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UniSpacer Arthroplasty of the Knee
Domenick J. Sisto, MD1; Isaac L. Mitchell, MD1
1 Los Angeles Orthopaedic Institute, 4955 Van Nuys Boulevard, Suite 615, Sherman Oaks, CA 91403. E-mail address for D.J. Sisto: laortho1@yahoo.com
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The authors did not receive grants or outside funding in support of their research 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. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
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Investigation performed at the Los Angeles Orthopaedic Institute, Sherman Oaks, California

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2005 Aug 01;87(8):1706-1711. doi: 10.2106/JBJS.D.02339
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Background: The operative treatment of medial compartment knee arthritis is controversial. The purpose of the present study was to report the experience of a single surgeon with the UniSpacer arthroplasty for the treatment of isolated medial compartment arthritis of the knee.

Methods: From April 2002 through November 2002, thirty-seven UniSpacer arthroplasties were performed in thirty-four patients for the treatment of arthritis that primarily involved the medial compartment of the knee. The Ahlbäck radiographic evaluation scale was used to grade the severity of arthritis; the mean preoperative score was 2.6 points for the medial compartment and 0.5 point for both the lateral and patellofemoral compartments. The study group included eighteen women (nineteen knees) and sixteen men (eighteen knees) who had a mean age of fifty-five years (range, forty-two to seventy-five years) at the time of surgery. Twelve patients had had a previous arthroscopic meniscectomy. The mean preoperative Knee Society function score was 60 points (range, 40 to 80 points), and the mean preoperative Knee Society objective score was 62 points (range, 40 to 76 points).

Results: After a mean duration of follow-up of twenty-six months (range, twenty-four to twenty-nine months), there were no excellent, ten good, fifteen fair, and twelve poor results. The mean postoperative total function score was 69 points (range, 40 to 82 points), and the mean Knee Society objective score was 72 points (range, 45 to 88 points). Six of the twelve poor results were in knees that had dislocation of the UniSpacer. All twelve knees were revised to a total knee arthroplasty.

Conclusions: On the basis of this experience, we do not recommend UniSpacer arthroplasty for the treatment of degenerative arthritis of the medial compartment of the knee.

Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.

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    Domenick J. Sisto, MD
    Posted on March 19, 2011
    Dr. Sisto responds to Dr. Anderson
    Orthopaedic Surgeon, Los Angeles Orthopaedic Institute, Sherman Oaks, California

    A patient who has had a failed unispacer due to subluxation should be revised to a unicompartment or total knee arthroplasty. The problem with revising the failed unispacer by placing a larger implant in the knee is that this increases the likelihood of pain and stiffness. The unispacer has been designed to rotate in the knee and a thicker spacer may prevent this rotation and lead to failure. This patient has already had a failed unispacer arthroplasty and I believe it would be more prudent to proceed with a unicompartment arthroplasty which has a more reliable long-term outcome.

    Tom Anderson
    Posted on March 19, 2011
    Management of Failure of the Unispacer
    Physician, Sansum Clinic, Santa Barbara, California

    To the Editor:

    In the authors' opinion, should a patient who had a failed unispacer due to subluxation be subjected to a second, larger unispacer after failure rather than proceed with the more invasive unicompartmental knee replacement or TKA?

    Domenick J Sisto, M.D.
    Posted on October 13, 2005
    Dr. Sisto responds to Dr. Papavasileiou
    Los Angeles Orthopaedic Institute, Sherman Oaks, CA 91403

    I thank Dr. Papavasileiou for his letter.

    The patients were ideal candidates to be revised to a unicompartmental arthroplasty following the failure of their Unispacer. I chose to perform a total knee arthroplasty because, in my hands, I can more reliably predict an excellent outcome with this procedure. I frequently perform unicompartmental arthroplasties but am still occasionally disappointed with their result and I must eventually perform a total knee arthroplasty a few years later. I felt that I had already subjected these patients to one failed procedure and I wanted to minimize the possibility of a second failure.


    Domenick J. Sisto, M.D.

    Athanasios V. PAPAVASILEIOU, BSc, M.D., Ph.D.
    Posted on September 21, 2005
    Management of Failed UniSpacer Arthroplasty of the Knee
    East Sussex Hospitals NHS Trust, Eastborne DGH, East Sussex, UK

    To the Editor:

    We would like to congratulate Drs. Sisto and Mitchell for their interesting article (1). However we feel that clarification is necessary regarding the management of the 12 failed UniSpacer arthroplasties.

    As described in great detail in the paper the patients that had undergone the procedure had isolated unicompartmental osteoarthritis clinically, radiologically and arthroscopically. We wonder why the failed implants were revised to a Total Knee rather than Unicompartmental Knee Arthoplasty (UKA) since the patients seem to be ideal candidates for it. Did the intra-operative findings reveal any changes that would make a UKA unsuitable?

    Yours truly,

    Dr A. Papavasileiou BSc, MD, PhD

    Mr A. Chipperfield MRCS

    Mr D. Isaac MRCS


    1. Sisto DJ, Mitchell IL. UniSpacer Arthroplasty of the Knee. J Bone Joint Surg Am. 2005;87:1706-1711

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