The effects of necrotic lesion size and orientation of the femoral component on stress alterations in the proximal femur in hip resurfacing - a finite element simulation

Abstract

BackgroundDue to the advantages of its bone-conserving nature, hip resurface arthroplasty (HRA) has recently gained the interest of orthopedic surgeons for the treatment of young and active patients who have osteonerosis of the femoral head. However, in long-term follow-up studies after HRA, narrowing of the femoral neck has often been found, which may lead to fracture. This phenomenon has been attributed to the stress alteration (stress shielding). Studies addressing the effects of necrotic size and the orientation of the implant on stress alterations are lacking.MethodsComputed tomography images of a standard composite femur were used to create a three-dimensional finite-element (FE) intact femur model. Based on the intact model, FE models simulating four different levels of necrotic regions (0°, 60°, 100°, 115°) and three different implant insertion angles (varus 10°, neutral, valgus 10°) were created. The von Mises stress distributions and the displacement of the stem tip of each model were analyzed and compared for loading conditions that simulated a single-legged stance.ResultsStress shielding occurred at the femoral neck after HRA. More severe stress shielding and an increased displacement of the stem tip were found for femoral heads that had a wider necrotic lesion. From a biomechanics perspective, the results were consistent with clinical evidence of femoral neck narrowing after HRA. In addition, a varus orientation of the implant resulted in a larger displacement of the stem tip, which could lead to an increased risk of implant loosening.ConclusionsA femoral head with a wide necrotic lesion combined with a varus orientation of the prosthesis increases the risk of femoral neck narrowing and implant loosening following HRA.

Hip Resurfacing Arthroplasty after Failure of Tantalum Rod Insertion in Patients with Osteonecrosis of the Femoral Head

“…Another advantage of resurfacing arthroplasty is that the previously inserted rod is maintained, providing mechanical support to the femoral component by filling the bone defect and securing stability of the femoral component. The remaining tantalum rod provides mechanical support to the femoral neck; therefore, it is expected that its presence will reduce the risk of femoral neck fracture, a common complication associated with HRA 3 28) .…”

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

“…Here, we used boundary conditions which produce physiological deflection of the femoral head under demanding loading conditions since it has been previously shown that the use of non‐physiological boundary conditions produced non‐physiological deflections of the femur and altered the strain patterns on the cortex . Along the same line, many of the FE studies investigating strains within the femur only take into account two bone material properties, namely cortical and cancellous bone. Because Taddei et al showed that the use of heterogeneous material properties has a significant influence on the predicted bone tissue strains, our computer models satisfy this requirement using patient‐specific material distributions obtained from patient‐specific CT‐scan data.…”

A Pilot Experiment to Measure the Initial Mechanical Stability of the Femoral Head Implant in a Cadaveric Model of Osteonecrosis of Femoral Head Involving up to 50% of the Remaining Femoral Head

“…Both hemi-resurfacing arthroplasty and HRA are potentially advantageous in preserving bone and the loading of the proximal femur, lowering a risk of dislocation and eliminating the polyethylene debris that may cause osteolysis as compared with conventional THA [ 30 , 33 , 34 ]. Consequently, HRA is considered an appropriate option for young and active patients with ONFH [ 35 ].…”