com o corpo. Foram mensurados os ângulos de Cobb e o equilíbrio sagital nas duas radiografias. RESULTADOS: não houve correlação entre a posição dos braços, os valores angulares de Cobb e o equilíbrio sagital. CONCLUSÃO: em nosso trabalho, observamos que a posição dos braços (90º versus 45º), não interfere estatisticamente no valor da cifose torácica e na variação do equilíbrio sagital.

Clinical and radiographic outcomes of the treatment of adolescent idiopathic scoliosis with segmental pedicle screws and combined local autograft and allograft bone for spinal fusion: a retrospective case series

Background

High morbidity has been reported with iliac crest bone graft harvesting; however, donor bone is typically necessary for posterior spinal fusion. Autograft bone combined with allograft may reduce the morbidity associated with iliac crest bone harvesting and improve the fusion rate. Our aim in this study was to determine the presence of complications, pseudarthrosis, non-union, and infection using combined in situ local autograft bone and freeze-dried cancellous allograft bone in patients undergoing posterior spinal fusion for the treatment of adolescent idiopathic scoliosis.

Methods

A combination of in situ local autograft bone and freeze-dried cancellous allograft blocks were used in 50 consecutive patients with adolescent idiopathic scoliosis treated by posterior fusion and Moss Miami pedicle screw instrumentation. Results were assessed clinically and radiographically and quality of life and functional outcome was evaluated by administration of a Chinese version of the SRS-22 survey.

Results

There were 41 female and 9 male patients included for analysis with an average age of 14.7 years (range, 12-17). All patients had a minimum follow-up of 18 months (range, 18 to 40 months). The average preoperative Cobb angle was 49.8° (range, 40° to 86°). The average number of levels fused was 9.8 (range, 6-15). Patients had a minimum postoperative follow-up of 18 months. At final follow-up, the average Cobb angle correction was 77.8% (range, 43.4 to 92.5%). There was no obvious loss in the correction, and the average loss of correction was 1.1° (range, 0° to 4°). There was no pseudarthrosis and no major complications.

Conclusions

In situ autograft bone combined with allograft bone may be a promising method enhances spinal fusion in AIS treated with pedicle screw placement. By eliminating the need for iliac crest bone harvesting, significant morbidity may be avoided.

Hospital cost analysis of adolescent idiopathic scoliosis correction surgery in 125 consecutive cases

BACKGROUND

Although achieving clinical success is the main goal in the surgical treatment of adolescent idiopathic scoliosis, it is becoming increasingly important to do so in a cost-effective manner. The goal of the present study was to determine the surgical and hospitalization costs, charges, and reimbursements for adolescent idiopathic scoliosis correction surgery at one institution.

METHODS

We performed a retrospective review of 16,536 individual costs and charges, including overall reimbursements, for 125 consecutive patients who were managed surgically for the treatment of adolescent idiopathic scoliosis by three different surgeons between 2006 and 2007. Demographic, surgical, and radiographic data were recorded for each patient. Stepwise multiple linear regression analysis was employed to assess independent correlation with total cost and charge. Nonparametric descriptive statistics were calculated for total cost with use of the Lenke curve-classification system.

RESULTS

The mean age of the patients was 15.2 years. The mean main thoracic curve measured 50 degrees, and the thoracolumbar curve measured 41 degrees. The cost varied with Lenke curve type: $29,955 for type 1, $31,414 for type 2, $31,975 for type 3, $60,754 for type 4, $32,652 for type 5, and $33,416 for type 6. Independently significant increases for total cost were found in association with the number of pedicle screws placed, the total number of vertebral levels fused, and the type of surgical approach (R(2) = 0.35, p <or= 0.03). Independently significant increases for reimbursement were found in association with the number of pedicle screws placed and the type of surgical approach (R(2) = 0.12, p <or= 0.02). The hospital was reimbursed 53% of total charges and 120% of total costs. Reimbursement was highly correlated with charge (r = 0.45, p < 0.001). For rehospitalizations, the hospital was reimbursed 65% of charges and 93% of costs.

CONCLUSIONS

The largest contributors to overall cost were implants (29%), intensive care unit and inpatient room costs (22%), operating room time (9.9%), and bone grafts (6%). There were three significant independent predictors of increased total cost: the surgical approach used, the number of pedicle screws placed, and the number of vertebral levels fused. This study characterizes the relative contributions of factors that contribute to total costs, charges, and reimbursements that can, in time, identify potential areas for cost reduction or redistribution of resources in the surgical treatment of adolescent idiopathic scoliosis.

Analysis of instrumentation/fusion survivorship without reoperation after primary posterior multiple anchor instrumentation and arthrodesis for idiopathic scoliosis

BACKGROUND

During the past 25 years, spinal instrumentation systems and surgical techniques used to treat idiopathic scoliosis have evolved, achieving fewer patient restrictions during arthrodesis healing, shorter constructs, and better correction. The purposes of this retrospective comparative study were to determine the survivorship of the implant/fusion without reoperation and the risk factors influencing such survival.

METHODS

From 1989 through 2002, 208 consecutive patients (index patient included, age 10-20 years) underwent primary posterior instrumentation and arthrodesis with the same multiple anchor implant system by one surgeon, a co-designer of the system. Two hundred seven were followed for more than 2 years; reoperation status was available for them at an average follow-up of 8.3 years. Twenty-one independent demographic, deformity, instrumentation, and process variables possibly influencing the need for reoperation were studied by comparing the reoperated group with the unreoperated group.

RESULTS

Nineteen patients (9.2%) had reoperation; 16 (7.7%) were for indications related to posterior spine instrumentation. Survival of the implant/fusion without reoperation for spine instrumentation-related indications was 96% (95% confidence interval [CI], 93.2-98.7%) at 5 years, 91.6% (95% CI, 86.9-96.3%) at 10 years, 87.1% (95% CI, 79.5-94.6%) at 15 years, and 73.7% (95% CI, 48.6-98.6%) at 16 years, when the number at risk was nine. Reoperation need was significantly influenced by two implant variables: transverse connector design (p=.0012) and the lower instrumented vertebra anchors used (p=.0004). At 9 years, the longest interval allowing comparison, survival of the implant/fusion without reoperation for these two variables was 100% (six subjects at risk) compared to 82% (95% CI, 74.2-90.3%) with 59 patients still at risk for reoperation for those who did not have them, p=.0014.

