2008 Abstract : 13

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Authors: Zalavras CG, Lee J, Rigopoulos N, Learch T, Patzakis MJ

Title: MRI Findings in Osteomyelitis of the Hip

Institution: University of Southern California, LAC + USC Medical Center, Los Angeles, CA

Purpose: Adult hip osteomyelitis due to hematogenous septic arthritis is rare. Extension of infection in adjacent tissues may not be apparent leading to inadequate debridement. We aimed to determine the extent of infection in hip osteomyelitis using MRI.

Methods: This is a retrospective study of adult patients with hematogenous hip osteomyelitis. Patients with prior injury or surgery to the hip were excluded. Eleven adult patients with 12 involved hips were identified and were included in the study. There were 9 male and 2 female patients with a mean age of 47 years (range, 33-59 years) Ten of 11 patients (91%) had one or more comorbidities, the most common being intravenous drug abuse (6 patients). S. aureus was the most common organism, present in 6 hips. All patients had undergone imaging evaluation of the hip and pelvis area with plain radiographs and MRI. All patients underwent surgical debridement with a Girdlestone procedure and received antibiotic therapy for 6 weeks. The soft tissue abscesses were managed either surgically or with CT-guided aspiration. The MRI images were reviewed by a musculoskeletal radiologist to evaluate in detail the extension of infection to adjacent structures.

Results: The MRI examination revealed hip effusion and femoral head edema in all 12 hips. Femoral head erosions were present in 10 hips, edema of the acetabulum in 11, and acetabular erosions in 6 hips. The intertrochanteric area of the proximal femur was involved in 7 cases and the femoral medullary canal in 3. One or more adjacent soft tissue abscesses were discovered in 8 of 12 hips (67%). Iliopsoas and subiliacus abscesses were the most common soft tissue abscesses, present in 4 hips each. Subgluteal and subadductor abscesses were identified in 3 hips each.

Discussion and Conclusion: MRI can delineate the extent of infection in structures other than the hip,such as the surrounding muscles and the medullary canal of the femur. This information may be useful for patient management and preoperative planning so that all locations of the infectious process are addressed.