The diagnosis of a periprosthetic joint infection (PJI) following total hip arthroplasty (THA) can be difficult. However, in 2014, the orthopaedic community is now faced with an especially difficult diagnostic problem. Now, larger numbers of patients are presenting with pain after THA with metal-on-metal (MOM) bearings or corrosion reactions;1-5 in this particular setting, ruling out the diagnosis of a PJI becomes even harder.1
Standard diagnostic tests to diagnose a deep infection after THA include the C-reactive protein, Erythrocyte Sedimentation rate (ESR), and synovial fluid analysis including the white blood cell count (WBC), the differential (or % polymorphonuclear (%PMNs) cells in the fluid), and culture. Previous studies have shown that the acceptable cutoffs (highest sensitivity and specificity) for diagnosing a chronic infection after THA, based on the synovial fluid analysis, include a synovial fluid WBC count >3,000 cells/μL and/or a differential with >80% PMNs;6 further, in the early post-operative period (< 6 weeks post-operative) after THA, optimal cutoffs for diagnosis of an acute infection include a WBC > 12,800 cells/μL and/or a %PMNs > 89%.7
While a PJI can occur concurrently with an adverse local tissue reaction (ALTR),8,9 during aseptic revision THA in the setting of metallic debris, the joint fluid often appears murky and purulent-like, mimicking a deep infection.10 Further, quite often the synovial fluid has “debris” that makes the synovial fluid difficult to interpret and/or read by automated machines.1,11-13 In these cases, manual counts or re-aspiration can be performed;1,11 however, the problem still remains of what to make of the data that is reported. Studies have shown that the WBC count is elevated from baseline in aseptic revision THAs in the setting of metal debris from a MOM bearing1,2,8,10,14 or taper corrosion;2,13 thus, no optimal cutoffs exist for diagnosing an infection in this group.
Future studies are needed to determine optimal cutoffs for the ESR, CRP, and especially the synovial fluid WBC count and differential, as this is often regarded by most to be the “gold standard” test to diagnose a PJI. Until these studies exist, the literature suggests that each individual diagnostic test used to diagnose a PJI in this patient population should be used with caution. Instead, ALL diagnostic tests available to the clinician including the appearance of the wound, the general appearance of the patient, signs and symptoms of the patient, CRP, ESR, the synovial fluid WBC count and differential, AND the synovial fluid culture should be used together to assist in making the diagnosis of PJI after THA in the setting of metal-on-metal (MOM) bearings or corrosion reactions.
Michael B. Cross, MD, Assistant Attending Orthopaedic Surgeon, Hospital for Special Surgery, New York, NY
1. Wyles CC, Larson DR, Houdek MT, Sierra RJ, Trousdale RT. Utility of synovial fluid aspirations in failed metal-on-metal total hip arthroplasty. J Arthroplasty 2013;28:818–823.
2. Wyles CC, Van Demark RE 3rd, Sierra RJ, Trousdale RT. High Rate of Infection After Aseptic Revision of Failed Metal-on-Metal Total Hip Arthroplasty. Clin Orthop Relat Res 2013.
3. Langton DJ, Jameson SS, Joyce TJ, Hallab NJ, Natu S, Nargol AVF. Early failure of metal-on-metal bearings in hip resurfacing and large-diameter total hip replacement: a consequence of excess wear. J Bone Joint Surg [Br] 2010;92-B:38–46.
4. Davies AP, Willert HG, Campbell PA, Learmonth ID, Case CP. An unusual lymphocytic perivascular infiltration in tissues around contemporary metal-on-metal joint replacements. J Bone Joint Surg [Am] 2005;87-A:18–27.
5. Langton DJ, Joyce TJ, Jameson SS, et al. Adverse reaction to metal debris following hip resurfacing: the influence of component type, orientation and volumetric wear. J Bone Joint Surg [Br] 2011;93-B:164–171.
6. Schinsky MF, Della Valle CJ, Sporer SM, Paprosky WG. Perioperative testing for joint infection in patients undergoing revision total hip arthroplasty. J Bone Joint Surg [Am] 2008;90-A:1869–1875. doi:10.2106/JBJS.G.01255
7. Yi PH, Cross MB, Moric M, Sporer SM, Berger RA, Della Valle CJ. The 2013 Frank Stinchfield Award: Diagnosis of Infection in the Early Postoperative Period After Total Hip Arthroplasty. Clin Orthop Relat Res 2014;472:424-9.
8. Judd KT, Noiseux N. Concomitant infection and local metal reaction in patients undergoing revision of metal on metal total hip arthroplasty. Iowa Orthop J 2011;31:59–63.
9. Watters TS, Eward WC, Hallows RK, Dodd LG, Wellman SS, Bolognesi MP. Pseudotumor with superimposed periprosthetic infection following metal-on-metal total hip arthroplasty: a case report. J Bone Joint Surg [Am] 2010;92-A:1666–1669.
10. Mikhael MM, Hanssen AD, Sierra RJ. Failure of metal-on-metal total hip arthroplasty mimicking hip infection. A report of two cases. J Bone Joint Surg [Am] 2009;91-A:443–446.
11. Lombardi AV Jr, Barrack RL, Berend KR, et al. The Hip Society: algorithmic approach to diagnosis and management of metal-on-metal arthroplasty. Bone Joint J 2012;94-B(Suppl A):14–18.
12. Cooper HJ, Della Valle CJ, Berger RA, et al. Corrosion at the head-neck taper as a cause for adverse local tissue reactions after total hip arthroplasty. J Bone Joint Surg [Am] 2012;94-A:1655–1661.
13. Cooper HJ, Urban RM, Wixson RL, Meneghini RM, Jacobs JJ. Adverse local tissue reaction arising from corrosion at the femoral neck-body junction in a dual-taper stem with a cobalt-chromium modular neck. J Bone Joint Surg [Am] 2013;95-A:865–872.
14. Earll MD, Earll PG, Rougeux RS. Wound drainage after metal-on-metal hip arthroplasty secondary to presumed delayed hypersensitivity reaction. J Arthroplasty 2011;26:338.e5–7.