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Letter to the Editor: Sagittal plane analysis

Antonio A. Faundez and Jean Charles Le Huec

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Sagittal alignment of the cervical spine in the setting of adolescent idiopathic scoliosis

Michael Akbar, Haidara Almansour, Renaud Lafage, Bassel G. Diebo, Bernd Wiedenhöfer, Frank Schwab, Virginie Lafage, and Wojciech Pepke

OBJECTIVE

The goal of this study was to investigate the impact of thoracic and lumbar alignment on cervical alignment in patients with adolescent idiopathic scoliosis (AIS).

METHODS

Eighty-one patients with AIS who had a Cobb angle > 40° and full-length spine radiographs were included. Radiographs were analyzed using dedicated software to measure pelvic parameters (sacral slope [SS], pelvic incidence [PI], pelvic tilt [PT]); regional parameters (C1 slope, C0–C2 angle, chin-brow vertical angle [CBVA], slope of line of sight [SLS], McRae slope, McGregor slope [MGS], C2–7 [cervical lordosis; CL], C2–7 sagittal vertical axis [SVA], C2–T3, C2–T3 SVA, C2–T1 Harrison measurement [C2–T1 Ha], T1 slope, thoracic kyphosis [TK], lumbar lordosis [LL], and PI-LL mismatch); and global parameters (SVA). Patients were stratified by their lumbar alignment into hyperlordotic (LL > 59.7°) and normolordotic (LL 39.3° to 59.7°) groups and also, based on their thoracic alignment, into hypokyphotic (TK < −33.1°) and normokyphotic (TK −33.1° to −54.9°) groups. Finally, they were grouped based on their global alignment into either an anterior-aligned group or a posterior-aligned group.

RESULTS

The lumbar hyperlordotic group, in comparison to the normolordotic group, had a significantly larger LL, SS, PI (all p < 0.001), and TK (p = 0.014) and a significantly smaller PI-LL mismatch (p = 0.001). Lumbar lordosis had no influence on local cervical parameters.

The thoracic hypokyphotic group had a significantly larger PI-LL mismatch (p < 0.002) and smaller T1 slope (p < 0.001), and was significantly more posteriorly aligned than the normokyphotic group (−15.02 ± 8.04 vs 13.54 ± 6.17 [mean ± SEM], p = 0.006). The patients with hypokyphotic AIS had a kyphotic cervical spine (cervical kyphosis [CK]) (p < 0.001). Furthermore, a posterior-aligned cervical spine in terms of C2–7 SVA (p < 0.006) and C2–T3 SVA (p < 0.001) was observed in the thoracic hypokyphotic group.

Comparing patients in terms of global alignment, the posterior-aligned group had a significantly smaller T1 slope (p < 0.001), without any difference in terms of pelvic, lumbar, and thoracic parameters when compared to the anterior-aligned group. The posterior-aligned group also had a CK (−9.20 ± 1.91 vs 5.21 ± 2.95 [mean ± SEM], p < 0.001) and a more posterior-aligned cervical spine, as measured by C2–7 SVA (p = 0.003) and C2–T3 SVA (p < 0.001).

CONCLUSIONS

Alignment of the cervical spine is closely related to thoracic curvature and global alignment. In patients with AIS, a hypokyphotic thoracic alignment or posterior global alignment was associated with a global cervical kyphosis. Interestingly, upper cervical and cranial parameters were not statistically different in all investigated groups, meaning that the upper cervical spine was not recruited for compensation in order to maintain a horizontal gaze.

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The impact of preoperative supine radiographs on surgical strategy in adult spinal deformity

Francis Lovecchio, Jonathan Charles Elysee, Renaud Lafage, Jeff Varghese, Mathieu Bannwarth, Frank Schwab, Virginie Lafage, and Han Jo Kim

OBJECTIVE

Preoperative planning for adult spinal deformity (ASD) surgery is essential to prepare the surgical team and consistently obtain postoperative alignment goals. Positional imaging may allow the surgeon to evaluate spinal flexibility and anticipate the need for more invasive techniques. The purpose of this study was to determine whether spine flexibility, defined by the change in alignment between supine and standing imaging, is associated with the need for an osteotomy in ASD surgery.

