Faculty Bibliography

BACKGROUND: A key component toward improving surgical outcomes is proper patient selection. Improved selection can occur through exploration of prognostic studies that identify variables which are associated with good or poorer outcomes with a specific intervention, such as lumbar discectomy. To date there are no guidelines identifying key prognostic variables that assist surgeons in proper patient selection for lumbar discectomy. The purpose of this study was to identify baseline characteristics that were related to poor or favourable outcomes for patients who undergo lumbar discectomy. In particular, we were interested in prognostic factors that were unique to those commonly reported in the musculoskeletal literature, regardless of intervention type. METHODS: This retrospective study analysed data from 1,108 patients who underwent lumbar discectomy and had one year outcomes for pain and disability. All patient data was part of a multicentre, multi-national spine repository. Ten relatively commonly captured data variables were used as predictors for the study: (1) age, (2) body mass index, (3) gender, (4) previous back surgery history, (5) baseline disability, unique baseline scores for pain for both (6) low back and (7) leg pain, (8) baseline SF-12 Physical Component Summary (PCS) scores, (9) baseline SF-12 Mental Component Summary (MCS) scores, and (10) leg pain greater than back pain. Univariate and multivariate logistic regression analyses were run against one year outcome variables of pain and disability. RESULTS: For the multivariate analyses associated with the outcome of pain, older patients, those with higher baseline back pain, those with lesser reported disability and higher SF-12 MCS quality of life scores were associated with improved outcomes. For the multivariate analyses associated with the outcome of disability, presence of leg pain greater than back pain and no previous surgery suggested a better outcome. CONCLUSIONS: For this study, several predictive variables were either unique or conflicted with those advocated in general prognostic literature, suggesting they may have value for clinical decision making for lumbar discectomy surgery. In particular, leg pain greater than back pain and older age may yield promising value. Other significant findings such as quality of life scores and prior surgery may yield less value since these findings are similar to those that are considered to be prognostic regardless of intervention type.

BACKGROUND: Identifying appropriate candidates for lumbar spine fusion is a challenging and controversial topic. The purpose of this study was to identify baseline characteristics related to poor/favorable outcomes at 1 year for a patient who received lumbar spine fusion. QUESTIONS/PURPOSES: The aims of this study were to describe baseline characteristics of those who received lumbar surgery and to identify baseline characteristics from a spine repository that were related to poor and favorable pain and disability outcomes for patient who received lumbar fusion (with or without decompression), who were followed up for 1 full year and discriminate predictor variables that were either or in contrast to prognostic variables reported in the literature. METHODS: This study analyzed data from 2710 patients who underwent lumbar spine fusion. All patient data was part of a multicenter, multi-national spine repository. Ten relatively commonly captured data variables were used as predictors for the study. Univariate/multivariate logistic regression analyses were run against outcome variables of pain/disability. RESULTS: Multiple univariate findings were associated with pain/disability outcomes at 1 year including age, previous surgical history, baseline disability, baseline pain, baseline quality of life scores, and leg pain greater than back pain. Notably significant multivariate findings for both pain and disability include older age, previous surgical history, and baseline mental summary scores, disability, and pain. CONCLUSION: Leg pain greater than back pain and older age may yield promising value when predicting positive outcomes. Other significant findings may yield less value since these findings are similar to those that are considered to be prognostic regardless of intervention type.