CONCLUSIONS

The most stable lower instrumented vertebra anchor configuration, bilateral pedicle screws, and the stronger transverse connector design, closed drop entry, provided the best survival of the implant/fusion without reoperation with this system and the techniques used at 9-year follow-up. We hope that this post-market study using survivorship techniques will be a guide for studies of other spinal implants.

Revision surgery after primary spine fusion for idiopathic scoliosis

STUDY DESIGN

Retrospective case series.

OBJECTIVE

The objective of this study was to review the overall prevalence of, and indications for, reoperations after the index spine fusion for idiopathic scoliosis at our center.

SUMMARY OF BACKGROUND DATA

Spine fusions for idiopathic scoliosis are expected to be the final therapeutic intervention in management. In a recent publication in 2006, reoperations after index spine fusion for idiopathic scoliosis were reported in 12.9% of patients at a single institution (n = 1046).

METHODS

A spinal deformity database search at our center identified all primary anterior, posterior, and circumferential spinal fusions performed for idiopathic scoliosis (1985-2003). A total of 1057 patients were identified whose mean age was 14.4 years (7-22 years) with minimum 2 year follow-up after index surgery. Study cohort consisted patients who underwent reoperation for any reason after index fusion procedure.

RESULTS

Of the 1057 spinal fusions for idiopathic scoliosis, 41 (3.9%) underwent reoperation. Primary surgeries were: 11 anterior spinal fusions, 25 posterior spinal fusions, and 5 circumferential spinal fusions. Mean follow-up was 5.7 years (2-10.8). Forty-seven additional procedures were performed during 46 reoperations at an average of 26 months after index procedure (1 week-73 months). Of the 47 reoperations, 20 (43%) were revision spinal fusions (for pseudarthroses, uninstrumented curve progression or junctional kyphosis), 16 (34%) because of infections (5 acute, 11 chronic), 7 (15%) for implant removals due to pain and/or prominence (4 complete, 3 partial), 2 (4%) were revision of loosened implants, and 2 (4%) were elective thoracoplasties.

CONCLUSION

This study documented a 3.9% overall reoperation rate at our medical center, a 3-fold lower reoperation rate than the previously reported 12.9%. The most common reoperations were for infections (34%), pseudarthroses (26%), and postoperative curve progression of the adjacent unfused spine (17%).

Radiographic outcomes over time after endoscopic anterior scoliosis correction: a prospective series of 106 patients

STUDY DESIGN

A prospective, consecutive series of 106 patients receiving endoscopic anterior scoliosis correction.

OBJECTIVE

To analyze changes in radiographic parameters and rib hump in the 2 years after surgery.

SUMMARY OF BACKGROUND DATA

Endoscopic anterior scoliosis correction is a level sparing approach and therefore, it is important to assess the amount of decompensation which occurs after surgery.

METHODS

All patients received a single anterior rod and vertebral body screws using a standard compression technique. Cleared disc spaces were packed with either mulched femoral head allograft or rib head/iliac crest autograft. Radiographic parameters (major, instrumented, minor Cobb, T5-T12 kyphosis) and rib hump were measured at 2, 6, 12, and 24 months after surgery. Paired t tests and Wilcoxon signed ranks tests were used to assess the statistical significant of changes between adjacent time intervals.

RESULTS

Mean loss of major curve correction from 2 to 24 months after surgery was 4 degrees. Mean loss of rib hump correction was 1.4 degrees. Mean sagittal kyphosis increased from 27 degrees at 2 months to 30.6 degrees at 24 months. Rod fractures and screw-related complications resulted in several degrees less correction than patients without complications, but overall there was no clinically significant decompensation after complications.

CONCLUSION

There are small changes in deformity measures after endoscopic anterior scoliosis surgery, which are statistically significant but not clinically significant.

A century of spine surgery: what can patients expect?

PURPOSE

To evaluate the hypothesis that spinal fusion surgery is an effective method to address spinal deformity-associated clinical problems, including magnitude of curvature (Cobb angle), pulmonary dysfunction, and pain.

METHOD

A systematic review was carried out using Science Citation Index (SCI) Expanded (1900 - present), Social Sciences Citation Index (1956 - present), Arts and Humanities Citation Index (1965 - present), Medline (1950 - present) and PubMed Central databases (1887 - present) to access information regarding efficacy of spine surgery in preventing or improving the health and function of patients diagnosed with scoliosis in adolescence.

RESULTS

Since 1950, more than 12,600 articles on scoliosis have been published, and nearly 50% (5721) focus on methods, rationale, outcome, and complications of surgical intervention. Among these, 82 articles have documented outcome for groups of > or =10 patients, treated for adolescent idiopathic scoliosis, and followed for at least 2 years after treatment. These data provide an overview of the impact of spine surgery on scoliosis for 5780 patients as surgery methods and approaches have evolved.

CONCLUSIONS

For most patients, a reduced magnitude of spinal curvature can be achieved through one or more spinal fusion surgeries. There is no evidence to support the premise that this result is correlated with improved pulmonary function or reduced pain.

Operative treatment of adolescent idiopathic scoliosis with posterior pedicle screw-only constructs: minimum three-year follow-up of one hundred fourteen cases

STUDY DESIGN

Preoperative review of a prospective study, single institution, consecutive series. OBJECTIVE.: To analyze the intermediate-term follow-up of consecutive adolescent idiopathic scoliosis (AIS) patients treated with pedicle screw constructs.

SUMMARY OF BACKGROUND DATA

There have been no reports of the intermediate-term findings in North America following posterior spinal fusion with the use of pedicle screw-only constructs.

METHODS

One hundred and fourteen consecutive patients having a minimum 3-year follow-up (mean 4.8 +/- 1.1; range, 3.0-7.3 years) with AIS were evaluated. The average age at surgery was 14.9 +/- 2.2 years. Radiographic measurements included preoperative (Preop), postoperative (PO), 2-year (2 years), and final follow-up (FFU). A chart review evaluated PFTs, Scoliosis Research Society scores, presence of thoracoplasty, Risser sign, Lenke classification, and complications.

