Shoulder replacement is a very successful procedure that provides pain relief and improved function to millions of people around the globe. However, like any surgery, complications occasionally occur, and infection is one possible complication after shoulder replacement. Since joint replacement involves implantation of prostheses, infection complicating replacement is called Periprosthetic (peri=around, prosthetic=implant) Joint Infection, or PJI.
Bacteria, fungi or other microorganisms can settle and grow on the surface of the prosthesis and the tissues around it. Deep, relentless pain is the most common consequence of shoulder PJI; loss of implant fixation to bone, drainage of liquid through the skin, redness, warmth, and bodily sickness may also occur. Symptoms are oftentimes severe enough to warrant further surgery. To be honest, the road to clear and cure a shoulder PJI is long and rocky, but there is a light at the end of the tunnel…!
Names I’ve never heard of, and everyone is talking about them!
Cutibacterium acnes (C. acnes formerly known as Proprionibacterium acnes): that is one of the names everyone is taking about! Infections after orthopedic surgery for hip replacement, knee replacement, or bone fracture fixation are often caused by “staph” (Staphylococcus spp). However, many shoulder PJIs are caused by C. acnes. Why?
Millions of C. acnes live in the skin of normal, healthy humans, especially in the chest and back of men. They are harbored in the skin (dermal) glands. When the skin is cut or incised at the time of shoulder surgery, C. acnes bacteria have an opportunity to spread deep into the joint tissues. The majority of the times, C. acnes will not survive deep in the joint, but occasionally deep infection will occur.
C. acnes has created a lot of confusion in the field of shoulder PJI. Since these bacteria can also be found in normal skin, when they are cultured in a sample obtained at the time of surgery, it may be difficult to tell if they are responsible for pain and failure of the replacement, or if they grew by chance (doctors call these non-meaningful culture growths “contaminants”). Also, C. acnes reproduces slowly, and as a consequence shoulder PJI by C. acnes will lead to pain and implant loosening, but will not manifest as fever, chills, drainage, warmth, or bodily pain. As a consequence of its slow growth, C. acnes may not show in culture until well after a week. On the contrary, other bacteria will create a more obvious infection.
Another name you may have never heard of: glycocalyx. One of the challenges with infections of bones in general is that, because bone is a complex tridimensional matrix of collagen and mineral, bacteria can easily “hide” from the immune system and antibiotics: this is one of the reasons why bone infections are so hard to cure. If there is a prosthesis in the joint, clearing the infection becomes even harder because some bacteria can deposit a layer of sugars on the surface of implants, the glycocalyx. This sugary layer acts as a glue that allow bacteria to stick to the prosthesis. If the implant is not removed, the bacteria are not removed either. That is why most shoulder PJIs cannot be cured if the prosthesis is not removed as part of the process. The glycocalyx also serves as a barrier for the bacteria, protecting bacteria from antibiotics and the immune system.
Why do periprosthetic joint infections happen?
Good question…, and sometimes we never find out why! In theory, there are three possibilities: (1) the shoulder joint had microorganisms prior to replacement, (2) microorganisms settled in the joint at the time of surgery, or (3) microorganisms gained access to the joint through the blood stream.
Microorganisms were there to begin with…
If bacteria gained access to the shoulder joint in the past, shoulder replacement surgery may “activate” microorganisms that were “dormant” (the inflammation and blood pooling that occurs after any surgery provides a good environment for bacteria to multiply). The most common reason is surgery on the same shoulder sometime in the past, especially if there were concerns for infection after that surgery. Even prior arthroscopic surgery may have allowed bacteria to access the joint. Recent or multiple prior shoulder injections, typically with corticosteroids, may also increase the rate of shoulder PJI; the exact explanation for how this happens is unknown but currently many surgeons recommend avoiding shoulder replacement for three months after an injection.
It happened at the time of surgery
Microorganisms can access the joint at the time of replacement. Depending on how quickly the bacteria grows, infection may come to surface days, weeks or many months after shoulder replacement. Even with the most careful surgical technique, a small number of bacteria access the shoulder in every replacement surgery. However, constant flushing of the joint with sterile saline during surgery, use of topical antibiotics or an antiseptic solution at the end of the procedure, and the patient’s immune system clear these bacteria in most. In fact, the rate of shoulder PJI seems to be well under 1 in 200 replacements.
So why do microorganisms win the battle and create an infection in some patients but not others? This depends on how powerful the bacteria is and whether the patient is in good health. Individuals who suffer from conditions that compromise their immune system are obviously at a higher risk, and these include patients with poorly controlled diabetes or inflammatory conditions such as rheumatoid arthritis. Shoulder replacement should also be postponed if a patient has an infection anywhere in their body (most commonly a urinary tract infection or a tooth infection in individuals with poor dental hygiene). Cleaning of the skin with surgical soap the night before and the morning of surgery decreases the chances of PJI. Also, two particularly dangerous bacteria (methicillin-resistant Staphylococcus aureus [MRSA] or epidermidis [MRSE]) can be identified in the nasal area of some patients prior to surgery, and treatment with a local ointment will decrease the risk of infection in these circumstances.
