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Darryl Lau, Cecilia L. Dalle Ore, Patrick Reid, Michael M. Safaee, Vedat Deviren, Justin S. Smith, Christopher I. Shaffrey and Christopher P. Ames

OBJECTIVE

The benefits and utility of routine neuromonitoring with motor and somatosensory evoked potentials during lumbar spine surgery remain unclear. This study assesses measures of performance and utility of transcranial motor evoked potentials (MEPs) during lumbar pedicle subtraction osteotomy (PSO).

METHODS

This is a retrospective study of a single-surgeon cohort of consecutive adult spinal deformity (ASD) patients who underwent lumbar PSO from 2006 to 2016. A blinded neurophysiologist reviewed individual cases for MEP changes. Multivariate analysis was performed to determine whether changes correlated with neurological deficits. Measures of performance were calculated.

RESULTS

A total of 242 lumbar PSO cases were included. MEP changes occurred in 38 (15.7%) cases; the changes were transient in 21 cases (55.3%) and permanent in 17 (44.7%). Of the patients with permanent changes, 9 (52.9%) had no recovery and 8 (47.1%) had partial recovery of MEP signals. Changes occurred at a mean time of 8.8 minutes following PSO closure (range: during closure to 55 minutes after closure). The mean percentage of MEP signal loss was 72.9%. The overall complication rate was 25.2%, and the incidence of new neurological deficits was 4.1%. On multivariate analysis, MEP signal loss of at least 50% was not associated with complication (p = 0.495) or able to predict postoperative neurological deficits (p = 0.429). Of the 38 cases in which MEP changes were observed, the observation represented a true-positive finding in only 3 cases. Postoperative neurological deficits without MEP changes occurred in 7 cases. Calculated measures of performance were as follows: sensitivity 30.0%, specificity 84.9%, positive predictive value 7.9%, and negative predictive value 96.6%. Regarding the specific characteristics of the MEP changes, only a signal loss of 80% or greater was significantly associated with a higher rate of neurological deficit (23.0% vs 0.0% for loss of less than 80%, p = 0.021); changes of less than 80% were not associated with postoperative deficits.

CONCLUSIONS

Neuromonitoring has a low positive predictive value and low sensitivity for detecting new neurological deficits. Even when neuromonitoring is unchanged, patients can still have new neurological deficits. The utility of transcranial MEP monitoring for lumbar PSO remains unclear but there may be advantages to its use.

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Justin S. Smith, Christopher I. Shaffrey, Christopher P. Ames and Lawrence G. Lenke

Care of the patient with adult spinal deformity (ASD) has evolved from being primarily supportive to now having the ability to directly treat and correct the spinal pathology. The focus of this narrative literature review is to briefly summarize the history of ASD treatment, discuss the current state of the art of ASD care with focus on surgical treatment and current challenges, and conclude with a discussion of potential developments related to ASD surgery.

In the past, care for ASD was primarily based on supportive measures, including braces and assistive devices, with few options for surgical treatments that were often deemed high risk and reserved for rare situations. Advances in anesthetic and critical care, surgical techniques, and instrumentation now enable almost routine surgery for many patients with ASD. Despite the advances, there are many remaining challenges currently impacting the care of ASD patients, including increasing numbers of elderly patients with greater comorbidities, high complication and reoperation rates, and high procedure cost without clearly demonstrated cost-effectiveness based on standard criteria. In addition, there remains considerable variability across multiple aspects of ASD surgery. For example, there is currently very limited ability to provide preoperative individualized counseling regarding optimal treatment approaches (e.g., operative vs nonoperative), complication risks with surgery, durability of surgery, and likelihood of achieving individualized patient goals and satisfaction. Despite the challenges associated with the current state-of-the-art ASD treatment, surgery continues to be a primary option, as multiple reports have demonstrated the potential for surgery to significantly improve pain and disability. The future of ASD care will likely include techniques and technologies to markedly reduce complication rates, including greater use of navigation and robotics, and a shift toward individualized medicine that enables improved counseling, preoperative planning, procedure safety, and patient satisfaction.

Advances in the care of ASD patients have been remarkable over the past few decades. The current state of the art enables almost routine surgical treatment for many types of ASD that have the potential to significantly improve pain and disability. However, significant challenges remain, including high complication rates, lack of demonstrated cost-effectiveness, and limited ability to meaningfully counsel patients preoperatively on an individual basis. The future of ASD surgery will require continued improvement of predictability, safety, and sustainability.

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Michael M. Safaee, Cecilia L. Dalle Ore, Corinna C. Zygourakis, Vedat Deviren and Christopher P. Ames

OBJECTIVE

Bone morphogenetic protein (BMP) is associated with reduced rates of pseudarthrosis and has the potential to decrease the need for revision surgery. There are limited data evaluating the cost-benefit of BMP for pseudarthrosis-related prevention surgery in adult spinal deformity.

METHODS

The authors performed a single-center retrospective review of 200 consecutive patients with adult spinal deformity. Demographic data and costs of BMP, primary surgery, and revision surgery for pseudarthrosis were collected. Patients with less than 12 months of follow-up or with infection, tumor, or neuromuscular disease were excluded.

