Total hip arthroplasty (THA) in obese patients (BMI ≥ 30 kg/m ² ) is technically more demanding and associated with a higher risk of postoperative morbidity. Its realization seems more complex by the direct anterior approach.

The hypothesis was that muscular mass would have a stronger impact than BMI on intraoperative difficulty during anterior THA. The study objectives were; 1. To assess the influence of body composition and BMI on intraoperative difficulty, 2. To determine the influence of body composition on early complications (<3 months) and short-term functional outcomes.

A total of 162 anterior approach THAs without traction table were included. Body composition (muscle and fat mass) was assessed preoperatively by bioelectrical impedance analysis of the operated limb and trunk.

Subgroup analyses were performed according to BMI (<30, 30–35, or ≥35) and muscle mass (threshold set at 67%). Intraoperative difficulty was evaluated based on operative time in minutes and total blood loss in mL, calculated using the OSTHEO formula. Perioperative complications, early complications (<3 months), and 3-month functional outcomes (Oxford Hip Score and Forgotten Joint Score) were assessed.

In univariate analysis, operative time (+19 min) and total blood loss (+615 mL) were significantly higher in patients with BMI ≥ 35 compared to those with BMI < 30 ( p < 0.001).

Operative time was also longer (+6 min) in muscular patients (≥67%) ( p = 0.009), with no significant difference in total blood loss.

No significant differences were observed in perioperative or early postoperative complications, nor in 3-month functional outcomes between obese/non-obese or muscular/non-muscular groups.

In multivariate analysis, BMI and total muscle mass were independently associated with intraoperative difficulty:

Operative time (min) = 22.2 + 0.25 × total muscle mass (kg) + 1.1 × BMI ( R ² = 0.24, p < 0.001)

Total blood loss (mL) = -692.6 + 13.3 × total muscle mass (kg) + 31.1 × BMI ( R ² = 0.29, p < 0.001)

BMI and total muscle mass are two preoperative factors associated with greater intraoperative difficulty, as reflected by increased operative time and total blood loss in anterior approach THA. These factors can be anticipated through a more detailed assessment of body composition. Despite the increased surgical complexity, they do not appear to be associated with a higher risk of early postoperative complications. In this cohort, muscle mass did not demonstrate a stronger impact than BMI on operative difficulty, contrary to the initial hypothesis.

III; Prospective comparative study.