Background

In-vitro testing of knee joints remains vital in the understanding of knee surgery and arthroplasty. However, based on the design philosophy of the original Oxford knee simulator, this in-vitro testing has mainly focused on squatting motion. As the activities of daily living might drastically differ from this type of motion, both from a kinematic and kinetic point of view, a new knee simulator is required that allows studying more random motion patterns. This paper describes a novel knee simulator that overcomes the limitations of traditional Oxford simulators, providing both kinematic and kinetic freedom with respect to the applied boundary conditions.

For evaluating the impact of knee surgery, cadaveric knee simulators are commonly applied. However, most of the knee simulators are based on the Oxford type as originally described by Zavatsky (Zavatsky, J. of Biomechanics, 1997). These simulators mainly focus on the squatting motion. Although a wide range of flexion angles can be examined while performing this motion, the significance for activities of daily living is limited.

To that extent a new knee simulator has recently been developed at Ghent University. In this simulator, the ankle motion is dynamically controlled in the sagittal plane; both in the proximal/distal direction and the anterior/posterior direction. As a result, this simulator allows simulating random motion patterns, e.g. cycling, stair ascent and descent, … The ankle translation is unrestrained in the medial/lateral direction. In addition, all rotational degrees of freedom are unrestrained at the ankle, resulting in four degrees of freedom at the ankle. The hip adds one rotational degree of freedom being the rotation in the sagittal plane. This leaves 5 degrees of freedom (DOF) to the knee; the sixth being flexion/extension that is controlled by the actuators at the ankle. During the simulation of different motion patterns, the quadriceps and hamstring force are actively controlled to mimic realistic conditions obtained through musculoskeletal simulations.

In this study, five cadaveric experiments have been performed on the simulator. While mounting the cadaveric specimens in the test rig, the initial alignment remains crucial. Whilst the rig leaves 5 DOF to the knee, it is important to restore the anatomical position of the hip and ankle. To minimize the impact of the mounting procedure, cadaver specific 3D printed guides are used to assure the alignment of the cadaver in the test rig. As a result, the kinematics are more likely to represent physiological conditions. These kinematics have been evaluated in accordance to the methodology described by Grood&Suntay (Grood & Suntay, Transactions of the ASME, 1983). Therefore, a CT scan of the examined knee is combined with motion tracking data from rigidly attached markers on both the femur and the tibia. The cadaveric knees have been subjected to a variety of motion patterns, i.e. squatting and cycling. The squatting experiments provide evidence that the knee simulator creates adequate boundary conditions as the kinematic patterns coincide with literature reportings. The cycling experiments however significantly differ from the squatting patterns. Most noteworthy is the difference in terms of internal/external rotation for these native knees (Figure 1). This internal/external rotations is highly fluctuating from flexion to extension. This is understood as the quadriceps force is not constant during the extension phase, representing physiological conditions.

Background

Glenoid component aseptic loosening is the most common source of total shoulder arthroplasty (TSA) revision. In an attempt to strengthen cemented glenoid component fixation, divergent pegged glenoids were designed. Divergent peg creation was intended to increase cement purchase and provide resistance to component rocking.

Background:

The use of reverse total shoulder arthroplasty (RTSA) has been increasing around the world. However, because of concerns over lack of internal rotation with the reverse prosthesis and the resultant difficulties with activities of daily living (ADLs), many have recommended against performing bilateral RTSA.

Purpose:

The reverse total shoulder arthroplasty (RTSA) was approved for use by the United States FDA in 2004. Since its introduction, its popularity for treating a number of shoulder conditions has grown considerably. However, many patients inquire about the potential to return to playing recreational golf, and at present there are no published data about how the RTSA prosthesis affects the golf swing. The purpose of this study is to evaluate the biomechanics of the golf swing in patients with RTSA, as well as the postoperative changes in handicap, driving distance, and holes played/week.

Introduction:

External rotation (ER) of the shoulder is a commonly used clinical measurement to assess the glenohumeral joint; however, the position in which these measurements are obtained varies between clinicians. The purpose of this study was to compare the following: ER in the upright & supine positions, motion capture & goniometric values of ER, active & passive ER, ER in the right & left shoulders, and ER in male & female subjects.