Fluoroscopy-based robotics in total hip arthroplasty mitigates laterality-based differences in acetabular cup placement when compared to the manual,fluoroscopic- assisted technique

Abstract

BACKGROUND:

Robotic assistance in total hip arthroplasty (RA-THA) has been shown to minimize laterality-based differences in acetabular cup positioning.

OBJECTIVE:

To determine if the use of a novel, fluoroscopy-based RA-THA system mitigates differences in acetabular cup placement between left (L) and right (R) side hip procedures, when compared to manual, fluoroscopic-assisted technique.

METHODS:

We conducted a retrospective review of 106 consecutive mTHA (40 L/66 R) and 102 RA-THA (48 L/54 R) primary direct anterior approach procedures. All cases were performed by a single right-hand-dominant surgeon, for a pre-operative diagnosis of osteoarthritis, avascular necrosis, or rheumatoid arthritis. Outcomes included acetabular cup inclination and anteversion, and the proportion of cups within the Lewinnek safe-zone.

RESULTS:

The average inclination of mTHA L cases was smaller than that of mTHA R cases (41.10^∘ $\pm$ 7.38 vs. 43.97^∘ $\pm$ 6.27; $p=$ 0.04). For RA-THA, L and R cup angles were similar. There were fewer overall mTHA hips within the Lewinnek safe-zone compared to RA-THA (0.59 vs. 0.78; $p=$ 0.003), as well as fewer mTHA R cases than RA-THA R cases (0.59 vs. 0.80; $p=$ 0.03) within safe zone.

CONCLUSION:

Use of a novel, fluoroscopy-based robotic system mitigates laterality-based differences in acetabular cup placement that were observed in a manual, fluoroscopic-assisted cohort.

Keywords

Arthroplasty hip acetabulum robotic-assisted surgery functional laterality

1. Introduction

Favorable outcomes following total hip arthroplasty (THA) are largely dependent on acetabular cup positioning [1, 2], with traditional goals of safe-zone inclination and anteversion angles [3]. Despite the importance of target-oriented cup placement, it is estimated that 52% of cups are positioned outside of this safe-zone in manual unassisted THA (mTHA) [4]. Surgeon “handedness,” or hand-dominance, has been cited as a driver of poor or inconsistent acetabulum positioning in mTHA, specifically when the operative hip conflicts with the ergonomics of the surgeon’s dominant hand [5, 6, 7, 8, 9]. For these procedures, positional, ergonomic, and energy-related challenges pertaining to reduced dexterity with the non-dominant arm, or use of the dominant arm in a contorted position during cup impaction, may be introduced [10].

The use of robotic assistance during total hip arthroplasty may address ergonomic issues pertaining to procedure laterality by providing additional peri-operative mechanical assistance and stability. The results of two recent studies suggested that robotic-assisted THA (RA-THA) mitigates laterality-based differences in cup placement quality [11, 12]. However, these findings were limited to a computerized tomography (CT)-based RA-THA system. There are an absence of similar publications in the literature which utilize alternative robotic platforms.

In August of 2021, a novel, fluoroscopy-based RA-THA system received United States Food and Drug Administration (FDA) approval for use in primary THA. To the authors’ knowledge, there are no existing studies which have explored the impact of using this system on laterality-based biases in acetabular cup placement for primary THA. Therefore, the primary purpose of this study was to determine if use of this fluoroscopy-based RA-THA platform mitigated differences in cup placement between Left-hip (L) and Right-hip (R) primary THA cases, relative to a control cohort of manual, fluoroscopic-assisted THA cases (mTHA).

2. Material and methods

An analysis of a consecutive series of 106 mTHA (40 L/66 R) and 102 RA-THA (48 L/54 R) patients who underwent primary THA using a direct anterior approach (DAA) between September of 2019 to July of 2022 was conducted. All procedures were performed by a single high-volume right-hand-dominant surgeon at the same institution, for a pre-operative diagnosis of osteoarthritis, avascular necrosis, or rheumatoid arthritis. Patients who underwent revision THA, or who were under 18 years of age, were excluded. All mTHA cases performed during the study period which met these criteria served as the control group, while qualifying RA-THA cases served as the study group. All RA-THA cases were performed with the assistance of the Zimmer ROSA^® Hip System (Zimmer Biomet, Warsaw IN, USA), which the principal surgeon began using in September of 2021. Institutional review board (IRB) approval was obtained prior to the initiation of this investigation (06/03/2022; IRB#: 22-528).

