David J. Hart

Anterior Fixation of Odontoid Fractures in an elderly Population

OBJECT Fractures of the odontoid process are the most common fractures of the cervical spine in patients over the age of 70 years. The incidence of fracture nonunion in this population has been estimated to be 20-fold greater than that in patients under the age of 50 years if surgical stabilization is not used. Anterior and posterior approaches have both been advocated, with excellent results reported, but surgeons should understand the drawbacks of the various techniques before employing them in clinical practice. METHODS A retrospective review was undertaken to identify patients who had direct fixation of an odontoid fracture at a single institution from 1991 to 2006. Patients were followed up using flexion-extension radiographs, and stability was evaluated as bone union, fibrous union, or nonunion. Patients with bone or fibrous union were classified as stable. In addition, the incidence of procedure- and nonprocedure-related complications was extracted from the medical record. RESULTS Of the 57 patients over age 70 who underwent placement of an odontoid screw, 42 underwent follow-up from 3 to 62 months (mean 15 months). Stability was confirmed in 81% of these patients. In patients with fixation using 2 screws, 96% demonstrated stability on radiographs at final follow-up. Only 56% of patients with fixation using a single screw demonstrated stability on radiographs. In the immediate postoperative period, 25% of patients required a feeding tube and 19% had aspiration pneumonia that required antibiotic treatment. CONCLUSIONS Direct fixation of Type II odontoid fractures showed stability rates > 80% in this challenging population. Significantly higher stabilization rates were achieved when 2 screws were placed. The anterior approach was associated with a relatively high dysphagia rate, and patients must be counseled about this risk before surgery.

Piezoresistive pressure sensors in the measurement of intervertebral disc hydrostatic pressure

BACKGROUND CONTEXT An implantable, freestanding, minimally invasive, intervertebral disc pressure sensor would vastly improve the knowledge of spinal biomechanics and the understanding of spinal disease. Additionally, it would improve clinical indications for surgical interventions in disc-related pathology. Adaptation of current commercially available materials, technology, and microfabrication techniques may now make the production of such a device feasible. PURPOSE To determine if piezoresistive pressure sensor (PPS) technology could be applied as the functional sensing element in an intervertebral disc microsensor. METHODS Commercially available PPS chips were modified, producing sensor chips measuring 0.8 cm(2) by 0.3 cm with an internal sensing element measuring 0.15 cm(2) by 0.1cm. A needle-mounted pressure sensor functionally identical to those used in discography procedures was also tested in parallel as a control. Both sensors were calibrated for hydrostatic pressure using a purpose-built pressure chamber and then tested in human functional spinal units. Methods were developed to implant the sensor and measure the intervertebral disc pressure in response to axial compressive loads. RESULTS Modified commercially available PPS elements were functionally adapted to measure intervertebral disc pressures. Both the PPS and the needle-mounted sensor measured a linear increase in hydrostatic disc pressure with applied axial load. Fluctuations between the slopes of the output versus load curves were observed in the PPS sensor experimental trials. These fluctuations were attributed to the large size of our working model and its impact on the hydrostatic and mechanical properties of the disc. CONCLUSIONS It is hypothesized that future miniaturization of this working model will eliminate mechanical disruption within the disc and the fluctuations in the slope of sensor output that this induces. It should be possible to construct an implantable sensor for the intervertebral disc. This may provide valuable clinical and physiological data.

To Screen or Not to Screen: Vertebral Artery Injuries in Blunt Cervical Spine Trauma

T t D a p t n i T a h s t o t b n I n the accompanying article “Clinical Outcome after Vertebral Artery Injury following Blunt Cervical Spine Trauma,” we are presented with results of a retrospective study from the arrow Neurological Institute examining their patient population ith blunt cervical spine trauma, selecting those considered at igh risk for vertebral artery (VA) injury, and radiographically tudying their VAs. The authors have found a lack of concordance etween abnormalities of the VA found on imaging and clinical utcomes, and thus rightly question the need for routine screenng studies in this population, while still acknowledging the otentially devastating outcomes that can be associated with issed VA injuries.

