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This study describes a new method for the treatment of osteochondritis dissecans (OCD) in the medial talar dome. Ten cadaveric lower extremities were used to develop and evaluate a retrograde osteochondral grafting technique applying computer-assisted surgery. With the help of a computed tomography (CT)-based navigation system, a guide wire was placed from the lateral talar process into the posteromedial talar trochlea where OCD lesions are predominantly located. Cannulated reamers and arthroscopic shavers were used for the preparation of the recipient hole. The grafts, with diameters of 4.5 mm, 6.5 mm or 8.5 mm were harvested from the lateral femoral trochlea and inserted in a retrograde fashion. The last five cadavers were analyzed for accuracy of surface reconstruction and graft stability. For this purpose a medial malleolar osteotomy and a CT scan was performed. We found steps in the joint surface to range from 0.5 mm to 1.5 mm (mean 0.9 mm, SD 0.4) with the graft always below the surrounding cartilage. Graft subsidence occurred at an applied force of 26.4 +/- 4.6 N. This study indicates that osteochondral cylinders can be inserted in a retrograde fashion to reconstruct the posteromedial talus. Good surface congruency and sufficient graft stability can be achieved.

Objective: CT-guided biopsy still plays a decisive role in the management of liver tumors, especially if the lesions are not visible or accessible by ultrasound. As CT-guided stereotaxy appears to be a very accurate targeting technique, the aim of this study was to evaluate the targeting accuracy, diagnostic yield, and complications of CT-guided stereotactic liver biopsy of primary and secondary liver tumors. Methods and Materials: Prior to stereotactic liver biopsy, patients under general anesthesia were immobilized using a vacuum cushion. Respiratory motion was controlled by temporary disconnections of the endotracheal tube. An opticalbased navigation system was used for 3D trajectory planning and placement of a 15-G coaxial needle via a stereotactic aiming device. The histological samples were obtained using a 16-G Tru-Cut TM biopsy needle system. For evaluation of targeting accuracy the control CT image with the needles in place was fused with the planning CT image. The lateral error at the tip and skin entry point and the angular error were calculated. In addition, the skin-to-liver-surface (SL) distance, the needle-to-liver-surface (NL) angle, and the presence of liver cirrhosis were evaluated. The diagnostic yield was evaluated by histological reports from the institutional pathologists. Results: The median lateral error was 2.5 mm (range: 0-6.5 mm) at the needle entry point and 3.2 mm (range: 0.01-9.4 mm) at the needle tip. The median angular error was 1.06(range: 0-6.64 ). Liver cirrhosis, NL angle and SL distance showed no significant impact on the targeting accuracy. Forty-five of the 46 liver biopsies (97.8%) were diagnostic according to the histological reports. No puncture-related complications such as bleeding or perforation of intestinal organs or lung tissue were recorded.

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