Quantification of Increase in Three-dimensional Spine Flexibility Following Sequential Ponte Osteotomies in a Cadaveric Model

The Comparison of Posterior Intervertebral Release Combined with Posterior Column Osteotomy and Posterior Column Osteotomy Alone for the Treatment of Moderate-to-Severe Rigid Scoliosis: A Prospective Controlled Study

OBJECTIVES

There is no consensus on the treatment of moderate-to-severe rigid scoliosis. Anterior release and three-column osteotomy are excessively traumatic, whereas posterior column osteotomy (PCO) alone results in poor outcomes. An emerging surgical technique, posterior intervertebral release (PR), can release the rigid spine from the posterior approach. This study was performed to compare the multi-segment apical convex PR combined with PCO and PCO alone in patients with moderate-to-severe rigid scoliosis.

METHODS

From June 2021 to June 2022, this prospective study of moderate-to-severe (Cobb: 70-90°) rigid scoliosis (flexibility of main curve <25%) involved two groups defined by surgical procedure: the PR group, the patients undergoing PR combined with PCO; and the PCO group, the patients undergoing PCO alone. Follow-up was at least 12 months. Radiographic results mainly included main curve Cobb, correction of per PR/PCO segment, apical vertebra rotation (AVR) and apical vertebra translation (AVT). Demographics, surgical data, complications were also recorded. Student's independent samples t test and Pearson's chi-square test were used to compare the differences between groups.

RESULTS

Forty patients with an average age of 16.65 years were included (PR group, n = 20; PCO group, n = 20). The main curves averaged 77.56° ± 5.86° versus 78.02° ± 5.72° preoperatively and 20.07° ± 6.73° versus 33.58° ± 5.76° (p < 0.001) at the last follow-up in the PR and PCO groups, respectively. The mean correction rates were 74.30% and 56.84%, respectively (p < 0.001). The average coronal curve correction was 13.49° per release segment, which was significantly higher than the PCO correction of 6.20° (p < 0.001). The correction of apical vertebra rotation and translation in the main thoracic curve was significantly better in the PR group than in the PCO group (p < 0.05). Several minor complications in the two groups improved after conservative treatment.

CONCLUSION

The multi-segment apical convex PR combined with PCO offers more advantages than PCO alone in the treatment of patients with moderate-to-severe rigid scoliosis. Owing to its excellent corrective effect and few complications, this is a high benefit-risk ratio surgical strategy for rigid scoliosis.

Evaluation of Topology Optimization Using 3D Printing for Bioresorbable Fusion Cages: A Biomechanical Study in a Porcine Model

STUDY DESIGN

Preclinical biomechanical study of topology optimization versus standard ring design for bioresorbable poly-ε-caprolactone (PCL) cervical spine fusion cages delivering bone morphogenetic protein-2 (BMP-2) using a porcine model.

OBJECTIVE

The aim was to evaluate range of motion (ROM) and bone fusion, as a function of topology optimization and BMP-2 delivery method.

SUMMARY OF BACKGROUND DATA

3D printing technology enables fabrication of topology-optimized cages using bioresorbable materials, offering several advantages including customization, and lower stiffness. Delivery of BMP-2 using topology optimization may enhance the quality of fusion.

METHODS

Twenty-two 6-month-old pigs underwent anterior cervical discectomy fusion at one level using 3D printed PCL cages. Experimental groups (N=6 each) included: Group 1: ring design with surface adsorbed BMP-2, Group 2: topology-optimized rectangular design with surface adsorbed BMP-2, and Group 3: ring design with BMP-2 delivery via collagen sponge. Additional specimens, two of each design, were implanted without BMP-2, as controls. Complete cervical segments were harvested six months postoperatively. Nanocomputed tomography was performed to assess complete bony bridging. Pure moment biomechanical testing was conducted in all three planes, separately. Continuous 3D motions were recorded and analyzed.

RESULTS

Three subjects suffered early surgical complications and were not evaluated. Overall, ROM for experimental specimens, regardless of design or BMP-2 delivery method, was comparable, with no clinically significant differences among groups. Among experimental specimens at the level of the fusion, ROM was <1.0° in flexion and extension, indicative of fusion, based on clinically applied criteria for fusion of <2 to 4°. Despite the measured biomechanical stability, using computed tomography evaluation, complete bony bridging was observed in 40% of the specimens in Group 1, 50% of Group 2, 100% of Group 3, and none of the control specimens.

CONCLUSION

A topology-optimized PCL cage with BMP-2 is capable of resulting in an intervertebral fusion, similar to a conventional ring-based design of the same bioresorbable material.

Posterior Multisegment Apical Convex plus Concave Intervertebral Release Combined with Posterior Column Osteotomy for the Treatment of Rigid Thoracic/Thoracolumbar Scoliosis

BACKGROUND

Intervertebral release (IVR) in the apical region is critical for full release of a rigid spine. Previous studies have mainly reported IVR techniques using an anterior approach or posterior apical convex IVR. We first report the surgical procedure of posterior multisegment apical convex plus concave IVR combined with posterior column osteotomy (PCO) for treating rigid thoracic/thoracolumbar scoliosis.

METHODS

This study retrospectively analyzed clinical, radiologic outcomes and technique notes of 18 patients with rigid scoliosis treated with posterior multisegment convex plus concave IVR combined with PCO.

RESULTS

The preoperative, postoperative, and final follow-up mean sagittal Cobb angles of the main curve were 75.2° (58.7°-110.2°), 18.4° (9°-35.1°), and 19.0° (8.2°-36.3°), respectively. The mean correction rate was 75.3% (66.7%-86.7%). In cases of thoracolumbar kyphosis, the preoperative, postoperative, and final follow-up mean sagittal Cobb angles were 45.7° (40.5°-52.6°), 18.8° (10.2°-27.5°), and 19.8° (11.1°-29°), respectively. The mean correction rate was 57% (42.1%-72.6%). The mean axial vertebral rotation (AVR) in the IVR region was 24.4° (14.3°-46.3°) preoperatively and was corrected to 10.9° (10.9°-26.6°) postoperatively. The mean correction rate for AVR was 55.9% (41.1%-78.6%). The coronal and sagittal Cobb angles and AVR postoperatively were significantly lower than those preoperatively (P < 0.001). This case series reported 2 cases of pleural effusion and 1 case of wound infection.

CONCLUSIONS

Single posterior multilevel apical convex plus concave IVR combined with PCO is a safe and effective surgical method for treating rigid thoracic/thoracolumbar scoliosis that does not need 3-column osteotomy.

