September 23, 2019

Episode 170.0 – Septic Arthritis

11 minutes

An overview of septic arthritis.

Hosts:

Audrey Bree Tse, MD

Brian Gilberti, MD

https://media.blubrry.com/coreem/content.blubrry.com/coreem/Septic_Arthritis.mp3

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Tags: Infectious Diseases, Orthopedics

Show Notes

Episode Produced by Audrey Bree Tse, MD

Background

Bacteria enters the joint by hematogenous spread due to absence of basement membrane in synovial space from invasive procedures, contiguous infection (e.g. osteomyelitis, cellulitis), or direct inoculation (e.g. plant thorns, nails)

WBCs migrate into joint → acute inflammatory process → synovial hyperplasia, prevents new cartilage from forming, pressure necrosis on surrounding joint, purulent effusion

Why do we care?

irreversible loss of function in up to 10% & mortality rate as high as 11%

Cartilage destruction can occur in a matter of hours

Complications include bacteremia, sepsis, and endocarditis

Etiology

Risk factors: extremes of age, RA, DJD, IVDA, endocarditis, GC, immunosuppression, trauma, or prosthesis

Organisms:

Staph: staph aureus (most common), MRSA, Staph epidermis

N gonorrhea: young healthy sexually active adults

Strep: group A & B

GNRs: IVDA, diabetics, elderly

Salmonella: sickle cell disease

Cutibacterium acnes: prosthetic shoulder infection

Consider mycobacterial & fungal in more indolent courses

Presentation

Typically a single, warm, erythematous, tender joint (#1: knee (50% of cases) → hip, shoulder, ankle)

*Any joint can be involved!

IVDA can involve sacroiliac, costochondral, & sternoclavicular joints

Classic teaching: very painful with ROM, but this is not always present!

Joint usually held in position of maximum joint volume

Prosthetic joints may have less pain than expected for a septic joint given changed anatomy and disrupted nerve endings

In 10-20% of cases, can see polyarticular involvement

GC typically monoarticular but commonly polyarticular

Often have fever & separate infection as well (only see fever in ~60% of cases)

Diagnostics

Arthrocentesis:

Gold standard

Tap joint even if acceptable ROM: septic joints can have normal motion so it does not exclude the diagnosis!

Use ultrasound if possible

Relative contraindications: overlying cellulitis (risk of seeding joint) or severe coagulopathies (weigh risk of creation or worsening of iatrogenic hemarthrosis)

Keep in mind that a “dry tap” may occur due to incorrect needle placement, absent/ minimal joint effusion, ort mechanical obstruction

Note: talk to ortho colleagues if prosthesis present prior to performing arthrocentesis

Ortho team may want to perform the arthrocentesis themselves because scar tissue formation and altered anatomic relationships make the procedure more challenging

Usually want to perform washout in OR plus/ minus antibiotic spacer

Send fluid for protein, glucose, cell count with differential, gram stain, culture, and crystals

Often see decreased glucose and elevated protein

The presence of crystals does not rule out septic arthritis

No clear number of synovial WBCs to define septic arthritis, but in general: >30 to 50K/ mm3 synovial WBCs with PMN predominance (>75%) seen in septic arthritis

A 2011 meta-analysis suggests +LRs of 4.7 (95% CI = 2.5 to 8.5) and +LR of 13.2 (95% CI = 3.6 to 51.1) for a sWBC count of >50L × 109 or >100K, respectively

Use the synovial WBC count plus the whole clinical picture to rule in or out the diagnosis of septic arthritis (do not use the synovial WBC in isolation)

Different threshold for prosthetic joints: WBC > 1100 or >64% PMNs = septic arthritis

Gram stains only identify causative organisms 1/3 of the time

Culture negative arthrocentesis can be seen in cases where abx have been given prior to arthrocentesis, or in TB/ brucella/ nocardia/ other indolent organisms like fungi

Labs:

No studies have demonstrated an acceptable sensitivity or overall diagnostic accuracy of peripheral WBC count for SA, but usually see leukocytosis with left shift

ESR and CRP are reasonably sensitive but there is no cutoff that significantly increases or decreases the pretest probability

UA, urine cultures, blood cultures: send even if no fever

Blood cultures are positive in 50-70% of nonGC SA

If GC suspected, do GC NAAT from throat/ rectal/ urethral/ cervical discharge

Imaging:

XRs: effusion, baseline status of joint, contiguous osteomyelitis, fractures, foreign body

US: effusion

CT, MRI: not really used in ED

Differential

Viral arthritis

gout/ pseudogout

HIV associated arthritis

Reactive arthritis

Lyme

Osteo

Septic bursitis

Trauma

Treatment

Septic arthritis is an orthopedic emergency!

