Basilar decompression via a far lateral transcondylar approach: technical note.

BACKGROUND: Treatments for symptomatic or unstable basilar invagination (BI) include posterior decompression, distraction/fusion, trans-nasal or trans-oral anterior decompression, and combined techniques, with the need for occipitocervical fusion based on the degree of craniocervical instability. Variations of the far lateral transcondylar approach are described in limited case series for BI, but have not been widely applied. METHODS: A single-institution, retrospective review of consecutive patients undergoing a far lateral transcondylar approach for odontoidectomy (± resection of the inferior clivus) followed by occipitocervical fusion over a 6-year period (1/1/2016 to 12/31/2021) is performed. Detailed technical notes are combined with images from cadaveric dissections and patient surgeries to illustrate our technique using a lateral retroauricular incision. RESULTS: Nine patients were identified (3 males, 6 females; mean age 40.2 ± 19.6 years). All patients had congenital or acquired BI causing neurologic deficits. There were no major neurologic or wound-healing complications. 9/9 patients (100%) experienced improvement in preoperative symptoms. CONCLUSIONS: The far lateral transcondylar approach provides a direct corridor for ventral brainstem decompression in patients with symptomatic BI. A comprehensive knowledge of craniovertebral junction anatomy is critical to the safe performance of this surgery, especially when using a lateral retroauricular incision.

Pre- and intraoperative thoracic spine localization techniques: a systematic review.

OBJECTIVE: In the era of modern medicine with an armamentarium full of state-of-the art technologies at our disposal, the incidence of wrong-level spinal surgery remains problematic. In particular, the thoracic spine presents a challenge for accurate localization due partly to body habitus, anatomical variations, and radiographic artifact from the ribs and scapula. The present review aims to assess and describe thoracic spine localization techniques. METHODS: The authors performed a literature search using the PubMed database from 1990 to 2020, compliant with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). A total of 27 articles were included in this qualitative review. RESULTS: A number of pre- and intraoperative strategies have been devised and employed to facilitate correct-level localization. Some of the more well-described approaches include fiducial metallic markers (screw or gold), metallic coils, polymethylmethacrylate, methylene blue, marking wire, use of intraoperative neuronavigation, intraoperative localization techniques (including using a needle, temperature probe, fluoroscopy, MRI, and ultrasonography), and skin marking. CONCLUSIONS: While a number of techniques exist to accurately localize lesions in the thoracic spine, each has its advantages and disadvantages. Ultimately, the localization technique deployed by the spine surgeon will be patient-specific but often based on surgeon preference.

Novel Lateral Approach for MIS Sacroiliac Joint Arthrodesis: An Assessment of Feasibility and Outcomes.

OBJECTIVE: The prevalence of physicians experiencing work-related musculoskeletal disorders is high. Traditionally, minimally invasive surgery (MIS) sacroiliac joint (SIJ) fusions are performed with the patient oriented in the prone position, with an incision made inferior to the iliac crest. However, a novel technique that orients the patient in the lateral decubitus position has the potential of significantly enhancing ergonomics and ease of approach. The primary objectives of this study were to quantify surgical parameters, describe this 'lateral-decubitus MIS' technique, and identify imaging angle parameters that predict feasibility. METHODS: A prospective cohort of patients who underwent MIS SIJ arthrodesis in the lateral decubitus position was evaluated at a single institution between 2017 and 2020. Medians and ranges of intraoperative blood loss, operative time, revision rate, infection, and total radiation dose were recorded. Sacral inlet and outlet angles were defined and collected to assess for operative candidacy. RESULTS: Thirty-nine cases were identified in 34 patients who underwent the technique with an age range of 31-78 years. Median blood loss was 22.5 mL, operating room time was 32.5 minutes, and radiation dose was 30.9 rads. Average sacral inlet was 24.51° and average sacral outlet was 65.44°. Median length of stay was 0.94 days. No cases were aborted or required revision. A total of 93% of study participants reported improvement in pain. Operative parameters were comparable to the traditional prone approach. CONCLUSIONS: The aim was to provide an insight into outcomes and metrics observed from pioneering this style of procedure. A future study comparing traditional perioperative parameters together with surgical ergonomics is needed.

Hematolymphoid Malignancies Presenting with Spinal Epidural Mass and Spinal Cord Compression: A Case Series with Rare Entities.