The primary outcome variables used to assess laterality-based (comparison of L and R hip procedures) differences in acetabular cup placement between cohorts included average inclination and anteversion angles, and the proportion of cups placed within the Lewinnek safe-zone of 40^∘ $\pm$ 10 inclination and 15^∘ $\pm$ 10 anteversion [3]. Martell Hip Analysis Suite Software (version 8.0.4.5., Martell Hip Analysis Suite™, Chicago IL, USA) was used to measure acetabular inclination and anteversion from standardized six-week post-operative standing antero-posterior (AP) radiographs for both cohorts, using a methodology previously published by Buchan et al. [13]. Six-week cup angle measurements were captured using standing AP X-rays for two reasons: 1) This is the post-operative standard of care for patients at our institution, and therefore high-quality images are routinely captured at this timepoint; 2) Intra-operatively, the radiographic plane of the pelvis is matched to the standing AP plane to best assess the functional position of the pelvis using DAA. All radiographic measurements were executed by the second and third authors. Intra-observer measurement validity tests were performed by having each observer analyze the same radiograph 10 times, yielding a range of 1.5^∘ for anteversion, and 0.8^∘ for inclination measurements. Additionally, inter-observer validity was assessed by comparing the measurements of the observers over 10 radiographs. A mean difference of 1.7^∘ for anteversion, and $-$ 0.1^∘ for inclination measurements was found.

Figure 1.

Intra-operative photograph of right hip arthroplasty with manual acetabular cup impaction, by the right-hand-dominant principal surgeon.

2.1 Surgical technique

For the mTHA cohort, the principal surgeon performed all cases in the supine position using a traction table, with intra-operative fluoroscopic C-arm imaging guidance to assist with pelvic leveling, bone preparation, and component positioning. For the RA-THA cohort, all cases were performed with the assistance of the ROSA^® Hip System, using an intra-operative workflow previously published by Kamath et al. [14]. Intra-operative fluoroscopic images were captured with the patient supine on a radiolucent table. The radiographic plane of the pelvis was matched to the standing AP plane (i.e. the beam was adjusted to match the fluoroscopic projection in the weight-bearing, standing projection), and cup position parameters were chosen according to this plane. For both cohorts, the principal surgeon utilized a DAA with a targeted acetabulum positioning of 40^∘ of inclination and 15^∘ of anteversion. Intra-operative photographs of manual and robotic-assisted acetabular cup impaction are included in Figs 1 and 2. The G7^® Acetabular System (Zimmer Biomet, Warsaw IN, USA) and Avenir Complete^® Femoral Stem (Zimmer Biomet, Warsaw IN, USA) with cementless fixation were implanted in all patients. Surgical techniques were identical between cohorts apart from the use of manual fluoroscopic guidance in the mTHA cohort and fluoroscopy-guided robotic assistance in the RA-THA cohort.

Figure 2.

Intra-operative photographs of left hip arthroplasty with robotic-assisted acetabular cup impaction.

2.2 Statistical analysis

Demographic characteristics and surgical data between cohorts were provided using descriptive statistics. Continuous variables were reported as means and standard deviations (SD), while categorical variables were presented as frequencies and percentages. Independent samples student $t$ -tests and Mann-Whitney U tests were used to compare the means of continuous variables between cohorts. Pearson’s chi-squared tests and Fisher’s exact tests were used to compare categorical variables. Shapiro-Wilk tests of normality were used to assess the distributions of data. $p<$ 0.05 was considered statistically significant. All analyses were performed using Microsoft Excel Software (Microsoft Corporation 2023, Redmond WA, USA).

3. Results

The mTHA and RA-THA cohorts were similar in their distributions of age, sex, race, body mass index (BMI), pre-operative diagnosis, procedure laterality and pre-operative American Society of Anesthesiologists (ASA) classification. A full report of cohort demographic and treatment data is included in Table 1.

