Faculty Bibliography

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.

OBJECTIVE: To review published series describing C1-2 posterior instrumented fusions and summarize clinical and radiographic outcomes of patients treated with screw-rod constructs (SRC). METHODS: Online databases were searched for English-language articles published between 1991 and April 2011 describing posterior atlantoaxial instrumentation with C1-2 SRC. There were 24 studies including 1073 patients treated with SRC that fulfilled inclusion criteria. Meta-analysis techniques were used to compare outcomes. RESULTS: All studies provided class III evidence. The 30-day perioperative mortality rate was 0.6%, and neurologic injury occurred in two patients with vertebral artery injury (VAI) from screw malpositions (0.2%). The incidence of clinically significant screw malpositions was 2.4% (confidence interval [CI], 1.1%-4.1%), the incidence of VAI was 2.0% (CI, 1.1%-3.4%), and the rate of fusion with the SRC technique was 97.5% (CI, 95.9%-98.5%). CONCLUSIONS: SRC is a safe and effective treatment option for C1-2 instability. The low but nonzero incidence of screw malposition and VAI emphasizes the necessity of having a thorough knowledge of atlantoaxial anatomy for successful insertion of screws.

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.

OBJECTIVE: Atlantoaxial osteoarthritis (AAOA) is an underrecognized source of neck pain, limitation of range of motion, and cervicogenic headaches. When conservative treatments such as facet injections fail, fusion may be indicated. We reviewed published series describing posterior fusions for atlantoaxial osteoarthritis of the facet joints. METHODS: Online databases were searched for English-language articles describing the diagnosis and treatment of AAOA. Twenty-three studies reporting on 246 patients treated with posterior fusion for lateral AAOA fulfilled inclusion criteria. Standard statistical and formal meta-analytic techniques were used to assess outcomes. RESULTS: All studies provided class III evidence. The 30-day perioperative mortality was 1.2% and neurologic injury did not occur. Patients were followed for a mean of nearly 5 years. Fusion was successful in 98% of patients with a single operation and with 99.5% of patients after revision surgery. Intractable preoperative neck pain either resolved completely or improved in 97.7% of patients. Using meta-analytic techniques, the point estimate for improvement or resolution of pain was 92.6% (confidence interval = 86.8%-96.0%) and the rate of arthrodesis for AAOA was 92.2% (confidence interval = 85.6%-95.9%) and there were no differences among the various techniques used for fusion. Operative complications were few. CONCLUSION: Posterior C1-2 fusion is a safe and effective treatment option for patients with intractable neck pain secondary to lateral AAOA. Modern fusion options offer a high rate of arthrodesis and low risk of morbidity if conservative therapies fail to provide adequate pain relief.

STUDY DESIGN: Retrospective review. OBJECTIVE: To assess the safety and efficacy of prophylactic low-molecular-weight heparin (LMWH) started 24 to 36 hours after degenerative spine surgery. SUMMARY OF BACKGROUND DATA: Venous thromboembolism (VTE) is a significant postoperative complication best averted with dual mechanical/pharmacological prophylaxis. Pharmacological prophylaxis is widely used in patients with spinal cord injury, but there is no consensus on its role in degenerative spine surgery, particularly after laminectomy with the concurrent risk of epidural hematoma. The literature suggests a small but potentially devastating hemorrhage risk when LMWH is started within 24 hours of spine surgery. An intermediate strategy is delayed LMWH initiation to minimize hemorrhage risk and retain benefits of dual prophylaxis. METHODS: Operative reports of the senior author were retrospectively reviewed for all cases of cervical and lumbar laminectomy from 2007 to 2011. Single-level decompressions without fusion and all nondegenerative cases were excluded. Baseline and operative details were recorded. Mechanical prophylaxis was used throughout admission, and prophylactic LMWH was started postoperative day 1 at 10 PM. All cases of postoperative hemorrhage (epidural hematoma, superficial hematoma, persistent wound drainage), deep venous thrombosis, and pulmonary embolism were noted. RESULTS: A total of 367 patients underwent multilevel laminectomy or laminectomy and fusion for degenerative disease. VTE risk factors (age >60 yr, smoking, obesity) were common. No patients receiving LMWH 24 to 36 hours after surgery developed postoperative hemorrhage (95% confidence interval: 0-0.8%). Nearly half of the study population underwent lower extremity ultrasonography or chest computed tomography, and acute VTE was diagnosed in 14 patients (3.8%; 95% confidence interval: 2.1-6.3). CONCLUSION: LMWH prophylaxis seems to carry a very low hemorrhage risk when started 24 to 36 hours after spine surgery. Larger, prospective studies are needed to assess the safety of early delayed LMWH administration more definitively. Even with aggressive prophylaxis, patients undergoing fusion or multilevel laminectomy for degenerative disease are at significant risk for VTE.