Initial rotational stability of distal tibial fractures nailed without proximal locking: the importance of fracture type and degree of cortical contact.

Although distally locked (dynamic) nailing is generally recommended for fractures below the isthmus of the tibia in the presence of adequate proximal nail-bone contact, rotational stability in the above situation appears to be a major concern and can increase the risk of malunion. However, there is no published experimental evidence to quantify this mechanical parameter or to relate factors such as the fracture pattern with the final clinical outcome. This in-vitro biomechanical experimental study was set out to measure the initial rotational stability of dynamically nailed fractures of the distal tibial diaphysis. Using a composite tibial model, three non-comminuted types (spiral, oblique and transverse) and various comminuted patterns (comminution, 0-85%) of dynamically nailed fractures of the distal tibial diaphysis were tested. Using a special rig to simultaneously apply axial and torsional loading measurements of torsional stiffness and the previously described "spring-back angle" were carried out. Our results showed that in terms of torsional stiffness and the "spring-back" angle oblique fractures are the most stable followed by transverse and spiral fractures. Furthermore, when testing of the above parameters against the degree of comminution was carried out, a significant reduction of rotational stability was evident with comminution of 50% or above. It is concluded that oblique fractures of the distal tibial third that can be reduced with at least 50% cortical apposition present the optimal rotational stability following dynamic nailing.