3.
Evaluation of ultrasound as a primary diagnostic tool for diagnosing
pseudo tumor in THA, with MRI as the gold standard.
Martin Schou, Trine Torfing, Søren Overgaard, Jens-Erik Varmarken
Orthopaedic Research Unit, Odense University Hospital/ Clinical Institute,
Faculty of Health sciences, Southern University Denm; Radiographic
diagnostic Department, Odense University Hospital, Odense, Denmark.;
Orthopaedic Research Unit,, Odense University Hospital/ Clinical Institute,
Faculty of Health sciences, Southern University Denm; Department of
Orthopaedic Surgery, Sygehus syd, Naestved Hospital, Region Sjaelland,
Denmark.
Background:
Metal-on-metal (MoM) total hip arthroplasty (THA) seems to
have a recognized complication in the formation of a reactive periprosthetic
soft tissue mass (pseudotumor), also known to be seen in standard THA.
Though magnetic resonance imaging (MRI) has become a major imaging
modality of the hip, ultrasound (US), especially when performed based on
relevant clinical data is extremely sensitive in detecting small joint and soft
tissue effusions.
Purpose / Aim of Study:
The purpose of this study was to evaluate the
specificity and sensitivity, along with positive predictive value (PPV) and
negative predictive value (NPV), of US in the diagnosis of pseudotumor, with
MRI as the gold standard.
Materials and Methods:
We studied 205 THA hips in 170 patients. 155
MoM-THA and 50 standard THA hips. MRI was performed using an open
scanner T1 weighted, and fore US was performed using a linear 5-10MHz
transducer. Findings of pseudotumor were classified using modified Oxford
type I-III. During both MRI and US the examiner evaluated the diagnostic
overview as poor, fair, good or excellent. Body mass index (BMI) was
calculated on all patients. MRI was evaluated by senior specialist in
musculoskeletal MRI. US was evaluated by a trained Ph.D.-student with
experience from more than 300 diagnostic musculoskeletal US.
Findings / Results:
Pseudotumors were seen in 48 hips by MRI but were
overlooked in 4 hips using US. US found 9 pseudotumors not recognized on
MRI. We thus found a sensitivity of US of 0,92 and a specificity of 0,94.
Finding a PPV of 0,84 and a NPV of 0,98. MRI verified cases overlooked on
US correlates with patients having a high BMI or categorized during US with a
poor or fair diagnostic overview. False positive findings seem to be located
primarily in the close periprosthetic region where MRI sometimes have its
limitations due to metal artifacts.
Conclusions:
US is a valuable tool for diagnosing pseudotumors, but its
sensitivity decreases with the diagnostic overview. The sensitivity of US for
finding pseudotumors in the periprosthetic region might be greater than that of
MRI due to a lack of metal artifacs when performing US.
