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Michael P. Kelly, Michael A. Kallen, Christopher I. Shaffrey, Justin S. Smith, Douglas C. Burton, Christopher P. Ames, Virginie Lafage, Frank J. Schwab, Han Jo Kim, Eric O. Klineberg, Shay Bess and the International Spine Study Group

OBJECTIVE

After using PROsetta Stone crosswalk tables to calculate Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Function (PF) and Pain Interference (PI) scores, the authors sought to examine 1) correlations with Scoliosis Research Society–22r (SRS-22r) scores, 2) responsiveness to change, and 3) the relationship between baseline scores and 2-year follow-up scores in adult spinal deformity (ASD).

METHODS

PROsetta Stone crosswalk tables were used to converted SF-36 scores to PROMIS scores for pain and physical function in a cohort of ASD patients with 2-year follow-up. Spearman correlations were used to evaluate the relationship of PROMIS scores with SRS-22r scores. Effect size (ES) and adjusted standardized response mean (aSRM) were used to assess responsiveness to change. Linear regression was used to evaluate the association between baseline scores and 2-year follow-up scores.

RESULTS

In total, 425 (425/625, 68%) patients met inclusion criteria. Strong correlations (all |r| > 0.7, p < 0.001) were found between baseline and 2-year PROMIS values and corresponding SRS-22r domain scores. PROMIS-PI showed a large ES (1.09) and aSRM (0.88), indicating good responsiveness to change. PROMIS-PF showed a moderate ES (0.52) and moderate aSRM (0.69), indicating a moderate responsiveness to change. Patients with greater baseline pain complaints were associated with greater pain improvement at 2 years for both SRS-22r Pain (B = 0.39, p < 0.001) and PROMIS-PI (B = 0.45, p < 0.001). Higher functional scores at baseline were associated with greater average improvements in both SRS-22r Activity (B = 0.62, p < 0.001) and PROMIS-PF (B = 0.40, p < 0.001).

CONCLUSIONS

The authors found strong correlations between the SRS-22r Pain and Activity domains with corresponding PROMIS-PI and -PF scores. Pain measurements showed similar and strong ES and aSRM while the function measurements showed similar, moderate ES and aSRM at 2-year follow-up. These data support further exploration of the use of PROMIS–computer adaptive test instruments in ASD.

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Thomas J. Buell, Shay Bess, Ming Xu, Frank J. Schwab, Virginie Lafage, Christopher P. Ames, Christopher I. Shaffrey and Justin S. Smith

OBJECTIVE

Proximal junctional kyphosis (PJK) is, in part, due to altered segmental biomechanics at the junction of rigid instrumented spine and relatively hypermobile non-instrumented adjacent segments. Proper application of posteriorly anchored polyethylene tethers (i.e., optimal configuration and tension) may mitigate adjacent-segment stress and help prevent PJK. The purpose of this study was to investigate the impact of different tether configurations and tensioning (preloading) on junctional range-of-motion (ROM) and other biomechanical indices for PJK in long instrumented spine constructs.

METHODS

Using a validated finite element model of a T7–L5 spine segment, testing was performed on intact spine, a multilevel posterior screw-rod construct (PS construct; T11–L5) without tether, and 15 PS constructs with different tether configurations that varied according to 1) proximal tether fixation of upper instrumented vertebra +1 (UIV+1) and/or UIV+2; 2) distal tether fixation to UIV, to UIV−1, or to rods; and 3) use of a loop (single proximal fixation) or weave (UIV and/or UIV+1 fixation in addition to UIV+1 and/or UIV+2 proximal attachment) of the tether. Segmental ROM, intradiscal pressure (IDP), inter- and supraspinous ligament (ISL/SSL) forces, and screw loads were assessed under variable tether preload.

RESULTS

PS construct junctional ROM increased abruptly from 10% (T11–12) to 99% (T10–11) of baseline. After tethers were grouped by most cranial proximal fixation (UIV+1 vs UIV+2) and use of loop versus weave, UIV+2 Loop and/or Weave most effectively dampened junctional ROM and adjacent-segment stress. Different distal fixation and use of loop versus weave had minimal effect. The mean segmental ROM at T11–12, T10–11, and T9–10, respectively, was 6%, 40%, and 99% for UIV+1 Loop; 6%, 44%, and 99% for UIV+1 Weave; 5%, 23%, and 26% for UIV+2 Loop; and 5%, 24%, and 31% for UIV+2 Weave.

