This was the question on everyone's mind as Dr. Donna Blankenbaker from the University of Wisconsin, Madison, presented modern practices and future trends in MR imaging of the hip during a keynote address held at the 2008 ARRS in Washington DC.

"It depends on the referring physician" says Blankenbaker, who suggests taking a look at the whole pelvis alongside dedicated imaging of the symptomatic hip.

Dr. Blankenbaker also discussed quadratus femoris muscle tear, which is usually unsuspected clinically. Although quadratus femoris muscle tear is an uncommon injury and mostly seen in women, it is another major cause of hip pain that should be radiologically investigated via MR imaging.

So what can we expect in the future of hip MR? Other than the strong suggestion of cartilage evaluation, Dr. Blankenbaker claims, "though best detected by arthroscopy, hip plicae will be one of the many findings radiologists should start looking for".

The pectinofoveal fold is a known internal structure of the hip and therefore should always be visualized at MR arthrography. According to a study by Dr. Blankenbaker and researchers from the Wisconsin School of Medicine and Public Health Oregon, Wisconsin, by determining the frequency and appearance, as well as defining the variations in appearance, the normal pectinofoveal fold may be distinguished from pathological hip plicae.

In this study, Dr. Blankenbaker et al retrospectively reviewed 152 hip arthrograms of subjects who had subsequent arthroscopy. If present during the evaluation of MR examination, the fold was measured in the anteroposterior, mediolateral and superior-inferior dimensions. The fold was also evaluated for smooth or irregular contour, and evaluated for site insertion. Out of the 152 subjects who had a hip MR arthrograms the pectinofoveal fold was present in 144 (95 per cent) of them.

"The pectinofoveal fold should not be mistaken and should always be visualized", says Blankenbaker.

On the other hand she also states, "Though the surgeons [at her institution] have shown a great appreciation of the finding, if it is not a cause of symptomatology there are no reasons to cut at this time".

"To understand hip imaging it is crucial to understand hip anatomy", suggests Dr. Andrew Ziegert from the University of Wisconsin.

MR arthrography of the hip has been a proven accurate method for the detection of acetabular labral tears.

In a retrospective review of 144 patients who had preoperative arthrograms prior to an arthroscopic diagnosis of an acetabular labral tear, researchers compared the sensitivity of multiple imaging planes for detection of arthroscopically-proven labral tears.

Results showed there were 65 distorted, 41 linear complete, and 38 linear partial tear types. Utilizing all six sequences, 97.2 per cent of the 144 tears were identified as "definite tear" on at least one sequence. By combining three sequences with high sensitivity, 95.8 per cent of the 144 tears were identified as definite tears. The axial oblique sequence had the highest individual sensitivity. Interestingly, Dr. Ziegert's results also showed a significant minority of tears had signal intensity less than gadolinium/fluid.

In this study, Ziegert concluded the axial oblique plane has the highest sensitivity for detection of acetabular labral tears and should be routinely included in MR hip arthrography.

Lastly Dr. Ziegert says, "Use caution when interpreting labral tears as the signal intensity within a tear does not have to be equal to gadolinium/fluid to diagnose a labral tear and in some instances may be less than the gadolinium/fluid signal."