Table 1
A comparison of demographic and treatment data between manual THA (mTHA) and robotic-assisted (RA-THA) cohorts

Variable	mTHA ( $n=$ 106)	RA-THA ( $n=$ 102)	$p$
Age at surgery (years)	60.2 (14.2)	60.0 (14.2)	0.81
Sex (%)			0.27
Male	45.3	52.9
Female	54.7	47.1
Race (%)			0.80
Caucasian	80.2	80.4
Black	19.8	18.7
Other/multiracial	0	0.9
Body mass index (kg/m²)	29.2 (5.0)	29.8 (4.9)	0.39
Laterality (%)			0.17
Left	37.7	47.1
Right	62.3	52.9
Pre-operative diagnosis (%)			0.49
Osteoarthritis	87.7	84.3
Avascular necrosis	12.3	13.7
Rheumatoid arthritis	0	2.0
ASA classification (%)			0.15
Class I	2.8	1.0
Class II	48.1	47.0
Class III	45.3	52.0
Class IV	3.8	0.0

Note: kg $=$ kilograms; m $=$ meter; ASA $=$ American Society of Anesthesiologists.

For the mTHA cohort, the average cup inclination angle of L cases was significantly less than that of R cases (41.10^∘ $\pm$ 7.38 vs. 43.97^∘ $\pm$ 6.27; $p=$ 0.04). This difference was not observed for anteversion (21.56^∘ $\pm$ 6.43 vs. 21.77^∘ $\pm$ 7.02; $p=$ 0.87). There were a similar proportion of L and R cups placed within the Lewinnek safe-zone (0.60 vs. 0.59; $p=$ 0.92).

For the RA-THA cohort, the average cup inclination (44.32^∘ $\pm$ 8.30 vs. 42.91^∘ $\pm$ 4.27; $p=$ 0.70) and anteversion (20.03^∘ $\pm$ 7.83 vs. 18.68^∘ $\pm$ 5.07; $p=$ 0.44) of L and R cases were similar. There were a similar proportion of L and R cups placed within the Lewinnek safe-zone (0.77 vs. 0.80; $p=$ 0.76). Box and whisker plots of mTHA and RA-THA acetabular cup inclination and anteversion angles, sub-divided by procedure laterality, are included in Fig. 3.

Figure 3.

Box and whisker plots of mTHA and RA-THA acetabular cup inclination and anteversion placement angles, sub-divided by procedure laterality. Note: mTHA $=$ Manual Total Hip Arthroplasty; RA-THA $=$ Robotic-Assisted Total Hip Arthroplasty; ^* $=$ Statistically significant difference in average cup placement angles between Left and Right hips ( $p<$ 0.05).

Overall (when combining L and R cases in each cohort), the mTHA hips were less consistently placed in the Lewinnek safe-zone when compared to RA-THA (0.59 vs. 0.78; $p=$ 0.003). While both manual and robotic cohorts had a similar proportion of L cases within the Lewinnek safe-zone (0.60 vs. 0.77; $p=$ 0.09), the mTHA cohort had a lesser proportion of R cases within the safe-zone when compared to the RA-THA cohort (0.59 vs. 0.80; $p=$ 0.03).

4. Discussion

Improper acetabular cup positioning has been associated with various post-operative complications following THA including dislocation [15], accelerated component wear [16, 17], and revision surgery [18], making proper alignment especially crucial to favorable outcomes. It is estimated that 85% of orthopaedic surgeons are right-hand-dominant [19], which may present ergonomic challenges affecting implant alignment for procedures performed on the left hip [5, 6, 7, 8, 9, 10]. The results of our study demonstrated that for an experienced right-hand-dominant orthopaedic surgeon, use of a novel, fluoroscopy-based RA-THA platform mitigated differences in acetabular cup placement between L and R hips as seen in the mTHA control cohort. Use of this novel technique has also been shown to produce similar radiation exposure [20], operative times [13], and treatment costs [21] relative to mTHA with fluoroscopic assistance in prior investigation. To the authors’ best knowledge, this is the first study which has utilized this platform in a laterality-focused analysis.

