Eight weeks post-surgery, rabbits were subjected to a densitometry to the vertebral column and tibia bone to verify the establishment of osteoporosis model. For the densitometric analysis, a Norland XR-26 densitometer was used (Norland Co., Fort Atkinson, WI, USA) calibrated prior to the measurement. The exploration parameters were as follows: speed 40 mm s⁻¹, resolution 1.0 × 1.0 mm, and measurement resolution 0.5 × 0.5 mm. Forty percent of the total length of each bone was analyzed, including metaphysis and diaphysis regions to verify differences between bone mass of healthy and osteoporotic groups. The value obtained was the bone mineral density (BMD) in grammes per centimetre.

Implant procedure. Surgery

The experimental design carried out with the experimental animals is summarized in Fig. 1. Rabbits were randomly divided into two groups: control (healthy rabbits) and OVX (osteoporotic rabbits). Both of them were subjected to surgery to insert commercial (no thermally treated Ti6Al4V) and modified (thermally treated Ti6Al4V) implants. The half of the healthy and osteoporotic rabbits was treated with 4 IU of recombinant human growth hormone (rhGH) as lyophilized powder (Genotonorm® Pfizer, NY, USA) directly located in the place of insertion. Healthy and osteoporotic rabbits without implants were also included as reference at both implantation times in the study.

Incision was performed in the inner side of the proximal epiphysis of each tibia, under intramuscular anaesthesia. Transcortical osteotomy followed by drilling to generate a bed of 3.1 mm diameter and 8 mm deep was made, where the implant was inserted until touching the opposite cortical bone (Fig. 2). In the experimental group with local GH, 4 IU of rhGH as powder was added into the bone hole just before the insertion of the Ti6Al4V implant. Commercial implant in the right tibia and the modified implant in the left tibia were inserted. Only one implant was inserted in each tibia.