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Angular Stable Locking of Intramedullary Nails (ASLS)—a new system
Dankward Höntzsch
Angular Stable Locking of Intramedullary Nails (ASLS)—a new system Intramedullary nailing of the tibia, femur, and humerus is a long-standing traditional approach to surgical fracture treatment. An important advance in intramedullary nailing was the so-called locking technique. In intramedullary nailing the fracture fragments of the long bones are threaded onto a tubular or solid intramedullary nail and secured. Additional stabilization of the large fragments is generally achieved by transverse insertion of locking screws. This technique neutralizes rotational and tilting movements. Due to this development almost all fractures in the mid-4/5ths of the long bones could and can be treated by insertion of a locked intramedullary nail. Previous locking techniques meant that there was always a certain amount of free toggling between the screw and the nail. Experimental studies [1, 2] have shown that blocked locking would, in principle, be advantageous. In fact, in the area of plating systems, this has already been achieved in the form of so-called angular stable plates. Why? The question of why this development was needed is quickly answered: The existing technical solution was not entirely adequate. Residual looseness was disadvantageous to fracture healing and stability and imperfect in terms of patient symptoms, especially in osteoporotic bones weakened by age. The correct technical approach is angular stable locking. Solution In the meantime, this technique has been successfully introduced in the form of a new system known as angular stable locking system (ASLS) for nails, which is designed so that all the holes in the nail can be locked at a stable angle. Biomechanically, the angular stable locked nail has similar features to a locked plate including the more even load distribution over the nail, therefore decreasing individual stress raisers, reducing loosening of locking screws. The system has also been designed to enable the use of all existing intramedullary nails so that there is no need to invest in new nails. It is also possible to decide during surgery whether and which parts of the nail and/or which bone fragments should be combined with the nail at a stable angle, ie, locked in position. Fig 1 Intramedullary nail with angular stable locking screws.
The dowels are made of 70:30 poly(L-lactide-co-D,L-Lactide). No critical reaction has been reported so far. Resorbtion of the sleeve may lead