Pharmacological agents and bone healing.

Osteoporosis is the most common alteration of bone metabolism. It derives from an increase in bone resorption with respect to bone formation and is characterized by microarchitectural alterations, decreased bone mass and increased risk of fracture. The coupling between bone formation and resorption is a fundamental concept in skeletal metabolism, and it explains how a certain amount of removed tissue can be replaced by the same amount of new bone. Various substances used to treat osteoporosis may also be used for orthopaedic conditions such as fracture healing, implant fixation, bone grafts and osteonecrosis. Fracture healing consists in the replacement of the lost bone by a tissue that has the same biomechanical properties as those preceding the fracture. The repair process is triggered by the local response to the tissue injury that damaged the continuity of bone. The duration of each phase of the healing process can vary significantly, depending on the site and characteristics of the fracture, on patient related factors and on the treatment choice. While most of the fractures heal with conventional treatment, they can also cause permanent damage and complications, especially in a certain kind of patients. Osteoporosis and old age may contribute in delaying or impairing the reparative process. In animal models the healing process is slower in older and/or ovariectomized animals. Biomechanical tests have also shown that bone strength is compromised in human osteoporotic cadaver bone. The same problems were highlighted in the surgical treatment of fractures in osteoporotic patients. Mainly in the treatment of hip fractures there is an increased risk of cut-out, re-fractures and implant failure in patients with osteoporosis. Preclinical studies have shown that certain pharmacological agents (bisphosphonates, strontium ranelate, teriparatide) may enhance osseointegration and stimulate reparative processes. They may be administered systemically and/or used locally at the fracture site on the implant surface. The aim of fracture treatment is to restore bone biomechanical properties and to allow restoring normal function at the affected site. If the new pharmacological approaches could be translated into clinical benefit and offered to patients with osteoporosis or other factors that put at risk the process of healing (subjects with severe loss of substance or fractures at high risk of complications), they could represent a valuable aid in the treatment of fractures.