Correlating KT-1000 Measurements with Clinical Tests of Knee Stability

Abstract & Commentary

Synopsis: KT-1000 measurements may have little correlation with the patient’s perception of knee function and stability.

Source: Tyler TF, et al. Association of KT-1000 measurements with clinical tests of knee stability one year following anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther 1999;29(9):540-545.

A variety of clinical tests are available that assist in determining the status of the knee after cruciate ligament reconstruction. The purpose of this study was to determine the relationship between measurements using the KT-1000 arthrometer at 89N and other outcome measures. Outcome measures used in this study included the Lysholm and Tegner questionnaires and Lachman and Pivot shift tests. The KT-1000 measurements (side-to-side difference measurements) have historically been used to evaluate the amount of knee joint laxity following anterior cruciate ligament (ACL) reconstruction. The question remains as to how KT-1000 values relate to the ability of the knee to function as well as to other clinical tests.

Tyler and colleagues studied 90 patients who had undergone ACL reconstruction using a patella tendon autograft by the same surgeon. Approximately one year following surgery, KT-1000 testing was performed by one of two experienced testers. In addition, patients were evaluated with the Lysholm and Tegner questionnaires for a subjective rating of knee function and activity level, and underwent a physical examination that included Lachman and pivot shift tests.

Data analysis included Pearson product moment correlations to determine the association between KT-1000 measurements, Lysholm scores, and Tegner scores. Spearman rank correlations were used to determine the relationship between KT-1000 measures, Lachman grades, and pivot shift grades. In addition, a one-way analysis of variance (ANOVA) was used to compare Lysholm and Tegner scores between patients with tight, moderate, and loose KT-1000 measurements (1, 3, and 5 mm, respectively). KT-1000 results indicated that there were 60 tight, 11 moderate, and 19 loose patients.

Lysholm and Tegner scores were not associated with KT-1000 scores. In addition, there was a weak relationship (r = 0.39) between KT-1000 measures and Lachman grades. This relationship went down even further when KT side-to-side differences were compared to the Lachman. Pivot shift grades, in addition, had a weak relationship to KT-1000 measures (r = 0.24) and this relationship became a negative one when side-to-side differences were addressed.

Comment by Clayton F. Holmes, EdD, PT, ATC

The results of this study indicate that the KT-1000 measure, while possibly a clinical measure of knee joint laxity, has little to do with the patient’s perception of the functional ability of the knee. In addition, while a relationship is acknowledged between Lachman and pivot shift tests and KT-1000 measures, these measures are weak. These findings do not indicate that any of these measures should be used solely to measure final outcome. Instead, the question becomes what is the "gold standard." In today’s health care environment, where the focus is on outcome measures, the seemingly best outcome measure is the patient’s perception of reality. If this is true, then questionnaires such as the Lysholm and Tegner would be more indicative of a positive outcome than more "objective" measures such as the KT-1000 or the Lachman and pivot shift. It should also be noted that this study was well done in many respects. However, there was no indication that the examiners who performed all KT-1000 measures had any data to support their reliability other than their experience with the instrument. In addition, there was no inclusion or exclusion criteria described in the article with regard to sample population. We do not know how the sample was chosen. These weaknesses notwithstanding, this study gives us another indication that our reliance on so-called "objective" data may need to be rethought. All of these measures have their value; however, any of them alone may be limited.

Which of the following tests were strongly related, according to the Tyler study?

a. KT-1000 results and Tegner scores.

b. KT-1000 results and Lysholm scores.

c. KT-1000 results and pivot shift.

d. KT-1000 results and Lachman exam.

e. None of the above