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    Are Gender-specific Femoral Stems Needed?

    The goal of this study was to compare the applicability of 2 femoral stem systems in male and female populations via preoperative templating.

    Authors

    Raj K. Sinha, MD, PhD; Vangalea Weems, BS, PA-C; and Margaret J. Cutler, RN

    Disclosures

    The authors have no disclosures relevant to this article.

    Editor’s Note: This article is an except of the authors’ study, No Rationale for Gender Specific Femoral Stems for Total Hip Arthroplasty, published in the journal Reconstructive Review. The full article can be found here. http://www.jisrf.org/pdfs/rr.4.3.32.pdf

    Variations in femoral anatomy [1-4] and acetabular anatomy [5] have been partially ascribed to gender differences. Traditionally, femoral stems for THA have been designed across an entire population including both males and females.

    The purpose of this study was to compare the applicability of 2 femoral stem systems, 1 with modular bodies and 1 with a 1-piece stem, in male and female populations via preoperative templating.

    All patients seen during a single month who presented complaining of knee pain had screening pelvis x-rays. These x-rays formed a consecutive cohort of hips for the templating study (20 females, 27 males).

    During templating, the acetabular component was placed in a fully medialized position at 45º of abduction. The center of rotation was marked. The femoral neck osteotomy was set at 15 mm proximal to the top of lesser trochanter, as recommended in the technique guide. Templates of equal magnification were utilized for both systems.

    System 1 had a double tapered wedge body design, a fixed 135º neck-shaft angle with 2 different offsets (6 mm difference) and 2 different neck lengths (4 mm difference). There were 7 head options with different lengths.

    System 2 had the same body design with a modular neck offering 20 different offsets/lengths and 7 different neck-shaft angles, with only 1 head option.

    Neck length and offset were independent of body size for both systems.

    Bone atlas and CT scan data suggests that women have:

    • Larger canals
    • Relatively shorter necks
    • More varus necks
    • Greater anteversion [2-4]
    • Less acetabular abduction
    • More acetabular anteversion [5]

    As a result, it has been suggested that a gender specific-implant is needed to adequately address such gender-related anatomical variations when considering cementless femoral stems in THA [8]. Significantly, there appear to be gender differences in applicability of femoral stems. Whether these differences translate into poorer outcomes is debatable [9,10].

    According to this study, with a fixed level of neck resection and more neck length and offset options seem to be required for female patients. However, by individualizing the level of neck resection, fewer stem options would be required to reconstruct most hips.

    Similarly, center of rotation of the acetabular component can be adjusted to overcome shortcomings in available stem sizes, although biomechanically, that may be less desirable.

    With appropriate preoperative planning, it would be expected that an experienced surgeon should be able to successfully perform THA regardless of patient gender, obviating the need for gender-specific implants.

    Increased stem modularity has also recently been implicated in pain and bone loss due to increased crevice corrosion [11]. Further, there have been several reports of modular neck disassociation and fracture [6,7], requiring additional surgeries with all of their associated morbidity.

    In these reports, excessive offset has been one associated factor with both modes of modular neck failure. In the present study, we specifically avoided the extremes of the product line, thereby likely reducing the risk of such failures. Nevertheless, recent data compel the surgeon to use caution when planning a hip arthroplasty with enhanced modularity stems.

    There are some limitations of this study:

    • We did not account for appropriateness of stem as a function of variation in anteversion.
    • We included both normal and arthritic hips, which may affect the results.

    Further investigation is necessary to determine the role of neck-shaft angle, bone quality, and adjustment of neck osteotomy height on stem design and patient outcome as a function of gender.

    Nevertheless, it would seem that no single stem product line can account adequately for all the anatomic variations encountered in routine arthroplasty practice, further underscoring the importance of preoperative templating and planning when choosing an implant.

    Author Information

    Raj K. Sinha, MD, PhD; Vangalea Weems, BS, PA-C; and Margaret J. Cutler, RN, are from STAR Orthopaedics, La Quinta, California. .

    Source

    Sinha RK, Weems V, Cutler MJ. No Rationale for Gender Specific Femoral Stems for Total Hip Arthroplasty. 2014; 4(3):32-35. doi: 10.15438/rr.4.3.32. Copyright 2014, Joint Implant Surgery & Research Foundation. Used with permission.

    References

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    2. Gender differences in 3D Morphology and bony impingement of human hips. Nakahara I, Takao M, Sakai T, Nishii T, Yoshikawa H, Sugano N. J Orthop Res. 2011 Mar;29(3):333-9.
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    11. Evaluation and treatment of painful total hip arthroplasties with modular metal taper junctions. Meneghini RM, Hallab NJ, Jacobs JJ Orthopedics, 2012 May 35(5):386-91.