04/19/23

INFECTION AND TOTAL KNEE ARTHROPLASTY : DIAGNOSIS AND TREATMENT

Scott M. Heithoff D.O.

INTRODUCTION Deep infection is one of the most disastrous

complications following total joint arthroplasty The incidence of infection is generally considered to be

between 1-2 % Rand et al reported on 3,000 TKA’s at the Mayo Clinic

with an incidence of 1.2% Wilson et al reported on 4,171 TKA’s at Brigham and

Women’s Hospital with an incidence of 1.6%

RISK FACTORS FOR INFECTION The risk of acquiring an infection of a TKA can be broken

into factors related to the patient and to the surgeon Host Factors : Usually unable to be altered Perioperative Factors

Intraoperative Factors Surgical Technique Factors

RISK FACTORS FOR INFECTION Host Factors Relative Risk

Rheumatoid Arthritis 3 - 4.4% Psoriasis 17% Diabetes 7% Transplant 14% Prior Knee Surgery 1 – 4.5%

RISK FACTORS FOR INFECTION Intraoperative Factors

Operating Room Time Air Turnover Rate Laminar Flow Operating Room Traffic Body Exhaust Suits

RISK FACTORS FOR INFECTION Surgical Technique Factors

Hinged Implant Prophylactic Antibiotics Iodophor Drape Previous Incisions Hematoma Wound Dehiscence

MICROBIOLOGY Most deep infections are caused by Staph Aureus (58 – 63%) Two studies reported on the causative organisms:

Bug Rand MorreyStaph 57% 64%

30% epiGram neg 13% 12%Strep 8%Anaerobes 4% 6%Mixed 9% 15%

CLINICAL PRESENTATION Can be broken down into 3 different time frames:

Early (<2 months) Intermediate (2 –24 months) Late (>2 years)

CLINICAL PRESENTATION Early Infection (<2 months)

Associated with wound healing problems Persistent drainage Hematoma Marginal necrosis Dehiscence

Often difficult to differentiate between a hematoma and infection

CLINICAL PRESENTATION Intermediate Infection (2 – 24 months)

Often will have persistent drainage Key to diagnosis is that they will have pain since the

surgery – no pain free interval Difficult to differentiate RSD from infection

CLINICAL PRESENTATION Late Infection (>2 years)

Usually spread hematogenously They has a pain free interval after surgery Acute:

Fever/Chills, Painful swelling

Insidious: Decrease motion, Pain at rest vs. ambulation (mechanical)

PLAIN RADIOGRAPHS Routine evaluation Usually unremarkable Nonspecific signs:

Subchondral bone resorption Periosteal new bone formation Periprosthetic osteolysis

PLAIN RADIOGRAPHS The development of a complete radiolucency around a

component over a short period of time = infection

LABORATORY TESTS WBC Count

Usually not elevated Morrey et al looked at 73 infected TKA’s, only 28%

had WBC count > 11,000 Insall found an average WBC count of 8,300 in

infected TKA’s

LABORATORY TESTS ESR and CRP

Markers of acute inflammation ESR usually 53 – 63 in TKA infections ESR elevated in other inflammatory conditions (RA) ESR has 80% PPV >6 months post-op CRP normalizes 3-4 weeks post-op

LABORATORY TESTS Finland Study on ESR and CRP

40 OA Hips

CRP ESR

Normal pre-op Elevated pre-op (28)

Max POD #2 Max POD #6 (64)

Normal POD #21 Elevated at 1 year (30)

NUCULEAR IMAGING Bone Scan

95% Sensitive 20% Specific May be positive for 1-2 years post-op Positive for loose prosthesis

WBC Scan 84% Accuracy Expensive

JOINT ASPIRATION Gold standard for diagnosing infection Fluid analysis:

WBC >25,000 with 75% PMN’s Glucose

Normally equal to serum Decreased in infection

Protein Normally 1/3 serum Increased in infection

Gram Stain only positive 25% of the time

JOINT ASPIRATION Many false negatives and false positives exist False negatives due to:

Infection localized to bone cement interface Glycocalyx surrounding bacteria Antibiotics prior to aspiration

Recommend 2-4 week antibiotic free interval

72% sensitivity

INTRAOPERATIVE EVALUATION Gram stain – Notorious for false negative results

Only positive 25% of the time Frozen Section – Sensitivity from 7 to 90%

Can be a valid test only if appropriate tissue is examined by an experienced pathologist

Definition Sensitivity Specificity PPV

5 PMNs/HPF 84% 95.5% 70%

10 PMNs/HPF 84% 99% 89%

POLYMERASE CHAIN REACTION Joint fluid is analyzed Advantages:

