Elsevier

World Neurosurgery

Volume 137, May 2020, Pages e499-e505
World Neurosurgery

Original Article
Minimally Invasive Spinal Deformity Surgery: Analysis of Patients Who Fail to Reach Minimal Clinically Important Difference

https://doi.org/10.1016/j.wneu.2020.02.025Get rights and content

Background

It is well known that clinical improvements following surgical intervention are variable. While all surgeons strive to maximize reliability and degree of improvement, certain patients will fail to achieve meaningful gains. We aim to analyze patients who failed to reach minimal clinically important difference (MCID) in an effort to improve outcomes for minimally invasive deformity surgery.

Methods

Data were collected on a multicenter registry of minimally invasive surgery adult spinal deformity surgeries. Patient inclusion criteria were age ≥18 years, coronal Cobb ≥20 degrees, pelvic incidence-lumbar lordosis ≥10 degrees, or a sagittal vertical axis >5 cm. All patients had minimum 2 years' follow-up (N = 222). MCID was defined as 12.8 or more points of improvement in the Oswestry Disability Index. Up to 2 different etiologies for failure were allowed per patient.

Results

We identified 78 cases (35%) where the patient failed to achieve MCID at long-term follow-up. A total of 82 identifiable causes were seen in these patients with 14 patients having multiple causes. In 6 patients, the etiology was unclear. The causes were subclassified as neurologic, medical, structural, under treatment, degenerative progression, traumatic, idiopathic, and floor effects. In 71% of cases, an identifiable cause was related to the spine, whereas in 35% the cause was not related to the spine.

Conclusions

Definable causes of failed MIS ASD surgery are often identifiable and similar to open surgery. In some cases the cause is treatable and structural. However, it is also common to see failure due to pathologies unrelated to the index surgery.

Introduction

There is a growing body of literature documenting the benefits of adult spinal deformity (ASD) surgery. These operations afford the ability to correct neural compression, segmental instability, and spinal imbalance, all of which can lead to relief of pain and functional loss.1, 2, 3 Similarly, minimally invasive surgery (MIS) options for managing ASD have also emerged and their efficacy has been shown in large case series and multicenter cohorts.4, 5, 6

However, the benefits that have been documented are aggregate measures, and the journey of each individual patient undergoing MIS ASD surgery is unique. Some patients will experience more improvement from an operation than others. Also, some patients initially experiencing improvement will lose the benefits of an operation over the course of time. All of these aspects of a postoperative population should be considered when analyzing the effects of operative interventions.

In the context of surgical management for ASD, these issues may be particularly salient for 2 reasons. First, the interventions involve substantial morbidity, financial cost, and prolonged recovery times. As such, for the individual patient who fails to achieve meaningful improvement, the risk-benefit analysis is, in retrospect, highly unfavorable. Second, MIS ASD surgery leverages newer techniques and technologies, so there is less experience to allow surgeons and patients to evaluate their efficacy from this perspective.

In order to determine the extent of improvement gained following surgical intervention, the concept of minimal clinically important difference (MCID) has been described. This distinction aims to identify the smallest score on the Oswestry Disability Index (ODI), for example, that would meaningfully impact a patient's quality of life.7

To date, there have been no studies published exploring the specific reasons why individual patients in a large multicenter cohort did not achieve improvement after MIS ASD surgery. This report analyzed a large experience at 8 tertiary spine care centers in an effort to identify the causes underlying a failure to achieve and/or maintain MCID following MIS treatment of ASD.

Section snippets

Methods

A total of 8 tertiary spine care centers with established expertise in MIS ASD surgery were selected to participate in the MIS-ISSG. All centers obtained local Institutional Review Board approval for participation in this study, and patient consent was obtained before enrollment in the database. In this series, data were collected retrospectively through an annual review process and data were housed centrally with centralized image processing and analysis. All patients had the following data at

Patient Series

Of the 222 patients in the database, 78 patients (35%) failed to meet MCID at final follow-up. The causes of their failure are shown in Table 1. Six patients (7.7%) had no identifiable cause, and 4 cases were identified as not meeting MCID due to a floor effect. This was particularly seen when the baseline ODI score was atypically low, making a 12.8-point decrease improbable. A total of 82 causes were identified, and 14 of the patients had more than 1 clearly identifiable cause. Causes were

