Decreased intramuscular calcium hydroxyapatite implant resorption in a murine model of osteoporosis

Objective: Calcium hydroxyapatite (CaHA) is a common material for vocal fold injection augmentation. Durability is variable, and factors involved in implant longevity are not understood. Animal models of osteoporosis show decreased bone density and increased mineral liberation, suggesting CaHA retention may be altered in these conditions. Study Design: Prospective murine investigation. Methods: Fourteen skeletally mature, 10-month-old female Sprague-Dewley rats were treated by one of three interventions: oophorectomy, laparotomy without oophorectomy (sham), or monthly risedronate injection (90 μg/kg, subcutaneous). CaHA was implanted into the right lateral thigh muscle in all animals at the time of procedure or first risedronate injection. After 17 weeks, all rats were sacrificed, and the residual CaHA isolated from excised lateral thigh muscle through incubation in a 900 °C calcinator for 9 hours. Results: Mean CaHA mass remaining in the oophorectomy group was 65.9 (standard deviation ± 16.1) mg, compared to 44.4 ± 10.0 mg CaHA in the risedronate group and 48.6 ± 7.5 mg in the sham group. One-way analysis of variance found a statistically significant difference between the oophorectomy and risedronate groups but not between the sham and other groups, F(2,11) = 4.404, P = 0.039. Conclusion: Persistent estrogen deficiency in a murine model of osteoporosis demonstrated decreased rate of CaHA resorption. This suggests that hormone alterations associated with osteoporosis may alter the longevity of CaHA implant resorption through an uncertain mechanism. Level of Evidence: NA. Laryngoscope, 2576–2580, 2018.