BACKGROUND CONTEXT: Surgical site infection (SSI) is an expensive complication associated with spine surgery. The application of intrawound vancomycin is rapidly emerging as a solution to reduce SSI following spine surgery. The impact of intrawound vancomycin has not been systematically studied in a well-designed multicenter study. PURPOSE: Our aim was to determine whether intrawound vancomycin application was associated with reduced risk of SSI in patients after spine surgery. STUDY DESIGN/SETTING: Multicenter retrospective study. PATIENT SAMPLE: Patients undergoing elective spine surgery over the period of four years at seven different sites across the United States were included in the study. OUTCOME MEASURES: The primary outcome was occurrence of SSI within postoperative 30 days; the secondary outcome included occurrence of SSI that necessitated return to the operating room (OR). METHODS: Patients were given standard IV antibiotics perioperatively and dichotomized based on whether intrawound vancomycin was applied. Multivariable random effect log-binomial regression analyses were conducted to determine the relative risk of having an SSI and an SSI with return to OR. A random effect was included a priori to account for clustering of patients within each site. Covariates significant at p<0.05 in bivariate regression analyses were entered into the multivariable model. Adding back in each excluded variable one at a time tested the stability of the final model. The fraction of the variance attributable to differences between sites was calculated by dividing the variance of the site random effect by the total variance in the model (site + participants). RESULTS: A total of 2,311 patients were included: 2,056 for degenerative spine pathologies (89%), 233 for trauma (10%) and 22 for tumor (1%). The mean number of levels exposed was 3.7 +/- 2.8. Eighty-three percent underwent arthrodesis of which 80% had insertion of instrumentation. The lumbar-sacral region was operated on in 65% of cases, cervical 27.5% and the thoracic region in 7.5%. The mean length of hospital stay was 5.6 days +/- 6.3 and 22.5% of patients were admitted to the ICU after surgery. Intrawound vancomycin was used in 45% of patients. The prevalence of SSI was 5.1% in absence of vancomycin use compared to 2.4% with intrawound vancomycin. The site-to-site variation in SSI ranged from 1.5% to 5.7%. In a multivariable random effect log-binomial regression model, the patients in whom intrawound vancomycin was not used (P<0.001, RR-2.3, CI-1.5-3.6), those with higher number of levels exposed (P=0.045, RR-1.1, CI 1.0-1.1), postoperative ICU admission (P=0.003, RR-2.1, CI-1.3-3.3) and obese patients (P=0.04, RR-1.8, CI-1.0-3.0) had higher risk of developing SSI. Using similar statistical methodology, the risk factors that contributed to need for return to OR to address an infection included: not applying intrawound vancomycin (P<0.001, RR-5.2, CI 2.6-10.4), having a higher number of levels operated on (P=0.001, RR-1.1, CI- 1.0-1.2) and admission to the ICU postoperatively (P=0.001, RR-2.5, CI-1.5-4.3). Geographical site contributed significantly to the model and accounted for 3% of the variance in SSI and 20% of the variance in SSI with return to the OR. CONCLUSIONS: Intrawound application of vancomycin after elective spine surgery was associated with reduced risk of SSI and return to OR associated with SSI, even after controlling for confounding variables

STUDY DESIGN:: Structured review of literature and application of meta-analysis statistical techniques. OBJECTIVE:: Review published series describing clinical and radiographic outcomes of patients treated with C1 lateral mass screws (C1LMS), specifically analyzing the impact of starting point and bicortical purchase on successful atlantoaxial arthrodesis. SUMMARY OF BACKGROUND DATA:: Biomechanical studies suggest posterior arch screws and C1LMS with bicortical purchase are stronger than screws placed within the center of the lateral mass or those with unicortical purchase. METHODS:: Online databases were searched for English-language articles between 1994 and 2012 describing posterior atlantal instrumentation with C1LMS. Thirty-four studies describing 1247 patients having posterior atlantoaxial fusion with C1LMS met inclusion criteria. RESULTS:: All studies provided Class III evidence. Arthrodesis was quite successful regardless of technique (~99.0% overall). Meta-analysis and multivariate regression analyses showed that neither posterior arch starting point nor bicortical screw purchase translated into a higher rate of successful arthrodesis. There were no complications from bicortical screw purchase. CONCLUSIONS:: The Goel-Harms technique is a very safe and successful technique for achieving atlantoaxial fusion, regardless of minor variations in C1LMS technique. Although biomechanical studies suggest markedly increased rigidity of bicortical and posterior arch C1LMS, the significance of these findings may be minimal in the clinical setting of atlantoaxial fixation and fusion with modern techniques. The decision to use either technique must be made after careful review of the preoperative multiplanar CT imaging, assessment of the unique anatomy of each patient and the demands of the clinical scenario such as bone quality.

