- Implant-associated infection is the most common indication for implant removal
- Without removal of the implants, infection will persist
- Appropriate antibiotic therapy is essential after implant removal for a minimum of 4 weeks
after surgery to eradicate the infection
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Surgical implants are made of stainless steel or titanium or other metal that has been used to repair bones. Implants may be metal plates, screws, pins, or wires. Metal implants are used typically to repair broken bones or repair or for joint replacement surgery. Metal, regardless of how smooth they may appear from the outside, from a microscopic level, they have many small pits, crevices and caverns that are good hiding places for bacteria. Once bacteria colonize a metal implant, it can very difficult to eradicate the infection, because the bacteria retreat into the crevices, pits and caverns which are not very accessible for the body's defense system, white blood cells. In addition, within about 10 days of colonization of a metal implant within the body, bacteria produce a biofilm which is a type of slime that is practically impenetrable to white blood cells. With colonization of the metal, the bacteria then extend into the surrounding bone via the Haversian canals which results in bone infection called osteomyelitis. Bone infection is very difficult to eradicate and rarely cured with treatment with antibiotics alone and frequently requires removal of the metal implants.
How do bacterial get on metal implants?
A common type of bacteria infection seen in dog and cat surgical site infections is due to Staphylococcus pseudointermedius and is a normal commensal bacteria of the skin. It is impossible to completely sterile skin at the surgical site, regardless of the type of antiseptic used or the aseptic technique used to clean the skin just prior to surgery. Bacteria located in the hair follicles of the skin are not killed by the antiseptic used to prepare the skin. Subsequently, as the skin is cut with the scalpel, hair follicles that are unavoidably cut, contaminate the scalpel and the surgical site. When there is enough bacterial that, as inoculated the surgical site, that is greater than 10, 000 bacteria per cubic centimeter of tissue, infection usually ensues. Other factors that increase the risk if infection include long surgical times, degree of surgical trauma, previous trauma to the area (damaged tissue due to being hit by a car), hypothermia during surgery, use of surgical implants, and failure to use of antibiotics during surgery.
Some dogs have their nasal and oral cavities colonized with methicillin resistant bacteria. In dogs, these are methicillin resistant Staphyloccocus pseudointermedius (MRSIP) and in humans metacillin resistant Staphylococcus aureus (MRSA). This dreaded bacteria commonly are only sensitive to a few, if any antibiotics. Dogs and humans are very susceptible to developing MRSIP or MRSA infections of the surgical site in the postop period, regardless of how sterile the procedure has been conducted during surgery. These bacteria get into the incision when the dog licks the incision after surgery or inoculation of the skin during surgery. They may also get to the surgery site from hair follicles that have this bacteria or via the blood stream from the site of nasal cavity. If a patient is a known MRSIP or MRSA carrier, preoperative and postoperative administration of antibiotics will be critical to prevent the infection at the surgical site. Recently, some surgical metal plates are coated with silver ions which provides antimicrobial effect against many bacteria including MRSIP and MRSA. TPLO plates are now available with this coating (BioMedtrix and Veterinary Orthopedic Implants).
What is the incidence of implant-associated infection?
We conducted a study of the incidence of implant-associated infection in our practice and found that in 800 consecutive cases, 1.9% of patients undergoing TPLO surgery needed to have the metal implants removed due to infection. These metal implants were not coated with silver ions. We have not conducted our secondary study investigating the incidence of infection with they silver-coated plates, but our impression is that it is less than the uncoated plates, thus we continue to use these in our clinical cases. We attribute our low surgical site infection rates following TPLO surgery to scrub of the limb with antiseptic, sterile scrub of the limb with antiseptic, application of Duraprep (povodone Iodine), application of Ioban drapes that covers all of the skin during surgery, meticulous tissue handling during surgery, use of Hyprotect TPLO plates, short surgery times, keeping the patient warm during anesthesia, administration of the IV antibiotics during surgery, postop administration of oral cephalexin for 5 days after surgery, covering the incision with a protective band aid immediately after surgery and mandatory use of an Elizabethan collar for 2 weeks postoperatively.
HyProtect Antimicrobial Implants
Metal implants can be coated with plasma impregnated elemental silver. These have been used in humans for 10 years and recently in dogs. They have been shown to have an antimicrobial effect for 100 days after surgery. Elemental silver coated plates will kill bacteria including those that are very resistant to antibiotics. There appears to be no ill effect of the elemental silver to the patient. The risk for developing infection is usually early on after surgery, thus even though the silver elutes of the metal plate with time, this becomes less important.
Clinical signs of bone infection
Bone infection commonly is associated with pain, swelling, and pain. With time, the incision may drain from a small opening called a draining tract (commonly near the bottom of the metal plate). Lameness of the operated limb is usually seen due to pain, but some dogs seem to remain sound on their operated limb.
