Purpose

In the literature, the hip is near-ubiquitously described as a mechanical ball-and-socket joint. This implies purely rotational motion as well as sphere-on-sphere contact geometry. However, previous works, by several authors, have quantitatively demonstrated asphericity of the articular hip surfaces in a variety of populations. This in turn implies the true kinematics of the hip joint may be more complex than purely rotational motion.

Previously, general ellipsoidal shapes have been used to model the articular surface of the acetabulii of dysplastic hips. This work aims to orient the major axis of these ellipsoids with respect to the anterior pelvic plane (APP).

Purpose

Prospective randomized intervention trial to determine whether patients undergoing rotating platform total knee arthroplasty have better clinical outcomes at two years when compared to patients receiving fixed bearing total knee arthroplasty as measured by the WOMAC, SF-36 and Knee Society (KSS) scores.

Purpose: The purpose of this clinical trial was to investigate the accuracy of a novel method for computer-assisted distal radius osteotomy, in which computer-generated patient-specific plastic guides were used for intra-operative guidance. Our hypothesis was that these guides combine the accuracy and precision of computer-assisted techniques with the ease of use of mechanical guides.

Method: In a consecutive series of 9 patients we tested the accuracy of the proposed method. Prior to surgery, CT scans were obtained of both radii and ulnae in neutral rotation. Three-dimensional virtual models for both the affected and unaffected radius and ulna were created. The models of the unaffected radius and ulna were reflected to serve as a template for the correction. Custom-made software was used to plan the correction. The locations of the distal and proximal drill holes for the plate were saved and the locations of the distal holes before the osteotomy were determined. The design of a patient-specific instrument guide was calculated, into which a mirror image of intra-operative accessible bone structure of the distal radius was integrated. This allowed for unique positioning of the guide intra-operatively. For each planned drill location a guidance hole was incorporated into the guide. A plastic model of the guide was created using a rapid prototyping machine. Intra-operatively, a conventional incision was made and the guide was positioned on the distal end of the radius. The surgeon drilled the holes for the plate screws into the intact radius. The guide was removed and the surgeon performed the osteotomy using the conventional technique and shaved the bone from the distal radius fragment to accommodate the plate. Using the pre-drilled holes the plate was affixed to the distal radius fragment. The distal fragment was reduced until the proximal screw holes in the plate aligned with the pilot holes in the bone. To analyze the accuracy of the intra-operative procedure we compared the post-operative alignment of the radius with the planned alignment. A lateral and an A/P digitally reconstructed radiograph (DRR) of the plan were calculated. These DRRs were used to evaluate the radial inclination, the volar tilt and the ulnar variance of the planned alignment. Post-operative lateral and A/P X-Rays were used to determine the same three post-operative radiographic indices. The post-operative values were compared with the planned values.

Results: We found an average deviation for the radial inclination of 0.5°(StDev 1.8), for the volar tilt of 0.7°(StDev 2.3), and for the ulnar variance of 0.8mm (StDev 1.9).

Conclusion: These results show that the computer-generated instrument guides accurately achieved the planned alignment. The guides were easy to integrate into the surgical workflow and eliminated the need for intra-operative fluoroscopy for guidance of the procedure.