1 Introduction

In 2019, the annual volume for total hip arthroplasty (THA) in the United States was greater than 260,000 cases, and demand for THA is expected to grow an average of 5.2 % annually.¹ It is predicted that this annual increase will create a burden on health-care systems across the country and around the world.² Additionally, national healthcare spending in 2019 increased by 4.6 % to $3.8 trillion, with hospital spending increasing by 4.5 % to $1.2 trillion.³ As increasing demand for THA procedures and rising health-care costs become more prevalent, hospitals and surgeons are tasked with improving their operating room (OR) efficiency to minimize costs while continuing to deliver optimal clinical outcomes.

Many hospitals and health systems have focused on identifying and improving efficiency during preoperative and postoperative periods. However, the intraoperative period, when patients are in the OR, has received less attention. A major portion of procedural costs are associated with the intraoperative OR period; therefore, surgeons have influence to identify and implement efficiency changes during this OR period.⁴ The direct anterior (DA) approach for THA is one example of how surgeons can implement efficiency efforts in their ORs by changing their intraoperative techniques.

The DA approach has demonstrated greater OR efficiencies by shortening the duration of THA procedures and improving OR setup techniques.^5,6 Additionally, the DA approach has positively impacted clinical outcomes by reducing length-of-stay and increasing mobilization compared to traditional approaches such as the posterior approach.⁷ Conventional use of the DA approach for THA requires the use of intraoperative fluoroscopy to evaluate the position of components and allow for intraoperative adjustments. However, the accuracy of implant placement during conventional DA THA with fluoroscopy has been shown to be highly variable.⁸

The implementation of computed tomographic (CT)-based robotic-assisted THA in intraoperative techniques also has the potential to improve efficiencies. The CT-based robotic-assisted THA relies on a preoperative CT scan to develop a 3D anatomic model of the patient's anatomy for preoperative and intraoperative case planning and visualization of the joint space and components. Therefore, robotic-assisted THA allows surgeons to incorporate the DA approach without the use of intraoperative fluoroscopy. In addition, THA cases performed with robotic assistance have demonstrated increased accuracy in the preparation and positioning of implants to plan, even with the DA approach.⁹ Studies have also shown that patients who received robotic-assisted THA used fewer hospital services in the post-index period, and greater average cost savings, and had shorter lengths of stay when compared to conventional THA.¹⁰

Robotic-assisted DA THA without fluoroscopy may offer a compelling alternative to conventional DA THA with fluoroscopy by increasing component accuracy and reducing costs. However, few studies have investigated the impact of robotic-assisted THA on surgical efficiencies. Therefore, the purpose of this study was to compare surgical efficiency between robotic-assisted DA THA without fluoroscopy and conventional DA THA with fluoroscopy.

2 Methods

There were two orthopaedic surgeons who regularly perform both conventional DA THA with fluoroscopy and robotic-assisted DA THA without fluoroscopy were included in this investigation. Both surgeons had considerable experience with the DA approach, with 11–20 years of experience performing conventional DA THA with fluoroscopy, and over 5 years of experience performing robotic-assisted DA THA without fluoroscopy.

There were six cadaver specimens (12 hips, 6 matched pairs) included for this study. On each cadaveric specimen, one hip underwent a conventional DA THA with fluoroscopy, while the contralateral side underwent a robotic-assisted DA THA without fluoroscopy.

The surgeons each performed three conventional THA and three robotic-assisted THA cases, utilizing their standard DA workflow for all cases. The use of conventional and robotic-assisted THA surgery was alternated between the right and left hips, ensuring that not all robotic-assisted cases were performed on one side.

The Mako Total Hip Application (Mako Surgical Corp. (Stryker) Weston, Florida, USA) was utilized for the robotic-assisted DA THA without fluoroscopy cases in which two cortical pins were placed into the acetabulum and femur, and trackers were affixed to both pins. Intraoperatively, the surgeon utilized a navigation probe to map out the acetabulum and femur; this intraoperative mapping was cross-checked against the preoperative CT scan to generate the 3D anatomic model of the patient's hip. This process allowed for haptic boundaries to be set, ensuring that the surgeons did not deviate beyond preset safe boundaries for acetabular reaming and femoral broaching.

Surgical efficiency data collected for all cases included total operative time from skin to trials, surgical task time for acetabular and femoral workflows, and the number of reamers and broaches used. Acetabular workflow was defined as acetabular preparation, reaming, and impaction. Femoral workflow was defined as femoral preparation, broaching, and impaction. The final acetabular shell size, final broach size, and number of intraoperative fluoroscopic shots taken during the conventional THA cases were also recorded. Student t-tests were performed to compare these surgical efficiency data points between robotic-assisted and conventional THA. A p-value of 0.05 was set for statistical significance.

