• Proceedings of the KSME Conference
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• 2000.11b
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• pp.410-415
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• 2000

Slip factor is defined as an empirical factor being multiplied to theoretical energy transfer for the estimation of real work input of a centrifugal compressor. Researchers have tried to develop a simple empirical model, for a century, to predict a slip factor. However most these models were developed on the condition of design point assuming inviscid flow. So these models often fail to predict a correct slip factor at off-design condition. In this study, we summarized various slip factor models and compared these models with experimental and numerical data at off-design condition. As a result of this study, Wiesner's and Paeng and Chung's models are applicable for radial impeller, but all the models are not suitable for backswept impeller. Finally, the essential avenues for future study is discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1459-1466
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• 2001

A slip factor is defined as an empirical factor, which should be multiplied to theoretical energy transfer to estimate real work input of a centrifugal compressor. During the last century, researchers have tried to develop simple empirical models to predict the slip factor. However most of these models have been developed based only on design point data. Furthermore flow is assumed inviscid. As a result, these models often fail to predict the correct slip factor at off-design condition. In this study, various models for the slip factor were analysed and compared with experimental and numerical data at off-design conditions. As a result of this study, Wiesner's and Paeng and Chung's models are shown to be applicable for radial impeller, but all the models are found to be inappropriate for backswept impellers.

• Journal of the Korean Orthopaedic Association
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• v.54 no.6
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• pp.547-556
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• 2019

Purpose: This study evaluated the results of surgical treatment for residual or recurrent deformity after the conservative treatment of idiopathic clubfoot. Materials and Methods: Fifty-one cases (32 patients), who were followed up to skeletal maturity, were reviewed retrospectively. The mean age at the last follow-up was 18.7 years. The surgical options included selective or comprehensive soft tissue release, tendon lengthening and transfer, and various types of osteotomy. The radiology measurements included the talocalcaneal angle and talo-first metatarsal angle in the anteroposterior (AP) view, and the talocalcaneal angle and calcaneal pitch in the lateral view. The radiology measurements were compared with the normal values for adults. The clinical evaluations were made using the ankle-hindfoot score and the midfoot score of the American Orthopaedic Foot and Ankle Society (AOFAS): excellent (>85), good (71-85), pair (56-70), and poor (<56). Results: At the last follow-up, the percentages of the 51 cases, whose parameter values fell within the normal ranges were as follows: in the AP view, 41.2% (talocalcaneal angle); and 90.2% (talo-first metatarsal angle). In the lateral view, the percentage was 84.3% (talocalcaneal angle). For the calcaneal pitch, the percentages were 61%. The mean AOFAS score was 88.1±10.7 on the ankle-hindfoot score and 86.7±11.5 on the midfoot score. Conclusion: The long-term outcome of patients with idiopathic clubfoot, who underwent surgical treatment after conservative treatment, was found to be 43%-90% of the normal range of radiographic indices. Clinically, the mean AOFAS scores were "excellent". Therefore, a satisfactory result can be obtained by analyzing the elements of deformity more accurately and then using the selective operation method, even if the non-surgical correction method fails.

• Journal of the Korean Orthopaedic Association
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• v.53 no.6
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• pp.490-497
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• 2018

Purpose: To evaluate the utility of ceramic-on-polyethylene articular bearing surface when cementless total hip arthroplasty is performed in patients older than 65 years through an analysis of the minimum five-year follow-up results using the ceramic femoral head and cross-linked polyethylene liner. Materials and Methods: From March 2010 to September 2012, 51 patients (56 hips) who were older than 65 years were enrolled in this retrospective study. The mean age at surgery was $70.9{\pm}5.1years$ old. A clinical assessment was analyzed using the Harris hip score. For the radiographic assessment, the cup inclination and anteversion, stem alignment, and wear amount were measured. The postoperative complications were also determined. Results: The mean Harris hip score was improved from preoperative 48 points to postoperative 87 points (p<0.05). The mean cup inclination was $40.9^{\circ}{\pm}6.4^{\circ}$ and the mean cup anteversion was $20.3^{\circ}{\pm}8.1^{\circ}$. The mean cup anteversion of the elevated liner-used group (16 cases) was $14.3^{\circ}{\pm}7.9^{\circ}$ and the mean cup anteversion of the neutral liner used group (40 cases) was $22.4^{\circ}{\pm}9.1^{\circ}$ (p<0.05). The mean stem alignment angle was $0^{\circ}$ (range, varus $4^{\circ}$-valgus $4^{\circ}$). The mean linear wear amount was $0.458{\pm}0.041mm$ and the average annual linear wear rate was $0.079{\pm}0.032mm/yr$. Six cases (10.7%) of intraoperative periprosthetic femoral fractures were encountered. Conclusion: Based on these results, the use of a ceramic-on-polyethylene articular bearing surface in elderly patients with cementless total hip arthroplasty is beneficial. On the other hand, careful effort is needed to prevent intraoperative periprosthetic femoral fractures.

