Bone Fracture Internal Fixation
Broken bones have always been challenging to manage due to the severity of the acute disability, the level of the pain and the functionally important negative consequences which can ensue, ensuring fracture treatment an important place in medical care. Fracture treatments have included amputation, immobilisation, replacement, internal fixation and traction. Infection is and was a significant risk in open fractures which might have important soft tissue damage, typically managed in the past by amputation. The surgeon who developed immunisation, Lister, promoted the concept of openly reducing and internally fixing patellar fractures.
Fixing bone fractures moved forward in the 1880s and 1890s by the introduction of wires, screws and plates but their effectiveness was compromised by allergy to metal, infections, implant structure and a lack of knowledge about the natural processes of fracture healing. In the 1950s the fixation of bone fractures was improved by clear technical guidelines and principles of bone fracture fixation, with this developing into the modern management of fractures.
The blood supplies through the solid bone and that through the surrounding membrane are both disrupted by a fracture and good fracture healing depends on having an adequate blood supply. Inflammation, soft callus, hard callus and remodelling are the four stages of bone fracture repair and a fracture exhibits the cardinal signs of inflammation which include redness, swelling, pain and heat. When a bone fractures the area bleeds and collects as a haematoma at the site. New blood vessels form and cells multiply secondary to immigration of inflammatory cells.
The Repair Biology of Fractured Bone
Around the fracture site the inflammatory phase is succeeded by fibrous tissue and cartilage producing cells, gradually growing fibrous tissue into the haematoma. The blood clot becomes stiffer with these changes and this is the steady process of stabilising which occurs during bone healing. Soft callus is transformed into hard bone via the hard callus stage as the cartilage is changed into bone and bone forms under the bone membrane. The fracture is judged to be united once a solid connection forms between the fragments and then the bone develops into mature, lacunar bone via a process of remodelling.
The normal way which fractures heal involves transformation of fibrous bone to lamellar or mature bone, this process being known as secondary bone union or indirect fracture repair. If a fracture is not fixed rigidly and is displaced to some extent then in secondary healing it heals by forming callus at the site. If the fragments are realigned very closely and then fixed with metal fixation the biology of the healing bone is different as the stabilisation and close connection of the break reduces the stresses operating across it. The allows the bone to heal without going through the callus process as the bone cells grow directly across the fracture, ensuring healing provided than high stresses are not permitted to the break. This process is known as direct bone healing and primary bone union.
The mechanical environment which the surgeon creates by his choice of internal fixation for the particular pattern of the fracture dictates the kind of bone healing process which will follow. With virtually no movement between the fracture segments and high stability this will lead to direct or primary bone healing via the remodelling process. With a certain amount of movement allowed between the fragments the reduced stability means that indirect or secondary bone union occurs.
Fixation with Pins and Wires
Many devices are used for fixing fractures and these include screws, plates, nails and wires, the choice of which depends on the severity, position and type of fracture. The simplest types of fixation of fracture are the use of wires and pins and the most commonly used are indicated by the name of the surgeon who designed them. Steinmann pins are between three and six millimetres in diameter and K-wires (Kirschner wires) are between 0.6 and three millimetres in diameter. The lack of stiffness of a normal wire means that K-wires are easy to bend so are used as an adjunct to more secure fixation. They can be used to perform the initial fracture stabilisation while the more permanent fixation is being planned, without damaging the site.