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    ICJR DEBATES: Is There Value in Custom Implants for TKA?

    Are patient-specific implants the answer to complaints that a new knee “doesn’t feel natural?” Dr. Raj Sinha and Dr. Steven MacDonald debate the pros and cons of this issue.

    Total knee arthroplasty (TKA) is a very successful procedure, with more than 90% good to excellent results in long-term studies.

    However, 15% to 20% of patients are not happy with their new knee – it “doesn’t feel natural” is one common complaint.

    One solution to the patient satisfaction issue might be custom TKA prostheses. At ICJR’s Pan Pacific Orthopaedic Congress, Raj K. Sinha, MD, PhD, and Steven J. MacDonald, MD, FRCSC, debated the pros and cons of custom implants.

    CUSTOM TKA: PRO
    Raj K. Sinha, MD, PhD
    STAR Orthopedics, La Quinta, California

    According to Dr. Sinha, “Custom TKA is not the way of the future, it is the way of now.”

    He noted that current surgical techniques are trying to make a symmetrical prosthesis design work in an asymmetrical knee that has asymmetrical kinematics and asymmetrical ligaments. It should be no surprise that it doesn’t work very well.

    Dr. Sinha said that reports from non-designing surgeons have shown that it is possible to use traditional materials to design a custom implant that, compared with conventional, off-the-shelf designs, provides:

    • Superior kinematics
    • Better short-term results (patient satisfaction and range of motion)
    • Shorter length of hospital stay

    Custom implants are accurate and fit well, Dr. Sinha said, and are easy to put in. In addition, the single-use instruments provided with custom implants help make the process simpler, contribute to the accuracy, and may be a factor in reducing infection rates.

    The only downside Dr. Sinha finds with custom implants is the relatively long manufacturing time.

    With modern manufacturing techniques, the cost of custom implants is no longer a factor, and compared with conventional implants, the overall cost for the episode of care – an important metric in bundled payment models – is actually lower with a custom TKA implant, Dr. Sinha said.

    Innovation comes from either current needs or a good idea with potential future application. Dr. Sinha said custom prostheses are both needed and a good idea.

    Dr. Sinha’s presentation can be found here.

    CUSTOM TKA: CON
    Steven J. MacDonald, MD, FRCSC
    University of Western Ontario, London, Ontario, Canada

    “Let’s remember that 80 to 85% of TKA patients are satisfied with the outcome of their surgery,” Dr. MacDonald responded, which makes custom prostheses a niche product trying to improve the satisfaction rate for 15% to 20 % of TKA patients.

    Custom implants require an expensive preoperative CT or MRI, used in proprietary modelling software to create the implant. The cost of the CT or MRI needs to be included in the calculated cost of this custom implant, Dr. MacDonald said.

    A PubMed search for custom implants reveal only 79 results, most of which are abstracts, not published papers, addressing custom instruments, not custom implants.

    One published study [1] looked at custom implants implanted in 18 cadavers. They were found to have more normal kinematics, which might improve function and patient satisfaction.

    Another study [2] comparing 307 patient-specific implants (PSI) with 314 conventional implants found decreased blood loss (44 mL), decreased length of stay, and decreased range of motion (ROM) for PSI. The authors concluded that there was unlikely to be any clinically significant difference between the 2 designs.

    A study published in Journal of Arthroplasty [3] comparing 21 PSI with 42 conventional implants found PSI patients to have decreased ROM; 28% of PSI patients required manipulation. At 2-year follow-up, the PSI patient had worse satisfaction rate and lower KSS pain scores.

    Summarizing, Dr. MacDonald said there’s no proven benefits to PSI. He questions the cost/quality/safety/logistics calculations, and points out the sizable cost increase of preoperative CT or MRI, custom implant, and instruments.

    He is also concerned with quality assurance: If each implant truly is different, can the outcome truly be better for all patients? How can performance be validated for all implants? And with the large number of standard implant sizes available from all manufacturers, is fit really an issue?

    Customized implants for TKA are not the way of the future, Dr. MacDonald said, unless it can be demonstrated that:

    • Cost is equal to or less than conventional implants
    • Survivorship and complications are equal
    • Patient satisfaction is equal or improved

    Dr. MacDonald’s presentation can be found here

    References

    1. Patil S, Bunn A, Bugbee WD, Colwell CW Jr, D’Lima DD. Patient-specific implants with custom cutting blocks better approximate natural knee kinematics than standard TKA without custom cutting blocks. Knee. 2015 Dec;22(6):624-9.
    2. Schwarzkopf R, Brodsky M, Garcia GA, Gomoll AH. Surgical and Functional Outcomes in Patients Undergoing Total Knee Replacement With Patient-Specific Implants Compared With “Off-the-Shelf” Implants. Orthop J Sports Med. 2015 Jun 24;3(7)
    3. White PB, Ranawat AS. Patient-Specific Total Knees Demonstrate a Higher Manipulation Rate Compared to “Off-the-Shelf Implants”. J Arthroplasty.2016 Jan;31(1):107-11.