RESULTS

The most frequent curve pattern was Lenke type 1 (45.6%), followed by type 3 (21.9%). The average main thoracic curve measured 59.2 degrees +/- 12.2 SD Preop, and corrected to 16.8 degrees +/- 9.9 PO (P < 0.0001). Sagittal thoracic alignment (T5-T12) decreased from 25.8 degrees to 15.5 degrees at FFU (P = 0.05). Nash-Moe grading for apical vertebral rotation (AVR) in the proximal thoracic curve decreased from 2.0 Preop to 1.1 at FFU (P < 0.0001), and AVR in the thoracolumbar/lumbar spine decreased from 1.6 Preop to 1.1 at FFU (P < 0.0001). Importantly, the horizontalization of the subjacent disc measured -8.3 degrees Preop which decreased to -0.9 degrees PO (P < 0.001). PFT follow-up averaged 2.4 years with a 7.1% improvement in FVC (P = 0.004) and 8.8% in FEV1 (P < 0.0001). SRS scores averaged 83.0% at latest follow-up. Age, gender, Risser sign, or complications did not have a significant effect on outcomes. There were 2 cases of adding-on, 3 late onset infections, 1 with a single pseudarthrosis, but no neurologic complications.

CONCLUSION

This is the largest (N = 114), consecutive series of North American patients with AIS treated with pedicle screws having a minimum of 3-year follow-up. The average curve correction was 68% for the main thoracic, 50% for the proximal thoracic, and 66% for the thoracolumbar/lumbar curve at final follow-up.

Financial analysis of circumferential fusion versus posterior-only with thoracic pedicle screw constructs for main thoracic idiopathic curves between 70 degrees and 100 degrees

PURPOSE

Reports on thoracic pedicle screw (TPS) constructs have demonstrated their safety and efficacy; however, concerns exist regarding their increased cost. This is a review of adolescents with main thoracic scoliosis surgically treated with anterior release and posterior fusion or posterior fusion only. The objectives were to compare the radiographic outcomes and financial data of two surgical treatments: anterior/posterior spinal fusion (APSF) versus posterior spinal fusion (PSF-TPS) alone with TPSs, in patients with large 70-100 degrees main thoracic adolescent idiopathic scoliosis (AIS) curves.

METHODS

We identified 43 patients with main thoracic Lenke type 1-4 AIS curves between 70 and 100 degrees who had been treated with either APSF or PSF-TPS.

RESULTS

Both groups had equivalent radiographic corrections postoperatively. The PSF-TPS group patients had higher implant charges, but the APSF group had higher surgeon procedural charges, operating room charges, anesthesia charges, and inpatient room charges. Total charges were $75,295 for the APSF group and $71,236 for the PSF-TPS group (P > 0.05). Analyses of two subgroups of the APSF group, anterior release via thoracotomy versus VATS and same-day versus staged surgeries, failed to change any of the above findings.

CONCLUSION

Based on this financial analysis, there was no statistically significant differences between the APSF and PSF-TPS groups, with equivalent radiographic corrections.

A huge presacral Tarlov cyst

✓ Perineural cysts have become a common incidental finding during lumbosacral magnetic resonance (MR) imaging. Only some of the symptomatic cysts warrant treatment. The authors describe the successful operative treatment of a patient with, to the best of their knowledge, the largest perineural cyst reported to date.

A 29-year-old woman had been suffering from long-standing constipation and low-back pain. During an obstetric investigation for infertility, the clinician discovered a huge presacral cystic mass. Computed tomography myelography showed the lesion to be a huge Tarlov cyst arising from the left S-3 nerve root and compressing the ipsilateral S-2 nerve. The cyst was successfully treated by ligation of the cyst neck together with sectioning of the S-3 nerve root. Postoperative improvement in her symptoms and MR imaging findings were noted.

Identification of the nerve root involved by the cyst wall, operative indication, operative procedure, and treatment of multiple cysts are important preoperative considerations.

Comparison of thoracic pedicle screw to hook instrumentation for the treatment of adult spinal deformity

STUDY DESIGN

Retrospective, case-control, matched cohort.

OBJECTIVE

Compare the radiographic and clinical outcomes of adult spinal deformity patients treated with thoracic pedicle screw (TPS) or thoracic hook constructs.

SUMMARY OF BACKGROUND DATA

The efficacy of TPS instrumentation for pediatric spinal deformity correction has been established. Little is known about TPS use in adult spinal deformity.

METHODS

Fifty-six patients (average age, 49 years; average follow-up, 3.58 years) were treated with TPS or thoracic hook constructs for coronal (n = 20) or sagittal (n = 36) plane deformities. Patients were evaluated radiographically and with SRS scores.

RESULTS

Coronal deformities treated with TPS demonstrated improved main thoracic curve correction compared with hook constructs at last follow-up (24.8 degrees vs. 13.8 degrees; P < 0.05), despite having larger (59.8 degrees vs. 44.9 degrees; P < 0.05) and more rigid preoperative curves (29.3% vs. 44.9% correction on side-bending radiographs; P < 0.001). Sagittal deformities treated with TPS constructs demonstrated greater thoracolumbar kyphosis correction than hook constructs at last follow-up (12.1 degrees vs. 2.5 degrees; P < 0.05). No TPS patient had a thoracic pseudarthrosis. Four hook patients (14%) had thoracic pseudarthroses.

CONCLUSIONS

TPS instrumentation allows greater coronal and sagittal plane correction and may reduce the risk of thoracic pseudarthrosis compared with hook constructs when treating adult spinal deformities.

Impact of spine surgery on signs and symptoms of spinal deformity

Paediatric scoliosis is associated with signs and symptoms including reduced pulmonary function, increased pain and impaired quality of life, all of which worsen during adulthood, even when the curvature remains stable. Spinal fusion has been used as a treatment for nearly 100 years. In 1941, the American Orthopedic Association reported that for 70% of patients treated surgically, outcome was fair or poor: an average 65% curvature correction was reduced to 27% at >2 year follow-up and the torso deformity was unchanged or worse. Outcome was worse in children treated surgically before age 10, despite earlier intervention. Today, a reduced magnitude of curvature obtained by spinal fusion in adolescence can be maintained for decades. However, successful surgery still does not eliminate spinal curvature and it introduces irreversible complications whose long-term impact is poorly understood. For most patients there is little or no improvement in pulmonary function. Some report improved pain after surgery, some report no improvement and some report increased pain. The rib deformity is eliminated only by rib resection which can dramatically reduce respiratory function even in healthy adolescents. Outcome for pulmonary function and deformity is worse in patients treated surgically before the age of 10 years, despite earlier intervention. Research to develop effective non-surgical methods to prevent progression of mild, reversible spinal curvatures into complex, irreversible structural deformities, is long overdue.

Fusionless surgery for scoliosis: 2-17 year radiographic and clinical follow-up

STUDY DESIGN

Descriptive case series.