INTRODUCTION: Surgical site infection (SSI) is an expensive complication associated with spine surgery. The application of intrawound vancomycin is rapidly emerging as a solution to reduce SSI. The impact of intrawound vancomycin has not been systematically studied in a well-designed multicenter study. We determine whether intrawound vancomycin application was associated with reduced risk of SSI in patients after spine surgery. METHODS: Patients undergoing elective spine surgery over the period of 4 years at 7 different sites across the United States were included in the study. Patients were given standard IV antibiotics perioperatively and dichotomized based on whether intrawound vancomycin was applied. Multivariable random-effects log-binomial regression analyses were conducted to determine the relative-risk of having a SSI and a SSI with return to the operating room (OR) within postoperative 30 days. Random effects was included a priori to account for clustering of patients within each site. Fraction of variance attributable to differences between sites was calculated by dividing the variance of site random effect by the total variance in the model (site + participants). RESULTS: Two thousand three hundred eleven patients were included: degenerative spine pathologies 89% (2056), trauma 10% (233), and tumor 1% (22) (Table 1). Intrawound vancomycin was used in 45% of patients. Prevalence of SSI was 5.1% in the absence of vancomycin use vs 2.4% with intrawound vancomycin. Site-to-site variation in SSI ranged from 1.5% to 5.7% (Table 2). In multivariable regression model, patients in whom intrawound vancomycin was not used (RR 2.3, CI 1.5-3.6), those with higher number of levels exposed (RR 1.1, CI 1.0-1.1), postoperative ICU admission (RR 2.1, CI 1.3-3.3), and obesity (RR 1.8, CI 1.0-3.0) had higher risk of developing SSI. Risk factors for SSI with return to OR included: not applying intrawound vancomycin (RR 5.2, CI 2.6-10.4), higher number of levels exposed (RR 1.1, CI 1.0-1.2), and postoperative ICU admission (RR 2.5, CI 1.5-4.3). Geographical site variation accounted for 3% of variance in SSI and 20% in SSI with return to the OR. CONCLUSION: Intrawound application of vancomycin after elective spine surgery was associated with reduced risk of SSI and return to OR associated with SSI, even after controlling for confounding variables.

STUDY DESIGN:: Literature review and meta-analysis. OBJECTIVE:: To compare clinical and radiographic outcomes of patients treated with C1 lateral mass screws (C1LMS), analyzing the impact of screw starting point and C2 nerve sectioning on malposition, vertebral artery injury (VAI) and C2 neuralgia and numbness. BACKGROUND:: Various starting points have been suggested for C1LMS insertion. Some advocate sectioning the C2 nerve root to ease placement. METHODS:: Online databases were searched for English-language articles between 1994 and 2012 reporting on C1LMS. Forty-two studies describing 1471 patients instrumented with 2905 C1LMS met inclusion criteria. Three surgical techniques included posterior arch starting point and center of lateral mass with nerve root preservation or sacrifice. RESULTS:: All studies provided Class III evidence. Three injuries to the vertebral artery occurred secondary to C1LMS insertion (0.1%) and 5 instances of clinically significant screw malpositions (0.2%). Postoperative imaging revealed 45 malpositioned screws (1.6%) without clinical consequences. Meta-analysis techniques demonstrated that sacrifice of the C2 nerve root caused greater postoperative numbness but less neuralgia and fewer screw malpositions. Similar rates of screw malposition and VAI arose with posterior arch screws and those starting below the arch with C2 nerve preservation, but the latter had greater numbness and pain. CONCLUSION:: A thorough understanding of atlantoaxial anatomy and modern surgical techniques renders the insertion of C1LMS safe and accurate. The incidence of clinically significant malpositioned screws or VAI is less than 0.5%. Sacrifice of the C2 nerve root did result in fewer malpositioned screws. Numbness occurred in 11% of patients, an outcome that may be unacceptable to certain patient populations, but neuropathic pain was nearly absent with nerve sectioning. C2 nerve preservation and retraction for C1 screw placement may have higher incidence of neuropathic pain. Posterior arch screws are a viable option for patients with arches that are of adequate height.

Spinal fixation in the osteoporotic patient can be challenging due to the poor trabecular bone quality of the vertebral body. Patients with osteoporotic vertebral body compression fractures are at risk for future compression fractures at adjacent levels, especially after cement augmentation. The purpose of this technical report is to describe the utilization of a cortical screw trajectory along with kyphoplasty for a patient with an osteoporotic compression fracture as well as degenerative spinal disease. This trajectory allows for the possibility of percutaneous pedicle access in the event of future compression fractures. Our patient underwent a decompressive laminectomy and kyphoplasty at the level of an osteoporotic compression fracture. The fracture was stabilized with cortical screw instrumentation and fusion at a level above and a level below the fracture. Subsequently the patient developed an adjacent level fracture within the fusion construct. Due to the utilization of a cortical screw trajectory for the initial fusion, the traditional pedicle trajectory was still accessible. As a result, the new fracture was treated with a percutaneous kyphoplasty through a standard pedicle trajectory. In conclusion, the use of a cortical screw trajectory for stabilization of osteoporotic compression fractures provides for a stronger bone screw interface and avoids osteoporotic trabecular vertebral body bone. At the same time this trajectory allows for future percutaneous pedicular access in the event that the patient suffers future compression fractures.