Tethers shared loads with posterior ligaments; consequently, increasing tether preload tension reduced ISL/SSL forces, but screw loads increased. Further attenuation of junctional ROM and IDP reversed above approximately 100 N tether preload, suggesting diminished benefit for biomechanical PJK prophylaxis at higher preload tensioning.

CONCLUSIONS

In this study, finite element analysis demonstrated UIV+2 Loop and/or Weave tether configurations most effectively mitigated adjacent-segment stress in long instrumented spine constructs. Tether preload dampened ligament forces at the expense of screw loads, and an inflection point (approximately 100 N) was demonstrated above which junctional ROM and IDP worsened (i.e., avoid over-tightening tethers). Results suggest tether configuration and tension influence PJK biomechanics and further clinical research is warranted.

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Shay Bess, Jeffrey E. Harris, Alexander W. L. Turner, Virginie LaFage, Justin S. Smith, Christopher I. Shaffrey, Frank J. Schwab and Regis W. Haid Jr.

OBJECTIVE

Proximal junctional kyphosis (PJK) remains problematic following multilevel instrumented spine surgery. Previous biomechanical studies indicate that providing less rigid fixation at the cranial aspect of a long posterior instrumented construct, via transition rods or hooks at the upper instrumented vertebra (UIV), may provide a gradual transition to normal motion and prevent PJK. The purpose of this study was to evaluate the ability of posterior anchored polyethylene tethers to distribute proximal motion segment stiffness in long instrumented spine constructs.

METHODS

A finite element model of a T7–L5 spine segment was created to evaluate range of motion (ROM), intradiscal pressure, pedicle screw loads, and forces in the posterior ligament complex within and adjacent to the proximal terminus of an instrumented spine construct. Six models were tested: 1) intact spine; 2) bilateral, segmental pedicle screws (PS) at all levels from T-11 through L-5; 3) bilateral pedicle screws from T-12 to L-5 and transverse process hooks (TPH) at T-11 (the UIV); 4) pedicle screws from T-11 to L5 and 1-level tethers from T-10 to T-11 (TE-UIV+1); 5) pedicle screws from T-11 to L-5 and 2-level tethers from T-9 to T-11 (TE-UIV+2); and 6) pedicle screws and 3-level tethers from T-8 to T-11 (TE-UIV+3).

RESULTS

Proximal-segment range of motion (ROM) for the PS construct increased from 16% at UIV−1 to 91% at UIV. Proximal-segment ROM for the TPH construct increased from 27% at UIV−1 to 92% at UIV. Posterior tether constructs distributed ROM at the UIV and cranial adjacent segments most effectively; ROM for TE-UIV+1 was 14% of the intact model at UIV−1, 76% at UIV, and 98% at UIV+1. ROM for TE-UIV+2 was 10% at UIV−1, 51% at UIV, 69% at UIV+1, and 97% at UIV+2. ROM for TE-UIV+3 was 7% at UIV−1, 33% at UIV, 45% at UIV+1, and 64% at UIV+2. Proximal segment intradiscal pressures, pedicle screw loads, and ligament forces in the posterior ligament complex were progressively reduced with increasing number of posterior tethers used.

CONCLUSIONS

Finite element analysis of long instrumented spine constructs demonstrated that posterior tethers created a more gradual transition in ROM and adjacent-segment stress from the instrumented to the noninstrumented spine compared with all PS and TPH constructs. Posterior tethers may limit the biomechanical risk factor for PJK; however, further clinical research is needed to evaluate clinical efficacy.

