• Clinics in Shoulder and Elbow
• /
• v.13 no.1
• /
• pp.167-174
• /
• 2010

Purpose: Anatomical repair of massive rotator cuff tear has been technically challenging because of medial retraction, muscle atrophy and fatty degeneration. Among several treatment options for massive rotator cuff tear, we reviewed rotator cuff repairs and investigated modalities for improvement of clinical outcomes, decreasing the re-tear rate, and increasing healing. Materials and Methods: Patient-related factors and rotator cuff-related factors were the two major groups of factors we considered when choosing a treatment plan. Results: Mobilization of a massive rotator cuff tear was increased by soft tissue release and by the interval slide technique. After meticulous soft tissue release, anatomical repair could be achieved. If the injury was not amenable to anatomical repair, alternative treatment options such as partial repair, the margin convergence technique and augmentation with a tenotomized biceps tendon were considered. Many reports of massive rotator cuff repair demonstrated satisfactory clinical outcomes, decreased pain, recovery of shoulder functions, and increases in muscle strength. However, the re-tear rate had been reported to be relatively high in long-term follow-up. Conclusion: Despite a high re-tear rate after massive rotator cuff repair, a better understanding of the pathogenesis, progression and clinical symptoms of massive rotator cuff tear and improved surgical materials and techniques will lead to satisfactory clinical outcomes.

• Journal of Korea Society of Waste Management
• /
• v.35 no.8
• /
• pp.762-769
• /
• 2018

This study was carried out to examine the improvement plan by analyzing the characteristics of imported wastes, operation rate, and benefits of energy recovery for incineration facilities with a treatment capacity greater than 50 ton/day. The incineration facility capacity increased by 3,280 tons over 15 years, and the actual incineration rate increased to 2,783 ton/day. The operation rate dropped to 76% in 2010 and then rose again to 81% in 2016. The actual calorific value compared to the design calorific value increased by 33.8% from 94.6% in 2002 to 128.4% in 2016. The recovery efficiency decreased by 29% over 16 years from 110.7% to 81.7% in 2002. Recovery and sales of thermal energy from the incinerator (capacity 200 ton/day) dominated the operation cost, and operating income was generated by energy sales (such as power generation and steam). The treatment capacity increased by 11% to 18% after the recalculation of the incineration capacity and has remained consistently above 90% in most facilities to date. In order to solve the problem of high calorific value waste, wastewater, leachate, and clean water should be mixed and incinerated, and heat recovery should be performed through a water-cooled grate and water cooling wall installation. Twenty-five of the 38 incineration facilities (about 70%) are due for a major repair. After the main repair of the facility, the operation rate is expected to increase and the operating cost is expected to decline due to energy recovery. Inspection and repair should be carried out in a timely manner to increase incineration and heat energy recovery efficiencies.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.45 no.3
• /
• pp.78-89
• /
• 2022

The purpose of this study was to propose useful suggestion by analyzing preventive replacement policy under which there are minor and major failure. Here, major failure is defined as the failure of system which causes the system to stop working, however, the minor failure is defined as the situation in which the system is working but there exists inconvenience for the user to experience the degradation of performance. For this purpose, we formulated an expected cost rate as a function of periodic replacement time and the number of system update cycles. Then, using the probability and differentiation theory, we analyzed the cost rate function to find the optimal points for periodic replacement time and the number of system update cycles. Also, we present a numerical example to show how to apply our model to the real and practical situation in which even under the minor failure, the user of system is not willing to replace or repair the system immediately, instead he/she is willing to defer the repair or replacement until the periodic or preventive replacement time. Optimal preventive replacement timing using two variables, which are periodic replacement time and the number of system update cycles, is provided and the effects of those variables on the cost are analyzed.

• Journal of Chest Surgery
• /
• v.56 no.2
• /
• pp.75-86
• /
• 2023

Background: We investigated the long-term outcomes of truncus arteriosus repair at a single institution with a 30-year study period. Methods: Patients who underwent repair of truncus arteriosus between 1993 and 2022 were reviewed retrospectively. Factors associated with early mortality, overall attrition, and reintervention were identified using appropriate statistical methods. Results: In total, 42 patients were enrolled in this study. The median age and weight at repair were 26 days and 3.5 kg, respectively. Thirty patients (71.4%) underwent 1-stage repair. There were 8 early deaths (19%). In the univariable analysis, undergoing surgery before 2011 was associated with early mortality (p=0.031). The overall survival rate at 10 years was 73.8%. In the multivariable analysis, significant truncal valve (TrV) dysfunction (p=0.010), longer cardiopulmonary bypass time (p=0.018), and the earlier era of surgery (p=0.004) were identified as risk factors for overall mortality. During follow-up, 47 reinterventions were required in 27 patients (64.3%). The freedom from all-cause reintervention rate at 10 years was 23.6%. In the multivariable analysis, associated arch obstruction (p<0.001) and significant TrV dysfunction (p=0.011) were identified as risk factors for all-cause reintervention. Arch obstruction (p=0.027) and a number of TrV cusps other than 3 (p=0.014) were identified as risk factors for right ventricle to pulmonary artery (RV-PA) reintervention, and significant TrV dysfunction was identified as a risk factor for TrV reintervention (p=0.002). Conclusion: Despite recent improvements in survival outcomes after repair of truncus arteriosus, RV-PA or TrV reinterventions were required in a significant number of patients during follow-up.