The Sagittal Plane in Spinal Fusion for Adolescent Idiopathic Scoliosis

Sagittal balance is widely recognized as the primary determinant of optimal outcomes in adult spinal deformity. In adolescent idiopathic scoliosis (AIS), coronal correction risks being obtained at the expense of sagittal malalignment after posterior spinal fusion. Apical lordosis, often underestimated on two-dimensional imaging, is the primary deforming factor in AIS. Failure to restore thoracic kyphosis and lumbar lordosis during posterior spinal fusion contributes to problematic early surgical complications, including proximal or distal junctional kyphosis and failure. Although adolescent patients often compensate for sagittal imbalance in the short-term and mid-term, late sequelae of iatrogenic sagittal imbalance include flatback syndrome, disk degeneration, cervical kyphosis, and late decompensation. Objective criteria using spinopelvic parameters and preoperative three-dimensional planning can guide sagittal plane correction during PSF for AIS. Technical caveats can help avoid sagittal plane complications, including instrumentation level selection, anchor type, and anatomic protection of adjacent levels. Other surgical techniques to optimize restoration of thoracic kyphosis include higher implant density, stiffer rod material, Ponte osteotomies, and deformity correction technique.

Evaluating flexibility and predicting curve correction using fulcrum-bending radiographs in Lenke type 2 adolescent idiopathic scoliosis

BACKGROUND

Fulcrum-bending (FB) correction is considered to provide the best estimation of main thoracic (MT) curve flexibility and postoperative correction in surgical treatment for adolescent idiopathic scoliosis (AIS). However, few studies evaluated the usefulness of FB radiographs for proximal thoracic (PT) curve. We aimed to perform flexibility assessments using both active side-bending (SB) and FB radiographs and evaluate surgical outcomes after posterior spinal fusion (PSF) for Lenke type 2 AIS.

METHODS

This study included 38 consecutive patients with Lenke type 2 AIS who underwent PSF using a pedicle screw construct with a minimum 2-year follow-up. Radiographic parameters, including correction rate, SB and FB flexibility, and FB correction index (FBCI: [correction rate/FB flexibility] × 100), were evaluated preoperatively, immediately after surgery, and at the 2-year follow-up. The clinical outcomes were preoperatively evaluated using the Scoliosis Research Outcomes Instrument-22 and at the follow-up.

RESULTS

All scoliosis curves significantly improved and shoulder balance shifted toward left shoulder elevation (all comparisons, p < 0.0001). There were significant differences between the SB and FB corrections in the PT and MT curves (p < 0.0001). The magnitudes of the discrepancies between the SB and FB corrections in the PT and MT curves were 11.2° ± 5.2° and 11.6° ± 7.2°, respectively. FB correction did not differ from postoperative Cobb angles correction immediately after surgery or at the 2-year follow-up; the mean FBCIs in the PT and MT curves were 98.8% and 105.5%, respectively. The self-image domain SRS-22 scores had significantly increased at the 2-year follow-up (p < 0.0001).

CONCLUSIONS

There were significant differences between the SB and FB corrections, and FB correction tended to approximate the postoperative curve correction (FBCI = 100%) for PT and MT curves in patients with Lenke type 2 AIS. FB flexibility is more reliable than SB flexibility in evaluating actual curve flexibility even for the PT curve.

Ponte osteotomies in a matched series of large AIS curves increase surgical risk without improving outcomes

PURPOSE

The routine use of Ponte osteotomies in adolescent idiopathic scoliosis (AIS) surgery is controversial with conflicting data for coronal plane correction and little analysis in the sagittal plane. The objective of this study was to analyze the efficacy of Ponte osteotomies in large curve AIS.

METHODS

A single institution, prospectively-collected series of consecutive AIS patients who had Ponte osteotomies (P cohort) was directly matched to patients with no Pontes (NP cohort) by age, gender, Lenke classification, surgeon, coronal, and sagittal Cobb angles. The radiographic review included adjusted values using a 3D-derived published formula for preoperative T5-T12 kyphosis. Patient-reported outcomes (PROs) were assessed with the SRS-30 and Spinal Appearance Questionnaire (SAQ).

RESULTS

There were 68 patients (34/cohort) with minimum 2-year follow-up with no differences between P and NP cohorts in age, preoperative coronal Cobb (74.5° vs 70.8°), flexibility index, measured or 3D-adjusted T5-T12 kyphosis. Rod material/diameter, fusion levels, blood loss, and operative time did not differ, but implant density was higher in the P group (1.53 vs 1.31, p < 0.001). The P group had 7.9% greater coronal Cobb correction (66.6% vs 58.7%, p < 0.003) without difference in final Cobb angles (24.7° vs. 29.1°, p = 0.052). There were no differences in measured or adjusted T5-T12 kyphosis in the sagittal plane. The P group had a 15% rate of critical intraoperative neuromonitoring changes versus 0% in the NP group (p = 0.053). At follow-up, there were no differences in scoliometer measurements or any domain of SRS-30 or SAQ scores.

CONCLUSION

In this first reported matched series of AIS patients, Ponte osteotomies provide small radiographic gains in the coronal plane with no improvement in the sagittal plane and no change in truncal rotation. There was a higher risk of critical intraoperative neuromonitoring changes, and no benefits in patient-reported outcomes. This calls into question the routine use of Ponte osteotomies in AIS, even for curves averaging 70 degrees.

LEVEL OF EVIDENCE

II.

Hi-PoAD technique for Adolescent Idiopathic Scoliosis in Adult: Personal case series

PURPOSE

The aim of this article is to present an original surgical technique for the treatment of rigid Adult Idiopathic Scoliosis (AdIS) and the results at minimum 2 years follow-up in a cohort of 40 patients.

METHODS

We retrospectively reviewed 40 patients affected by rigid AdIS, older than 40 years and operated with a posterior one stage surgical technique summarized with the acronym Hi-PoAD, (high-density pedicle screws, Ponte osteotomies, asymmetric rods contouring, direct vertebral rotation). The demographic and surgical data were collected, and the improvement of clinical scores and radiologic parameters was obtained after surgery, at 1 and 2 years and at final follow-up, to assess deformity correction, coronal and sagittal balance and clinical outcome.

RESULTS

The average follow-up was 2.9 years (range 2-3.5). Average coronal Cobb angle decreased from 65.0° ± 8.4 to 18.9° ± 3.9 (p < 0.01). Rotation sagittal angle decreased from 26.2° ± 4.4° to 12.4° ± 2.8° (p < 0.01). Mean thoracic kyphosis improved from 23.1° ± 3.6° to 36.0° ± 3.9°. SRS-22 improved form 2.9 ± 0.4 to 3.7 ± 0.6 (p < 0.01). Four early post-operative deep wound infections were observed, all healed after debridement and implant retention. No mechanical complication, junctional kyphosis, deformity progression or non-union were recorded at the last follow-up.

