Introduction: Within the last few years numerous operative procedures have been described aiming a biological repair of damaged articular cartilage. Current techniques are: Microfracture, Osteochondral Autografting (Mosaicplasty) and Autologous Chondrocyte Transplantation (ACT).

Several new studies have shown, that the defect size plays a major role in the clinical outcome of the different procedures. Thus, it makes sense to measure the size of a cartilage defect before indicating a certain method for biological repair.

Material and Methods: We have developed a software (beta-version) for measuring the size of a cartilage defect during a routine arthroscopy in a real-time mode. The programme is based on an Infrared-Navigation tool (Orthopilot, B.Braun-Aesculap, Germany).

In order to proof the reliability and the usefulness of this device, we carried out following study: in each of 6 cadaver-knees we performed 2 full-thickness cartilage defects (MFC and LFC) of different size.

In a first run 3 surgeons had to scope the joint and estimate the defect size with means of a scaled probe-hook. In a second run we performed a measurement of the defect with the Orthopilot™; finally an open measurement after arthrotomy was done to act as reference.

Results: Measurement of the cartilage defect size was clearly superior to an estimation by probehook. Especially the inter-observer difference between the surgeons was widely spread, whereas the max. mismeasurement with the Orthopilot was 2mm.

Discussion: Our study has shown, that navigational-assisted determination of chondral defects is superior to a simple estimation of a defect size by a probehook. Considering that the defect size is a crucial point in choosing the appropriate procedure for the treatment of cartilage defects, navigation devices like the CDM-software is maybe a helpful tool in making the right decision for a suitable method of biological cartilage repair.