Ron I. Riesenburger, G. Alexander Jones, Marie Roguski and Ajit A. Krishnaney
The goal of this study was to characterize the anatomy relevant to placement of crossing C-2 translaminar screws, including morphometric data, and to evaluate the risk of violating the vertebral artery (VA) during the screw placement. Placement of bilateral crossing C-2 translaminar screws has become an increasingly popular method for dorsal C-2 instrumentation as it is felt to avoid the known risk of VA injury associated with C1–2 transarticular screw fixation and C-1 lateral mass–C-2 pars screw fixation.
The source images from 50 CT angiograms of the neck obtained from October to November 2007 were studied. Digital imaging software was used to measure lamina thickness and maximum screw length, perform angulation of screw trajectories in the axial plane, and evaluate the potential for VA injury. In cases where the VA could be injured, the distance between the maximal screw length and artery was measured. Logistic regression was performed to evaluate lamina width, axial angle, and screw length for predicting the potential for VA injury.
Mean lamina thickness, axial angle, and maximal screw length were determined for 100 laminae, and a potential for VA injury was noted in 55 laminae. The anatomically defined ideal screw length was longer in laminae with potential for VA injury than in laminae with no apparent risk (35.2 vs 33.6 mm, p = 0.0131). Only increasing optimal screw length was noted to be a statistically significant predictor of potential VA injury (p = 0.0159). The “buffer zone” (the distance between an optimally placed screw and the VA) was 5.6 ± 1.9 mm (mean ± SD, range 1.8–11.4 mm). A screw limited to 28 mm in length appeared to be safe in all laminae studied.
Crossing C-2 translaminar screws have been reported to be safe and effective. In addition to morphometric characteristics, the authors have found that screws placed in this trajectory could jeopardize the vertebral arteries in the foramen transversarium or the C1–2 interval. A C-2 translaminar screw limited to 28 mm in length appeared to be safe in all 100 screw trajectories studied in this series.
G. Alexander Jones, John Butler, Isador Lieberman and Richard Schlenk
Deep infections of the spine are a significant cause of morbidity and death. Such infections complicate 0.7 to 11.9% of spinal procedures. Management includes intravenous antibiotic therapy, debridement and irrigation with primary closure, placement of drains, use of irrigation systems, and/or healing through secondary intention with wound packing. Vacuum-assisted closure (VAC) is a new alternative for treatment of patients with complex postoperative spinal infections. The aim of this study was to investigate the safety of this treatment method in this patient population.
The authors reviewed the charts of 16 consecutive patients treated with negative-pressure wound therapy at their institution between 2002 and 2006. All had deep infections of the spine and were treated with surgical debridement and placement of VAC dressings. All infections were postoperative. Members of the infectious disease service were involved in the care of all patients, and all patients received intravenous antibiotic therapy. The authors reviewed operative notes, discharge summaries, and notes from follow-up visits and assessed outcome on the basis of the same records.
Three patients were lost to follow up, leaving a group of 13 with follow up of at least 90 days. Two patients experienced bleeding complications related to the continuous negative pressure of the VAC device. In two cases, the infections persisted and required reoperation. In one case, a skin graft was required because of nonhealing granulation tissue. One of the patients with bleeding complications died as a result of delayed complications related to intraoperative blood loss, blood loss via the VAC system, and refusal of a blood transfusion on religious grounds.
Negative-pressure wound therapy has been employed as a treatment strategy for patients with complex postoperative spinal infections, but little is known of the complications associated with VAC in the spinal surgery patient population. Serious complications, including death, may be associated with use of the VAC system.
Ryan C. Hofler, Muturi G. Muriuki, Robert M. Havey, Kenneth R. Blank, Joseph N. Frazzetta, Avinash G. Patwardhan and G. Alexander Jones
The authors conducted a study to determine whether a change in T1 tilt results in a compensatory change in the cervical sagittal vertical axis (SVA) in a cadaveric spine model.