Treatment of bone infection
If an implant-associated infection has been present for more than 10 days, the protective biofilm will allow bacteria to thrive in spite of administration of an appropriate antibiotic. Therefore, early treatment of infection is imperative. For those patients whose implant is coated with bacterial biofilm, antimicrobial treatment will significantly help resolve the infection that is in the bone around the implant, but shortly after the antibiotic therapy is terminated, the clinical signs of infection commonly begin again.
When can implants be removed from a bone?
Once bone healing has been completed, then the metal can be safely removed. This varies depending on the age of the pet and the site in which the metal is located. Young dogs have very quick bone healing. Bones that are fractured near the end of the bone (metaphysis) will heal much more quickly than those located in the middle of the bone (diaphysis). Your dog or cat's surgeon will let you know when it is safe to remove the metal implants from the bone.
What are other indications to remove metal implants?
Implants such as pins may protrude from the bone and cause a fluid pocket to form under the skin. This can be very irritating to the pet.
Another consideration for removal of metal implants is to prevent stress protection. This is a phenomenon in which the bone becomes very dependent on the metal plate for its strength, thus the bone gets resorbed beneath the plate and weakens the bone making it more susceptible to breaking, typically at the end of the bone plate. This condition is seen more commonly in small breed dogs.
Another reason to remove a metal plate is that the metal is believed to be a risk factor for the development of bone cancer in the area. In our busy surgical practice, thousands of dogs have surgery involving use of metal implants and rarely is bone cancer at the site ever seen. I do not feel that there is enough benefit for routine implant removal of all surgical implants in every patient.
Preparation for surgery
Your pet should be fasted prior to surgery, as instructed by the surgical team. Water is usually permitted up to the time of admission to our hospital. You should inform the surgical team of any medications that your pet is currently receiving and of any pertinent medical alerts (allergies, seizures, drug insensitivities, etc). Just prior to surgery, your pet will receive a sedative, have an intravenous catheter placed for the administration of intravenous fluids and intravenous medications, be induced under general anesthesia with medication(s), and have a breathing tube (endotracheal tube) placed to allow delivery of oxygen and gaseous anesthesia. The surgical site will be clipped and cleansed with an anti-septic solution in preparation for surgery. While under general anesthesia, your pet’s breathing will be assisted with a ventilator and vital parameters such as heart rate, respiratory rate, core body temperature, blood pressure, oxygenation of the blood (pulse oximetry), exhaled/inhaled carbon dioxide (capnography), and heart rhythm (EKG) will be monitored to ensure the pet’s well being. Pain will be controlled both during and after surgery with analgesics (pain-controlling medication). Please note that each surgical and anesthesia team may elect to choose a different, but effective analgesia protocol, pending the needs of the patient.
Surgery
An incision is made over the metal implant, tissues are sharply incised, protecting vital structures as the surgeon exposes the metal implant. If there is no infection and screws have previously snapped off flush with the bone they may not be retrieved. In the case of infection, if a snapped off screw is encountered, it will be removed by burring a rim of bone surrounding the screw base and then grasping it with special instruments or forceps. A screw or two along with samples collected from the bed beneath the plate are submitted for bacterial culture. The area is flushed with sterile saline and the incision is usually closed. Some surgeons prefer to leave the incision open and allow the incision to drain for a few weeks before performing the delayed secondary incisional closure.
Postoperative care
Most patients that have surgical metal implant removal will go home on the day of surgery. Pain controlling medication such as nonsteroidal anti-inflammatory and narcotic may be prescribed. We commonly infiltrate the surgical site with a sustained-release 72-hour local anesthetic called Nocita. Thus minimal to no narcotics are needed. We also do not find that this impedes resolution of infection when this medication is used.
A bandage likely will be applied to the limb to protect the incision and give support to the limb. The surgeon may also add splinting or casting material to the bandage to provide more rigid support, especially if the bone is believed to be at risk for re-fracture after implant removal. The duration of support of the limb in a splint/cast will vary and is patient dependent.
An antibiotic will be empirically prescribed; this means the surgeon will make his/her best guess as to the type of antibiotic to be used. After the bacterial culture results are available, which is typically within 1 week after submission of the sample to the lab, the surgeon will prescribe an antibiotic to which the bacteria is sensitive. Most dogs that have a bone infection are treated with antibiotics for at least 4 to 8 weeks, depending on the case. We find that only a 2-week course of antibiotics is frequently inadequate to resolve the infection after implant removal.
Success
Most cases that receive appropriate treatment for implant-associated bone infection will have clinical resolution of the infection.
