Alternative approach for the removal of problem miniscrews--a serendipitous finding.
1 Removal of devices used for osteosynthesis can be difficult t times, particularly when there is a degree of osseointegraion, the wrong kit is used, or the head of the screw has become amaged.1 During one such procedure we were attempting to remove miniplate from the infraorbital margin in a patient having secondary operation after repair abroad. Initial attempts to emove the screws using our “universal screwdriver kit” were ot successful, and eventually damage to the heads of two crews prevented the screwdriver being engaged securely. As an alternative we decided to drill the bone circumferntially, and use a clip to grasp the head – a commonly used, nd a tried and tested technique, although others have been escribed.2 However, unknown to us the drill motor was set in everse and when applied, the Toller fissure burr engaged the rst screw with enough frictional torque to remove it easily Fig. 1). The second screw was removed in a similar way by placing he burr directly over it to maximise grip. It also came out ith relative ease. The technique has now worked on several ccasions and is a conservative way of removing problem
Removal of broken screws using a hollow rubber tube (Nelaton catheter).
mplant removal is controversial, and not without omplications.1 Our policy is that unless the manoeure is difficult and invasive, the screw should be removed o avoid later complications such as dehiscence, infection, nd palpation, sometimes reflecting the patient’s subjective iscomfort often provoked by cold. We also think that it s not until the normal structural dynamics of bone are chieved that the treatment of a fracture ends, because the xation devices in situ will be foreign bodies and potential ources of secondary problems in future. Because of excessive torque during removal, surgeons ften encounter stripping of the head of the screw and breakge at the neck, particularly when long screws have been used r the implant has been in place for some time. We therefore eed a recovery strategy for removal of the retained broken crew. The conventional method involves excavating the bone round the screw with a burr, holding it with pliers, and turnng repeatedly. This, however, does not always recover the crew and often makes it worse, because it wears the thread idge from the screw, sometimes making the axial surface hine as if it were polished. If this happens, the more that the urgeon tries to twist with pliers, the less the frictional force etween the screw and the pliers. We present a new way to emove the retained screw by increasing the frictional force etween the screw and pliers. Instead of using rubber-grip liers we have covered the screw with rubber. A man fractured the symphysis of his mandible in a road raffic crash. It was reduced and fixed using a Lock plate with screws (Compact Lock Mandible, Synthes, Davos, Switzerand), one of which was 11 mm long, and three 13 mm long.
Mechanics of deformable directed surfaces
Abstract The paper develops a simple, yet complete and consistent non-linear dynamic thermo-elastic shell theory based on the concepts of a two-dimensional directed continuum. The constitutive equations are postulated in a general form. Stress-strain relations are derived using the equation of energy balance and the two entropy production inequalities, which are rewritten in a special form. The linear theory is discussed in detail. The structure of the stress-strain relations is presented in the most general form and then specialized to concrete examples, in particular, to the classical shell theory, using their invariance properties with respective to certain symmetry groups. The elastic moduli are determined by demanding the coincidence of the frequency dispersion surfaces obtained using the two-dimensional theory with the lowest foils of the corresponding surfaces resulting from the three-dimensional theory of elasticity.