Ultrafast nonlinear optical studies of silicon nanowaveguides.

Results of a self-consistent ultrafast study of nonlinear optical properties of silicon nanowaveguides using heterodyne pump-probe technique are reported. The two-photon absorption coefficient and free-carrier absorption effective cross-section were determined to be 0.68cm/GW, and 1.9x10(-17) cm2, respectively and the Kerr coefficient and free-carrier-induced refractive index change 0.32x10(-13) cm2/W, and -5.5x10(-21) cm3, respectively. The effects of the proton bombardment on the linear loss and the carrier lifetime of the devices were also studied. Carrier lifetime reduction from 330ps to 33ps with a linear loss of only 14.8dB/cm was achieved using a proton bombardment level of 10(15)/cm2.

Incidence, Positional Distribution, Severity, and Time Missed in Medial Collateral Ligament Injuries of the Knee in NCAA Division I Football Athletes.

INTRODUCTION: We studied injury to the medial collateral ligament (MCL) in National Collegiate Athletic Association (NCAA) Division I football players, their incidence, magnitude of injury, distribution by position, and missed time, which has not previously been described in a consecutive series. METHODS: The knee injuries sustained in 163 consecutive NCAA Division I collegiate football players at our institution were evaluated over a span of 6 years. RESULTS: The incidence of MCL injuries with any knee injury was 29% (47 of 163). Of 47 MCL injuries, 34% occurred in defensive linemen and 29% in offensive linemen. The average days missed by linemen were 14.65 compared with 4.5 by nonlinemen (P = 0.07). The MCL injuries in linemen were more severe than nonlinemen (0.018). DISCUSSION: MCL injuries occur most commonly in linemen in whom the magnitude of injury is also more significant than nonlinemen. Linemen miss more days than do nonlinemen to MCL injury. STUDY DESIGN: Descriptive Epidemiology Study.

Can the reparability of meniscal tears be predicted with magnetic resonance imaging?

BACKGROUND: Historically, magnetic resonance imaging (MRI) has been very useful in diagnosing meniscal tears but not as valuable in predicting whether a meniscal tear is reparable. Given that several recent studies suggested that MRI can be used to predict tear reparability, the topic has resurfaced as a controversy in the orthopaedic and radiology literatures. HYPOTHESIS: Experienced musculoskeletal radiologists can use MRI to predict the reparability of meniscal tears with good to excellent accuracy using the same arthroscopic criteria used by surgeons intraoperatively. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 3. METHODS: Fifty-eight patients with meniscal tears treated with repair were matched by age and sex with 61 patients with tears treated with meniscectomy. Two senior musculoskeletal radiologists independently and blindly reviewed preoperative MRI of these 119 meniscal tears. Using established arthroscopic criteria, the radiologists were asked to grade each tear 0 to 4, with 1 point for each of the following: a tear larger than 10 mm, within 3 mm of the meniscosynovial junction, greater than 50% thickness, and with an intact inner meniscal fragment. Only a tear with a score of 4 would be predicted to be reparable. RESULTS: The 2 radiologists' ability to correctly estimate reparability was poor, with 58.0% and 62.7% correct predictions (κ = 0.155 and 0.250, respectively). Interrater reliability assessment showed that the raters agreed on a score of 4 (reparable) versus <4 (not reparable) 73.7% of the time (κ = 0.434) but came to identical scores only 38.1% of the time (κ = 0.156). Determining the status of the inner fragment was the most predictive individual criterion and the only one to reach statistical significance (χ(2) = 14.9, P <.001). CONCLUSION: Magnetic resonance imaging is not an effective or efficient predictor of reparability of meniscal tears with the current arthroscopic criteria.

Accuracy of magnetic resonance imaging in determining the presence and size of recurrent rotator cuff tears.

We attempted to assess the accuracy of magnetic resonance imaging (MRI) in determining the size of recurrent cuff tears in correlation with size measured at surgery. Thirty-seven shoulders in 33 patients who had reoperation for a presumed failed rotator cuff repair were retrospectively evaluated. All patients had preoperative MRI, the results of which were read by a musculoskeletal radiologist to determine the presence of a tear and to estimate its size. All tears were measured intraoperatively in sagittal and coronal planes. Thirty-three shoulders had recurrent tears of the rotator cuff, and MRI correctly identified the presence of 30 of them. MRI correctly identified only 1 of the 4 patients without a recurrent tear of the cuff. The correlation coefficient for MRI accurately defining the size of cuff tears was 0.46. The sensitivity of MRI for the diagnosis of retear was 91%, and the specificity was 25%. MRI is accurate in diagnosing a recurrent full-thickness cuff tear in postsurgical shoulders. However, it is relatively inaccurate in correctly defining the size of the tear. MRI also has a tendency to overdiagnose cuff tears in postsurgical patients with continued pain and symptoms.