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Alex Soroceanu, Douglas C. Burton, Bassel Georges Diebo, Justin S. Smith, Richard Hostin, Christopher I. Shaffrey, Oheneba Boachie-Adjei, Gregory M. Mundis Jr., Christopher Ames, Thomas J. Errico, Shay Bess, Munish C. Gupta, Robert A. Hart, Frank J. Schwab, Virginie Lafage and International Spine Study Group

OBJECT

Adult spinal deformity (ASD) surgery is known for its high complication rate. This study examined the impact of obesity on complication rates, infection, and patient-reported outcomes in patients undergoing surgery for ASD.

METHODS

This study was a retrospective review of a multicenter prospective database of patients with ASD who were treated surgically. Patients with available 2-year follow-up data were included. Obesity was defined as having a body mass index (BMI) ≥ 30 kg/m2. Data collected included complications (total, minor, major, implant-related, radiographic, infection, revision surgery, and neurological injury), estimated blood loss (EBL), operating room (OR) time, length of stay (LOS), and patient-reported questionnaires (Oswestry Disability Index [ODI], Short Form-36 [SF-36], and Scoliosis Research Society [SRS]) at baseline and at 6 weeks, 1 year, and 2 years postoperatively. The impact of obesity was studied using multivariate modeling, accounting for confounders.

RESULTS

Of 241 patients who satisfied inclusion criteria, 175 patients were nonobese and 66 were obese. Regression models showed that obese patients had a higher overall incidence of major complications (IRR 1.54, p = 0.02) and wound infections (odds ratio 4.88, p = 0.02). Obesity did not increase the number of minor complications (p = 0.62), radiographic complications (p = 0.62), neurological complications (p = 0.861), or need for revision surgery (p = 0.846). Obesity was not significantly correlated with OR time (p = 0.23), LOS (p = 0.9), or EBL (p = 0.98). Both groups experienced significant improvement overtime, as measured on the ODI (p = 0.0001), SF-36 (p = 0.0001), and SRS (p = 0.0001) questionnaires. However, the overall magnitude of improvement was less for obese patients (ODI, p = 0.0035; SF-36, p = 0.0012; SRS, p = 0.022). Obese patients also had a lower rate of improvement over time (SRS, p = 0.0085; ODI, p = 0.0001; SF-36, p = 0.0001).

CONCLUSIONS

This study revealed that obese patients have an increased risk of complications following ASD correction. Despite these increased complications, obese patients do benefit from surgical intervention; however, their improvement in health-related quality of life (HRQL) is less than that of nonobese patients.

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Justin S. Smith, Ellen Shaffrey, Eric Klineberg, Christopher I. Shaffrey, Virginie Lafage, Frank J. Schwab, Themistocles Protopsaltis, Justin K. Scheer, Gregory M. Mundis Jr., Kai-Ming G. Fu, Munish C. Gupta, Richard Hostin, Vedat Deviren, Khaled Kebaish, Robert Hart, Douglas C. Burton, Breton Line, Shay Bess, Christopher P. Ames and The International Spine Study Group

Object

Improved understanding of rod fracture (RF) following adult spinal deformity (ASD) surgery could prove valuable for surgical planning, patient counseling, and implant design. The objective of this study was to prospectively assess the rates of and risk factors for RF following surgery for ASD.

Methods

This was a prospective, multicenter, consecutive series. Inclusion criteria were ASD, age > 18 years, ≥5 levels posterior instrumented fusion, baseline full-length standing spine radiographs, and either development of RF or full-length standing spine radiographs obtained at least 1 year after surgery that demonstrated lack of RF. ASD was defined as presence of at least one of the following: coronal Cobb angle ≥20°, sagittal vertical axis (SVA) ≥5 cm, pelvic tilt (PT) ≥25°, and thoracic kyphosis ≥60°.

