Painful TKR

Differential Diagnosis of the Painful TKA 

 

Surgical Diagnosis  

 

1.  Prosthetic loosening and failure 

2.  Infection 

3.  Patellofemoral tracking problems  

4.  Instability 

5.  Recurrent intra-articular soft-tissue impingement / Component overhang  

 

Nonsurgical Diagnoses  

 

1.  Referred pain - Hip / Back  

2.  Reflex sympathetic dystrophy  

3.  Bursitis-tendonitis  - Pes anserine / patella / popliteal bursitis  

4.  Persistent crystalline deposition - Gout / pseuodogout 

5.  Neurovascular problems  - Neuropathy / Radiculopathy / Vascular claudication / Thrombophlebitis / DVT

6.  Expectation / Result mismatch  - Multiply operated knee / Secondary gain issues / Unrealistic expectations  

7.  Psychiatric disorders and depression  

 

Infection v Loosening

 

History

 

Postoperative course

- infection / course of antibiotics / persistent drainage post operatively

 

Nature of Pain

 

°Pain-free interval  

- indolent infection

- pathology elsewhere (pain same as pre-op)

 

Pain-free interval 

- loosening / infection / implant failure

 

Mechanical pain 

- loosening

 

Rest pain / night pain 

- infection

 

Start up pain

- loosening

- as implant settles then pain subsides

 

Examination

 

Knee painful

 

Signs infection

 

Effusion

- able to aspirate

 

Careful examination of spine / hip / vascular status

 

Xray

 

Problems

- may be normal in face of pathology

- can't DDx infection vs loosening on XR

- serial comparison very important

 

Bone Scan

 

Problems 

- very sensitive, poor specificity

- can have increased vascularity for several months

- 1 year post cemented TKR

- 18 months post uncemented TKR

 

Bone Scan TKR 12 months Diffuse Uptake

 

Advantage

- pathology unlikely if negative

 

Infection

- diffuse uptake all 3 phases (blood flow, early and delayed bone phase)

 

Bone Scan Infected TKR

 

Loosening

- focal uptake unless whole prosthesis loose

- nil increase on blood flow or blood pool

 

Bone Scan Loose TKR Normal Blood Pool PhaseBone Scan Loose TKR Increased Bone Phase

 

Bone Scan Loose TKR

 

Also diagnose

- stress Fractures

- RSD

 

Technetium Labelled White Cell Scan 

 

Uncertain role 

- expensive, difficult to perform

- have to harvest WC, label with technicium

- alone not superior, use in conjunction with bone scan

- increase sensitivity if increase on bone phase in WC and bone scan

 

White Cell Scan Infected TKR

 

Van Acker et al Eur J Nuc Med 2001

- WCC 100% sensitive but 53% specific in infected TKR


Bloods

 

WCC

 

Little value

- increased in 15%

- raised only if very septic

 

ESR 

 

> 30 mm 

- 80% sensitivity & specific 

 

Problem

- raised post operatively for up to 12 months

- remote pathology can elevate

- permanently raised in RA

- can be raised in aseptic loosening

 

CRP 

 

> 10 mg/l

- 90% sensitive & specific

- negative predictive value 99%

 

Advantage

- more predictable response post OT

- peak at day 2 (~400), normal after 3 weeks

- rarely increased with loosening

 

Aspiration

 

Technique

- no antibiotics > 4 weeks

- no LA (bacteriostatic)

- if only 1 specimum positive then repeat

 

> 65% white cells very high risk for infection

> 1700 white cells per microlitre

 

Intra-Operative Frozen Section

 

PMN Cell Count per HPF / average over 10

 

> 5 per hpf

- 84% sensitive

- 96% specific

 

> 10 per hpf

- 84% sensitive

- 99% specific

 

Intraoperative gram stain & M/C/S

 

Sensitivity < 20%, but very specific

- 10% false positive

 

Surgical Opinion

 

Sensitivity 70%

Specificity 85%