Abstrakt
The main objective of this paper is to assess the change of callus diameter ratio observed 6 months and later after device removal and explain the modelling and increase of the diaphysis diameter. At Human Biomechanics 2008 we reported on relationship between the callus diameter ratio (CDR, %) during leg lengthening (by monolateral external fixation or original Ilizarov's rings) of Czech achondroplastic (ACH) patients with the aim to predict occurrence of late deformities or fractures.
We proved no fractures and angular deformities in cases where the CDR was higher than 85 %. Authors retrospectively reviewed 7 from original 14 elongated ACH patients (because of X-ray validity) and assessed the change of callus diameter ratio observed 6 months and later after device removal.
Patients and Methods. Retrospectively were reviewed 8 tibia and 5 femoral lengthening on both anteroposterior and lateral radiographs taken in the time of device removal and later.
The minimum diameter of the callus was measured using a ruler. The callus diameter ratio was calculated as the minimum callus diameter divided by original diaphysis diameter of the tibia/femur at the level of proximal osteotomy end.
Results. 6, 12 and 18 months after device removal we proved growth of CDR on 10-18 % at both anteroposterior and lateral X-ray projections in comparison with time of device removal. Conclusion.
The negative influence on the neoosteogenesis during leg lengthening results from undesirable shield effect (rigidity) of the external fixator. Simple axial loading of low intensity (due to external fixator) is not a sufficient mechanical impulse for restoration of the physiological geometry (shape) of diaphysis and biomechanical properties.
Unlimited axial loading, bending and torsion stresses after device removal are necessary for increase of the diaphysis diameter. We propose to call this modelling of diaphysis as "post-lengthening peripheral drift of corticalis".