Selected Knee Osteotomies and Meniscal Replacement: Effects on Dynamic Intra-Joint Loading
Jack T. Andrish, MD; Helen E. Kambic, MS; Antonio D.C. Valdevit, MSc; Ryosuke Kuroda, MD; Richard D. Parker, MD; Eric Aronowitz, MD; Theodore Elster, BS

Dynamic Range-of-Motion Testing Protocol for Intra-Joint Load Measurement

Through the use of pressure-sensitive color film under static loading conditions, intra-joint loads, contact area, and contact pressure have been determined. Intra-joint loads have also been elucidated through the use of computationally intensive computer simulations. We present an experimental technique and loading mechanism that can provide dynamic intra-joint loads during range of motion. The goal of the study was to establish a dynamic range-of-motion testing protocol encompassing measurement of intra-joint loads while retaining the characteristics of joint compressive loads under minimal constraints to motion.

Materials and Methods

Cadaveric knee specimens were mounted in a testing frame as shown in Figure 1. The quadriceps muscle was fastened to the hydraulic actuator of a materials testing machine (MTS Systems, Eden Prairie, Minnesota) through the proximal insertion site of the patellar tendon. The vastus lateralis and medialis and hamstrings muscles were each loaded with 45 N of tensile load at angles of 17°, 50°, and 0°, respectively, in relation to the femoral axis as described by Lieb and Perry1. A knee flexion moment was generated by a 90-N force equally distributed on both sides of the tibial fixture. All pulleys were terminated and mounted with free rotating swivel joints to reduce external bending moments (Fig. 1).

Fig. 1:

Apparatus for dynamic testing. MTS = materials testing machine, VL = vastus lateralis, and VMO = vastus medialis oblique.

To account for the varied stiffness of the knee during range of motion, an external goniometer mounted at the approximate center of knee rotation was used by the servohydraulic controller as control feedback for the actuator motion. This feedback provided reduced actuator displacement rates at increased flexion angles, at which increased resistance to knee motion was encountered as a result of muscle forces. For all of the specimens tested, knee range of motion was from 15° to …

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