METHODS

A single-center, dual-surgeon retrospective analysis was performed of adult patients with ASD who underwent correction of a thoracolumbar deformity between 2014 and 2018 (pelvis to upper instrumented vertebra between L1 and T9). Patients were stratified into osteotomy (Ost) and no-osteotomy (NOst) cohorts according to whether an osteotomy was performed (Schwab grade 2 or higher). Demographic, surgical, and radiographic parameters were compared. The sagittal correction from intraoperative prone positioning alone (sagittal flexibility percentage [Sflex%]) was assessed by comparing the change in lumbar lordosis (LL) between preoperative supine to standing radiographs and preoperative to postoperative alignment.

RESULTS

Demographics and preoperative and postoperative sagittal alignment were similar between the Ost (n = 60, 65.9%) and NOst (n = 31, 34.1%) cohorts (p > 0.05). Of all Ost patients, 71.7% had a grade 2 osteotomy (mean 3 per patient), 21.7% had a grade 3 osteotomy, and 12.5% underwent both grade 3 and grade 2 osteotomies. Postoperatively, the NOst and Ost cohorts had similar pelvic incidence minus lumbar lordosis (PI-LL) mismatch (mean PI-LL 5.2° vs 1.2°; p = 0.205). Correction obtained through positioning (Sflex%) was significantly lower for in the osteotomy cohort (38.0% vs 76.3%, p = 0.004). A threshold of Sflex% < 70% predicted the need for osteotomy at a sensitivity of 78%, specificity of 56%, and positive predictive value of 77%.

CONCLUSIONS

The flexibility of the spine is quantitatively related to the use of an osteotomy. Prospective studies are needed to determine thresholds that may be used to standardize surgical decision-making in ASD surgery.

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The utility of supine radiographs in the assessment of thoracic flexibility and risk of proximal junctional kyphosis

Francis Lovecchio, Renaud Lafage, Jonathan Charles Elysee, Alex Huang, Bryan Ang, Mathieu Bannwarth, Han Jo Kim, Frank Schwab, and Virginie Lafage

OBJECTIVE

Supine radiographs have successfully been used for preoperative planning of lumbar deformity corrections. However, they have not been used to assess thoracic flexibility, which has recently garnered attention as a potential contributor to proximal junctional kyphosis (PJK). The purpose of this study was to compare supine to standing radiographs to assess thoracic flexibility and to determine whether thoracic flexibility is associated with PJK.

METHODS

A retrospective study was conducted of a single-institution database of patients with adult spinal deformity (ASD). Sagittal alignment parameters were compared between standing and supine and between pre- and postoperative radiographs. Thoracic flexibility was determined as the change between preoperative standing thoracic kyphosis (TK) and preoperative supine TK, and these changes were measured over the overall thoracic spine and the fused portion of the thoracic spine (i.e., TK fused). A case-control analysis was performed to compare thoracic flexibility between patients with PJK and those without (no PJK). The cohort was also stratified into three groups based on thoracic flexibility: kyphotic change (increased TK), lordotic change (decreased TK), and no change. The PJK rate was compared between the cohorts.

RESULTS

A total of 101 patients (mean 63 years old, 82.2% female, mean BMI 27.4 kg/m2) were included. Preoperative Scoliosis Research Society–Schwab ASD classification showed moderate preoperative deformity (pelvic tilt 27.7% [score ++]; pelvic incidence–lumbar lordosis mismatch 44.6% [score ++]; sagittal vertical axis 42.6% [score ++]). Postoperatively, the average offset from age-adjusted alignment goals demonstrated slight overcorrection in the study sample (−8.5° ± 15.6° pelvic incidence–lumbar lordosis mismatch, −29.2 ± 53.1 mm sagittal vertical axis, −5.4 ± 10.8 pelvic tilt, and −7.6 ± 11.7 T1 pelvic angle). TK decreased between standing and supine radiographs and increased postoperatively (TK fused: −25.3° vs −19.6° vs −29.9°; all p < 0.001). The overall rate of radiographic PJK was 23.8%. Comparisons between PJK and no PJK demonstrated that offsets from age-adjusted alignment goals were similar (p > 0.05 for all). There was a significant difference in the PJK rate when stratified by thoracic flexibility cohorts (kyphotic: 0.0% vs no change: 18.4% vs lordotic: 35.0%; p = 0.049). Logistic regression revealed thoracic flexibility (p = 0.045) as the only independent correlate of PJK.

CONCLUSIONS

Half of patients with ASD experienced significant changes in TK during supine positioning, a quality that may influence surgical strategy. Increased thoracic flexibility is associated with PJK, possibly secondary to fusing the patient’s spine in a flattened position intraoperatively.

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Should realignment goals vary based on patient frailty status in adult spinal deformity?