OBJECTIVE

To determine whether fusionless, multiple vertebral wedge osteotomy can safely obtain correction of the deformity with adolescent idiopathic scoliosis (AIS).

SUMMARY OF BACKGROUND DATA

To our knowledge, no such attempts to manage the AIS with fusionless, vertebral osteotomies have been reported.

METHODS

A total of 20 consecutive patients were treated since 1987. Deformity correction, complications, respiratory function, and patient-oriented outcome were investigated.

RESULTS

There were 20 patients (17 females and 3 males), including 19 with idiopathic and 1 with syringomyelia scoliosis, who underwent surgery at an average age of 16.4 years and were followed for 8.9 years (range 2-17) on average. There were no neurologic complications. One superficial wound infection necessitated debridement. There were 2 patients converted to posterior instrumentation surgery because of deterioration of the deformity. The average Cobb angle of 64.0 degrees before surgery was corrected to 48.2 degrees at 8.9 years after surgery. Decline of the pulmonary function test after surgery was not statistically significant. The patients' responses to questions about function and pain were favorable.

CONCLUSION

Deformity with AIS was safely corrected with fusionless, multiple vertebral wedge osteotomy.

Thoracic adolescent idiopathic scoliosis curves between 70 degrees and 100 degrees: is anterior release necessary?

STUDY DESIGN

A retrospective review of adolescents with main thoracic scoliotic curves surgically treated with either anterior release and posterior fusion or posterior fusion only.

OBJECTIVES

To compare the radiographic and clinical outcomes of two surgical treatments: anterior-posterior spinal fusion (APSF) versus posterior spinal fusion (PSF) alone in patients with large 70 degrees to 100 degrees thoracic adolescent idiopathic scoliosis (AIS) curves.

SUMMARY OF BACKGROUND DATA

Surgical treatment of thoracic AIS curves between 70 degrees and 100 degrees often consists of anterior and posterior fusion to improve the coronal correction and fusion rate, with the anterior release and fusion performed through either an open thoracotomy or by video-assisted thoracoscopy.

METHODS

All patients (n = 84) with main thoracic major AIS curves between 70 degrees and 100 degrees who underwent spinal fusion (APSF or PSF) at one center between 1987 and 2001 were included for analysis. The minimum follow-up was 2 years after surgery (mean, 4.5 years; range, 2.0-10.2 years). The mean age of patients was 13.8 years (range, 10.7-18.2 years), with 66 females and 18 males. Multiple radiographic measures were assessed. The primary and secondary statistical analyses performed were nonparametric analyses, using the Wilcoxon-Mann-Whitney tests for the primary analysis of APSF and PSF groups. The PSF subgroup analysis was performed with the Kruskal-Wallis test.

RESULTS

There were 22 patients in the APSF (open ASF in 18, and video-assisted thoracoscopy in 4) group and 62 patients in the PSF group. There were no statistically significant differences between the groups for gender, age, number of levels fused, Cobb measurement of preoperative coronal or sagittal thoracic curve magnitude, or coronal curve flexibility. The APSF group, when compared with the PSF group, had greater intraoperative correction of the coronal curve (48.3 degrees vs. 38.7 degrees, P = 0.0087) as well as final overall correction (47.2 degrees vs. 34.2 degrees, P = 0.0008). There were no significant differences seen in the sagittal alignment from T5-T12 (P = 0.3150) or the SRS outcomes data between the APSF and PSF only groups. Subanalysis of the PSF only group identified three distinct groups based on implants: hook-only constructs (n = 36), hybrid constructs of proximal hooks and distal pedicle screws (n = 15), and pedicle screw-only constructs (n = 11). Pedicle screw-only constructs corrected the coronal Cobb measurements more than the other two groups (47.5 degrees vs. hooks 37.7 degrees vs. hybrid 34.4 degrees , P = 0.0110), and to a similar extent as to the APSF group with no statistically significant difference in coronal correction (PSF, 47.5 degrees; APSF 48.3 degrees; P = 0.9014), nor any other parameter except for sagittal T5-T12 changes. There were no reoperations for implant failure/pseudarthroses in any of the patients.

CONCLUSION

APSF of large thoracic curves allows greater coronal correction of thoracic curves between 70 degrees and 100 degrees, when compared with PSF alone using thoracic hook constructs, but not with the use of thoracic pedicle screw constructs. Scoliosis surgeons not using pedicle screw constructs need to decide if the modest improvement in coronal correction with a combined approach justifies its routine use in this patient population.

Does gender affect outcome of surgery in adolescent idiopathic scoliosis?

STUDY DESIGN

A retrospective follow-up study comparing 2 matched groups.

OBJECTIVE

To compare long-term results of operative treatment of adolescent idiopathic scoliosis (AIS) between males and females matched for age, curve magnitude and type, and the instrumentation used.

SUMMARY OF BACKGROUND DATA

It has been suggested that in AIS, the spine is more rigid in males than in females, because brace treatment fails to halt progression of the curves in males. However, there are no studies comparing the results of surgical treatment of AIS between males and females.

METHODS

Thirty male and female pairs were matched for age (+/-1 year), major curve magnitude (+/-5 degrees), curve type according to the King classification, and the instrumentation used (Harrington in 11 pairs, Cotrel-Dubousset in 9 pairs, and Universal Spine System in 10 pairs). The mean age at the time of operation was 16.2 +/- 2.6 years for the males and 15.5 +/- 2.3 years for the females. The mean follow-up times were 14.3 years (range 6.7-23.0 years) and 14.1 year (range 6.4-23.7 years), respectively. Radiographs were obtained presurgery and after surgery, at the 2-year follow-up assessment, and at the final follow-up visit. In addition, a physical examination was performed, and the Scoliosis Research Society (SRS) questionnaire was completed. Spine mobility and nondynamometric trunk strength were measured at the final follow-up visit.

RESULTS

Before surgery, the mean Cobb angle of the thoracic curve was 55 degrees (range 42-83 degrees) in the males and 56 degrees (range 43-80 degrees) in the females. In bending radiographs, the major curve reduced significantly more in females than in males (P = 0.027). The mean angles of the thoracic and lumbar curves were similar at all follow-up visits. The final correction of the thoracic curves was 30% (range -19-65%) in the males and 33% (range -7-71%) in the females (not significant). No significant difference was observed in thoracic kyphosis or lumbar lordosis between the study groups at the final follow-up. The total SRS questionnaire score averaged 96 (range 66-113) in the males and 95 (range 75-108) in the females. None of the males and 2 of the females reported back pain often or very often in the questionnaire. Nondynamometric trunk strength measurements corresponded with reference values, on average, and were similar in both groups. Abnormal trunk side bending tended to be more common in the males than in the females (43% vs. 23%, P = 0.10, not significant).

