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Scientific Exhibits   |    
Use of a Sentinel Pin as a Guide to Acetabular Component Anteversion in Total Hip Arthroplasty
Wayne M. Goldstein, MD; Matthew L. Jimenez, MD; Alexander C. Gordon, MD; Jill Jasperson Branson, RN, BSN; Kimberly Berland, CST, FA
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The authors did not receive grants or outside funding in support of their research for or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. A commercial entity (Innomed payment of future royalties to Illinois Bone and Joint Foundation) paid or directed, or agreed to pay or direct, benefits to a research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2006 Dec 01;88(suppl 4):97-100. doi: 10.2106/JBJS.F.00590
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Extract

Malpositioning of the acetabular component is a common problem associated with the posterior or posterolateral approach to total hip arthroplasty. Retroversion is also a common problem due to forward rolling (or internal rotation) of the patient during anterior femoral retraction (Fig. 1). Hassan et al. stated that anteversion cannot be assessed accurately during surgery1. Dorr et al. recommended the use of anatomical landmarks at the time of surgery to avoid this problem2. Others have recommended the use of computer-assisted navigation as a method to ensure proper acetabular component alignment3. Asayama et al. assessed intraoperative pelvic motion during total hip arthroplasty with use of a pelvic tilt goniometer that was composed of a digital compass and a three-direction indicator4. We describe an accurate and simple method to measure and correct forward roll during total hip arthroplasty.
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    Wayne M. Goldstein, M.D.
    Posted on January 30, 2007
    Dr. Goldstein et al. respond to Dr. Liaw et al.
    University of Ilinois at Chicago & President, Illinois Bone & Joint Institute, Chicago, IL

    Thank you for your letter on the paper “Use of a Sentinel Pin as a Guide to Acetabular Component Anteversion”. This paper represented a Scientific Exhibit at the American Academy of Orthopedic Surgeons Annual Meeting in 2006. This exhibit contained a video which demonstrated the use of the device during a total hip arthroplasties. The pictures were snapshots in time of the device as we tilted a patient to an appropriate position to insert the cup. These photos were used at the extreme positions to demonstrate how the device worked. This device was only one of many references the surgeon used in the procedure. The Sentinel Pin itself gives a subjective picture of how much forward tilt is occurring and the bubble is used to help approximate the initial angle the body was in prior to placing retractor. That is all it provides. The senior author uses internal references for visual cues. These are the medial wall of the acetabulum, the 12 o’ clock position of the prepared acetabulum for abduction, and either the 9 o’clock or 3 o’clock position for the posterior lip (depending on the side). These three points will generally be accurate for a range near 45 degrees of abduction and 25 degrees of flexion.

    Since the procedure is performed in a teaching institution, the device was developed for residents as an additional visual cue during reaming and cup insertion. This can be more difficult in dysplasia, the presence of osteophytes, and poor visualization in the extremely obese patient. While residents may use the OR table and the external alignment device, the Sentinel Pin allows them to appreciate alignment as the patient is rolling forward during the reaming and cup impaction. We recognize that an experienced surgeon might compensate for forward rolling of the patient, but recommend that less experienced surgeons have the surgical assistant manually correct the roll during preparation and impaction of the cup.

    The postoperative radiographs were AP and cross-table lateral x-ray views (which necessitates the flexion of the contralateral hip). The forward flexion, which some refer to as anteversion, is measured off a cross-table lateral radiograph. While there are many methods in the literature to precisely measure the exact postoperative cup position, there are influences which affect the position of the pelvis while performing the cross table lateral radiograph, and diminish its accuracy. One example is when the opposite hip joint is stiff; flexion of the opposite hip will tilt the pelvis to a greater degree than a patient with a normal hip. We found the position of the cup on postoperative radiographs were within this acceptable range. We agree that operative anteversion is the most important as its relationship to the femoral head and neck will affect stability and wear. Ultimately, the use of computer assisted surgery may provide the added the precision in implant placement we strive for.

    Chen-Kun Liaw
    Posted on January 10, 2007
    Use of a Sentinel Pin as a Guide to Acetabular Component Anteversion in Total Hip Arthroplasty
    En Chu Kong Hospital & Ph.D. candidate of Nat'l Taiwan U. Comp. Sci & Info. Engineering Dept.

    To The Editor:

    In the paper "Use of a Sentinel Pin as a Guide to Acetabular Component Anteversion in Total Hip Arthroplasty", Goldstein et al.(1) presented a new device to measure pelvic position intraoperatively. Moreover they showed excellent results in cup orientation after operation. However, we have some questions.

    1. Goldstein et al.(1) presented 5 figures (Fig. 2 to Fig. 6) to demonstrate the application of the new device. We measured the arc angle of the device in these figures and found that the tilt angle ranged from about 17 degrees to 20 degrees as shown in our Figure 1. In Figure 4 of their article, we note that the tilt indicator is located at the extreme position. This implies that the real tilt may actually be beyond the limits of the device to measure it. How could the authors get the results of 25 degrees of tilt at the time of both acetabular retractor placement and reaming?

    2. Furthermore, we can see clearly that the tilt angles are different in Figures 4 and 5, but the captions in Figures 4 and 5 say that they are all 25 degrees.

    3. There are three definitions of anteversion: the anatomic anteversion; the radiographic (planar) anteversion: and the operative anteversion(flexion)(2,3). The authors should define which type of anteversion was investigated in their study. In our opinion, the most important anteversion values to be obtained should be the operative anteversion.

    4. The authors stated that, "postoperative anteroposterior and lateral radiographs demonstrated 45 degrees of abduction and 20 degrees of anteversion in forward flexion in all ten hips." It would be helpful if they provided more information about the methods and reference points used to make these measurements.


    Fig. 1. The arc angle of the device is measured. In this figure, á is the arc angle from one end to the center, about 17 degrees. The range of tilt it can measure is about -17 to +17 degrees.

    The authors of this did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.

    References:

    1. Goldstein WM, Jimenez ML, Gordon AC, Branson JJ, Berland K. Use of a sentinel pin as a guide to acetabular component anteversion in total hip arthroplasty. J Bone Joint Surg Am. 2006;88(Supp 4):97-100.

    2. Liaw CK, Hou SM, Yang RS, et al. A New Tool for Measuring Cup Orientation in Total Hip Arthroplasties from Plain Radiographs. Clin Orthop. 2006;451:134-139.

    3. Murray DW. The definition and measurement of acetabular orientation. J Bone Joint Surg Br. 1993;75:228-232.

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