Howard Y. Park

Current management of aneurysmal bone cysts

Aneurysmal bone cysts (ABCs) are benign bone lesions arising predominantly in the pediatric population that can cause local pain, swelling, and pathologic fracture. Primary lesions, which constitute roughly two thirds of all ABCs, are thought to be neoplastic in nature, with one third of ABCs arising secondary to other tumors. Diagnosis is made with various imaging modalities, which exhibit characteristic features such as “fluid-fluid levels,” although biopsy is critical, as telangiectatic osteosarcoma cannot be excluded based on imaging alone. Currently, the standard of care and most widely employed treatment is intralesional curettage. However, tumor recurrence with curettage alone is common and has driven some to propose a multitude of adjuvants with varying efficacy and risk profiles. Historically, therapies such as en bloc resection or radiation therapy were utilized as an alternative to decrease the recurrence rate, but these therapies imposed high morbidity. As a result, modern techniques now seek to simultaneously reduce morbidity and recurrence, the pursuit of which has produced preliminary study into minimally invasive percutaneous treatments and medical management.

Prognostic determinants and treatment outcomes analysis of osteosarcoma and Ewing sarcoma of the spine

BACKGROUND CONTEXT Osteosarcoma (OGS) and Ewing sarcoma (EWS) are the two classic primary malignant bone tumors. Due to the rarity of these tumors, evidence on demographics, survival determinants, and treatment outcomes for primary disease of the spine are limited and derived from small case series. PURPOSE To use population-level data to determine the epidemiology and prognostic indicators in patients with OGS and EWS of the osseous spine. STUDY DESIGN/SETTING Large-scale retrospective study. PATIENT SAMPLE Patients diagnosed with OGS and EWS of the spine in the Surveillance, Epidemiology, and End Results (SEER) registry from 1973 to 2012. OUTCOME MEASURES Overall survival (OS) and disease-specific survival (DSS). METHODS Two separate queries of the SEER registry were performed to identify patients with OGS and EWS of the osseous spine from 1973-2012. Study variables included age, sex, race, year of diagnosis, tumor size, extent of disease (EOD), and treatment with surgery and/or radiation therapy. Primary outcome was defined as OS and DSS in months. Univariate survival analysis was performed using the Kaplan-Meier method and the log-rank test. Multivariate analysis was performed using Cox proportional hazards regression models. RESULTS The search identified 648 patients with primary OGS and 736 patients with primary EWS of the spine from 1973 to 2012. Mean age at diagnosis was 48.1 and 19.9 years for OGS and EWS, respectively, with OGS showing a bimodal distribution. The median OS and DSS were 1.3 and 1.7 years, respectively, for OGS, with OGS in Pagets disease having worse OS (0.7 years) relative to the mean (log-rank p=.006). The median OS and DSS for EWS were 3.9 and 4.3 years, respectively. Multivariate cox regression analysis showed that age (OS p<.001, DSS p<.001), decade of diagnosis (OS p=.049), surgical resection (OS p<.001, DSS p<.001), and EOD (OS p<.001, DSS p<.001) were independent positive prognostic indicators for spinal OGS; radiation therapy predicted worse OS (hazard ratio [HR] 1.48, confidence interval [CI] 1.05-2.10, p=.027) and DSS (HR 1.74, CI 1.13-2.66, p=.012) for OGS. For EWS, age (OS p<.001, DSS p<.001), surgical resection (OS p=.030, DSS p=.046), tumor size (OS p<.001, DSS p<.001), and EOD (OS p<.001, DSS p<.001) were independent determinants of improved survival; radiation therapy trended toward improved survival but did not achieve statistical significance for both OS (HR 0.76, CI 0.54-1.07, p=.113) and DSS (0.76, CI 0.54, 1.08, p=.126). CONCLUSIONS Age, surgical resection, and EOD are key survival determinants for both OGS and EWS of the spine. Radiation therapy may be associated with worse outcomes in patients with OGS, and is of potential benefit in EWS. Overall prognosis has improved in patients with OGS of the spine over the last four decades.

