Preoperative MRI predictors of health-related quality of life improvement after microscopic lumbar discectomy

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Preoperative MRI Predictors of Health Related Quality of Life Improvement after Microscopic Lumbar Discectomy Christopher G. Varlotta , Jordan H. Manning , Ethan W. Ayres , Erik Wang , Dainn Woo , Dennis Vasquez-Montes , Haddy Alas , Avery Brown , Max Egers , Yong Kim , John A. Bendo , Charla R. Fischer , Themistocles S. Protopsaltis , Jonathan R. Stieber , Aaron J. Buckland PII: DOI: Reference:

S1529-9430(19)31005-8 https://doi.org/10.1016/j.spinee.2019.09.020 SPINEE 58029

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The Spine Journal

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Please cite this article as: Christopher G. Varlotta , Jordan H. Manning , Ethan W. Ayres , Erik Wang , Dainn Woo , Dennis Vasquez-Montes , Haddy Alas , Avery Brown , Max Egers , Yong Kim , John A. Bendo , Charla R. Fischer , Themistocles S. Protopsaltis , Jonathan R. Stieber , Aaron J. Buckland , Preoperative MRI Predictors of Health Related Quality of Life Improvement after Microscopic Lumbar Discectomy, The Spine Journal (2019), doi: https://doi.org/10.1016/j.spinee.2019.09.020

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Preoperative MRI Predictors of Health Related Quality of Life Improvement after Microscopic Lumbar Discectomy Christopher G. Varlotta1, Jordan H. Manning1, Ethan W. Ayres1, Erik Wang1, Dainn Woo1, Dennis VasquezMontes1, Haddy Alas1, Avery Brown1, Max Egers1, Yong Kim1, John A. Bendo1, Charla R. Fischer1, Themistocles S. Protopsaltis1, Jonathan R. Stieber1, Aaron J. Buckland1

Affiliations: 1. Department of Orthopaedic Surgery, Hospital for Joint Diseases, NYU Langone Health, New York, NY, USA Corresponding Author: Aaron J. Buckland, MBBS, FRACS Spine Research Center NYU Langone Medical Center - Hospital for Joint Diseases 306 East 15th Street New York, New York 10003, USA Phone: 646-794-8640 Fax: 646-602-6927 E-mail: [email protected]

Device Status/Drug Statement:

The manuscript submitted does not contain information about medical device(s)/drug(s).

Disclosure of Funding:

There was no source of study funding for the manuscript submitted.

Conflicts of Interest:

There are no relative conflicts of interest associated with the manuscript submitted.

ABSTRACT BACKGROUND: Lumbar herniated nucleus pulposus (HNP) is a common spinal pathology often treated by microscopic lumbar discectomy (MLD), though prior reports have not demonstrated which preoperative MRI factors may contribute to significant clinical improvement after MLD.

PURPOSE: To analyze the MRI characteristics in patients with HNP that predict meaningful clinical improvement in Health Related Quality of Life scores (HRQoL) after MLD.

STUDY DESIGN/SETTING: Retrospective clinical and radiological study of patients undergoing MLD for HNP at a single institution over a two-year period.

PATIENT SAMPLE: 88 patients receiving MLD treatment for HNP.

OUTCOME MEASURES: Cephalocaudal Canal Migration; Canal & HNP Anterior-Posterior (AP) Lengths and Ratio; Canal & HNP Axial Areas and Ratio; Hemi-Canal & Hemi-HNP Axial Areas and Ratio; Disc appearance (black, grey or mixed), Baseline (BL) and 3-Month (3M) postoperative Health Related Quality of Life Scores.

METHODS: Patients > 18 years old who received MLD for HNP with BL and 3M HRQoL scores of PROMIS (Physical Function, Pain Interference, and Pain Intensity), ODI, VAS Back, and VAS Leg scores were included. HNP and spinal canal measurements of cephalocaudal migration, AP length, area, hemi-area, and disc appearance were performed using T2 axial and sagittal MRI. HNP measurements were divided by corresponding canal measurements to calculate AP, Area, and HemiArea ratios. Using known minimal clinically important differences (MCID) for each ΔHRQoL score,

patients were separated into two groups based on whether they reached MCID (MCID+) or did not reach MCID (MCID–). The MCID for PROMIS Pain Intensity was calculated using a decision tree. A linear regression illustrated correlations between PROMIS vs ODI and VAS Back/Leg scores. Independent t-tests and chi2 tests were utilized to investigate significant differences in HNP measurements between the MCID+ and MCID– groups.

