Fixing an Internal Bone Fracture

                                                                                         

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.

Using plates, wires and screws to fix fractures was introduced in the 1880s and 1890s but there were difficulties with design of the implants, infection, metal allergies and an inadequate knowledge of the background fracture healing biology. The 1950s saw a more advanced development of the principles and techniques of the fixation of bone fractures and modern scientific research has promoted the modern assessment, fixation and management of bone 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

The inflammatory phase is followed by the haematoma around the fracture site being infiltrated by fibrous tissue and cells which secrete cartilage, called chondroblasts. This material is more stable than the blood clot and begins the process of gradual stabilisation. Steadily the soft callus is converted into rigid bone, the hard callus phase, by conversion of the cartilage to bone and bone formation below the periosteum. Once the connection between the fracture fragments is more solid the fracture is said to have united and then it proceeds to remodelling where it becomes mature or lacunar bone.

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 surgeon's decisions about which form of internal fixation to use for a particular fracture determines the method of fracture healing which occurs at the operated site. If a high level of stability is provided, with little or no movement at the fracture, then primary or direct bone healing will occur with remodelling. If a lower degree of stability and more potential movement is present at the fracture the healing will be secondary or indirect bone repair.

Types of Fixation - Pins and Wires

Fracture fixation involves a number of different pieces of equipment which covers nails, screws, wires and plates, with the surgeon choosing them in regard to the type and location of fracture. Most simple is the use of wires and pins, typically called after the names of the surgeons who introduced them into practice. Thin wires, from 0.6 to 3 millimetres in diameter, are known as K-wires after Kirschner, with pins from 3-6 millimetres referred to as Steinmann pins. Wires have no significant stiffness and are bent easily so are usually used to add to the stability of other fixation methods. Early fracture stabilisation can also be performed by using these objects initially while more definitive fixation is planned later.

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

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