Ratio of lumbar 3-column osteotomy closure: patient-specific deformity characteristics and level of resection impact correction of truncal versus pelvic compensation

The "Sandwich" Extended Pedicle Subtraction Osteotomy for the Treatment of Fixed Sagittal Malalignment: Technical Description, Case Series, and Early Results With 2-Year Outcomes

BACKGROUND AND OBJECTIVES

Adult spinal deformity (ASD) with fixed sagittal malalignment (FSM) may require a pedicle subtraction osteotomy (PSO) for greater focal lordosis and restoration of global alignment. Despite growing trends in minimizing PSOs given their associated high risks, a considerable portion of patients with ASD still require a lumbar PSO most commonly because of iatrogenic flat back deformity. The purpose of this article is to describe a modified extended PSO technique with additional anterior column support coined the "sandwich" extended PSO (SE-PSO) to promote arthrodesis and report the outcomes in a consecutive case series.

METHODS

Patients with ASD treated with a lumbar SE-PSO at a single institution from 2015 to 2020 were analyzed. Complications, radiographic data, and patient-reported outcomes were compared preoperatively, at immediate postoperative follow-up, and at a 2-year postoperative follow-up (FU).

RESULTS

Fourteen patients who underwent revision operations for FSM were included. Improvements in segmental lordosis across the PSO site (14.8 ± 6.8 vs 39.9 ± 7.1, P < .0001), overall lumbar lordosis (14.6 ± 15.4 vs 44.6 ± 12.1, P < .0001), sacral slope (21.0 ± 10.5 31.1 ± 10.7, P = .0150), C7 sagittal vertical axis (140.1 ± 59.0 mm vs 35.9 ± 28.5, P < .0001), and spinopelvic mismatch (52.5 ± 21.3 vs 18.6 ± 14.1, P = .0001) were obtained in all patients. Eight patients experienced perioperative complications, with intraoperative durotomy being the most common (n = 7). Eight patients had a 2-year FU and demonstrated improvements in their segmental lordosis across the PSO site (14.3 ± 7.0 vs 41.3 ± 7.3, P = .0003), overall lumbar lordosis (8.7 ± 17.8 vs 46.1 ± 14.2, P = .0014), sacral slope (19.1 ± 12.8 vs 32.3 ± 12.5, P = .0479), C7 sagittal vertical axis (173.6 ± 54.4 mm vs 35.8 ± 30.0, P < .0001), and spinopelvic mismatch (63.0 ± 19.7 vs 21.1 ± 18.3, P < .0001), all of which were maintained at final FU (P > .05). At 2 years, a significant increase in Scoliosis Research Society-22r total score (2.5 ± 0.8 vs 3.6 ± 0.7, P = .0023 was reported. There were no reports of symptomatic pseudarthrosis or mechanical complications.

CONCLUSION

SE-PSO is an effective technique to correct FSM and is associated with low complications, improved patient-reported outcomes, and spinopelvic parameters that are maintained at 2 years.

Is the pelvic incidence a determinant factor for kyphosis curve patterns of ankylosing spondylitis patients?

To investigate the influence of pelvic incidence (PI) on the kyphosis curve patterns and clinical outcomes in ankylosing spondylitis (AS) patients with thoracolumbar kyphosis and to construct a classification of AS according to the PI value for surgical decision-making. 107 AS patients underwent single-level lumbar pedicle subtraction osteotomy (PSO) and finished a minimal of 2-year follow-up. All patients were divided into three groups: low PI (PI ≤ 40°), moderate PI (40° < PI ≤ 60°), and high PI (PI > 60°). Standing lateral radiographs were taken to evaluate the location of kyphotic apex, thoracic kyphosis (TK), lumbar lordosis (LL), C7 sagittal vertical axis (SVA), spino-sacral angle (SSA), global kyphosis (GK), PI, sacral slope (SS), and pelvic tilt (PT). Visual Analogue Scale (VAS) score, Oswestry Disability Index (ODI) and Bath Ankylosing Spondylitis Functional Index (BASFI) were used to evaluate quality of life. Before surgery, a significant difference was shown in the average LL and the mean GK in high PI group was the largest among the three groups. Correction of SVA, GK and LL in high PI group was the smallest among the three group. No significant difference in clinical outcomes was found among the three groups before surgery and at the final follow-up. Regarding the preoperative sagittal profile, the kyphosis curve pattern of moderate PI group is similar to that of low PI group. For AS patients in these two groups, harmonious sagittal alignment can be restored by a single-level PSO. However, the sagittal imbalance is insufficiently realigned by a single-level PSO in a patient with high PI.

