Initial Stability of Two Different Hip Revision Concepts. A Biomechanical Study

Two fundamentally different revision concepts, a standard stem cemented in a bed of firmly impacted morselized bone graft, and an uncemented long stem implanted with proximal bone grafting, were compared in terms of initial stability under torsional load immediately after implantation. A stem cemented without bone graft was used as a baseline reference. The stems were implanted in identically prepared composite femora inclined at 45° and loaded vertically. During 9 individual tests of each concept, the stems displaced into retroversion with no detectable axial displacement. At a load of 1000 N the average displacement in retroversion of the prosthetic head was 3.9° ± 2.6° for the uncemented long stem and 9.1° ± 2.6° for the stem cemented in impacted morselized bone graft (P < 0.001). Both revision concepts displaced rather dramatically compared to the stem cemented without bone grafting. The magnitude of displacement may indicate insufficient initial rotational stability of both concepts particularly with the stem cemented in impacted morselized bonegraft.