Comparative biomechanical analysis of two techniques of radiolunate plate-fusion: oblique screw vs. parallel screws.

The purpose of this prospective randomized comparative biomechanical study on four pairs of human cadaveric forearms was to discern whether primary stability following plate arthrodesis differs from the position of the screws. Four wrists were randomly assigned to either group such that one wrist of each pair was fixed via parallel screws and the other via an oblique screw crossing the radius and the lunate. Under fluoroscopic guidance, passive extension and flexion of each wrist was performed using a spring balance. Traction force increased by 5 N at each step, ranging from 0 N to a maximum of 100 N. Fixation using a plate and oblique screw demonstrated lower recoverable deformation of the implant and a higher primary stability at the fusion site than parallel screws. The current investigators conclude that an oblique screw crossing radius and lunate increase primary stability which is consistent with the radiological results of comparable clinical trails.

Progress towards intra-operative measurement of femoral antetorsion.

Rotational malalignment following intramedullary nailing is a well-recognised problem. The threshold for clinically relevant malrotation has been established to be in the region of 15° whereas the incidence of significant malrotation following femoral nailing ranges from 22 to 43 percent. Many studies have been performed to address this issue with the major challenge acknowledged to be intraoperative control of femoral anteversion. In the current study, the investigators developed and analysed a novel method to estimate the femoral antetorsion based on computed tomography (CT) data. They hypothesized that this method would be intra-operatively feasible and repeatable without further radiation. CT scans (n=166) of femoral neck fractures performed between 2005 and 2010 were evaluated. Twenty patients had a femoral neck fracture and thus were excluded. Every femoral neck was measured according the method described by Jend et al. and the current authors. In contrast to the Jend method, the current authors described femoral antetorsion as the angle between the ventral cortex of the femoral neck and the posterior condylar line. To determine this angle, the axial cuts from computed tomography data were studied. In order to maximise measurement consistencty among cases, the axial cut which displayed the intertrochanteric crest was selected. Mean femoral antetorsion is 12.15°±10.04° according to Jend et al. In comparison, a mean angle of 12.61°±11.16° was demonstrated in the current study. The absolute difference in measuring the femoral neck angle when these different methods are compared was 4.44°. Statistically, there is no significant difference between the mean results for femoral antetorsion. The advantage of the method proposed in the current study, is the opportunity to enter the ventral femoral cortex during the surgical procedure without disturbing the process of femoral nailing. Thus, the surgeon can avail of continuous control of femoral rotation intra-operatively.

Linear bearing device as a solution for optical navigation of fine needle procedures.

BACKGROUND: Optical navigation of needles < 1 mm diameter remains a challenging task. Bending of these tools is the limiting factor. OBJECTIVE: To use a conventional optical navigation system for interventional fine needle procedures. MATERIALS AND METHODS: A novel custom-made device was constructed to guide the needle in the direction of the planned trajectory. Accuracy of this device was analyzed with two setups (A = ballistic gelatin; B = used pork meat). For both setups, a Plexiglas cube with integrated Plexiglas reference arrays was used. Metal targets of 1 mm diameter were placed in the center. Images were acquired using a 3D fluoroscope connected to a conventional optical navigation system. After trajectory planning, ten navigated injections were performed freehand and with the linear bearing device for each setup. A 3D scan was performed to measure the distance between contrast medium and metal target after each injection. RESULTS: Freehand navigation with a needle of 0.9 mm in diameter was not accurate with either setup (Setup A: mean 33.4 mm; range, 3-63 mm; Setup B: mean 40.1 mm; range, 12-75 mm). Linear bearing navigation was significant more precisely (Setup A: mean 0.7 mm; range, 0-0.75 mm; Setup B: mean 0.29 mm, range 0-1.3 mm) than freehand navigation. CONCLUSION: The linear bearing device reduced all bending. Optical fine needle navigation was accomplished with precision comparable to electromagnetic navigation. This device may provide useful for minimally-invasive clinical applications. Follow-up studies should compare electromagnetic and optical navigation systems in the same setup.

Replication of the range of native anterior cruciate ligament fiber length change behavior achieved by different grafts: measurement using computer-assisted navigation.