CONCLUSIONS

Hi-PoAD technique proved to be safe and effective in the treatment of rigid Adult Idiopathic Scoliosis. The reason for the success is related to the combined strategies adopted, that dissipates corrective forces over several levels, reducing mechanical stress at the screw-bone interface and optimizing corrective potential.

Impact of multilevel facetectomy on segmental spinal flexibility in patients with thoracic adolescent idiopathic scoliosis

BACKGROUND

The aim of this study was to intraoperatively assess the effects of multilevel facetectomy on segmental spinal flexibility in patients with thoracic adolescent idiopathic scoliosis.

METHODS

Twenty patients who underwent posterior thoracic adolescent idiopathic scoliosis curve correction were evaluated. Compressive or distractive loaded force of 50N was applied on the handle of a compressor or distractor connected to the necks of pedicle screws inserted at T7 to T11. Segmental spinal flexibility rates were calculated based on the distance between screw heads under the loaded and unloaded conditions. In addition, the flexibility rates were obtained before and after multilevel facetectomy.

FINDINGS

Absolute flexibility rates of all segments significantly increased after multilevel facetectomy under both compressive and distractive forces (P < 0.01). The absolute change in the flexibility rate was significantly higher at the concave side than at the convex side under both compressive (P < 0.01) and distractive loaded forces (P = 0.046). No significant correlation was found between change in the flexibility rates and preoperative Cobb angle or preoperative curve flexibility.

INTERPRETATION

From a biomechanical point of view, multilevel facetectomy provides proper spinal flexibility to improve the correction rate of posterior adolescent idiopathic scoliosis surgery. The effects are higher at the concave side than at the convex side.

Increasing loads and diminishing returns: a biomechanical study of direct vertebral rotation

STUDY DESIGN

Biomechanical simulation of DVR and pure-moment testing on thoracic spines.

OBJECTIVES

Characterize load-deformation response of thoracic spines under DVR maneuvers until failure, and compare to pure-moment testing of same spines. Despite reports of surgical complications, few studies exist on increase in ROM under DVR torque. Biomechanical models predicting increases from surgical releases have consistently used "pure-moments", a standard established for non-destructive measurement of ROM. Yet, DVR torque is not accurately modeled using pure moments and, moreover, magnitudes of torque applied during DVR maneuvers may be substantially higher than pure-moment testing.

METHODS

Cadaveric thoracic spines (N = 11) were imaged, then prepared. Polyaxial pedicle screws were implanted at T7-T10 after surgical releases. Bilateral facetectomies and Ponte osteotomies were completed at T10-T11. A custom apparatus, mounted into an 8-dof MTS load frame, was used to attach to pedicle screws, allowing simulation of surgical DVR maneuvers. Motions of vertebrae were measured using optical motion tracking. Torque was increased until rupture of the T10-T11 disc or fracture at the pedicle screw sites at any level. The torque-rotation behavior was compared to its behavior under pure-moment testing performed prior to the DVR maneuver.

RESULTS

Under DVR maneuvers, failure of the T10-T11 discs accompanied in most cases by pedicle screw loosening, occurred at 13.7-54.7 Nm torque, increasing axial rotation by 1.4°-8.9°. In contrast, pure-moment testing (4 Nm) increased axial rotation by only 0.0°-0.9°.

CONCLUSIONS

DVR resulted in substantially greater correction potential increases compared to pure-moment testing even at the same torque. These results suggest increased flexibility obtained by osteotomies and facetectomies is underestimated using pure-moment testing, misrepresenting clinical expectations. The present study is an important and necessary step toward the establishment of a more accurate and ultimately surgically applied model.

LEVEL OF EVIDENCE

III.

Stabilizing effect of the rib cage on adjacent segment motion following thoracolumbar posterior fixation of the human thoracic cadaveric spine: A biomechanical study

BACKGROUND

Although the rib cage provides substantial stability to the thoracic spine, few biomechanical studies have incorporated it into their testing model, and no studies have determined the influence of the rib cage on adjacent segment motion of long fusion constructs. The present biomechanical study aimed to determine the mechanical contribution of the intact rib cage during the testing of instrumented specimens.

METHODS

A cyclic loading (CL) protocol with instrumentation (T4-L2 pedicle screw-rod fixation) was conducted on five thoracic spines (C7-L2) with intact rib cages. Range of motion (±5 Nm pure moment) in flexion-extension, lateral bending, and axial rotation was captured for intact ribs, partial ribs, and no ribs conditions. Comparisons at the supra-adjacent (T2-T3), adjacent (T3-T4), first instrumented (T4-T5), and second instrumented (T5-T6) levels were made between conditions (P ≤ 0.05).

FINDINGS

A trend of increased motion at the adjacent level was seen for partial ribs and no ribs in all 3 bending modes. This trend was also observed at the supra-adjacent level for both conditions. No significant changes in motion compared to the intact ribs condition were seen at the first and second instrumented levels (P > 0.05).

INTERPRETATION

The segment adjacent to long fusion constructs, which may appear more grossly unstable when tested in the disarticulated spine, is reinforced by the rib cage. In order to avoid overestimating adjacent level motion, when testing the effectiveness of surgical techniques of the thoracic spine, inclusion of the rib cage may be warranted to better reflect clinical circumstances.

Patient-Reported SRS-24 Outcomes Scores After Surgery for Adolescent Idiopathic Scoliosis Have Improved Since the New Millennium

STUDY DESIGN

Observational.

OBJECTIVE

To examine changes in patient-reported two-year postoperative outcomes via the Scoliosis Research Society (SRS)-24 Outcomes Instrument from 2001 through 2015.

SUMMARY OF BACKGROUND DATA

Techniques for correction of adolescent idiopathic scoliosis (AIS) have evolved over the years, but it is unclear how these changes have impacted patient-reported outcomes.

METHODS

AIS patients with two-year postoperative follow-up from a prospective multicenter registry were divided into three-year groups based on trends in surgical approach and construct type (2010-2014: 52% anterior, 43% posterior hybrids; 2005-2011: 3% anterior, 5% posterior hybrids; 2012-2015: 0% anterior, 0.2% posterior hybrids). Because of the ordinal scale (1-5) and bipolar nature of the response sets for the SRS-24, domain/total scores were categorized as ≤3 (predominantly negative) or 4-5 (predominantly positive). Variables were compared across the three groups.

RESULTS

A total of 1,695 patients were analyzed; 172 (2010-2014), 926 (2005-2011), and 597 (2012-2015). Average age was 14.7 ± 2 years, the average primary curve was 55° ± 13°, and the group was primarily female (82%). There was a decline in the rate of positive scores for preoperative pain and self-image across the three groups (p < .05). There was an increase in the rate of positive scores for two-year postoperative self-image after surgery, function after surgery, and satisfaction (p < .05). Decreases in length of hospital stay, blood loss, surgical time, preoperative kyphosis, and postoperative trunk shift were observed (p < .05). Increases were observed in levels fused, preoperative major coronal curve, preoperative rib prominence, preoperative trunk shift, percentage correction of major curve, kyphosis restoration, and the rate of double/triple curves (p < .05).