3 Results

Average total operative time (from skin incision to implanting trials) for conventional DA THA with fluoroscopy was 3 min longer compared to robotic-assisted DA THA without fluoroscopy (26 ± 7.0 versus 23 ± 5.6 min); however, the times were not significantly different (p = 0.452).

Acetabular workflow duration, including acetabular preparation, reaming, and impaction, was longer for conventional THA (6 ± 3.1 min) compared to robotic-assisted THA (3 ± 1.7 min, p = 0.070). One reamer was used during each robotic-assisted THA case, compared to an average of 2.67 ± 0.52 reamers used during conventional THA (p < 0.001). In addition, robotic-assisted DA THA without fluoroscopy resulted in significantly less acetabular reaming time compared to conventional DA THA with fluoroscopy (0.4 ± 0.2 versus 2.4 ± 0.6 min, p < 0.001). Final shell size was similar between robotic-assisted THA and conventional THA, respectively (51.0 ± 3.3 versus 51.7 ± 2.9, p = 0.720).

Femoral workflow time was longer for conventional THA by an average of 1.5 min compared to robotic-assisted THA (6.5 ± 4.8 versus 5.0 ± 1.7 min), but was not significantly different (p = 0.495). There was no difference between robotic-assisted THA and conventional THA femoral broaching times, respectively (2.3 ± 1.6 versus 2.3 ± 0.9 min, p = 1.000). On average, 4.3 ± 2.3 broaches were used during robotic-assisted THA cases compared to 5.0 ± 1.8 broaches used during conventional THA (p = 0.593). Final broach size was similar between robotic-assisted THA and conventional THA with fluoroscopy, respectively (4.5 ± 1.1 versus 4.8 ± 1.2, p = 0.616).

For conventional DA THA cases with fluoroscopy, there was an average number of 21 ± 8.9 fluoroscopic shots taken during the surgical workflow. Intraoperative fluoroscopy was not used for robotic-assisted DA THA cases, therefore there were no fluoroscopic shots taken (p = 0.002).

4 Discussion

Optimizing surgical efficiency is crucial amid mounting surgical demand and escalating healthcare expenditures. The DA approach for THA has been associated with intraoperative efficiencies, earlier mobilization, and shorter lengths of stay.^5–7 However, it is not without limitations, namely the requirement of intraoperative fluoroscopy to ascertain appropriate acetabular component positioning. Utilization of robotic-assisted THA with the DA approach may eliminate concerns associated with the accuracy of component placement with fluoroscopic guidance, as robotic-assisted THA relies on a preoperative CT scan, which allows for visualization of components relative to patient anatomy.

This cadaver-based study demonstrated that robotic-assisted DA THA without fluoroscopy was associated with statistically significant efficiencies throughout the workflow, including fewer reamers used, shorter acetabular reaming time, and no fluoroscopy usage. Additional findings, such as a reduction in operative time, femoral workflow time, and fewer broaches used, demonstrate additional efficiencies of robotic-assisted DA THA without fluoroscopy; however, these were not statistically significant. These findings suggest that robotic-assisted DA THA without fluoroscopy may enhance surgical efficiency by reducing time during acetabular reaming with the execution of single-staged reaming, and eliminating the use of intraoperative fluoroscopy. These findings should be interpreted carefully to help better characterize the role robotic-assisted DA THA without fluoroscopy may play in the future of hip arthroplasty.

Robotic-assisted DA THA without fluoroscopy demonstrated increased surgical efficiency during acetabular reaming by executing single-stage reaming for all cases in significantly less time compared to conventional DA THA without fluoroscopy. These findings are likely associated with the intraoperative mapping and haptic capabilities of the robotic-assisted system, which allows the surgeon to ream directly up to the final acetabular component size within a preset boundary. Robotic-assisted single-stage reaming has been shown to significantly preserve acetabular bone stock compared to conventional techniques, therefore providing a significant clinical benefit to patients.¹¹ The use of single-staged reaming has also been integrated into efficient clinical surgical techniques, as seen in Nessler et al., where DA approach was used for all cases without the supplemental use of fluoroscopy and all acetabular preparation was performed with single-staged reaming.¹² Since single-stage reaming was executed in significantly less time, this may have an impact on the potential cost savings associated with the adoption of robotic-assisted THA in ORs.

