Abstract
Fracture bending stiffness of 15 Nm/° measured in the sagittal plane provides an objective end-point for healing in tibial fractures treated with external fixation (1). Fracture stiffness in other planes has been shown to be significantly different (2). A method for measuring three-dimensional fracture stiffness has been developed (3) and refined. This study describes the results of omni-planar stiffness measurements.
A series of omniplanar fracture stiffness measurements were undertaken on patients with tibial fractures treated by external fixation. The first measurements were performed when the fracture was deemed sufficiently stiff to allow the fixator to be removed safely. These were continued at regular intervals until union, defined as a uniplanar stiffness of greater than 15Nm/° in at least two planes.
Polar stiffness plots were obtained and analysed. The stiffness envelope varied significantly in all planes but the general shape of the polar plot remained the same with successive tests, with an overall increase in stiffness. The polar stiffness measurements were significantly different than concurrent uniplanar measurements; this reflects the difficulty in defining the plane of bending accurately in uniplanar measurements. The fracture configuration and healing fibula had unpredictable effects on the polar stiffness.
The measurement of polar fracture stiffness polar gives new insight into how the mechanical environment of a fracture changes during healing. Fracture stiffness is not uniform and this may have implications on when it is safe to remove the fixator.
Abstracts prepared by Dr P E Watkins, Hodgkin Building, Guys Campus, King’s College London.
1 Richardson et al.(1994) J Bone Joint Surg [B]77: 389–94. Google Scholar
2 Wade et al. (2001) J Bone Joint Surg [B]83: 533–5. Google Scholar
3 Wade et al. (2000) J Bone Joint Surg [B]82 (Supp III). Google Scholar
