Joint Fluid to lab or exudate to Surgical Pathology: Should the joint not look infected at surgery, think of an acute exudative urate effusion and have pathology do a fast intra-operative exam for crystals [L13-14888], HERE. Either as a primary acute presentation or as a possible postop complication, the physician may aspirate an acute joint effusion and send fluid for exam and culture. If there are
numerous polys (neutrophiles) on the fluid exam, they could be due to infectious organisms = septic (bacterial or Lyme disease)...but culture results could be negative vs crystallosis (such as gouty pyoarthrosis) vs rare STERILE ASEPTIC PYARTHROSIS due to such as PAPA syndrome...
pyogenic arthritis, pyoderma gangrenosum, & acne6 vs rare "streaking leukocyte syndrome" (recurrent episodes of sterile pyarthrosis unresponsive or poorly responsive to antibiotic therapy but rapidly and completely responsive to prednisone therapy) or even vs rare FMF (Melungeon [mixed American Indian, black & white...tri-racial] USA people...and others of Mediterranean ancestry...tend to run an elevated total WBC & a proportion may reflect "familial Mediterranean fever" [FMF...a cause of night sweats, fever, pains, chronic fatigue]). ALSO, significant polys can be present in biopsies of acute-phase reactive arthritis [L11-8899]. Joint
fluid exam should include looking for other morphological evidence of prosthesis failure such as joint-prosthesis detritic metallic particles or other debris.
Postop joint appliance loosening due to sepsis (or non-septic causes) & leading to joint revision (one stage if non-septic & 2 stage if septic) often lacks solid clinical clues as to sepsis BUT is primarily9 a clinical diagnosis at surgery. But,
preop quantitative serum ESR & CRP levels being normal confers a strong likelihood that the loosening is non-septic4. Frozen section has excellent specificity and
negative predictive value4. It is best performed on the macroscopic periprosthetic interface tissue membrane (rather than joint capsule or pseudocapsular tissue8) that accumulates between the surgically exposed bone surface and that contact zone with the prosthesis (we are NOT talking about some nearly invisible biofilm) & composed in four patterns7:
- Type I, wear particle induced (aseptic) type: foreign debris (sometimes polarized visible) (20% or more composed by mix of foreign matter, macrophages & giant cells).
- Type II, infectious induced type: (reactive tissue with polys, a few plasma cells, scant if any detritic wear particles.
- Type III, combined type: mixed infectious & wear components.
- Type IV, indeterminate type: negative for type I or type II components.
Pre-operative joint aspirations of these loosening cases are notoriously false negative by culture when
the joint is actually septic (and, intra-operative cultures are also 50% false negative2). Until shown to be septic, a non-crystalosis pyarthrosis can still include
rare instances of "idiopathic sterile pyarthrosis
" [CN08-43]...see first paragraph, above. And, of course, the loosening can be due to truly aseptic reasons & include significant histiocytosis with both endogenous (bone & cartilage "dust") and exogenous (prosthetic "dust" or lubricant material) detritic material (which can be very subtle [L10-10642]). Joint
fluids also may be sent looking for morphological evidence of prosthesis failure: polys and/or organisms or joint-prosthesis detritic debris.
Unless a frozen section is performed, special processing is advisable [HERE] so that the urate crystals in the specimen avoid
aqueous processing and can be visualizable in wet preps or permanent
tissue sections as refractile under polarized light exam.
CAUTION: Microbiologic culture of joint samples at surgery has been shown to yield both false positive & false negative results4. And innoculating a joint
sample into a blood culture flask/bottle gains a better rate of true "positive cultures"3...& case positivity can also be enhanced if the
prosthesis (in addition to that media innoculation) is sent sterile to microbiology for special handling. Septic positivity CRITERIA: Feldman2 modified Mirra's criteria: the surgeon
(decisions 70% specific for sepsis2) selects the clinically "most suspcious" area...pink-tan tissue and
NOT white fibrous scar tissue (of a pseudocapsule or
the joint-cement interface) and sends at least two samples (or more) for frozen sections. The pathologist finds the 5 most cellular areas in a specimen for evaluation of
concentration of tissue polys (do not count any surface exudate). Not counting any degenerating cells (cell margins and nuclei must be intact), 40x exam of at least the 5
makes a diagnosis of "septic" IF there are MORE than 5 polys per high power field in at least 5 separate high power fields. But, even
this has only a 50% sensitivity. And, are all such positive cultures actually reflective of septic pathogenicity or just a reaction to "biofilms" of bacteria on the prosthesis
surface which somehow impede the osteointegration of the prosthesis3? The most common organism is coag. neg. Staph3. And, aseptic calcinosis
may be additionally documented [L07-9036].
- Kaplan DL, et. al., "Pyogenic Arthritis...", J. Clinical Rheumatology 8(5): 273-275, October 2002.
- Feldman DS, et. al., "The Role of Intraoperative Frozen Sections in Revision Total Joint Arthroplasty", J. Bone & Joint Surgery 77:1807-1813, 1995.
- Bori G, et. al., "Low Sensitivity of Histology to Predict the Presence of Microorganisms in Suspected Aseptic Loosening of a Joint Prosthesis" , Modern Pathology
19(6):874-877, June 2006.
- Kanner WA, et. al., "Reassessment of the Usefulness of Frozen Section Analysis for Hip and Knee Joint Revisions", AJCP 130(3):363 - 368, September 2008.
- Mirra JM, et. al. 1976 & 1982.
- Edrees AF, et. al., Pyogenic Arthritis...", J. Clin. Rheum. 8(5):273-275, October 2002.
- Morawietz L, et. al., Proposal for a histopathological consensus classification of the periprosthetic interface membrane, J Clin Pathol. 59(6): 591–597, June 2006.
- Bori G, et. al., Interface Membrane is the best sample for histological study to diagnose prosthetic joint infection, Modern Pathology 24(4): 579-584, April 2011.
- expert opinion, member of our orthopedic medical staff.
(posted 21October 2007; latest addition 22 November 2013)