Efficacy of MRI in classifying proximal focal femoral deficiency.

OBJECTIVE: To evaluate the efficacy of MRI in classifying PFFD and to compare MRI to radiographic classification of PFFD.

DESIGN: Radiographic and MRI classification of the cases was performed utilizing the Amstutz classification system.

PATIENTS: Retrospective evaluation of radiographs and MRI exams in nine hips of eight patients with proximal focal femoral deficiency was performed by two radiologists.

RESULTS: The cases were classified by radiographs as Amstutz 1: n=3, Amstutz 3: n=3, Amstutz 4: n=1 and Amstutz 5: n=2. The classifications based on MRI were Amstutz 1: n=6, Amstutz 2: n=1, Amstutz 3: n=0, Amstutz 4: n=2 and Amstutz 5: n=0. Three hips demonstrated complete agreement. There were six discordant hips. In two of the discordant cases, follow-up radiographs of 6 months or greater intervals were available and helped to confirm MRI findings. Errors in radiographic evaluation consisted of overestimating the degree of deficiency.

CONCLUSION: MRI is more accurate than radiographic evaluation for the classification of PFFD, particularly early on, prior to the ossification of cartilaginous components in the femurs. Since radiographic evaluation tends to overestimate the degree of deficiency, MRI is a more definitive modality for evaluation of PFFD.