PROSTHETIC JOINT INFECTION: TYPES, SYMPTOMS, CAUSES, & TREATMENT
Joint replacement is a commonly performed orthopedic surgery that aims to restore function and relieve pain in damaged joints using prostheses.
The most commonly replaced joints are the knee and hip joints. The reason for joint replacement can be degenerative diseases (osteoarthritis), inflammatory diseases (rheumatoid arthritis), or traumatic joint injury.
Prosthetic joint infection (PJI) is one of the most feared complications after joint replacement surgery. It can occur in up to 1% of patients, which is not uncommon.
PJI usually requires long-term antibiotic treatment, surgical revision, prosthetic replacement, and physical therapy. Diagnosis and treatment require multidisciplinary collaboration between orthopedics, rheumatology, and infectious disease teams.
What is Prosthetic Joint Infection?
Prosthetic joint infection (PJI) is one of the uncommon, but serious, complications that can occur after having a prosthetic joint installed.
It’s the result of bacterial infection and growth around the prosthetic joint. This leads to tissue and joint damage, pain, and decreased joint function. The symptoms can range in severity and speed of occurrence depending on many factors.
It is estimated that prosthetic joint infections occur in 0.8-1.9% of knee replacements and 0.3-1.7% of hip replacements.
Prosthetic joint infections can be classified according to the time of their occurrence relative to the initial surgery:
- Early: Occurs within the first 3 months after joint replacement
- Delayed: Occurs between 2 months and 2 years after joint replacement
- Late: Occurs after more than 2 years of joint replacement
The timing, speed, and severity of PJI depend on many factors, like the mechanism of infection, type of microbe, patient characteristics, and health of the joint.
Symptoms
The symptoms of prosthetic joint infection vary a lot in severity and speed of onset from one case to another. These symptoms affect the replaced joint and can include:
- Wound dehiscence (early)
- Sinus tract opening leading to the joint (early)
- Drainage of pus (early)
- Joint pain that increases with movement
- Limited joint range of motion
- Joint swelling
- Joint redness
- Fever
- Chills
- In severe cases, signs of sepsis (low blood pressure, loss of consciousness, trouble breathing)
Early infections that happen right after surgery tend to be more acute and dramatic, causing more obvious pain, signs of inflammation, wound abnormalities, and limitation in joint movement.
Late occurring prosthetic joint infections tend to be more indolent and cause less obvious symptoms. They often resemble those of non-infected mechanical prosthetic failure that happens with time. The infection in such cases can only be established through laboratory testing.
Since prosthetic joint infection can be a result of the spread of infection from another body part (see below), symptoms of the main infection may overshadow those of PJI.
Causes
Septic endoprosthetic infections occur as a result of bacterial invasion of the implant and subsequent damage of the surrounding tissue. There are two possible pathways for the bacteria to reach the joint:
- Direct invasion: This is the pathway that usually leads to early infections; in the first 3 months after joint replacement. If bacteria manage to contaminate the prosthesis during surgery (due to lack of sterility), then a resultant infection could develop. Alternatively, lack of proper wound care in the post-operative period can lead to wound infection, which can extend to reach your joint if not treated. This happens when a sinus tract (a hollow connection) forms between the skin outside and the inside of your joint.
- Hematogenous spread: This is when bacteria infect an unrelated part of your body (e.g. the gallbladder), spread to the blood, and reach your prosthetic joint to infect it. This can also happen after dental surgery, where bacteria get into your bloodstream and reach your joint. Prosthetic joints are very attractive to bacteria and are usually not spared after blood invasion. Hematogenous spread is usually the mechanism of infection in late occurring prosthetic joint infections (more than 2 years after surgery).
Many organisms have been identified as common causes of prosthetic joint infections. Staphylococcus aureus is the most commonly isolated organism, leading to up to 44% of endoprosthetic infections. Enteric gram-negative bacilli, like E. Coli and Klebsiella, come in second with 25%.
Diagnosis
The diagnosis of septic endoprosthetic infection can be very challenging, especially in those occurring late with a slowly progressing pace. Your orthopedic surgeon will suspect that you have a prosthetic joint infection based on your symptoms, history of joint replacement, and physical exam. Once prosthetic joint infection is suspected, a combination of tests will be ordered to confirm:
Radiologic Imaging
Your surgeon might order any one or more of the following tests to diagnose and assess the health of your joint, presence or absence of joint damage, the extent of infection, the extent of soft tissue involvement, and more:
- Plain X-ray: This is routinely ordered to get a general overview of the prosthesis and joint
- MRI: Only titanium or tantalum implants can be assessed using MRI safely. MRI can provide detailed images of the joint and surrounding tissue.
