Overview
Definition:
Implant infection refers to a bacterial or fungal colonization of a prosthetic implant, which can lead to significant morbidity and implant failure
Washout and exchange are critical surgical interventions aimed at eradicating the infection and preserving or restoring function.
Epidemiology:
Implant-associated infections occur in approximately 1-2% of total joint arthroplasties, with higher rates in complex revisions, spine surgery, and trauma cases
Risk factors include patient comorbidities (diabetes, obesity, immunosuppression), surgical site contamination, and prolonged operative times.
Clinical Significance:
Untreated implant infections can result in chronic pain, functional loss, systemic sepsis, and necessitate multiple complex revision surgeries
Prompt diagnosis and appropriate management, including washout and exchange, are vital for successful outcomes and patient well-being.
Clinical Presentation
Symptoms:
Deep incisional pain
Increasing warmth and redness around the surgical site
Purulent drainage from the wound
Fever and chills
Systemic signs of infection like malaise and fatigue
Loosening of the implant with instability
Restricted range of motion.
Signs:
Erythema, warmth, and swelling at the surgical site
Tenderness to palpation
Purulent discharge from drains or wound
Joint effusion
Fever (>38.5°C) and tachycardia
Positive aspiration of purulent fluid from the joint or surrounding tissues
Radiographic evidence of loosening or osteolysis.
Diagnostic Criteria:
Definitive diagnosis often relies on a combination of clinical findings, laboratory markers (elevated CRP, ESR, WBC count), synovial fluid analysis (high WBC count, low glucose, positive Gram stain/culture), and intraoperative findings (purulence, positive intraoperative cultures)
The Musculoskeletal Infection Society (MSIS) criteria are widely used.
Diagnostic Approach
History Taking:
Detailed history of the index surgery
Onset and progression of symptoms
Presence of fever, chills, or wound drainage
Previous surgical interventions
History of diabetes, immunosuppression, or other comorbidities
Trauma history
Use of antibiotics
Red flags: sudden onset of severe pain, purulent discharge, systemic symptoms.
Physical Examination:
Inspection of the surgical site for erythema, swelling, and drainage
Palpation for tenderness and warmth
Assessment of range of motion and joint stability
Examination of surrounding soft tissues
Check for peripheral pulses and neurovascular status.
Investigations:
Laboratory tests: Complete Blood Count (CBC) with differential, Erythrocyte Sedimentation Rate (ESR), C-Reactive Protein (CRP)
Synovial fluid aspiration: Cell count and differential, Gram stain, aerobic and anaerobic cultures with sensitivities
Imaging: Radiographs (AP, lateral views) to assess implant position, loosening, and osteolysis
CT scan may reveal periosteal reaction and bone loss
Bone scan or PET scan can identify infection foci, especially in difficult cases
MRI is useful for soft tissue assessment and detecting small abscesses.
Differential Diagnosis:
Aseptic loosening
Postoperative inflammation
Seroma
Gout or pseudogout
Superficial wound infection
Stress fracture
Osteomyelitis without implant
Soft tissue infection
Rheumatoid arthritis flare.
Management
Initial Management:
Prompt diagnosis and initiation of empirical broad-spectrum antibiotics, particularly if systemic signs of infection are present
Pain management
If there is purulent discharge, wound exploration and drainage may be necessary.
Medical Management:
Empirical antibiotics based on Gram stain results and likely pathogens
Definitive antibiotic therapy is guided by culture and sensitivity results
Duration typically extends for 4-6 weeks or longer, depending on the intervention and clinical response
Intravenous administration is preferred initially, followed by oral step-down therapy.
Surgical Management:
Two main surgical approaches: 1
Irrigation and Debridement (I&D) with implant retention: Suitable for early, superficial infections without implant loosening
Involves thorough irrigation of the joint/surgical site, debridement of infected tissue, and insertion of antibiotic-impregnated beads or cement
2
Implant Exchange: Required for established infections, implant loosening, or if I&D fails
This can be a one-stage exchange (removal of infected implant, debridement, and immediate insertion of a new prosthesis) or a two-stage exchange (removal of infected implant, debridement, insertion of antibiotic spacer, and subsequent reimplantation after infection control).
Supportive Care:
Nutritional support to aid healing
Physical therapy to maintain range of motion and strength, especially after implant retention or during the spacer phase in two-stage exchange
Close monitoring of vital signs and laboratory parameters
Psychological support for the patient experiencing prolonged treatment and recovery.
Complications
Early Complications:
Wound dehiscence
Persistent drainage
Recurrence of infection
Septic shock
Deep vein thrombosis (DVT) and pulmonary embolism (PE)
Nerve or vascular injury during surgery.
Late Complications:
Chronic osteomyelitis
Persistent pain
Implant loosening
Arthrofibrosis
Joint stiffness
Pseudarthrosis
Amputation
Development of antibiotic-resistant organisms.
Prevention Strategies:
Strict aseptic techniques during surgery
Use of prophylactic antibiotics perioperatively
Optimization of patient comorbidities
Careful implant selection and handling
Thorough surgical site preparation
Minimizing operative time
Effective wound closure and drainage strategies.
Prognosis
Factors Affecting Prognosis:
Virulence of the organism
Patient's immune status
Delay in diagnosis and treatment
Extent of bone and soft tissue involvement
Successful eradication of the infection
Type of surgical intervention (I&D vs
exchange)
Choice and duration of antibiotic therapy.
Outcomes:
Successful treatment with I&D and implant retention can lead to good functional outcomes and preservation of the native joint or prosthesis
Two-stage exchange typically offers higher infection eradication rates but involves longer treatment periods and potentially more functional compromise temporarily
One-stage exchange may be suitable in select cases with less virulent organisms and no significant bone loss.
Follow Up:
Long-term follow-up is crucial, often for at least one year, to monitor for recurrent infection
This includes regular clinical assessments, serial laboratory markers (CRP, ESR), and imaging (radiographs) to detect early signs of recurrence or implant failure
Patients should be educated on signs and symptoms of infection to report promptly.
Key Points
Exam Focus:
Understand the criteria for diagnosis (MSIS)
Differentiate between I&D with retention and one-stage vs
two-stage exchange procedures
Know the common pathogens and their typical antibiotic sensitivities
Recognize risk factors for implant infection
Recall the importance of microbiological cultures.
Clinical Pearls:
Always suspect infection in a patient with a prosthesis presenting with pain or drainage, even years after surgery
Synovial fluid analysis is paramount for diagnosis
Intraoperative cultures from multiple sites are essential
Consider antibiotic-impregnated cement or beads for prophylaxis or treatment adjunct
Two-stage exchange is often the gold standard for difficult-to-treat infections.
Common Mistakes:
Initiating antibiotics before obtaining cultures
Performing I&D in the presence of frank purulence without adequate debridement
Failure to recognize aseptic loosening as a cause of pain
Inadequate duration or incorrect choice of antibiotic therapy
Delaying surgical intervention when indicated.