A periprosthetic joint infection (PJI) is a serious, yet uncommon, complication following a total hip replacement. PJI occurs when bacteria colonize the surface of the artificial hip components, creating a protective layer called a biofilm. The incidence of PJI is low, affecting approximately 1% to 2% of patients who undergo a primary hip replacement. Because the infection is attached to the non-living implant, it is difficult for the body’s immune system and standard antibiotics to eradicate it. Early detection is paramount, as the timing of diagnosis determines the available treatment options and the likelihood of successfully clearing the infection.
Recognizing the Signs of Infection
The way a hip infection presents depends heavily on how long the bacteria have been present, leading to two distinct clinical pictures: acute and chronic. An acute infection typically occurs soon after surgery or suddenly years later, presenting with pronounced signs of inflammation. A patient will often experience severe, new-onset pain, along with redness, swelling, and warmth around the hip or incision site. Systemic signs like fever, chills, and fluid drainage from the surgical wound are also commonly observed.
A chronic infection, in contrast, often develops gradually and is caused by less virulent bacteria that take time to establish a biofilm. The primary symptom is a persistent, dull ache or pain in the hip joint that does not improve over time. Unlike acute cases, chronic infections may not cause a fever or significant redness and swelling. A definitive sign of a chronic infection is the formation of a sinus tract, an abnormal channel opening in the skin that connects the infected joint space to the outside environment.
Clinical Diagnosis and Infection Timing
When a periprosthetic infection is suspected based on symptoms, clinicians confirm the diagnosis using blood tests and specialized joint fluid analysis. Blood work checks for elevated inflammatory markers, specifically C-Reactive Protein (CRP) and Erythrocyte Sedimentation Rate (ESR), which indicate a systemic response to infection. The definitive diagnostic test is a joint aspiration, where fluid is drawn directly from the hip joint. This fluid is analyzed for an abnormal count of white blood cells and then cultured to identify the specific type of bacteria causing the infection.
The timing of the infection’s onset is a crucial element of the diagnosis, as it directly guides the treatment strategy. Infections are generally classified into three categories based on their presentation and origin:
Acute Post-Operative Infection
This occurs within weeks of the hip replacement, often resulting from bacterial contamination during the original surgery.
Acute Hematogenous Infection
This occurs months or years after the surgery, appearing suddenly when bacteria from another source, such as a skin or dental infection, travel through the bloodstream and settle on the implant.
Chronic Infection
This is the most common type, established when symptoms have been present for more than four weeks. This duration allows the bacteria to fully mature the protective biofilm. Understanding this classification allows the multidisciplinary team to select the most appropriate surgical and antibiotic treatment plan.
The Comprehensive Treatment Pathway
The treatment for a hip replacement infection is complex and involves a combination of surgical intervention and a prolonged course of antibiotic therapy. The choice of surgical procedure is determined by the infection classification, the stability of the implant, and the patient’s general health. Antibiotic treatment is highly specific, often beginning with an initial course of intravenous (IV) drugs for several weeks. This IV phase is followed by an extended period of oral antibiotics, lasting three to six months, aimed at penetrating the bacterial biofilm.
For acute infections where the implant is stable and symptoms have been present for less than four weeks, a less invasive procedure called Debridement, Antibiotics, and Implant Retention (DAIR) may be performed. This involves surgically opening the joint, thoroughly washing it out, removing infected tissue, and exchanging only modular components, such as the plastic hip liner. The implant itself is retained, allowing the patient to avoid a complete hip revision surgery. Success rates for DAIR are variable, and it is usually reserved for select cases to reduce the overall surgical burden.
For most chronic infections, or any acute infection where the implant is loose or DAIR has failed, the gold standard treatment is the Two-Stage Exchange Arthroplasty. The first stage involves the complete removal of all prosthetic components, cement, and infected tissue, followed by the placement of a temporary antibiotic-loaded cement spacer. This spacer maintains the joint space and delivers a high concentration of antibiotics directly to the infected area. During the interval between surgeries, patients receive systemic antibiotic therapy, and blood markers must normalize to confirm the infection has been cleared.
The second stage involves removing the antibiotic spacer and implanting a new, permanent hip replacement, but only after laboratory tests confirm the infection is eradicated. A less common option for chronic infections is the One-Stage Exchange Arthroplasty, where the infected components are removed and the new replacement is implanted during the same surgery. This single-stage approach is typically reserved for highly select cases involving less virulent bacteria or in patients who cannot tolerate a second operation.
In rare situations where the infection cannot be cleared despite multiple surgical attempts, or in patients with severely compromised health, a salvage procedure may be necessary. This often involves a Girdlestone procedure, where the hip replacement is permanently removed, and no new implant is inserted. The resulting fibrous joint provides pain relief and clears the infection, but it leaves the patient with a shorter leg and a poorer functional outcome.