Excimer lasers have been demonstrated to provide a very precise and circumscribed ablation of synthetic polymers and biological tissues. We investigated in vitro the use of ultrashort pulsed ultraviolet excimer-laser energy for controlled removal of meniscus cartilage under the aspects of arthroscopic meniscectomy. A krypton-fluorine gas mixture was used to achieve laser emission of 248-nm wavelength. A total of 22 human menisci obtained either by operation or necropsy were irradiated over a range of energy fluence (2.15-3.07 J/cm2/pulse), repetition rates (5-20 Hz), and exposure time (15-60s). Ablation rates of 4.00-5.76 microns per pulse were obtained. Light-microscopic examinations demonstrated tissue ablation without any evidence of pathological changes associated with continuous-wave laser irradiation. Effects of laser energy were clearly limited to the target of the laser beam, and tissue removal proceeded without production of heat or smoke. Due to the lack of pathological alterations observed, excimer-laser irradiation of meniscus cartilage may prove to be advantageous for precisely cutting and removing menisci without injury to the surrounding normal tissue. Clinical application of excimer-laser irradiation includes the development of suitable fiberoptics and laser coupling, as well as modification of fiber tips.
From general physical laws simple formulae have been deduced from which the rigidity of an external fixation unit mounted in different ways becomes mathematically calculable. Furthermore, the stability of various mounting systems under bending forces was investigated experimentally. Particular attention was paid to details of operating technique which are of special importance to the stability of the whole construction. The calculated data are consistent with the mechanical test results. The best arrangement of the Steinmann pins and Schanz screws is discussed, and how to mount the frame optimally, depending on the specific type and location of the fracture. Special instructions concerning the mounting of the external fixation unit are given which, depending on the specific circumstances, guarantee optimum stability of the unit.
Due to the increasing popularity of unilateral dynamizable external fixators for treating tibial shaft fractures, many new devices are being introduced onto the market. Especially in such half-frame fixators, the choice of any particular device depends above all on the stability of its construction. This study compares the biomechanical stability of three systems tested in axial compression, torsion, and both anterior-posterior and medial-lateral bending. In terms of the nondynamized phase, the AO/ASIF tubular fixator (as a one-plane, double-tube, unilateral frame) and the Martin Mono-Dynafix are, in general, less stable than the Orthofix fixator. After dynamization, the AO/ASIF system becomes particularly weak and offers low resistance especially to torque and any force that is perpendicular to the plane of assembly. The other two tested devices evinced much more stability; the Orthofix fixator seems superior to the Dynafix due to the different diameter of its screws.
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