Evaluation of an external device measuring knee joint rotation: an in vivo study with simultaneous Roentgen stereometric analysis

Abstract

D c~( I I . / I I I~~I~ AbstractAn external device ("rottometer") specially designed to measure knee joint rotation was developed and evaluated with respect to its validity. Simultaneous measurements were made with the rottometer and Roentgen stereometric analysis (RSA) in five patients with implanted tantalum markers in the tibia and femur. Measurements of internal and external rotation were made at 90" and 60" of knee flexion using 3, 6 and 9 N m torques. The coefficients of determination ( r 2 ) between the results obtained with the rottometer and RSA were around 0.9 for the total rotation. The rottometer consistently overestimated the rotation by about loo'%, and this systematic error was most constant at 90" Aexion for the different torques. The magnitude of this error from soft tissue deformation as well as the rotatory movements in the hip, foot and ankle joints must be considered when using external devices to measure knee rotation in clinical studies. The most accurate registrations were found in 90" flexion with 9 N ni force (r2 = 0.94).

Objective measurement devices to assess static rotational knee laxity: focus on the Rotameter

“…The results of the knee navigation measurements were slightly different in our setting; however, this is in accordance with the measurements of Almquist et al [1] who also found increased differences in tibial rotation with an increasing torque compared with RSA measurements. This possible measurement error might have an influence on the measured tibial rotation.…”

Objective measurements of static anterior and rotational knee laxity

“…Most researchers apply this torque from internal to external rotation or from external to internal rotation to obtain a complete cycle of rotation. A solution to avoid the hysteresis phenomenon, which comes along with this technique and influences the reproducibility of the measurements [25,26], is to perform separate measurements of internal and external rotation and to include Bpreconditioning trials.R otational knee laxity is influenced by the patient's position and by the location of rotation measurement. Knee rotation is higher if the knee is flexed at 90°compared to 20°and if the hip is extended compared to the flexed position at 90° [ 27].…”

“…-Rottometer [26]: The patient sits on a modified chair with knees and hips flexed to 90°. The inter-rater ICC varied between 0.49 and 0.85 depending on the amount of torque and degree of knee flexion.…”

Design of a knee rotatory kinaesthetic device

“…Using the KRKD software, the moveable platform was randomly moved through ten different angles chosen to include the range to be used in testing. These angles were chosen because they are in the midrange of normal knee rotation [1,29]. The three researchers, who were blinded to the angle set by the software, read and recorded the digital inclinometer reading.…”