Between January 2015 to December 2018, a total of 1360 THAs were performed in our department. A continuous series of 75 DAA THA (group 1) were performed with the use of a traction table (Schaerer MIS-Extension, Scharer Medical, Münsingen, Switzerland) by a single surgeon (C.T). These cases were matched for age, BMI and ASA score (table 1) with 75 patients (group 2) operated without table by the same surgeon (C.T).
Inclusion criteria were adult patients undergoing primary THA for symptomatic unilateral hip osteoarthritis through DAA by a single surgeon (C.T) at our institution. Baseline demographics including preoperative Harris Hip Score (HHS), comorbidities likely to influence on postoperative complication rates, and the patient’s physical status according to the American Society of Anesthesiologists (ASA) were recorded. A total of 150 THA through DAA (male: 62, female: 88) with an average age of 68 years (range 29-93) were identified. The average follow-up period was 33 months (range 15-48). This study was performed in line with the principles of the Declaration of Helsinki and approved by our institutional review board (ID 2018-02131).
Preoperative imaging and templating
All the patients underwent routine preoperative standing anteroposterior pelvic radiograph and anteroposterior and lateral radiographs of the operated hip. In both groups, preoperative templating was performed using Traumacad software (Traumacad, PetachTikva, Israel) with regard to the femoral osteotomy level, implant size and positioning and leg length correction was obtained. The goal of preoperative templating was to restore the native center of rotation of the hip and a similar femoral offset to the sound contralateral side. Any pre-existing leg-length discrepancy was corrected as well during templating.
Surgical Technique and Perioperative Care
All THAs were performed in the supine position. Intraoperative fluoroscopy imaging was used during the insertion of the acetabular component to assess its positioning. A single fellowship-trained hip surgeon (C.T) with adequate experience in minimally invasive anterior approach (> 100 THAs using DAA) performed all the procedures. The implants used in the current cohort were: 1) for the patients under 70 years, a ceramic-on-ceramic (April ®, SPS® or Harmony®, Symbios, Yverdon, Switzerland) and 2) for the patients over 70 years, a dual mobility cup construct (Symbol ® dual mobility construct, Dedienne santé, Mauguio, France). Most of the implants used were cementless. The use of cemented Harmony® stems was only necessary in 25 cases as the standard regime in our department is the use of uncemented stems independent of the age of the patient. Bone quality in these 25 patients were considered very poor intraoperatively. Patients, which required custom made implants were not included in the study.
The surgical time was measured from skin incision to wound dressing. When performing THA through the DAA without table, leg length was examined intraoperatively with the surgeon palpating and comparing both malleoli (figure 1). The total operation time was measured from the end of the anesthetic procedure to the transfer to its bed. The blood loss was calculated at the end of the surgery by measuring fluid accumulation in the suction device after subtracting irrigation and the visual estimation of the blood absorbed by surgical gauze.
All the patients were mobilized out of bed on surgery day with full weight-bearing. A standardized physical therapy protocol was followed. Patients were discharged once they were able to safely perform daily activities, walk on stairs and once that pain was adequately controlled with oral medications. The hospital stay duration was considered from the day of surgery to hospital discharge.
Clinical and radiologic evaluation
Patients were followed up clinically and radiographically at six weeks, three months, one year and then every year. Medical records including outpatient clinic notes, operative reports, hospital records for readmission, and Harris Hip Score were reviewed. The clinical examination was performed in a standardized manner by an orthopedic surgeon not involved in the care or management of the included patients. In the present study, complications considered were: excessive intraoperative blood loss requiring transfusion, femoral fracture, dislocation, wound dehiscence, and periprosthetic infection.
The postoperative X-rays were evaluated by a junior and a senior orthopedic resident (D.W and G.L) not involved in the patient management and blinded to patient’s clinical details. The residents performed the measurements individually and concurred with the results. Measurements were performed twice and the results were evaluated using a single-measure intraclass correlation coefficient (ICC) with a 2-way random effect model for absolute agreement.
A standardized protocol has been applied for obtaining pre- and post-operative radiographs. Lower limbs were held together in a neutral position with the anterior superior iliac spine parallel to each other and to the X-ray table. On the anteroposterior view of the pelvis, the inferior margin of the acetabular teardrop, the most prominent point of the lesser trochanter and the centre of rotation of the femoral head were chosen as reference points. Distances between them were measured to the nearest millimeter. This method does not take into account other discrepancies of length in the lower limb but does give an accurate assessment of the situation before and after surgery (22). A positive leg-length discrepancy value was documented when the operated limb was longer than the contralateral side, and a negative one when it was shorter. Acetabular cup inclination was defined as the angle between the plane of the cup bigger diameter and a line bisecting both the acetabular teardrops. Cup anteversion was defined as the angle between the transverse axial plane and the plane of the cup bigger diameter in the lateral view (23). The horizontal and vertical center of rotation (CoR) was defined as the preoperative distance of the CoR to the distance of the postoperative CoR on the horizontal and vertical axes, respectively (24). A negative value indicated that the postoperative CoR was reconstructed more medial and more superior, respectively.
The achieved power of the study according to the post hoc power analysis with a total sample size of 150 hips, medium effect size, and alpha = 0.05 was 94%. Descriptive statistics are presented as mean +/- standard deviation (SD). All parameters were tested for normality to compare normal variables, parametric unpaired t-tests were used. Otherwise, the Wilcoxon signed-rank tests were used. For the radiological measurements of the cup inclination and anteversion, and leg length, intra- and inter-observer variabilities of the measurements were evaluated by two independent and blinded observers using single-measure intraclass correlation coefficients (ICC) with a 2-way random effects model for absolute agreement. Intra- and inter-observer ICC were respectively 0.93 and 0.91 for cup anteversion, 0.95 and 0.92 for cup inclination, and 0.96 and 0.94 for leg length. The level of statistical significance was set at p ≤ 0.05.