CONCLUSION

The percentage of patients with positive postoperative SRS scores has increased in the modern era, providing evidence that newer surgical techniques are resulting in improved outcomes based on the patients' perspectives. Interestingly, recent patients were more afflicted with negative pain and self-image before surgery.

One-Stage Posterior Multiple-Level Asymmetrical Ponte Osteotomies Versus Single-Level Posterior Vertebral Column Resection for Severe and Rigid Adult Idiopathic Scoliosis: A Minimum 2-Year Follow-up Comparative Study

STUDY DESIGN

Retrospective comparative study.

OBJECTIVE

To compare the efficacy and safety of one-stage posterior multiple-level asymmetrical Ponte osteotomies (MAPOs) and single-level posterior vertebral column resection (VCR) for severe and rigid adult idiopathic scoliosis (ADIS).

SUMMARY OF BACKGROUND DATA

The surgical treatment of severe and rigid ADIS is a demanding and difficult challenge due to its complicated characteristics. Spine surgeons have often pursued advanced correction techniques such as VCR for such patients, which reported to present excellent correction outcomes. But this attractive procedure brought the greatest risk to both surgeons and patients.

METHODS

A total of 48 patients who underwent MAPO or VCR and fusion surgery with minimum 2-year follow-up between February 2009 and November 2015 were enrolled. Twenty-six patients were included in MAPO group and 12 patients in VCR group with an average age of 26.65 ± 8.40 and 27.92 ± 7.50 years, respectively. The average follow-up was 30.24 ± 10.55 months. The surgical details and complications were recorded. The radiological parameters and clinical outcome including Oswestry Disability Index and Scoliosis Research Society-22 questionnaire scores were collected and analyzed.

RESULTS

The main curve in MAPO and VCR group were corrected from an average of 98.52° ± 16.50° to 44.11° ± 17.72° and 108.91° ± 16.56° to 56.49° ± 18.82° with no significant difference. The postoperative coronal and sagittal parameters of the two groups were all improved and it showed no significant differences between the two groups. The mean operative time and blood loss of VCR group were significantly greater than those of MAPO group. All the clinical scores were significantly improved at final follow-up, with no significant difference. The incidence of complications in MAPO group was 3.85%, which was significantly lower than that of VCR group.

CONCLUSION

The surgical procedure of multiple asymmetrical Ponte osteotomy is a safe, easy-to-operate, and effective technique that can correct scoliosis and restore the sagittal alignment. It can gain similar correction outcome to VCR, offering the advantages of reduced operation time, blood loss, and greatly reduced the complication.

LEVEL OF EVIDENCE

3.

Cadaveric biomechanical testing of torque - to - failure magnitude of Bilateral Apical Vertebral Derotation maneuver in the thoracic spine

It remains unclear what is the real safe limit of torque magnitude during Bilateral Apical Vertebral Derotation (BAVD) in thoracic curve correction. Up to author's knowledge there is no study except this one, to reproduce in-vivo real measurements and intraoperative conditions during BAVD maneuver. The objective of this study was to evaluate the torsional strength of the instrumented thoracic spine under axial rotation moment as well as to define safety limits under BAVD corrective maneuver in scoliosis surgery. 10 fresh, full-length, young and intact human cadavers were tested. After proper assembly of the apparatus, the torque was applied through its apical part, simulating thoracic curve derotation. During each experiment the torque magnitude and angular range of derotation were evaluated. For more accurate analysis after every experiment the examined section of the spine was resected from the cadaver and evaluated morphologically and with a CT scan. The average torque to failure during BAVD simulation was 73,3 ± 5,49Nm. The average angle of BAVD to failure was 44,5 ± 8,16°. The majority of failures were in apical area. There was no significant difference between the fracture occurrence of left or right side of lateral wall of the pedicle. There was no spinal canal breach and/or medial wall failure in any specimen. The safety limits of thoracic spine and efficacy of BAVD for axial plane correction in the treatment of Adolescent Idiopathic Scoliosis (AIS) were established. It provided qualitative and quantitative information essential for the spinal derotation under safe loading limits.

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.

Posterior Multiple-Level Asymmetrical Ponte Osteotomies for Rigid Adult Idiopathic Scoliosis

OBJECTIVE

To evaluate the efficacy and safety of posterior multiple-level asymmetrical Ponte osteotomies for rigid adult idiopathic scoliosis.

METHODS

A retrospective study was conducted for adult patients with rigid idiopathic scoliosis (flexibility of main curve <25%) who underwent one-stage multiple-level asymmetrical Ponte osteotomies with a minimum of 2-year follow-up between February 2009 and November 2015. The demographic data and surgical issues were collected, and the improvement of clinical function scores and radiologic parameters were obtained after surgery and during the follow-up to assess deformity correction, spinal balance, and clinical outcome.

RESULTS

A total of 49 patients were included (10 male and 39 female) in this study, with an average age of 26.53 years old. The average follow-up was 28.37 ± 6.98 months. All the cases presented a significant improvement of the main curve and focal kyphosis from 85.62 ± 19.80° to 36.19 ± 16.74° and 53.98 ± 26.80° to 30.88 ± 18.69°, with a mean correction rate of 57.73% and 41.23%. The postoperative coronal and sagittal parameters were all significantly improved, except coronal balance. The mean operative time and blood loss were 267.86 ± 54.49 minutes and 838.78 ± 538.93 mL. All the clinical function scores of patients were significantly improved at the final follow-up. Only one patient had a complication related to surgical incision, with no neurologic complications occurring.

CONCLUSIONS

The surgical procedure of multiple-level asymmetrical Ponte osteotomy is a safe and effective technique, with reduced operation time, blood loss, and complications, and may offer an appropriate option to address the problems of rigid adult idiopathic scoliosis.

Selection of posterior spinal osteotomies for more effective periapical segmental vertebral derotation in adolescent idiopathic scoliosis-An in vivo comparative analysis between Ponte osteotomy and inferior facetectomy alone

BACKGROUND

Ponte osteotomy is a useful method in posterior spinal release. However, it is unclear whether Ponte osteotomy itself contributes to vertebral derotation in surgery for adolescent idiopathic scoliosis (AIS) patients compared to inferior facetectomy alone. This study aimed to assess the effect of Ponte osteotomy on the magnitude of periapical vertebral body rotation compared to inferior facetectomy alone. This study was a prospective collected data.

