A Hydroxyapatite Graft Substitute Reduces Subsidence in a Femoral Impaction Grafting Model

Abstract

Synthetic bone graft substitutes have been developed for impaction grafting revision hip surgery in response to concerns about the availability and potential infection risk of allograft. We performed an in vitro experiment to determine whether a synthetic porous hydroxyapatite material might improve resistance to cumulative subsidence and cyclic (elastic) movement on loading. We impacted different ratios of hydroxyapatite and allograft (0%, 50%, 70%, and 90% hydroxyapatite) into composite femoral models (eight per group) and implanted tapered, polished stems with cement. Models were loaded for 18,000 cycles on a servohydraulic materials testing machine. Migration of the femoral prostheses and the distal cement was determined using radiostereometric analysis, and cyclic movement was measured mechanically by the testing machine. Hydroxyapatite decreased overall subsidence and subsidence at the prosthesis-cement interface, but there was no difference at the cement-femur interface. This decrease may have occurred because the hydroxyapatite-containing graft was more rigid, or because it resulted in a thicker cement mantle. Cyclic prosthesis movement also was lower with hydroxyapatite. While the biologic response to porous hydroxyapatite remains to be determined, its mechanical properties appear promising.

In Vitro Testing of Femoral Impaction Grafting With Porous Titanium Particles: A Pilot Study

“…The distal migration of the Exeter™ stem relative to the Sawbones ® femurs was in line with other in vitro studies. In two recent studies similar to our experiment, Exeter™ stems were used in combination with the impaction grafting technique [ 30 , 44 ]. In one study, subsidence values of 0.44 mm and 0.13 mm were observed after 18,000 cycles for reconstructions with only bone chips and reconstructions that contained allografts and hydroxyapatite graft extenders, respectively [ 30 ].…”

“…In two recent studies similar to our experiment, Exeter™ stems were used in combination with the impaction grafting technique [ 30 , 44 ]. In one study, subsidence values of 0.44 mm and 0.13 mm were observed after 18,000 cycles for reconstructions with only bone chips and reconstructions that contained allografts and hydroxyapatite graft extenders, respectively [ 30 ]. The other study had subsidence values of 2.31 mm and 0.99 mm after 10,000 loading cycles for reconstructions with pure allografts and reconstructions with a mix of allografts and hydroxyapatite graft extenders, respectively [ 44 ].…”

Impaction grafting with a bone-graft substitute in a sheep model of revision hip replacement

“…Stem subsidence can occur through failure of the cement and the graft at interfaces between these materials and the stem or cortex. Munro et al 14 performed an experiment in vitro to investigate whether increasing ratios of a synthetic porous HA material might also improve resistance to cumulative subsidence and cyclical movement on loading compared to 100% allograft in impaction grafting of the femur. Their results demonstrated that subsidence at the prosthesis-cement mantle and cyclical movement both significantly decreased with the addition of HA.…”

Minimum 10 years clinical and radiological outcomes of acetabular revisions of total hip arthroplasties with tricalcium phosphate/hydroxyapatite bone graft substitute

“…TCP/HA particles mixed with bone grafts showed better stability than bone grafts alone. Similar results of mechanical engineering testing as well as animal model were presented of femoral reconstructions with the use of TCP/HA bone graft substitutes [ 11 , 21 ]. The papers presenting outcomes of bone grafts substitutes used in bone stock reconstruction during revision hip arthroplasty differ in relation to the type of material used and include as follows: xenograft [ 22 , 23 ], glass ionomer ceramics [ 9 ], corraline derived hydroxyapatite [ 24 ], calcium sulphate [ 18 , 25 ], HA [ 7 , 26 – 28 ], TCP [ 7 , 29 ] and TCP/HA [ 10 , 30 – 34 ].…”

“…Biphasic granules of TCP/HA have pores whose size has been revealed to be optimal for osteoconduction. TCP/HA granules are manufactured in particulate form with harder consistency than morsellized allograft to withstand impaction grafting forces and enhance the initial stability of the implant [ 10 , 20 , 21 , 36 ]. TCP/HA particles are slowly replaced by host bone [ 34 ].…”