Bone Fractures and Internal Fixation

The challenge of fractures through the ages has been how to manage the severe pain, immediate disability and long term sequelae of these acutely presenting emergencies, making broken bones clear priorities due to the large number of incidences. The variety of fracture treatments includes traction, joint replacement, immobilisation, amputation and internal fixation. Open fractures with significant soft tissue injury and damage were and remain at risk of infection which was commonly treated with amputation in the past. Lister, who pioneered immunisation, developed the ideas of the open reduction of patella fractures and their internal fixation.

In the 1880s and 1890s the use of plates, screws and wires was introduced but was compromised by infection, implant design, allergy to the metals and a poor understanding of the biology underlying fracture healing. The techniques and principles of fracture fixation developed in the 1950s and more recent scientific advancement in mechanical and biological understanding of fractures and their healing have led to modern methods of assessing, managing and fixing fractures.

The fracture cuts the supply of blood running through the periosteum, the membrane surrounding the bone, and that through the bone itself. The circulation needs to be adequately maintained for good fracture healing. Bone repair is described as having four stages, inflammation, formation of soft callus, formation of hard callus and remodelling. Inflammation is indicated by redness, heat, swelling and pain, with the bleeding which follows a fracture forming a local haematoma at the site. New blood vessel formation and cell multiplication is aided by inward migration 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.

Once the internal fixation of the fracture has been applied, the technique used will determine which way the fracture will heal due to the mechanical environment provided. If the operative fixation provides for some fracture movement and does not stabilise the fracture completely then healing with secondary or indirect healing will be the result. If the fixation provides for very little movement between the fragments and therefore a highly stable site, direct or primary healing will be the result.

Wire and Pin Fixation

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.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapists, physiotherapy, Physiotherapists in Coventry, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK