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

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 2-year period.

PATIENT SAMPLE

Eighty-eight 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, gray, or mixed); Baseline (BL); and 3-month (3M) postoperative HRQoL 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 Hemi-Area 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 chi-squared 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≥0.505), and physical function correlated with ODI and VAS Back/Leg (R=−0.349) (all p<.01). The strongest MRI predictors of meeting HRQoL MCID were gray disc appearance, HNP area (>116.6 mm²), and Hemi-Area Ratio (>51.8%). MCID+ patients were 2.7 times more likely to have a gray HNP MRI signal than a mixed or black HNP MRI signal in five out of six HRQoL score comparisons (p<.025). MCID+ patients had larger HNP areas than MCID– patients had in five out of six HRQoL score comparisons (116.6 mm²±46.4 vs 90.0 mm²±43.2, p<.04). MCID+ patients had a greater Hemi-Area Ratio than MCID– patients had in four out of six 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 2.7× more likely to have a gray 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.

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], [4], [5], [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], [8], [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 United States, as over 300,000 discectomy procedures are conducted annually [8,10]. There are also a multitude of patients who opt to receive nonoperative HNP treatment, such as epidural steroid injections or physical therapy, as it serves as a low risk and low cost option [11], [12], [13], [14]. MLD itself is a proven cost-effective treatment option that provides rapid relief of pain, improved quality of life [15], [16], [17], [18], [19], [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 preoperative and postoperative 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 preoperative 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 morphologic characteristics in HNP patients to predict meaningful short-term clinical improvement after MLD using preoperative and postoperative HRQoL metrics.