Needs IV abx + often washout of the joint

Hold abx as much as possible prior to tap unless pt is unstable or tap cannot be performed easily

Initiate empiric IV antibiotic therapy prior to definitive cultures based

Transition to organism-specific antibiotic therapy once culture sensitivities result

Start empiric abx based on gram stain if available (in non-=GC SA, grain stain is positive in 50% of cases), age group, & risk factors

Empiric abx: Vancomycin 15mg/kg q12h (to cover MRSA) + cefepime 2gr IV q8h (to cover gram-negatives)

If gram stain with GPC = Vancomycin 15mg/kg q12h

If gram stain with GN diplococci = ceftriaxone 1gr IV q24h + Azithromycin 1gr q24h

If gram stain with GN rods = cefepime 2gr IV q8h

If penicillin allergy: ciprofloxacin 500mg q12h or aztreonam 2gr q8h

No need to cover anaerobes unless human/dog/cat bite (then use Unasyn to cover eikenella, pastereulla, capnocytophaga, anaerobes, etc.)

They usually need antibiotics for 2-6 weeks: 2 weeks for strep, up to 6 weeks if S aureus

Pain control: consider moderately flexed splinting

Admit all patients with suspected septic arthritis until SA is ruled out, abx, monitoring, likely operative intervention

Take-Home Points

Patients may present with either a single affected joint or polyarticular; they may or may not have a fever

Have a high index of suspicion for SA, and a low threshold to tap: pts do not necessarily present w/ “classic” findings and it is difficult to distinguish SA from crystal arthropathy

ESR, CRP, serum WBC are not definitive diagnostic tools for septic arthritis

There is no exact cutoff for synovial WBCs for diagnosis: use whole clinical picture & keep 50K in mind for native joints, and >1100 for prostheses

Treat with empiric abx after tap then narrow accordingly, & admit all patients with septic arthritis

Involve your ortho colleagues early especially for prosthesis

References

Carpenter CR, Schuur JD, Everett WW, et al. Evidence-based diagnostics: Adult septic arthritis. Acad Emerg Med. 2011;18:781-796.

Jones D, Clements C. Physical exam and bloodwork do not adequately differentiate infectious from inflammatory arthritis. In: Mattu A, Chanmugam A, Swadron S, Woolridge D, Winters M. Avoiding Common Errors in the Emergency Department. 2nd Edition. Philadelphia, PA: Wolters Kluwer; 2017; 412-414.

Kazzi A, Zaghrini E. Septic Arthritis. In: Schaider J, Barkin R, Hayden S, Wolfe R, Barkin A, Shayne P, Rosen P. Rosen and Barkin’s 5-Minute Emergency Medicine Consult. 5th Edition. Philadelphia, PA: Wolters Kluwer; 2015; 102-103.

Osmon D, Berbari E, Berendt A, Lew D, Zimmerli W, Steckelberg J, Rao N, Hanssen A, Wilson W.

Diagnosis and Management of Prosthetic Joint Infection: Clinical Practice Guidelines by the Infectious Diseases Society of America, Clinical Infectious Diseases, Volume 56, Issue 1, 1 January 2013, Pages e1–e25, https://doi.org/10.1093/cid/cis803

Mlynarek C, Sullivan A. Arthrocentesis Tips. In: Mattu A, Chanmugam A, Swadron S, Woolridge D, Winters M. Avoiding Common Errors in the Emergency Department. 2nd Edition. Philadelphia, PA: Wolters Kluwer; 2017; 684-686.

Purcell D, Terry B, Sharp B. Joint Arthrocentesis. In: Purcell D, Chinai S, Allen B, Davenport M. Emergency Orthopedics Handbook. 1st Edition. Cham, Switzerland: Springer; 2019; 87-104.

Sheth U, Moore D. Septic Arthritis — Adult. OrthoBullets. [https://www.orthobullets.com/trauma/1058/septic-arthritis–adult]. Updated 1/9/19. Accessed 8/2/19.

A special thanks to our Infectious Diseases Editor:

Angelica Cifuentes Kottkamp, MD

Infectious Diseases & Immunology

NYU School of Medicine

A special thanks to our Orthopedics Editor:

Daniel Purcell, MD

Emergency Medicine

NYU Langone Brooklyn

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