Computer-aided pedicle screw placement using frameless stereotaxis.

STUDY DESIGN: In vitro assessment of accuracy and reliability of frameless stereotaxis for insertion of pedicle screws in human cadaveric lumbar spine. OBJECTIVES: To assess a new method of targeting and placing pedicle screws in a human cadaver study. SUMMARY OF BACKGROUND DATA: Pedicle screw instrumentation is common. Complications may occur from improper placement of screws. Even when performed by experienced spinal surgeons, improper placement can occur in 5.2% of pedicles instrumented. Development of computer-guided methods of pedicle screw insertion may decrease this complication rate. METHODS: The technique used preoperative computed tomography scans together with a commercial neurosurgical navigational computer system to assist in placing guidewires in the pedicles. A section of human cadaver spine was first scanned and the data transferred to the workstation. The image data set and physical specimen were then registered by using an instrumented articulated arm to identify selected points on the specimen and randomly sample surface points. Eight highly repeatable locations on each vertebral body were found to be suitable for registration, but better overall accuracy was obtained when surface matching was used in combination with these points. Under guidance of image on the computer, Kirschner wires were inserted into the pedicles of four vertebral bodies. The spine was rescanned, and the planned and resulting positions of the wires compared. RESULTS: The average distance between the planned and resulting wire entry point was 1.2 mm, with an average difference in planned and resulting trajectories of 6.0 degrees. CONCLUSIONS: Computer-aided pedicle screw instrumentation is feasible. Further technical points require clarification before widespread use is possible.

Opening versus closing wedge osteotomy of the curved ulna in radial clubhand.

The use of an opening or closing wedge osteotomy to straighten the curved ulna in radial clubhands was simulated by using a specially designed computer program. Sixty-eight lateral x-ray films of curved ulnas in 39 children aged from a few weeks to early adolescence were examined. When lengthening is possible, closing wedge osteotomies yield, at best, only millimeters gain in length. Many will decrease bone length. There is no advantage in using multiple closing wedges. Opening wedges of reasonable angle will lengthen the ulna by 5 mms or more. Some multiple opening wedges can produce slightly better gains in length, but no more than two wedges should be used.

The excimer laser in orthopaedics.

This review details clinical and laboratory experience with the 308 nm XeCl excimer laser. This ultraviolet laser is not approved yet for use in arthroscopy, but has been shown to be extremely proficient for debridement of degenerate articular cartilage and meniscus. It has fewer advantages than conventional techniques for synovectomy, meniscectomy, and lateral release. Preliminary in vitro and in vivo studies were performed to investigate the character of laser-irradiated articular cartilage and to search for evidence of regeneration. A model of arthritis was created in rabbits to test the effects of the laser. Partial-thickness cuts in articular cartilage also were irradiated to test for cartilage regeneration. In vitro results indicated that the cartilage was sealed, with only a negligible loss in thickness. The results of live rabbit studies initially showed a similar sealing under scanning electron and light microscopy; however, it tended to break down in time. The results of autoradiographic and histologic studies showed no evidence of cartilage regeneration. Recent evidence suggests that the laser may adversely affect chondrocyte vitality in a region beyond the region of visible damage. There is no evidence to suggest that the laser is mutagenic.

Anterior cruciate ligament insufficiency: a dynamic three-dimensional motion analysis.

An electrogoniometer, capable of measuring all six degrees of freedom of knee movement, was developed in our laboratory. This Instrumented Spatial Linkage system was then used to generate data for a three-dimensional assessment of 20 ACL deficient and 30 normal subjects during level walking. The system proved to be a viable method for describing total knee motion. We found the ACL deficient knees to have increased anterior/posterior translation and significant pattern differences compared to the controls. The results of this study may have implications in the treatment of the ACL deficient patient.

Structurally integrated fiber optic damage assessment system for composite materials.

Progress toward the development of a fiber optic damage assessment system for composite materials is reported. This system, based on the fracture of embedded optical fibers, has been characterized with respect to the orientation and location of the optical fibers in the composite. Together with a special treatment, these parameters have been tailored to yield a system capable of detecting the threshold of damage for various impacted Kevlar/epoxy panels. The technique has been extended to measure the growth of a damage region which could arise from either impact, manufacturing flaws, or static overloading. The mechanism of optical fiber fracture has also been investigated. In addition, the influence of embedded optical fibers on the tensile and compressive strength of the composite material has been studied. Image enhanced backlighting has been shown to be a powerful and convenient method of assessing internal damage to translucent composite materials.