Cam-type FAI: is the alpha angle the best MR arthrography has to offer? (Skeletal Radiol 2009;38(9):855-62).

Skeletal Radiol (2010) 39:203–204 DOI 10.1007/s00256-009-0837-0 LETTER TO THE EDITOR Cam-type FAI: is the alpha angle the best MR arthrography has to offer? (Skeletal Radiol. 2009;38(9):855–62) Derek G. Lohan & Leanne L. Seeger & Kambiz Motamedi & Sharon Hame & James Sayre Received: 3 November 2009 / Accepted: 3 November 2009 / Published online: 26 November 2009 # The Author(s) 2009. This article is published with open access at Springerlink.com The authors welcome this opportunity to respond to and clarify a number of issues raised by the letter of Drs. Beaule and Rakhra in relation to our recent paper entitled “Cam- type FAI: is the alpha angle the best MR arthrography has to offer?” [1] Drs. Beaule and Rakhra express concern regarding our use of intra-operative femoral head–neck osteochondro- plasty/arthroscopic debridement in differentiating between the presence or absence of cam-type femoral-acetabular impingement (FAI). Specifically, they refer to the potential of the introduction of significant observer bias using this approach, drawing particular attention to the discrepancy in experience between the two surgeons involved in this study (i.e. 10 versus 25 years). However, as stated in their letter, surgical intervention for FAI has gained mainstream acceptance only as recently as the turn of the century. Regardless of the existence or otherwise of a learning curve, both of these surgeons have therefore had similar time periods in order to become familiar with this entity and its various surgical indications. We are therefore of the opinion that this discrepancy in surgical experience has little impact upon our reported findings. In response to Drs. Beaule’s and Rakhra’s specific questions relating to the activity of each surgeon, the breakdown is as follows: 78 patients were included in the study group, 39 designated as having cam-type FAI and 39 as not having this condition. Of the affected group, 14 underwent trochanteric osteotomy and osteochondroplasty, D. G. Lohan (*) : L. L. Seeger : K. Motamedi : S. Hame : J. Sayre David Geffen School Of Medicine At UCLA, Los Angeles, CA, USA e-mail: derek.lohan@gmail.com 14 underwent osteochondroplasty alone and 1 underwent arthroscopic debridement. All 39 patients in the FAI- negative group underwent arthroscopy, no open procedures were performed in this group. Of course, it should be borne in mind that the decision to proceed with open or arthroscopic evaluation was based upon a combination of patient history, symptomatology and imaging findings, in addition to perhaps other unknown contributing factors. This is a limitation inherent to the retrospective design of any study, a limitation that was discussed at length in our paper. It is likely that this distribution of procedures reflects selection of those considered most likely to warrant surgical correction for an open procedure, while those with atypical symptoms or imaging findings were evaluated with arthroscopy. As a result of only one patient having undergone arthroscopic femoral osteochondral debride- ment, correlation between type of surgical procedure and alpha angle measurement cannot be assessed. It seems that Drs. Beaule and Rakhra have misinter- preted the use of clinical impingement throughout our study. In not a single instance do we use or advocate the use of a positive clinical impingement test as the gold standard for the presence or absence of FAI. Rather we simply evaluated the potential use of this rapidly and routinely- performed clinical examination in suggesting the presence or absence of this condition and compared its performance with that of the alpha angle, AFD (anterior femoral distance) and FNR (femoral neck ratio). It is widely recognized that a positive clinical impingement test is quite non-specific, merely suggesting the presence of acetabular rim “disease.” It is our opinion, however, that it speaks volumes that this clinical test out-performed alpha-angle measurement in suggesting the presence or absence of cam- type FAI in the current study.