Complications in Surgical Treatment of Cervical Spondylotic Myelopathy: What We Think We Know

Cervical spondyloticmyelopathy(CSM)isthe primarycause of spinal cord dysfunction in adult patients, and is due to a heterogeneous spectrum of etiologies, from degenerative disk disease to ossification of the posterior longitudinal ligament (OPLL). Due to the prevalence of CSM, surgical procedures addressing this pathology comprise a significant proportion of all spinal operations performed worldwide. Recent debate has centered around the superiority of anterior versus posterior approaches in the effectiveness of treating CSM and the risk of complications each confers. Controversy still exists as to the best procedure; however, the diversity of etiologies likely excludes a solitary optimal approach. The technical considerations, as well as the differential anatomy involved with each approach, contribute to potential complications. There is a wide variance in the literature regardingtheincidenceanddistributionofcomplicationsassociated

Traumatic, high-cervical, coronal-plane spondyloptosis with unilateral vertebral artery occlusion: treatment using a prophylactic arterial bypass graft, open reduction, and instrumented segmental fusion.

The authors present a case of traumatic, complete, high cervical spine injury in a patient with gradual worsening deformity and neck pain while in rigid cervical collar immobilization, ultimately resulting in coronal-plane spondyloptosis. Due to the extent of lateral displacement of the spinal elements, preoperative evaluation included catheter angiography, which revealed complete right vertebral artery (VA) occlusion. A prophylactic arterial bypass graft from the right occipital artery to the extradural right VA was fashioned to augment posterior circulation blood supply prior to reduction and circumferential instrumented fusion. Following surgery, the patient was able to participate in an aggressive rehabilitation program allowing early mobilization, and he ceased to be ventilator-dependent following implantation of a diaphragmatic pacer. The authors review factors leading to progression of this type of injury and suggest technical pearls as well as highlight specific management pitfalls, including operative risks.

Advanced Imaging Techniques in Cervical Spinal Cord Trauma

paper recently published in WORLD NEUROSURGERY contains a very important article by Vedantam et al. that A expands on the use of fractional anisotropy (FA) and diffusion tensor imaging (DTI) in spinal cord injury (SCI). Acute SCI is a condition that carries potentially grave consequences for the patient, the health care system, and society in general. Successful treatment of acute SCI begins with rapid identification and characterization of the injury, and initiation of treatment. Although diagnosis by physical examination remains of the utmost importance, imaging has become a critical and ubiquitous component of assessing patients with acute SCI. Often in the acute trauma setting, computed tomography is the initial imaging of choice due to its low cost, detailed evaluation of bony anatomy, and rapid image acquisition. With a negative computed tomography scan and high clinical suspicion, physicians often rely on magnetic resonance imaging for further delineation of a possible spinal injury. However, recent literature suggests that T2-weighted imaging alone has a low sensitivity for identification of acute myelopathy (2, 5). Furthermore, high signal intensity on T2-weighted images appears in late clinical stages of compression. DTI images of the spinal cord white matter tracts reveal well-organized pathways traveling in different directions, with those oriented in the craniocaudal direction having a higher apparent diffusion coefficient compared with those extending primarily in a transverse direction (12).

Toward Clarity of Management Options in Spinal Synovial Cysts

Synovial cysts represent an uncommon cause of spinal stenosis. However, their frequent association with back pain and radicular symptoms and the relative ease of diagnosis via magnetic resonance imaging make them an increasingly prevalent diagnosis for many patients. The current article in this issue of WORLD NEUROSURGERY by Bydon et al., entitled “Treatment of Synovial Cysts,” provides a thorough review of treatment options for patients with synovial cysts. The authors’ description of conservative treatment covers both observation and steroid injections. A case can certainly be made for observation in patients with mild symptoms and is clearly appropriate in patients with small, asymptomatic, incidentally discovered cysts. Although reliable data regarding the overall incidence of spontaneous cyst regression are lacking (there are case reports, but no higher-level evidence regarding the true frequency of cyst regression), most of us in the field have observed this phenomenon in our patients now and then. Whatever the exact percentagesmightbe,wecanreliablycounselourpatientsthatarelatively