Clinical outcomes Estimated blood loss, operation time and length of hospital stay were obtained from the electronic medical records. The patients' hemoglobin level was checked routinely on the day before operation and on the first and second post-operative days. The investigators also calculated the decreased amount of hemoglobin level as a more objective parameter for blood loss. Visual analogue scale (VAS) was recorded 4 times a day by nurse practitioners during hospitalization. The mean VAS on the first, second and third post-operative days were used for analysis respectively. Besides, the morphine dosage during hospitalization also served as another parameter of pain intensity. In addition to chart review, Harris hip score, Oxford hip score (OHS), and EQ5d scores were obtained for outcome evaluation at 3 months, 6 months, and 2 years after operation.