Modified Anterolateral Minimally Invasive Surgery (ALMIS) for Total Hip Replacement: Anatomical Considerations, Range of Motion and Clinical Outcomes.

Background and Objectives: In the modified anterolateral minimally invasive surgery (ALMIS) for total hip arthroplasty (THA), the intermuscular plane between the tensor fasciae latae and the gluteus maximus (GM) is exposed, while the anterior ¼ of the GM is detached. There are scarce data regarding this surgical approach. The purpose of the present study is to thoroughly describe this approach, encompassing the anatomical background, and to present the results of a retrospective two-center study of 603 patients. Materials and Methods: The present study includes a two-center retrospective observational cohort of 603 patients undergoing the ALMIS technique with minimum 5-year follow-up. Demographics were recorded, while range of motion (ROM) of the hip joint and the Harris Hip Score (HHS) were evaluated preoperatively, at 1, 3 and 12 months postoperatively and at the final follow-up (>5 years). Surgery-related complications were also recorded. Results: The studied population's mean age was 69.4 years, while most of them were females (397; 65.8%). The mean follow-up was 6.9 years. The median HHS at the 1-month follow-up was 74, compared to the 47 preoperatively ( p -value < 0.0001). At the final follow-up, median HHS was 94. At the 1-month follow-up, mean adduction was 19.9° (compared to 15.4° preoperatively; p < 0.0001), mean abduction 24.3° (18.2° preoperatively; p < 0.0001), mean flexion 107.8° (79.1° preoperatively; p < 0.0001), mean external rotation 20.1° (12.1° preoperatively; p < 0.0001) and mean internal rotation 15.3° (7.2° preoperatively; p < 0.0001). ROM further improved until the final follow-up; mean adduction reached 22°, mean abduction 27.1°, mean flexion 119.8°, mean external rotation 24.4° and mean internal rotation 19.7°. Regarding complications, 1.3% of the sample suffered anterior traumatic dislocation, in 1.8% an intraoperative femoral fracture occurred, while 1.2% suffered periprosthetic joint infection. Conclusions: The modified ALMIS technique exhibited excellent clinical outcomes at short-, mid- and long-term follow-up, by significantly improving hip ROM and the HHS. Careful utilization of this technique, after adequate training, should yield favorable outcomes, while minimal major complications should be expected.