Monitoring image guidance system accuracy during spinal surgery with mini-screw fiducials: technical note.

STUDY DESIGN: A technical note. OBJECTIVE: To describe a technique for measuring accuracy of intraoperative image guidance systems in spine surgery. SUMMARY OF BACKGROUND DATA: Image guidance may be of use when performing complex procedures on the spine. However, as the operation progresses and, in particular, once any deformity has been corrected, the image guidance system may become unreliable. In practice, this often results in repeated image acquisitions thus increasing the radiation exposure to the patient. METHODS: Small titanium, cranio-facial screws were placed on the dorsal aspect of the spine intraoperatively, before the acquisition of images and used as fiducials. RESULTS: The authors were able to accurately discern the true precision of the image guidance system used with an intraoperative computed tomography scanner, throughout the procedure. CONCLUSIONS: By using intraoperatively placed mini-screw fiducials, the surgeon may check and quantify the underlying system accuracy both initially and throughout the surgery. In the future, "auto-adjust" functions may be integrated into the computer software to automatically recalibrate the system when a probe is placed into the fiducials without the need for rescanning.

Atlantoaxial stabilization using multiaxial C-1 posterior arch screws.

The authors present a novel technique of atlantoaxial fixation using multiaxial C-1 posterior arch screws. The technique involves the insertion of bilateral multiaxial C-1 posterior arch screws, which are connected by crosslinked rods to bilateral multiaxial C-2 pars screws. The clinical results are presented in 3 patients in whom anomalies of the vertebral arteries, C-1 lateral masses, and/or posterior arch of C-1 presented difficulty using existing fixation techniques with transarticular screws, C-1 lateral mass screws, or posterior wiring. The C-1 posterior arch screws achieved solid fixation and their insertion appeared to be technically less demanding than that of transarticular or C-1 lateral mass screws. This technique may reduce the risk of complications compared with existing techniques, especially in patients with anatomical variants of the vertebral artery, C-1 lateral masses, or C-1 posterior arch. This technique may prove to be an attractive fixation option in patients with normal anatomy.

Subaxial injury classification scoring system treatment recommendations: external agreement study based on retrospective review of 185 patients.

STUDY DESIGN: Retrospective case series. OBJECTIVE: To test validity of subaxial injury classification (SLIC) treatment recommendations. SUMMARY OF BACKGROUND DATA: Although SLIC has been tested for reliability, external studies that test the validity of its treatment recommendations are lacking. METHODS: The SLIC score was determined by reviewing imaging studies and clinical records in a consecutive series of 185 patients with subaxial cervical spine trauma presenting to a level 1 spinal injury referral center. Details including attending surgeon responsible for treatment decision, treatment received, and surgical approach were collected. RESULTS: Treatment received matched SLIC guidelines in 93.6% nonsurgically managed patients and 96.3% surgically managed patients. The mean SLIC score of the surgically treated group of patients was significantly higher than that of the nonsurgical group (7.14 vs. 2.22; P<0.001). Sixty-six patients had a SLIC score of 3 or less, and 94% of them were nonsurgically managed (P<0.001). One hundred two patients had a SLIC score of 5 or more, and 95% of them were surgically managed (P<0.001). Seventeen patients had a SLIC score of 4, and 65% were nonsurgically managed (P=0.032). Injury morphology scores were not predictive of surgical approach. Increasing SLIC scores correlated with increasing complexity of treatment (r=0.77; P<0.001). The distribution of patients with regard to severity of injuries and treatment delivered by the 7 spinal surgeons was comparable. The past practice of these 7 fellowship-trained spine surgeons was individually in agreement with SLIC treatment recommendations. CONCLUSION: Our past practice reflects SLIC treatment recommendations for nonsurgical treatment of patients with SLIC scores of 3 or less and surgical treatment of patients with SLIC scores of 5 or more. The use of SLIC as an ordinal severity scale is validated as increasing SLIC scores correlated with increasing complexity of treatment. The injury morphology score did not predict a surgical approach. Significantly higher numbers of patients with a SLIC score of 4 were treated nonsurgically. LEVEL OF EVIDENCE: 3.

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%.