• Journal of Korean Orthopaedic Sports Medicine
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• v.10 no.2
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• pp.69-77
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• 2011

Purpose: This study was retrospectively performed to compare the clinical outcomes of modified Brostrom procedures using the single suture anchor and the double suture anchor for chronic lateral ankle instability. Materials and Methods: Thirty-seven patients were followed up for more than 1 year after the modified Brostrom procedures using suture anchor. Single surgeon treated seventeen cases with single suture anchor and 20 cases with double suture anchor. The clinical evaluation was performed according to the Karlsson scale and Sefton grading system. Radiologic measurement of the talar tilt and anterior talar translation was performed through anterior and varus stress radiographs using Telos device. Results: The Karlsson scale had improved significantly from preoperative average of 45.2 points to 89.4 points in single suture anchor group, and from 46.4 points to 90.5 points in double suture anchor group. According to the Sefton grading system, 15 cases (88.2%) in single suture anchor group and 18 cases (90%) in double suture anchor group achieved satisfactory results. The talar tilt angle and anterior talar translation had improved significantly from preoperative average of $13.6^{\circ}$ and 8.6 mm to $5.4^{\circ}$ and 4.1 mm in single suture anchor group, from $14.1^{\circ}$ and 8.4mm to $3.9^{\circ}$ and 4 mm in double suture anchor group. Double suture anchor technique was significantly superior in postoperative talar tilt. Conclusion: Single and double suture anchor techniques produced similar clinical and functional outcomes except for talar tilt, which was significantly superior in double suture anchor group. Both modified Brostrom procedures using the single and double suture anchor appear to be effective treatment methods for chronic lateral ankle instability. Further evaluation of clinical outcomes and biomechanical studies in athletes are needed.

• Journal of the Korean Orthopaedic Association
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• v.56 no.3
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• pp.215-223
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• 2021

Purpose: Distal radius fractures in youth are treated conservatively in most cases, but there are some cases of redisplacement in the follow-up period after cast immobilization, even after complete reduction. This study examined the risk factors of redisplacement in reduced unstable distal radius fractures. Materials and Methods: From February 2011 to June 2018, 44 unstable distal radius fractures were managed with a closed reduction and cast immobilization. The patients were aged between 6 and 14 years. The cases of redisplacement were analyzed with the fracture characteristics (fracture obliquity, fracture level ratio, ulnar fracture combined), cast qualities (gap index, cast index, 3 point index, and radius-2nd metacarpal angle) and host factors (age, sex). Results: The mean angulation in the union was 9.2° (0°-32.8°). In the categorical grouping 29 cases were within 10° angulation, and 15 cases were more than 10°. No significant differences in the factors of the cast indices or host factors were noted. The meaningful factor was the fracture level calculated by the relative width of the fracture site divided by the sum of width of diaphysis and epiphysis (p=0.001) and combined ulnar fracture (p=0.019). Conclusion: Unstable distal radius fractures should be treated with more stubborn guidelines lest the fracture loses its anatomical alignment. In particular, in patients with less remodeling power, operative treatment would secure a better result if the fracture occurs in a more proximal location.

• Journal of the Korean Orthopaedic Association
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• v.54 no.3
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• pp.244-253
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• 2019

Purpose: Total hip arthroplasty was performed using a direct anterior approach (DAA) on an ordinary operation table and a short femoral stem. The clinical radiographic results were evaluated by a comparison with those performed using the modified hardinge (anterolateral approach, ALA) method. Materials and Methods: From January 2013 to November 2015, 102 patients who underwent total hip arthroplasty using DAA (DAA group) and the same number of patients using ALA (ALA group), both performed by a single surgeon, were compared and analyzed retrospectively. The operation time and amounts of bleeding were compared, and the improvement in post-operative pain, ambulatory capacity and functional recovery of the hip joint were checked. The location of insertion of the acetabular cup and femoral stem were evaluated radiologically, and the complications that occurred in the two groups were investigated. Results: The amount of bleeding was significantly smaller in the DAA group (p=0.018). Up to 3 weeks postoperatively, recovery of hip muscle strength was significantly higher in the DAA group (flexion/extension strength p=0.023, abduction strength p=0.031). The Harris hip score was significantly better in the DAA group for up to 3 months (p<0.001) and the Koval score showed significantly better results in the DAA group up to 6 weeks (p≤0.001). The visual analogue scale score improvement was significantly higher in the DAA group by day 7 (p=0.035). The inclination angle (p<0.001) and anteversion angle (p<0.001) of the acetabular cup were located in the safe zone of the DAA group more than in the ALA group, and there was no statistically significant difference in the position of the femur stem and leg length difference. During surgery, two cases of greater trochanter fracture occurred in the DAA group (p=0.155). Conclusion: The DAA performed in the ordinary operation table using a short femoral stem showed post-operative early functional recovery. Because a simple to use fluoroscope was used during surgery with an anatomical position familiar to the surgeon, it is considered to be useful for the insertion of implants into the desired position and for an approach that is useful for the prevention of leg length differences.

• The korean journal of orthodontics
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• v.34 no.2 s.103
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• pp.165-175
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• 2004

Information on the limits of treatment could allow for more rational treatment Planning and better results after treatment. From this point of view, this article has attempted to discuss the limits of orthodontic tooth movement. A relatively wider range of tooth movement is expected after Class III surgical-orthodontics than after conventional orthodontic treatment in general. The purposes of this Paper were: first, to evaluate the reliability of teeth position measuring gauge; and second, to elucidate the limits of orthodontic tooth movement. Dental casts of fifty-fine subjects were analyzed by using Set-up model checker (InVisitec Co., Korea) before and aster the Class III surgical-orthodontic treatment. The changes of maxillary and mandibular dental arch widths were also measured from the canines to the second molars. To test the inter-examiner reliability, randomly selected casts were measured by another examiner. Descriptive statistics and paired t tests were used to explain the tooth movement during treatment. The results showed a relatively good reliability of measuring instruments and a very diverse range of tooth movement. Collective changes by the orthodontic tooth movement evaluated in Class III surgical-orthodontics allowed for a suggestive interpretation of specific treatment patterns. Arch width changes during the inter-arch coordination were mainly the result of tipping in both buccal segments. Based on the results of this study, the possibility of a change in dentition as a result of orthodontic treatment should be understood in order to launch a well-organized plan of treatment.