• Journal of the Korean Data and Information Science Society
• /
• v.20 no.6
• /
• pp.999-1007
• /
• 2009

This paper considers the optimal periodic preventive maintenance (PM) policy following the expiration of free-repair warranty. We assume that two periodic PM models with random maintenance quality which were proposed by Wu and Clements-Croome (2005) and Jung (2006b), respectively. Given the cost structure to the user during the cycle of the product, we derive the expressions for the expected cost rate per unit time. Also, we obtain the optimal PM number and the optimal PM period by minimizing the expected cost rate per unit time. The numerical examples are presented for illustrative purpose.

• Journal of the Korean Data and Information Science Society
• /
• v.22 no.4
• /
• pp.775-784
• /
• 2011

In this paper, we consider the periodic preventive maintenance model for repairable system following the expiration of non-renewing free replacement-repair warranty (NFRRW). Under this preventive maintenance model, we derive the expressions for the expected cycle length, the expected total cost and the expected cost rate per unit time. Also, we determine the optimal preventive maintenance period and the optimal preventive maintenance number by minimizing the expected cost rate per unit time. Finally, the optimal periodic preventive maintenance policy is given for Weibull distribution case.

• Clinics in Shoulder and Elbow
• /
• v.11 no.2
• /
• pp.96-103
• /
• 2008

Purpose: This study investigated the rate of retear and related factors after arthroscopic repair of rotator cuff tears involving more than one tendon. Materials & Methods: Arthroscopic repair of 22 rotator cuff tears (average size 3.2cm: average age 58 years old) involving the supraspinatus and part or all of the infraspinatus were investigated using MRI on average 10 months after repair. The status of the repaired cuff was investigated using Sugaya's classification, and the change in muscle was evaluated with Goutallier's classification. Results: Retear (Sugaya grade IV, V) was found in 7cases(32%). Tears larger than 3cm had a higher retear rate(67%) than smaller tears(8%). Retear cases had Goutallier grade II or higher muscle changes preoperatively and showed aggravation of muscle atrophy postoperatively. Even without retear, reversal of muscle change was not seen Conclusion: Rotator cuff tears not confined to the supraspinatus had a 32% retear rate after arthroscopic repair. The size of the tear was the most crucial factor influencing retear. Retear was frequent in tear over 3cm. Atrophy of the cuff muscle worsened when the repair failed but did not improve even without retear.

• Journal of Korean Society for Quality Management
• /
• v.25 no.3
• /
• pp.86-95
• /
• 1997

This paper considers a repairable system, which is maintained preventively at periodic times and is minimally repaired at each failure. Most preventive maintenance policies for such repairable systems assume that the cost of minimal repair is constant regardless of its age at failure. However, it is more practical to consider the situations where the cost of minimal repair is dependent not only on its age at failue, but also on the number of preventive maintenance carried out prior to its failure. We consider the preventive maintenance carried out prior to its failure. We consider the preventive maintenance policy with age-dependent minimal repair cost. The optimal policies which minimize the expected cost rate over an infinite time span are discussed. We obtain the optimal period and number of preventive maintenance prior to replacement of the system.

• Journal of Korean Institute of Industrial Engineers
• /
• v.8 no.1
• /
• pp.3-12
• /
• 1982

Three types of repair-ordering polices for the production facility with r-out-of-n configuration are considered. Policies are characterized by states of the system and two types of lead times ; regular lead time and expedited lead time. Optimum repair-ordering policy is determined by minimizing the cost rate for the system. Optimum policy consists of the type of policies and repair-ordering time. Variations of the optimum policies are observed with respect to variations of lead times and associated ordering costs and downtime cost, respectively.

• Journal of Korean Society for Quality Management
• /
• v.31 no.3
• /
• pp.185-192
• /
• 2003

In this paper, the properties on the optimal replacement policies for the general failure model are developed. In the general failure model, two types of system failures may occur : one is Type I failure (minor failure) which can be removed by a minimal repair and the other, Type II failure (catastrophic failure) which can be removed only by complete repair. It is assumed that, when the unit fails, Type I failure occurs with probability 1-p and Type II failure occurs with probability p, $0\leqp\leq1$. Under the model, the system is minimally repaired for each Type I failure, and it is repaired completely at the time of the Type II failure or at its age T, whichever occurs first. We further assume that the repair times are non-negligible. It is assumed that the minimal repair times in a renewal cycle consist of a strictly increasing geometric process. Under this model, we study the properties on the optimal replacement policy minimizing the long-run average cost per unit time.