OTA 1998 Posters

LISS - The Less Invasive Stabilization System for Metaphyseal Fractures of Femur and Tibia

Robert Schavan, MSC; Robert Frigg; Markus Hehli, AO Development Institute, Switzerland

Internal fixation with plates and screws applied in accordance with AO techniques has led to an improvement in fracture treatment with regard to the restoration of full function to the injured limb and the mobilization of the patient. Although the majority of fractures heal without complication, infection and refracture do occur. Today we understand these complications as the result of invasive operative techniques which damage the blood supply to the bone, delay fracture healing, and increase the risk of infection. Indirect reduction techniques, implants with minimal contact to the bone, developments in internal fixators, and further developments in the area of intramedullary devices are the product of this knowledge. In recent years, a new type of bridging osteosynthesis has evolved using a plate which is inserted between the muscles and the periosteum.

An extramedullary internal fixator has been developed to meet the demands of the new scientific findings and new operative techniques. Its main features are minimal bone contact and atraumatic insertion technique. The unicortical, self-drilling, and self-tapping screws with angular stability offer optimal anchorage in the bone. The specifically designed anatomical shape of the internal fixator means that intraoperative contouring to fit the bone is unnecessary. The screws can be inserted with the aid of a corresponding insertion guide once the internal fixator has been positioned supraperiosteally by means of minimally invasive technique. The angle of the screws and the shape of the fixator were designed in anatomical studies and assessed on approximately 50 pairs of bones and against their CT data. Comparative biomechanical tests using standard implants indicated similar stability.

The internal fixator presented here has been applied in over 130 cases by means of a less invasive operative technique in the treatment of fractures to the distal femur (33 A1 - C3). The application of the implant has shown itself to be straightforward. Excellent results in osteopenic and periprosthetic distal femur fractures show that the LISS is a valid concept to optimize fixation stability.

The internal fixator inserted supraperiosteally in bridging technique can be regarded as an extramedullary splint similar to the intramedullary nail. Indications include metaphyseal and intra-articular fractures in the polytraumatized patient and those with concomitant cranio-cerebral trauma. Complex fractures demand a good understanding of indirect reduction techniques.