The epidural space is an uncommon site for involvement by hematolymphoid malignancies, and may present unexpectedly with neurological symptoms related to spinal cord compression. Our objective was to review the clinical and pathologic features of cases with initial presentations of cord compression, subsequently diagnosed as a hematolymphoid malignancy after pathologic examination. Review of the Department of Pathology's archives revealed 15 patients who presented with spinal cord compression due to epidural hematolymphoid malignancies between 2008-2019. These cases involved five primary epidural lymphomas, including an ALK-negative anaplastic large T-cell lymphoma previously not reported at this site, three diffuse large B cell lymphomas, one B-lymphoblastic lymphoma, four cases of myeloid sarcoma, one case with a previous history of acute myeloid leukemia, five cases with plasma cell neoplasms and epidural lesions as the initial presentation of plasma cell myeloma, one case showing aberrant T-cell marker expression, and one case being a histiocytic sarcoma that is rarely reported in the spine. A hematolymphoid malignancy was suspected clinically or radiologically in only five of these cases. These cases represent the spectrum of hematolymphoid malignancies that can involve the epidural space and present for the first time with cord compression, resulting in clinical, radiological and pathologic diagnostic challenges. Their diagnoses require a high degree of awareness, suspicion, and thorough histologic evaluation with ancillary studies for appropriate disease classification and therapeutic intervention. To our knowledge, this is one of the largest and most diverse of such series in the English language literature.

Management of an odontoid synchondrosis fracture causing chronic translational anterior atlanto-axial subluxation in a child with autism: case report.

The authors report an unusual case of an odontoid synchondrosis fracture causing chronic translational anterior atlanto-axial subluxation and present a discussion of the unique management of this case. Traumatic translational anterior atlanto-axial subluxation is a rare manifestation within pediatrics. Patients with preexisting abnormalities in ligamentous or bony structures may present with unusual symptomatology, which could result in delay of treatment. A 6-year-old male patient with autism who presented with acute respiratory arrest was noted to have an odontoid synchondrosis fracture and severe anterior translational atlanto-axial subluxation. Initial attempts at reduction with halo traction were tried for first-line treatment. However, because of concern regarding possible inadvertent worsening of the impingement, the presence of comorbid macrocephaly, and possible instability with only C1-2 fusion, a posterior C1 laminectomy was performed. Further release of the C1-2 complex and odontoid peg from extensive fibrous tissue allowed for complete reduction. Acute injuries of the C1-2 complex may not present as expected, and the presence of pain is not a reliable symptom. Halo traction is an appropriate initial treatment, but some patients may require surgical realignment and stabilization.

Utility of MRI neurography in neurofibromatosis type I: Case example and review of MRI neurography literature.

BACKGROUND: Neurofibromatosis is an autosomal dominant disorder of the nerves, resulting in café-au-lait spots, axillary freckling, macules, and neurofibromas throughout the nervous system. Diagnosis of this condition has in the past been mainly clinical, but the usage of magnetic resonance imaging neurography (MRN) is a new diagnostic modality. Here, we report on a case of neurofibromatosis type I (NF-1) that was diagnosed using MRN after a protracted clinical course. CASE DESCRIPTION: A 23-year-old female presented with several months of worsening right upper and lower quadrant abdominal pain. The patient underwent computed tomography (CT) of the abdomen and pelvis demonstrating multiple neurofibromas involving the psoas muscle and mesentery of the lower abdomen. Subsequent total neuronal axis magnetic resonance imaging (MRI) using the neurography protocol (MRN) showed multiple neurofibromas in both the right brachial plexus and lumbar plexus. CONCLUSION: We present a case of NF-1 that was diagnosed using MRN following a protracted clinical course. MRN is a diagnostic modality for NF-1 and other peripheral nerve disorders.

The Incremental Value of Magnetic Resonance Neurography for the Neurosurgeon: Review of the Literature.