Chondrosarcoma of the Osseous Spine: An Analysis of Epidemiology, Patient Outcomes, and Prognostic Factors Using the Seer Registry From 1973 to 2012

Study Design. Retrospective analysis. Objective. To determine the epidemiology and prognostic indicators in patients with chondrosarcoma of the osseous spine. Summary of Background Data. Chondrosarcoma of the spine is rare, with limited data on its epidemiology, clinicopathologic features, and treatment outcomes. Therapy centers on complete en bloc resection with radiotherapy reserved for subtotal resection or advanced disease. Methods. The Surveillance, Epidemiology, and End Results Registry was queried for patients with chondrosarcoma of the osseous spine from 1973 to 2012. Study variables included age, sex, race, year of diagnosis, size, grade, extent of disease, and treatment modality. Results. The search identified 973 cases of spinal chondrosarcoma. Mean age at diagnosis was 51.6 years, and 627% of patients were males. Surgical resection and radiotherapy were performed in 75.2% and 21.3% of cases, respectively. Kaplan-Meier analysis demonstrated overall survival (OS) and disease-specific survival (DSS) of 53% and 64%, respectively, at 5 years. Multivariate Cox regression analysis showed that age (OS, P < 0.001; DSS, P = 0.007), grade (OS, P < 0.001; DSS, P < 0.001), surgical resection (OS, P < 0.001; DSS, P < 0.001), and extent of disease (OS, P < 0.001; DSS, P < 0.001) were independent survival determinants; tumor size was an independent predictor of OS (P = 0.006). For confined disease, age (P = 0.013), decade of diagnosis (P = 0.023), and surgery (P = 0.017) were independent determinants of OS. For locally invasive disease, grade (OS, P < 0.001; DSS, P = 0.003), surgery (OS, P = 0.013; DSS, P = 0.046), and size (OS, P = 0.001, DSS, P = 0.002) were independent determinants of OS and DSS. Radiotherapy was an independent indicator of worse OS for both confined (P = 0.004) and locally invasive disease (P = 0.002). For metastatic disease, grade (OS, P = 0.021; DSS, P = 0.012) and surgery (OS, P = 0.007; DSS, P = 0.004) were survival determinants for both OS and DSS, whereas radiotherapy predicted improved OS (P = 0.039). Conclusion. Surgical resection confers survival benefit in patients with chondrosarcoma of the spine independent of extent of disease. Radiotherapy improves survival in patients with metastatic disease and worsens outcomes in patients with confined and locally invasive disease. Level of Evidence: 4

Combinatory antibiotic therapy increases rate of bacterial kill but not final outcome in a novel mouse model of Staphylococcus aureus spinal implant infection

Background Management of spine implant infections (SII) are challenging. Explantation of infected spinal hardware can destabilize the spine, but retention can lead to cord compromise and biofilm formation, complicating management. While vancomycin monotherapy is commonly used, in vitro studies have shown reduced efficacy against biofilm compared to combination therapy with rifampin. Using an established in vivo mouse model of SII, we aim to evaluate whether combination therapy has increased efficacy compared to both vancomycin alone and infected controls. Methods An L-shaped, Kirschner-wire was transfixed into the L4 spinous process of 12-week-old C57BL/6 mice, and inoculated with bioluminescent Staphylococcus aureus. Mice were randomized into a vancomycin group, a combination group with vancomycin plus rifampin, or a control group receiving saline. Treatment began on post-operative day (POD) 7 and continued through POD 14. In vivo imaging was performed to monitor bioluminescence for 35 days. Colony-forming units (CFUs) were cultured on POD 35. Results Bioluminescence peaked around POD 7 for all groups. The combination group had a 10-fold decrease in signal by POD 10. The vancomycin and control groups reached similar levels on POD 17 and 21, respectively. On POD 25 the combination group dropped below baseline, but rebounded to the same level as the other groups, demonstrating a biofilm-associated infection by POD 35. Quantification of CFUs on POD 35 confirmed an ongoing infection in all three groups. Conclusions Although both therapies were initially effective, they were not able to eliminate implant biofilm bacteria, resulting in a rebound infection after antibiotic cessation. This model shows, for the first time, why histologic-based, static assessments of antimicrobials can be misleading, and the importance of longitudinal tracking of infection. Future studies can use this model to test combinations of antibiotic therapies to see if they are more effective in eliminating biofilm prior to human trials.

