Introduction to the AO Spine Knowledge Forum Deformity Focus Issue: Adult Spinal Deformity: Where We Are,What We Know,Where We Need to Go

Adult spinal deformity (ASD) is a common indication for surgery and has been performed for many years. Despite the vast experience and expanding knowledge around the topic, innovative tools and rapidly evolving technologies, the complication rates remain very high. In this AO Spine Knowledge Forum Deformity Focus Issue, we identify the main sources of perioperative concerns facing surgeons with the goals of summarizing the existing literature, highlighting the current shortcomings and looking for areas of controversy that require further study to advance the field and our understanding of this complex and heterogenous condition.

This issue will review multiple aspects of topics related to ASD. Considerations of timing of surgery, determining the magnitude of surgery that should be undertaken, intra-operative decision making and planning, managing intra-operative neuromonitoring and other neurological issues, approach to osteoporosis, pre-operative medical optimization, measuring outcome, determining the appropriate alignment, blood management strategies, pelvic fixation, peri-operative adverse events and approaches to minimally invasive techniques will be reviewed.

Patient stratification and factors determining the choice of treatment are important topics to ensure good clinical outcomes. The duration and severity of symptoms that should guide the choice between non-surgical and surgical treatment options in spinal deformity patients have not been thoroughly studied. Identifying patients that are suitable for major spinal deformity reconstructions is essential, however, chosing appropriate indications where more limited surgeries could achieve the desired outcomes is equally important. Further work to match similar patients can help clarify some of these issues and identify where lesser or minimally invasive surgeries would be preferable based on a patient’s symptoms, expectations, comorbidities, and features of their deformity. Further, identifying the potential for novel technologies like robotics and augmented reality to innovate ASD surgeries is another important topic that is addressed.

The treatment of ASD patient starts long before the surgery itself. Assessing a patient’s comorbidities and optimizing them for surgery is a key component in achieving the desired surgical results. Recognizing and addressing modifiable risk factors prior to major surgery can potentially limit or prevent adverse events, or reduce their severity. Pre-operative interventions, such as maximizing bone health, controlling diabetes and hypertension, smoking and alcohol cessation, and limiting narcotic use can significantly impact the peri-operative course of the patient.

Recent progress in research and technology aids the understanding and planning of alignment goals in spinal deformity surgery. Despite the advancements in knowledge on optimal alignment, junctional failure remains a major issue in ASD surgery. Significant controversy exists on whether to assess alignment outcomes based on patient reported outcome scores (PROMs) or on mechanical failures. Further studies are required to determine whether alignment goals should be based on segmental or global parameters, or whether measures based on the relationships of lordosis to the pelvis that include vertebra-pelvic angles, are more closely related to outcome.

Intra-operatively, multiple factors contribute to surgical efficiency and good clinical outcomes, minimizing the risk of complications for the patients. Blood management and strategies to limit and manage blood loss is a continually evolving process. Interpreting and responding to intra-operative neuromonitoring alerts is the subject of much controversy in the quest to avoid the occurrence of new neurological deficits, which frequently occur in complex spinal deformity cases. Standardization of surgical indications and techniques remains a highly controversial topic that has led to much confusion among surgeons, patients, payees and hospital administrations. Strategies on pelvic fixation are undergoing further refinement in helping to determine the ideal number and location of pelvic screws, and whether the sacro-iliac joints require a fusion. Questions remain on which rods, what diameter and how many are required in an optimal and durable construct. Correction strategies and choice of release or osteotomy remains highly variable without a good consensus among practitioners.

Determining the outcome in ASD, that include PROMs, radiographic alignment and complications, is a well-studied yet debatable topic. We highlight the current widely used PROMs and their significance and shortcomings. We address early and late complications that include infection, junctional pathologies and pseudarthrosis. Establishing the true prevalence and incidence of these and understanding the potential mitigating factors can help limit their occurrence.

ASD is a very heterotopic disorder with significant variability in its clinical presentation, radiographic features, and treatment indications and selection. This variability leads to a multitude of different techniques and outcomes and is associated with substantial controversy when considering treatment options and expected outcomes. We hope that this Focus Issue will shed light on current best practices, guide answers to some of the most controversial questions in the field and stimulate the pursuit of new knowledge in the areas where it is most needed.