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Comparison of a Standard and a Gender-Specific Posterior Cruciate-Substituting High-Flexion Knee ProsthesisA Prospective, Randomized, Short-Term Outcome Study
Young-Hoo Kim, MD1; Yoowang Choi, MD1; Jun-Shik Kim, MD1
1 The Joint Replacement Center of Korea, Ewha Womans University MokDong Hospital, 911-1, Mokdong, YangChun-Gu, Seoul 158-710, South Korea. E-mail address for Y.-H. Kim: younghookim@ewha.ac.kr
View Disclosures and Other Information
Disclosure: The authors 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.

Investigation performed at The Joint Replacement Center of Korea, Ewha Womans University School of Medicine, Seoul, South Korea

Copyright © 2010 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2010 Aug 18;92(10):1911-1920. doi: 10.2106/JBJS.I.00910
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Abstract

Background: 

Recently, much debate has focused on the effect of gender-specific total knee arthroplasty. The purpose of the present study was to compare clinical and radiographic results as well as femoral component fit in patients receiving either a standard posterior cruciate-substituting LPS-Flex or gender-specific posterior cruciate-substituting LPS-Flex total knee prosthesis.

Methods: 

Sequential simultaneous bilateral total knee arthroplasty was performed for eighty-five patients (170 knees). Eighty-five women (mean age, 69.7 years) received a standard LPS-Flex prosthesis in one knee and a gender-specific LPS-Flex prosthesis in the contralateral knee. The mean duration of follow-up was 2.13 years. At each follow-up, the Knee Society score, the Hospital for Special Surgery knee score, the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) score, and radiographs were evaluated. The aspect ratio of the distal part of the femur was compared with those of the standard LPS-Flex prosthesis and the gender-specific LPS-Flex prosthesis.

Results: 

The mean postoperative Knee Society scores (95.5 points in the standard implant group, compared with 96.5 points in the gender-specific implant group) and Hospital for Special Surgery knee scores (90.7 points in the standard implant group, compared with 91.2 points in the gender-specific implant group) were similar in both groups. The mean postoperative WOMAC score was 36.6 points. Postoperatively, the mean ranges of knee motion in the supine position (125° in the standard implant group, compared with 126° in the gender-specific implant group), patient satisfaction (8.3 points in the standard implant group, compared with 8.1 points in the gender-specific implant group), and radiographic results were similar in both groups. The femoral component in the standard implant group fit significantly better than that in the gender-specific implant group (p < 0.0001).

Conclusions: 

The present study did not show any clinical benefits of a gender-specific LPS-Flex total knee prosthesis at the time of short-term follow-up. Longer follow-up is needed to determine whether there will be an advantage in terms of longer-term function.

Level of Evidence: 

Therapeutic Level I. See Instructions to Authors for a complete description of levels of evidence.

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    References

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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    Young-Hoo Kim, MD
    Posted on October 06, 2010
    Dr. Kim and colleagues respond to Dr. Scuderi and colleagues
    Ewha Womans University School of Medicine, Seoul, South Korea

    Thank you very much for your interest in our article entitled, "Comparison of a Standard and a Gender-Specific Posterior Cruciate-Substituting High-Flexion Knee Prosthesis: A Prospective, Randomized, Short-Term Outcome Study" (2010;92:1911-20).

    The first question raised from Scuderi et al. was that we did not explain how we determined the appropriate size of the femoral component, and how many components were upsized, downsized, or a perfect fit. We clearly described in the article how we determined appropriate size. After the cut of the distal femur, the size of the femoral component was determined with a sizer. At the end of the implantation of the selected standard or gender-specific femoral component, the aspect ratios of the distal femur (the transepicondylar width divided by the average anteroposterior dimension of the lateral and medial condyles) and of the standard or gender-specific femoral component (the distance from the medial to the lateral margin at the transepidcondylar line divided by the average anteroposterior dimension of the lateral and medial condyles of the component) were compared. We defined as "close fit (perfect fit)" if the aspect ratios of the distal femur and the femoral component were equal. We defined as "overhang (upsized)" if the aspect ratio of the distal femur was smaller than that of the femoral component. We defined as "underhang (downsized)" if the aspect ratio of the distal femur was larger than that of the femoral component. As mentioned in Table IV, fifty-one of eight-five (60%) standard knees and fourteen of eighty-five (16%) gender-specific knees were close fit (perfect fit). Ten (12%) standard knees and zero (0%) gender-specific knee were overhang (upsized). Twenty-four (28%) standard knees and seventy-one (84%) gender-specific knees were underhang (downsized).

    We performed bilateral simultaneous total knee arthroplasties in the same patients. We found that the morphological data of the distal femur in each knee were similar. Therefore, seventy-one knees (84%) cannot be moved into the overhang (upsized) group. These seventy-one knees (84%) consistently belong to underhang (downsized) group. We had similar results in another study (1).

