Measurement of anterior-posterior knee laxity: a comparison of three techniques.

Several non-invasive techniques have been developed to assess anterior-posterior (A-P) laxity of the knee, however, their accuracy remains unclear. Roentgen Stereophotogrammetry Analysis (RSA) is a three-dimensional motion analysis method that has been shown to be an accurate tool for evaluating joint kinematics. Thus. RSA provides a means that can be used to evaluate other less invasive techniques. The objectives of this study were to compare A-P laxity values as measured using the KT-1000 Knee Arthrometer, planar stress radiography and RSA, and to determine if they detect similar changes in A-P laxity over time in 15 subjects following anterior cruciate ligament reconstruction with patellar tendon autografts. The A-P laxity values of the injured knee were measured immediately following surgery and at their 3-, 6-, and 12-month follow-up visits. A-P laxity was defined as the A-P translation of the tibia relative to the femur that occurred between the posterior and anterior shear load limits of -90 to +130 N, respectively. The values of A-P laxity across all time points were 11.4 +/- 3.0, 10.2 +/- 3.3, and 6.9 +/- 3.0 mm (mean +/- standard deviation) for the KT-1000, planar stress radiography and the RSA methods, respectively. These values were significantly different from each other (p < 0.001). The two-dimensional analyses techniques (planar stress radiography and the KT-1000) consistently over-estimated the true laxity values that were obtained using the three-dimensional RSA technique. Significant increases in A-P laxity values over time were also detected with the KT-1000 (p = 0.04) and the RSA technique (p = 0.04). However, this increase was not evident when using planar stress radiography (p = 0.89). This study determined that the KT-1000 and RSA document temporal changes in A-P laxity following ACL reconstruction that were not documented by planar stress radiography.