Local Osteo-Enhancement Procedure with a Triphasic Calcium Based Implant Increases FEA-Estimated Proximal Femur Strength in Osteoporotic Women at 5 – 7 Years

Introduction:

Hip fragility fractures are costly, catastrophic, and are associated with high mortality rates. One treatment to lower hip fracture risk uses a minimally-invasive local osteo-enhancement procedure (LOEP) to deliver a novel triphasic calcium sulfate/calcium phosphate implant material (AGN1) into the proximal femur, with the intent of increasing femoral strength by regenerating bone lost due to osteoporosis. The purpose of this study was to evaluate the Finite Element Analysis (FEA) estimated femoral strength of postmenopausal osteoporotic women treated with the procedure.

Methods:

One proximal femur from each of 12 post-menopausal osteoporotic women was treated with AGN1 LOEP and the non-treated femurs served as the control. CT scans were taken preoperatively and at 12 weeks (N = 12), 24 weeks (N = 12), and an average of 315 weeks (5 – 7 years) (N = 10). Patient-specific, non-linear FEA was conducted to non-invasively estimate hip strength in simulated sideways fall and stance loading conditions (O.N. Diagnostics, Berkeley, CA). A scale factor was applied assuming either 100% (α= 1.0) or, conservatively, 30% (α= 0.30) of new tissue performed as normal, load-bearing bone.

Results:

Mean patient age was 72 years old (range 56 – 89). At baseline, T-scores of the treated and control hips were identical (-3.1 ± 0.5 and -3.0 ± 0.7). Regardless of assumed scale factor, femoral strength in sideways fall was substantially higher in treated than in control hips. At 12 weeks, hip strength increased by 63 ± 32% (α= 1.00) and 45 ± 30% (α= 0.30) (p < 0.01). At 24 weeks, hip strength increased by 58 ± 27% (α= 1.00) and 40 ± 25% (α= 0.30) (p < 0.01). At 315 weeks, hip strength increased by 37 ± 15% (α= 1.00) and 23 ± 15% (α= 0.30) (p < 0.01). Stance loading effects were statistically significant across all time points with α= 1.00 only (p < 0.01). Mechanistically, at early time points newly formed bone adjacent to the implant area provided additional pathways for load transfer. At 315 weeks, the analysis suggests there is new integrated load-bearing bone within the treatment region.

Discussion:

These results suggest that AGN1 LOEP treatment of the proximal femur in osteoporotic women can substantially increase proximal femoral strength for sideways fall and this benefit is apparent soon after treatment and persists for at least 5 – 7 years.