DETECTION OF INFECTION IN LOOSENED HIP PROSTHESES - EFFICACY OF SONOGRAPHY

OBJECTIVE. The purpose of this study was to determine the efficacy of sonography in the detection of infection in loosened hip prostheses. M ATERIALS AND METHODS. The normal capsular morphology in 15 asymptomati c patients with total hip replacements was studied sonographically. So nograms were then obtained in 33 patients who had pain in the hip afte r arthroplasty and radiologic findings of loosening of the prosthesis. These patients subsequently underwent aspiration and arthrography of the hip. Six of the 33 symptomatic patients proved to have prosthetic joint infection. RESULTS. On sonograms, the normal pseudocapsule is ad herent to the proximal part of the anterior femoral cortex, and the ca psule-to-bone distance is less than 3.2 mm (average, 2.6 mm). No hips with a capsule-to-bone distance less than 3.2 mm were infected. Sonogr ams in the six patients with infection showed marked intraarticular ef fusion with a mean capsule-to-bone distance of 10.2 mm. Five of these six had extracapsular fluid collections. Two patients with hip disloca tions and four with aseptic loosening of the prosthesis had capsular d istension on sonograms and cultures of aspirated material that showed no growth. CONCLUSION. Sonography can be used to diagnose infection ar ound loosened hip prostheses. All patients who had an intraarticular e ffusion with extraarticular extension seen on sonograms had infection.