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Robotic-assisted total knee arthroplasty (RTKA) was introduced to improve surgical accuracy and patient outcomes. However, RTKA may also increase operating time and add cost to TKA. This study sought to compare the differences in cost and quality measures between manual TKA (MTKA) and RTKA
Methods
All MTKAs and RTKAs performed between January 1, 2017 and December 31, 2019, by 6 high volume surgeons in each cohort, were retrospectively reviewed. Cohorts were propensity score matched. Operative time, length of stay (LOS), total direct cost, 90-day complications, utilization of postacute services, and 30-day readmissions were studied.
Results
After one-to-one matching, 2392 MTKAs and 2392 RTKAs were studied. In-room/out-of-room operating time was longer for RTKA (139 minutes) than for MTKA (107 minutes) P < .0001, as was procedure time (RTKA 78 minutes; MTKA 70 minutes), P < .0001. Median LOS was equal for MTKA and RTKA (33 hours). Total cost per case was greater for RTKA ($11,615) than MTKA ($8674), P < .0001. Home health care was utilized more frequently after RTKA (38%) than MTKA (29%), P < .0001. There was no significant difference in 90-day complication rates. Thirty-day readmissions occurred more often after MTKA (4.9%) than RTKA (1.2%), P < .0001.
Conclusion
RTKA was a longer and costlier procedure than MTKA for experienced surgeons, without clinically significant differences in LOS or complications. Home health care was utilized more often after RTKA, but fewer readmissions occurred after RTKA. Longer term follow-up and functional outcome studies are required to determine if the greater cost of RTKA is offset by lower revision rates and/or improved functional results.
Total knee arthroplasty (TKA) is the gold standard treatment for painful degenerative joint disease of the knee. More than 600,000 TKAs are performed annually in the United States alone, and this has been forecast to increase to 935,000 by 2030 [
], but technical factors may also be responsible. Optimal TKA alignment and soft tissue balance have been associated with improved short-term and long-term outcomes [
]. In manual TKA (MTKA), alignment and balance are primarily tactile and result from surgical skill and experience.
Robotics were introduced to TKA (RTKA) to make bone cuts and ligament balance more accurate and reproducible. In the platform most widely used today, a 3-dimensional model based on a preoperative computed tomography (CT) scan of the knee is used to prepare the operative plan. Intraoperatively, the robotic arm guides the saw, within stereotactic boundaries, to execute the plan and achieve alignment and soft tissue balance.
Prior studies have confirmed the accuracy of RTKA [
Improved mediolateral load distribution without adverse laxity pattern in robot-assisted knee arthroplasty compared to a standard manual measured resection technique.
Robotic-assisted total knee arthroplasty combined with a robotic tensioning system can help predict and achieve accurate postoperative ligament balance.
Iatrogenic bone and soft tissue trauma in robotic-arm assisted total knee arthroplasty compared with conventional jig-based total knee arthroplasty: a prospective cohort study and validation of a new classification system.
Theoretical benefits notwithstanding, the addition of robotics increases the cost of TKA. The purchase of the robot and other associated costs must be considered when evaluating robotic surgery. In addition, some studies of RTKA have reported longer operating times than MTKA[
Making the transition from traditional to robotic-arm assisted TKA: what to expect? A single-surgeon comparative-analysis of the first-40 consecutive cases.
Robotic-arm assisted total knee arthroplasty is associated with improved early functional recovery and reduced time to hospital discharge compared with conventional jig-based total knee arthroplasty.
Robotic-arm assisted total knee arthroplasty is associated with improved early functional recovery and reduced time to hospital discharge compared with conventional jig-based total knee arthroplasty.
Robotic-arm assisted total knee arthroplasty is associated with improved early functional recovery and reduced time to hospital discharge compared with conventional jig-based total knee arthroplasty.
]. In the era of value-based healthcare, any additional costs are of concern to both providers and healthcare systems. As margins continue to decrease, additional expenditures must add value to the delivery of care.
Unfortunately, outcome studies of RTKA are few. Some have reported short-term benefits over MTKA [
Patient-reported functional and satisfaction outcomes after robotic-arm-assisted total knee arthroplasty: early results of a prospective multicenter investigation.