Key Results

To our knowledge this is the largest series of MIS ASD cases evaluated for achievement and maintenance of MCID postoperatively. Numerous causes for these failures or lapses in MCID were identified in this series. The most obvious of these etiologies are structural issues including adjacent segment disease, proximal junctional kyphosis, nonunion, and hardware failure, which occurred in 28% of the failures. These cases are potentially preventable or manageable with additional surgical

Conclusions

Definable causes of failed MIS ASD surgery are similar to open surgery. In many cases the cause is treatable and structural. However, it is also common to see failure due to pathologies unrelated to the index surgery. Larger multicenter, prospective databases with increasingly granular data elements may help further elucidate the etiology of failed cases.

CRediT authorship contribution statement

Michael Y. Wang: Conceptualization, Methodology, Investigation, Data curation, Writing - original draft, Writing - review & editing. Juan Uribe: Investigation, Writing - review & editing, Visualization. Praveen V. Mummaneni: Conceptualization, Methodology, Investigation, Writing - review & editing. Stacie Tran: Formal analysis, Data curation. G. Damian Brusko: Writing - review & editing, Visualization. Paul Park: Investigation, Writing - review & editing. Pierce Nunley: Investigation, Writing -

References (13)

There are more references available in the full text version of this article.

Conflict of interest statement: Dr. Wang receives grants from the US Department of Defense; personal fees from DePuy-Synthes Spine, Inc.; personal fees from Stryker Spine; personal fees from K2M; personal fees from Spineology; other from DePuy-Synthes Spine, Inc.; other from Children's Hospital of Los Angeles; other from Springer Publishing; other from Quality Medical Publishing; other from Vallum; other from Spinicity; and other from Innovative Surgical Devices. Dr. Uribe receives research support, stock options, and consulting fees from NuVasive, Inc., as well as consulting fees from SI-Bone. Dr. Mummaneni receives personal fees from DePuy Spine, personal fees from Globus, personal fees from Stryker, other from ISSG, other from Spineart, other from Thieme Publishing, other from Springer Publishing, grants from NREF, grants from AO Spine, other from DePuy Spine, other from Spinicity, and other from ISD. Dr. Park receives personal fees from Globus, personal fees from NuVasive, personal fees from Allosource, grants from Pfizer, grants from Vertex, and personal fees from Medtronic. Dr. Nunley has patents with royalties paid to K2M, a patent with royalties paid to LDR Medical, receives other from Amedica Corporation, other from ZimmerBiomet, other from K2M, other from Paradigm, other from Spineology, other from Vertiflex, other from Camber Spine, other from Integrity, and other from Centinel Spine. Dr. Kanter receives other from Nuvasive and other from Zimmer Biomet. Dr. Okonkwo is a consultant for NuVasive, Zimmer Biomet, and Stryker; is a patent holder with Zimmer Biomet; and receives royalties from Zimmer Biomet and NuVasive. Dr. Anand receives personal fees from Medtronics, other from Medtronics, other from Medtronics, other from Globus Medical, other from Globus Medical, other from GYS Tech, other from Paradigm Spine, other from Theracell, and other from Elsevier. Dr. Chou receives personal fees and other from Medtronic and personal fees and other from Globus. Dr. Shaffrey received grants from the ISSF Foundation during the conduct of the study, personal fees from Medtronic, personal fees from NuVasive, and personal fees from Zimmer Biomet. Dr. Fu is a consultant for SI-Bone, DePuy, and Globus. Dr. Mundis Jr. receives personal fees from Nuvasive, personal fees from K2M, personal fees from Allosource, personal fees from Seaspine, and personal fees from Viseon; patent Nuvasive with royalties paid; and patent K2M with royalties paid. Dr. Eastlack receives personal fees from Globus Medical, personal fees from Nuvasive, personal fees from Seaspine, other from Invuity, other from Aesculap, other from Baxter, other from K2M Stryker, other from Nuvasive, other from SI Bone, other from Titan, other from Aesculap, nonfinancial support from Seaspine, other from AO, other from Seaspine, other from Nuvasive, other from Nuvasive, other from Seaspine, and other from Alphatec. The other authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

View full text