Saline injection technique to confirm pedicle screw path: a cadaveric study.

Pedicle screws are frequently misdirected during placement, which may lead to complications such as pedicle fracture, inadequate biomechanical strength, and neurologic deficit. Roentgenographic confirmation and manual probing are important but are not 100% accurate. We have developed a simple saline injection technique to assist in confirming the correct path of the pedicle screw prior to its insertion. In this study, five fresh frozen cadaveric spines were dissected from T-12 to L-5, and a total of 60 data points were recorded. Saline injection tests confirmed 31 of 32 (97%) drill paths that were in the pedicles. Two specimens were used to intentionally misdirect the pedicle drill path to determine the rate of false-negative results. Pedicle drilling was misdirected medially, laterally, superiorly, and and inferiorly (six of each). There were a total of 24 intentional and four unintentional, radiographically confirmed missed drillings of the pedicle. Of the 28 misdirected pedicle paths, the saline injection test correctly diagnosed the problem in 23 (82%) cases. Seven misdirected drillings were falsely negative by the injection test (five superior and two inferior directions). This study shows that a simple saline injection test can be a useful adjunct in confirming a correct pedicle path in 97% of the cases. If an incorrect path has been created, false-negative tests are possible in 18% of the cases.

Routine predeposit of autologous blood is not warranted before breast reduction surgery.

OBJECTIVE: To assess perioperative blood losses and transfusion requirements in patients who undergo breast reduction surgery and to gauge the impact of an autologous blood program on homologous transfusion requirements. DESIGN: A chart review of patients who underwent breast reduction surgery between 1988 and 1992. SETTING: The Ottawa General Hospital, a teaching hospital with a surgical training program but with no plastic surgery program. PATIENTS: Included in the review were all 153 patients who had breast reduction surgery during the study period. Twenty patients were excluded because either the predonation or the final hemoglobin concentration was not available. The remaining 133 patients were divided into three groups: group 1--patients who had not predonated blood (63); group 2--patients who predonated blood and received a transfusion (55); and group 3--patients who had predonated blood but did not receive a transfusion (15). MAIN OUTCOME MEASURES: The mean final hemoglobin concentrations, the number of patients who lost more than 30 g/L of hemoglobin and the requirements for homologous transfusions. RESULTS: The rate of homologous transfusion was 1% whether the patients had predonated blood or not. If a more restricted pattern of transfusion been used this rate would have been lower. The final hemoglobin concentration was similar in all three groups. More patients in group 3 (60%) lost more than 30 g/L of hemoglobin compared with the initial hemoglobin value than either group 1 (23%) or group 2 (20%) (p < 0.01). CONCLUSION: The routine inclusion in autologous blood programs of patients scheduled to undergo breast reduction surgery is not warranted.

Modification of transmitter release by ions which prolong the presynaptic action potential.

1. The action of ions which increase the nerve spike duration at Ranvier's node has been studied at the neuromuscular junction of the frog.The duration of the presynaptic action potential is increased by UO(2), Ni, Nz and TEA ions.2. The release of transmitter after a nerve impulse is delayed and prolonged in the presence of the four ions, but the amount of evoked transmitter release estimated from the mean quantal content of e.p.p. is increased only by UO(2) (2+) and TEA. Both Ni(2+) and Zn(2+) decrease it.3. The frequency of m.e.p.p.s is increased by UO(2) (2+) and decreased by Ni(2+) and Zn(2+) at KCl-depolarized junctions. It is not affected by TEA.4. It has been concluded that the increased presynaptic spike duration is responsible for the delayed and prolonged transmitter release in the presence of ions which increase the nerve spike duration at Ranvier's node. It is demonstrated that some ;specific' effects possibly resulting from ionic competition for presynaptic sites between UO(2) (2+), Ni(2+) or Zn(2+) and other ions present in the Ringer may increase, interfere with, or hide the increased transmitter release that may be predicted from the lengthened presynaptic depolarization.