MECHANICAL CONSEQUENCES OF CORE DRILLING AND BONE-GRAFTING ON OSTEONECROSIS OF THE FEMORAL-HEAD

We employed an anatomically realistic three-dimensional finite-element model to explore several biomechanical variables involved in coring or bone-grafting of a segmentally necrotic femoral head. The mechanical efficacy of several variants of these procedures was indexed in terms of their alteration of the stress:strength ratio in at-risk necrotic cancellous bone. For coring alone, the associated structural compromise was generally modest, provided that the tract did not extend near the subchondral plate. Cortical bone-grafting was potentially of great structural benefit for femoral heads in which the graft penetrated deeply into the superocentral or lateral aspect of the lesion, ideally with abutment against the subchondral plate. By contrast, central or lateral grafts that stopped well short of the subchondral plate were contraindicated biomechanically because they caused marked elevations in stress on the necrotic cancellous bone. Calculated levels of stress were relatively insensitive to variations in the diameter of the graft. CLINICAL RELEVANCE: Preservation of the natural femoral head in the presence of osteonecrosis depends on avoidance of collapse of structurally incompetent necrotic cancellous bone. Coring and cortical bone-grafting both alter the distribution of mechanical stress in the necrotic femoral head. The alterations in stress depend on the location, diameter, and degree of penetration of the core or graft tract. Intraoperatively, there is usually substantial latitude for placement of the tract, but the associated effects on mechanical stresses in the head are not well understood. This finite-element model provides a systematic means to study such influences and identifies several technical factors that bear on the biomechanical efficacy of these head-preserving procedures.