Study design and participants
arthroplasty
SECONDARY
The present study is a secondary analysis of a prospective clinical trial that was approved by our institutional research ethics board and registered with ClinicalTrials.gov (NCT03558217). Patients undergoing unilateral primary THA were eligible to participate in the initial prospective randomized control trial (RCT).Depending on their surgeon referral, patients recruited to this study underwent THA using either the direct lateral (DL) or the direct anterior (DA) surgical approach. 2 fellowship-trained arthroplasty surgeons specialised in their respective approach performed all the operations; 1 surgeon (EMV) performed all the DL surgeries, and 1 surgeon (BAL) performed all the DA surgeries. Although surgical approach was not randomised, the expertise-based study design used has been reported to reduce challenges related to differential expertise bias and clinical equipoise in orthopaedics.The DA surgeon routinely opts to supplement acetabular press-fit cup fixation with the use of 1 or 2 screws as his standard surgical procedure, while the DL surgeon uses no screws as their routine. For screw placement, the DA surgeon affirmed the appropriate screw hole position as part of the multi-screw hole cup insertion and after suitable visualisation, each hole was drilled under direct visualisation with the appropriate drill bit and guide. As needed, the depth gauge was used to confirm depth and containment within bone. The appropriate screw length was then selected for each hole and inserted with the applicable screwdriver. Patients received either 1 or 2 screws in accordance with surgeon discretion based on adequacy of bone stock and purchase of the first screw at the time of screw insertion. For acetabular cup placement, the DL surgeon targets an inclination of 40–45° and an anteversion that is parallel to the transverse acetabular ligament. The DA surgeon targets an inclination of 30–35° and an anteversion of 10–20°. Although each surgeon has a different cup placement target, both fall into the recommended safe zones.