Surgical Planning for Adult Spinal Deformity: Anticipated Sagittal Alignment Corrections According to the Surgical Level

STUDY DESIGN

Retrospective cohort study.

OBJECTIVES

Establish simultaneous focal and regional corrective guidelines accounting for reciprocal global and pelvic compensation.

METHODS

433 ASD patients (mean age 62.9 yrs, 81.3% F) who underwent corrective realignment (minimum L1-pelvis) were included. Sagittal parameters, and segmental and regional Cobb angles were assessed pre and post-op. Virtual postoperative alignment was generated by combining post-op alignment of the fused spine with the pre-op alignment on the unfused thoracic kyphosis and the pre-op pelvic retroversion. Regression models were then generated to predict the relative impact of segmental (L4-L5) and regional (L1-L4) corrections on PT, SVA (virtual), and TPA.

RESULTS

Baseline analysis revealed distal (L4-S1) lordosis of 33 ± 15°, flat proximal (L1-L4) lordosis (1.7 ± 17°), and segmental kyphosis from L2-L3 to T10-T11. Post-op, there was no mean change in distal lordosis (L5-S1 decreased by 2°, and L4-L5 increased by 2°), while the more proximal lordosis increased by 18 ± 16°. Regression formulas revealed that Δ10° in distal lordosis resulted in Δ10° in TPA, associated with Δ100 mm in SVA or Δ3° in PT; Δ10° in proximal lordosis yielded Δ5° in TPA associated with Δ50 mm in SVA; and finally Δ10° in thoraco-lumbar junction yielded Δ2.5° in TPA associated with Δ25 mm in SVA and no impact on PT correction.

CONCLUSIONS

Overall impact of lumbar lordosis restoration is critically determined by location of correction. Distal correction leads to a greater impact on global alignment and pelvic retroversion. More specifically, it can be assumed that 1° L4-S1 lordosis correction produces 1° change in TPA / 10 mm change in SVA and 0.5° in PT.

Center of rotation analysis for thoracic and lumbar 3-column osteotomies in patients with sagittal plane spinal deformity: insights in geometrical changes can improve understanding of correction mechanics

OBJECTIVE

Three-column osteotomy (3CO) is used for severe spinal deformities. Associated complications include sagittal translation (ST), which can lead to neurological symptoms. Mismatch between the surgical center of rotation (COR) and the concept of the ideal COR is a potential cause of ST. Matching surgical with conceptual COR is difficult with pedicle subtraction osteotomy (PSO) and vertebral column resection (VCR). This mismatch influences correction geometry, which can prevent maximum possible correction. The authors' objective was to examine the sagittal correction geometry and surgical COR of thoracic and lumbar 3CO.

METHODS

In a retrospective study of patients with PSO or VCR for severe sagittal plane deformity, analysis of surgical COR was performed using pre- and postoperative CT scans in the PSO group and digital radiographs in the VCR group. Radiographic analysis included standard deformity measurements and regional kyphosis angle (RKA). All patients had 2-year follow-up, including neurological outcome. Preoperative CT scans were studied for rigid osteotomy sites versus mobile osteotomy sites. Additional radiographic analysis of surgical COR was based on established techniques superimposing pre- and postoperative images. Position of the COR was defined in a rectangular net layered onto the osteotomy vertebrae (OVs).

