Effects of instability on bone healing. Femoral osteotomies studied in rats

Instability was induced in transversally osteotomized rat femora by means of intramedullary nails with various degrees of interlocking. Osteotomies that were stably pinned healed with less callus than those unstably pinned; no differences were found between rotational stable and unstable pinned osteotomies. Mechanical testing revealed that osteotomies treated by rotational stability and axial telescoping healed better than stably fixed and rotational unstable osteotomies. No differences were found between osteotomies treated by rotational instability and rigidily fixed fractures. We conclude that instability favors fracture healing as compared to rigidity. However, rotational instability in addition to telescoping impairs callus formation.