Cervical transfacet versus lateral mass screws: a biomechanical comparison.

The authors directly the compared biomechanical pullout strength of screws placed in the cervical lateral masses to that of screws placed across the facet joints. Posterior cervical fixation with lateral mass plates is an accepted adjunctive technique for cervical spine fusions. Altered anatomy resulting from congenital malformation, tumor, trauma, infection, or failed lateral mass fixation may limit traditional screw placement options. Transfacet screw placement, which has been studied extensively in the lumbar spine, may offer an alternative when posterior cervical fusion is required. Ten fresh human cadaveric cervical spines (postmortem age range, 69 to 91 years) were harvested. On one side, transfacet screws were placed at the C3-4, C5-6, and C7-T1 levels. On the other side, lateral mass screws were placed at the C3, C5, and C7 levels. The screw insertion technique at each level was randomized for right or left. After screw placement, each set of vertebral bodies were dissected and mounted in a custom jig for axial pullout testing using a servohydraulic testing machine. The load-displacement curves were obtained for each screw pullout. The mean pullout strength for the screws placed across the facets was 467 N (range, 192 to 1,176 N). This compares with 360 N (range, 194 to 750 N) for the lateral mass screws (p = 0.008). At each level, transfacet screws exhibited greater pullout resistance compared with the lateral mass placement, but the difference was most pronounced at the C7-T1 level (lateral mass = 373 N, transfacet = 539 N, p = 0.042). Cervical transfacet screw placement provides pullout resistance that is comparable to, if not greater than, lateral mass placement. This type of placement, although technically difficult, may be an alternative to lateral mass screws in cases with unusual anatomy, stripped screws, or when additional intermediate points of fixation are desired.

No influence of large volume blood loss on serum vancomycin concentrations during orthopedic procedures.

We prospectively studied orthopedic patients with either large or small blood loss who also received vancomycin prophylaxis to determine the effect of intraoperative volume shifts on serum vancomycin concentrations. There were 6 index patients in the large blood loss group (greater than 2 L), and 7 in the control group (less than 2 L). Mean estimated blood loss for index and controls was 4.4 L and 1.0 L, respectively. Mean intraoperative fluid resuscitation, excluding blood products, was 12.4 L and 5.1 L, respectively. There was a modest inverse correlation between blood loss and intraoperative serum half-life of vancomycin. Although controls maintained slightly higher intraoperative vancomycin concentrations at each time-point, there was no statistically significant difference between the groups with regard to absolute concentrations or rate of decline. After 8 hours, the serum vancomycin concentration exceeded the MIC-90 for Staphylococcus aureus by approximately eightfold in all but one case patient. This was a morbidly obese patient with massive blood loss. Thus, blood loss during orthopedic procedures has minimal effects on intraoperative kinetics of vancomycin. Redosing is rarely indicated, although a preoperative 1.5 gram-dose should be considered for patients weighing more than 90 kg.

Paravertebral inflammation mistaken for neoplasm or abscess by MRI.

Magnetic resonance imaging (MRI) is a useful procedure for the evaluation of spinal pathology in children. The high sensitivity of soft tissue changes may lead to misinterpretation of paravertebral swelling caused by inflammation. We present a report of three patients with paravertebral soft tissue swelling caused by disk space infection or intervertebral disk space calcification. The findings shown by MRI were initially interpreted as neoplasm or abscess, which led to surgical procedures either planned or done. Surgeons need to exercise extreme care when interpreting soft tissue changes shown by MRI.