Intrinsic passive stiffness of 2 constructs of varus proximal femoral osteotomy: external fixator or blade plate.

Background: Despite the published clinical evidence of the implementation of external fixation of proximal femoral osteotomies, there is lack of specific laboratory justification.

Methods: Two groups of 5 adult composite femur constructs of varus proximal femoral osteotomy were tested under incremental and cyclical loading of up to 600N along the mechanical axis. Five were fixed with a blade plate and another 5 with a monolateral external fixator. Load versus displacement curves were produced, and passive stiffness of all constructs was calculated. The described loading regime aimed to simulate the initial postoperative state and provide data for the assessment of vertical intrinsic passive stiffness in partial weight-bearing conditions.

Results: Although the blade plate constructs showed higher average stiffness, this was not statistically significant [F(1,8)=1.712, P=0.23]. No construct failed. No failure or plastic deformation was observed under the described loading regime.

Conclusions: Vertical intrinsic passive stiffness in partial weight-bearing conditions during the initial postoperative period can be considered satisfactory subsequent to unilateral external fixation of a varus intertrochanteric osteotomy.

Clinical Relevance: The results support the hypothesis that external fixation is a biomechanically sound alternative to internal fixation of varus intertrochanteric osteotomies, in selected patients.