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Hospital de la Ribera Valencia, Spain

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We thank Dr. Wettstein and colleagues [1] for their interest in our article [2]. We agree that preoperative knowledge of the status of the articular cartilage is of utmost importance because such knowledge may be a deciding factor regarding open versus arthroscopic surgery. To date, imaging of subtle hip articular cartilage defects remains challenging, although improvements are anticipated given recent advances in both MR and CT hardware and software and possibilities of combined or sequential MR and CT arthrography. However, despite these improvements, the subtle cartilage lesions and flaps, particularly those that are seen in cam-type femoroacetabular impingement, remain difficult to image, moreover some patients might have cartilage lesions with normal articular space.

We have found that applying traction improves our ability to visualize the acetabular and femoral cartilage surfaces. Regarding the amount of traction force applied, we applied a standard load to all patients without accounting for differences in patient weight. This was done in an attempt to standardize the procedure and increase efficiency in a busy clinical setting. We found that 6 kg provided sufficient traction in most patients without causing any significant discomfort or neurologic damage. Currently, we are assessing the feasibility of having three standard traction weights to account for small, medium, and large patients. Per haps we will get more consistent traction when adapting the traction load to patient weight.

To achieve adequate traction, there are two critical steps. First, introduction of fluid into the joint helps overcome the inherent negative intraarticular pressure. This is used in arthroscopy when the concept of "no distraction without distention" is applied. Second, manual traction is essential initially and applied in the MR suite to overcome femoroacetabular coaptation and thus separate the cartilage surfaces. After this, 6 kg is generally sufficient to maintain distraction. If manual traction is not first applied, 6 kg is not sufficient to initially overcome coaptation. However, we did not independently study this point, although we already tried.

Although we measured the distance between cartilage surfaces, we did so predominantly for academic reasons. We think that such measurements are not clinically important. The key point is to achieve separation of the femoral and acetabular cartilage surfaces and thus improve visualization of subtle cartilage lesions.

References

1. Wettstein M, Guntern D, Theumann N. Direct MR arthrography of the hip with leg traction: feasibility for assessing articular cartilage. (letter)AJR 2008;191 :[web]W206[Free Full Text]
2. Llopis E, Cerezal L, Kassarjian A, Higueras V, Fernandez E. Direct MR arthrography of the hip with leg traction: feasibility for assessing articular cartilage. AJR 2008;190 :1124 –1128[Abstract/Free Full Text]

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This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by LLopis, E. Articles by Kassarjian, A. Search for Related Content PubMed Articles by LLopis, E. Articles by Kassarjian, A. Social Bookmarking                      What's this? Hotlight (NEW!) What's Hotlight?