New Hope for KT Knee Ligament Testing


Call me an incurable nerd, but there are few things I enjoy more than a serious chat with a scientist, especially if there is an opportunity for collaborative study. At the recent AOSSM meeting in Toronto, I discovered a small engineering firm that not only is making a slightly modified version of the venerable KT 1000 knee ligament arthrometer, but is willing to take old models into their shop in the Florida panhandle and help knee surgeons recondition the devices. When I say the new version is “slightly” modified, I mean that the original nylon gear and independent arm mechanism haven’t been altered. The dial has been replaced by an LED readout. This preserves the key mechanical linkage feature that has been the key to its reliability for the measurement of AP displacement of the knee.

Let me back up a second. For years, those of us who were trained to use the KT 1000 and KT 2000 have been worrying how or if we’d be able to get help refurbishing and repairing our devices as they have become worn. The original maker, MedMetric Inc., went out of business several years ago. Since then, we have had to do whatever repairs we could do ourselves, without the good engineering support that MedMetric had provided through the years. Fortunately, the internal workings require little maintenance, but the Velcro straps and some cosmetic features, as well as the electronic load cell and wiring, wear out with time and use.

This is more than just nostalgia for an old and trusted gadget: a KT 1000 manual maximum side-to-side difference has been shown to be the most reliable way to diagnose ACL deficiency in any given patient. It is at least as good as direct visualization via arthroscopic examination (Daniel, et al. 1994), and superior to manual examination by even the world’s most experienced knee surgeons (Daniel et al. 1991). So the measurement device allows us to apply diagnostic criteria in an extremely reliable and safe way, at very little cost, in order to identify and treat knee ligament injuries.

Today, many people assume that an MRI is all you need to diagnose a ligament injury. This approach defies logic and sound practice, in my view. Even if you are convinced that MRI can show you injury in all cases, every patient deserves an exam to test the functional integrity of the ligament. As I teasingly point out to my radiologist colleagues: you don’t use a brain MRI to see how the brain works, so why would you trust an MRI to tell if a ligament is working? Any question of function requires a functional test for a conclusive answer.

Although the study remains to be done, I hypothesize that, in the hands of all but the most novice examiners, this clinical test (manual maximum side-to-side diffference of >= 3mm with KT 1000) is better than MRI. At any rate, the potential loss of our ability to perform ligament arthrometry would represent an enormous backward leap in clinical evaluation of knee laxity and ligament injury. I am happy to say that there are some very interesting tools being developed that will further enhance our ability to test ligament function in the clinic and in the field. But it is worth pointing out that none to date has been shown superior to this very easily applied test with a validated measurement tool. It will be very helpful if we can continue to maintain the KT1000 as a known standard against which newer techniques and tools can be compared.

Interestingly, the principal engineer at this company spent six years in San Diego during the 1980’s. He knew Dale Daniel and Larry Malcom, the designers of the KT1000 and 2000 arthrometer models, and of course he has chatted many times over the years with Dick Watkins, who took over the company from Larry but eventually closed the doors. And he knew of Mary Lou Stone’s role as Dale’s long-time collaborator. Perhaps these connections are why he has taken up the mantle; I’ll ask him the next time we talk.

Take a look at the website,, if you are interested. For me, it was a highlight of the meeting to talk to an engineer who understands and appreciates the role of arthrometry (objective measurement) in clinical evaluation, and who is ready to help us get our gear in shape as well as to look at new ways to apply modern gadgetry to laxity measurement.