RESULTS: There were 88 MLD patients included in the study (Age=44.6±14.9, 38.6% Female). PROMIS Pain Interference and Pain Intensity were strongly correlated with ODI and VAS Back/Leg (R≥.505), and Physical Function correlated with ODI and VAS Back/Leg (R=-.349) (all p<.01). The strongest MRI predictors of meeting HRQoL MCID were grey disc appearance, HNP area (>116.6 mm2), and Hemi-Area Ratio (>51.8%). MCID+ patients were 2.7 times more likely to have a grey HNP MRI signal than a mixed or black HNP MRI signal in 5 out of 6 HRQoL score comparisons (p<.025). MCID+ patients had larger HNP areas than MCID– patients had in 5 out of 6 HRQoL score comparisons (116.6mm2 ± 46.4 vs 90.0mm2 ± 43.2, p<.04). MCID+ patients had a greater HemiArea Ratio than MCID– patients had in 4 out of 6 HRQoL score comparisons (51.8% ± 14.7 vs 43.9% ± 14.9, p<.05).

CONCLUSIONS: Patients who met MCID after MLD had larger HNP areas and larger Hemi-HNP Areas than those who did not meet MCID. These patients were also 2.7x more likely to have a grey MRI signal than a mixed or black MRI signal. When accounting for HNP area relative to canal area, patients who met MCID had greater Hemi-HNP canal occupation than patients who did not meet MCID. The results

of this study suggest that preoperative MRI parameters can be useful in predicting patient reported improvement after MLD.

KEY WORDS: Herniated Nucleus Pulposus, Microlumbar Discectomy, Health Related Quality of Life Scores, Magnetic Resonance Imaging, Patient Reported Outcome Measurement Information System Metrics, Oswestry Disability Index, Visual Analogue Scale

INTRODUCTION Lumbar herniated nucleus pulposus (HNP) is considered to be one of the most prevalent spinal degenerative disorders, often leading to lower back pain and radiculopathy.1,2 Disc degeneration and herniation vary in severity, as a small protrusion or a complete annular fibrous tear can both contribute to inflammation, nerve root compression, and impending lower back pain.3–6 Although there exists a complexity in determining how HNP morphology directly contributes to symptom presentation, it is useful for physicians to visualize this morphology using magnetic resonance imaging (MRI) when determining the optimal treatment for pain relief.7–9 Operative treatment, in the form of microlumbar discectomy (MLD), is commonly utilized to treat HNPs. For patients suffering from back pain and sciatica, MLD is the most common surgical procedure performed in the U.S., as over 300,000 discectomy procedures are conducted annually.8,10 There are also a multitude of patients who opt to receive non-operative HNP treatment, such as epidural steroid injections or physical therapy, as it serves as a low risk and low cost option.11–14 MLD itself is a proven cost-effective treatment option that provides rapid relief of pain, improved quality of life.15–20 It remains to be determined which radiological characteristics of HNP indicate that patients are more likely to have a favorable short-term outcome after MLD.

With the goal of providing value-based care for patients, surgeons utilize Health Related Quality of Life (HRQoL) metrics to quantify patient reported improvement from surgical intervention. The advent of computer adaptive Patient Reported Outcome Measurement Information System (PROMIS) allows for standardized assessment across health conditions and provides the ability to calculate patient improvement after procedures. Previous studies have explored the benefits of surgical treatment for HNP through the comparison of pre-operative and post-operative HRQoL scores including Oswestry Disability Index, EQ-5D, and SF-12 Physical Component Scores (PCS).21,22 Additionally, the high validity that PROMIS carries when measuring patient reported improvement after HNP surgical treatment has been reported.23 However, prior reports have not investigated specific pre-operative MRI parameters that may contribute to clinically meaningful HRQoL improvement following MLD treatment. Minimal clinical important difference (MCID) values for MLD derived in the literature help quantify significant clinical improvement in patients with surgical HNP.24 Consequently, using MCID values, this study aimed to meticulously analyze the ability of MRI morphological characteristics in HNP patients to predict meaningful short-term clinical improvement after MLD using preoperative and postoperative HRQoL metrics.

METHODS Study Design This study was an Institutional Review Board (IRB) approved retrospective review of consecutive patients presenting to a single academic center from March 2017 until August 2018.