Ambulatory anterior cervical discectomy and fusion is associated with a higher risk of revision surgery and perioperative complications: an analysis of a large nationwide database

BACKGROUND CONTEXT With the changing landscape of health care, outpatient spine surgery is being more commonly performed to reduce cost and to improve efficiency. Anterior cervical discectomy and fusion (ACDF) is one of the most common spine surgeries performed and demand is expected to increase with an aging population. PURPOSE The objective of this study was to determine the nationwide trends and relative complication rates associated with outpatient ACDF. STUDY DESIGN/SETTING This is a large-scale retrospective case control study. PATIENT SAMPLE The patient sample included Humana-insured patients who underwent one- to two-level ACDF as either outpatients or inpatients from 2011 to 2016 OUTCOME MEASURES: The outcome measures included incidence and the adjusted odds ratio (OR) of postoperative medical and surgical complications within 1 year of the index surgery. MATERIALS AND METHODS A retrospective review was performed of the PearlDiver Humana insurance records database to identify patients undergoing one- to two-level ACDF (Current Procedural Terminology [CPT]-22551 and International Classification of Diseases [ICD]-9-816.2) as either outpatients or inpatients from 2011 to 2016. The incidence of perioperative medical and surgical complications was determined by querying for relevant ICD and CPT codes. Multivariate logistic regression adjusting for age, gender, and Charlson Comorbidity Index was used to calculate ORs of complications among outpatients relative to inpatients undergoing ACDF. RESULTS Cohorts of 1,215 patients who underwent outpatient ACDF and 10,964 patients who underwent inpatient ACDF were identified. The median age was in the 65-69 age group for both cohorts. The annual relative incidence of outpatient ACDF increased from 0.11 in 2011 to 0.22 in 2016 (R2=0.82, p=.04). Adjusting for age, gender, and comorbidities, patients undergoing outpatient ACDF were more likely to undergo revision surgery for posterior fusion at both 6 months (OR 1.58, confidence interval [CI] 1.27-1.96, p<.001) and 1 year (OR 1.79, CI 1.51-2.13, p<.001) postoperatively. Outpatient ACDF was also associated with a higher likelihood of revision anterior fusion at 1 year postoperatively (OR 1.46, CI 1.26-1.70, p<.001). Among medical complications, postoperative acute renal failure was more frequently associated with outpatient ACDF than inpatient ACDF (OR 1.25, CI 1.06-1.49, p=.010). Adjusted rates of all other queried surgical and medical complications were comparable. CONCLUSIONS Outpatient ACDF is increasing in frequency nationwide over the past several years. Nationwide data demonstrate a greater risk of perioperative surgical complications, including revision anterior and posterior fusion, as well as a higher risk of postoperative acute renal failure. Candidates for outpatient ACDF should be counseled and carefully selected to reduce these risks.

Outcomes of Instrumented and Noninstrumented Posterolateral Lumbar Fusion

The purpose of this study was to evaluate the long-term clinical and radiographic outcomes of posterolateral lumbar fusion for lumbar stenosis cases requiring bilateral facetectomy in conjunction with a laminectomy. The authors evaluated 34 consecutive patients who had undergone a lumbar laminectomy, bilateral partial facetectomy, and posterolateral fusion at a single institution between 1981 and 1996. They included 25 men and 9 women with a mean age of 42 years (range, 27-57 years). Twenty-three cases were instrumented and 11 were noninstrumented. Mean follow-up was 21 years (range, 15-29 years). Outcomes evaluated included reoperation rate, clinical outcomes evaluated by the Oswestry Disability Index (ODI) score, radiographic evaluations of adjacent segmental degeneration (ASD) and lumbar lordosis, and contributing demographic factors to disease progression. At final follow-up, 17 of the 34 patients had undergone reoperation (43% of the instrumented group and 64% of the noninstrumented group). There were no differences in the reoperation rate or ODI improvement between the instrumented and noninstrumented groups (P>.05). Female patients required more revisions, had less ODI improvement, had greater postoperative ASD, and had less maintenance of their postoperative lumbar lordosis. There was no difference in maintenance of postoperative lumbar lordosis or ASD between the instrumented and noninstrumented groups. Instrumentation did not improve revision rates, clinical outcomes, or radiographic outcomes in laminectomies requiring contemporaneous facetectomies.

