Key Insights For Addressing Infected Hardware
- Volume 19 - Issue 8 - August 2006
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Screws, plates, staples, pins and wires are the hardware that the foot and ankle surgeon uses to fixate fractures, fusions and/or osteotomies. An infection involving hardware may jeopardize the bone healing process and is a precarious situation for both the patient and the surgeon. In some situations, the infection may be easily managed yet it can be limb threatening in other situations. Like any infection, early diagnosis is paramount.
Hardware is necessary to stabilize osseous segments until one achieves complete bone healing, a process that typically takes six to eight weeks. After that, the implants are theoretically unnecessary and one may remove them. Generally, most surgeons will not recommend hardware removal for at least six months after the index operation, mostly for soft tissue and bone remodeling purposes. However, when the hardware becomes infected, most attempts focus on immediate removal but this often depends on whether or not the underlying bone has healed.
The term “infected hardware” is often loosely used in clinical practice but is probably an inappropriate designation. The hardware, being an inanimate object, cannot become infected. Rather, it becomes coated with bacteria and may secondarily infect its associated bone.
Staphylococcus aureus and epidermidis are the most frequent infecting bacteria of orthopedic implants and prostheses, accounting for approximately 50 to 70 percent of infections.1 These bacteria adhere to the implant surface and produce an extracellular glycocalix (slime layer or biofilm) that protects the organism from antibiotics as well as the host immune responses.2 As a result, retained hardware that has been exposed to bacteria may become a nidus for persistent infection if it is not treated or removed.
How To Identify Infected Hardware
Identifying infected hardware may be a challenging task. In some situations, the diagnosis is straightforward. Subtle infections are frequently more difficult to diagnose and require a detailed workup, and the presence of infection may only be presumptive.
A thorough timeline detailing the clinical circumstances before and after hardware implantation is crucial. Hardware may become hematogenously infected so one should investigate any bacteremic episode, such as recent dental procedures, upper respiratory or urinary tract infections.3 In stable joint prosthesis, a Staphylococcus aureus bactermia has been associated with a 34 percent implant infection rate.4 In particular, intravenous drug users may be at risk for a hematogenous spread of infections. Patients who are biologically or pharmacologically immunocompromised are theoretically susceptible as well. A septic joint adjacent to retained hardware may secondarily seed the hardware.
Any information from the patient history that may help identify the infecting agent will help tailor the course of action and treatment program. Though Staphylococcus aureus and epidermidis are most commonly identified, other bacteria (gram negatives, streptococci, enterococci and anaerobes) are common enough and one should consider them.5 Exposure of the implant to bacteria during the index operation is thought to be a leading cause for hardware infection.
Researchers have reported the incidence of infection following clean orthopedic surgery to be as high as 6.5 percent although certain procedures may have a greater risk for postoperative infection.6 Surgeries that involve percutaneous fixation with pins exiting the skin, like one would see with hammertoe surgery, are at risk for pin tract infections. A study involving distal radius fractures treated with percutaneous exposed Kirschner wires versus those buried deep to the skin demonstrated a significantly greater infection rate with percutaneous wires.7