with little shifting. Surgery Surgical methods of treating fractures have their own risks and benefits, but usually, surgery is performed only if conservative treatment has failed, is very likely to fail, or is likely to result in a poor functional outcome. With some fractures such as hip fractures (usually caused by osteoporosis), surgery is offered routinely because non-operative treatment results in prolonged immobilisation, which commonly results in complications including chest infections, pressure sores, deconditioning, deep vein thrombosis (DVT), and pulmonary embolism, which are more dangerous than surgery. When a joint surface is damaged by a fracture, surgery is also commonly recommended to make an accurate anatomical reduction and restore the smoothness of the joint. Infection is especially dangerous in bones, due to the recrudescent nature of bone infections. Bone tissue is predominantly extracellular matrix, rather than living cells, and the few blood vessels needed to support this low metabolism are only able to bring a limited number of immune cells to an injury to fight infection. For this reason, open fractures and osteotomies call for very careful antiseptic procedures and prophylactic use of antibiotics. Occasionally, bone grafting is used to treat a fracture. Sometimes bones are reinforced with metal. These implants must be designed and installed with care. Stress shielding occurs when plates or screws carry too large of a portion of the bone's load, causing atrophy. This problem is reduced, but not eliminated, by the use of low-modulus materials, including titanium and its alloys. The heat generated by the friction of installing hardware can accumulate easily and damage bone tissue, reducing the strength of the connections. If dissimilar metals are installed in contact with one another (i.e., a titanium plate with cobalt-chromium alloy or stainless steel screws), galvanic corrosion will result. The metal ions produced can damage the bone locally and may cause systemic effects as well. Other A Cochrane review of low-intensity pulsed ultrasound to speed healing in newly broken bones found insufficient evidence to justify routine use. Other reviews have found tentative evidence of benefit. It may be an alternative to surgery for established nonunions. Children In children, whose bones are still developing, there are risks of either a growth plate injury or a greenstick fracture. A greenstick fracture occurs due to mechanical failure on the tension side. That is since the bone is not so brittle as it would be in an adult, it does not