Straight-nosed pipefish Nerophis ophidion and broad-nosed pipefish Syngnathus typhle avoid eelgrass overgrown with filamentous algae.

In a habitat choice experiment straight-nosed pipefish Nerophis ophidion and broad-nosed pipefish Syngnathus typhle avoided eelgrass Zostera marina covered with filamentous algae. Both juveniles as well as brooding adult males of the two species clearly preferred to position themselves in Z. marina without growth of filamentous algae.

Spinal canal remodelling after stabilization of thoracolumbar burst fractures.

Spinal canal areas were measured prospectively in 22 consecutive burst fractures of the thoracolumbar junction, preoperatively, within 1 week postoperatively and 1 year after operation. Preoperative canal encroachment averaged 38% (range 10%-70%) of the estimated original area. The 11 patients with neurological impairment had a significantly more severe initial canal encroachment (mean 48%) than those who were neurologically intact (mean 33%). Postoperatively, canal encroachment had decreased to a mean of 18% (range 0%-62%). Within 12 to 15 months postoperatively, canal encroachment was further reduced by resorption of bone fragments to a mean of 2%. The largest observed remaining encroachment was 29%. The amount of bone resorption correlated significantly with the persistent postoperative encroachment. A critical appraisal of the methods used to assess the pre-fracture canal area revealed that reconstructing the vertebral foramen of the fractured vertebra on CT scans substantially overrated the original area as compared with averaging the canal area of the two adjacent vertebrae.

CT analysis of pedicles and screw tracts after implant removal in thoracolumbar fractures.

Twenty-one burst fractures of the thoracolumbar junction were stabilized with a transpedicular fixator by surgeons experienced in this technique. Screws 5 or 6 mm in diameter were used. After the removal of the device 1 year postsurgery, axial CT scans were obtained of the instrumented vertebrae. Eighty-two pedicles were examined. In 16 pedicles, medial or lateral cortical defects were found. Five screws had intruded into the spinal canal by a maximum of 3.5 mm. In 48 pedicles a correlative comparison with the preoperative examinations was possible. Compared with the dimensions of the pedicles on the preoperative CT scans, 31 had increased in width, and 14 showed deformation indicative of fractures of the lateral pedicle wall. When the screw diameter exceeded 65% of the pedicles' outer diameter, 85% of the pedicles expanded. One of four screws had penetrated the anterior wall of the vertebra. Pedicle screw penetration on the left side above L2 poses potential risk of erosion of the aorta. The use of pedicle screws at the thoracolumbar junction by experienced surgeons carries some risk for malplacement and neurological damage. Mismatch between pedicle dimension and screw size results in pedicle expansion and lateral wall fractures, probably during screw insertion. Preoperative CT examinations should be used to help in choosing appropriate screw diameter presurgery.