], not contemporary platforms. To further complicate matters, much of the published outcomes and basic science literature on RTKA has been sponsored by the manufacturer or authored by researchers with potential conflicts of interest [
Improved mediolateral load distribution without adverse laxity pattern in robot-assisted knee arthroplasty compared to a standard manual measured resection technique.
Robotic-assisted total knee arthroplasty combined with a robotic tensioning system can help predict and achieve accurate postoperative ligament balance.
Iatrogenic bone and soft tissue trauma in robotic-arm assisted total knee arthroplasty compared with conventional jig-based total knee arthroplasty: a prospective cohort study and validation of a new classification system.
Making the transition from traditional to robotic-arm assisted TKA: what to expect? A single-surgeon comparative-analysis of the first-40 consecutive cases.
Robotic-arm assisted total knee arthroplasty is associated with improved early functional recovery and reduced time to hospital discharge compared with conventional jig-based total knee arthroplasty.
Patient-reported functional and satisfaction outcomes after robotic-arm-assisted total knee arthroplasty: early results of a prospective multicenter investigation.
Robotic-arm assisted total knee arthroplasty has a learning curve of seven cases for integration into the surgical workflow but no learning curve effect for accuracy of implant positioning.
The goals of this study were to compare both cost and quality measures between MTKA and RTKA, performed by high volume surgeons, free of industry influence. Our hypothesis was that RTKA would be a longer and more expensive procedure than MTKA but would not demonstrate significant differences in quality measures for high volume surgeons.
Materials and Methods
Study Cohort
Institutional Review Board approval was obtained prior to commencement of this study. The 6 highest volume RTKA (Mako-Stryker, Kalamazoo, MI) surgeons in the Providence Health System were identified. Robotic cases are uniquely coded and easily identified in the Providence electronic health record.
Next, a matching cohort of the 6 highest-volume MTKA surgeons using the same implants (Stryker Triathlon) was established. Each surgeon performed a minimum of 75 RTKAs or MTKAs annually during the study period. All TKAs performed by these surgeons between January 1, 2017, and December 31, 2019 were identified. All surgeries were performed in nonacademic hospitals. The first 20 consecutive cases of each surgeon were excluded to allow for the so-called “learning curve” of RTKA and as a control in the MTKA cohort. Data from the remaining cases were then collected. Bilateral cases were excluded.
Clinical Data
The electronic health record was queried. Demographic variables collected were patient age, gender, body mass index (BMI), and American Society of Anesthesiologists (ASA) score. Acute stay metrics collected were operative time (in-room/out-of-room and procedure time) and LOS. Postoperative metrics were utilization of postacute services (Home health care [HHC], skilled nursing facility [SNF] discharge), 90-day complications myocardial infarction, pneumonia, sepsis, surgical site bleeding, wound infection, mechanical complications [fracture, loosening, instability, pulmonary embolism, death, and 30-day readmissions].
Cost Data
Total direct cost, supply cost, and labor cost of the acute stay were analyzed. Supply costs for both cohorts included implant costs plus any other supplies used during the stay. Robotic costs were calculated as follows:
plus per case disposables. Labor costs were charges related to any labor “touch” during the patient visit, including OR personnel, nursing, and physical therapy. The cost of the preoperative CT scan for robotic cases was not included.
Statistical Analysis
Basic descriptive analyses of patient characteristics and surgical outcomes between MTKA and RTKA patients were performed. Continuous variables were described using means and standard deviations and compared using independent 2-sample t-tests. Cost and time-related outcomes were described using medians and interquartile ranges and compared using Wilcoxon rank-sum tests. Categorical variables were analyzed using the chi-squared test. To balance the demographic differences between the 2 groups, propensity score matching methods were used. A propensity score for each patient was estimated by using a logistic regression model that treated the comparison group as the outcome and the matching variables (ie, age, BMI, and ASA scores) as the covariate. One-to-one nearest neighbor method was used to match the propensity score between MTKA and RTKA patients. Outcome and demographic variables were compared again within the matched cohort to provide a comparable basis of the covariates. All other analyses were conducted using AS Enterprise Guide 7.1 (SAS Institute Inc, Cary, NC). Significance was considered at P-value <.05.
