Long Bone Fractures and Healing (3/3)
The second type of healing is the external bridging callus. It is initiated often with the primary callus response. This type of healing is also known as the 'natural' one , where callus is formed on the outside of the bone. Its major function is to join and immobilise the moving fragments of the bone. Healing by external bridging callus is tolerant of slight fracture motion, which can be achieved using external skeletal fixation. However, total rigidity at the fracture may lead to suppression of this type of healing. The success is highly dependent on the blood supply from surrounding tissues, as oxygen supply to the fracture site is one of the primary factors influencing successful union of the bone. External bridging callus, like primary callus formation, will not continue indefinitely unless the fracture is bridged. Once satisfactory bridging is achieved, the remodelling of the bone, stage 6, is initiated. Unwanted bone is removed and the geometry of the bone is restored to best effect.
Under conditions of higher stability, late medullary callus formation, the third type of healing, can be initiated. It is a slow process principally but not exclusively initiated from the intermediary cavity of the bone. In some cases, it follows failure of the external bridging callus formation. The unique properties of this type of healing are relative independence from mechanical influences and ability to replace fibrous tissues with new bone tissues.
In the case of extreme mechanical rigidity at the fracture site, primary cortical healing takes place. It is the slowest healing process of all four. During this type of healing, bone union is achieved by direct osteonal penetration. Normally, this healing process is supported by the medullary callus activity.
Since each fracture environment can differ significantly and undergo various mechanical stabilities, more than one type of healing may occur simultaneously or in sequence. The next section describes factors influencing the success and speed of bone fraction treatment.Discuss this article, in our forum.
Bone fracture and healing references
1. McKibbin B. The biology of fracture healing in long bones. Journal of Bone & Joint Surgery - British Volume, 1978. 60-B(2): p. 150-62.
2. Kenneth J and Koval MD. Orthopaedic Knowledge Update 7: Home Study Syllabus. 1st ed. 2002, New York: Amer Acad of Orthopaedic Surgeons.
3. McKellop H, Hoffmann R, Sarmiento A, and Ebramzadeh E. Control of motion of tibial fractures with use of a functional brace or an external fixator. A study of cadavera with use of a magnetic motion sensor. Journal of Bone & Joint Surgery - American Volume, 1993. 75(7): p. 1019-25.