Presented at the 2023 AANS/CNS Joint Section on the Disorders of the Spine and Peripheral Nerves

Peter G. Passias, Jamshaid M. Mir, Tyler K. Williamson, Peter S. Tretiakov, Pooja Dave, Virginie Lafage, Renaud Lafage, and Andrew J. Schoenfeld

OBJECTIVE

The objective of this study was to adjust the sagittal age-adjusted score (SAAS) to accommodate frailty in alignment considerations and thereby increase the predictability of clinical outcomes and junctional failure.

METHODS

Surgical adult spinal deformity (ASD) patients with 2-year data were included. Frailty was assessed with the continuous ASD modified frailty index (ASD-mFI). Two-year outcomes were proximal junctional kyphosis (PJK), proximal junctional failure (PJF), major mechanical complications, and best clinical outcome (BCO), defined as Oswestry Disability Index (ODI) score < 15 and Scoliosis Research Society outcomes questionnaire total score > 4.5 by 2 years. Linear regression analysis established a 6-week score based on the component scores of SAAS, frailty, and US normal values for ODI score. Logistic regression analysis followed by conditional inference tree run forest analysis generated categorical thresholds. Multivariate analysis, controlling for age, baseline deformity, and history of revision, was used to compare outcome rates, and logistic regression generated odds ratios for the continuous score. Thirty percent of the cohort was used as a random sample for internal validation.

RESULTS

In total, 412 patients were included (mean ± SD age 60.1 ± 14.2 years, 80% female, BMI 26.9 ± 5.4 kg/m2). Baseline frailty categories were as follows: 57% not frail, 30% frail, and 14% severely frail. Overall, by 2 years, 39% of patients had developed PJK, 8% PJF, and 21% mechanical complications; 22% had undergone a reoperation; and 15% met BCO. When the cohort as a whole was assessed, the 6-week SAAS had a correlation with the development of PJK and PJF, but not mechanical complications, reoperation, or BCO. Development of mechanical complications, PJF, reoperation, and BCO demonstrated correlations with ASD-mFI (all p < 0.05). Regression analysis modifying SAAS on the basis of ODI norms and frailty generated the following equation: frailty-adjusted SAAS (FAS) = 0.108 × T1 pelvic angle + 0.162 × pelvic tilt − 0.39 × pelvic incidence − lumbar lordosis − 0.03 × ASD-mFI − 1.6771. With conditional inference tree analysis, thresholds were derived for FAS: aligned < 1.7, offset 1.7–2.2, and severely offset > 2.2. Significance between FAS categories was found for PJK, PJF, mechanical complications, reoperation, and BCO by 2 years. Binary logistic regression, controlling for baseline deformity and revision status, demonstrated significance between FAS and all 5 outcome variables (all p < 0.01). Internal validation saw each outcome variable maintain significance between categories, with even greater odds for PJF (OR 13.4, 95% CI 4.7–38.3, p < 0.001).

CONCLUSIONS

Consideration of physiological age, in addition to chronological age, may be beneficial in the management of operative goals to maximize clinical outcomes while minimizing junctional failure. This combination enables the spine surgeon to fortify a surgical plan for even the most challenging patients undergoing ASD corrective surgery.

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Role of pelvic translation and lower-extremity compensation to maintain gravity line position in spinal deformity

Emmanuelle Ferrero, Barthelemy Liabaud, Vincent Challier, Renaud Lafage, Bassel G. Diebo, Shaleen Vira, Shian Liu, Jean Marc Vital, Brice Ilharreborde, Themistocles S. Protopsaltis, Thomas J. Errico, Frank J. Schwab, and Virginie Lafage

OBJECT

Previous forceplate studies analyzing the impact of sagittal-plane spinal deformity on pelvic parameters have demonstrated the compensatory mechanisms of pelvis translation in addition to rotation. However, the mechanisms recruited for this pelvic rotation were not assessed. This study aims to analyze the relationship between spinopelvic and lower-extremity parameters and clarify the role of pelvic translation.

METHODS

This is a retrospective study of patients with spinal deformity and full-body EOS images. Patients with only stenosis or low-back pain were excluded. Patients were grouped according to T-1 spinopelvic inclination (T1SPi): sagittal forward (forward, > 0.5°), neutral (−6.3° to 0.5°), or backward (< −6.3°). Pelvic translation was quantified by pelvic shift (sagittal offset between the posterosuperior corner of the sacrum and anterior cortex of the distal tibia), hip extension was measured using the sacrofemoral angle (SFA; the angle formed by the middle of the sacral endplate and the bicoxofemoral axis and the line between the bicoxofemoral axis and the femoral axis), and chin-brow vertical angle (CBVA). Univariate and multivariate analyses were used to compare the parameters and correlation with the Oswestry Disability Index (ODI).

