The role of magnetic resonance arthrography (MRA) in the evaluation of patients with femoroacetabular impingement (FAI) to assess femoral head-neck junction asphericity and labral pathology is well established. However, in our experience, the presence of acetabular cysts on MRA, which may signify underlying full thickness articular cartilage delamination and progression towards arthropathy, is also an important feature.

We retrospectively reviewed 142 hips (mean age 32 years, 47 men, 95 women), correlating the findings on MRA with those found at the time of open surgical hip debridement to ascertain the prevalence of acetabular cysts and the association with underlying acetabular changes. Fourteen MRAs demonstrated features consistent with underlying acetabular cystic change. At the time of surgery, this was confirmed in eleven cases that demonstrated a full thickness articular chondral flap in all cases and an underlying acetabular cyst. The sensitivity, specificity, positive predictive value and negative predictive value of MRA in relation to acetabular cysts was 55%, 97.5%, 78.5% and 92.9% respectively.

We believe acetabular cysts on MRA to be a significant finding. Such patients are likely to have an associated full thickness chondral lesion and features of early degenerative change, influencing outcome and prognosis. Our clinical practice has changed to reflect this finding. For those patients with cysts on MRA, we offer open debridement only to the severely affected young and favour arthroscopic debridement in older patients with smaller cams. We believe hip preservation surgeons should be aware of the significance of acetabular cysts and be prepared to adjust treatment accordingly.