Deformation across the zone of callotasis during loading. Radiostereometric analysis in a patient with achondroplasia

The present study demonstrates that high-resolution radiostereometric analy sis (RSA) can be used to assess global longitudinal compressive deformation across the callotasis zone during loading. In an achondroplastic patient o perated with bifocal lengthening of the tibia by use of the Ilizarov extern al fixator, the axial compressive intersegmental strain in the proximal len gthening zone under a load of 71% of body weight was 7.7 mm. The proximal l engthening zone was 51.0 mm, and accordingly the overall linear strain acro ss the callotasis was 15.1%. This large strain value found in distraction o steogenesis 6 weeks after end of distraction is not consistent with classic al theory of the magnitude of micromotion needed for adequate stimulation o f bone formation in fracture healing. The increased axial displacement did not stimulate bone healing and delayed union was observed. This one single observation does not allow for any conclusions to be drawn about the relati onship of strain to fracture healing, but further and refined use of the RS A method will certainly improve our understanding of the role of axial stra ins in distraction osteogenesis. (C) 2001 Orthopaedic Research Society. Pub lished by Elsevier Science Ltd. All rights reserved.