Injection of a Triphasic Calcium-Based Implant into Cadaveric Proximal Femurs Provides Immediate Biomechanical Improvement

Introduction:

Current osteoporosis pharmaceutical therapies reduce fracture risk. Yet compliance is poor and efficacy is seen only after up to 18 months. New approaches to reduce hip fracture risk are needed. One approach is local enhancement at sites weakened by osteoporotic bone loss, such as the proximal femur. This study evaluated the biomechanics of cadaveric femurs following a local-osteo enhancement procedure (LOEP) to inject a resorbable triphasic calcium-based implant material (AGN1) within the proximal femur.

Methods:

45 pairs of fresh frozen, female, cadaveric femurs were obtained from anatomic gift registries. One femur from each matched pair was treated with LOEP and the other served as an untreated control. Femoral neck and total hip aBMD (g/cm2) and sex-specific T-scores were obtained by DXA. Under fluoroscopy a 5.3 mm lateral entry portal was created in the femur. The proximal femur was manually debrided to loosen fat and marrow elements which were removed via irrigation and suction. AGN1 was then injected into the site under low-pressure. Distribution of AGN1 was assessed using CT. Femurs were mechanically tested in sideways fall configuration (10 ° adduction and 15 ° internal rotation) 24 ± 3 hours following the injection. Failure load, work to failure, and stiffness were calculated from force displacement data. Comparisons were made using a paired t-test, with p-value < 0.05 considered significant.

Results:

Average donor (N = 45) age was 77.8 ± 8.8 years with an average T-Score of -2.8 ± 1.3. CT imaging showed consistent distribution of AGN1 in the femoral neck and intertrochanteric region. For all specimens, femurs injected with AGN1 had a 20.5% higher failure load (p < 0.0001) compared to the paired controls. Cadaveric femurs were stratified by femoral T-score into normal femurs (N = 4), osteopenic (N = 16), and osteoporotic (N = 45). Osteopenic femurs injected with AGN1 increased failure load 20.6% (p = 0.00035). Similarly, work to failure increased 17.4% compared to control femurs (p = 0.047). Osteoporotic femurs injected with AGN1 had increased failure load 26.0% (p = 0.00005), yield load 24.8% (p = 0.0001), and work to failure 44.6% (p = 0.0004) compared to control femurs. Normal femurs treated with AGN1 showed no significant differences in any tested variables. AGN1 treatment did not significantly affect femoral stiffness in any group.

Discussion:

In osteopenic and osteoporotic cadaveric femurs, failure load and work-to-failure increased significantly with the injection of AGN1 when tested in a sideways fall scenario. These findings provide evidence that the local treatment of osteoporosis with AGN1 is technically feasible and provides immediate biomechanical improvement. Local osteo-enhancement of the proximal femur with AGN1 is a promising treatment to improve biomechanical properties that warrants further investigation.

Fig. 1: Failure load (A) and work to failure (B) from all femurs and femurs stratified by T-score. Significant increases (p < 0.05) were observed in both osteopenic and osteoporotic groups.