Abstract
Objective The aim of this study was to develop an in vitro biomechanical protocol for canine cementless hip arthroplasty that represents physiological
gait loading (compression and torsion) and to evaluate if three alternative implant
designs improve fixation compared with the traditional collarless, tapered stem in
the clinically challenging case of moderate canal flare index.
Study Design Twenty-four (six/group) laboratory-prepared canine constructs were tested using a
simulated gait and overload (failure) protocol. Construct stiffness, failure load/displacement
and migration were measured as outcome variables.
Results Simulated gait loading did not show any significant differences between implant types
for peak displacement, peak rotation, torsional stiffness, subsidence or inducible
displacement. The collared and collarless stem groups were stiffer in compression
compared with the collarless with a lateral bolt and short-stem groups. Increasing
the loading above simulated gait showed significant reductions in compressive and
torsional stiffness for all implant constructs. Despite the reductions, the short-stem
group showed significantly higher stiffness compared with the other three groups.
Conclusion Peak failure loads (compressive and torsional) in this study were approximately four
to seven times the simulated gait loading (430 N, 1.6 Nm) regardless of implant type
and highlight the importance of limiting activity level (trotting, jumping) following
hip replacement in the postoperative period and during the osseointegration of the
implant.
Keywords
hip - arthroplasty - implant fixation - biomechanical performance of implants - gait
mechanics - simulated gait loading - dogs