RESULTS

The study included 34 patients undergoing PSO and 35 undergoing VCR, with mean ages of 57 and 29 years and mean RKA corrections of 31° and 49°, respectively. In the PSO group, COR was mainly in the anterior column, and surgical and conceptual COR matched in 22 patients (65%). Smaller RKA correction (27° vs 32°, p = 0.09) was seen in patients with anterior eccentric COR. Patients with rigid osteotomy sites were more likely to have an anterior eccentric COR (41% vs 11%, p = 0.05). In the VCR group, 20 patients (57%) had single-level VCR and 15 (43%) had multilevel VCR. COR was mainly located in the anterior or middle column. Mismatch between surgical and conceptual COR occurred in 24 (69%) patients. Larger RKA correction (63° vs 45°, p = 0.03) was seen in patients with anterior column COR. Patients with any posterior COR had a smaller RKA correction compared to the rest of the patients (42° vs 61°, p = 0.007).

CONCLUSIONS

Matching the surgical with the conceptual COR is difficult and in this study failed in one- to two-thirds of all patients. In order to avoid ST during correction of severe deformities, temporary rods, tracking rods, or special instruments should be used for correction maneuvers.

Reducing revision rates following Pedicle Subtraction Osteotomy surgery: a single-center experience of trends over 7 years in patients with Adult Spinal Deformity

STUDY DESIGN

This is a single-center, retrospective study.

OBJECTIVE

To assess if implemented changes to clinical practice have reduced mechanical complications following pedicle subtraction osteotomy (PSO) surgery. Adult spinal deformity (ASD) is increasing in prevalence with concurrent increasing demands for surgical treatment. The most extensive technique, PSO, allows for major correction of rigid deformities. However, surgery-related complications have been reported in rates up to 77% and especially mechanical complications occur at unsatisfactory frequencies.

METHODS

We retrospectively included all patients undergoing PSO for ASD between 2010 and 2016. Changes to clinical practice were introduced continuously in the study period, including rigorous patient selection; inter-disciplinary conferences; implant-material; number of surgeons; surgeon experience; and perioperative standardized protocols for pain, neuromonitoring and blood-loss management. Postoperative complications were recorded in the 2-year follow-up period. Competing risk survival analysis was used to assess cumulative incidence of revision surgery due to mechanical complications. The Mann-Kendall test was used for analysis of trends.

RESULTS

We included 185 patients undergoing PSO. The level of PSO changed over the study period (P < 0.01) with L3 being the most common level in 2010 compared to L4 in 2016. Both preoperative and surgical corrections of sagittal vertical axis were larger towards the end of the study period. The 2-year revision rate due to mechanical failure steadily declined over the study period from 52% in 2010 to 14% for patients treated in 2016, although without statistically significant trend (P = 0.072). In addition, rates of mechanical complications steadily declined over the study period and significant decreasing trends were observed in time trend analyses of overall complications, major complications and rod breakage.

CONCLUSIONS

We observed decreased risks of revision surgery due to mechanical complications following PSO in patients with ASD over a 7-year period. We attribute these improvements to advancements in patient selection, surgical planning and techniques, surgeon experience and more standardized perioperative care.

LEVEL OF EVIDENCE

III.

Preoperative Planning and the Use of Free Available Software for Sagittal Plane Corrective Osteotomies of the Lumbar Spine in Ankylosing Spondylitis

Background

Ankylosing spondylitis (AS) may cause a severe rigid thoracolumbar kyphotic deformity (TLKD) that leads to considerable disturbances of posture and spinal balance. In few patients, a corrective osteotomy of the lumbar spine may be considered. Preoperative planning of a lumbar osteotomy for correction of a severe TLKD due to AS is important to correct patient's sagittal balance and view angle. There is a need for accurate preoperative planning that can be used easily in daily practice.

Methods

The basic biomechanical and mathematical principles of preoperative planning for correction of a TLKD due to AS are described. A search was performed for free available computer programs that can be used for pre-operative planning of spinal osteotomies in AS. Finally, the use of these computer programs is illustrated and described.

