Purpose To compare post-operative physical activity and return to work after combined posterolateral corner (PLC) reconstruction (PLC-R) in anterior cruciate ligament (ACL)- or posterior cruciate ligament (PCL)-based injuries. Methods Patients aged > 18 years undergoing PLC-R using the Larson technique combined with either ACL or PCL reconstruction were included. Outcome was evaluated retrospectively after a minimum follow-up of 24 months using Tegner Activity Scale, Activity Rating Scale (ARS), Knee Injury and Osteoarthritis Outcome Score (KOOS), work intensity according to REFA classification, and a questionnaire about type of occupation and time to return to work. Results A total of 32 patients (11 ACL-based injuries and 21 PCL-based injuries) were included. Mean follow-up was 56 ± 26 months in the ACL-based injury group and 59 ± 24 months in the PCL-based injury group. All patients in the ACL-based injury group and 91% of patients in the PCL-based injury group returned to sports activities. Comparing pre- and post-operative values, a significant deterioration of the Tegner Activity Scale and ARS was observed in the PCL-based injury group, whereas no significant change was observed in the ACL-based injury group. KOOS subscales were generally higher in the ACL-based injury with significant differences in the subscale sports and recreational activities. Patients with ACL-based injuries returned to work significantly earlier compared to patients with PCL-based injuries (11 ± 4 weeks vs. 21 ± 10 weeks, p < 0.05). Conclusion High rates of return to sports and work can be expected after combined PLC-R in both ACL- and PCL-based injuries. However, deterioration of sports ability must be expected in PCL-based injuries. ACL-based injuries led to superior patient-reported outcomes and an earlier return to work, as compared to PCL-based injuries. Level of evidence Level IV.

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Transients following switching in the network and/or the tripping of generating unit auxiliaries can excite oscillatory torques on the turbine-generator-rotor-shaft system. The oscillations can be damped or amplified with time. Damped oscillations affect the power quality and if the oscillations grow with time they may even lead to generating unit outages (and damages) resulting in possible system instabilities. Deregulation of electricity markets has resulted in separation of Utility Companies (responsible for power generation) and Transmission Companies (responsible for power transmission). The decision making is no more under the same umbrella. Companies on both the sides have severe cost reduction focus and each side is tempted to make independent decision favourable to it. The Transmission Companies want to enhance transmission capacity of existing systems by introducing measures like series capacitor compensation. However incorporation of series capacitor compensation may under certain conditions lead to oscillations and also snbsynchronous resonance. Currently, there is an urgent need to establish a systematic methodology to investigate the root cause of such oscillations so that preventive measures can be taken by both the Utility Companies and the Transmission Companies. This paper is a contribution in this direction. In this work, comprehensive dynamic model of synchronous generator system has been developed in software Matlab/Simulink. Generating unit start up and ramp loading to rated load has been simulated to get deeper insight into the oscillatory behaviour of the synchronous generator. Block loading of the turbine generator and sudden load shedding due to auxiliary trip have been investigated in detail. Further, power system network with bus connected parallel generating units and parallel transmission lines, having different series capacitor compensation ratio have been simulated in power system software NETOMAC. Transient conditions have been modelled to investigate the oscillations and the consequent torsional torques and angles between adjacent masses of the rotor shaft system causing fatigue life reduction. This work has very clearly revealed the complex dynamic interrelationship among variables responsible for power system oscillations.

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