Qualitative and quantitative comparison of Thiel and phenol-based soft-embalmed cadavers for surgery training.

INTRODUCTION: Surgical skills training has traditionally been limited to formalin embalming that does not provide a realistic model. The aim of this study was to qualitatively and quantitatively compare Thiel and phenol-based soft-embalming techniques: qualitatively in a surgical training setup, and quantitatively by comparing the mechanical and histomorphometric properties of skin specimens embalmed using each method. MATERIALS AND METHODS: Thirty-four participants were involved in surgical workshops comparing Thiel and phenol-based embalmed bodies. Participants were asked to evaluate the utility of the different models for surgical skills training. In parallel, tensile elasticity evaluation was performed on skin flaps from six fresh-frozen cadavers. Flaps were divided into three groups for each specimen: fresh-frozen, Thiel, and phenol-based embalmed and compared together at 1 month or 1 year after embalming. A histological investigation of the skin structural properties was performed for each embalming type using haematoxylin and eosin and Masson's trichrome. RESULTS: All participants rated the phenol-based specimens consistently better or equivalent to Thiel for the evaluated parameters. Quantitatively, there were statistically significant differences for the tensile elasticity between the embalming techniques (p < .05). There were no significant differences for the tensile elasticity between phenol-based embalmed skin and fresh state (p = .30), and no significant difference between embalming time was reported (p = .47). Histologically, the integrity of the skin was better preserved with the phenol-based technique. CONCLUSION: Phenol-based embalming provides as realistic or better of a model as Thiel embalming for surgical training skills and was generally preferred over Thiel model. The phenol-based embalming better preserved the integrity of the skin.

Does Wrist Laxity Influence Three-Dimensional Carpal Bone Motion?

Previous two-dimensional (2D) studies have shown that there is a spectrum of carpal mechanics that varies between row-type motion and column-type motion as a function of wrist laxity. More recent three-dimensional (3D) studies have suggested instead that carpal bone motion is consistent across individuals. The purpose of this study was to use 3D methods to determine whether carpal kinematics differ between stiffer wrists and wrists with higher laxity. Wrist laxity was quantified using a goniometer in ten subjects by measuring passive wrist flexion-extension (FE) range of motion (ROM). In vivo kinematics of subjects' scaphoid and lunate with respect to the radius were computed from computed tomography (CT) volume images in wrist radial and ulnar deviation positions. Scaphoid and lunate motion was defined as "column-type" if the bones flexed and extended during wrist radial-ulnar deviation (RUD), and "row-type" if the bones radial-ulnar deviated during wrist RUD. We found that through wrist RUD, the scaphoid primarily flexed and extended, but the scaphoids of subjects with decreased laxity had a larger component of RUD (R2 = 0.48, P < 0.05). We also determined that the posture of the scaphoid in the neutral wrist position predicts wrist radial deviation (RD) ROM (R2 = 0.46, P < 0.05). These results suggest that ligament laxity plays a role in affecting carpal bone motion of the proximal row throughout radial and ulnar deviation motions; however, other factors such as bone position may also affect motion. By developing a better understanding of normal carpal kinematics and how they are affected, this will help physicians provide patient-specific approaches to different wrist pathologies.

Electromagnetically tracked personalized templates for surgical navigation.

PURPOSE: An electromagnetic (EM) surgical tracking system was developed for orthopedic navigation. The reportedly poor accuracy of point-based EM navigation was improved by using anatomical impressions, which were EM-tracked personalized templates. Lines, rather than points, were consistently used for calibration and error evaluation. METHODS: Technical accuracy was tested using models derived from CT scans of ten cadaver shoulders. Tracked impressions were first designed, calibrated, and tested using lines as fiducial objects. Next, tracked impressions were tested against EM point-based navigation and optical point-based navigation, in environments that were either relatively empty or that included surgical instruments. Finally, a tracked impression was tested on a cadaver forearm in a simulated fracture-repair task. RESULTS: Calibration of anatomical impressions to EM tracking was highly accurate, with mean fiducial localization errors in positions of 0.3 mm and in angles of [Formula: see text]. Technical accuracy on physical shoulder models was also highly accurate; in an EM field with surgical instruments, the mean of target registration errors in positions was 2.2 mm and in angles was [Formula: see text]. Preclinical accuracy in a cadaver forearm in positions was 0.4 mm and in angles was [Formula: see text]. The technical accuracy was significantly better than point-based navigation, whether by EM tracking or by optical tracking. The preclinical accuracy was comparable to that achieved by point-based optical navigation. CONCLUSIONS: EM-tracked impressions-a hybrid of personalized templates and EM navigation-are a promising technology for orthopedic applications. The two technical contributions are the novel hybrid navigation and the consistent use of lines as fiducial objects, replacing traditional point-based computations. The accuracy improvement was attributed to the combination of physical surfaces and line directions in the processes of calibration and registration. The technical studies and preclinical trial suggest that EM-tracked impressions are an accurate, ergonomic innovation in image-guided orthopedic surgery.

