[A novel knee endoprosthesis with a physiological joint shape. Part 1: Biomechanical basics and tribological studies]. / Eine neuartige Knieendoprothese mit physiologischer Gelenkform. Teil 1: Biomechanische Grundlagen und tribologische Untersuchungen.

The natural tibiofemoral joint (TFJ) functions according to a roll-glide mechanism. In the stance phase (0-20 degrees flexion), the femur rolls backwards over the tibia plateau, while further flexion causes increased gliding. This kinematics is based on the principle of a quadruple joint. The four morphological axes of rotation are the midpoints of the curvatures of the medial and lateral femoral condyles and the medial and lateral tibia plateau. In addition, the medial and lateral compartments are shifted a few millimetres in a sagittal direction, the medial tibia plateau being concave and the lateral plateau convex. In most knee arthroplasties, these factors are not taken into account; instead they are equipped with symmetrical medial and lateral joint surfaces. Thereby, the midpoints of the curvatures of the sagittal contours of the lateral and medial joint surfaces, on the femoral as well as on the tibial sides, create a common axis of rotation which does not allow a physiological roll-glide mechanism. The goal of this study was therefore to report on the biomechanical basis of the natural knee and to describe the development of a novel knee endoprosthesis based on a mathematical model. The design of the structurally new knee joint endoprosthesis has, on the lateral side, a convex shape of the tibial joint surface in a sagittal cross section. Furthermore, from a mathematical point of view, this knee endoprosthesis possesses essential kinematic and static properties similar to those of a physiological TFJ. Within the framework of the authorization tests, the endoprosthesis was examined according to ISO/WC 14243 in a knee simulator. The abrasion rates were, thereby, lower than or at least as good as those for conventional endoprostheses. The presented data demonstrate a novel concept in knee arthroplasty, which still has to be clinically confirmed by long term results.

A novel total knee replacement by rolling articulating surfaces. In vivo functional measurements and tests.

The purposes of the paper were as follows: to show the fundamental functional differences between the natural knee and common total knee replacements (TKR), to describe the ideas on how main properties of the natural knee can be adopted by a novel TKR and to present some main biomechanical functions of this TKR. By analyzing the morphology of the articulating surfaces and the kinematics of the natural knee the design of the novel TKR was developed. The use was made of the test procedures established in vitro and of lateral X-ray photographs as well as fluoroscopy in vivo. The function of the novel TKR is comparable to that of the natural knee joint in terms of kinematics (roll/slide behaviour), loads of the articulating surfaces (diminished shear loads), stability and leeway under external impacts, reduction of the load in the patellofemoral joint, and ligament balancing.

[A novel device for active shoulder rehabilitation with glenohumeral traction or compression]. / Ein neuartiges Gerät zur aktiven Schulterrehabilitation unter glenohumeraler Traktion oder Kompression.

The equipment available for rehabilitation of patients with joint conditions still lacks a device that, in common with usual physiotherapeutic measures (manipulation, proprioceptive neuromuscular facilitation, Bobath therapy), is based on traction and/or compression or oscillating forms. The novel "Shoulder Rotator" is such a simple device for the variable treatment of shoulder disorders in all three spatial dimensions. After individual instruction, the patient performs rotating glenohumeral exercises with simultaneous glenohumeral joint traction, compression, or oscillations against static or dynamic resistance. The "Shoulder Rotator" is similar to the established continuous passive motion device for the shoulder and is mounted on a mobile chair. The electronic device control is computerised and permits a wide variety of treatment options, individual regimes, and documentation. The oscillating, compression/distraction mode of operation provides an analgesic effect. The isolated compression mode along the rotatory axis enables conditioning of joint proprioception. The distraction mode along the rotatory axis facilitates muscular relaxation. Resistive rotatory exercises strengthen the rotatory glenohumeral muscles and help centre the humeral head in the glenoid. In addition to the advantage of adding documentation of treatment progress as required for evidence-based medicine, this novel device may bring about a cost-effective, genuine quality improvement in shoulder rehabilitation.