Overall wrist biomechanics are conserved by phenol-based embalming.

Although cadaveric specimens that have been fresh-frozen then thawed are considered the gold standard for biomechanics research, because they most closely represent in vivo tissues, potential problems include a relatively short useful time-span and risk of infection. A recently reported new method of phenol-based "soft" embalming has been found to preserve tissues in a fresh-like state over an extended period of time and simultaneously reduced infection risks. This study presents radio-ulnar deviation end-range data from 4 soft-embalmed and refrigerated human cadaveric forearm specimens over 12 months. All end-range comparisons were found to be statistically equivalent to within a clinically acceptable range of ±5 degrees of radio-ulnar deviation with a 95% con. dence measure of p < 0.01 in every case. These soft-embalmed specimens provide promising results for further use in biomechanical studies.

Investigating the performance of a wrist stabilization device for image-guided percutaneous scaphoid fixation.

PURPOSE: Conventional navigated surgery relies on placement of a reference marker on the anatomy of interest. However, placement of such a marker is not readily feasible in small anatomic regions such as the scaphoid bone of the wrist. This study aimed to develop an alternative mechanism for patient tracking that could be used to perform navigated percutaneous scaphoid fixation. METHODS: A prototype wrist stabilization device was developed to immobilize the scaphoid relative to a reference marker attached to the device. A position measurement system and 3D fluoroscopy were used to study the accuracy and limitations of wrist stabilization during simulated clinical usage with a cadaver specimen. Reference markers mounted on the device were used to measure intra-device motion. Radiometallic beads implanted in the scaphoid were used to measure patient-device motion. Navigated planning and guidance of scaphoid fixation were performed in five cadaver and eight "ideally immobilized" plastic specimens. Postoperative 3D fluoroscopy was used to assess the accuracy of navigated drilling. RESULTS: The average intra-device motion was 1.9 mm during load application, which was elastically recovered upon release of the load. Scaphoid motion relative to the reference marker was predominately rotational with an average displacement of 1.25 mm and 2.0°. There was no significant difference in the accuracy of navigated drilling between the cadaver specimens and the ideally immobilized group. CONCLUSIONS: The prototype wrist stabilization device meets the criteria for effective wrist stabilization. This study provides insight concerning proper use of the device to minimize scaphoid displacement and design recommendations to improve immobilization.

Bone alignment using the iterative closest point algorithm.

Computer assisted surgical interventions and research in joint kinematics rely heavily on the accurate registration of three-dimensional bone surface models reconstructed from various imaging technologies. Anomalous results were seen in a kinematic study of carpal bones using a principal axes alignment approach for the registration. The study was repeated using an iterative closest point algorithm, which is more accurate, but also more demanding to apply. The principal axes method showed errors between 0.35 mm and 0.49 mm for the scaphoid, and between 0.40 mm and 1.22 mm for the pisiform. The iterative closest point method produced errors of less than 0.4 mm. These results show that while the principal axes method approached the accuracy of the iterative closest point algorithm in asymmetrical bones, there were more pronounced errors in bones with some symmetry. Principal axes registration for carpal bones should be avoided.

Ultrasound-guided percutaneous scaphoid pinning: operator variability and comparison with traditional fluoroscopic procedure.

This paper reports on pilot laboratory experiments with a recently proposed surgical procedure for percutaneous screw insertion into fractured scaphoid bones using ultrasound guidance. The experiments were intended to determine the operator variability of the procedure and its performance in comparison with a traditional pinning procedure using fluoroscopy. In the proposed procedure, a three-dimensional surface model is created from pre-operative computed tomography images and intra-operatively registered to the patient using ultrasound images. A graphical interface that communicates with an optical camera tracking the surgical tools, guides the surgeon during the procedure in real time. The results of the experiments revealed non-significant differences between operators for the error in the entry location of the drill hole (p=0.90); however, significant differences for the exit location (p<0.05). Comparison with the traditional pinning procedure shows that the outcome of the recently proposed procedure appears to be more consistent.