RESULTS

In total, 336 patients (71% female; mean age 57 years; mean body mass index 27 kg/m2) had mean T1SPi values of −8.8°, −3.5°, and 5.9° in the backward, neutral, and forward groups, respectively. There were significant differences in the lower-extremity and spinopelvic parameters between T1SPi groups. The backward group had a normal lumbar lordosis (LL), negative SVA and pelvic shift, and the largest hip extension. Forward patients had a small LL and an increased SVA, with a large pelvic shift creating compensatory knee flexion. Significant correlations existed between lower-limb parameter and pelvic shift, pelvic tilt, T-1 pelvic angle, T1SPi, and sagittal vertical axis (0.3 < r < 0.8; p < 0.001). ODI was significantly correlated with knee flexion and pelvic shift.

CONCLUSIONS

This is the first study to describe full-body alignment in a large population of patients with spinal pathologies. Furthermore, patients categorized based on T1SPi were found to have significant differences in the pelvic shift and lower-limb compensatory mechanisms. Correlations between lower-limb angles, pelvic shift, and ODI were identified. These differences in compensatory mechanisms should be considered when evaluating and planning surgical intervention for adult patients with spinal deformity.

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Global sagittal axis: a step toward full-body assessment of sagittal plane deformity in the human body

Bassel G. Diebo, Jonathan H. Oren, Vincent Challier, Renaud Lafage, Emmanuelle Ferrero, Shian Liu, Shaleen Vira, Matthew Adam Spiegel, Bradley Yates Harris, Barthelemy Liabaud, Jensen K. Henry, Thomas J. Errico, Frank J. Schwab, and Virginie Lafage

OBJECTIVE

Sagittal malalignment requires higher energy expenditure to maintain an erect posture. Because the clinical impact of sagittal alignment is affected by both the severity of the deformity and recruitment of compensatory mechanisms, it is important to investigate new parameters that reflect both disability level and compensatory mechanisms for all patients. This study investigated the clinical relevance of the global sagittal axis (GSA), a novel measure to evaluate the standing axis of the human body.

METHODS

This is a retrospective review of patients who underwent full-body radiographs and completed health-related quality of life (HRQOL) questionnaires: Oswestry Disability Index (ODI), Scoliosis Research Society–22, EuroQol-5D (EQ-5D), and the visual analog scale for back and leg pain. The GSA was defined as the angle formed by a line from the midpoint of the femoral condyles to the center of C-7, and a line from the midpoint between the femoral condyles to the posterior superior corner of the S-1 sacral endplate. After evaluating the correlation of GSA/HRQOL with sagittal parameters, linear regression models were generated to investigate how ODI and GSA related to radiographic parameters (T-1 pelvic angle, pelvic retroversion, knee flexion, and pelvic posterior translation).

RESULTS

One hundred forty-three patients (mean age 44 years) were included. The GSA correlated significantly with all HRQOL (up to r = 0.6 with EQ-5D) and radiographic parameters (up to r = 0.962 with sagittal vertical axis). Regression between ODI and sagittal radiographic parameters identified the GSA as an independent predictor (r = 0.517, r2 = 0.267; p < 0.001). Analysis of standardized coefficients revealed that when controlling for deformity, the GSA increased with a concurrent decrease in pelvic retroversion (−0.837) and increases in knee flexion (+0.287) and pelvic posterior translation (+0.193).

CONCLUSIONS

The GSA is a simple, novel measure to assess the standing axis of the human body in the sagittal plane. The GSA correlated highly with spinopelvic and lower-extremities sagittal parameters and exhibited remarkable correlations with HRQOL, which exceeded other commonly used parameters.

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

Renaud Lafage, Ibrahim Obeid, Barthelemy Liabaud, Shay Bess, Douglas Burton, Justin S. Smith, Cyrus Jalai, Richard Hostin, Christopher I. Shaffrey, Christopher Ames, Han Jo Kim, Eric Klineberg, Frank Schwab, Virginie Lafage, and the International Spine Study Group

OBJECTIVE

The 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.

METHODS

This 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.

RESULTS

After 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).

CONCLUSIONS

Although 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.