CONCLUSIONS

Curves in males appear to be more rigid than in females with AIS. However, posterior surgery for AIS provides similar short and long-term results in males and females.

Cotrel-Dubousset (CD) or Universal Spine System (USS) instrumentation in adolescent idiopathic scoliosis (AIS): comparison of midterm clinical, functional, and radiologic outcomes

STUDY DESIGN

A retrospective comparison of the clinical, radiologic, and functional results of Cotrell-Dubousset (CD) and Universal Spine System (USS) instrumentation for adolescent idiopathic scoliosis (AIS).

OBJECTIVES

To establish whether there are any differences in outcome between the 2 instrumentation systems.

SUMMARY OF BACKGROUND DATA

CD is the first complex posterior double rod instrumentation system to provide multiple hook fixation. USS instrumentation permits the use of rod translation instead of rod rotation, the option to secure pedicle hooks with fixation screws, and the option to use transpedicular screws in the lower thoracic and lumbar spine. Midterm and long-term results of USS instrumentation are lacking.

METHODS

Fifty-seven (mean age, 28 years at follow up) patients treated with CD instrumentation and 55 (mean age, 23 years at follow up) patients treated with USS instrumentation for AIS participated in the study. The average follow-up rate was 80% and time 13.0 years for the CD group, and 95% and 7.8 years for the USS group. Radiographs were obtained before surgery, at 2-year follow up, and at final follow up. Additionally, a physical examination was performed by 2 independent observers, and the Scoliosis Research Society (SRS) questionnaire was completed; spinal mobility and nondynamometric trunk strength were measured at the final follow-up visit. RESULTS.: The mean Cobb angle of the instrumented thoracic curve was before surgery 55 degrees (range, 36-83 degrees for the CD and 52 degrees (range, 35-85 degrees) for the USS group. The mean number of instrumented vertebrae was 9.9 (range, 7-12) in the CD and 9.8 (range, 6-12) in the USS group. At final follow up, the mean angles were 32 degrees (range, 13-63 degrees) for the CD group and 29 degrees (range, 9-63 degrees) for the USS group (not significant). No significant difference was observed in thoracic kyphosis or lumbar lordosis between the study groups at final follow up. In the SRS questionnaire, the total score averaged 97 for the CD and 101 for the USS groups, respectively. In the questionnaire, 6 (11%) patients in the CD group, but none in the USS group, reported having low back pain often or very often at rest. No correlation was found between the Cobb angle of the thoracic or lumbar curves at follow up and the total score or back pain indexes of this questionnaire. Nondynamometric trunk strength measurements corresponded with age- and sex-adjusted reference values, on average, but patients in the CD group performed significantly better in the squatting test (P = 0.021) and patients in the USS group performed better in trunk side bending (P = 0.004). Complications were recorded in 15 (26%) patients in the CD and in 13 (24%) patients in the USS group (not significant).

CONCLUSIONS

The midterm radiologic and functional outcomes were quite similar in both groups as were the SRS scores. The patients performed, on average, as well as did the reference population in nondynamometric trunk strength measurements. Intraoperative and late complications were similar in both groups.

Results of thoracoscopic instrumented fusion versus conventional posterior instrumented fusion in adolescent idiopathic scoliosis undergoing selective thoracic fusion

STUDY DESIGN

Retrospective review of 31 consecutive female patients with adolescent idiopathic scoliosis undergoing selective thoracic fusion.

OBJECTIVE

To compare safety and efficacy of two techniques in treating adolescent idiopathic scoliosis undergoing selective thoracic fusion.

SUMMARY OF BACKGROUND DATA

There is paucity in the literature comparing posterior versus thoracoscopic instrumented fusion in scoliosis.

METHODS

Nineteen patients (group 1) underwent posterior instrumented fusion. Twelve patients (group 2) had thoracoscopic anterior instrumented fusion. All patients had a minimum of 25 months of follow-up observation.

RESULTS

Both groups were similar in terms of age at menarche and surgery. Preoperative Cobb angles in the coronal (erect and bending) and sagittal planes did not differ between the two groups. Group 1 patients had higher estimated blood loss (P = 0.006). Operative time (P < 0.001) and intensive care unit stay (P = 0.01) were longer in group 2 patients. There was no difference in parenteral analgesia requirement. There were no complications in group 1. Complications in group 2 included lobar collapse (1) and scapula winging (1). Improvement in scoliosis among group 1 patients averaged 77 (1 week), 72 (6 months), and 67% (most recent follow-up review). In group 2 patients, mean improvement in scoliosis was 66 (1 week), 62 (6 months), and 62% (most recent follow-up review). The differences between the two groups in terms of scoliosis improvement were not significant. Thoracic kyphosis (T2-T12) did not increase significantly with thoracoscopic versus posterior instrumentation. No significant change in lumbar lordosis (T12-S1) was noted with either procedure.

CONCLUSIONS

The efficacy of thoracoscopic surgery was similar to standard posterior procedures. Advantages included lower intraoperative blood loss. The longer operative time and intensive care unit stay were attributed to the steep learning curve of this technique.

Safety and efficacy of Isola instrumentation and arthrodesis for adolescent idiopathic scoliosis: two- to 12-year follow-up

STUDY DESIGN

Retrospective case series including patient outcome assessment.

OBJECTIVE

To study the safety and efficacy of Isola instrumentation in comparison with similar series.

SUMMARY OF BACKGROUND DATA

Both the technique and technology used in the surgical treatment of adolescent idiopathic scoliosis continue to evolve, the common theme since the 1980s being provision of instrumentation stable and strong enough to eliminate the need for postoperative immobilization. The purpose of this study is to determine the safety and efficacy of a system deliberately integrating hook, wire, and screw anchors to deliver torsional and countertorsional corrective loads.

METHODS

A total of 185 consecutive patients, index patient included, were treated by posterior instrumentation and arthrodesis from January 1989 through December 2000. Safety was studied by complications, and reoperation type and occurrence. Effectiveness was studied by deformity correction and health-related quality of life questionnaire response. Variables affecting effectiveness were sought. A total of 179 patients (97%) had outcome assessment at an average of 6 years postoperative, and 176 had radiographic evaluation at an average of 5 years postoperative.