Patient Population Inclusion criteria consisted of patients older than 18 years old presenting symptoms, examination, and imaging consistent with primary lumbar disc herniation (HNP) treated through

MLD, along with baseline and 3-month HRQoL scores of PROMIS (Physical Function, Pain Interference, and Pain Intensity), ODI, VAS Back, and VAS Leg. Patients were excluded if they underwent surgical treatment other than MLD for their presentation, which would indicate a secondary diagnosis such as degenerative lumbar stenosis or instability.

Data Collection and Radiographic Analysis Collected demographic data included age, gender, and BMI. Date of surgery and level of operation were also recorded. HRQoL scores were collected at Baseline (BL) and 3-Month (3M) post-operative time points. Radiographic measurements were performed on axial and sagittal T2weighted MRI images (slice thickness: 3-5mm) using Surgimap version 2.2.15.5 (Nemaris Inc, New York, NY), a validated software. Carragee et al. study on MRI analysis in patients with lumbar disc herniation was used as a model for disc and canal measurement techniques.9 HNP cephalocaudal migration was measured using sagittal imaging (Figure 1), while HNP and spinal canal measurements of anteroposterior (AP) length, cross-sectional area, cross-sectional hemi-area, and disc appearance were measured using axial imaging (Figure 2). Hemi-area was defined as the cross-sectional area, split by the midline, containing the majority of the HNP protrusion area (Figure 3). To calculate the relative HNP protrusion into the spinal canal, HNP measurements were divided by corresponding spinal canal measurements to calculate AP, area, and hemi-area ratios. Disc appearance was classified into either black, grey, or mixed (black and grey) color categories.

Statistical Analysis Regarding statistical analyses, R version 3.3 (The R Foundation for Statistical Computing, Vienna, Austria) and IBM SPSS version 23.0 (IBM Corp., Armonk, N.Y., USA) were utilized for pre-processing and analysis of the data. For each patient, change in each HRQoL score from BL to

3M was calculated. Patients were subsequently grouped based on whether their change in HRQoL score exceeded the minimal clinical important difference (MCID) for each HRQoL metric. Previously reported MCID values in literature for Physical Function, Pain Interference, ODI, VAS Back, and VAS Leg were utilized24,25, while a decision tree analysis was utilized to compute the Pain Intensity MCID. Linear regression analysis demonstrated correlation between PROMIS vs ODI, VAS Back, and VAS Leg scores to show similarities among the six metrics in measuring patient reported improvement. Patients who had a greater absolute change than the reported MCID were placed in the MCID+ group, while patients whose absolute change was smaller than the reported MCID were place in the MCID– group. For each respective HRQoL metric, independent t-tests and chi-squared tests compared differences in HNP measurements between the MCID+ and MCID– patient groups, with significance threshold of p < 0.05.

RESULTS Demographic Assessment The patient cohort contained 88 patients who received MLD treatment. The mean age of the cohort was 44.6 years old, the mean BMI of the cohort was 28.5. The cohort was 38.6% female. The only demographic variable that was significantly different between the MCID+ and MCID– groups was age within the Physical Function comparison, as MCID+ patients were significantly younger than MCID– patients (41.0 ± 13.7 years vs 47.9 ± 15.3 years, p=0.028).

Linear Regression and Overall Radiographic Analyses Linear regression analysis demonstrated a strong correlation between the change in PROMIS metrics and ODI, VAS Back, and VAS Leg from baseline to 3M post-surgery. Pain Interference and

Pain Intensity were strongly correlated with ODI and VAS Back/Leg (R≥.505), and Physical Function was significantly correlated with ODI and VAS Back/Leg (R=-.349) (all p<.01).

PROMIS Physical Function Analysis The MCID cutoff for PROMIS Physical Function was 8.0. There were 42 patients who exceeded the cutoff (MCID+) while 46 patients fell below the cutoff (MCID–). Patients in the MCID+ group had a significantly larger HNP area (117.1 ± 54.7 vs. 88.3 ± 32.7 mm2), larger HemiHNP area (85.9 ± 43.4 vs. 65.2 ± 22.1 mm2), larger HNP AP length (9.4 ± 3.1 vs. 8.2 ± 2.7 mm), and higher grey HNP signal frequency (61.9% vs. 34.8%) than patients in the MCID– group (all p<.05) (Table 1).

