KNEE Structured oralexamination question3: Infected total knee arthroplasty ( TKA )
Figures 3.3a and 3.3b Anteroposterior
(AP) and lateral radiographs of left TKA.
EXAMINER: A 78-year-old lady who underwent left TKA 2 years ago is re
ferred to your Painful Arthroplasty Clinic because of increasing pain, stiffness and recurrent swelling of the left knee for 4 months. Prior to onset of symptoms, she was very active and enjoyed long-distance walking. She is systemically well. These are the plain radiographs. (Figure 3.3.)
CANDIDATE: This is an AP and lateral radiograph showing a cemented cruciate sacrificing total knee arthroplasty taken on 16/8/11. There is an area of subchondral radiolucency underneath the medial side of the tibial component. There is no obvious periosteal reaction. Both components appear to be well fixed. I would like to see the initial postoperative radiograph and compare it with the most recent radiograph.
EXAMINER: This is the most recent radiograph and there are no other postoperative radiographs available! What would you like to do for this patient?
CANDIDATE: I would start by taking a detailed history of the perioperative events, general health as well current problem. I would like to know the date of index operation,
if there was prolonged discharge from the wound, redness or persistent swelling in the immediate postoperative period. A pain-free interval after the operation followed by sudden deterioration may be suggestive of haematogenous spread precipitated by bacteraemia from UTI, URTI or dental procedure. I would also like to know the pattern of pain: mechanical or non-mechanical and whether it’s relieved by rest. The clinical examination should be focused on identifying instability and localizing the problem.
EXAMINER: So you think this joint is infected?
CANDIDATE: My working diagnosis is infected TKA. My main differential diagnoses are aseptic loosening, inflammatory arthropathy in a prosthetic joint, instability and malalignment.
EXAMINER: How would you investigate this patient?
CANDIDATE: I would start with routine blood investigations including CRP and ESR.
EXAMINER: How sensitive and specific are these?
CANDIDATE: In a recent systematic review in the American JBJS by Berbari et al., the pooled sensitivities for ESR and CRP were 75% and 88% respectively while the pooled specificities were 70% and 74% respectively. The study also reported that interleukin 6 (IL-6) level assay was more sensitive and specific at 97% and 91% respectively. If the blood inflammatory markers are elevated, I would proceed with radioisotope bone scan and arrange for alignment check under image intensifier and joint aspiration in theatre.
EXAMINER: Are you aware of any guidelines regarding diagnosis of periprosthetic joint infections?
CANDIDATE: I am aware of the AAOS clinical guideline practice summary for diagnosis of periprosthetic joint infection of the knee. The working group strongly recommend:
Testing ESR and CRP.
Joint aspiration.
The use of intraoperative frozen sections.
Obtaining multiple intraoperative cultures.
Against initiating antibiotic treatment until after cultures. Against the use of intraoperative Gram stain.
Nuclear imaging was weakly recommended as an option in patients in whom diagnosis of periprosthetic joint infection has not been established and who are not scheduled for re-operation.
Berbari E, Mabry T, Tsaras G et al. Inflammatory blood laboratory levels as markers of prosthetic joint infection: a systematic review and meta-analysis. J Bone Joint Surg Am 2010;92-A:2102–2109.
Della Valle C, Parvizi J, Bauer TW et al. Diagnosis of periprosthetic joint infections of the hip and knee. J Am Acad Orthopaed Surg 2010;18(12):760–770.
EXAMINER: Let’s say the aspiration yields heavy growth of
Staphylococcus aureus. How would you proceed from here?
CANDIDATE: With raised inflammatory markers and a positive bone scan and aspiration, I would offer this patient two-stage revision total knee replacement. I have opted for two-stage procedure because the investigations show severe infection caused by a virulent organism. The first stage would be extraction of the implants, debridement of joint and bone followed by application of antibiotic-loaded spacer. Antibiotic treatment depending on sensitivity is started after the first
stage usually for a period of 4–6 weeks with close monitoring of CRP and ESR as well as clinical progress. The timing of the second stage depends on achieving normal CRP and ESR, healing of wounds or sinus and general well-being of the patient. Recent studies have shown that two-stage revision has better infection eradication rate and no difference in clinical outcome (knee scores, range of motion) compared with single stage (Jämsen et al.). Some of the disadvantages of two-stage revision are soft tissue scarring, dislocation of spacers, disuse atrophy and loss of bone density which makes the secondstage procedure difficult. I am aware that some surgeons have reported encouraging results from single-stage revision such as Buechel et al. who reported infection eradication rate of 90.9 % over an average follow-up of 10.2 years. This compared favourably with the results of two-stage revision surgery while remaining cost-effective. However, I believe that single-stage revision should be reserved for cases where the organism and its sensitivities are known and it is of low virulence; in the very elderly patients and those with multiple medical problems.
[Debrief: The examiner has allowed the candidate to talk about the topic without interrupting.]
Jämsen E, Stogiannidis I, Malmivaara A et al. Outcome of prosthesis exchange for infected knee arthroplasty: the effect of treatment approach. Acta Orthop 2009;80 (1):67–77.
Buechel FF, Femino FP, D’Alessio J. Primary exchange revision arthroplasty for infected total knee replacement: a long-term study. Am J Orthop (Belle Mead NJ) 2004;33 (4):190–198; discussion 198.