METHODS

The study included 63 patients with AIS (Thoracic curve type, 35; thoracolumbar/lumbar curve type, 27), who underwent surgery between August 2011 and January 2015. All AIS patients underwent posterior spinal fusion with uniplanar screws and Ponte osteotomies on three periapical intervertebral segments. We measured and analyzed the flexibility of periapical intervertebral rotation pre- and post-bilateral inferior facetectomy, and post-Ponte osteotomy with our device (three times). The difference in intervertebral rotation between pre- and post-Ponte osteotomy was analyzed.

RESULTS

The mean increase in angle was 5.6° for thoracic curves and 6.4° for thoracolumbar curves. The increase in angle for thoracolumbar curves was significantly larger than that for thoracic curves (P < 0.05). The more an apical region of the scoliosis was located at caudal side of spine, the more the flexibility due to Ponte osteotomy increased (P < 0.05). The significant differences of the increase in intervertebral flexibility between inferior facetectomies and Ponte osteotomies were recognized at middle thoracic and thoracolumbar regions (P < 0.005).

CONCLUSIONS

Our data suggest that Ponte osteotomy has a loosening effect on periapical scoliotic curvature compared to inferior facetectomy alone. Ponte osteotomy is likely to be associated with an increase in loosening of the middle thoracic and thoracolumbar regions.

Challenging the Conventional Standard for Thoracic Spine Range of Motion: A Systematic Review

BACKGROUND

Segmental motion is a fundamental characteristic of the thoracic spine; however, studies of segmental ranges of motion have not been summarized or analyzed. The purpose of the present study was to present a summary of the literature on intact cadaveric thoracic spine segmental range of motion in each anatomical plane.

METHODS

A systematic MEDLINE search was performed with use of the terms "thoracic spine," "motion," and "cadaver." Reports that included data on the range of motion of intact thoracic human cadaveric spines were included. Independent variables included experimental details (e.g., specimen age), type of loading (e.g., pure moments), and applied moment. Dependent variables included the ranges of motion in flexion-extension, lateral bending, and axial rotation.

RESULTS

Thirty-three unique articles were identified and included. Twenty-three applied pure moments to thoracic spine specimens, with applied moments ranging from 1.5 to 8 Nm. Estimated segmental range of motion pooled means ranged from 1.9° to 3.8° in flexion-extension, from 2.1° to 4.4° in lateral bending, and from 2.4° to 5.2° in axial rotation. The sums of the range of motion pooled means (T1 to T12) were 28° in flexion-extension, 36° in lateral bending, and 45° in axial rotation.

CONCLUSIONS

The pooled ranges of motion were similar to reported in vivo motions but were considerably smaller in magnitude than the frequently referenced values reported prior to the widespread use of biomechanical testing standards. Improved reporting of biomechanical testing methods, as well as specimen health, may be beneficial for improving on these estimations of segmental cadaveric thoracic spine range of motion.

The True Ponte Osteotomy: By the One Who Developed It

STUDY DESIGN

Technique and applications.

OBJECTIVES

To define the anatomy, biomechanics, indications, and surgical technique of the true Ponte osteotomy.

SUMMARY OF BACKGROUND DATA

The Ponte osteotomy, originally developed for thoracic kyphosis, was the first one to obtain posterior shortening of the thoracic spine, maintaining the anterior column load-sharing capacity. It has become a widely applied technique in various types of spine deformities and a frequent topic of presentations at meetings and in scientific articles. Several of them offer unquestionable evidence of an incorrect execution, with consequently distorted outcomes and erroneous conclusions. A clearing up became essential.

METHODS

Our original experience is based on a series of 240 patients with thoracic hyperkyphosis operated in the years 1969-2015, at first with a standard posterior Harrington technique and then by using the Ponte osteotomy with different instrumentations. A series of 78 of them, operated in the years 1987-1997, who had Ponte osteotomies at every level, is presented.

RESULTS

The average preoperative kyphosis has been corrected from 80° (range 61°-102°) to 31° (range 15°-50°) by a substantial posterior shortening.

CONCLUSIONS

A number of publications use the term Ponte osteotomy loosely for by far incomplete resections and mixing it up with Smith-Petersen's osteotomy. The true Ponte osteotomy is capable of producing marked flexibility in extension, flexion and rotation, justifying its wide use in thoracic deformities, mainly in scoliosis. An exact performance of the osteotomy with adequate bony resections, including the laminae, is an absolute condition to take full advantage of its properties.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Multilevel Posterior Column Osteotomies Are Not Inferior For the Correction of Rigid Adult Spinal Deformity Compared with Pedicle Subtraction Osteotomy

BACKGROUND

Posterior column osteotomy (PCO) has been used for the correction of various spinal deformities. However, little evidence is available regarding the effects of multilevel PCO in adult spinal deformity (ASD) surgery. This study aimed to show the usefulness of PCO in rigid ASD surgery by assessing radiographic and clinical outcomes. We also aimed to assess the corrective potential of multilevel PCOs compared with a single-level pedicle subtraction osteotomy (PSO).

METHODS

Between 2012 and 2016, the medical records of 70 consecutive patients who underwent a multilevel PCO (35 patients) or a single-level PSO (35 patients) for ASD in a single institute were reviewed. Baseline data, radiographic measurements, and clinical outcomes using the Scoliosis Research Society-22 (SRS-22) questionnaire were compared between groups.

RESULTS

The following variables were no different between the groups: age at surgery, sex, level fused, preoperative and postoperative radiologic parameters, and bone mineral density T score. However, operation time (380.0 vs. 483.6 minutes), estimated blood loss (1175.7 vs. 1362.6 mL), and the number of complications (8 vs. 20) were significantly reduced in the PCO group compared with the PSO group. A significant improvement in the SRS-22 score was seen in both groups after surgery, although no difference was observed between the groups postoperatively.

CONCLUSIONS

Multilevel PCOs for the correction of rigid ASD were slightly superior to PSO, regarding clinical outcomes. Radiographic outcomes were similar between groups. Thus, multilevel PCOs may be a viable option for the treatment of rigid ASD with a mobile segment.

Influence of Sequential Ponte Osteotomies on the Human Thoracic Spine With a Rib Cage

STUDY DESIGN

Biomechanical cadaveric study.

OBJECTIVES

The purpose of this study was to determine the change in range of motion (ROM) of the human thoracic spine and rib cage due to sequential Ponte osteotomies (POs).

SUMMARY OF BACKGROUND DATA

POs are often performed in deformity correction surgeries to provide flexibility in the sagittal plane at an estimated correction potential of 5° per PO, but no studies have evaluated the biomechanical impact of the procedure on a cadaveric model with an intact rib cage.