RESULTS

There were no deaths, spinal cord or nerve root problems, or acute posterior wound infections. Proven pseudarthrosis occurred in 4 patients (2.2%) and delayed deep wound infection in 2 patients (1.1%). The implant-related reoperation rate was 8% and was necessary more often in the first quarter of the series (17% vs. 4.6%, P = 0.0062). The largest Cobb angle averaged 62 degrees preoperative and 23 degrees at latest follow-up, 63% correction. The largest angle of trunk inclination averaged 16.7 degrees before surgery and 9.9 degrees at latest follow-up, a 39% correction (P < 0.0001). Eighty-eight percent of patients were satisfied or very satisfied with the outcome. The principal problems identified were the need for a stronger transverse connector, stable end-instrumented vertebrae foundations, and convex thoracic anchorage.

CONCLUSIONS

Isola instrumentation seems to be at least as safe and effective as other instrumentations being used for the surgical treatment of adolescent idiopathic scoliosis.

Operative correction of adolescent idiopathic scoliosis in male patients. A radiographic and functional outcome comparison with female patients

BACKGROUND

The outcomes following surgical treatment of adolescent idiopathic scoliosis have traditionally been assessed on the basis of radiographic parameters and, more recently, functional outcome measures. However, we know of no published studies in which radiographic and functional outcomes following surgery were compared between male and female patients.

METHODS

Fifty-two male patients who had had surgery for adolescent idiopathic scoliosis were compared retrospectively with two groups of female patients: a random sample of 130 female patients who had had surgical treatment for adolescent idiopathic scoliosis during the same time period and a subgroup of fifty-two of these female patients who had been matched to the male patients with regard to curve type and magnitude. Radiographic parameters were compared between the male and female patients, and the Scoliosis Research Society outcome questionnaire was used to compare functional results between the male patients and the matched female group.

RESULTS

Compared with the random sample of female patients, the male patients were older at the time of presentation (average [and standard deviation], 13.9 +/- 1.9 compared with 12.8 +/- 1.4 years) and at the time of surgery (average, 15.9 +/- 2.0 compared with 14.2 +/- 1.4 years) (p < 0.05). The male and female patients presented with primary coronal curves of similar magnitudes (average, 48 degrees +/- 19 degrees compared with 47 degrees +/- 13 degrees ), but the male patients had larger curves at the time of surgery (average, 62 degrees +/- 11 degrees compared with 56 degrees +/- 10 degrees ) with greater coronal plane imbalance. Compared with the subset of female patients matched for curve type and magnitude, the male patients had, on average, a longer surgical time (263 +/- 61 compared with 202 +/- 40 minutes), greater intraoperative blood loss (1148 +/- 660 compared with 944 +/- 408 mL), and less curve correction in the coronal plane (from 62 degrees +/- 11 degrees to 31 degrees +/- 11 degrees compared with from 59 degrees +/- 10 degrees to 23 degrees +/- 9 degrees ) (p < 0.05). The loss of coronal plane correction, the final coronal balance, all measured sagittal plane parameters, and the prevalence of complications were the same in these two groups. With regard to functional outcome, the scores were similar with the exception that the male patients had lower scores in the category of "function from back condition" when compared with the matched female patients (3.8 +/- 0.2 compared with 4.3 +/- 0.3 points) (p < 0.05).

CONCLUSIONS

Adolescent idiopathic scoliosis is identified at a later age in male patients than in female patients with similar curve types. The curve magnitudes in the male patients are greater at the time of surgery. When surgeons are planning operative correction of adolescent idiopathic scoliosis in male patients, they should expect longer operative time, greater blood loss, and less coronal plane correction of the primary curve. However, balance in the coronal and sagittal planes should be achieved and complication rates and functional outcomes can be expected to be similar to those in female patients.

Recombinant human bone morphogenetic protein-2 enhances anterior spinal fusion in a thoracoscopically instrumented animal model

BACKGROUND

Thoracoscopically assisted anterior spinal arthrodesis and instrumentation is being used more widely to treat idiopathic scoliosis. However, harvesting autologous bone increases operative time and morbidity. The purpose of this study was to compare autologous iliac crest and rib graft with recombinant human bone morphogenetic protein-2 (rhBMP-2) in thoracoscopically assisted anterior spinal arthrodesis and instrumentation in an animal model.

METHODS

Twenty-two pigs underwent thoracoscopically assisted anterior spinal arthrodesis. Each animal had five contiguous thoracic discectomies followed by anterior instrumentation. The animals were randomly assigned to five treatment groups. Group I consisted of control animals that received no graft material; group II, animals treated with autologous rib graft; group III, animals treated with autologous iliac crest graft; group IV, animals treated with an rhBMP-2-composite sponge (collagen-hydroxyapatite-tricalcium phosphate carrier); and group V, animals treated with a composite sponge carrier alone. The animals were killed four months after the procedure, and the spines were harvested. The fusion mass was assessed with use of axial and sagittal computed tomography scans. The spines were tested biomechanically with incremental loads applied in the frontal and axial planes to achieve bending moments of up to 6.0 N-m. Angular motion at each segment was recorded with use of a three-dimensional motion analysis system. Histomorphometric analysis of each undecalcified disc segment was also performed.

RESULTS

The fusion grades, according to computed tomography analysis with use of a 4-point grading system in which scores of 3 and 4 indicated a solid fusion, were 0.6 point for group I, 2.1 points for group II, 2.3 points for group III, 3.8 points for group IV, and 0.4 point for group V. Group IV (the rhBMP-2-treated animals) had a higher grade than all of the other groups. Group II (rib graft) and group III (iliac crest) had similar grades, and both were greater than group I (the untreated controls) and group V (composite sponge alone) (p < 0.05). In axial rotation, lateral bending, and flexion-extension, the spines in group IV were stiffer than those in the four other groups (p < 0.05); the spines in groups II and III were similar, and the spines in both of those groups were stiffer than those in groups I and V (the control groups). Histologic analysis demonstrated that the total new-bone area, expressed as a percentage of the total disc space area, was 23.2% in group I, 37.1% in group II, 37.2% in group III, 48.5% in group IV, and 5.9% in group V. Group IV had significantly greater bone formation than all of the other groups (p < 0.001). The animals treated with rib graft (group II) and iliac crest (group III) had a similar amount of bone formation, and it was greater than that in both control groups (p < 0.001).

CONCLUSIONS

The rhBMP-2 significantly increased the prevalence and quality of the spinal fusion after thoracoscopically assisted anterior arthrodesis and instrumentation in an animal model compared with that in the other treatment groups and in the controls.

