A biomechanical comparison of all-inside cruciate ligament graft preparation techniques.

BACKGROUND: The all-inside cruciate ligament graft preparation technique has become popular due to its utility in sparing a growing physis, preserving a tendon in ACL surgery, and/or reduction of pain. However, few studies have compared graft preparation techniques to determine the ideal construct for cruciate ligament reconstruction. We sought to compare biomechanical properties of two quadrupled all-inside cruciate ligament graft preparation techniques and three alternative all-inside graft preparation techniques that may be used when the available tendon is too short to be quadrupled. METHODS: Fifty porcine extensor tendons were evenly divided into five groups (n = 10) representing all-inside graft preparation techniques, including two quadrupled (Quad-A, Quad-B) and three alternative methods (Tripled, Folded, Two-Doubled). Each graft construct underwent preconditioning (10 loading cycles from 20 to 50 N at 0.1 Hz), cyclic loading (500 loading cycles from 50 to 250 N at 1.0 Hz) and load-to-failure (tension applied at 20 mm/min). RESULTS: Quad-A and Quad-B demonstrated no significant differences in cyclic displacement (10.5 ± 0.3 vs 11.7 ± 0.4 mm; p = 0.915), cyclic stiffness (1086.2 ± 487.3 vs 460.4 ± 71.4 N/mm; p = 0.290), pullout stiffness (15.9 ± 4.3 vs 7.4 ± 4.4 N/mm; p = 0.443), ultimate failure load (641.2 ± 84.7 vs 405.9 ± 237.4 N; p = 0.672), or ultimate failure displacement (47.3 ± 6.7 vs 55.5 ± 0.7 mm; p = 0.778). The mean cyclic displacement of the Two-Doubled group was significantly greater than the Quad-A (29.7 ± 2.2 vs 10.5 ± 0.3 mm; p < 0.001), Quad-B (29.7 ± 2.2 vs 11.7 ± 0.4 mm; p < 0.001), Tripled (29.7 ± 2.2 vs 11.3 ± 0.2 mm; p < 0.001), and Folded group (29.7 ± 2.2 vs 13.3 ± 0.2 mm; p < 0.001). There were no other statistically significant differences between the three alternative all-inside graft preparation techniques. CONCLUSION: The current study demonstrates the biomechanical properties of two quadrupled all-inside graft constructs, Quad-A and Quad-B, are not significantly different. When the available tendon is of insufficient length, the Two-Doubled group demonstrated more than twice the cyclic displacement of all other graft preparation techniques, and is therefore not recommended for use in all-inside cruciate ligament reconstruction.

Drill Penetration Injury to Extensor Tendons: A Biomechanical Analysis.

BACKGROUND: Little is known about extensor tendon failure following drill injury at the time of volar plate fixation. Our goals were to analyze extensor tendon injury following simulated drill penetration, and change in tendon displacement during cyclic loading following simulated drill penetration injury. METHODS: Extensor pollicis longus (EPL) and extensor carpi radialis brevis (ECRB) tendons were harvested from 9 fresh frozen cadaveric arms. Eighteen EPL and 18 ECRB samples were created from harvested tendons. Drill penetration injury was performed in either a continuous or an oscillating mode. Injured tendons were subjected to 1200 cycles at 1- to 15-kg cyclic load at a frequency of 1 Hz, and analyzed for failure at drill sites and change in displacement throughout the testing cycle. RESULTS: Ten EPL samples and 16 ECRB samples completed testing without failure. Tendon type (ECRB, EPL), mode of injury (continuous, oscillating), and location (proximal, distal) did not affect tendon displacement during loading. A single EPL tendon failed following continuous drill penetration injury. Extensor carpi radialis brevis samples had a mean change in displacement of 2.8 (standard deviation [SD]: 1.5 mm) and 5.9 mm (SD: 4.7 mm) for oscillating and continuous modes, respectively. Six EPL samples had a mean change in displacement of 4.7 (SD: 2.7 mm) and 4.3 mm (SD: 1.8 mm) for oscillating and continuous modes, respectively. CONCLUSIONS: Complete extensor tendon failure due to drill penetration was rare. Drill mode did not affect the degree of elongation. Increasing cyclic loading of extensor tendons after drill injury caused modest extensor tendon elongation.

Functional remineralization of dentin lesions using polymer-induced liquid-precursor process.

