Tibial lengthening apparatus with distractive force measurement system

Abstract A tibial lengthening apparatus has been developed which incorporates a distractive force measurement system. Lengthening is carried out generally in accordance with the 2-stage Anderson method. After closed percutaneous osteoclosis (clinically performed fracture), the tibial fragments are held in place by Steinmann pins and novel Steinmann pin-clamping blocks to ensure rigid fixation and accurate alignement. The blocks provide electrical insulation between the patient and the apparatus and are able to accommodate different sizes of Steinmann pins and misalignment of the pins as a result of their insertion in the tibia by drilling. A metric distraction mechanism provides controlled lengthening and the distractive force is sensed by two transducers, each consisting of an aluminium ring to which are bonded electrical resistance strain gauges in a full bridge configuration. Electronic instrumentation is used to process the transducer signals and the resulting force readings are displayed on a digital panel meter as well as being recorded on a digital printer.