[Kinematic investigations of the talocrural joint in human cadaver specimens. Basic studies for the development of a hinged fixator]. / Biomechanische Untersuchungen der Achsenkinematik an menschlichen Sprunggelenken Grundlagenuntersuchungen für die Entwicklung eines Bewegungsfixateurs.

To determine the specifications of a hinged fixator for the upper ankle joint, biomechanical investigations were performed on 20 human cadaver specimens and the talocrural axis was recorded by X-ray cinematography in all levels of the space. The results showed a medium variation of the axis in zero position (mean: 5.8 degrees ) from 3 degrees to 10 degrees in the anterior-posterior view. The span of the axis migration around zero position amounted to a minimum of 3 degrees and a maximum value of 10 degrees (mean: 7.2 degrees ). It could be ascertained that the axis kinetics does not move linearly in all cases. The talus rotation (the axle deviation from the sagittal plane) amounted to a minimum value of 2 degrees and a maximum value of 12 degrees (mean: 5.3 degrees ). In the transverse level, the axis kinetics was tracked by separate X-ray markings of the lateral and medial cortical of the talus in the zero point of the talocrural axis. The results were typical migration curves of the X-ray markings, demonstrating a ventral convex curve at the medial and lateral cortex. This migration of the cortex crossing point of the axis was geometrically entered in a coordinate system. The variance of the axis cortex crossing point at the medial cortical was X(M)=4.2 mm (min: 2 mm, max: 7 mm) and Y(M)=4.7 mm (2-7 mm), at the lateral cortical X(L)=3.7 mm (1-9 mm) and Y(L) =4.1 mm (1-8 mm). Regarding the clinical relevance for the development of a hinged fixator for the upper ankle joint, the results indicate that an external axis guidance of these axoids is not possible, but that an adjusted axis is necessary taking into consideration the values measured using ligamentotaxis.