Robotic-assisted technology was also shown to improve surgical efficiency through the elimination of intraoperative fluoroscopy. During conventional THA, the use of intraoperative fluoroscopy impacts the surgical workflow and increases the overall time of the cases. In this study, the average number of fluoroscopic shots taken during conventional THA was 21 shots, and there were no fluoroscopic shots taken during robotic-assisted THA. This may have directly contributed to the increased time of the surgical workflow for conventional THA cases compared to robotic-assisted THA cases. Additionally, to obtain accurate component placement with intraoperative fluoroscopy, the C-arm must be properly positioned over the operating field, which may require multiple attempts to determine the proper position. For robotic-assisted THA cases, the 3D anatomic model generated from a preoperative CT scan allows for surgeons to visualize the joint space during acetabular component positioning without the use of intraoperative fluoroscopy.

In general, the literature supports the use of robotic-assisted DA THA without fluoroscopy, especially when considering improved surgical outcomes,¹³ patient outcomes,¹⁴ and a reduction in costs.¹⁵ For example, in a systematic review and meta-analysis of seven studies and 1516 patients, Chen et al. concluded that robotic-assisted THA was associated with lower intraoperative complications (odds ratio 0.12; p < 0.001), improved cup placement within Lewinnek safe zones, more accurate stem placement, and more optimized global offset compared to conventional THA.¹³ Another study concluded that robotic-assisted THA resulted in significantly improved satisfaction outcomes on multiple patient-reported outcome measured scores as early as six months postoperatively and maintained improved satisfaction out to two years.¹⁴ Also, an extensive, cross-platform search of robotic-assisted THA identified 24 studies that concluded CT-based robotic-assisted THA led to decreased dislocations and decreased episode-of-care costs when compared to conventional THA.¹⁵

Robotic-assisted DA THA without fluoroscopy may have additional advantages over conventional DA THA with fluoroscopy, aside from surgical efficiency. A recent study that compared soft tissue injury between robotic-assisted DA THA and conventional DA THA found that there was less damage to the gluteus minimus, sartorius, vastus lateralis, and tensor fascia lata muscles in the robotic-assisted THA cases.¹⁶ Additionally, another study determined that robotic-assisted DA THA without fluoroscopy resulted in less physical and mental demand for orthopaedic surgeons for the overall procedure and individual surgical steps when compared to the demand experienced when performing conventional DA THA with fluoroscopy.¹⁷ This study evaluated biometric parameters, including heart rate, respiratory rate, caloric expenditure, stress (heart rate variability), and sweat loss, and questionnaire based responses to characterize the physical and mental demands the surgeon experienced throughout the procedure.¹⁷ There was a correlation in the results of the biometric and questionnaire data that demonstrated robotic-assisted DA THA was associated with less physical and mental demand for the overall procedure and during acetabular reaming.¹⁷ These findings are important to interpret collectively as they help to better characterize the impact robotic-assisted DA THA without fluoroscopy may have on surgeons, patients, and the healthcare system as a whole.

The design of this cadaver-based study is subject to limitations. Since the evaluation of surgical efficiency was based on the utilization of cadaver specimens, the environment does not accurately reflect the conditions of an operating room. Additionally, the surgeons selected for this study were highly experienced with the type of procedure; therefore, the results may not be transferable to surgeons earlier in their learning curve. Also, given the sample size of six cadavers (12 hips), this study may be underpowered to reject the null hypothesis. Despite these limitations, the authors maintain that the study findings have important implications for the perception and adoption of robotic-assisted DA THA without fluoroscopy.

5 Conclusion

The use of robotic-assisted DA THA without fluoroscopy was associated with increased surgical efficiency, especially during acetabular reaming and the number of reamers used, when compared to conventional DA THA with fluoroscopy. Amidst the changing healthcare environment and focus on identifying and implementing efficiencies, these findings have important consequences for the continued and accelerated use of robotic-assisted THA in primary settings.

Consent

Patient consent was not necessary for this investigation.

Ethics

We acknowledge Kevin Abbruzzese for his expertise and guidance regarding the wearable devices used in the study.

Funding

No funding was obtained for this investigation.

CRediT authorship contribution statement

Melanie Caba: Conceptualization, Methodology. Christina O'Neill: Conceptualization, Methodology. Joseph Nessler: Writing – review & editing, Software, Validation. Benjamin Frye: Writing – review & editing, Software, Validation. Laura Scholl: Writing – review & editing, Software, Validation. Sean B. Sequira: Writing – original draft, Writing – review & editing. Michael A. Mont: Conceptualization, Methodology, Software, Validation, Writing – review & editing.