It was hypothesized that applying the polymer-induced liquid-precursor (PILP) system to artificial lesions would result in time-dependent functional remineralization of carious dentin lesions that restores the mechanical properties of demineralized dentin matrix. 140 µm deep artificial caries lesions were remineralized via the PILP process for 7-28 days at 37°C to determine temporal remineralization characteristics. Poly-L-aspartic acid (27 KDa) was used as the polymeric process-directing agent and was added to the remineralization solution at a calcium-to-phosphate ratio of 2.14 (mol/mol). Nanomechanical properties of hydrated artificial lesions had a low reduced elastic modulus (E(R) = 0.2 GPa) region extending about 70 µm into the lesion, with a sloped region to about 140 µm where values reached normal dentin (18-20 GPa). After 7 days specimens recovered mechanical properties in the sloped region by 51% compared to the artificial lesion. Between 7-14 days, recovery of the outer portion of the lesion continued to a level of about 10 GPa with 74% improvement. 28 days of PILP mineralization resulted in 91% improvement of E(R) compared to the artificial lesion. These differences were statistically significant as determined from change-point diagrams. Mineral profiles determined by micro x-ray computed tomography were shallower than those determined by nanoindentation, and showed similar changes over time, but full mineral recovery occurred after 14 days in both the outer and sloped portions of the lesion. Scanning electron microscopy and energy dispersive x-ray analysis showed similar morphologies that were distinct from normal dentin with a clear line of demarcation between the outer and sloped portions of the lesion. Transmission electron microscopy and selected area electron diffraction showed that the starting lesions contained some residual mineral in the outer portions, which exhibited poor crystallinity. During remineralization, intrafibrillar mineral increased and crystallinity improved with intrafibrillar mineral exhibiting the orientation found in normal dentin or bone.

Clinical evaluation of a dentifrice containing calcium sodium phosphosilicate (novamin) for the treatment of dentin hypersensitivity.

PURPOSE: To evaluate the efficacy of a dentifrice containing calcium sodium phosphosilicate (NovaMin) study versus a placebo and a commercially-available SrCl2 containing dentifrice for the treatment of dentin hypersensitivity. METHODS: This was a 6-week, randomized, parallel-arm, double-blind clinical study. 71 subjects ranging in age from 21 to 56 years old completed the study. Evaporative and thermal stimuli were used to measure pain using a VAS scale. Measurements were obtained at baseline, 2 weeks and 6 weeks. RESULTS: The placebo and the NovaMin groups showed a statistically significant decrease in sensitivity by both measures after 6 weeks (P < 0.05). The SrCl2 group showed a statistically significant decrease from baseline at the 2-week time point, but not at the 6-week time point for the evaporative stimulus. The percent reduction in sensitivity at 6 weeks for the NovaMin test group was 35% for air and 39% for cold water stimulus, versus 11% for air and 22% for cold water for the SrCl2 paste. The reductions for the placebo paste were 21% for the air stimulus and 18% for water. A cross tabulation measure of the reduction in sensitivity at each time point for all three treatments showed that the NovaMin product was more effective than either of the other products. For the air stimulus in the NovaMin group, 58% of subjects improved at each time point compared with 26% for the SrCl2 group and 20% for the placebo group. These results demonstrate that the NovaMin dentifrice was more effective at reducing sensitivity compared with a commercial dentifrice and placebo control.

Do audible and ultrasonic sounds of intensities common in animal facilities affect the autonomic nervous system of rodents?

In animal facilities, noises, often poorly controlled, occur over a wide range of frequencies and intensities. Evidence demonstrates that audible noise and ultrasound have deleterious effects on rodent physiology, but it is not known how they affect the autonomic nervous system (ANS). This study exposed 3 unrestrained, male, Sprague-Dawley rats daily to a 15-min white noise regime (90 dB), a quiet regime, or a 15-min ultrasound regime (90 dB at 4 frequencies in the range 20 to 40 kHz)--each for several weeks--and used radiotelemetry to monitor their cardiovascular responses. Exposure to audible noise increased heart rate and mean arterial pressure. Spectral analysis of HR variability showed diminished stimulation of the parasympathetic nervous system, shifting the sympathovagal balance. However, ultrasound, at the frequencies used, did not reproducibly affect cardiovascular parameters. The preliminary data obtained from this study indicate that audible noise, but not ultrasound (delivered using the same protocol), affects the ANS. Because the cardiovascular, respiratory, renal, and gastrointestinal systems are under autonomic control, such noise could have wide-ranging effects on animal physiology.