INTRODUCTION: Magnetic resonance neurography (MRN) is a newer imaging technique that is increasingly used for detailed visualization of peripheral nerves not reliably achieved with conventional imaging modalities. Although MRN has been previously characterized in the literature, few studies have assessed its utility to neurosurgery, where there is potentially substantial impact particularly with preoperative assessment. In this article, we performed a retrospective review of cases in which MRN was used for clinical evaluation and surgical decision making. METHODS: MRN, clinical assessment, and operative decision making were retrospectively assessed in 206 consecutive patients at our institution between 2015 and 2018. RESULTS: MRN was determined to lead to a change in diagnosis or surgical decision making in 44 patients (21.4%: 27 female, 17 male). These were classified into 6 major diagnostic categories: trauma, postsurgical evaluation, compressive/degenerative conditions, tumors, neuritis/inflammation, and other neurogenic lesions. Nine representative cases were selected from these categories to highlight the range of neurosurgical pathologies in which MRN was useful in diagnostic assessment and surgical decision making. CONCLUSIONS: MRN is an underused resource with great potential value in the diagnoses, surgical planning, and postoperative assessment of various neurosurgical conditions. These present incremental utility to the neurosurgeon as well as socioeconomic benefit in the detection of potentially surgically treatable lesions.

Neurosurgical Management of Sacral Tumors: Review of the Literature and Operative Nuances.

BACKGROUND: Sacral tumors present a significant challenge to the spine surgeon. As new techniques have evolved in recent years, these lesions have become more amenable to aggressive surgical treatment. Although sacral tumors make up only a small minority of spinal tumors, their surgical management warrants special consideration. METHODS: Based on our experience, we highlight 3 important surgical nuances specifically for the treatment of sacral tumors: preservation and maximization of neurologic function, protection of ventral abdominal and pelvic structures, and lumbopelvic fixation. RESULTS: Two cases of patients with sacral tumors treated at our institution are presented to illustrate these points. Both patients had successful postoperative courses, and remained pain free, well-fixated, and neurologically intact at 3-4 month follow-up. They had no evidence of biomechanical instability. CONCLUSIONS: To ensure a successful outcome, a goal-directed, methodical approach is required.

Minimally invasive approach to resection of paraspinal schwannoma.

In this video, the authors demonstrate a minimally invasive approach and resection of a paraspinal schwannoma. Using an expandable retractor, the authors were able to identify important adjacent bony landmarks and hence visualize and remove this peripheral nerve sheath tumor. While a tubular retractor is commonly used for interbody fusion procedures, the location of the tumor allowed this minimally invasive approach resulting in excellent access, minimal soft-tissue injury, and a short hospital stay. The authors present this approach as a less invasive and yet effective technique for resection of otherwise difficult-to-access nerve lesions. The video can be found here: https://youtu.be/89OY5wdMB_k .

Clinical Presentation, Diagnosis, and Surgical Treatment of Spontaneous Cervical Intradural Disc Herniations: A Review of the Literature.

OBJECTIVE: Spontaneous cervical intradural disc herniation (IDH) is a rare occurrence with limited and disparate information available regarding its presentation, diagnosis, and treatment. However, its accurate detection is vital for planning surgical treatment. In this review of the literature, we collected data from all cervical IDHs described to date. Particular attention was paid to diagnostic findings, surgical approach, and causation for cervical IDH, especially at the cervicothoracic junction. METHODS: A review for cases of cervical IDH was performed via the following search criteria: ("neck"[MeSH Terms] OR "neck"[All Fields] OR "cervical"[All Fields]) AND intradural[All Fields] AND disc[All Fields]. Thirty-seven cases of cervical disc herniation were identified. Demographic variables identified included age, sex, cervical level of herniation, history of associated cervical trauma, presence of Brown-Séquard syndrome, Horner syndrome, and other neurologic findings, radiographic findings, direction of surgical approach, and postoperative outcomes. RESULTS: A total of 37 cases of cervical IDH were identified. Most of the cases occurred at the lower levels of the cervical spine, with 35.1% at the C5-C6 level, followed by 24.3% at C6-C7, and lower still at other levels. Of the patients reviewed, 44.4% had a previous history of trauma before manifestation of symptom, with the majority being spontaneous IDH with no previous history of trauma or spine surgery. Brown-Séquard syndrome was present in 43.2% of the patients, whereas 10.8% of patients experienced Horner syndrome. The most common presentations of IDH included quadriplegia, finger/gait ataxia, radiculopathy, and nuchal pain. The degree of neurologic recovery was not associated with patient age. Most of the cervical IDHs in the literature were treated surgically via an anterior approach, but a larger portion of patients who underwent a posterior approach had improved recovery. CONCLUSIONS: Cervical IDH is a rare event, with this review of the literature outlining the clinical and radiographic parameters of its presentation as well as comparing common surgical strategies for treatment. We outline theories underlying the development of cervical IDH and argue for a posterior surgical approach in which the disc herniation is sequestrated with migration.

