Smaller cross-sectional areas of the hamstring tendon measured from preoperative ultrasonography are likely to need additional gracilis harvesting for double-bundle anterior cruciate ligament reconstructions.

BACKGROUND/PURPOSE: Hamstring tendon autografts are commonly used for double-bundle anterior cruciate ligament reconstruction (DB-ACLR). If the volume of the semitendinosus (ST) tendon is insufficient, the gracilis (G) tendon is also harvested. Additional harvesting of the G autograft can affect patients' short-term postoperative outcome, such as muscle recovery; thus, preoperative information about whether an additional G autograft is needed would be useful. The purpose of this study was to investigate whether preoperative measurement of the ST tendon using ultrasonography could inform the intraoperative decision to harvest the G tendon. METHODS: We enrolled 20 patients (13 men and seven women) who underwent DB-ACLR between October 2017 and March 2019. The mean patient age was 28.5 years. The ipsilateral ST tendon was measured using ultrasonography before surgery. Measurements included the diameter and breadth of the short-axis image. The cross-sectional area (CSA) was calculated from these measurements. During surgery, when two grafts with diameters of ≥ 5.0 mm could not be made, the G tendon was also harvested. Patients were categorized into two groups: the ST group where only the ST tendon was harvested, and the semitendinosus gracilis tendon (STG) group where the ST and G tendons were both harvested. The CSA value was compared between the two groups, and the cutoff value was calculated. RESULTS: In the ST group (n = 8), the mean diameter and breadth of the semitendinosus tendon were 4.21 and 2.34 mm, respectively. In the STG group (n = 12), the mean diameter and breadth of the ST tendon were 3.39 and 1.78 mm, respectively. The CSAs calculated for the ST group and the STG group were 7.74 mm2 and 4.79 mm2, respectively. A cutoff value of 7.0 mm2 was found to correspond to a specificity and sensitivity to harvest the G tendon of 87.5% and 75.0%, respectively. CONCLUSIONS: The preoperative CSA of the ST tendon determined using ultrasonography can, therefore, be informative for deciding whether to harvest the G tendon for DB-ACLR. The results of this study provide valuable information for graft selection in anterior cruciate ligament reconstruction. LEVEL OF EVIDENCE: IV (Retrospective case series design).

Central patellar portal placement frequently provokes anterior knee compartment radiological abnormalities in anterior cruciate ligament reconstruction.

PURPOSE: A central patellar (CP) portal can be used to view the native femoral insertion site of the anterior cruciate ligament (ACL). It aids in the drilling of an anatomical tunnel; however, its impact on the patellar tendon and the infrapatellar fat pad remains a concern. The aim of this study was to investigate complications associated with the CP portal use in arthroscopic ACL reconstruction (ACLR). METHODS: A total of 105 patients (107 knees, 60 females) who underwent ACLR with a CP portal from 2012 to 2017 were included in this study. The mean age was 28.3 ± 12.4 years. All surgeries were single-bundle reconstructions using the trans-tibial technique via the CP and anteromedial portals. Post-operative events, magnetic resonance imaging (MRI), and arthroscopic findings associated with CP portal creation were evaluated. RESULTS: Five patients (4.7%) had symptomatic postoperative complications, which included two patients with patellar tendonitis and three patients with fibrosis in the anterior knee compartment. Abnormal signal intensity of the patellar tendon on MRI and increased thickness at the CP portal area were found in 18 of 25 knees (72%). Three of 56 knees (5.4%) that underwent second-look arthroscopy showed fibrosis of the infrapatellar fat pad. Seven patients (12.5%) showed hypertrophy of the ligamentum mucosum. CONCLUSIONS: The rate of symptomatic complications associated with CP portal placement was 4.7%; however, abnormal MRI or follow-up arthroscopy findings were much higher than clinically symptomatic patients. This study suggests that CP portal placement could provoke anterior knee compartment fibrosis or hypertrophy. LEVEL OF EVIDENCE: IV.

Generation of frequency-modulated sub-terahertz signal using microwave photonic technique.

We present a photonic technique for generating a frequency- modulated sub-terahertz signal for non-destructive or noninvasive sensing and imaging applications. Large frequency deviation was achieved by using optical phase modulation and heterodyne photomixing with an uni-travelling photodetector. The operation principle is theoretically derived and explained. In addition, the generation of 350-GHz frequency- modulated sub-terahertz signal with 6.7-GHz frequency deviation is experimentally demonstrated, and the possibility of frequencies up to 1 THz and wider frequency deviations is discussed.

High-sweeping-speed optically synchronized dual-channel terahertz-signal generator for driving a superconducting tunneling mixer and its application to active gas sensing.

We propose a high-sweeping-speed optically synchronized dual-channel terahertz (THz) signal generator for an active gas-sensing system with a superconductor-insulator-superconductor (SIS) mixer. The generator can sweep a frequency range from 200 to 500 GHz at a speed of 375 GHz/s and a frequency resolution of 500 MHz. With the developed gas-sensing system, a gas-absorption-line measurement was successfully carried out with N(2)O gas in that frequency range.

Generation of two-mode optical signals with broadband frequency tunability and low spurious signal level.

For continuous millimeter and terahertz-wave applications, a two-mode optical signal generation technique that uses two arrayed waveguide gratings and two optical switch units is presented. In addition to easy and fast operation, this scheme offers broadband frequency tunability and high signal purity with a low spurious mode level. Mode spacing, which corresponds to the frequency of the generated MM/THz-wave signal after photomixing, was successfully swept in the range of 200 ~ 550 GHz and the optical spurious mode suppression ratio higher than 25 dBc was achieved. In addition, spurious modes characteristics were investigated by using second harmonic generation (SHG) autocorrelation methods for several frequencies.