STRENGTH RECOVERY IN FRACTURED SHEEP TIBIA TREATED WITH A PLATE OR ANINTERNAL FIXATOR - AN EXPERIMENTAL-STUDY WITH A 2-YEAR FOLLOW-UP

Objectives: Comparison of fracture healing with two different implants : a conventional Dynamic Compression Plate (DCP) and a new internal Po int Contact Fixator (PC-Fix). Design: Randomized prospective study in experimental animals. Observation times: 12, 24, 48 and 96 weeks, with six sheep per group. Setting: Following surgery, animals were kept wi th unrestricted weight-bearing in individual stalls for 12 weeks, ther eafter in groups. Animals: 56 adult Swiss mountain sheep. Intervention : a standardized oblique fracture of the sheep tibia was reduced and c ompressed by a lag screw and ''neutralized'' with one of the implants. Main Outcome Measurements: Standard radiographs were used for callus size measurements. After sacrifice the implant uas removed and both th e treated bone and the contralateral bone were tested for static stren gth in bending with the plate side under tension. Broken bones were pr ocessed for histological evaluation. Results: In the DCP group all six bones failed through the original fracture at 12 weeks. At 24 and 48 weeks two out of six, at 96 weeks one out of six bones failed through the original fracture, others through one of the screw holes. In the P C-Fix group there were no failures through the original fracture with a single exception at 96 weeks. The strength values in the PC-Fix grou ps of 12 and 96 weeks were significantly higher then in the correspond ing DCP groups.Conclusions: Healing of simple diaphysial fractures tre ated by PC-Fix was superior to that achieved by conventional plating. The histological evaluation suggested that the observed differences ca n be accounted for by the absence of implant-related cortical necrosis and by the circumferentially uninterrupted (if smaller) callus in the PC-Fix group.