METHODS

Seven human thoracic cadavers with intact rib cages were loaded with pure moments in flexion, extension, axial rotation, and lateral bending for five conditions: intact, PO at T9-T10, PO at T8-T9, PO at T7-T8, and PO at T6-T7. Motion of T1, T6, and T10 were measured, and overall (T1-T12) and regional (T6-T10) ROMs were reported for each mode of bending at each condition.

RESULTS

POs increased ROM in flexion both overall (T1-T12) and regionally (T6-T10), although the magnitude of the increase was marginal (<1°/PO). No significant differences were found in axial rotation or lateral bending.

CONCLUSIONS

POs may increase sagittal correction potential before fusion in patients with hyperkyphosis, though more work should be done to determine the magnitude of the changes.

LEVEL OF EVIDENCE

Level V.

The effect of sublaminar wires on the rib hump deformity during scoliosis correction manoeuvres

INTRODUCTION

During thoracic curve correction, the tightening of the sublaminar wires through concavity creates a medial and a dorsal translation of the spine. However, little is known about the effect of the sublaminar wires on the axial plane.

METHODS

This is prospective case series analysis of 30 consecutive surgical patients with main thoracic adolescent idiopathic scoliosis. All of the patients were fused with hybrid instrumentation (apical concavity-sublaminar wires) and differential rod contouring (over-kyphosis concavity/under-kyphosis convexity). The degrees of the rib hump were measured with a scoliometer placed at the apex of the deformity at five different times: (1) preoperatively through the Adam's test, and during surgery (sterilised scoliometer), (2) with the patient lying prone, (3) after the Ponte osteotomies, (4) after the apical sublaminar tightening, and (5) after convexity apical derotation and compression manoeuvres.

RESULTS

(1) Preoperatively, the Adam's test was 16.3° ± 4.6. (2) Lying prone and under general anaesthesia, it decreased to 11.4° ± 3.9. (3) After exposure and Ponte osteotomies, it was 7.1° ± 4. (4) After the wire tightening, it was 10.8° ± 4.7. (5) After the convexity manoeuvres, it was 4.8° ± 3.7. The degrees of the rib hump final correction were 11.6° ± 4 (70 % correction). The tightening of the sublaminar wires increased the rib hump by 3.5°.

CONCLUSIONS

The sublaminar wire tightening towards the concave rod seemed to create an effect opposite of the desired effect, increasing the apical rotation and the thoracic rib hump deformity. Convexity manoeuvres (apical screw derotation and compression) are necessary and must be coupled with an under-bending of the convex rod to neutralise this effect.

Strength of Thoracic Spine Under Simulated Direct Vertebral Rotation: A Biomechanical Study

BACKGROUND

Direct vertebral rotation (DVR) has gained increasing popularity for deformity correction surgery. Despite large moments applied intraoperatively during deformity correction and failure reports including screw plow, aortic abutment, and pedicle fracture, to our knowledge, the strength of thoracic spines has been unknown. Moreover, the rotational response of thoracic spines under such large torques has been unknown.

PURPOSE

Simulate DVR surgical conditions to measure torsion to failure on thoracic spines and assess surgical forces.

STUDY DESIGN

Biomechanical simulation using cadaver spines.

METHODS

Fresh-frozen thoracic spines (n = 11) were evaluated using radiographs, magnetic resonance imaging (MRI) and dual-energy x-ray absorptiometry. An apparatus simulating DVR was attached to pedicle screws at T7-T10 and transmitted torsion to the spine. T11-T12 were potted and rigidly attached to the frame. Strain gages measured the simulated surgical forces to rotate spines. Torsional load was increased incrementally till failure at T10-T11. Torsion to failure at T10-T11 and corresponding forces were obtained.

RESULTS

The T10-T11 moment at failure was 33.3 ± 12.1 Nm (range = 13.7-54.7 Nm). The mean applied force to produce failure was 151.7 ± 33.1 N (range = 109.6-202.7 N), at a distance of approximately 22 cm where surgeons would typically apply direct vertebral rotation forces. Mean right rotation at T10-T11 was 11.6°±5.6°. The failure moment was significantly correlated with bone mineral density (Pearson coefficient 0.61, p = .047). Failure moment also positively correlated with radiographic degeneration grade (Spearman rho > 0.662, p < .04) and MRI degeneration grade (Spearman rho = 0.742, p = .01).

CONCLUSION

The present study indicated that with the advantage of lever arms provided with DVR techniques, relatively small surgical forces, <200 N, can produce large moments that cause irreversible injury. Although further studies are required to establish the safety of surgical deformity correction surgeries, the present study provides a first step in the quantification of thoracic spine strength.

Biomechanical analysis of Ponte and pedicle subtraction osteotomies for the surgical correction of kyphotic deformities

PURPOSE

Biomechanical analysis of Ponte (PO) and pedicle subtraction osteotomies (PSO) in kyphotic deformity instrumentation.

METHODS

Patient-specific biomechanical model was used to computationally simulate seven hyperkyphotic instrumentation cases with three osteotomy strategies-1-level PSO, 3-level PO, or 6-level PO; forces within the instrumented spine were assessed and results were analyzed through rANOVA tests.

RESULTS

Corrections with multi-level PO were close to those with one-level PSO. In upright position, average implant forces were from 225 to 280 N and rod bending moments were around 10 Nm with no significant difference between the three strategies (p < 0.05). In simulations of 30° flexion, rod bending moments increased by 38, 2, and 8 %, implant forces increased by 28, 23 and 26 % for the 1-level PSO, 3-level PO, and 6-level PO, respectively. Correction per vertebral level was smaller than the maximum correction allowed by PO and PSO.

CONCLUSIONS

Multi-level PO allows similar kyphotic correction to 1-level PSO in spinal deformities with mixed indications for PO and PSO. Loads on the instrumentation constructs in PSO were higher than multi-level PO and higher in 6-level PO than 3-level PO. High loads were located more on the osteotomy sites. The rod shape should be adapted to the anticipated spine correction on the osteotomy sites.

How Does Spinal Release and Ponte Osteotomy Improve Spinal Flexibility? The Law of Diminishing Returns

STUDY DESIGN

Experimental study.

OBJECTIVES

To evaluate the effect of stepwise resection of posterior spinal ligaments, facet joints, and ribs on thoracic spinal flexibility.

SUMMARY OF BACKGROUND DATA

Posterior spinal ligaments, facet joints and ribs are removed to increase spinal flexibility in corrective spinal surgery for deformities such as adolescent idiopathic scoliosis (AIS). Reported clinical results vary and biomechanical substantiation is lacking.

METHODS

Ten fresh-frozen human cadaveric thoracic spinal specimens (T6-T11) were studied. A spinal motion simulator applied a pure moment of ±2.5 Nm in flexion, extension, lateral bending (LB) and axial rotation (AR). Range of motion (ROM) was measured for the intact spine and measured again after stepwise resection of the supra/interspinous ligament (SIL), inferior facet, flaval ligament, superior facet, and rib heads.

