Tonically Active cAMP-Dependent Signaling in the Ventrolateral Medulla Regulates Sympathetic and Cardiac Vagal Outflows.

The ventrolateral medulla contains presympathetic and vagal preganglionic neurons that control vasomotor and cardiac vagal tone, respectively. G protein-coupled receptors influence the activity of these neurons. Gα s activates adenylyl cyclases, which drive cyclic adenosine monophosphate (cAMP)-dependent targets: protein kinase A (PKA), the exchange protein activated by cAMP (EPAC), and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. The aim was to determine the cardiovascular effects of activating and inhibiting these targets at presympathetic and cardiac vagal preganglionic neurons. Urethane-anesthetized rats were instrumented to measure splanchnic sympathetic nerve activity (sSNA), arterial pressure (AP), heart rate (HR), as well as baroreceptor and somatosympathetic reflex function, or were spinally transected and instrumented to measure HR, AP, and cardiac baroreflex function. All drugs were injected bilaterally. In the rostral ventrolateral medulla (RVLM), Sp-cAMPs and 8-Br-cAMP, which activate PKA, as well as 8-pCPT, which activates EPAC, increased sSNA, AP, and HR. Sp-cAMPs also facilitated the reflexes tested. Sp-cAMPs also increased cardiac vagal drive and facilitated cardiac baroreflex sensitivity. Blockade of PKA, using Rp-cAMPs or H-89 in the RVLM, increased sSNA, AP, and HR and increased HR when cardiac vagal preganglionic neurons were targeted. Brefeldin A, which inhibits EPAC, and ZD7288, which inhibits HCN channels, each alone had no effect. Cumulative, sequential blockade of all three inhibitors resulted in sympathoinhibition. The major findings indicate that Gα s-linked receptors in the ventral medulla can be recruited to drive both sympathetic and parasympathetic outflows and that tonically active PKA-dependent signaling contributes to the maintenance of both sympathetic vasomotor and cardiac vagal tone.

Complications with K-wire insertion for percutaneous pedicle screws.

STUDY DESIGN: Retrospective study. OBJECTIVE: To determine the risk profile and complications associated with anterior vertebral body breach by Kirschner (K)-wire during percutaneous pedicle screw insertion. SUMMARY OF BACKGROUND DATA: Percutaneous techniques and indications are rapidly expanding with numerous studies now supporting the use of percutaneous pedicle screw stabilization as an adjunct for multiple pathologies such as degenerative, tumor, and trauma. With regards to complication rates, little has been documented. MATERIALS AND METHODS: A total of 525 consecutive percutaneous pedicle screws were retrospectively reviewed and the rate of anterior vertebral body breach was recorded, including any potential adverse clinical outcomes. RESULTS: Of 525 percutaneous pedicle screw insertions, there were 7 anterior breaches recorded. We rated the breaches as a minor breach (<5 mm; n=3), moderate breach (5-25 mm; n=2), and major breach (>25 mm; n=2). Two patients had a postoperative ileus with a retroperitoneal hematoma on postoperative computed tomography scan. No patient required reoperation or blood transfusion. CONCLUSIONS: The indications for minimally invasive spinal fusion have expanded to include conditions such as degenerative, trauma, deformity, infection, and neoplasia. Although the rate of anterior K-wire breach is low, the technique requires the acquisition of a new set of skills including the safe passage of a K-wire, and knowledge of potential complications that may ensue.

Retrospective computed tomography scan analysis of percutaneously inserted pedicle screws for posterior transpedicular stabilization of the thoracic and lumbar spine: accuracy and complication rates.

STUDY DESIGN: Retrospective clinical data analysis. OBJECTIVE: To investigate the misplacement rate and related clinical complications of percutaneous pedicle screw insertion in the thoracic and lumbar spine. SUMMARY OF BACKGROUND DATA: Percutaneous insertion of cannulated pedicle screws has been developed as a minimally invasive alternative to the open technique during instrumented fusion procedures of the thoraco-lumbar spine. The reported rate of screw misplacement using open techniques is well described, however data is lacking on the exact failure rate of the percutaneous technique. METHODS: A total of 424 percutaneously inserted pedicle screws from 2007 to 2010 were analyzed in 88 patients, from a single surgeon series (RJM). Axial reformatted computer tomographic images were examined by 2 independent observers and individual and consensus interpretation was obtained for each screw position. A simple grading system was used for assessment of screw accuracy--Grade 0: screw within cortex of pedicle; Grade 1: screw thread breach of wall of pedicle <2 mm; Grade 2: significant breach >2 mm with no neurological compromise; Grade 3: complication including pedicle fracture, anterior breach with neuro-vascular compromise, and lateral or medial breach with neurological sequelae. RESULTS: The indications for percutaneous pedicle screw insertion include: degenerative (78%), trauma (13%), tumour (8%), and infection (1%). Pedicle screws were inserted into level T4 to S1. The most common levels performed include L4 and L5 with the most common indication for surgery being an L4/5 spondylolisthesis. 383 out of 424 screws (90.3%) were placed in the cortical shell of the pedicle (Grade 0). Forty-one screws (9.7%) were misplaced from T4 to S1. Of these, the majority were Grade 1 pedicle violations (24 screws; 5.7%), with 15 Grade 2 violations (3.5%) and 2 Grade 3 violations (0.5%). Of the 2 Grade 3 pedicle violations, both were pedicle fractures but only 1 had associated neurological deficit (L4 radiculopathy postoperatively). CONCLUSION: Percutaneous insertion of cannulated pedicle screws in the thoracic and lumbar spine is an acceptable technique with a low complication rate in experienced hands. The overall rate of perforation is below the higher rates reported in the literature for the open technique. Complication rates including pedicle fracture were low.