Diagnosis of Periprosthetic Joint Infects of the Hip and Knee Case Study
IntroductionPeriprosthetic joint infection (PJI) remains one of the major complications that can ensue following total joint arthroplasty, with an incidence of 1% to 2% at 2 years postoperatively for both total hip and knee arthroplasty1,2 and up to 7% after revision surgery.3 Although the incidence of infection appears to be small, the total number of joint arthroplasties being performed is increasing,4 which likely will lead to a greater number of infected patients.
PJI poses a challenge on many fronts. One of the main challenges is to correctly diagnose PJI to implement effective treatment regimens. There is currently no standard of care for diagnosis of PJI, and no concrete definition for PJI exists.5 Hence, the preoperative workup for PJI is not standardized, and various tests, including invasive procedures, are performed in an effort to reach the diagnosis of PJI. The AAOS work group was convened to evaluate the available evidence for each diagnostic modality and propose an algorithm that can be used by clinicians in reaching the diagnosis of PJI.
History
A 65-year-old woman who underwent total knee arthroplasty 14 months ago has continued to have pain in the operated knee that has recently been increasing in severity. The pain is anterior to the knee and present at all times. She describes the pain as moderate to severe. The patient has difficulty ambulating long distances. She denies fever or chills and has not been systemically ill. The knee appeared swollen and red recently, which prompted the general practitioner to start a course of antibiotic therapy. The patient has just completed a 14-day course of oral antibiotics. On close questioning, the patient admits to having had wound-healing problems in the immediate postoperative period following total knee arthroplasty that required wash-out of the wound on postoperative day 6.
The AAOS guideline recommends against initiating antibiotic treatment in patients with suspected periprosthetic joint infection until after cultures from the joint have been obtained (Grade of Recommendation: Strong).
Physical Examination
The clinical examination reveals a slightly swollen knee with a range of motion from 5° to 110°. Extreme of motion is painful. There is no identifiable instability of the knee, and the extensor mechanism is intact with good patellar tracking. A previous anterior incision is well healed. The knee feels slightly warm to the touch and is tender in the medial joint line. The neurovascular examination of the extremity is normal. The skin is intact with no evidence of ulceration. There is minor ankle edema bilaterally.
Imaging Studies
Physical examination did not reveal a specific diagnosis. Anteroposterior, lateral, and skyline radiographs of the knee were performed. The patient has also had bone scan images performed at an outside institution, copies of which were brought for evaluation.
The AAOS guideline includes recommendations for risk stratification of the patients (Grade of Recommendation: Consensus). Because this patient had a history of wound-related problems in the postoperative period following the index arthroplasty, she is considered high risk for chronic PJI. Hence, further tests need to be ordered.
The AAOS guideline states that for patients in whom diagnosis of PJI cannot be reached, performing other tests, such as nuclear imaging (labeled-leukocyte imaging combined with bone or bone marrow imaging, F-18 fluorodeoxyglucose–positron emission tomography imaging, gallium imaging, or labeled-leukocyte imaging) is an option. Bone scan alone without labeling of the white cell, performed in this case study, has no role in diagnosis of PJI (Grade of Recommendation: Weak).
Further Tests
At this point, there is no specific diagnosis for this patient. However, PJI remains as a possible diagnosis. Thus, a series of tests was ordered, including erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) level, and white blood cell count with differential. The ESR is 35 mm/h (normal, 0 to 15 mm/h for men, 0 to 20 mm/h for women); the CRP level is 12 mg/dL (normal, <1 mg/dL). Aspiration of the joint is performed. The neutrophil count of the fluid is 2,350 cells/µl, with a neutrophil differential of 85%. The Gram stain of the aspirate is negative, and cultures showed no growth. Reaspiration of the joint is planned in 3 weeks, given the recent history of antibiotic use. The patient is instructed to stop the antibiotics that were started recently by her primary care physician.
The AAOS recommendations endorse ordering serology (ESR and CRP level) for workup of patients with suspected PJI. There is no evidence supporting the role of white blood cell count and/or white blood cell differential in diagnosis of PJI (Grade of Recommendation: Strong).
The AAOS guideline recommends that, for patients with abnormal serology (defined as ESR >30 mm/h and CRP level >1 mg/dL), aspiration of the joint be performed (Grade of Recommendation: Strong).
The AAOS guideline recommends that joint aspirate fluid be sent for microbiologic culture, synovial fluid white blood cell count, and differential (Grade of Recommendation: Strong).
The AAOS guideline recommends against the use of intraoperative Gram stain to rule out periprosthetic joint infection (Grade of Recommendation: Strong).
The AAOS guideline recommends that patients be off antibiotics for 2 weeks before obtaining intraarticular culture (Grade of Recommendation:Consensus).
Follow-up
Repeat aspiration in this patient is performed. The synovial fluid white blood cell count is now 7,383, and the differential is 89%, which are both consistent with PJI. The samples sent for Gram stain do not reveal any organisms. The culture isolates Staphylococcus aureus after 3 days. The diagnosis of PJI is reached, and surgical treatment is planned.
References
1.Kurtz SM, Ong KL, Lau E, Bozic KJ, Berry D, Parvizi J: Prosthetic joint infection risk after TKA in the Medicare population. Clin Orthop Relat Res 2010; 468(1):52-56.
2. Ong KL, Kurtz SM, Lau E, Bozic KJ, Berry DJ, Parvizi J: Prosthetic joint infection risk after total hip arthroplasty in the Medicare population. J Arthroplasty 2009;24(6 suppl):105-109.
3. Hanssen AD, Rand JA: Evaluation and treatment of infection at the site of a total hip or knee arthroplasty. InstrCourse Lect 1999;48:111-122.
4. Kurtz SM, Lau E, Ong K, Zhao K, Kelly M, Bozic KJ: Future young patient demand for primary and revision joint replacement: National projections from 2010 to 2030. Clin Orthop Relat Res 2009;467(10):2606-2612.
5. Bauer TW, Parvizi J, Kobayashi N, Krebs V: Diagnosis of periprosthetic infection. J Bone Joint Surg Am 2006; 88(4):869-882.Case Study: Diagnosis and Treatment of Periprosthetic Joint Infections of the Hip and Knee