    We have performed more than 30,000 total knee arthroplasties using North American or European designed standard knee prostheses and fortunately we have not encountered any specific problem because of the design or size of the standard total knee prosthesis. Very rarely, we needed a very small component for patients with childhood pyogenic or TB arthritis with severe hypoplasia of knees. Also, we have not had any problem with the patella because of the thickness or angle of the theanterior femoral condyle.

    We agree with Dr. Scuderi et al. that, since the cohort in our study had good functional scores preoperatively, the knee scoring systems used in this study may not be sensitive enough to discern subtle differences between the two groups postoperatively. Certainly, we need longer follow-up to clarify the benefit of the gender-specific total knee prosthesis.

    Reference

    1. Kim YH, Choi Y, Kim JS. Comparison of standard and gender-specific posterior-cruciate-retaining high-flexion total knee replacement: a prospective, randomised study. J Bone Joint Surg Br. 2010;92:639-45.

    Giles R. Scuderi, MD
    Posted on September 17, 2010
    The Influence of Gender and Ethnicity on Femoral Component Sizing in Total Knee Arthroplasty
    ISK Institute, New York, NY

    To the Editor:

    We read the article, "Comparison of a Standard and a Gender-Specific Posterior Cruciate-Substituting High-Flexion Knee Prosthesis: A Prospective, Randomized, Short-Term Outcome Study" by Kim et al. (2010;92:1911-20) with interest and congratulate the authors for reporting that all patients had an improved clinical outcome and a low complication rate. However, we believe the authors failed to structure this study to provide the information required to support their conclusions about the gender-specific implant design.

    A major shortcoming of this article is failure of the authors to explain how they determined appropriate size for the femoral component, and how many components were upsized, downsized, or a perfect fit. Their statement that the gender implant did not fit better than the standard implant is not supported by the data in Table IV. Realizing that the gender implant has a narrower medial lateral dimension than the standard implant, and the under-hang reported with the gender implant was 2.8 + 1.277 mm, then the majority of those 71 knees (84%) would actually move into the overhang group if a standard implant was chosen. Those observations, in addition to the 10 knees in the standard group with overhang, are not best fit with the standard prosthesis and the implications of femoral component overhang are under-reported (1,2).

    As the gender knee was optimized for the North American and European female, it is not surprising that it is not a perfect fit for the majority of Korean females. Furthermore, standard total knee components do not optimally fulfill the requirements of the anthropometrically smaller Asian population, especially in the smaller sizes (3-6). The data in this article shows that even with these anatomic differences, there is still a need for gender specific prostheses in Korean females.

    Regarding the anterior femur, we would agree that placing a thinner anterior condyle in someone who had a larger anterior condyle would have a negative effect on the efficiency of the extensor mechanism. However, in contrast, overstuffing the anterior compartment would also have a negative effect resulting in pain and limited motion (7). Implants should be designed with the variability of the anterior condylar anatomy taken into consideration (8).

    Finally, this cohort had such good functional scores preoperatively that the knee scoring systems used in this study may not be sensitive enough to discern subtle differences between the two groups post-operatively. We believe that if the authors re-evaluated their data and provided more in-depth information about the distal femoral morphology, femoral component sizing and position, they may have reached different conclusions.

    In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from Zimmer. In addition, one or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (Zimmer).

    References

    1. Mahoney OM, Kinsey T. Overhang of the femoral component in total knee arthroplasty: risk factors and clinical consequence. J Bone Joint Surg Am. 2010;92:1115–21.

    2. Hitt K, Shurman JR 2nd, Greene K, McCarthy J, Moskal J, Hoeman T, Mont MA. Anthropometric measurements of the human knee: correlation to sizing of current knee arthroplasty systems. J Bone Joint Surg Am. 2003;85 Suppl 4:115–22.

    3. Vaidya SV, Ranawat CS, Aroojis AL, Laud NS. Anthropometric measurements to design total knee prostheses for the Indian population. J Arthroplasty. 2000;15:79-85.

    4. Chin KR, Dalury DF, Zurakowski D, Scott RD. Intraoperative measurements of male and female distal femurs during primary total knee arthroplasty. J Knee Surg. 2002;15:213–7.

    5. Kwak DS, Surendran S, Pengatteeri YH, Park SE, Choi KN, Gopinathan P, Han SH, Han CW. Morphometry of the proximal tibia to design the tibial component of total knee arthroplasty for the Korean population. Knee. 2007;14:295–300.

    6. Cheng FB, Ji XF, Lai Y, Feng JC, Zheng WX, Sun YF, Fu YW, Li YQ. Three dimensional morphometry of the knee to design the total knee arthroplasty for Chinese population. Knee. 2009;16:341-7.

    7. Chin KR, Bae DS, Lonner JF, Scott RD. Revision surgery for patellar dislocation after primary total knee arthroplasty. J Arthroplasty. 2004;19:956-61.

    8. Fehring TK, Odum SM, Hughes J, Springer BD, Beaver WB Jr. Differences between the sexes in the anatomy of the anterior condyle of the knee. J Bone Joint Surg Am. 2009;91:2335–41.

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