Chemical staining of particulate organic matter for improved contrast in soil X-ray µCT images

Degradability of organic matter (OM) in soil depends on its spatial location in the soil matrix. A recent breakthrough in 3D-localization of OM combined dual-energy X-ray CT-scanning with OsO₄ staining of OM. The necessity for synchrotron-based µCT and the use of highly toxic OsO₄ severely limit applications in soil biological experiments. Here, we evaluated the potential of alternative staining agents (silver nitrate, phosphomolybdenic acid (PMA), lead nitrate, lead acetate) to selectively enhance X-ray attenuation and contrast of OM in CT volumes of soils containing specific mineral soil particle fractions, obtained via lab-based X-ray µCT. In comparison with OsO₄, administration of Ag⁺ and Pb²⁺ resulted in insufficient contrast enhancement of OM versus fine silt (< 20 µm) or clay (< 2 µm) mineral particles. The perfusion procedure used in this work induced changes in soil structure. In contrast, PMA staining resulted in a selective increase of OM's attenuation contrast, which was comparable to OsO₄. However, OM discrimination from other soil phases remained a challenge. Further development of segmentation algorithms accounting for grey value patterns and shape of stained particulate OM may enable its automated identification. If successful in undisturbed soils, PMA staining may form an alternative to OsO₄ in non-synchrotron based POM detection.

Clinical value of routine preoperative magnetic resonance imaging in adolescent idiopathic scoliosis. A prospective study of three hundred and twenty-seven patients

BACKGROUND

The prevalence of intraspinal pathology associated with scoliosis has been reported to be as high as 26% in some series, and, on the basis of this finding, preoperative magnetic resonance imaging is used in the screening of patients with adolescent idiopathic scoliosis. However, this practice continues to be highly controversial. In order to better resolve this issue, we performed what we believe to be the largest prospective study to evaluate the need for preoperative magnetic resonance imaging in patients with adolescent idiopathic scoliosis requiring arthrodesis of the spine.

METHODS

A total of 327 consecutive patients with adolescent idiopathic scoliosis were evaluated between December 1991 and March 1999. All patients in the study presented with an adolescent idiopathic scoliosis curve pattern and had a complete physical and neurologic examination. Magnetic resonance imaging of the brain and the spinal cord were performed as part of their preoperative work-up.

RESULTS

Seven patients had an abnormality noted on magnetic resonance imaging. These abnormalities included a spinal cord syrinx in two patients (0.6%) and an Arnold-Chiari type-I malformation in four (1.2%). One patient had an abnormal fatty infiltration of the tenth thoracic vertebral body. No patient required neurosurgical intervention or additional work-up. All patients who underwent spinal arthrodesis with segmental instrumentation tolerated the surgery without any immediate or delayed neurologic sequelae.

CONCLUSIONS

The fact that magnetic resonance imaging did not detect any important pathology in the large number of patients in this study strongly suggests that magnetic resonance imaging is not indicated prior to arthrodesis of the spine in patients with an adolescent idiopathic scoliosis curve pattern and a normal physical and neurologic examination.

Autogenous bone grafting for severe angular deformity in total knee arthroplasty

Fourteen patients with severe angular knee deformities (range, 30 degrees varus to 35 degrees valgus) had total knee arthroplasty using autogenous bone graft to the tibia. Twelve knees had osteoarthritis, one rheumatoid arthritis, and one gouty arthritis. The preoperative knee motion averaged -5 degrees of extension to 80 degrees of flexion and the average motion arc was 70 degrees. All tibial defects were greater than 25% of the tibial component support surface and more than 10 mm deep. Twelve knees were reconstructed with Insall-Burstein posterior stabilized total condylar knee implants and two knees, with severe preoperative ligamentous instability, with the constrained Total Condylar III implant. Postoperative rehabilitation was routine, and weight bearing was begun, on average, on the third postoperative day. The follow-up period averaged 4.1 years (range, 2-7.3 years). Radiographic analysis revealed no change in knee or component alignment compared with immediate postoperative position. All grafts consolidated without evidence of collapse, resorption, or prosthetic subsidence. All patients had good or excellent clinical results (Hospital for Special Surgery Knee Rating Scale). The average postoperative arc of motion was 90 degrees. There were no infections and no need for implant removal. The technique developed by the senior author (T.P.S.) utilizes bone resected from the distal femur during knee arthroplasty. An oblique planar cancellous surface is created on the recipient side, and coaptation of cancellous distal femoral graft surface to this recipient bed is ensured by vitallium screw fixation. The proximal tibia is reconstituted by the graft, and subchondral femoral bone after shaping of the graft forms the tibial periphery.