BACKGROUND: The native anterior cruciate ligament (ACL) does not behave as a simple bundle of fibers with constant tension but as a continuum of ligament fibers with differential length change during knee flexion/extension. Computer-assisted navigation can be used to assess length change in different fibers within the native ACL and to evaluate how different reconstruction grafts replicate the range of native ligament fiber length change behavior. HYPOTHESIS: Anterior cruciate ligament reconstruction graft size and configuration (single-vs double-bundle) are deciding factors as to how much of the native ACL fiber length change behavior is replicated. STUDY DESIGN: Controlled laboratory study. METHODS: The fiber length change behavior of the entire native ACL was assessed by measuring the length change pattern of representative anteromedial (AM) and posterolateral (PL) bundle fibers (1 at the center and 4 at the periphery of each bundle). The tibial and femoral ACL attachment areas in 5 fresh-frozen cadaveric knees were digitized, and the length change of each representative fiber was recorded during knee flexion/extension using an image-free, optical navigation system. Subsequently, single-bundle ACL reconstructions of different diameters (6, 9, and 12 mm) positioned at the center of the overall native femoral and tibial attachment sites were modeled to assess how much of the range of ligament fiber length change of the native ligament was captured. This was compared with a double-bundle graft using 6-mm-diameter AM and PL grafts positioned at the centers of the femoral and tibial attachment sites of each separate bundle. RESULTS: The 6-, 9-, and 12-mm single-bundle grafts simulated 32%, 51%, and 66% of the ligament fiber length change behavior of the native ACL, respectively. The length change patterns in these grafts were similar to the central fibers of the native ACL: the PL fibers of the AM bundle and AM fibers of the PL bundle. However, even a 12-mm graft did not represent the most AM and PL native fibers. The 6-mm AM and PL bundle grafts (equivalent in cross-sectional area to a 9-mm single-bundle graft) simulated 71% of the native ACL and better captured the extremes of the range of native ligament fiber length change. CONCLUSION: Increasing single-bundle graft size appears to capture more of the range of native ACL fiber length change. However, for a similar graft cross-sectional area, a 2-bundle graft simulates the length change behavior of the native ligament more precisely and thus may better emulate the synergistic actions of anisometric and isometric fibers of the native ligament in restraining knee laxity throughout the range of flexion. CLINICAL RELEVANCE: The range of native ACL fiber length change behavior is better replicated by larger diameter grafts but may be best reproduced by double-bundle reconstruction.

Effects of bile acids on base hydroxylation in a model of human colonic mucosal DNA.

BACKGROUND AND AIMS: Increased intestinal bile acids as a possible consequence of a high fat/meat, low fiber diet are believed to play an important role in the formation of colon cancer. Interactions of bile salts particularly secondary bile acids with different cell components including DNA may contribute to carcinogenesis. To further investigate DNA damage by bile salts, we assessed the effects of a bile salt mixture containing deoxycholate and chenodeoxycholate on base hydroxylation in Chelex-treated DNA from calf thymus as a model of human colonic mucosal DNA in the presence and absence of reactive oxygen metabolites (ROM). METHODS: Chelex-treated DNA from calf thymus (to remove residual iron impurities) was incubated with different bile salt concentrations (4 microM, 4.0 mM) (20.0% deoxycholate, 21.0% chenodeoxycholate) in the presence and absence of an OH generating system (25 microM FeCl3, 50 microM H2O2, 100 microM nitrilotriacetic acid) for 18 h (37 degrees C). After hydrolyzation, lyophilization and derivatization hydroxylated DNA bases were characterised and quantitated with gas chromatography-mass spectrometry (GS-MS) and SIM analysis. Two concentration ranges of bile salts were used, micromolar concentrations being present in plasma, millimolar in the gut lumen. RESULTS: In the absence of ROM Chelex-treated DNA preparations contain only small amounts of hydroxylated base products. Bile salts at 4.0 mM significantly increased the amounts of 5-OH uracil and cis-thymine glycol. In the presence of ROM bile salts at 4.0 microM increased the production of 8-OH adenine and 8-OH guanine whereas bile salts at 4.0 mM inhibited ROM-induced base hydroxylation. DISCUSSION: In the absence of ROM millimolar concentrations of a bile salt mixture with deoxycholate and chenodeoxycholate increase basal (spontaneous) DNA hydroxylation, whereas, they are without effects at micromolar concentrations. In the presence of ROM micromolar concentrations enhance oxidative DNA damage and millimolar concentrations were inhibitory. These results support the view that bile acids may cause oxidative DNA damage depending on their concentrations and the surrounding conditions both directly (enhancement of basal hydroxylation) and indirectly (enhancement of ROM-induced hydroxylation).