Late hematogenous infection
Shoulder PJI can also occur years later if microorganisms circulating through the blood stream settle around the prosthesis. Again, a small number of bacteria from the mouth or gut get into our blood stream every day, but the immune system clears them. However, in circumstances when the immune system is weak, or if certain number or type of bacteria access the blood stream, they can settle and grow around the prosthesis. This is why during the first year after shoulder replacement, patients are recommended to take a single dose of antibiotics if they undergo a dental procedure or colonoscopy. This is also why patients with a prior shoulder replacement should be placed on antibiotics as soon as possible if they develop a bacterial infection anywhere in their body.
I have a shoulder PJI, what are my options?
If your surgeon has determined that your shoulder replacement is infected, several options may be discussed with you. These include just treatment with antibiotics, cleaning the joint surgically (irrigation and debridement), or removal of the prosthesis. If prosthesis removal is recommended, the question then becomes if and when a new prosthesis can be implanted safely with little to no risk of the infection coming back. In North America, the most common course of treatment recommended is a two-stage reimplantation: the infected prosthesis is removed in a first surgery (stage one), and a few weeks later – after treatment with antibiotics –, a brand-new prosthesis is implanted in a second surgery (stage two). Occasionally, it is safe to remove the prosthesis and implant a new one in a single surgery (one-stage reimplantation). Rarely, implantation of another prosthesis is too risky and patients are recommended to live with no shoulder joint (resection) or have their shoulder joint fused (arthrodesis).
Identification of the microorganism responsible for the shoulder PJI is extremely useful –but not always possible– prior to surgery. Your shoulder specialist will review all x-rays and other images obtained in the past.
Blood work is recommended to measure levels of two parameters that may help monitor infection (sedimentation rate and c-reactive protein [cRP]). A sample of liquid may be drawn using a needle inserted into the joint space under image control (typically ultrasound); this is called a joint aspiration. The sample obtained may be sent for culture and also analyzed to determine the number and proportion of cells present; other tests may be run in this fluid as well. Rarely, when the diagnosis of PJI is unclear, your shoulder specialist may recommend obtaining samples of joint tissue through arthroscopic surgery. Cultures of fluid or tissue cannot be discarded for at least 14 days. Physicians with special interest in infections are oftentimes involved in the evaluation and management of shoulder PJI along with the shoulder specialist.
The first stage
In the first surgery, your shoulder specialist will remove the prosthesis components and other foreign material (cement, sutures, anchors, etc). Samples of tissue are typically obtained for culture and microscopic analysis. Most of the times, a cement spacer is inserted into the canal of the humeral bone prior to closure. Cement spacers are fabricated with bone cement (polymethylmethacrylate) and antibiotics. They serve two functions: local delivery of antibiotics, and avoidance of excessive scarring and shortening of the muscles and tendons around the shoulder joint.
One or more antibiotics are given to the patient starting right after the first stage. Most of the times, antibiotics are administered intravenously to ensure that the whole dose of antibiotics is distributed through the body. This requires access to the patient’s vein system, most commonly using a PICC (Peripherally Inserted Central Catheter) line.
Depending on their level of familiarity with health care, some patients can receive their antibiotics at home with the help of a family member or friend. Alternatively, patients will need to go to an infusion center or local hospital. Blood work may be required several times during the “in-between stage” period to measure antibiotic levels, detect any kidney or liver toxicity that might occur, and monitor sedimentation rate and cRP values.
The second stage
Most commonly, the second surgery for implantation of the new prosthesis occurs 8 to 10 weeks after the first surgery, although occasionally further delay or even another surgery to clean the joint and exchange the spacer are recommended. Two weeks after your intravenous antibiotics are finalized, your shoulder specialist will want to check your shoulder to make sure that the infection is not returning. If there are any concerns about lingering infection, you may be recommended to undergo another aspiration (drawing fluid from the joint), which would require delaying the second surgery two additional weeks until the cultures are considered final. On the second surgery, or reimplantation, the temporary spacer is removed, a new prosthesis is implanted, and additional samples of tissue are obtained for culture. If cultures remain negative, no further treatment is required, but if cultures turn positive over the first few days after the second stage reimplantation, a new course of six weeks of intravenous antibiotics may be required. It may even be recommended to continue treatment with antibiotics by mouth indefinitely.
Can the infection come back?
Unfortunately,… yes. How likely this is to happen will depend on the overall health of the patient affected by a shoulder PJI and the kind of microorganism that was involved. Although microorganisms may be cultured in up to 15% of shoulders at the second stage, additional surgery to treat an ongoing infection is required in less than 5%.