The main finding of the study indicates that the R-PL and DAA THA had comparable short-term clinical and radiological outcomes, along with similar complication rates. Nevertheless, statistically significant differences were identified regarding multiple investigated parameters, precisely, patients in the R-PL group notably required fewer rescue opioids, acetaminophen and NSAIDs compared with the DAA group during hospitalization, resulting in a shorter LOS.

Historically, the DAA was considered to be less painful than the posterolateral approach [15, 16] but available studies do not report comparative results of robotic arm-assisted surgery. The current research addressed potential confounders related to sample populations (i.e. age and sex), excluding the influence of patient specific features on pain level and drug metabolism, by demonstrating that the robotic technique is less painful in the post-operative period. This finding can be clarified by the minimized invasiveness of robotic arm-assisted THA, specifically concerning cup reaming.

In contrast to literature [17,18,19], the present study demonstrates that the R-PL approach is comparable to DAA in terms of operative time with a mean difference of 5 min. We emphasize that all the procedures were performed by experienced surgeons with proven experience in hip arthroplasty and robotic surgery. We also highlight that the operative time of R-PL can be increased only if compared with the traditional posterolateral approach performed by expert surgeons [20].

This study showed a significantly lower Hb drop in the R-PL group compared with the DAA group as well as a higher Hb value at post-operative day 1. Despite the overall reduction of blood loss, which supports the reduced surgical invasiveness of the robotic technique, the transfusion rate was the same for the DAA and R-PL groups, indicating limited blood loss also in the DAA group [7]. Furthermore, the higher Hb drop and lower Hb level of post-operative day 1 of the DAA group can be justified by the lower, although not significant, peri-operative Hb level of this group.

Enhanced recovery following THA played a key role in the last decade and the LOS has been evaluated as an important outcome measure in the latest studies on robotic-assisted arthroplasty [6, 21, 22]. A retrospective cohort study comparing MAKO (n = 56) with standard surgery (n = 51) showed that the robotic-assisted system was associated with shorter LOS [21]. The results of the present research agree with the latest evidence in literature, suggesting that specific robotic preoperative planning tailored to a patient’s anatomy can further promote pain control. Rapid patient discharge is also associated with excellent pain control, supporting the data in this study on the diminished requirement for analgesics during hospitalization in the R-PL group.

No significant mid-term differences were found regarding clinical outcomes assessed by HHS and FJS showing that both techniques achieved excellent clinical outcomes at 1 year. Accordingly, experienced surgeons can achieve the same results performing the traditional technique. The literature reports contrasting findings related to functional outcomes in robotic THA, but the meta-analysis confirmed no significant differences between manual and robotic THA, substantially confirming the results of the present study [6, 22, 23].

Component positioning in THA is essential to ensure joint stability and long-term survivorship of prosthetic implants. Implant malpositioning is associated with a higher risk of complications, including impingement, dislocation, wear and revision [24, 25]. The current study demonstrated that cup inclination and stem sizing were comparable and experienced surgeons achieved equivalent radiological results as robotic-assisted hip arthroplasty with a mean difference of 2°. Despite these findings, meta-analyses [26,27,28] reported an improved radiological positioning with the robotic technique, but the participation of less experienced surgeons among the operators could influence the radiological results justifying this difference.

The LLD following a THA is still a debated point and literature reported contrasting findings with different hip approaches [29,30,31]. The present study reported no significant differences in LLD at 1 year follow-up, and the results are confirmed by other authors [29, 30] who demonstrated comparable LLD in R-PL THA and DAA. The reasons for the accuracy of the DAA can be related both to the surgeon’s experience and to the supine position used in DAA that provides an intuitive intra-operative assessment of leg length.

Post-operative complications during the follow-up period were also assessed and compared but no significant differences were found except for meralgia paresthetica which typically affects 30% of hip replacement with anterior approach [32]. In this series, 36% of patients in the DAA group had lateral femoral cutaneous nerve palsy and results are comparable with those reported in the literature focused on this complication [32].

The infection rates were comparable between R-PL and conventional THA; however, it is important to highlight that robotic surgery exhibited a 4% infection rate (over 2% of DAA), higher than the one reported in literature [33], raising concern regarding the request of additional healthcare personnel as biomedical engineers potentially increasing the risks of contamination. In addition, the proper draping preparation and use of the robot can also represent a potential criticism related to prosthetic joint infection.

There is a lack of studies directly comparing clinical and radiological results of THA performed through DAA with conventional instruments and a robotic-assisted THA through the posterolateral approach. To the best of our knowledge, this is the first study directly comparing R-PL and DAA in a single centre with standardized protocol and expert surgeons.

Additional strengths are the precise design (retrospective, with a pair-matched cohort of patients), the limited number of surgeons involved (three expert surgeons performing more than 100 hip replacements per year), the single-institution series and data collected by blinded observers not involved in the surgical procedures. Furthermore, strict inclusion and exclusion criteria were applied to address and evaluate potential confounders.

Limitations of this study are the limited sample size, the retrospective design, and the limited follow-up period reporting only short to mid-term follow-up results. Furthermore, the two techniques require different implants, precisely short cementless stems were used for DAA and standard cementless collarless Corail-type stems for the R-PL technique, and this was related to the robotic technique. Moreover, no cost-effectiveness analysis was performed to further assess robotic surgery in total hip replacement.