Two processes of bone remodeling in plated intact femora: an experimental study in dogs

Bone loss is known to occur under plates used for internal fixation. Its exact location and extent and its relationship to the plate-bone contact area was investigated in 36 adult beagles. Plates with two different contact areas were fixed unilaterally to intact femora for periods of 8 and 24 weeks. After removal, the bones were assessed radiographically, histologically, histomorphometrically, and biomechanically. Two processes that affect the bone after plating became apparent. One is a short-term process, possibly caused by the interference of the plate with the blood supply to the cortex. This is followed by necrosis, which induces porosis. The second independent process is caused by the tendency of the bone to adapt to the new state of mechanical loads that results from the load sharing by the plate. The first stage of this process is expressed through swift changes in the bone cross-sectional area under the plate by remodeling in all three envelopes: haversian, periosteal, and endosteal. This stage is followed by a gradual remodeling towards a steady state, in which the final cross-section of the bone is attained. Both processes affected the bone simultaneously during plate fixation. The process caused by the vascular interference ceases after some time, and only the process due to stress-shielding prevails for a long period.