- CT Scan: Can provide excellent images of the joint and soft tissue
- Positron emission tomography (PET) Scan: Show areas of high metabolic activity, which can be a sign of prosthetic joint infection
- Radionuclide imaging: Using technetium-99m, can detect immune cells inside the joint
Blood Tests
Several routine blood tests will be ordered to check for inflammation. Most of these tests just give a general idea about how severe the inflammation is, but don’t give any clue about its location:
- C-Reactive Protein (CRP) and Erythrocyte Sedimentation Rate (ESR): Inflammatory markers that are elevated during infections
- Procalcitonin: A marker of infection
- Blood count with differential (CBCD): Shows an elevated white blood cell count and an elevated neutrophil percentage in case of bacterial infection
Other blood tests might also be ordered if your physician suspects that other body systems are also involved.
Joint Aspiration
This is probably the most important test for the diagnosis of prosthetic joint infection. Using a fine needle, your surgeon will puncture your joint and aspirate some fluid. The fluid will be sent to the lab for:
- Microscopic examination (with gram staining)
- Chemical analysis
- Bacterial culture
Microscopic examination and analysis can quickly signify the presence or absence of infection. The presence of high white blood cell count and high polymorphonuclear (PMN) cells is a strong indicator of infection. Bacterial cultures can take a few days to grow, and they help identify the causative organism to guide treatment.
Treatment
The treatment of infected prosthetic joints is very complex. There are no strict guidelines for treatment since the proper therapy varies largely from one case to another. Treatment always involves long-term antibiotic therapy and almost always involves surgery.
Antibiotic therapy
These are the mainstay of treatment and are always indicated to treat prosthetic joint infections regardless of whether surgery will or will not be performed. The duration of therapy depends on several factors, such as the type of microbe, extent of infection, planned surgery, and patient’s response.
The minimum period of antibiotic therapy is 2 weeks and can extend for up to 6 or more months. In non-acute cases with minimal symptoms, antibiotic therapy might be delayed until the culprit bacteria is identified (through intra-operative specimen collection or pre-operative joint fluid aspiration).
Initially, antibiotic therapy is started intravenously, but can usually be shifted to oral therapy in many cases after the organism is identified.
Antibiotic therapy alone without surgery might be used in patients who:
- Refuse surgery
- Are poor candidates for surgery
Nevertheless, the success rate of antibiotic-only therapy is below 25% of cases.
Surgery
In most cases of prosthetic joint infection, revision surgery is indicated. The choice of surgery depends on several factors, such as joint health, the timing of infection, and patient wishes. Here are the possible techniques:
- Debridement without prosthetic joint removal: This strategy is only appropriate in limited scenarios. Your surgeon might opt to clean the joint without removing the prosthesis in cases that occur early (<30 days after initial surgery) and still have a healthy prosthetic joint. A prerequisite for this strategy is that the infective organism is sensitive to available long-term antibiotic therapy.
- Multi-stage revision: The joint is removed in the first stage of surgery. Antibiotic therapy is given for at least 6 weeks. Multi-stage surgeries are performed to install a new prosthetic joint.
- Resection arthroplasty: This is when the prosthetic joint is removed without inserting a new one. Instead, the old joint is fused together (arthrodesis). This method is done for patients who fail to respond to multiple PJI therapies and who lack the mechanical and biological requirements for further surgery.
- Amputation: In patients who have failed to respond to all therapies and still have an active infection, amputation is the final solution. This can be a more realistic option in patients who are already bed-ridden and don’t ambulate.
Outlook
Prosthetic joint infection can be very tough to deal with. It can become frustrating to both the patient and their healthcare team. Despite the long and demanding treatment regimens, joint prosthesis infections can be effectively cured.
With the advances in surgical sterility techniques and the rise in joint replacement surgeries, the risk of prosthetic joint infections will hopefully be declining in the near future.
Please contact Sana Hospital Group or Sana Rummelsberg Hospital for more information on Prosthetic Joint Infection.
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