Many orthopaedic surgeons have difficulty with precise angular approximation in the absence of peri-operative guidance systems [22], especially when assessing cup inclination [4, 23]. This approximation may be further complicated by a surgeon’s standing position relative to the operative hip, with unaccustomed perspectives from a surgeon’s non-dominant side contributing to inconsistencies in angular estimation and final cup placement [11]. Our results indicated that use of the novel RA-THA platform reduced differences in acetabular inclination angles between L and R hip procedures. These findings align with those of two investigations using the Stryker MAKO^® system by Kong and Chai et al., who found that L hip anteversions were significantly larger than those of the R hip in mTHA, but were similar among the RA-THA cohorts [11, 12]. This study adds to the growing body of literature which suggest that the use of RA-THA may normalize outcomes across a variety of surgical scenarios.

We also found that a significantly greater proportion of RA-THA cases were placed in the Lewinnek safe-zone compared to mTHA. While there were no differences between the proportion of L and R hip cups placed within the Lewinnek safe-zone in either cohort, there were a greater proportion of R cases placed within the safe-zone in the RA-THA cohort. These findings are consistent with those of the previously mentioned study by Kong et al. [11]. Laterality-based differences in placement consistency could be attributable to the system being a haptically-guided semi-active robotic system, which can theoretically still be influenced by surgeon-based ergonomic and comfort considerations with regards to hand-dominance [24]. In 2011, Callanan et al. proposed a narrowing of the Lewinnek safe-zone to 30^∘–45^∘ of inclination and 5^∘–25^∘ of anteversion to account for increased liner wear observed in cups with inclination $>$ 45^∘, leaving smaller margins for cup placement error [4]. There are a number of factors which impact acetabular cup placement angles and consistency, including pre-operative acetabular head coverage [23], surgeon planning and templating [23], and surgical approach [13, 14, 25]. These differences are not known to be controlled for by a surgeon’s level of arthroplasty experience [23]. In light of this, robotic assistance systems may serve an important role in maintaining consistently favorable outcomes.

Our study has several limitations to note. First, this was a retrospective analysis, which introduces the possibility of documentation biases. However, all records were obtained from standardized institutional electronic health records to mitigate this likelihood. Second, the principal surgeon of this investigation is an experienced, high-volume arthroplasty surgeon operating out of a large healthcare institution, which may limit the generalizability of our findings. Third, this was an unmatched investigation. However, the results of our demographic analysis indicated that the cohorts were similar in key characteristics. Fourth, investigators were not blinded to surgical technique when obtaining radiographic measurements. Both intra- and inter-observer reliability analyses were preformed to mitigate the risk of measurement bias. Lastly, the results of this investigation relied on the use of six-week post-operative radiographs, which could introduce slight variations in positioning between patients. To account for the limitations of two-dimensional measurement technique, investigators prioritized the matching of pre-operative AP standing pelvis imaging to those obtained post-operatively during review [13].

5. Conclusion

Use of a novel, fluoroscopy-based robotic system for primary THA mitigated laterality-based differences in acetabular cup placement that were observed in the manual, fluoroscopic-assisted cohort. Accurate component placement, regardless of hip laterality, is crucial to maintaining consistently favorable procedural outcomes following THA. The findings of our investigation expand upon the literature with regards to the utility of peri-operative robotic assistance in various surgical scenarios. Future investigation involving an expanded cohort and a matched study design is still needed to validate these findings.

Ethical approval

This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Institutional Review Board (06/03/2022; IRB#: 22-528).

Data availability statement

The data that support the findings of this study are available upon reasonable request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

Funding

The authors report that no funding was received for this investigation.

Footnotes

Acknowledgments

The authors have no acknowledgements.

Conflict of interest

Authors C.B.O., G.B.J.B., C.J.H., Y.H., D.J.H., and J.P. declare that they have no relevant competing interests. Author D.O.K. serves on the speakers’ bureau and receives royalties from Zimmer Biomet. Author A.F.K. serves on the speakers’ bureau, is a paid consultant, and owns stock or stock options in Zimmer Biomet.

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Fluoroscopy-based robotics in total hip arthroplasty mitigates laterality-based differences in acetabular cup placement when compared to the manual,fluoroscopic- assisted technique

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

2. Material and methods

3. Results

Table 1 A comparison of demographic and treatment data between manual THA (mTHA) and robotic-assisted (RA-THA) cohorts

5. Conclusion

Ethical approval

Data availability statement

Funding

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
A comparison of demographic and treatment data between manual THA (mTHA) and robotic-assisted (RA-THA) cohorts