PROMIS Pain Interference Analysis The MCID cutoff for PROMIS Pain Interference was -8.0. There were 48 patients who exceeded the cutoff (MCID+) while 40 patients fell below the cutoff (MCID–). Patients in the MCID+ group had significantly larger HNP area (114.3 ± 50.4 vs. 87.3 ± 37.1 mm2), greater Area Ratio (36.7 ± 11.9% vs. 30.1 ± 10.6%), larger Hemi-HNP area (82.4 ± 38.2 vs. 66.3 ± 29.6 mm2), greater Hemi-Area ratio (50.8 ± 16.0% vs. 43.5 ± 13.5%), and higher grey HNP signal frequency (62.5% vs. 30.0%) than patients in the MCID– group (all p<.05) (Table 1).

PROMIS Pain Intensity Analysis The MCID cutoff for PROMIS Pain Intensity was -8.4. There were 49 patients who exceeded the cutoff (MCID+) while 39 patients fell below the cutoff (MCID–). Patients in the MCID+ group had significantly larger cephalocaudal migration (6.8 ± 2.7 vs. 5.6 ± 2.5 mm), larger HNP area (112.6 ± 44.6 vs. 88.7 ± 46.1 mm2), larger Hemi-HNP area (83.2 ± 36.2 vs. 64.9 ± 31.8

mm2), larger Hemi-Area ratio (51.8 ± 14.9% vs. 42.1 ± 14.1%), and higher grey HNP signal frequency (71.5% vs. 17.9%) than patients in the MCID– group (all p<0.05) (Table 1).

ODI Analysis The MCID cutoff for ODI was -23.4. There were 20 patients who exceeded the cutoff (MCID+) while 33 patients fell below the cutoff (MCID–). Patients in the MCID+ group had a significantly larger cephalocaudal migration (7.4 ± 2.5 vs. 5.7 ± 2.8 mm), larger HNP area (119.3 ± 36.9 vs. 91.7 ± 49.9 mm2), and higher grey HNP signal frequency (70.0% vs. 39.4%) than patients in the MCID– group (all p<0.05) (Table 2).

VAS Back Analysis The MCID cutoff for VAS Back was -3.5. There were 33 patients who exceeded the cutoff (MCID+) while 48 patients fell below the cutoff (MCID–). Patients in the MCID+ group had a significantly larger HNP area (119.6 ± 43.5 vs. 94.2 ± 47.5 mm 2), larger Area ratio (36.2 ± 11.1% vs. 31.9 ± 11.9%), larger Hemi-HNP area (86.9 ± 37.2 vs 68.7 ± 33.9 mm2), and larger Hemi-Area ratio (51.6 ± 14.7% vs. 44.7 ± 15.7%) than patients in the MCID– group (all p<0.05) (Table 2).

VAS Leg Analysis The MCID cutoff for VAS Leg was -6.3. There were 22 patients who exceeded the cutoff (MCID+) while 59 patients fell below the cutoff (MCID–). Patients in the MCID+ group had a significantly larger Area ratio (38.3 ± 9.0% vs. 32.7 ± 12.6%), larger Hemi-Area ratio (52.9 ± 13.0% vs. 45.5 ± 16.1%), and higher grey HNP signal frequency (77.3% vs. 37.3%) than patients in the MCID– group (all p<0.05) (Table 2).

Cumulative Analysis To determine the cumulative value of each variables’ predictability of meaningful clinical improvement, significant predictors’ mean values in the MCID+ groups for all HRQoL tests were calculated. For grey HNP signal, an odd’s ratio analysis for was used to calculate the likelihood of MCID+ patients across all HRQoL tests having a grey HNP signal compared to a black or mixed HNP signal. The strongest predictors of meeting HRQoL MCID and the accumulated mean values were grey HNP signal (OR = 2.7), HNP area (>116.6 mm 2), Hemi-HNP Area (>84.6 mm2), and Hemi-Area Ratio (>51.8%).

DISCUSSION This study systematically analyzed the MRI morphological characteristics of lumbar HNP to determine the likelihood of achieving MCID following MLD. These radiological characteristics were compared in patients who met and did not meet MCID for MLD reported in recent literature. The results suggest that these radiological characteristics do in fact have clinical significance in patient improvement following MLD. More specifically, patients with large, grey signal HNP with larger percentage of canal compromise experienced greater benefit from MLD than patients with smaller, darker signaled HNPs. Similar studies in literature have previously reported on the predictive value of MRI HNP morphology with regard to clinical patient outcomes. The Carragee et al. study similarly investigated quantitative MRI characteristics of lumbar HNP and clinical variables on outcomes. This study’s results revealed that larger morphometric features of HNP, such as anteroposterior HNP length and ratio of HNP:Canal areas were powerful predictors of improved sciatica in surgical patients specifically.9 As the Carragee study served as a useful model for MRI measurement analyses, our study focused on the comparison of these elaborate measurement