RESULTS

One hundred fifty-one patients (107 [71%] women) with a mean age of 65 years met the inclusion criteria. The mean number of levels fused was 10; BMP was used in 98 cases (65%), and the mean follow-up was 23 months. Fifteen patients (10%) underwent surgical revision for pseudarthrosis; BMP use was associated with an 11% absolute risk reduction in the rate of reoperation (17% vs 6%, p = 0.033), with a number needed to treat of 9.2. There were no significant differences in age, sex, upper instrumented vertebra, or number of levels fused in patients who received BMP. In a multivariate model including age, sex, number of levels fused, and the upper instrumented vertebra, only BMP (OR 0.250, 95% CI 0.078–0.797; p = 0.019) was associated with revision surgery for pseudarthrosis. The mean direct cost of primary surgery was $87,653 ± $19,879, and the mean direct cost of BMP was $10,444 ± $4607. The mean direct cost of revision surgery was $52,153 ± $26,985. The authors independently varied the efficacy of BMP, cost of BMP, and cost of reoperation by ± 50%; only reductions in the cost of BMP resulted in a cost savings per 100 patients. Using these data, the authors estimated a price point of $5663 in order for BMP to be cost-neutral.

CONCLUSIONS

Use of BMP was associated with a significant reduction in the rates of revision surgery for pseudarthrosis. At its current price, the direct in-hospital costs for BMP exceed the costs associated with revision surgery; however, this likely underestimates the true value of BMP when considering the savings associated with reductions in rehabilitation, therapy, medication, and additional outpatient costs.

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Cecilia L. Dalle Ore, Christopher P. Ames, Vedat Deviren and Darryl Lau

OBJECTIVE

Spinal deformity causing spinal imbalance is directly correlated to pain and disability. Prior studies suggest adult spinal deformity (ASD) patients with rheumatoid arthritis (RA) have more complex deformities and are at higher risk for complications. In this study the authors compared outcomes of ASD patients with RA following thoracolumbar 3-column osteotomies to outcomes of a matched control cohort.

METHODS

All patients with RA who underwent 3-column osteotomy for thoracolumbar deformity correction performed by the senior author from 2006 to 2016 were identified retrospectively. A cohort of patients without RA who underwent 3-column osteotomies for deformity correction was matched based on multiple clinical factors. Data regarding demographics and surgical approach, along with endpoints including perioperative outcomes, reoperations, and incidence of proximal junctional kyphosis (PJK) were reviewed. Univariate analyses were used to compare patients with RA to matched controls.

RESULTS

Eighteen ASD patients with RA were identified, and a matched cohort of 217 patients was generated. With regard to patients with RA, 11.1% were male and the mean age was 68.1 years. Vertebral column resection (VCR) was performed in 22.2% and pedicle subtraction osteotomy (PSO) in 77.8% of patients. Mean case length was 324.4 minutes and estimated blood loss (EBL) was 2053.6 ml. Complications were observed in 38.9% of patients with RA and 29.0% of patients without RA (p = 0.380), with a trend toward increased medical complications (38.9% vs 21.2%, p = 0.084). Patients with RA had a significantly higher incidence of deep vein thrombosis (DVT)/pulmonary embolism (PE) (11.1% vs 1.8%, p = 0.017) and wound infections (16.7% vs 5.1%, p = 0.046). PJK occurred in 16.7% of patients with RA, and 33.3% of RA patients underwent reoperation. Incidence rates of PJK and reoperation in matched controls were 12.9% and 25.3%, respectively (p = 0.373, p = 0.458). At follow-up, mean sagittal vertical axis (SVA) was 6.1 cm in patients with RA and 4.5 cm in matched controls (p = 0.206).

CONCLUSIONS

Findings from this study suggest that RA patients experience a higher incidence of medical complications, specifically DVT/PE. Preoperative lower-extremity ultrasounds, inferior vena cava (IVC) filter placement, and/or early initiation of DVT prophylaxis in RA patients may be indicated. Perioperative complications, morbidity, and long-term outcomes are otherwise similar to non-RA patients.

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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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Dominic Amara, Praveen V. Mummaneni, Christopher P. Ames, Bobby Tay, Vedat Deviren, Shane Burch, Sigurd H. Berven and Dean Chou

OBJECTIVE

Many options exist for the surgical management of adult spinal deformity. Radiculopathy and lumbosacral pain from the fractional curve (FC), typically from L4 to S1, is frequently a reason for scoliosis patients to pursue surgical intervention. The purpose of this study was to evaluate the outcomes of limited fusion of the FC only versus treatment of the entire deformity with long fusions.

