Aims: The accuracy of percutaneous CT-Fluoro navigation is compared with the accuracy of the surface-matching procedure. Methods: 68 transpedicular and transvertebral canals were placed percutaneously in an in vitro. The deviation between probe-position and pre-planed trajectory was measured. Evaluated were the mean deviation of the entry point, the exit point, the transverse trajectory angle deviation and the cranio-caudal trajectory angle deviation. Next the soft tissue was removed and the same procedure was done using CT-based surface matching navigation with a registration root mean square of < 1.0 mm. Results: For CT-Fluoro the mean deviation of the entry point was 1.9 mm ± 0.8 (range 0.1–3.2 mm), the mean exit point deviation on the anterior vertebral cortex was 2.1 mm ± 1.1 (range 0.2–3.8 mm). The measurement after surface matching resulted in 1.5 mm ± 0.6 (range 0.0–3.0 mm) for entry point deviation, 1.9 mm ± 0.9 (range 0.1–5.0 mm) for exit point deviation. Conclusions: There is no statistical significant difference of the accuracy between both procedures (Students T-test). Tissue trauma can be reduced as the posterior surface of the vertebra needs not to be exposed as for contemporary registration methods. This offers new promising aspects in percutaneous and minimally invasive spinal techniques

The Blackburne and Peel method of assessing the position of the patella was applied to 185 knees with Osgood--Schlatter disease in 125 patients. The normal index of 0.80 was confirmed in 73 control knees. The average index in the knees with Osgood--Schlatter disease measured 1.01 (patella alta) boys and 0.91 in girls. The value increased to 1.06 in boys with radiological evidence of loose ossicles in the tibial tuberosity or the patellar tendon. This finding indicates that the strong pull of the well-developed quadriceps muscle is probably the most important aetiological factor in patella alta associated with Osgood--Schlatter disease.