Respiratory motion compensation with tracked internal and external sensors during CT-guided procedures.

This paper investigates the possibility of using the motion of a patient's anterior surface in combination with a motion model to compensate for internal respiratory motion during tracked biopsies. Position data from two electromagnetically tracked sensors, one placed on the patient's sternum, the other incorporated into a biopsy needle, were acquired during a liver biopsy. The data were used to evaluate the correlation between the position measurements of the two sensors and to derive an affine motion model to assess respiratory motion compensation for image-guided interventional procedures. The correlation reached up to 94% for ranges of steady respiration. The residual motion of the internal sensor after compensation is reduced by a factor of approximately four.

Interlocked feedback loops within the Drosophila circadian oscillator.

Drosophila Clock (dClk) is rhythmically expressed, with peaks in mRNA and protein (dCLK) abundance early in the morning. dClk mRNA cycling is shown here to be regulated by PERIOD-TIMELESS (PER-TIM)-mediated release of dCLK- and CYCLE (CYC)-dependent repression. Lack of both PER-TIM derepression and dCLK-CYC repression results in high levels of dClk mRNA, which implies that a separate dClk activator is present. These results demonstrate that the Drosophila circadian feedback loop is composed of two interlocked negative feedback loops: a per-tim loop, which is activated by dCLK-CYC and repressed by PER-TIM, and a dClk loop, which is repressed by dCLK-CYC and derepressed by PER-TIM.

The 69 bp circadian regulatory sequence (CRS) mediates per-like developmental, spatial, and circadian expression and behavioral rescue in Drosophila.

The period (per) gene is an essential component of the circadian timekeeping mechanism in Drosophila. This gene is expressed in a circadian manner, giving rise to a protein that feeds-back to regulate its own transcription. A 69 bp clock regulatory sequence (CRS) has been identified previously upstream of the period gene. The CRS confers wild-type mRNA cycling when used to drive a lacZ reporter gene in transgenic flies. To determine whether the CRS also mediates proper developmental and spatial expression and behavioral rescue, we used the CRS to drive either lacZ or per in transgenic flies. The results show that the CRS is able to activate expression in pacemaker neuron precursors in larvae and essentially all tissues that normally express per in pupae and adults. The CRS is sufficient to rescue circadian feedback loop function and behavioral rhythms in per01 flies. However, the period of locomotor activity rhythms shortens if a stronger basal promoter is used. This study shows that regulatory elements sufficient for clock-dependent and tissue-specific per expression in larvae, pupae, and adults are present in the CRS and that the period of adult locomotor activity rhythms is dependent, in part, on the overall level of per transcripts.

Disconnected mutants show disruption to the central projections of proprioceptive neurons in Drosophila melanogaster.

We used a P[GAL4] enhancer-trap line, C161, in conjunction with the UAS-lacZ reporter construct to visualize the central projections of a defined set of thoracic and abdominal sensory neurons in a disconnected (disco) mutant background. The results show defects in the organization of sensory axons in the larval and adult central nervous system. The defects are indicative of problems with axon growth and development and include (a) poor axon fasciculation, (b) aberrant axon growth, (c) excessive terminal branching, and (d) ectopic innervation. Sensory neuron identity appears to be normal. The defects are comparable to those previously described for larval photoreceptor and adult retinular cells in disco mutants and extend the known effects of this mutation. Reduced larval and adult viability are likely to result from locomotory defects related to the disruption of the sensory system.

Assessment of vertebral body motion during spine surgery.

STUDY DESIGN: In vitro and in vivo assessment of the accuracy of devices proposed for tracking spine motion during surgery; in vivo assessment of vertebral motion during spine surgery. OBJECTIVES: 1) To quantify the accuracy of newly designed vertebral body trackers; 2) to demonstrate the feasibility of tracking vertebral motion in a cadaveric model; and 3) to quantify the vertebral motion that occurs during spinal surgery. SUMMARY OF BACKGROUND DATA: Computer techniques are beginning to be applied to spine surgery. Validation of accuracy of methods of spinal tracking has not been reported. No information exists on the amount of vertebral motion that occurs during surgery. Because the new techniques require accurate positional information for the vertebral body, it is important to understand and evaluate methods of tracking vertebrae. METHODS: An optical tracking system (Northern Digital, Waterloo, Ontario, Canada) was used to track custom-designed trackers. The reliability and accuracy of the trackers were evaluated in vitro. The proposed tracking methodology for human testing was performed using a cadaveric model, and after successful completion, human testing was done in the operating room to evaluate the motion of two vertebral bodies during exposure for instrumentation of the lumbar spine. This technique was used to evaluate the custom designed trackers effectiveness for tracking vertebral bodies for pedicle screw insertion. RESULTS: The trackers developed were accurate and capable of tracking the motion of the spine. Measured motion of L3 and L4 during breathing was 1.3 mm, peak to peak. Maximal intraoperative motion of the vertebral bodies was 12.3 mm during maneuvers simulating dissection of soft tissue and targeting of spinal pedicles. CONCLUSIONS: Significant motion occurs in lumbar vertebral bodies during surgery. Breathing motion alone is up to 1.3 mm, and surgeon-induced motion up to 10 times greater. Vertebral body trackers for use with an optical position sensor were capable of measuring this motion.

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.

Full-thickness rotator cuff tears. A biomechanical comparison of suture versus bone anchor techniques.

We performed a biomechanical comparison of two rotator cuff repair techniques using fresh-frozen human cadavers. Nine pairs of cadaveric shoulders had standardized full-thickness tears made at the supraspinatus tendon insertion. One of each pair of the cadaveric shoulders was repaired by pulling the tendon into a bone trough in the humeral head using standard sutures. The remaining half of the pairs was repaired using anchor sutures. The repairs were tested using a servohydraulically operated material testing system. The anchor suture repair was significantly stronger than the standard suture technique irrespective of bone quality. Failure occurred predominantly through bone in the suture repairs and as a result of suture breakage in the anchor repairs. The anchors should be placed into the edge of the subchondral bone adjacent to the articular surface. The surgeon should direct the anchor so that the direction of the pull is approximately 90 degrees to the anchor, with the humerus at 30 degrees of abduction.

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.

An in vivo study of the effect of excimer laser irradiation on degenerate rabbit articular cartilage.

Eighteen adult rabbits with mechanically induced degenerative arthritis of one knee were divided into two groups. The first group underwent arthrotomy and lavage of the arthritic joint. The second group underwent arthrotomy and irradiation of the degenerate articular surface with the Excimer (xenon chloride ultraviolet, 308-nm) laser (Arthrex Arthrolase MAX-10, Germany) in a saline environment. Rabbits from each group were killed at intervals up to 12 weeks for histological and metabolic studies of their articular cartilage. In the control group there was no improvement in the macroscopic or microscopic appearance of the articular surface. In the laser-irradiated group initially there was macroscopic and microscopic smoothing of the fibrillated surface. By 6 weeks the surface had begun to show the reappearance of fibrillation. There was no evidence that there was any increase or decrease in mitotic or metabolic activity in the laser-irradiated group as compared with the controls.

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.