Principal components of wrist circumduction from electromagnetic surgical tracking.

PURPOSE: An electromagnetic (EM) surgical tracking system was used for a functionally calibrated kinematic analysis of wrist motion. Circumduction motions were tested for differences in subject gender and for differences in the sense of the circumduction as clockwise or counter-clockwise motion. METHODS: Twenty subjects were instrumented for EM tracking. Flexion-extension motion was used to identify the functional axis. Subjects performed unconstrained wrist circumduction in a clockwise and counter-clockwise sense. Data were decomposed into orthogonal flexion-extension motions and radial-ulnar deviation motions. PCA was used to concisely represent motions. Nonparametric Wilcoxon tests were used to distinguish the groups. RESULTS: Flexion-extension motions were projected onto a direction axis with a root-mean-square error of [Formula: see text]. Using the first three principal components, there was no statistically significant difference in gender (all [Formula: see text]). For motion sense, radial-ulnar deviation distinguished the sense of circumduction in the first principal component ([Formula: see text]) and in the third principal component ([Formula: see text]); flexion-extension distinguished the sense in the second principal component ([Formula: see text]). CONCLUSION: The clockwise sense of circumduction could be distinguished by a multifactorial combination of components; there were no gender differences in this small population. These data constitute a baseline for normal wrist circumduction. The multifactorial PCA findings suggest that a higher-dimensional method, such as manifold analysis, may be a more concise way of representing circumduction in human joints.

Characterization of the fatigue behavior of the medial collateral ligament utilizing traditional and novel mechanical variables for the assessment of damage accumulation.

Ligaments are regularly subjected to repetitive loading in vivo. Typically, mechanical studies focus on repetitive loading protocols of short duration, while those characterizing damage accumulation over a longer duration (i.e., fatigue studies) are lacking. The aims of this study were as follows: (a) to demonstrate that damage does accumulate in ligament tissue subjected to repetitive loading and (b) to evaluate existing and new methods for characterizing fatigue damage accumulation. It was hypothesized that ligaments would accumulate damage with repetitive loading as evidenced by failure at stresses well below ultimate tensile strength, creep curve discontinuities, and by reductions in stiffness during loading. Eight normal medial collateral ligaments from female New Zealand white rabbits were cycled in tension, between 0 MPa and 28 MPa, to failure or until 259,200 cycles, whichever came first. Medial collateral ligaments that did not fail were subsequently loaded to failure. Displacement rates (dl(max)/dt) as well as primary, secondary, and tertiary creeps were monitored as indices of damage accumulation and impending mechanical failure. Additionally, the relative utilities of tangent, secant, and chord stiffness parameters were critically evaluated. Finally, new uses for the second derivative of force-displacement data were explored. Three out of eight ligaments failed during testing, demonstrating that ligaments can fail in fatigue under moderate tensile stress in vitro. The evaluation of displacement rates (dl(max)/dt), as well as primary through tertiary creep patterns, were not well suited to predicting failure in normal ligaments until rupture was all but imminent. Tangent stiffness, which was calculated from a mathematically defined start of the "linear region," was surprisingly constant throughout testing. Secant stiffness dropped in a predictable fashion, providing a global indicator of tissue stiffness, but did not provide any insight into fiber mechanics. Chord stiffness, on the other hand, appeared to be sensitive to fiber recruitment patterns. The second derivative of force-displacement data proved to be a useful means of (a) objectively defining the start of the linear region and (b) inferring changes in fiber recruitment patterns within ligament tissue. Tangent, secant, and chord stiffnesses highlight different attributes of ligament responses to loading; hence these parameters cannot be used interchangeably. Additionally, the second derivative of the force-displacement curve was introduced as a useful descriptive and analytical tool.

A novel application of the principles of linear elastic fracture mechanics (LEFM) to the fatigue behavior of tendon tissue.

BACKGROUND: Experiments on the fatigue of tendons have shown that cyclic loading induces failure at stresses lower than the ultimate tensile strength (UTS) of the tendons. The number of cycles to failure (Nf) has been shown to be dependent upon the magnitude of the applied cyclic stress. METHOD OF APPROACH: Utilizing data collected by Schechtman (1995), we demonstrate that the principles of Linear Elastic Fracture Mechanics (LEFM) can be used to predict the fatigue behavior of tendons under cyclic loading for maximum stress levels that are higher than 10% of the ultimate tensile strength (UTS) of the tendon (the experimental results at 10% UTS did not fit with our equations). CONCLUSIONS: LEFM and other FM approaches may prove to be very valuable in advancing our understanding of damage accumulation in soft connective tissues.