Results

Of 287 patients who otherwise met inclusion criteria, 200 (70%) either demonstrated RF or had radiographic imaging obtained at a minimum of 1 year after surgery showing lack of RF. The patients' mean age was 54.8 ± 15.8 years; 81% were women; 10% were smokers; the mean body mass index (BMI) was 27.1 ± 6.5; the mean number of levels fused was 12.0 ± 3.8; and 50 patients (25%) had a pedicle subtraction osteotomy (PSO). The rod material was cobalt chromium (CC) in 53%, stainless steel (SS), in 26%, or titanium alloy (TA) in 21% of cases; the rod diameters were 5.5 mm (in 68% of cases), 6.0 mm (in 13%), or 6.35 mm (in 19%). RF occurred in 18 cases (9.0%) at a mean of 14.7 months (range 3–27 months); patients without RF had a mean follow-up of 19 months (range 12–24 months). Patients with RF were older (62.3 vs 54.1 years, p = 0.036), had greater BMI (30.6 vs 26.7, p = 0.019), had greater baseline sagittal malalignment (SVA 11.8 vs 5.0 cm, p = 0.001; PT 29.1° vs 21.9°, p = 0.016; and pelvic incidence [PI]–lumbar lordosis [LL] mismatch 29.6° vs 12.0°, p = 0.002), and had greater sagittal alignment correction following surgery (SVA reduction by 9.6 vs 2.8 cm, p < 0.001; and PI-LL mismatch reduction by 26.3° vs 10.9°, p = 0.003). RF occurred in 22.0% of patients with PSO (10 of the 11 fractures occurred adjacent to the PSO level), with rates ranging from 10.0% to 31.6% across centers. CC rods were used in 68% of PSO cases, including all with RF. Smoking, levels fused, and rod diameter did not differ significantly between patients with and without RF (p > 0.05). In cases including a PSO, the rate of RF was significantly higher with CC rods than with TA or SS rods (33% vs 0%, p = 0.010). On multivariate analysis, only PSO was associated with RF (p = 0.001, OR 5.76, 95% CI 2.01–15.8).

Conclusions

Rod fracture occurred in 9.0% of ASD patients and in 22.0% of PSO patients with a minimum of 1-year follow-up. With further follow-up these rates would likely be even higher. There was a substantial range in the rate of RF with PSO across centers, suggesting potential variations in technique that warrant future investigation. Due to higher rates of RF with PSO, alternative instrumentation strategies should be considered for these cases.

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Justin S. Smith, Manish Singh, Eric Klineberg, Christopher I. Shaffrey, Virginie Lafage, Frank J. Schwab, Themistocles Protopsaltis, David Ibrahimi, Justin K. Scheer, Gregory Mundis Jr., Munish C. Gupta, Richard Hostin, Vedat Deviren, Khaled Kebaish, Robert Hart, Douglas C. Burton, Shay Bess and Christopher P. Ames

Object

Increased sagittal vertical axis (SVA) correlates strongly with pain and disability for adults with spinal deformity. A subset of patients with sagittal spinopelvic malalignment (SSM) have flatback deformity (pelvic incidence–lumbar lordosis [PI-LL] mismatch > 10°) but remain sagittally compensated with normal SVA. Few data exist for SSM patients with flatback deformity and normal SVA. The authors' objective was to compare baseline disability and treatment outcomes for patients with compensated (SVA < 5 cm and PI-LL mismatch > 10°) and decompensated (SVA > 5 cm) SSM.

Methods

The study was a multicenter, prospective analysis of adults with spinal deformity who consecutively underwent surgical treatment for SSM. Inclusion criteria included age older than 18 years, presence of adult spinal deformity with SSM, plan for surgical treatment, and minimum 1-year follow-up data. Patients with SSM were divided into 2 groups: those with compensated SSM (SVA < 5 cm and PI-LL mismatch > 10°) and those with decompensated SSM (SVA ≥ 5 cm). Baseline and 1-year follow-up radiographic and health-related quality of life (HRQOL) outcomes included Oswestry Disability Index, Short Form–36 scores, and Scoliosis Research Society–22 scores. Percentages of patients achieving minimal clinically important difference (MCID) were also assessed.

