The Effects of Interlocking a Universal Hip Cementless Stem on Implant Subsidence and Mechanical Properties of Cadaveric Canine Femora

Abstract

ObjectiveTo determine if an interlocking bolt would limit subsidence of the biological fixation universal hip (BFX®) femoral stem under cyclic loading and enhance construct stiffness, yield, and failure properties.Study DesignEx vivo biomechanical study.AnimalsCadaveric canine femora (10 pairs).MethodsPaired femora implanted with a traditional stem or an interlocking stem (constructs) were cyclically loaded at walk, trot, and gallop loads while implant and bone motions were captured using kinematic markers and high‐speed video. Constructs were then loaded to failure to evaluate failure mechanical properties.ResultsImplant subsidence was greater (P = .037) for the traditional implant (4.19 mm) than the interlocking implant (0.78 mm) only after gallop cyclic loading, and cumulatively after walk, trot, and gallop cyclic loads (5.20 mm vs. 1.28 mm, P = .038). Yield and failure loads were greater (P = .029 and .002, respectively) for the interlocking stem construct (1155 N and 2337 N) than the traditional stem construct (816 N and 1405 N). Version angle change after cyclic loading was greater (P = .020) for the traditional implant (3.89 degrees) than for the interlocking implant (0.16 degrees), whereas stem varus displacement at failure was greater (P = .008) for the interlocking implant (1.5 degrees) than the traditional implant (0.17 degrees).ConclusionAddition of a stabilizing bolt enhanced construct stability and limited subsidence of a BFX® femoral stem. Use of the interlocking implant may decrease postoperative subsidence. However, in vivo effects of the interlocking bolt on osseointegration, bone remodeling, and stress shielding are unknown.

Comparison of femoral stem subsidence between three types of press‐fit cementless total hip replacement in dogs

“…In this study, subsidence was lower after implantation of BFX Lateral Bolt than after implantation of BFX Collared and traditional BFX in dogs treated with THR. The reduced subsidence was likely due to immediately increased construct stability provided by the bolt early in the postoperative period, prior to bone ingrowth . The authors expected that the BFX Collared would also be more resistant to subsidence compared with the traditional BFX, but this supposition was not supported by the results of this study because similar subsidence was identified between BFX Collared and traditional BFX.…”

“…The BFX EBM lateral bolt stem (BFX Lateral Bolt) is a recently developed femoral stem modification that incorporates a lateral bolt into the traditional BFX cementless stem. This lateral bolt stem accepts a stabilizing bolt that is threaded into the femoral stem from the lateral side and achieves angular stability via a conical coupling design . The lateral bolt stem was designed to make the stem more resistant to subsidence and rotation after THR .…”

“…This lateral bolt stem accepts a stabilizing bolt that is threaded into the femoral stem from the lateral side and achieves angular stability via a conical coupling design . The lateral bolt stem was designed to make the stem more resistant to subsidence and rotation after THR . An ex vivo cyclic loading study was performed to evaluate femoral stem subsidence with the BFX Lateral Bolt compared with the traditional BFX, and, in that study, the BFX Lateral Bolt was more resistant to subsidence associated with axial loading in an ex vivo setting compared with the traditional BFX …”

Total hip arthroplasty to address chronic hip luxation with pseudoacetabulum formation in seven dogs

“…Because of the retrospective nature of the study, there was variability in the implants used. All dogs were implanted with BioMedtrix BFX implants; however, newer modified versions of the BFX stems were used in some dogs, including the use of a BFX stem with lateral locking bolt in two dogs and a collared stem in another two dogs, both designed to help prevent stem subsidence (Table ) . The only stem complication (subsidence) noted was in a dog with a stem not specifically modified to help prevent subsidence.…”

“…All dogs were implanted with BioMedtrix BFX implants; however, newer modified versions of the BFX stems were used in some dogs, including the use of a BFX stem with lateral locking bolt in two dogs and a collared stem in another two dogs, both designed to help prevent stem subsidence (Table 1). 30,31 The only stem complication (subsidence) noted was in a dog with a stem not specifically modified to help prevent subsidence. Assessment of dogs with pseudoacetabulum treated by THA with no variability in implants used may give a truer reflection of the complication rate associated with these cases.…”