Multidisciplinary surgical treatment of presacral meningocele and teratoma in an adult with Currarino triad.

BACKGROUND: Currarino syndrome (CS) is a rare genetic condition that presents with the defining triad of anorectal malformations, sacral bone deformations, and presacral masses, which may include teratoma. Neurosurgeons are involved in the surgical treatment of anterior meningoceles, which are often associated with this condition. The accepted surgical treatment is a staged anterior-posterior resection of the presacral mass and obliteration of the anterior meningocele. CASE DESCRIPTION: This case involved a 36-year-old female who presented with late onset of symptoms attributed to CS (e.g., presacral mass, anterior sacral meningocele, and sacral agenesis). She successfully underwent multidisciplinary single-stage approach for treatment of the anterior sacral meningocele and resection of the presacral mass. This required obliteration of the meningocele and closure of the dural defect. One year later, her meningocele had fully resolved. CONCLUSION: While late presentations with CS are rare, early detection and multidisciplinary treatment including single-state anterior may be successful for managing these patients.

Lateral Thoracic Osteoplastic Rib-Sparing Technique Used for Lateral Spine Surgery: Technical Note.

Of patients who have undergone lateral approaches to the thoracic spine, surgical site postoperative pain appears to be greater among those who have undergone transection and removal of a rib segment than those who have not. Therefore, techniques that conserve anatomical position and minimize tissue disruption would theoretically result in less pain and a quicker recovery. Herein, we describe a rib-sparing osteoplastic technique used when rib segments need to be displaced in order to create an unobscured corridor to the operative target. Our approach minimizes soft tissue disruption and restores the anatomical function of the rib. Based on our experience, these patients report less pain, mobilize earlier, and are discharged sooner than those who have had rib segments sacrificed as part of a lateral approach to the spine.

Postoperative Complications for Elderly Patients After Single-Level Lumbar Fusions for Spondylolisthesis.

OBJECTIVE: A large-scale study on postoperative complications of lumbar fusion surgery for spondylolisthesis comparing patients >80 years old with younger patients has not been performed. The purpose of this study is to assess the effects of extreme age (>80 years old) on early postoperative outcomes after single-level lumbar fusions for spondylolisthesis. METHODS: From a validated multicenter surgical database, 2475 patients who underwent a single-level lumbar fusion procedure for spondylolisthesis were selected retrospectively. An extreme age cohort with 227 patients >80 years old was compared with a typical age cohort with 2248 patients 45-65 years old. RESULTS: The preoperative characteristics and comorbidities were different between the typical age cohort and the extreme age cohort, with older patients having more preoperative comorbidities, including a lack of independent functional health status before surgery (P < 0.001), severe chronic obstructive pulmonary disease (P <0.020), and hypertension requiring medication (P < 0.001). There was significantly greater morbidity among the >80 cohort regarding urinary tract infection (P = 0.008; odds ratio = 3.30; 95% confidence interval, 1.47-7.40) and intraoperative and postoperative transfusions (P < 0.001; odds ratio = 2.186; 95% confidence interval, 1.54-3.11). There was significantly greater morbidity among the younger cohort regarding cardiac arrest requiring cardiopulmonary resuscitation (P = 0.043; odds ratio = 0.099; 95% confidence interval, 0.014-0.704). CONCLUSIONS: This is the first large study comparing the rates of postoperative complications of lumbar fusion surgery for spondylolisthesis in patients >80 years old versus younger patients. The data support that age alone should not exclude a patient for this procedure. However, extra caution is warranted given the slightly increased morbidity.

Utility of positron emission tomography in schwannomatosis.

Schwannomatosis is characterized by multiple non-intradermal schwannomas with patients often presenting with a painful mass in their extremities. In this syndrome malignant transformation of schwannomas is rare in spite of their large size at presentation. Non-invasive measures of assessing the biological behavior of plexiform neurofibromas in neurofibromatosis type 1 such as positron emission tomography (PET), CT scanning and MRI are well characterized but little information has been published on the use of PET imaging in schwannomatosis. We report a unique clinical presentation portraying the use of PET imaging in schwannomatosis. A 27-year-old woman presented with multiple, rapidly growing, large and painful schwannomas confirmed to be related to a constitutional mutation in the SMARCB1 complex. Whole body PET/MRI revealed numerous PET-avid tumors suggestive of malignant peripheral nerve sheath tumors. Surgery was performed on multiple tumors and none of them had histologic evidence of malignant transformation. Overall, PET imaging may not be a reliable predictor of malignant transformation in schwannomatosis, tempering enthusiasm for surgical interventions for tumors not producing significant clinical signs or symptoms.

