This research was approved by the Medical Ethics Committee of the West China Hospital, Sichuan University, Sichuan, China. Patients with bilateral ONFH was recruited from our department from March 2017 to March 2018. Subjects included were: (1) adult surgical candidates of bilateral THA for ONFH, (2) signed consent to be implanting of the specified prosthesis for the SuperPath, and (3) ability to complete scheduled postoperative 12 months follow-ups. Subject excluded were: those with non-inflammatory degenerative joint diseases (e.g. osteoarthritis and posttraumatic arthritis), inflammatory joint diseases (e.g. reactive arthritis, ankylosing spondylitis, rheumatoid arthritis, and gout), inadequate neuromuscular status (e.g. prior paralysis and inadequate abductor strength), and overt infections or distant foci of infections.
Operations were performed by a senior surgeon specialized in traumatology and lower limb reconstruction with over 15-year experience performing primary and revision THAs with the posterior approach (over 250 cases annually). The surgeon also has accomplished more than 50 SuperPath cases. Each patient underwent bilateral staged THA with one side SuperPath and the other side PLA with an average interval of 3 months, allowing for a compensation of the possible impact of the first operation on the second one (and vice versa). Both approaches were randomizedly selected for the first operation, using a shuffled deck of cards (even - SuperPath, odd – PLA; Blinding status, patients and outcome assessors), and performed in either right or left hip. The SuperPath was performed with specific prostheses (Microport Orthopedics, Arlington, TN, USA) as described by Chow et al. , and the PLA was accomplished with prostheses (DePuy Synthes, Warsaw, IN, USA) as described by Moore AT et al. .
Preoperative data were collected for each subject, including the age, gender, etiology, age of pain onset, history of hip injury/surgery, BMI, occupation category , American Society of Anesthesiologists (ASA) score , and Ficat stage . Operation time was recorded from the initiation of incision to end of closure, and incision length was approximated with the linen tape along the surgical incision. The LOS, transfusion, complications, and readmission were also recorded.
Standardized patient care was provided including infection prophylaxis, venous thromboembolism prevention, nausea and vomiting management, wound care, and functional rehabilitation.
Identical rehabilitation program was undertaken for all patients after both SuperPath and PLA. Briefly, Immediate hip flexion, pneumatic compression with foot pumps, and deep breathing exercise were emphasized to minimize thromboembolic and pulmonary complications. After obtaining approvals from the physical therapists, patients began indoor walking independently using crutches with tolerated weight-bearing. Self-care and home-based rehabilitation were educated before discharge, in which patients were instructed to daily walk and gradually increase the walking distance towards a goal of 2 kilometers. All patients were generally discharged and allowed for walking with a cane on the postoperative day 3.
Perioperative total blood loss
Perioperative total blood loss was indirectly calculated from the change in the hematocrit (Hct) according to the Gross formula :
Total blood loss = PBV × (Hctpre - Hctpost) / Hctave
where Hctpre is the initial preoperative Hct, Hctpost is the Hct on the morning of the postoperative day 3, and Hctave is the average of the Hctpre and Hctpost.
The patient's blood volume (PBV, mL) was estimated according to the Nadler formula :
PBV = k1 × height (m) + k2 × weight (kg) + k3
where k1 = 0.3669, k2 = 0.03219, and k3 = 0.6041 for males; and k1 = 0.3561, k2 = 0.03308, and k3 = 0.1833 for females.
Perioperative serum markers
Serum markers are widely used to evaluate soft tissue damage in the hip arthroplasty [23-27] and mainly include the creatine kinase (CK), C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR). Levels of these serum markers were recorded for each patient on the day of hospital admission, postoperative day 1, day 3, and day 14, respectively.
Acetabular component positioning analysis
Standardized anteroposterior pelvic radiographs were acquired on the postoperative day 1. Inclination and anteversion angles were measured with a computer-assisted measurement system (Japan Medical Material, Osaka, Japan). Concisely, an ellipse was fitted to the rim of the acetabular shell on radiographs. Inclination angle was defined as the angle between the longitudinal axis of the body and the acetabular axis . Anteversion angle was defined with the ratio between the lengths of the minor and major axes of the ellipse .
Pain, range of motion, hip function, patient satisfaction
The patient reported pain was measured with a visual analogue scale from 0 (no pain) to 10 (worst imaginable pain) at the day of hospital admission, postoperative day 1, day 3, day 14, 3 months, 6 months, and 12 months, respectively . The ROMs was measured using a goniometer at the day before surgery, postoperative 3 months, 6 months, and 12 months . The Harris hip score (HHS) was determined for each patient at the day of hospital admission, postoperative day 1, day 3, day 14, 3 months, 6 months, and 12 months, respectively . Patient satisfaction was recorded based on the dichotomous responses (satisfied or unsatisfied) of each patient at the postoperative 3 months .
Values are expressed as mean ± standard deviation. One-way ANOVA was performed to compare the VAS and HHS between the different assessment timepoints.