METHODS

All adult scoliosis patients treated at the authors’ institution in the period from 2006 to 2016 were retrospectively analyzed. Patients with FCs from L4 to S1 > 10° and radiculopathy ipsilateral to the concavity of the FC were eligible for study inclusion and had undergone three categories of surgery: 1) FC only (FC group), 2) lower thoracic to sacrum (LT group), or 3) upper thoracic to sacrum (UT group). Primary outcomes were the rates of revision surgery and complications. Secondary outcomes were estimated blood loss, length of hospital stay, and discharge destination. Spinopelvic parameters were measured, and patients were stratified accordingly.

RESULTS

Of the 99 patients eligible for inclusion in the study, 27 were in the FC group, 46 in the LT group, and 26 in the UT group. There were no significant preoperative differences in age, sex, smoking status, prior operation, FC magnitude, pelvic tilt (PT), sagittal vertical axis (SVA), coronal balance, pelvic incidence–lumbar lordosis (PI-LL) mismatch, or proportion of well-aligned spines (SVA < 5 cm, PI-LL mismatch < 10°, and PT < 20°) among the three treatment groups. Mean follow-up was 30 (range 12–112) months, with a minimum 1-year follow-up. The FC group had a lower medical complication rate (22% [FC] vs 57% [LT] vs 58% [UT], p = 0.009) but a higher rate of extension surgery (26% [FC] vs 13% [LT] vs 4% [UT], p = 0.068). The respective average estimated blood loss (592 vs 1950 vs 2634 ml, p < 0.001), length of hospital stay (5.5 vs 8.3 vs 8.3 days, p < 0.001), and rate of discharge to acute rehabilitation (30% vs 46% vs 85%, p < 0.001) were all lower for FC and highest for UT.

CONCLUSIONS

Treatment of the FC only is associated with a lower complication rate, shorter hospital stay, and less blood loss than complete scoliosis treatment. However, there is a higher associated rate of extension of the construct to the lower or upper thoracic levels, and patients should be counseled when considering their options.

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Justin K. Scheer, Taemin Oh, Justin S. Smith, Christopher I. Shaffrey, Alan H. Daniels, Daniel M. Sciubba, D. Kojo Hamilton, Themistocles S. Protopsaltis, Peter G. Passias, Robert A. Hart, Douglas C. Burton, Shay Bess, Renaud Lafage, Virginie Lafage, Frank Schwab, Eric O. Klineberg, Christopher P. Ames and the International Spine Study Group

OBJECTIVE

Pseudarthrosis can occur following adult spinal deformity (ASD) surgery and can lead to instrumentation failure, recurrent pain, and ultimately revision surgery. In addition, it is one of the most expensive complications of ASD surgery. Risk factors contributing to pseudarthrosis in ASD have been described; however, a preoperative model predicting the development of pseudarthrosis does not exist. The goal of this study was to create a preoperative predictive model for pseudarthrosis based on demographic, radiographic, and surgical factors.

METHODS

A retrospective review of a prospectively maintained, multicenter ASD database was conducted. Study inclusion criteria consisted of adult patients (age ≥ 18 years) with spinal deformity and surgery for the ASD. From among 82 variables assessed, 21 were used for model building after applying collinearity testing, redundancy, and univariable predictor importance ≥ 0.90. Variables included demographic data along with comorbidities, modifiable surgical variables, baseline coronal and sagittal radiographic parameters, and baseline scores for health-related quality of life measures. Patients groups were determined according to their Lenke radiographic fusion type at the 2-year follow-up: bilateral or unilateral fusion (union) or pseudarthrosis (nonunion). A decision tree was constructed, and internal validation was accomplished via bootstrapped training and testing data sets. Accuracy and the area under the receiver operating characteristic curve (AUC) were calculated to evaluate the model.

RESULTS

A total of 336 patients were included in the study (nonunion: 105, union: 231). The model was 91.3% accurate with an AUC of 0.94. From 82 initial variables, the top 21 covered a wide range of areas including preoperative alignment, comorbidities, patient demographics, and surgical use of graft material.

CONCLUSIONS

A model for predicting the development of pseudarthrosis at the 2-year follow-up was successfully created. This model is the first of its kind for complex predictive analytics in the development of pseudarthrosis for patients with ASD undergoing surgical correction and can aid in clinical decision-making for potential preventative strategies.

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Thomas J. Buell, Davis G. Taylor, Ching-Jen Chen, Christopher I. Shaffrey, Justin S. Smith and Shay Bess

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Cecilia L. Dalle Ore, Darryl Lau, Jessica L. Davis, Michael M. Safaee and Christopher P. Ames

Juvenile ossifying fibroma (JOF) is a rare benign bone tumor that occurs most frequently in the craniofacial bones of children and young adults. There are few case reports that describe its involvement outside the craniofacial skeleton, especially within the spinal column. While JOF is classified as a benign lesion, it may be locally aggressive and demonstrate a high propensity for recurrence, even after resection. Definitive surgical management may be challenging in naive cases, but it is particularly challenging in recurrent cases and when extensive spinal reconstruction is warranted. In this report, the authors describe the diagnosis and surgical management of a 29-year-old man who presented with a large recurrent sacral trabecular-subtype JOF. A review of literature regarding JOFs, management of recurrent primary spinal tumors, and sacral reconstruction are discussed.