RESULTS

SIL resection increased ROM in flexion (10.2%) and AR (3.1%). Successive inferior facetectomy increased ROM in flexion (4.1%), LB (3.8%) and AR (7.7%), and flavectomy in flexion (9.1%) and AR (2.5%). Sequential superior facetectomy only increased ROM in flexion (6.3%). Rib removal provided an additional increase in flexion (6.3%), LB (4.5%) and AR (13.0%). Extension ROM increased by 10.5% after the combined removal of the SIL, inferior facet and flaval ligament.

CONCLUSIONS

Posterior spinal releases in these non-scoliotic spines led to an incremental increase in spinal flexibility, but each sequential step had less effect. As compared to SIL resection with inferior facetectomy, additional superior facetectomy did not improve flexibility in AR and LB and only 6.3% in flexion. The data presented from this in vitro study should be interpreted with care, as no representative cadaveric spine model for AIS was available, However, the results presented here at least question the benefits of performing routine complete facetectomies (i.e. Ponte osteotomies) to increase spinal flexibility in scoliosis surgery.

Mechanical Contribution of the Rib Cage in the Human Cadaveric Thoracic Spine

STUDY DESIGN

An in vitro biomechanical human cadaveric study of T1-T12 thoracic specimens was performed with 4 conditions (with and without rib cage, instrumented and uninstrumented) in flexion-extension, lateral bending, and axial rotation.

OBJECTIVE

The objective was to understand the influence of the rib cage on motion and stiffness parameters of the human cadaveric thoracic spine. Hypotheses tested for overall motion in all modes of bending for both uninstrumented and instrumented specimens were (i) in-plane range of motion and neutral and elastic zones will be greater without the rib cage, (ii) neutral and elastic zone stiffness values will be different for specimens without the rib cage, and (iii) out-of-plane rotations will be different for specimens without the rib cage.

SUMMARY OF BACKGROUND DATA

The rib cage is presumed to provide significant stability to the thoracic spine, but no studies have been conducted to determine the influence of the rib cage in both uninstrumented and instrumented conditions in the full thoracic human cadaveric specimens.

METHODS

Seven human cadaveric spine specimens (T1-T12) with 4 conditions (with and without rib cage, instrumented and uninstrumented) were subjected to 5 N·m pure moments in flexion-extension, lateral bending, and axial rotation. Range of motion, neutral and elastic zones, neutral and elastic zone stiffness values, and out-of-plane rotations were calculated for the overall specimen.

RESULTS

In-plane range of motion was significantly higher without a rib cage for most modes of bending. Out-of-plane motions were also influenced by the rib cage. Neutral zone stiffness was significantly higher with a rib cage present.

CONCLUSION

Testing without a rib cage yields different motion and stiffness measures, directly impacting the translation of research results to clinical interpretation. Researchers should consider these differences when evaluating the mechanical impact of surgical procedures or instrumentation in cadaveric or computational models.

LEVEL OF EVIDENCE

5.

Treatment of severe pediatric spinal deformities

The management of severe pediatric spinal deformities continues to evolve as advances in spinal instrumentation, surgical techniques, and neuromonitoring occur. The techniques of spinal osteotomies have been refined to allow surgeons to perform better corrections with less operative time, more safely, and through a posterior approach alone, making multiple patient positioning changes during surgery a less common occurrence. With these techniques comes a learning curve for the entire surgical team, wherein communication and planning can help minimize major complications and morbidity. This overview will review various techniques used in the correction of severe spinal deformities. Topics reviewed include the role of anterior release, traction, posterior releases, and osteotomies. Indications, techniques, and pitfalls will be reviewed. A clear understanding of the patient's deformity, normal sagittal parameters, spinal anatomy, and the principles of neuromonitoring will help improve surgical planning and patient outcome.

How do different anterior tibial tendon transfer techniques influence forefoot and hindfoot motion?

BACKGROUND

Idiopathic clubfoot correction is commonly performed using the Ponseti method and is widely reported to provide reliable results. However, a relapsed deformity may occur and often is treated in children older than 2.5 years with repeat casting, followed by an anterior tibial tendon transfer. Several techniques have been described, including a whole tendon transfer using a two-incision technique or a three-incision technique, and a split transfer, but little is known regarding the biomechanical effects of these transfers on forefoot and hindfoot motion.

QUESTIONS/PURPOSE

We used a cadaveric foot model to test the effects of three tibialis anterior tendon transfer techniques on forefoot positioning and production of hindfoot valgus.

METHODS

Ten fresh-frozen cadaveric lower legs were used. We applied 150 N tension to the anterior tibial tendon, causing the ankle to dorsiflex. Three-dimensional motions of the first metatarsal, calcaneus, and talus relative to the tibia were measured in intact specimens, and then repeated after each of the three surgical techniques.

RESULTS

Under maximum dorsiflexion, the intact specimens showed 6° (95% CI, 2.2°-9.4°) forefoot supination and less than 3° (95% CI, 0.4°-5.3°) hindfoot valgus motion. All three transfers provided increased forefoot pronation and hindfoot valgus motion compared with intact specimens: the three-incision whole transfer provided 38° (95% CI, 33°-43°; p < 0.01) forefoot pronation and 10° (95% CI, 8.5°-12°; p < 0.01) hindfoot valgus; the split transfer, 28° (95% CI, 24°-32°; p < 0.01) pronation, 9° (95% CI, 7.5°-11°; p < 0.01) valgus; and the two-incision transfer, 25° (95% CI, 20°-31°; p < 0.01) pronation, 6° (95% CI, 4.2°-7.8°; p < 0.01) valgus.

CONCLUSION

All three techniques may be useful and deliver varying degrees of increased forefoot pronation, with the three-incision whole transfer providing the most forefoot pronation. Changes in hindfoot motion were small.

CLINICAL RELEVANCE

Our study results show that the amount of forefoot pronation varied for different transfer methods. Supple dynamic forefoot supination may be treated with a whole transfer using a two-incision technique to avoid overcorrection, while a three-incision technique or a split transfer may be useful for more resistant feet. Confirmation of these findings awaits further clinical trials.

Validation of a Novel Spine Test Machine

A novel spine test machine was developed for physiological loading of spinal segments. It can be used in conjunction with external motion-capture systems (EMCS) to measure angular displacement, but can also measure in-plane rotations directly, though the inherent error is unknown. This study quantified error inherent in the displacement measurement of the machine. Synthetic specimens representative of cadaveric spinal specimens were tested. Machine displacement was compared to EMCS displacement. The maximum machine displacement error was <2 deg for lumbar and thoracic specimens. The authors suggest that researchers use EMCS in conjunction with the test machine when high accuracy measurements are required.

