An In-Vitro Evaluation of the Initial Stability of Cementless Pressfit Hip Stems using Injectable HA Bone Substitute

INTRODUCTION Stability of a cementless press-fit total hip arthroplasty is essential for osteointegration and long-term success of the implant. Areas of noncontact between the bone and implant (gaps) may reduce the initial stability of the resulting construct. Gaps occur naturally and as a result of surgical preparation. Better initial fixation is desired to improve long term clinical results. Hydroxyapatite (HA) bone substitutes have been used in conjunction with orthopaedic implants because of their osetoinductive and osteoconductive properties as well as their biocompatibility and mechanical properties. We proposed the use of an injectable HA bone substitute to eliminate the gaps created at the bone/implant surface. This will theoretically increase surface contact area between the implant and HA/bone and ultimately improve initial stability of the implant. This theory was tested by measuring interfacial micromotion of an orthopaedic cementless hip stem implanted into a composite femur both with and without an injectable HA bone substitute. A physiological loading profile consisting of axial and cyclic torsional loading was implemented.