Spinal shape changes resulting from scoliotic spine surgical instrumentation expressed as intervertebral rotations and centers of rotation

This paper reports the changes in spinal shape resulting from scoliotic spine surgical instrumentation expressed as intervertebral rotations and centers of rotation. The objective is to test the hypothesis that the type of spinal instrumentation system (Cotrel-Dubousset versus Colorado) does not influence these motion parameters. Intervertebral rotations and centers of rotation of the scoliotic spines were computed from the pre- and post-operative radiographs of 82 patients undergoing spinal correction. The three-dimensional (3D) reconstruction of six anatomical landmarks was achieved for each of the thoracic and lumbar vertebrae. A least-squares approach based on singular value decomposition was used to calculate the rigid body transformation parameters. Average centers of rotation for all intervertebral levels are located in the neural canal at the mid-sagittal plane and approximately at the superior endplate level of the inferior vertebra. Intervertebral rotations have components in all planes: 6.7 degrees (frontal), 5.5 degrees (sagittal) and 4.5 degrees (transverse) RMS for all intervertebral levels. Nearly all intervertebral rotations and centers of rotation are not significantly different for the two instrumentation systems. Various intervertebral rotations and 3D reconstruction errors were simulated on a theoretical model of a lumbar functional unit to assess the proposed method. Intervertebral rotation errors were 1.7 degrees when simulating 3D errors of 3mm on the position of the landmarks. Maximum errors for the position of centers of rotation were below 1cm in the case of intervertebral rotations larger than 2.5 degrees (most cases), but were larger (38 mm) for small intervertebral rotations (<1 degrees ). The type of instrumentation system did not influence intervertebral rotations and centers of rotation. These results provide valuable data for the development and validation of simulation models for surgical instrumentation of idiopathic scoliosis.

Harrington and Cotrel-Dubousset instrumentation in adolescent idiopathic scoliosis. Long-term functional and radiographic outcomes

BACKGROUND

Previous studies have shown that the long-term clinical outcome does not correlate with the radiographic outcome in patients treated with Harrington instrumentation for adolescent idiopathic scoliosis. Cotrel-Dubousset instrumentation has been reported to provide better correction radiographically, but it is unclear whether it provides better long-term clinical or functional outcomes. We are not aware of any long-term studies comparing Harrington and Cotrel-Dubousset instrumentation.

METHODS

Seventy-eight patients in whom adolescent idiopathic scoliosis was treated with Harrington instrumentation and fifty-seven in whom it was treated with Cotrel-Dubousset instrumentation participated in this study. The mean duration of follow-up was 20.8 years for the Harrington instrumentation group and 13.0 years for the Cotrel-Dubousset instrumentation group. The mean age at the time of follow-up was thirty-six years and twenty-eight years, respectively. Radiographs were made preoperatively and at the two-year and final follow-up examinations. The Scoliosis Research Society questionnaire was completed, a physical examination was performed, and spinal mobility and non-dynamometric trunk strength were measured at the final follow-up visit.

RESULTS

The mean preoperative Cobb angle of the thoracic curves was 53 degrees in the Harrington instrumentation group and 55 degrees in the Cotrel-Dubousset instrumentation group. The mean numbers of vertebrae included in the instrumentation were 10.7 and 9.9, respectively. At the two-year follow-up evaluation, the mean postoperative Cobb angles were 38 degrees and 25 degrees, respectively (p < 0.0001). At the final follow-up evaluation, the mean angles were 45 degrees and 32 degrees (p < 0.0001). No significant difference in thoracic kyphosis or lumbar lordosis was observed between the study groups at the final follow-up evaluation. The average score on the Scoliosis Research Society questionnaire was 97 points in both groups. Measurements of non-dynamometric trunk strength corresponded with age and sex-adjusted reference values, on the average, but patients with Cotrel-Dubousset instrumentation performed significantly better in the squatting test (p = 0.010). Abnormal lumbar extension and trunk side-bending were significantly more common in the Harrington instrumentation group (p = 0.050 and p = 0.0061, respectively). Complications were recorded for nine (12%) of the patients treated with Harrington instrumentation and fifteen (26%) of those treated with Cotrel-Dubousset instrumentation (p = 0.027).

CONCLUSIONS

Cotrel-Dubousset instrumentation yielded better long-term functional and radiographic outcomes in patients with adolescent idiopathic scoliosis than did Harrington instrumentation. However, complications were more common in the Cotrel-Dubousset instrumentation group.

Anterior single-rod instrumentation of the thoracic and lumbar spine: saving levels

STUDY DESIGN

To evaluate the ability of single-rod anterior instrumentation to save or preserve fusion levels and improve thoracic hypokyphosis in patients with adolescent idiopathic thoracic, thoracolumbar, or lumbar scoliosis.

OBJECTIVE

To provide indications for single anterior rod instrumentation for the treatment of adolescent idiopathic scoliosis and demonstrate effectiveness in properly selected cases.

SUMMARY OF BACKGROUND DATA

Posterior multisegmented dual rod instrumentation is the most commonly used instrumentation for the surgical treatment of adolescent idiopathic scoliosis. The issue of longer fusion levels and inability to correct hypokyphosis with posterior instrumentation continues to be debated in the literature. Anterior instrumentation has the ability in certain curve patterns to preserve distal and proximal levels as well as correct thoracic hypokyphosis.

METHODS

A brief discussion of the Lenke adolescent idiopathic scoliosis classification system is presented. Surgical treatment options for each of the curve types are discussed in detail.

RESULTS

Single-rod anterior instrumentation for adolescent idiopathic scoliosis will predictably save levels in Type I curves without hyperkyphosis as well as Type 5 curves; however, it is usually contraindicated in Type 2, Type 4, and Type 6 curves. Single-rod anterior instrumentation can occasionally be utilized in Type 3 curves if the magnitude of the lumbar curve is significantly less than the thoracic curve and the flexibility of the lumbar curve approaches 25 degrees on the side-bending radiograph.

CONCLUSIONS

Single-rod anterior instrumentation will often saved one to three distal fusion levels when treating isolated major thoracic, thoracolumbar, or lumbar curves. Fusion levels should include upper to lower Cobb levels. Additionally, anterior single-rod instrumentation because its kyphogenic nature will predictably correct hypokyphosis of the thoracic spine.

