Backscattering of Acoustic Signals from Inhomogenuities in Solids

Examination of the backscattering of ultrasonic waves has been suggested as a possible technique for the non-destructive evaluation of materials because it involves a simple measurement requiring access to a single surface only and because the conversion of normally incident, longitudinal waves to shear waves is minimal at a scattering angle of 180°. While the measurement is simple to carry out, the return signal may be quite complicated, especially for polycrystalline or composite materials. These materials possess local inhomogeneities of differing sizes,orientation and elastic properties from which a plane wave may scatter, often more than once, and then the scattered waves from one or more sources may interfere among themselves. These difficulties are often compounded by coupling among the several modes of propagation associated with inhomogeneity and lead to a dispersion of the incident wave. Thus the backscattered signal represents the complex, three-dimensional, phase sensetive scattering from a material that mat not be well characterized. While there has been substantial effort and much progress in developing techniques for the reconstruction of characteristics of the medium from the scattering of an acoustic wave an accurate prediction of the scattering from inhomogeneous and anisotropic medium, such as a composite material, remains a difficult problem. Generally speaking, our lack of a detailed knowledge of the structure of the medium over distances large enough to support a significant dispersal of the wave makes the development of a reliable model of the medium a formidible task

Description of the attachment geometry of the anteromedial and posterolateral bundles of the ACL from arthroscopic perspective for anatomical tunnel placement

The anterior cruciate ligament (ACL) consists of an anteromedial bundle (AMB) and a posterolateral bundle (PLB). A reconstruction restoring the functional two-bundled nature should be able to approximate normal ACL function better than the most commonly used single-bundle reconstructions. Accurate tunnel positioning is important, but difficult. The purpose of this study was to provide a geometric description of the centre of the attachments relative to arthroscopically visible landmarks. The AMB and PLB attachment sites in 35 dissected cadaver knees were measured with a 3D system, as were anatomical landmarks of femur and tibia. At the femur, the mean ACL centre is positioned 7.9 ± 1.4 mm (mean ± 1 SD) shallow, along the notch roof, from the most lateral over-the-top position at the posterior edge of the intercondylar notch and from that point 4.0 ± 1.3 mm from the notch roof, low on the surface of the lateral condyle wall. The mean AMB centre is at 7.2 ± 1.8 and 1.4 ± 1.7 mm, and the mean PLB centre at 8.8 ± 1.6 and 6.7 ± 2.0 mm. At the tibia, the mean ACL centre is positioned 5.1 ± 1.7 mm lateral of the medial tibial spine and from that point 9.8 ± 2.1 mm anterior. The mean AMB centre is at 3.0 ± 1.6 and 9.4 ± 2.2 mm, and the mean PLB centre at 7.2 ± 1.8 and 10.1 ± 2.1 mm. The ACL attachment geometry is well defined relative to arthroscopically visible landmarks with respect to the AMB and PLB. With simple guidelines for the surgeon, the attachments centres can be found during arthroscopic single-bundle or double-bundle reconstructions

Reconstructive versus non-reconstructive treatment of anterior cruciate ligament insufficiency. A retrospective matched-pair long-term follow-up

In this retrospective case series 80 patients divided in 40 matched pair groups with an arthroscopically proven ACL insufficiency were followed up for 15 years. One half was reconstructed using an autologous BTB patella graft, the other half was treated by a conservative physiotherapeutic based rehabilitation program. At follow-up the clinical scores (Lysholm, IKDC) showed no significant differences between subjects who had undergone ACL reconstruction and those who had not. Furthermore there was no detectable difference in the incidence of osteoarthritis between the cohorts. Patients having a negative pivot shift test showed significantly less signs of radiographic osteoarthritis and better functional assessment scores whether reconstructed or not. Based on these results and a review of the literature there is no clear evidence that ACL reconstruction reduces the rate of OA development or improves the long-term symptomatic outcome. Probably review of reconstruction by an anatomical approach will be more successful than operative techniques decades ago

Validation of the position of the femoral tunnels in anatomic double-bundle ACL reconstruction with 3-D CT scan

This study compares the positioning of femoral AM and PL tunnels obtained with specific ancillary instruments during anatomic double-bundle ACL reconstruction with the native ACL footprint using three-dimensional computed tomography (3-D CT). In 35 consecutive patients, anatomic double-bundle ACL reconstruction was performed with specific ancillary instruments. Three-dimensional CT reconstruction of both knees was performed using the volume rendering technique. In the controls (contralateral knee, with intact ACL), the angle between the longitudinal axis of the footprint and the axis of the femur, the "footprint angle" (FA) was measured. On the involved side, using the axis passing through the tunnel centers, FA was also measured. In both the groups, footprint's length and width, and distances to cartilage margins were measured. FA was 28.1A degrees A A +/- A 5.0A degrees in the controls and 32.9A degrees A A +/- A 15.8A degrees on the involved side (n.s.). There was no statistical difference between the two groups for the other morphometric parameters: footprint's length and width, and distances to cartilage margins. Using specific ancillary instruments the morphometric parameters of the reconstructed femoral ACL footprint were similar to the native ACL