Results

A total of 125 patients (27 compensated and 98 decompensated) met inclusion criteria. Compared with patients in the compensated group, patients in the decompensated group were older (62.9 vs 55.1 years; p = 0.004) and had less scoliosis (43° vs 54°; p = 0.002), greater SVA (12.0 cm vs 1.7 cm; p < 0.001), greater PI-LL mismatch (26° vs 20°; p = 0.013), and poorer HRQOL scores (Oswestry Disability Index, Short Form-36 physical component score, Scoliosis Research Society-22 total; p ≤ 0.016). Although these baseline HRQOL differences between the groups reached statistical significance, only the mean difference in Short Form–36 physical component score reached threshold for MCID. Compared with baseline assessment, at 1 year after surgery improvement was noted for patients in both groups for mean SVA (compensated –1.1 cm, decompensated +4.8 cm; p ≤ 0.009), mean PI-LL mismatch (compensated 6°, decompensated 5°; p < 0.001), and all HRQOL measures assessed (p ≤ 0.005). No significant differences were found between the compensated and decompensated groups in the magnitude of HRQOL score improvement or in the percentages of patients achieving MCID for each of the outcome measures assessed.

Conclusions

Decompensated SSM patients with elevated SVA experience significant disability; however, the amount of disability in compensated SSM patients with flatback deformity caused by PI-LL mismatch but normal SVA is underappreciated. Surgical correction of SSM demonstrated similar radiographic and HRQOL score improvements for patients in both groups. Evaluation of SSM should extend beyond measuring SVA. Among patients with concordant pain and disability, PI-LL mismatch must be evaluated for SSM patients and can be considered a primary indication for surgery.

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Kseniya Slobodyanyuk, Caroline E. Poorman, Justin S. Smith, Themistocles S. Protopsaltis, Richard Hostin, Shay Bess, Gregory M. Mundis Jr., Frank J. Schwab and Virginie Lafage

Object

The goal of this study was to determine the outcome and risk factors in patients with adult spinal deformity (ASD) who elected to receive nonoperative care.

Methods

In this retrospective study the authors reviewed a nonoperative branch of the International Spine Study Group database, derived from 10 sites across the US. Specific inclusion criteria included nonoperative treatment for ASD and the availability of Scoliosis Research Society (SRS)-22 scores and radiographic data at baseline (BL) and at 1-year (1Y) follow-up. Health-related quality of life measures were assessed using the SRS-22 and radiographic data. Changes in SRS-22 scores were evaluated by domain and expressed in number of minimum clinically important differences (MCIDs) gained or lost; BL and 1Y scores were also compared with age- and sex-matched normative references.

Results

One hundred eighty-nine patients (mean age 53 years, 86% female) met inclusion criteria. Pain was the domain with the largest offset for 43% of patients, followed by the Appearance (23%), Activity (18%), and Mental (15%) domains. On average, patients improved 0.3 MCID in Pain over 1Y, without changes in Activity or Appearance. Baseline scores significantly impacted 1Y outcomes, with up to 85% of patients in the mildest category of deformity being classified as < 1 MCID of normative reference at 1Y, versus 0% of patients with the most severe initial deformity. Baseline radiographic parameters did not correlate with outcome.

Conclusions

Patients who received nonoperative care are significantly more disabled than age- and sex-matched normative references. The likelihood for a patient to reach SRS scores similar to the normative reference at 1Y decreases with increased BL disability. Nonoperative treatment is a viable option for certain patients with ASD, and up to 24% of patients demonstrated significant improvement over 1Y with nonoperative care.

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Christopher P. Ames, Justin S. Smith, Justin K. Scheer, Christopher I. Shaffrey, Virginie Lafage, Vedat Deviren, Bertrand Moal, Themistocles Protopsaltis, Praveen V. Mummaneni, Gregory M. Mundis Jr., Richard Hostin, Eric Klineberg, Douglas C. Burton, Robert Hart, Shay Bess, Frank J. Schwab and the International Spine Study Group

Object

Cervical spine osteotomies are powerful techniques to correct rigid cervical spine deformity. Many variations exist, however, and there is no current standardized system with which to describe and classify cervical osteotomies. This complicates the ability to compare outcomes across procedures and studies. The authors' objective was to establish a universal nomenclature for cervical spine osteotomies to provide a common language among spine surgeons.