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Are the sagittal cervical radiographic modifiers of the Ames-ISSG classification specific to adult cervical deformity?

Ziad Bakouny, Nour Khalil, Joeffroy Otayek, Aren Joe Bizdikian, Fares Yared, Michel Salameh, Naji Bou Zeid, Ismat Ghanem, Khalil Kharrat, Gaby Kreichati, Renaud Lafage, Virginie Lafage, and Ayman Assi

OBJECTIVE

The Ames–International Spine Study Group (ISSG) classification has recently been proposed as a tool for adult cervical deformity evaluation. This classification includes three radiographic cervical sagittal modifiers that have not been evaluated in asymptomatic adults. The aim of this study was to determine whether the sagittal radiographic modifiers described in the Ames-ISSG cervical classification are encountered in asymptomatic adults without alteration of health-related quality of life (HRQOL).

METHODS

The authors conducted a cross-sectional study of subjects with an age ≥ 18 years and no cervical or back-related complaints or history of orthopedic surgery. All subjects underwent full-body biplanar radiographs with the measurement of cervical, segmental, and global alignment and completed the SF-36 HRQOL questionnaire. Subjects were classified according to the sagittal radiographic modifiers (chin-brow vertical angle [CBVA], mismatch between T1 slope and cervical lordosis [TS-CL], and C2–7 sagittal vertical axis [cSVA]) of the Ames–ISSG classification for cervical deformity, which also includes a qualitative descriptor of cervical deformity, the modified Japanese Orthopaedic Association (mJOA) myelopathy score, and the Scoliosis Research Society (SRS)–Schwab classification for spinal deformity assessment. Characteristics of the subjects classified by the different modifier grades were compared.

RESULTS

One hundred forty-one asymptomatic subjects (ages 18–59 years, 71 females) were enrolled in the study. Twenty-seven (19.1%) and 61 (43.3%) subjects were classified as grade 1 in terms of the TS-CL and CBVA modifiers, respectively. Ninety-eight (69.5%) and 4 (2.8%) were grade 2 for these same respective modifiers. One hundred thirty-six (96.5%) subjects had at least one modifier at grade 1 or 2. There was a significant relationship between patient age and grades of TS-CL (p < 0.001, Cramer’s V [CV] = 0.32) and CBVA (p = 0.04, CV = 0.22) modifiers. The HRQOL, global alignment, and segmental alignment parameters were similar among the subjects with different modifier grades (p > 0.05).

CONCLUSIONS

The CBVA and TS-CL radiographic modifiers of the Ames-ISSG classification do not seem to be specific to subjects with cervical deformities and can occur in asymptomatic subjects without alteration in HRQOL.

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Etiology of lumbar lordosis and its pathophysiology: a review of the evolution of lumbar lordosis, and the mechanics and biology of lumbar degeneration

Carolyn J. Sparrey, Jeannie F. Bailey, Michael Safaee, Aaron J. Clark, Virginie Lafage, Frank Schwab, Justin S. Smith, and Christopher P. Ames

The goal of this review is to discuss the mechanisms of postural degeneration, particularly the loss of lumbar lordosis commonly observed in the elderly in the context of evolution, mechanical, and biological studies of the human spine and to synthesize recent research findings to clinical management of postural malalignment. Lumbar lordosis is unique to the human spine and is necessary to facilitate our upright posture. However, decreased lumbar lordosis and increased thoracic kyphosis are hallmarks of an aging human spinal column. The unique upright posture and lordotic lumbar curvature of the human spine suggest that an understanding of the evolution of the human spinal column, and the unique anatomical features that support lumbar lordosis may provide insight into spine health and degeneration. Considering evolution of the skeleton in isolation from other scientific studies provides a limited picture for clinicians. The evolution and development of human lumbar lordosis highlight the interdependence of pelvic structure and lumbar lordosis. Studies of fossils of human lineage demonstrate a convergence on the degree of lumbar lordosis and the number of lumbar vertebrae in modern Homo sapiens. Evolution and spine mechanics research show that lumbar lordosis is dictated by pelvic incidence, spinal musculature, vertebral wedging, and disc health. The evolution, mechanics, and biology research all point to the importance of spinal posture and flexibility in supporting optimal health. However, surgical management of postural deformity has focused on restoring posture at the expense of flexibility. It is possible that the need for complex and costly spinal fixation can be eliminated by developing tools for early identification of patients at risk for postural deformities through patient history (genetics, mechanics, and environmental exposure) and tracking postural changes over time.