A quantitative assessment of compression plate fixation in vivo: An experimental study using the sheep radius

Abstract

Commercial 6-hole dynamic compression plates (DCP's) and instrumented 4-hole DCP's were fixed to the tension (cranial) surface of intact and osteotomised radii in sheep. Strain gauges were attached to the cranial and caudal surfaces of the intact radius on one side, and in similar locations underneath and opposite the plate on the contralateral side. Recordings were taken of the static strain changes imposed at the time of plate fixation, the decline in static strain in the plate over the experimental period, and the locomotor strains on bone and measuring plates. Recordings indicated a decline in the initial static plate tension from 711 N to 382.5 N after 21 days. The peak plate load during walking was an additional tension of 402 N which, by 8 weeks, rose to 520 N. Over the 8-week post-operative period the longitudinal locomotor strain on the bone increased from 17 to 29% of normal, beneath the plate and 71 to 95% of normal on the opposite cortex. After plate removal at 21 weeks locomotor strain on the cranial cortex was 17% higher than normal, and within 14 days it had been restored to normal. All areas of the bones to which plates has been attached were more porotic than their contralateral pair.