Methods

A proposed nomenclature with 7 anatomical grades of increasing extent of bone/soft tissue resection and destabilization was designed. The highest grade of resection is termed the major osteotomy, and an approach modifier is used to denote the surgical approach(es), including anterior (A), posterior (P), anterior-posterior (AP), posterior-anterior (PA), anterior-posterior-anterior (APA), and posterior-anterior-posterior (PAP). For cases in which multiple grades of osteotomies were performed, the highest grade is termed the major osteotomy, and lower-grade osteotomies are termed minor osteotomies. The nomenclature was evaluated by 11 reviewers through 25 different radiographic clinical cases. The review was performed twice, separated by a minimum 1-week interval. Reliability was assessed using Fleiss kappa coefficients.

Results

The average intrarater reliability was classified as “almost perfect agreement” for the major osteotomy (0.89 [range 0.60–1.00]) and approach modifier (0.99 [0.95–1.00]); it was classified as “moderate agreement” for the minor osteotomy (0.73 [range 0.41–1.00]). The average interrater reliability for the 2 readings was the following: major osteotomy, 0.87 (“almost perfect agreement”); approach modifier, 0.99 (“almost perfect agreement”); and minor osteotomy, 0.55 (“moderate agreement”). Analysis of only major osteotomy plus approach modifier yielded a classification that was “almost perfect” with an average intrarater reliability of 0.90 (0.63–1.00) and an interrater reliability of 0.88 and 0.86 for the two reviews.

Conclusions

The proposed cervical spine osteotomy nomenclature provides the surgeon with a simple, standard description of the various cervical osteotomies. The reliability analysis demonstrated that this system is consistent and directly applicable. Future work will evaluate the relationship between this system and health-related quality of life metrics.

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Frank J. Schwab, Ashish Patel, Christopher I. Shaffrey, Justin S. Smith, Jean-Pierre Farcy, Oheneba Boachie-Adjei, Richard A. Hostin, Robert A. Hart, Behrooz A. Akbarnia, Douglas C. Burton, Shay Bess and Virginie Lafage

Object

Pedicle subtraction osteotomy (PSO) is a surgical procedure that is frequently performed on patients with sagittal spinopelvic malalignment. Although it allows for substantial spinopelvic realignment, suboptimal realignment outcomes have been reported in up to 33% of patients. The authors' objective in the present study was to identify differences in radiographic profiles and surgical procedures between patients achieving successful versus failed spinopelvic realignment following PSO.

Methods

This study is a multicenter retrospective consecutive PSO case series. The authors evaluated 99 cases involving patients who underwent PSO for sagittal spinopelvic malalignment. Because precise cutoffs of acceptable residual postoperative sagittal vertical axis (SVA) values have not been well defined, comparisons were focused between patient groups with a postoperative SVA that could be clearly considered either a success or a failure. Only cases in which the patients had a postoperative SVA of less than 50 mm (successful PSO realignment) or more than 100 mm (failed PSO realignment) were included in the analysis. Radiographic measures and PSO parameters were compared between successful and failed PSO realignments.

Results

Seventy-nine patients met the inclusion criteria. Successful realignment was achieved in 61 patients (77%), while realignment failed in 18 (23%). Patients with failed realignment had larger preoperative SVA (mean 217.9 vs 106.7 mm, p < 0.01), larger pelvic tilt (mean 36.9° vs 30.7°, p < 0.01), larger pelvic incidence (mean 64.2° vs 53.7°, p < 0.01), and greater lumbar lordosis–pelvic incidence mismatch (−47.1° vs −30.9°, p < 0.01) compared with those in whom realignment was successful. Failed and successful realignments were similar regarding the vertebral level of the PSO, the median size of wedge resection 22.0° (interquartile range 16.5°−28.5°), and the numerical changes in pre- and postoperative spinopelvic parameters (p > 0.05).

Conclusions

Patients with failed PSO realignments had significantly larger preoperative spinopelvic deformity than patients in whom realignment was successful. Despite their apparent need for greater correction, the patients in the failed realignment group only received the same amount of correction as those in the successfully realigned patients. A single-level standard PSO may not achieve optimal outcome in patients with high preoperative spinopelvic sagittal malalignment. Patients with large spinopelvic deformities should receive larger osteotomies or additional corrective procedures beyond PSOs to avoid undercorrection.