Results

Sagittal balance is measured on a standing lateral full-length radiograph of the spine. The assessment of the pelvic parameters (PI, PT, SS) in conjunction with sagittal vertical axis (SVA) and chin-brow-to-vertical angle (CBVA) provides a comprehensive picture of the sagittal spinal alignment and compensatory mechanisms of the patient. The relation between the level of lumbar osteotomy and the amount of correction needed can be calculated with different elementary trigonometric equations. Two free available computer programs, ASKyphoplan and Surgimap, are illustrated and described that can be used for pre-operative planning of spinal osteotomies in AS.

Conclusion

Preoperative planning of the lumbar osteotomy in AS involves assessment of the combined effect of location of the osteotomy, amount of bone resection, SVA, CBVA, and pelvic parameters. Two free available computer programs, ASKyphoplan and Surgimap, are easy to use in clinical practice to predict postoperative sagittal balance of lumbar osteotomies in patients with severe TLKD due to AS.

Should Sagittal Spinal Alignment Targets for Adult Spinal Deformity Correction Depend on Pelvic Incidence and Age?

STUDY DESIGN

Retrospective analysis.

OBJECTIVE

Determine whether deformity corrections should vary by pelvic incidence (PI).

SUMMARY OF BACKGROUND DATA

Alignment targets for deformity correction have been reported for various radiographic parameters. The T1 pelvic-angle (TPA) has gained in applications for adult spinal deformity (ASD) surgical-planning since it directly measures spinal alignment separate from pelvic- and lower-extremity compensation. Recent studies have demonstrated that ASD corrections should be age specific.

METHODS

A prospective database of consecutive ASD patients was analyzed in conjunction with a normative spine database. Clinical measures of disability included the Oswestry Disability Index (ODI) and Short Form 36 Survey (SF-36) Physical Component Score (PCS). Baseline relationships between TPA, age, PI, and ODI/SF-36 PCS scores were analyzed in the ASD and asymptomatic patients. Linear regression modeling was used to determine alignment targets based on PI and age-specific normative SF-36-PCS values.

RESULTS

Nine hundred three ASD patients (mean 53.7 yr) and 111 normative subjects (mean 50.7 yr) were included. Patients were subanalyzed by PI: low, medium, high (<40, 40-75, >75); and age: elderly (>65 yr, n = 375), middle age (45-65 yr, n = 387), and young (18-45 yr, n = 141). TPA and SRS-Schwab parameters correlated with age and PI in ASD and normative subjects (r = 0.42, P < 0.0001). ODI correlated with PCS (r = 0.71, P < 0.0001). Linear regression analysis using age-normative SF-36-PCS values demonstrated that ideal spinopelvic alignment is less strict with increasing PI and age.

CONCLUSION

Targets for ASD correction should vary by age and PI. This is demonstrated in both asymptomatic and ASD subjects. Using age-normative SF-36 PCS values, alignment targets are described for different age and PI categories. High-PI patients do not require as rigorous realignments to attain age-specific normative levels of health status. As such, sagittal spinal alignment targets increase with increasing age as well as PI.

LEVEL OF EVIDENCE

3.

Location of correction within the lumbar spine impacts acute adjacent-segment kyphosis

