Patrick Cooper

Using lamina screws as a salvage technique at C-7: computed tomography and biomechanical analysis using cadaveric vertebrae. Laboratory investigation.

OBJECT Transpedicular instrumentation at C-7 has been well accepted, but salvage techniques are limited. Lamina screws have been shown to be a biomechanically sound salvage technique in the proximal thoracic spine, but have not been evaluated in the lower cervical spine. The following study evaluates the anatomical feasibility of lamina screws at C-7 as well as their bone-screw interface strength as a salvage technique. METHODS Nine fresh-frozen C-7 cadaveric specimens were scanned for bone mineral density using dual energy x-ray absorptiometry. Prior to testing, all specimens were imaged using CT to obtain 1-mm axial sections. Caliper measurements of both pedicle width and laminar thickness were obtained. On the right side, pedicle screws were first inserted and then pulled out. Salvage intralaminar screws were inserted into the left lamina from the right spinous process/lamina junction and then pulled out. All screws were placed by experienced cervical spine surgeons under direct fluoroscopic visualization. Pedicle and lamina screws were 4.35- and 3.5-mm in diameter, respectively. Screws sizes were chosen based on direct and radiographic measurements of the respective anatomical regions. Insertional torque (IT) was measured in pounds per inch. Tensile loading to failure was performed in-line with the screw axis at a rate of 0.25 mm/sec using a MiniBionix II system with data recorded in Newtons. RESULTS Using lamina screws as a salvage technique generated mean pullout forces (778.9 +/- 161.4 N) similar to that of the index pedicle screws (805.3 +/- 261.7 N; p = 0.796). However, mean lamina screw peak IT (5.2 +/- 2.0 lbs/in) was significantly lower than mean index pedicle screw peak IT (9.1 +/- 3.6 lbs/in; p = 0.012). Bone mineral density was strongly correlated with pedicle screw pullout strength (r = 0.95) but less with lamina screw pullout strength (r = 0.04). The mean lamina width measured using calipers (5.7 +/- 1.0 mm) was significantly different from the CT-measured mean lamina width (5.1 +/- 0.8 mm; p = 0.003). Similarly, the mean pedicle width recorded with calipers (6.6 +/- 1.1 mm) was significantly different from the CT-measured mean pedicle width (6.2 +/- 1.3 mm; p = 0.014). The mean laminar width measured on CT at the thinnest point ranged from 3.8 to 6.8 mm, allowing a 3.5-mm screw to be placed without difficulty. CONCLUSIONS These results suggest that using lamina screws as a salvage technique at C-7 provides similar fixation strength as the index pedicle screw. The C-7 lamina appears to have an ideal anatomical width for the insertion of 3.5-mm screws commonly used for cervical fusions. Therefore, if the transpedicular screw fails, using intralaminar screws appear to be a biomechanically sound salvage technique.

Computed tomography and biomechanical evaluation of screw fixation options at the cervicothoracic junction: intralamina versus intrapedicular techniques.

Study Design. In vitro cadaveric biomechanical analysis. Objective. Define the T1 and T2 anatomic lamina size and evaluate the bone-screw interface strength of various pedicle screw options and intralamina techniques. Summary of Background Data. Transpedicular instrumentation is well accepted, but salvage techniques in the proximal thoracic spine are limited. Intralamina fixation has been described at C2 with favorable biomechanical characteristics. In addition, this technique has been introduced clinically in the proximal thoracic spine. However, the biomechanical potential has not been evaluated. Methods. Fourteen fresh-frozen cervicothoracic cadaveric specimens were scanned using dual-energy radiograph absorptiometry for bone mineral density, imaged under computed tomography, and then instrumented in the following configuration: (1) Right-sided pedicle screws in a straight-forward trajectory, (2) “salvage anatomic trajectory pedicle screws, and (3) “salvage” intralamina screws into the contralateral lamina. Insertional torque (IT) was recorded with each revolution and screws were pulled out in-line (POS) with the screw axis to simulate intraoperative failure of fixation. Results. Lamina screws as a salvage technique generated statistically greater peak IT (P = 0.002) and relative POS (P < 0.05) in comparison with straight-forward transpedicular screws as the initial fixation type. Furthermore, lamina screws, when compared to the salvage anatomic trajectory pedicle screws, had a significantly greater peak IT (P = 0.011). The peak IT showed a stronger correlation with POS in lamina screws than straight-forward or anatomic pedicle screws with a similar trend noted in mean IT. Bone mineral density correlated with POS in all methods of fixation. The mean lamina width measured on computed tomography at the thinnest point was 5.9 ± 0.7 mm (range, 4.9–7.9). Conclusion. Our results suggest that lamina screws, used as a salvage technique in the proximal thoracic spine, provide stronger fixation than transpedicular screws when using standard 4.5-mm cervical screws. In-tralamina screws appear to be a biomechanically sound salvage technique in the region, and appear to be a safe, effective technique for instrumenting the proximal thoracic spine.

Chapter 57 – Traumatic Brain Injury

Publisher Summary This chapter presents a discussion on traumatic brain injury (TBI). The chapter presents a practical approach to the diagnosis and management of the TBI patient, with a discussion of the basic pathologic conditions that drive that management.TBI is the leading cause of death and disability in young adults in the United States. Brain injury may be caused by any of several types of head trauma, including the more typical closed head injury, in which rapid acceleration or deceleration produces shearing and other forces in the brain and impacts against the frontal and temporal fossae of the skull; direct impact to the head; and penetration by a bullet or other foreign object. Although some details of the pathosis of these types of trauma may differ, the principles of acute and especially long-term management are similar in most cases. TBI is traditionally classified by its severity, but distinctions between mild, moderate, and severe head injury can often be blurred. Nevertheless, the distinctions are generally useful in guiding the approach to the patient. Proper evaluation and diagnosis of the TBI patient is made especially challenging by the multifactorial nature and complexity of the pathologic conditions induced by the trauma and their evolving character. The discussion on the pathology of TBI includes focal injury, diffuse microvascular injury, hypoxia-ischemia, diffuse axonal injury (DAI), neuronal loss/excitotoxic injury, and diffuse gray matter dysfunction.