Thyroid hormones are important factors that regulate metabolism and cell differentiation throughout the human body. A complication of thyroid pathology is represented by an alteration of the bone metabolism which can lead to osteoporosis and fragility fractures, known to have a high mortality rate. Although there is a consensus on the negative impact of hyperthyroidism on bone metabolism, when referring to hypothyroidism, subclinical hypothyroidism, or subclinical hyperthyroidism, there is no general agreement. The aim of our review was to update clinicians and researchers about the current data regarding the bone health in hypothyroidism, subclinical hypothyroidism, and subclinical hyperthyroidism patients. Thyroid disorders have an important impact on bone metabolism and fracture risk, such that hyperthyroidism, hypothyroidism, and subclinical hyperthyroidism are associated with a decreased bone mineral density (BMD) and increased risk of fracture. Subclinical hypothyroidism, on the other hand, is not associated with osteoporosis or fragility fractures, and subclinical hyperthyroidism treatment with radioiodine could improve bone health.

Bone is a complex tissue with unique properties such as high strength and regeneration capabilities while carrying out multiple functions. Bone regeneration occurs both in physiological situations (bone turnover) and in pathological situations (e.g. fractures), being performed by osteoblasts and osteoclasts. If this process is inadequate, fracture nonunion or aseptic loosening of implants occurs and requires a complex treatment. Exogenous factors are currently used to increase bone regeneration process when needed, such as bisphosphonates and vitamin D, but limitations do exist. Cannabinoid system has been shown to have positive effects on bone metabolism. Cannabinoids at bone level mainly act on two receptors called CB-1 and CB-2, but GPR55, GPR119, TPRV1, TPRV4 receptors may also be involved. The CB-2 receptors are found in bone cells at higher levels compared to other receptors. Endocannabinods represented by anandamide and 2-arachidonoylglycerol, can stimulate osteoblast formation, bone formation and osteoclast activity. CB-2 agonists including HU-308, HU-433, JWH133, and JWH015 can stimulate osteoblast proliferation and activity, while CB-2 antagonists such as AM630 and SR144528 can inhibit osteoclast differentiation and function. CB-1 antagonist AM251 has been shown to inhibit osteoclast differentiation and activity, while GPR55 antagonist cannabidiol increases osteoblast activity and decreases osteoclast function. An optimal correlation of dose, duration, moment of action, and affinity can lead to an increased bone regeneration capacity, with important benefits in many pathological situations which involve bone tissue. As adverse reactions of cannabinoids have not been described in patients under controlled medication, cannabinoids can represent future treatment for bone regeneration.

Purpose: Bone consolidation after severe trauma is the most challenging task in orthopedic surgery. This study aimed to develop biomimetic composite for coating Ti implants. Afterwards, these implants were tested in vivo to assess bone consolidation in the absence or the presence of high-frequency pulsed electromagnetic short-waves (HF-PESW). Materials: Biomimetic coating was successfully developed using multi-substituted hydroxyapatite (ms-HAP) functionalized with collagen (ms-HAP/COL), embedded into poly-lactic acid (PLA) matrix (ms-HAP/COL@PLA), and subsequently covered with self-assembled COL layer (ms-HAP/COL@PLA/COL, named HAPc). Methods: For in vivo evaluation, 32 Wistar albino rats were used in four groups: control group (CG) with Ti implant; PESW group with Ti implant+HF-PESW; HAPc group with Ti implant coated with HAPc; HAPc+PESW group with Ti implant coated with HAPc+HF-PESW. Left femoral diaphysis was fractured and fixed intramedullary. From the first post-operative day, PESW and HAPc+PESW groups underwent HF-PESW stimulation for 14 consecutive days. Biomimetic coating was characterized by XRD, HR-TEM, SEM, EDX and AFM. Results: Osteogenic markers (ALP and osteocalcin) and micro-computed tomography (CT) analysis (especially bone volume/tissue volume ratio results) indicated at 2 weeks the following group order: HAPc+PESW>HAPc≈PESW (P>0.05) and HAPc+PESW>control (P<0.05), indicating the higher values in HAPc+PESW group compared to CG. The fracture-site bone strength showed, at 2 weeks, the highest average value in HAPc+PESW group. Moreover, histological analysis revealed the most abundant COL fibers assembled in dense bundles in HAPc-PESW group. At 8 weeks, micro-CT indicated higher values only in HAPc+PESW group vs CG (P<0.05), and histological results showed a complete-healed fracture in groups: HAPc+PESW, HAPc and PESW, but with more advanced bone remodeling in HAPc+PESW group. Conclusion: Using Ti implants coated by HAPc jointly with HF-PESW stimulation positively influenced the bone consolidation process, especially in its early phase, thus potentially providing a superior strategy for clinical applications.