parameters in patients who did relatively favorably or unfavorably depending on MCID cutoffs of HRQoL tests. Another study performed by Dewing et al. also investigated clinical outcomes in MLD patients with symptomatic HNP. Though HNP size still served as the independent variable, this study grouped HNP by a previously reported system, classifying HNP as being either protruded, extruded, or sequestered, listed in increasing order of severity of canal integrity and annular fiber disruption.3 Nonetheless, patients in the Dewing study with extruded or sequestered HNP had significantly more improvement in ODI and VAS scores and quicker return to normal activities than patients who had protruded HNP.26 Though the present study used a more quantified system to measure HNP size, results of both studies emphasize the importance of larger HNP area as a meaningful predictor of favorable clinical outcomes following MLD treatment. More recently developed studies also investigated HNP location as a possible factor contributing to improved patient outcomes. These studies classified HNP by their location of intrusion into the canal, similar to how the present study utilized the Hemi-HNP area measurement. In both studies, HNP location within the canal was valuable in predicting good to excellent outcomes in surgical patients. Specifically, HNP that were not contained to the central area of the canal (i.e. larger Hemi-HNP area) actually experienced greater clinical benefit from MLD.8,27,28 The investigators deduced that surgical removal of such HNP types relieved nerve root compression or canal impingement, leading to more successful post-operative outcomes. Though studies have explored and reported upon the meaningful influence that HNP MRI morphology has on patient outcomes, few studies have implemented standardized HRQoL metrics such as PROMIS into their analyses. The present study incorporated a comprehensive analysis of PROMIS scores complementary to ODI and VAS scores that are more ubiquitous in HNP patient outcome studies. Thus far, studies have only specifically investigated the validity of PROMIS

physical function score analyses in surgical HNP patients. Not only was the physical function metric found to be reliable in measuring patient outcomes following discectomy, but this metric was also found to strongly correlate with the more commonly used ODI and VAS metrics in the same surgical HNP population.23,26,29 Ultimately, PROMIS can serve as a highly valuable metric - since many HNP patients report concurrent conditions, a more standardized outcome metric may be more applicable for this patient population. Although MRI morphology has noticeable predictive strength with regard to patient reported outcomes, HNP pathology and the root causes of symptom onset do not solely depend on radiographic morphology. Studies have elaborated on the complexity of herniation pathology and its relationship with lower back pain and radiculopathy. Research on this relationship has shown that nerve compression, inflammatory marker response, and pain specificity have significant influence on the efficacy of surgical treatment in improving patient outcomes. 4 Other studies looked specifically into MRI morphology in symptomatic and asymptomatic patients. The results from these studies revealed the presence of disc displacement on MRI imaging in their respective asymptomatic cohorts.30–32 Furthermore, Karppinen et al. could not distinguish sciatic patients by symptom severity based on MRI characteristics of the disc displacement in the canal.33 Though the present study focused on the evaluation HNP MRI morphology, further study could be useful for evaluating additional factors and their contribution to patient reported improvement after MLD. As with any study, this study has its limitations. First, this study was conducted at a singlecenter institution, which may reduce the generalizability of our findings towards other institutions with dissimilar practices. Second, our patient cohort excluded patients with concurrent spinal stenosis, therefore the results of this study may not be applicable to such patients. Lastly, this study looks at 3 month follow-up, and although a great deal of clinical improvement occurs by this timepoint, the longevity of these results remains unknown.

CONCLUSIONS

This study investigated the MRI morphological characteristics in HNP patients that may predict meaningful clinical improvement after MLD, measured by HRQoL metrics. MLD patients who met MCID for the respective HRQoL tests had larger total HNP areas and larger Hemi-HNP Areas than those who did not meet MCID. These patients were also 2.7x more likely to have a grey HNP signal as opposed to having a mixed or black HNP signal. MRI morphological parameters can aid in predicting the likelihood of meaningful improvement in patient outcomes following MLD, though these parameters do not serve as the sole predictors of such outcomes.

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Figure 1

Figure 2

Figure 3

Table 1. HNP Morphological Measurements in Patients Above (+) and Below (–) MCID for Change in Baseline and 3-Month Post-Operative Physical Function, Pain Interference, and Pain Intensity Scores

Table 2. HNP Morphological Measurements in Patients Above (+) and Below (–) MCID for Change in Baseline and 3-Month Post-Operative ODI, VAS-Back, and VAS-Leg Scores