Titanium 3D-printed ankle cage infection

Case contributed by Dr Alex Ansaldo

Presentation

Investigation of potential metalware infection in the right ankle in the context of ankle pain and raised C-reactive protein on a background of ankle trauma and numerous revisional surgeries.

Patient Data

Age: 35 years
Gender: Male

There has been internal fixation of the right tibia, ankle and calcaneus with an intramedullary nail extending to the foot from the tibia, a screw through the calcaneus and a metal ball spacer replacing the posterior portion of the calcaneus. There is considerable soft tissue swelling around the ankle.

Nuclear medicine

1. Significantly increased uptake localizing to the metallic spacer device at the site of absent/excised right talus, most marked anteriorly, new relative to the previous FDG PET scan. In the clinical setting this is highly suspicious for active infection.

2. Less marked uptake along the remainder of the right ankle intramedullary/arthrodesis nail, most marked proximally and distally, which may be reactive or due to lower grade infective/inflammatory change.

3. Diffuse skin thickening and subcutaneous edema in the right lower leg distally, extending into the right ankle and foot, with diffuse mild FDG avidity, suspicious for associated cellulitis, for clinical correlation.

Case Discussion

Further case specifics:

  1. Injury: Motorbike accident 3 years prior with compound fracture-dislocation of the right ankle posteriorly (with talar fracture).
  2. Pertinent surgical history:
    • washout and debridement following by external fixation at time of injury
    • right ankle syndesmosis fusion 2 years ago
    • planned elective removal of metalware 1 year ago with titanium 3D-printed cage insertion
    • four debridements 6 months ago for graft infection
  3. Non-surgical management: Despite short-course intravenous antibiotics and long-course oral antibiotics, ankle pain persistent and this coupled with the low-grade C-reactive protein elevation prompted the above workup.
  4. Outcome: As a result of the FDG PET findings, the patient is on the waitlist for metalware removal.

Discussion:

Orthopedic metalware infection is estimated to occur in 16% of traumatic fractures and can be a difficult entity to distinguish from aseptic loosening. FDG PET is more sensitive than 111In-labeled leukocyte/99mTc-sulfur colloid bone marrow (WBC/BM) imaging for the purposes of detecting infection in hip and knee prostheses and avoids the complexity and contamination risks of the latter. This is at the cost of only a moderate decrease in specificity as seen below.

Sensitivity/specificity for infection detection for hip prostheses:

  • FDG PET: 82% / 93%
  • WBC/BM: 39% / 96%

Sensitivity/specificity for infection detection for knee prostheses:

  • FDG PET: 95% / 88%
  • WBC/BM: 33% / 89%
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Case information

rID: 69865
Published: 31st Jul 2019
Last edited: 14th Aug 2019
Inclusion in quiz mode: Excluded

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