Preoperative Predictors of Spinal Infection within the National Surgical Quality Inpatient Database.

BACKGROUND: Surgical-site infections (SSIs) are a major cause of morbidity and mortality, increasing the length and cost of hospitalization. In patients undergoing spine surgery, there are limited large-scale data on patient-specific risk factors for SSIs. METHODS: The American College of Surgeons National Surgical Quality Improvement Program database was reviewed for all spinal operations between 2006 and 2012. The rates of 30-day SSIs were calculated, and univariate analysis of selected preoperative risk factors was performed. Multivariate analysis was then used to identify independent predictors of SSIs. RESULTS: A total of 1110 of the 60,179 patients (1.84%) had a postoperative wound infection. There were 527 (0.87%) deep and 590 (0.98%) superficial infections. Patients with infections had greater rates of sepsis, longer lengths of stay, and more return visits to the operating room. Independent predictors of infection were female sex, inpatient status, insulin-dependent diabetes, preoperative steroid use greater than 10 days, hematocrit less than 35, body mass index greater than 30, wound class, American Society of Anesthesiologists class, and operative duration. CONCLUSIONS: Analysis of a large national patient database revealed many independent risk factors for SSIs after spinal surgery. Some of these risk factors can be modified preoperatively to reduce the risk of postoperative infection.

Fungal osteomyelitis with vertebral re-ossification.

INTRODUCTION: We present a rare case of thoracic vertebral osteomyelitis secondary to pulmonary Blastomyces dermatitides. PRESENTATION OF CASE: A 27-year-old male presented with three months of chest pains and non-productive cough. Examination revealed diminished breath sounds on the right. CT/MR imaging confirmed a right-sided pre-/paravertebral soft tissue mass and destructive lytic lesions from T2 to T6. CT-guided needle biopsy confirmed granulomatous pulmonary Blastomycosis. Conservative management with antifungal therapy was initiated. Neurosurgical review confirmed no clinical or profound radiographic instability, and the patient was stabilized with TLSO bracing. Serial imaging 3 months later revealed near-resolution of the thoracic soft tissue mass, with vertebral re-ossification from T2 to T6. DISCUSSION: Fungal osteomyelitis presents a rare entity in the spectrum of spinal infections. In such cases, lytic spinal lesions are classically seen in association with a large paraspinous mass. Fungal infections of the spinal column may be treated conservatively, with surgical intervention reserved for progressive cases manifesting with neurological compromise and/or spinal column instability. Here, we found unexpected evidence for vertebral re-ossification across the affected thoracic levels (T2-6) in response to IV antibiotic therapy and conservative bracing, nearly 3 months later.

The future of spine surgery: New horizons in the treatment of spinal disorders.

BACKGROUND AND METHODS: As with any evolving surgical discipline, it is difficult to predict the future of the practice and science of spine surgery. In the last decade, there have been dramatic developments in both the techniques as well as the tools employed in the delivery of better outcomes to patients undergoing such surgery. In this article, we explore four specific areas in spine surgery: namely the role of minimally invasive spine surgery; motion preservation; robotic-aided surgery and neuro-navigation; and the use of biological substances to reduce the number of traditional and revision spine surgeries. RESULTS: Minimally invasive spine surgery has flourished in the last decade with an increasing amount of surgeries being performed for a wide variety of degenerative, traumatic, and neoplastic processes. Particular progress in the development of a direct lateral approach as well as improvement of tubular retractors has been achieved. Improvements in motion preservation techniques have led to a significant number of patients achieving arthroplasty where fusion was the only option previously. Important caveats to the indications for arthroplasty are discussed. Both robotics and neuro-navigation have become further refined as tools to assist in spine surgery and have been demonstrated to increase accuracy in spinal instrumentation placement. There has much debate and refinement in the use of biologically active agents to aid and augment function in spine surgery. Biological agents targeted to the intervertebral disc space could increase function and halt degeneration in this anatomical region. CONCLUSIONS: Great improvements have been achieved in developing better techniques and tools in spine surgery. It is envisaged that progress in the four focus areas discussed will lead to better outcomes and reduced burdens on the future of both our patients and the health care system.

