How Bad are Bipolar Articular Cartilage Lesions of the Knee, Really?

We won't fib to you, they're not great — but maybe not as bad as you thought; or maybe unipolar lesions don't do quite as well as we hoped . . . ?

What’s the Claim?

A registry-based study on articular cartilage restoration procedures in the knee (most commonly autologous chondrocyte implantation [ACI]) that compared unipolar to bipolar lesions found:

  • A surprisingly low percentage of patients in either group improved by a clinically important margin. Even 2 years after surgery, only 46% of patients with bipolar lesions and 65% of patients with unipolar lesions improved their KOOS scores by the minimum clinically important difference (MCID) of 10 points.
  • No clinically important difference between unipolar and bipolar lesions in the KOOS score at 24 months, and no differences between the groups at any other time point from 6 to 36 months.
  • No between-group difference in the risk of reoperation (8% in the bipolar group versus 4% in the unipolar group; p = 0.26) or the time to reoperation (17 versus 32 months, respectively; p = 0.23).

On balance, the bipolar lesions did not do nearly as poorly as expected and in most important respects were little different from the unipolar lesions, though a lower percentage of them improved by a clinically important margin at 2 years. Our summary differs from that of the authors, which is important because the authors claimed a number of differences that fell below the MCID — meaning patients probably wouldn’t care about or notice them — as well as some that were not borne out by their own analyses (using language like “this difference was not statistically significant,” which is misleading in this context).

How’s It Stack Up?