[PSI-technique for kinematic alignment]

Compared with the current gold standard of knee endoprosthetics, the concept of kinematic alignment is more responsive to the individual anatomy of the patient as it enables the three-dimensional restoration of individual axes, joint lines and capsule tension. One point of criticism is the lack of intraoperative control over individual bone resections with conventional instrumentation. However, with the help of CT-based individual 3D-printed cutting blocks, a precise preoperative plan can be transferred to the operating room. The aim of this article is to explain the operative technique of patient-specific instrumentation (PSI)-protected kinematic alignment.

The procedure is based on a preoperative 3D model of the bony anatomy of the patient, with the aid of which the planning of the operation, with the positioning and size of the implant, as well as the necessary bone resections, are carried out. With this information about anatomy and resection levels the individual cutting blocks are produced, aided by a 3D printer. Intraoperative control is achieved by measuring the resection by means of a gage and comparison with the digital 3D design.

With the aid of the 3D-printed PSI cutting blocks the preoperative plan of kinematic alignment can be implemented in a precise manner. It is a simple tool and does not require any great expense. Compared with the conventional instrumentation, the operating time is shortened. However, because of the purely CT-based design, no information about the state of the soft tissue is obtained.