- causes a compression or depression fracture
3)
.
- causes a transverse or a greenstick fracture
4)
(twist)
- causes a spiral fracture
Any combination of these forces may be involved in the formation a single fracture. As bone is loaded, it absorbs energy, when the load is released the energy escapes causing the bone to fracture. The higher the loading velocity, the greater the damage seen at the site of fracture. This means that fractures occurring at high speeds or when jumping result in greater injury to the bone and surrounding tissue.
Fracture Healing Bone is capable of
, therefore it can return to its original structure and
physical properties after injury.
Factors affecting bone repair include age, hormones nerve function, nutrition, systemic disease, degree of trauma, angiogenesis, bone loss, displacement of the fracture edges, ability to immobilize the fracture site, and contamination and infection of the area of injury. Fracture healing occurs in three stages. The first stage is inflammation, the second stage is repair and the third stage is remodelling. Inflammation occurs immediately after injury and can last for two to three weeks. Inflammation occurs in response to the haemorrhage, hypoxia, acidosis & tissue necrosis that occurs at the site of fracture. Inflammation is critical for the repair phase to occur. Without inflammation repair cannot be achieved. During the inflammation stage the typical vascular and cellular inflammatory responses are seen. If inflammation is excessive the repair may be abnormal or delayed.
Repair occurs from two weeks to twelve months post injury. It begins with
and callus formation. The periosteal callus, or external callus, is made of
mesenchymal cells, fibroblasts, macrophages and blood vessels that form a cartilaginous “bridge” across the fracture gap along the external surface of the bone. The periosteal callus is covered by the new periosteum. Overtime the cartilage is replaced by woven bone. The primary function of the external callus is to the fracture, as movement at the fracture site causes the deposition of fibrous tissue and may cause a hypertrophic non-union of the fracture ends. The endosteal callus, or internal callus, is woven bone formed directly into the fracture gap. It is responsible for the actual repair of the bone. Woven bone is used as for Haversian remodelling to occur during the remodelling stage. Angiogenesis into fracture site and the debridement of necrotic tissue also occurs during the repair stage.
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