[Biomechanical study of the initial stability of various arthrodesis methods for the upper ankle joint]

Arthrodesis of the ankle joint is commonly, performed to treat severe arthritis. Three different techniques have been biomechanically evaluated for initial stability: fusion with three isolated tibio-talar lag screws (type I), which was inaugurated by Wagner; a second fusion technique with two isolated tibio-talar lag screws and an anterior tibio-talar three-hole 3.5 mm AO compression plate (type II); and type-II fusion with an additional lag screw through the center hole of the anterior plate (type III). Ten fresh cadaver ankles were used for biomechanical evaluation. Bone stock quality was compared before fusion by CT scan and osteodensitometry. Osteopenic ankle joints (bone density less than 80% of the median density) were excluded. Each ankle fusion was stressed with 15 Nm in a universal testing machine (UTS 10, Ulm, Germany) in antero-posterior and medio-lateral directions and in a rotational torque technique. The movements at the fusion gap were recorded by computer-assisted image analysis. A video camera recorded the displacement of four active markers on both sides of the fusion line during loading in real time. A computer-assisted calculation of the dislocation at the fusion gap was performed. This technique provides comparable results except for systemic failure induced by the fixation device of the testing machine. The results revealed comparable initial stability with types I (0.063 mm/Nm) and III (0.074 mm/Nm; P = 0.95) ankle fusion. Type-II fusion was significantly less favorable concerning initial stability (0.14 mm/Nm; P < 0.01, Duncan's test for multiple comparisons). Our biomechanical results advertise isolated lag screws for ankle fusion.