Managing the Patient with an Unstable TKA

    Instability is the cause of about a quarter of revision total knee arthroplasty (TKA) procedures, making it one of the most common reasons for revision. [1-3]

    At ICJR’s 11th Annual Winter Hip & Knee Course, William P. Barrett, MD, from Proliance Orthopedic Associates in Reston, Washington, discussed the workup of the patient who presents with suspected knee instability and shared insights on revising the knee.

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    Diagnosing instability after TKA can be challenging and will likely require multiple visits. Typically, patients will report that:

    • The knee doesn’t feel right.
    • They have difficulty going up and down the stairs and getting out of a chair.
    • The knee is swollen.
    • They have anterior knee pain.

    Physical examination will generally reveal:

    • Effusion
    • Good range of motion
    • Tenderness over anterior structures of the knee

    The surgeon should also establish where the knee is loose, either in extension or flexion (or, rarely, both). Weight-bearing radiographs can be helpful, as can loaded flexed lateral radiographs of the knee, to determine if there is abnormal translation in the lateral view. Comparing lateral radiographs of the operated knee with the contralateral knee can show whether posterior condylar offset has been restored.

    In a patient with minor instability, Dr. Barrett will recommend a trial of physical therapy, which generally will help. It is not appropriate, however, for patients with more significant instability.

    Once Dr. Barrett determines that the patient is a candidate for a revision procedure, the surgical technique will depend on why the knee is unstable.

    • If the knee is loose in flexion, the goal is to fill the flexion space by upsizing the femoral component to increase the posterior condylar offset. If a rotational-type stem is being used, translate the femoral component posteriorly and use posterior augments to fill the flexion gap. Also, be sure to correct any excess posterior tibial slope.
    • If the knee is loose in extension, move the femoral component distally and use distal augments.
    • If the knee is loose in flexion and extension – which is very rare – use a thicker tibial insert.
    • If, despite all efforts, the gaps can’t be balanced, used constrained implants.

    Dr. Barrett noted that research shows the degree of improvement in the unstable TKA is typically modest compared with other reasons for revision surgery, [4,5] primarily because patients with instability tend to have better preoperative functioning than patients whose TKAs are being revised for aseptic or septic loosening.

    Something to keep in mind when counseling patients with TKA instability who are considering revision surgery.

    Click the image above to watch Dr. Barrett’s presentation, including his review of the classification and etiology of the unstable TKA.

    Disclosures: Dr. Barrett has disclosed that he receives royalties and research support from and is a consultant for DePuy Synthes.


    1. Fehring TK, Odum S, Griffin WL, Mason JB, Nadaud M. Early failures in total knee arthroplasty. Clin Orthop Relat Res. 2001 Nov;(392):315-8.
    2. Sharkey PF, Hozack WJ, Rothman RH, Shastri S, Jacoby SM. Insall Award paper. Why are total knee arthroplasties failing today? Clin Orthop Relat Res. 2002 Nov;(404):7-13.
    3. Pitta M, Esposito CI, Li Z, Lee YY, Wright TM, Padgett DE. Failure after modern total knee arthroplasty: a prospective study of 18,065 knees. J Arthroplasty. 2018 Feb;33(2):407-414. doi: 10.1016/j.arth.2017.09.041. Epub 2017 Sep 25.
    4. Grayson CW, Warth LC, Ziemba-Davis MM, RM Meneghini. Functional improvement and expectations are diminished in total knee arthroplasty patients revised for flexion instability compared to aseptic loosening and infection. J Arthroplasty. 2016 Oct;31(10):2241-6. doi: 10.1016/j.arth.2016.03.001. Epub 2016 Mar 10.
    5. Rajgopal A, Panjwani TR, Rao A, Dahiya V. Are the outcomes of revision knee arthroplasty for flexion instability the same as for other major failure mechanisms? J Arthroplasty. 2017 Oct;32(10):3093-3097. doi: 10.1016/j.arth.2017.05.010. Epub 2017 May 15.