OBJECTIVEThe surgical correction of adult spinal deformity (ASD) often involves modifying lumbar lordosis (LL) to restore ideal sagittal alignment. However, corrections that include large changes in LL increase the risk for development of proximal junctional kyphosis (PJK). Little is known about the impact of cranial versus caudal correction in the lumbar spine on the occurrence of PJK. The goal of this study was to investigate the impact of the location of the correction on acute PJK development.METHODSThis study was a retrospective review of a prospective multicenter database. Surgically treated ASD patients with early follow-up evaluations (6 weeks) and fusions of the full lumbosacral spine were included. Radiographic parameters analyzed included the classic spinopelvic parameters (pelvic incidence [PI], pelvic tilt [PT], PI-LL, and sagittal vertical axis [SVA]) and segmental correction. Using Glattes' criteria, patients were stratified into PJK and noPJK groups and propensity matched by age and regional lumbar correction (ΔPI-LL). Radiographic parameters and segmental correction were compared between PJK and noPJK patients using independent t-tests.RESULTSAfter propensity matching, 312 of 483 patients were included in the analysis (mean age 64 years, 76% women, 40% with PJK). There were no significant differences between PJK and noPJK patients at baseline or postoperatively, or between changes in alignment, with the exception of thoracic kyphosis (TK) and ΔTK. PJK patients had a decrease in segmental lordosis at L4-L5-S1 (-0.6° vs 1.6°, p = 0.025), and larger increases in segmental correction at cranial levels L1-L2-L3 (9.9° vs 7.1°), T12-L1-L2 (7.3° vs 5.4°), and T11-T12-L1 (2.9° vs 0.7°) (all p < 0.05).CONCLUSIONSAlthough achievement of an optimal sagittal alignment is the goal of realignment surgery, dramatic lumbar corrections appear to increase the risk of PJK. This study was the first to demonstrate that patients who developed PJK underwent kyphotic changes in the L4-S1 segments while restoring LL at more cranial levels (T12-L3). These findings suggest that restoring lordosis at lower lumbar levels may result in a decreased risk of developing PJK.

Negative Sagittal Balance Following Adult Spinal Deformity Surgery

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

Elucidate negative sagittal balance following adult spinal deformity surgery.

METHODS

We conducted a retrospective review of adult spinal deformity patients who underwent long fusion (>5 levels) to the sacrum by a single surgeon at a single institution between 2011 and 2015. Patients were divided into cohorts of postoperative sagittal vertical axis (SVA) <-10 mm, between -10 and +10 mm, or >+10 mm, denoted as groups 1, 2, and 3, respectively. Univariate analysis compared preoperative factors between the groups, and a multivariable logistic regression model was used to determine independent risk factors for developing a negative sagittal balance (SVA<-10 mm) following adult spinal deformity correction.

RESULTS

We reviewed 8 patients in group 1, 9 patients in group 2, and 25 patients in group 3. The average postoperative SVA for group 1, group 2, and group 3 were -30.99, +3.67, and +55.56 mm, respectively. There was a trend toward higher upper-instrumented vertebra (UIV) in group 1 (T2) compared with group 2 (T10) and group 3 (T9) (P = .05). A trend toward lower preoperative SVA in groups 1 and 2 compared with group 3 was also seen (+53.36 vs +71.73 vs +122.80 mm) (P = .06). Finally, we found a trend toward lower body mass index in group 1 compared with groups 2 and 3 (24.71 vs 25.92 vs 29.33 kg/m²) (P = .07). Based on multivariable regression, higher UIV was found to be a statistically significant independent predictor for developing a postoperative negative sagittal balance of <-10 mm (P = .02, odds ratio = 0.67).

CONCLUSIONS

Our results demonstrate that a higher UIV may predispose patients undergoing adult spinal deformity correction to have a postoperative negative sagittal balance.

Osteotomies in ankylosing spondylitis: where, how many, and how much?

INTRODUCTION

This article presents the current concepts of correction of spinal deformity in ankylosing spondylitis (AS) patients. Untreated AS can be a debilitating disease. In a few patients, disease progression results in severe spinal deformity affecting not only the thoracolumbar, but also the cervical spine. Surgery for correction in AS patients has a long history. With the advent of modern instrumentation, standardization of surgical and anesthesiologic techniques, surgical safety and corrective results could be improved and experiences from lumbar osteotomies could be transferred to the cervical spine.

METHODS

This article presents the current concepts of correction of spinal deformity in AS patients. In particular, questions regarding the localization and number of osteotomies, the optimal surgical target angle as well as planning and prediction of postoperative alignment are discussed.

RESULTS

Insight into recent technical developments, current challenges with correction and geometric analysis of center of rotation (COR) in cervical 3-column osteotomies (3CO) will be presented.

CONCLUSION

The article should encourage readers to improve surgical correction efficacy and provide a better understanding of correction geometry in 3CO for thoracolumbar and cervical spinal deformities.