Six fresh-frozen cadavers (occiput [C0]–T1) were cleaned of soft tissue and mounted on a customized test apparatus. A 5-kg mass was applied to simulate head weight. Infrared fiducials were used to track segmental motion. The occiput was constrained to maintain horizontal gaze, and the mounting platform was angled to change T1 tilt. The SVA was altered by translating the upper (occipital) platform in the anterior-posterior plane. Neutral SVA was defined by the lowest flexion-extension moment at T1 and recorded for each T1 tilt. Lordosis was measured at C0–C2, C2–7, and C0–C7.
Neutral SVA was positively correlated with T1 tilt in all specimens. After increasing T1 tilt by a mean of 8.3° ± 2.2°, neutral SVA increased by 27.3 ± 18.6 mm. When T1 tilt was reduced by 6.7° ± 1.4°, neutral SVA decreased by a mean of 26.1 ± 17.6 mm.
When T1 tilt was increased, overall (C0–C7) lordosis at the neutral SVA increased from 23.1° ± 2.6° to 32.2° ± 4.4° (p < 0.01). When the T1 tilt decreased, C0–C7 lordosis at the neutral SVA decreased to 15.6° ± 3.1° (p < 0.01). C0–C2 lordosis increased from 12.9° ± 9.3° to 29.1° ± 5.0° with increased T1 tilt and decreased to −4.3° ± 6.8° with decreased T1 tilt (p = 0.047 and p = 0.041, respectively).
Neutral SVA is not a fixed property but, rather, is positively correlated with T1 tilt in all specimens. Overall lordosis and C0–C2 lordosis increased when T1 tilt was increased from baseline, and vice versa.
Ryan C. Hofler, Daniel M. Heiferman, Ayrin Molefe, Ryan LeDuc, Stephen J. Johans, Jordan D. Rosenblum, Russ P. Nockels and G. Alexander Jones
Atlantoaxial instability is an important cause of pain and neurological dysfunction in patients with Down syndrome (DS), frequently requiring instrumented fusion of the upper cervical spine. This study provides a quantitative analysis of C2 morphology in DS patients compared with their peers without DS to identify differences that must be considered for the safe placement of instrumentation.
A retrospective chart review identified age-matched patients with and without DS with a CT scan of the cervical spine. Three-dimensional reconstructions of these scans were made with images along the axis of, and perpendicular to, the pars, lamina, facet, and transverse foramen of C2 bilaterally. Two of the authors performed independent measurements of anatomical structures using these images, and the average of the 2 raters’ measurements was recorded. Pedicle height and width; pars axis length (the distance from the facet to the anterior vertebral body through the pars); pars rostrocaudal angle (angle of the pars axis length to the endplate of C2); pars axial angle (angle of the pars axis length to the median coronal plane); lamina height, length, and width; lamina angle (angle of the lamina length to the median coronal plane); and transverse foramen posterior distance (the distance from the posterior wall of the transverse foramen to the tangent of the posterior vertebral body) were measured bilaterally. Patients with and without DS were compared using a mixed-effects model accounting for patient height.
A total of 18 patients with and 20 patients without DS were included in the analysis. The groups were matched based on age and sex. The median height was 147 cm (IQR 142–160 cm) in the DS group and 165 cm (IQR 161–172 cm) in the non-DS group (p < 0.001). After accounting for variations in height, the mean pars rostrocaudal angle was greater (50.86° vs 45.54°, p = 0.004), the mean transverse foramen posterior distance was less (−1.5 mm vs +1.3 mm, p = 0.001), and the mean lamina width was less (6.2 mm vs 7.7 mm, p = 0.038) in patients with DS.
Patients with DS had a steeper rostrocaudal trajectory of the pars, a more posteriorly positioned transverse foramen posterior wall, and a narrower lamina compared with age- and sex-matched peers. These variations should be considered during surgical planning, as they may have implications to safe placement of instrumentation.