Primary and long-term stability of a short-stem hip implant

Abstract

The new generation short-stem hip implants are designed to encourage physiological-like loading, to minimize stress-strain shielding and therefore implant loosening in the long term. As yet there are no long-term clinical studies available to prove the benefits of these short-stem implants. Owing to this lack of clinical data, numerical simulation may be used as a predictor of longer term behaviour. This finite element study predicted both the primary stability and long-term stability of a short-stem implant. The primary implant stability was evaluated in terms of interface micromotion. This study found primary stability to fall within the critical threshold for osseointegration to occur. Longer term stability was evaluated using a strain-adaptive bone remodelling algorithm to predict the long-term behaviour of the bone in terms of bone mineral density (BMD) changes. No BMD loss was observed in the classical Gruen zones 1 and 7 and bone remodelling patterns were comparable with hip resurfacing results in the literature.

Determination of remodeling parameters for a strain-adaptive finite element model of the distal ulna

“…14,16 Moving forward, this model will be used to evaluate the impact of stress shielding caused by orthopedic implants on the density distribution in the distal ulna, allowing for better informed orthopedic design decisions. …”

Strain shielding inspired re‐design of proximal femoral stems for total hip arthroplasty

“…A 175% increase in the current number of patients undergoing total hip replacements (THR) is expected in the next 15 years in the United States . While the implant design problem is much more complex than 20 years ago because of longer life expectancy, increasingly complex demands in terms of loading conditions and more active lifestyle, loss of bone stock caused by remodeling as well as revision surgery is becoming an increasing concern …”

“…The implantation of a hip prosthesis significantly alters the internal mechanical conditions within the femur and leads to a periprosthetic bone remodeling response . Bone loss was found especially in the proximal Gruen zones, which are critical for primary implant stability as well as long‐term stability . An alteration of bone mineral density (BMD) in the proximal region of up to −23% after 3 years has been reported for proximally anchoring implant designs .…”

“…Ideally, short stem implants should keep a physiological load transfer, withstand torsional as well as axial loads and any micro‐movement to fast primary fixation and secondary bone anchorage; therefore, the bone stock surrounding an implanted femoral stem would not diminish due to remodeling if the mechanical environment at the proximal femur that closely resembles the intact state is determined . However, that does not seem to be the case with current short stem designs since many studies have reported significant bone loss for patients with short stems . In addition, optimization algorithms have been previously used to analyze the remodeling response of several long stem hip implant designs .…”

Reproducing the Hip Center With a Femoral Neck-Retaining Implant

“…9,10 Bone-preserving procedures include hip resurfacing, 11 and shorter metaphyseal stems may allow a more normal proximal femoral strain pattern while leaving more bone stock for a subsequent revision procedure if necessary. [12][13][14][15] The Metha Short Hip System (Aesculap AG, Tuttlingen, Germany), a metaphyseal femoral neck-retaining short hip stem, was introduced into the market in 2004 and has since been implanted in more than 50,000 patients, with several studies reporting good short-to mid-term clinical results. [16][17][18][19] Unlike many other stems, this design is a true metaphyseal stem based on previous short stem designs.…”