Biomechanical comparison of ponte osteotomy and discectomy

STUDY DESIGN

Biomechanical cadaver study.

OBJECTIVE

To evaluate the relative effectiveness of Ponte osteotomies for spinal release in deformity correction.

SUMMARY OF BACKGROUND DATA

Controversy exists as to the role of Ponte osteotomy in deformity correction surgery. Very little has been written about the biomechanical effects of Ponte osteotomy. Past biomechanical studies have been limited to application of forces through endplates, single functional units, or lack of comparison with anterior release.

METHODS

Twelve fresh-frozen human full thoracic spinal units were tested for motion in axial rotation, flexion/extension, and lateral bending in a custom-designed robotic environment. Testing was repeated after sequential facetectomy and Ponte osteotomy (6 specimens) and compared with partial and full discectomy (6 specimens).

RESULTS

Motion in axial rotation is increased 21% by Ponte osteotomy compared with 35% for full discectomy. Anterior displacement of the spinal column, creating lordosis, was increased 15% by Ponte osteotomy and 40% by full discectomy. Posterior displacement of the spinal column, creating kyphosis, was increased 23% by Ponte osteotomy and 89% by full discectomy. Finally, in coronal force application the Ponte osteotomy had virtually no effect (2%) compared with 40% increased motion by full discectomy.

CONCLUSION

Posterior Ponte osteotomy releases produced more motion than facetectomy alone in axial rotation and sagittal correction maneuvers, but had no effect on coronal correction. Anterior discectomy release destabilized spinal column significantly more than posterior releases in all force applications. Despite ample clinical experience demonstrating the effectiveness of posterior-only surgery, the biomechanical effect of Ponte osteotomies is modest.

LEVEL OF EVIDENCE

N/A.

An alternative measurement tool for the identification of hysteretic responses in biological joints

In structural engineering, sophisticated multi-dimensional analysis techniques, such as the Restoring Force Method (RFM), have been established for complex, nonlinear hysteretic systems. The purpose of the present study was to apply the RFM to quantify nonlinear spine hysteresis responses under applied moments. First, synthetic hysteretic spine responses (n=50) were generated based on representative results from pure moment flexion-extension loading of a human cadaveric lumbar spine segment. Then, the RFM was applied to each hysteresis response to describe the flexion-extension rotation as a function of applied moment and simulated axial displacement using a set of 16 unique coefficients. Range of motion, neutral zone, elastic zone, and stiffness were also measured. The RFM coefficient corresponding to the 1st-order linear dependence of rotation on applied moment was dominant, and paralleled changes in elastic zone. The remaining RFM coefficients were not captured from the traditional biomechanical analysis. Therefore, the RFM may potentially supplement the traditional analysis to develop a more comprehensive, quantitative description of spine hysteresis. The results suggest the potential for more thorough and specific characterization of spine kinematics, and may lead to future applications of such techniques in characterizing biological structures.

Blood loss during posterior spinal fusion for adolescent idiopathic scoliosis

STUDY DESIGN

Retrospective uncontrolled case series.

OBJECTIVE

The purpose of this study was to determine the association, if any, between intraoperative blood loss and need for transfusion with the use of periapical (Ponte) osteotomies, as well as other patient and surgical variables among patients with adolescent idiopathic scoliosis (AIS) undergoing posterior spinal instrumentation and fusion.

SUMMARY OF BACKGROUND DATA

Blood loss during posterior spinal fusion for AIS can be substantial. Numerous techniques are used to minimize intraoperative blood loss and the need for allogeneic transfusion. However, it is unclear which patient and surgeon variables affect blood loss most significantly.

METHODS

A review was conducted on consecutive patients with AIS who had undergone posterior spinal fusion from July 1997 to February 2013 by a single primary surgeon at 1 institution. The relationship of estimated blood loss, normalized blood loss (normalized blood loss = estimated blood loss/number of levels fused/patient's weight in kilograms), autologous blood retrieved, and allogeneic transfusion received with various patient- and procedure-related variables were analyzed.

RESULTS

Estimated blood loss, normalized blood loss, and autologous blood retrieved were higher in patients who underwent periapical Ponte osteotomies (n = 38) (P < 0.0001, P < 0.001, P < 0.01, respectively). The mean major curve correction was 64% in patients without osteotomies, and 65% in patients with osteotomies (P = 0.81). All patients who underwent osteotomies (38/38) received allogeneic transfusion versus 26% (19/73) of those without osteotomies (P < 0.001). The likelihood of transfusion correlated with increasing number of osteotomies and a lower preoperative hemoglobin level (odds ratio, 3.34; P = 0.003; and odds ratio, 0.51; P = 0.02, respectively).

CONCLUSION

In patients with AIS undergoing posterior spinal fusion with instrumentation, performing periapical osteotomies increased all measures of intraoperative blood loss and need for transfusion without substantially improving major curve correction. As expected, a lower preoperative hemoglobin level was observed in patients who received a blood transfusion after posterior instrumentation and fusion.

LEVEL OF EVIDENCE

4.

Flexibility of thoracic spines under simultaneous multi-planar loading

PURPOSE

The corrective potential of two posterior-only destabilization procedures for scoliosis deformity was quantified under single and multi-planar loading using cadaveric spines.

METHODS

Ten full-length human cadaveric thoracic spines were mounted in an 8-df servohydraulic load frame. Cyclic, pure moments were applied in: (1) flexion-extension, (2) lateral bending, (3) axial rotation, (4) flexion-extension with axial rotation, and (5) lateral bending with axial rotation at 0.5°/s, to ±4 Nm. Each specimen was tested intact, and again after nine en bloc bilateral total facetectomies, and one, two, three, and four levels of Ponte osteotomies. Motion was measured throughout loading using optical motion tracking.

RESULTS

Under single-plane loading, facetectomies and Ponte osteotomies increased thoracic spine flexibility in all three planes. Compared to total facetectomies, higher per-level increases were seen following Ponte osteotomies, with increases in total range of motion (total ROM) of up to 2.7° in flexion-extension, 1.4° in lateral bending, and 3.1° in axial rotation following each osteotomy. Compared to the facetectomies, four supplemental osteotomies increased total ROM by 23 % in flexion (p < 0.01) and 8 % in axial rotation (p < 0.01). Increases in lateral bending were smaller. Under multi-planar loading, each Ponte osteotomy provided simultaneous increases of up to 1.4°, 1.6°, and 2.2° in flexion-extension, lateral bending, and axial rotation.

CONCLUSIONS

Ponte osteotomies provided higher per-level increases in ROM under single-plane loading than total facetectomies alone. Further, Ponte osteotomies provided simultaneous increase in all three planes under multi-planar loading. These results indicated that, to predict the correction potential of a surgical release, multi-planar testing may be necessary.