Unaffected by antibiotics Takes only 4-6 hours Low cost PPV 100%

Disadvantage : No bacteriology or sensitivities

TREATMENT Six options

Chronic antibiotic suppression Debridement with prosthesis retention Resection arthroplasty Arthrodesis Amputation Exchange arthroplasty

CHRONIC ANTIBIOTIC SUPPRESSION Will not eliminate a deep infection Criteria:

Poor medical condition Low virulent organism Antibiotics needed are low toxicity Prosthesis well fixed

DEBRIDEMENT WITH PROSTHESIS RETENTION

Criteria: Short duration of infection (<2-3 weeks) Susceptible Gram Positive organism No draining sinus tracts Well fixed prosthesis

Success in only 20-30% of cases Best used in early post-op (<4 weeks) – 71% success

RESECTION ARTHROPLASTY Implies that the implant is removed with no intention of

subsequent knee reconstruction Ideal candidate = polyarticular RA with limited ambulatory

demands Allows patients

to sit more

readily than

with an

arthrodesis Rarely used

ARTHRODESIS

Traditionally the gold standard for treatment of an infected TKA

Indications: Patient with high functional

demands Single joint disease Young age Extensor mechanism

disruption Poor soft tissue envelope Systemic

Immunocompromise Highly resistant organism

ARTHRODESIS Contraindications:

Bilateral disease Severe ipsilateral ankle or hip disease Severe bone loss Contralateral extremity amputation

Position : 10-15 deg of flexion

ARTHRODESIS Types:

Uniplanar Ex-Fix : 33% Union Biplanar Ex-Fix : 71% Union IM Nail : 83% Union

Not to be used in active infection

AMPUTATION Most feared result following infection Factors leading to amputation:

Multiple revision attempts for infection Use of hinged prosthesis Severe bone loss Intractable pain Life threatening sepsis

Frequency 5.7% in 1058 infected TKA’s

EXCHANGE ARTHROPLASTY Direct exchange of implants – most reports demonstrate

poor results Two-stage

Stage 1 – Removal of all implants and cement, debridement of soft tissue

6 weeks of IV antibiotics

Stage 2 – Reimplant of prosthesis Debate exists on what to do with the knee for the 6 weeks

of antibiotics

EXCHANGE ARTHROPLASTY Types of “spacers” for the knee

Nothing Antibiotic impregnated cement spacer Prosthesis of Antibiotic-Loaded Acrylic Cement

(PROSTLAC) Articulating spacer

EXCHANGE ARTHROPLASTY

Nothing Has been abandoned because

of multiple problems Contracture of the soft tissue Extensor mechanism scarring Instability of knee during antibiotic

administration

EXCHANGE ARTHROPLASTY Antibiotic cement spacer

Spacer serves many roles:

Maintains soft tissue length

Elutes high levels of antibiotics locally

Preserves joint space

90% success rate Complications include

dislodging of spacer, scarring of quadriceps, and decrease motion

EXCHANGE ARTHROPLASTY

PROSTALAC Spacer Produced to combat the problems of decreased

motion and quadriceps scarring after block spacers Purpose is to allow mobility and weight bearing

between stages, while maintaining adequate soft-tissue tension and joint stability

It is also intended to simplify the reimplantation procedure

EXCHANGE ARTHROPLASTY

PROSTALAC Spacer First implanted in 1987 –

flexible polyethylene mold with cement

Was a high friction system Fraught with instability

PROSTALAC Spacer New design decreases friction Posterior stabilized design

EXCHANGE ARTHROPLASTY

EXCHANGE ARTHROPLASTY PROSTALAC ROM

Pre – op : 8 – 70 degrees PROSTALAC implant : 8 – 72 degrees Final ROM : 5 – 91 degrees

EXCHANGE ARTHROPLASTY Popularized by Hofmann

Made by cleaning and autoclaving the removed femoral component

This is reinserted during the same operation and articulates with a new tibial polyethylene insert and sometimes a new all-polyethylene patellar component with pegs removed

Cement is mixed with 4.8g tobramycin to 1, 40g batch of cement

Components are placed with cement in a very doughy state

EXCHANGE ARTHROPLASTY Patients are allowed

50% weight bearing Allowed to move

knee

EXCHANGE ARTHROPLASTY Components are easily

removed at the time of stage II

EXCHANGE ARTHROPLASTY ROM final 5 – 106 degrees Compares with other 2 stage protocols The articulating spacer allows easier reimplantation,

improves bone quality, and improves ROM.

CONCLUSIONS Infection is a feared complication of TKA Standard treatment is two stage exchange arthroplasty

with 6 weeks of IV antibiotics Antibiotic block spacer has a proven track record PROSTALAC and Articulating spacers are on the

horizon