In the UK, the posterior approach (PA) and direct lateral approach (DLA) are the most common total hip arthroplasty (THA) procedures. Few studies however, have compared the subsequent functional outcomes. This exploratory study aimed to examine the effect of PA and DLA approaches on post-operative hip kinematics, strength and hip muscle cross-sectional area (CSA), compared to healthy controls.

Participants comprised of 15 cases in the DLA group, > 12 month post-operatively, (ten male, age 68.9+/-5.5 years, BMI 26.9+/-3.0), 13 cases in the PA group (six male; age 72.9+/-6.9 years, BMI 27.1+/-3.6) and 11 age/BMI-matched healthy control participants. All participants underwent 3D kinematic (Vicon, Oxford, UK) and kinetic (AMTI, USA) analysis whist performing self-selected and fast walking as well as sit-to-stand and stand-to-sit. Isometric dynamometry was performed (Biodex Medical systems, USA) for all major muscle groups around the operated hip, and a subset of five participants (three DLA v two PA) underwent “slice encoding for metal artefact correction” (SEMAC) MRI imaging to measure muscle CSA. Patient-reported outcome measures were collected.

Both post-operative surgical groups exhibited altered gait, particularly in limited hip extension, compared to the control participants. The DLA group demonstrated forced hip extension matching controls only under fast walking conditions while the PA group did not achieve hip extension. Both surgical approaches achieved high PROMs scores.

The PA group were weaker for all strength activities tested, whereas the DLA cases demonstrated similar hip strength to controls. SEMAC imaging revealed reduced CSA for those muscles dissected during surgery, compared to the contralateral side.

This exploratory study demonstrated small but measurable differences between surgical approaches for muscle CSA, hip strength of major hip muscle groups and a number of gait variables, although both approaches produce satisfactory functional outcomes for patients after surgery.