Use of the subcutaneous lumbar spine (SLS) index as a predictor for surgical complications in lumbar spine surgery

BACKGROUND CONTEXT Lumbar spine surgeries require adequate exposure to visualize key structures and limited exposure can make surgery more technically difficult, thus increasing the potential for complications. Body mass index and body mass distribution have been shown to be associated with worse surgical outcomes. PURPOSE This study aims to further previous investigations in elucidating the predictive nature of body mass distribution with peri- and postoperative complications in lumbar surgery. STUDY DESIGN/SETTING This is a retrospective study conducted at a single institution. PATIENT SAMPLE Two hundred eighty-five patients who underwent lumbar laminectomy, laminotomy, or posterior lumbar interbody fusion or transforaminal lumbar interbody fusion procedures between 2013 and 2016. OUTCOME MEASURES Magnetic resonance imaging (MRI) results and electronic medical records were reviewed for measurements and relevant complications. METHODS Previously known risk factors were identified and MRI measurements of subcutaneous adipose depth (SAD) relative to spinous process height (SPH) were measured at the surgical site to generate the subcutaneous lumbar spine (SLS) index. This measurement was then analyzed in association with recorded surgical complications. RESULTS The SLS index was found to be a significant risk factor for total complications (0.292, p=.041), perioperative complications (0.202, p=.015), and need for revision surgery (0.285, p<.001). The SAD alone proved to be negatively associated with perioperative complications (-0.075, p=.034) and need for revision surgery (-0.104, p=.001), with no predictive association seen for total or postoperative complications. Linear regression revealed an SLS index of 3.43 as a threshold value associated with a higher risk of total complications, 5.8 for perioperative complications, and 3.81 for the need for revision surgeries. CONCLUSION Body mass distribution of the surgical site as indicated by SAD to SPH (SLS index) is significantly associated with increasing risk of postoperative and perioperative complications as well as increased likelihood for necessary revision surgery. This relationship was shown to be a more accurate indication of perioperative risk than previous standards of body mass index and SAD alone, and may allow spine surgeons to assess surgical risk when considering lumbar spine surgery using simple calculations from standard preoperative MRI results.

Does approach matter? a comparative radiographic analysis of spinopelvic parameters in single level lumbar fusion.

BACKGROUND CONTEXT Lumbar fusion is a popular and effective surgical option to provide stability and restore anatomy. Particular attention has recently been focused on sagittal alignment and radiographic spinopelvic parameters that apply to lumbar fusion as well as spinal deformity cases. Current literature has demonstrated the effectiveness of various techniques of lumbar fusion; however, comparative data of these techniques are limited. PURPOSE This study aimed to directly compare the impact of various lumbar fusion techniques (anterior lumbar interbody fusion [ALIF], lateral lumbar interbody fusion [LLIF], transforaminal lumbar interbody fusion [TLIF], and posterolateral fusion [PLF]) based on radiographic parameters. STUDY DESIGN/SETTING A single-center retrospective study examining preoperative and postoperative radiographs was carried out. PATIENT SAMPLE A consecutive list of lumbar fusion surgeries performed by multiple spine surgeons at a single institution from 2013 to 2016 was identified. OUTCOME MEASURES Radiographic measurements used included segmental lordosis (SL), lumbar lordosis (LL), pelvic incidence (PI), pelvic incidence-lumbar lordosis (PI-LL) mismatch, anterior and posterior disc height (DH-A, DH-P, respectively), and foraminal height (FH). METHODS Radiographic measurements were performed on preoperative and postoperative lateral lumbar radiographs on all single-level lumbar fusion cases. Demographic data were collected including age, gender, approach, diagnosis, surgical level, and implant lordosis. Paired sample t test, one-way analysis of variance (ANOVA), McNemar test, and independent sample t test were used to establish significant differences in the outcome measures. Multiple linear regression was performed to determine a predictive model for lordosis from implant lordosis, fusion technique, and surgical level. RESULTS There were 164 patients (78 men, 86 women) with a mean age of 60.1 years and average radiographic follow-up time of 9.3 months. These included 34 ALIF, 23 LLIF, 63 TLIF, and 44 PLF surgeries. ALIF and LLIF significantly improved SL (7.9° and 4.4°), LL (5.5° and 7.7°), DH-A (8.8 mm and 5.8 mm), DH-P (3.4 mm and 2.3 mm), and FH (2.8 mm and 2.5 mm), respectively (p≤.003). TLIF significantly improved these parameters, albeit to a lesser extent: SL (1.7°), LL (2.7°), DH-A (1.1 mm), DH-P (0.8 mm), and FH (1.1 mm) (p≤.02). PLF did not significantly alter any of these parameters while significantly reducing FH (-1.3 mm, p=.01). One-way ANOVA showed no significant differences between ALIF and LLIF other than ALIF with greater ΔDH-A (3.0 mm, p=.02). Both ALIF and LLIF significantly outperformed PLF in preoperative to postoperative changes in all parameters p≤.001. Additionally, ALIF significantly outperformed TLIF in the change in SL (6.2°, p<.001), and LLIF significantly outperformed TLIF in the change in LL (5.0°, p=.02). Both outperformed TLIF in ΔDH-A (7.7 mm and 4.7 mm) and ΔDH-P (2.6 mm and 1.5 mm), respectively (p≤.02). ALIF was the only fusion technique that significantly improved the proportion of patients with a PI-LL<10° (0.410.66, p=.02). Lordotic cages had superior improvement of all parameters compared with non-lordotic cages (p<.001). Implant lordosis (m=1.1), fusion technique (m=6.8), and surgical level (m=6.9) significantly predicted postoperative SL (p<.001, R2=0.56). CONCLUSIONS This study demonstrated that these four lumbar fusion techniques yield divergent radiographic results. ALIF and LLIF produced greater improvements in radiographic measurements postoperatively compared with TLIF and PLF. ALIF was the most successful in improving PI-LL mismatch, an important parameter relating to sagittal alignment. Lordotic implants provided better sagittal correction and surgeons should be cognizant of the impact that these differing implants and techniques produce after surgery. Surgical technique is an important determinant of postoperative alignment and has ramifications upon sagittal alignment in lumbar fusion surgery.