Survivorship analysis of Cotrel-Dubousset instrumentation in idiopathic scoliosis

This study presents a survivorship analysis of Cotrel-Dubousset instrumentation in the surgical treatment of idiopathic scoliosis. Between 1987 and 1995, a total of 133 patients with idiopathic scoliosis received posterior spine fusion and instrumentation with the CD system at our center. The patients' mean age at surgery was 16.5 years (range 11-43 years). The magnitude of the thoracic scoliosis averaged 62.7 degrees (range 40 degrees -125 degrees ) and that of the lumbar curve was 58.8 degrees (range 40 degrees -100 degrees ). On average, 12.2 segments were fused (range 8-17) and, excluding the rods, 14.1 implants were set for each patient (range 10-21). Survivorship analysis was carried out using the Kaplan-Meier method. Implant removal was considered the terminal event, or "death". The effect of several variables on survival rate was determined with the Cox regression method. The patients remained in the study for 56.7 months (range 2-120 months). One-hundred and ten patients were withdrawn ("censored"): 90 "alive" (did not require repeat surgery and attended follow-up control in 1997) and 20 "lost" (did not attend control in 1997). Twenty-three patients attained the terminal event of implant removal for a variety of reasons: acute infection (three cases), late infection (ten cases), implant failure requiring revision (six cases) and local pain (four cases). The survival rate was 95.5% at 3 months, 94.7% at 6 months, 93.9% at 1 year, 91.5% at 2 years, 82.2% at 5 years and 76.5% at 10 years. The magnitude of the curves, total number of implants and number of fused segments did not correlate with survival probability. A positive correlation was found between survival rate and correction loss between surgery and last control. A survival rate of 76.5% at 10 years is unexpectedly low. Current data suggest that the incapacity to maintain correction after initial surgery plays a major roll in the long-term evolution of Cotrel-Dubousset instrumentation.

Thoracoscopic anterior instrumentation and fusion for idiopathic scoliosis

Thoracoscopically assisted surgery is a new approach to access the anterior spine to perform biopsies, anterior releases, diskectomies, and anterior instrumentation and fusion for idiopathic thoracic scoliosis. This approach compromises the chest wall less than an open thoracotomy does because it uses several small portal incisions. It has been suggested that this approach allows fusion of fewer motion segments and better correction of curvature than does posterior spinal fusion and instrumentation. The technique, which is still evolving, is technically demanding, requiring advanced training and special instrumentation and anesthesia techniques.

Lumbar end plate osteotomy in adult patients with scoliosis

The maintenance of mobile segments in the lumbar spine may prevent complications associated with long fusions to the sacrum and permit improved postoperative patient function and mobility. The purpose of the current study was to describe the technique of end plate osteotomy for surgical treatment of fractional curves in the lumbosacral region. This technique serves to allow the end lumbar vertebra to become horizontal, to reduce lumbosacral fractional curves, and to create a stable end vertebra above the pelvis. A review of long-term clinical and radiographic outcomes in patients treated with the technique have been satisfactory. The authors show that the techniques of end plate osteotomy with concave osteophyte excision is a clinically valuable technique for the treatment of adults with fixed lumbosacral fractional curves.

Proximal kyphosis after short posterior fusion for thoracolumbar scoliosis

Thoracolumbar idiopathic scoliosis usually is treated by anterior spinal fusion. However, short posterior spinal fusion that includes only the structural curve has been tried in a limited number of patients. The fusion may end cranially in the lower thoracic region and cause an increase in sagittal decompensation at the proximal junction. From July 1989 to July 1998, 14 patients were treated with thoracolumbar idiopathic scoliosis by short posterior spinal fusion. The lateral radiographs were evaluated preoperatively, immediately postoperative, and during followup. The focal kyphotic angle was used to examine the changes in focal sagittal alignment. A 10 degrees progression was defined as the radiographic criterion for the development of junctional kyphosis. Proximal junctional kyphosis occurred in six of the 14 patients, in which one patient needed revision surgery. In all six patients, the average preoperative lumbar lordosis was greater than 35 degrees, and decreased more than 10 degrees during surgery. In the five patients with a focal kyphotic angle larger than 10 degrees, four had proximal junctional kyphosis develop. According to the current findings, short posterior spinal fusion can be done only if the focal kyphotic angle proximal to the fusion is less than 10 degrees, and the lumbar lordosis must be preserved carefully during surgery.

Anterior thoracic scoliosis constructs: effect of rod diameter and intervertebral cages on multi-segmental construct stability

BACKGROUND CONTEXT

Many studies have reported on the use of anterior instrumentation for thoracolumbar scoliosis and more recently thoracic scoliosis. However, the optimal construct design remains an issue of debate.

PURPOSE

To optimize construct design and enhance implant survival until a successful spinal arthrodesis is achieved.

STUDY DESIGN

This study evaluated the effect of rod diameter and intervertebral cages on construct stiffness and rod strain using a long-segment, anterior thoracic scoliosis model with varying levels of intervertebral reconstruction.

METHODS

Sixteen fresh-frozen calf spine specimens (T1 to L1) were divided into two groups based on rod diameter reconstruction (4 mm and 5 mm). Testing included axial compression, anterior flexion, extension and lateral bending with variations in the number and level of intervertebral cage reconstructions: apical disc (one), end discs (two), apical and end discs (three), all seven levels (seven). Multisegmental construct stiffness and rod strain were determined and normalized to the intact specimen for analysis.

RESULTS

The seven-level intervertebral cage construct showed significantly greater stiffness in axial compression for both the 4-mm (366% increased stiffness) and 5-mm (607% increased stiffness) rod groups (p<.001). The remaining constructs were not significantly different from each other (p>.05). In flexion, similar results were obtained for the 4-mm construct (p<.001) but not the 5-mm construct, because the reconstruction-alone, one-, two- and three-cage constructs were all significantly stiffer than the intact specimen (p<.05). Multisegmental construct stiffness under extension loading, as well as right and left lateral bending, also exhibited significant differences between the seven-level interbody cage reconstructions and the remaining constructs. Apical rod strain for both the 4-mm-rod and 5-mm-rod groups were significantly higher for the two cage constructs (a cage at either end but not the apex where the strain gauges were located) as compared with the other constructs (p<.05). These differences were more pronounced in the 4-mm-rod group. Similar results were obtained in anterior flexion, extension and lateral bending.

CONCLUSIONS

Intervertebral cages at every level significantly improved construct stiffness compared with increasing rod diameter alone. Moreover, cages markedly decreased rod strain, and when structural interbody supports were not used, axial compression created the greatest rod strain.