Statistical parametric mapping demonstrates asymmetric uptake with Tc-99m ECD and Tc-99m HMPAO SPECT in normal brain.

Tc-99m ethyl cysteinate diethylester (ECD) and Tc-99m hexamethyl propylene amine oxime (HMPAO) are commonly used for single-photon emission computed tomography (SPECT) studies of a variety of neurologic disorders. Although these tracers have been very helpful in diagnosing and guiding treatment of neurologic disease, data describing the distribution and laterality of these tracers in normal resting brain are limited. Advances in quantitative functional imaging have demonstrated the value of using resting studies from control populations as a baseline to account for physiologic fluctuations in cerebral perfusion. Here, we report results from 30 resting Tc-99m ECD SPECT scans and 14 resting Tc-99m HMPAO scans of normal volunteers with no history of neurologic disease. Scans were analyzed with regions of interest and with statistical parametric mapping, with comparisons performed laterally (left vs. right), as well as for age, gender, and handedness. The results show regions of significant asymmetry in the normal controls affecting widespread areas in the cerebral hemispheres, but most marked in superior parietotemporal region and frontal lobes. The results have important implications for the use of normal control SPECT images in the evaluation of patients with neurologic disease.

Incidence and prevalence of surgery at segments adjacent to a previous posterior lumbar arthrodesis.

BACKGROUND CONTEXT: Adjacent segment disease (ASD) after lumbar spinal fusion has been an important reason behind the development of nonfusion stabilization technology. However, the incidence, prevalence, and factors contributing to adjacent segment degeneration in the lumbar spine remain unclear. A range of prevalence rates for ASD have been reported in the lumbar spinal literature, but the annual incidence has not been widely studied in this region. Conflicting reports exist regarding risk factors, especially fusion length. PURPOSE: To determine the annual incidence and prevalence of further surgery for adjacent segment disease (SxASD) after posterior lumbar arthrodesis and examine possible risk factors. STUDY DESIGN: Retrospective cohort study. PATIENT SAMPLE: Nine hundred twelve patients who underwent 1,000 consecutive posterior lumbar interbody fusion procedures, with mean follow-up duration of 63 months (range, 5 months-16 years). OUTCOME MEASURES: Further surgery for ASD or surgery-free survival. METHODS: A postal and telephone survey. Follow-up rate: 91% of patients. The annual incidence and prevalence of ASD requiring further surgery were determined using Kaplan-Meier survivorship analysis. Cox proportional-hazards (Cox) regression was used for multivariate analysis of possible risk factors. Significance was set at p<.05. RESULTS: Further surgery for ASD occurred following 130 of 1,000 or 13% of procedures at a mean time of 43 months (range, 2.3-162 months). The mean annual incidence of SxASD over the first 10 years, in all patients, was 2.5% (95% confidence interval [95% CI], 1.9-3.1) with prevalences of 13.6% and 22.2% at 5 and 10 years, respectively. Cox regression modeling found that the number of levels fused (p≤.0003), age of the patient, fusing to L5, and performing an additional laminectomy adjacent to a fusion all independently affect the risk of SxASD. The mean annual incidence figures in the first 10 years after a lumbar fusion were 1.7% (95% CI, 1.3-2.2) after fusion at single levels, 3.6% (2.1-5.2) after two levels, and 5.0% (3.3-6.7) after three and four levels. The 5- and 10-year prevalences were 9% and 16%, 17% and 31%, and 29% and 40% after single-, two-, and three-/four-level fusions, respectively. The risk of SxASD in patients younger than 45 years was one-quarter (95% CI, 10-64) the risk of patients older than 60 years (p=.003). A laminectomy adjacent to a fusion increases the relative risk by 2.4 times (95% CI, 1.1-5.2; p=.03). Stopping a fusion at L5 is associated with a 1.7-fold increased risk (95% CI, 1.2-2.4; p=.007) of SxASD compared with a fusion to S1, for fusions of the same length. CONCLUSION: The overall annual incidence and predicted 10-year prevalence of further surgery for ASD after lumbar arthrodesis were 2.5% and 22.2%, respectively. These rates varied widely depending on the identified risk factors. Although young patients who underwent single-level fusions were at low risk, patients who underwent fusion of three or four levels had a threefold increased risk of further surgery, compared with single-level fusions (p<.0001), and a predicted 10-year prevalence of 40%.