The combined administration of vancomycin IV, standard prophylactic antibiotics, and vancomycin powder in spinal instrumentation surgery: does the routine use affect infection rates and bacterial resistance?

Background Surgical site infections (SSI) poses significant risk following spinal instrumentation surgery. The 2013 North American Spine Society (NASS) Evidence-Based Clinical Guidelines found that the incidence of SSI in spine surgery ranged from 0.7-10%, with higher rates with medical comorbidities. National guidelines currently recommend first-generation cephalosporins as first line prophylaxis. Due to an increase in MRSA cases in our institution, a combined antibiotic strategy using vancomycin IV, standard prophylactic antibiotics, and vancomycin powder was implemented for all spinal instrumentation surgeries. Methods All spinal instrumentation surgeries performed at this institution from 2013-2016 were identified. Chart review was then performed to identify the inclusion and exclusion criteria, demographic data, diagnosis, type of surgery performed, and bacterial culture results. Rates of SSI, as defined by the Center for Disease Control (CDC), were calculated and antibiotic resistance was determined. As control, SSIs were identified and reviewed from 2010, prior to the implementation of the combined strategy. Results One thousand and seventy four subjects were identified in the combined cohort. Mean age was 52.3 years, 540 males (50.2%), 534 females (49.8%). There were 960 primary surgeries (89.4%), 114 cases revision surgeries (10.6%). Cervical myelopathy (27.9%), lumbar stenosis (16.2%), lumbar spondylolisthesis (14.0%), and scoliosis (pediatric and adult)/deformity (13.7%) were leading diagnoses. The standard prophylactic antibiotic was cefazolin IV in 524 cases (48.8%), gentamicin IV in 526 cases (49.0%), vancomycin powder was used in 72.3% of cases. Four SSI cases out of 1,074 were identified (0.37%), 3 deep and 1 superficial, with no antibiotic resistance. In the control group, there were 11 infections of 892 cases (1.23%). There were significantly lower rates of SSI in the combined group versus control (P=0.05). Conclusions The combined antibiotic strategy led to low SSI rates in this retrospective case control study. Limitations of this study include retrospective design and small sample size. A large multicenter randomized clinical trial may provide further insight in the effectiveness of this strategy. Level of evidence 3. Clinical relevance: the combined antibiotic protocol may be considered in institutions with concern for SSI and methicillin resistant infections associated with spinal instrumentation surgeries.

Long-term outcomes of cement in cement technique for revision endoprosthesis surgery

Cemented endoprosthetic reconstruction after resection of primary bone sarcomas has been a standard‐of‐care option for decades. With increased patient survival, the incidence of failed endoprostheses requiring revision surgery has increased. Revision of cemented endoprotheses by cementing into the existing cement mantle (CiC) is technically demanding.