Background: Seroprevalence studies of coronavirus disease 2019 (COVID-19) from many countries have shown that the number of undiagnosed missing cases is much larger than that of confirmed cases, irrespective of seroprevalence levels. Considering the strategy of Korea entailing massive testing and contact tracing from the beginning of epidemic, the number of undiagnosed missing cases in Korea may be negligible. This study was conducted to estimate the seroprevalence of COVID-19 among individuals who were never diagnosed with COVID-19 in Daegu, the epicenter of COVID-19 epidemic in Korea. Methods: Serologic testing for immunoglobulin G antibody based on immunochromatographic assay was conducted in 103 patients and 95 guardians aged 18 to 82 years without any history of COVID-19 diagnosis, who visited outpatient clinics of a single university-affiliated hospital from May 25 to June 5, 2020. Results: The estimated seroprevalence was 7.6% (95% confidence interval, 4.3%-12.2%) with 15 positive cases. Among them, only one had a polymerase chain reaction (PCR)-confirmed case among their close contacts and 13 did not experience COVID-19-related symptoms. Seroprevalence was similar between patients and guardians. Based on this figure, the number of undiagnosed missing cases in Daegu was estimated to be a dozen times more than the number of confirmed cases based on PCR testing. Conclusion: Despite the limitation of a small and unrepresentative sample, this is the first study on seroprevalence of COVID-19 in Korea. Our study suggested that the number of undiagnosed missing cases was substantial even with the stringent strategy adopted in Korea, similar to that of other countries.

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We retrospectively investigated the natural course of hemoglobin (Hb) level after total knee arthroplasty (TKA) and identified the benefit of tranexamic acid injection at the operation field for unilateral TKA patients who have not received blood transfusions. There were 115 cases conducted by a surgeon who performed TKA without injecting tranexamic acid and 62 cases by another surgeon with injection. During 2-weeks of hospitalization, Hb level was checked on the day of surgery and 1, 2, 3, 5, 7, 11 days after surgery. Regardless of whether whom the operator was and tranexamic acid was injected or not, the same natural course of Hb level after TKA was observed. The lowest value of Hb was shown at postoperative day 3, after which it tended to recover. In repeated measures analysis of variance test, mean difference from preoperative Hb level showed a statistically significant difference between tranexamic acid injected and noninjected groups ( P = .01). In post hoc test, the differences from preoperative Hb levels were significantly lower at all measurements in surgeon with injection of tranexamic acid. When deciding whether to transfuse after TKA, it should be noted that the patient tends to show the lowest Hb level on postoperative day 3. Also, the authors emphasize that tranexamic acid injection in the joint at the operation field is an effective method to reduce the loss of Hb after TKA.

Improper functional orientation of the acetabular cup can result in improper positions when dynamic pelvic positions are not considered. The purpose of this study was to evaluate changes on acetabular anteversion according to pelvic tilt under various acetabular inclinations. Two artificial pelvic models were selected for this study. Acetabular inclinations on the coronal plane were 25°, 32°, 50°, and 60°. Acetabular anteversion of all components were 15°. Changes of anteversion according to pelvic tilt were measured at angles of 0°, 10°, 20°, 30°, and 40°. Computer Navigation, PolyWare 3D pro, CT, and plain radiography were used to measure each angle. The anatomical anteversions against pelvic tilt were calculated using the following formulae: anatomical anteversion (°) = −14.48Χ + 90.18 (inclination angle 25°); anatomical anteversion (°) = −12.26Χ + 80.10 (inclination angle 32°); anatomical anteversion (°) = −7.468Χ + 61.13 (inclination angle 50°); and anatomical anteversion (°) = −5.328Χ + 44.84 (inclination angle 60°) (Χ: pelvic tilt angle). Radiographic anteversion against pelvic tilt were calculated using the following formulae: radiographic anteversion (°) = −9.50Χ + 57.09 (inclination angle 25°); radiographic anteversion (°) = −8.577Χ + 50.89 (inclination angle 32°); radiographic anteversion (°) = −6.794Χ + 45.73 (inclination angle 50°); radiographic anteversion (°) = −5.226Χ + 33.08 (inclination angle 60°). In conclusion, changes in anteversion according to pelvic tilt were lesser at higher degrees of acetabular inclination.

Purpose: We have analyzed the surgical outcomes of primary total knee arthroplasty (TKA) using computer-assisted navigation that were performed by a single surgeon in terms of postoperative coronal alignment depending on preoperative varus deformity. Methods: We conducted a retrospective study of patients who have undergone navigated primary TKA from January 2016 through December 2019. Two hundred and fifty-six cases with varus deformity of 10° or less were assigned to group 1, and 216 cases with varus deformity of more than 10° were assigned to group 2. The postoperative mechanical hip–knee–ankle (mHKA) angle was measured from scanograms which were taken preoperatively and 3 months after surgery. The postoperative mHKA angle was targeted to be 0°, and the appropriate range of coronal alignment was set as 0 ± 3°. Results: The Pearson correlation showed a significant correlation with the degree of preoperative varus deformity and with the absolute error of postoperative mHKA ( p = 0.01). Among all patients, 64 cases (13.6%) were detected as outliers (mHKA > 0° ± 3°) at 3 months after surgery. Of the 64 cases, 25 cases (9.8%) were affiliated to group 1 and 39 cases (18.1%) were affiliated to group 2. Group 2 showed significantly higher occurrence of outliers than group 1 ( p = 0.01). Multiple variables logistic regression analysis, which analyzed the difference in the occurrence rate of outliers (mHKA > 0° ± 3°), showed that the occurrence rate of group 2 was 2.04 times higher than group 1. After adjusting for patient’s age, gender, and body mass index, the occurrence rate of outliers in group 2 was 2.01 times higher than group 1. Conclusion: The benefit of computer-assisted navigation during TKA in obtaining coronal alignment within 0 ± 3° may be lessened when the preoperative varus deformity is severely advanced.