STUDY DESIGN:: Literature review and meta-analysis. OBJECTIVES:: To compare the incidence of screw malposition and vertebral artery injury (VAI) with transarticular screws (TAS) and C2 pedicle screws (C2PS) using meta-analysis techniques. SUMMARY OF BACKGROUND DATA:: Posterior instrumentation for atlanto-axial fusions can be challenging and risky. Some centers report a higher incidence of VAI with the implantation of TAS compared to C2PS, while other data do not support this. METHODS:: Online databases were searched for English-language articles between 1994 and April of 2011 describing the clinical and radiographic outcomes following insertion of C2PS or TAS. Forty-one studies reporting on 3627 TAS and 33 studies describing 2979 C2PS met inclusion criteria for VAI or clinically significant misplacements (VAI, neurological deficits or misplacements requiring surgical revision) and 36 studies reporting on 3280 TAS and 28 studies describing 2532 C2PS met inclusion criteria for radiographic misplacement outcomes. RESULTS:: All studies comprised Class III evidence. VAI occurred in 26 of 3627 (0.72%) implanted TAS and in 10 of 2979 (0.34%) implanted C2PS (P=0.01). Clinically significant misplacements occurred in 67 TAS (1.84%) and in 10 C2PS (0.34%; P<0.0001). The point estimate of VAI for TAS was 1.68% (CI: 1.23-2.29%) and was higher than C2PS (1.09%; CI: 0.73-1.63%; P=0.01). The point estimate of clinically significant screw malposition for TAS was 2.33% (CI: 1.61-3.37%) and was higher than that of C2PS (1.15%; CI: 0.77-1.70%; P<0.001). CONCLUSIONS:: With training, experience and anatomical knowledge, both TAS and C2PS can be inserted accurately and safely. However, improper insertion and VAI can have catastrophic consequences. Our review identified a higher risk of VAI, neurological injury and clinically significant malpositions with TAS compared to C2PS. These data provide preliminary support for the supposition that C2PS have a lower risk of morbidity.

STUDY DESIGN:: Literature review and meta-analysis. OBJECTIVE:: To compare clinical and radiographic outcomes of patients treated with transarticular screws (TAS) and screw rod constructs (SRC) for posterior atlantoaxial fusion. BACKGROUND:: Modern techniques for C1-2 fusions include Magerl and Seeman's TAS and SRC using C1 lateral mass screws and C2 pars/pedicle screws as described by Goel and Laheri and later modified by Harms and Melcher. METHODS:: Online databases were searched for English-language articles between 1986 and April of 2011 describing posterior atlantoaxial instrumentation with C1-2 TAS or SRC. Forty-five studies (2073 patients) treated with TAS and 24 studies (1073 patients) treated with SRC fulfilled inclusion criteria. Standard and formal meta-analysis techniques were used to compare outcomes. RESULTS:: All studies provided Class III evidence. There were no differences in 30-day mortality (0.8 vs. 0.6%) or neurological injury (0.2 vs. 0%). There was a higher incidence of vertebral artery injury (4.1% [CI: 2.8-5.4%] vs. 2.0% [CI: 1.1-3.4%]; P=0.02) and malpositioned screws (7.1% [CI: 5.7-8.8%] vs. 2.4% [CI: 1.1-4.1%]; P<0.001) and a slightly lower rate of fusion with the TAS technique 97.5% [CI: 95.9-98.5%] vs. 94.6% [CI: 92.6-96.1%]; P<0.001). CONCLUSIONS:: TAS and SRC are safe and effective treatment options for C1-2 instability but require a thorough knowledge of atlantoaxial anatomy for successful insertion of screws. Slightly higher rates of fusion and less risk of injury to the vertebral artery during screw placement were observed with the SRC technique. However, differences in graft material and techniques were noted. Prospective, randomized studies with validated radiographic and clinical outcome metrics are necessary for proper comparison of these techniques.