Results
Study Population
The original cohorts were composed of 6347 patients. Seventy-nine patients were excluded due to incomplete data sets, and 47 bilateral patients were excluded, leaving 6221 patients. After 1:1 propensity score matching there were 2392 MTKAs and 2392 RTKAs in each cohort, with no significant differences in age, gender, BMI, or ASA score (Table 1). The distributions of case volume and surgeon are shown in Table 2. The distribution of case volume by year is shown in Table 3. All patients had minimum 90-day follow-up, and no patients were lost to follow-up.
Table 1Demographics of Matched Cohorts.
Value
MTKA (N = 2392)
RTKA (N = 2392)
P-Value
Age
68.6 (8.7)
68.6 (8.5)
.7493
Female
1363 (57%)
1361 (57%)
.9534
BMI
30.6 (5.6)
30.4 (5.7)
.3794
ASA
.7920
I
86 (4%)
93 (4%)
II
1550 (65%)
1560 (65%)
III
747 (31%)
733 (31%)
IV
9 (0.4%)
6 (0.3%)
MTKA, manual total knee arthroplasty; RTKA, robotic-assisted total knee arthroplasty; BMI, body mass index; ASA, American Society of Anesthesiologists.
Median operative time was longer for RTKA than MTKA, both in-room/out-of-room time (RTKA 139 minutes [124, 155]; MTKA 107 minutes [82, 130], P < .0001) and procedure time (RTKA 78 minutes [69, 88]; MTKA 70 minutes [50, 87], P < .0001) (Fig. 1).
Fig. 1In-room/out-of-room time and procedure time. MTKA, manual total knee arthroplasty; RTKA, robotic-assisted total knee arthroplasty.
Median LOS was equal for MTKA (33 hours [28, 54]) and RTKA (33 hours [30, 52]), P = .0118. However, mean LOS for RTKA was less (42.3 hours [23.4]) than MTKA (44.2 [38.2]), P = .0408 (Fig. 2A and B).
Fig. 2(A) Median LOS and (B) mean LOS. LOS, length of stay.
Median total direct costs were greater for RTKA ($11,615 [9975, 13,025]) than MTKA ($8674 [7880, 9543], P < .0001). Supply costs were greater for RTKA ($6030 [5102, 7108]) than MTKA ($4831 [4170, 5298], P < .0001) as were labor costs: RTKA ($3361 [2765, 3859], P < .0001) and MTKA ($2825 [2378, 3421], P < .0001) (Fig. 3A and B).
Fig. 3(A) Supply and labor cost and (B) median total cost.
Home discharge was equal in both cohorts (95%), but more RTKA patients utilized HHC (38%) than MTKA (29%), P < .0001. SNF discharge was equal between the 2 cohorts (5%) (Fig. 4).
Fig. 4Postdischarge disposition and postacute care utilization.
Overall, 90-day complications in MTKA (0.9%) and RTKA (0.7%) were not significantly different (P = .5147). No deaths or mechanical complications were observed in either group. Wound complications (surgical site bleeding: 0% MTKA/RTKA; wound infection: MTKA 0.3%, RTKA 0.4%) were not significantly different between the 2 groups (P = .6367). A complete list of complications is shown in Table 4.
Table 4Complications.
Complication
MTKA (N = 2392)
RTKA (N = 2392)
P-Value
Myocardial infarction (7 d)
2 (0.1%)
2 (0.1%)
1.0000
Pneumonia (7 d)
3 (0.1%)
1 (0.04%)
.3171
Sepsis (7 d)
3 (0.1%)
1 (0.04%)
.3171
Surgical site bleeding (30 d)
0 (0%)
0 (0%)
NA
Death
0 (0%)
0 (0%)
NA
Joint wound infection (90 d)
8 (0.3%)
10 (0.4%)
.6367
Mechanical complications (90 d)
0 (0%)
0 (0%)
NA
Pulmonary embolism (30 d)
7 (0.3%)
4 (0.2%)
.3652
Any complication
21 (0.9%)
17 (0.7%)
.5147
MTKA, manual total knee arthroplasty; RTKA, robotic-assisted total knee arthroplasty; OSM, Orthopaedics and Sports Medicine Institute; NA, not applicable.
A recent survey of arthroplasty surgeons indicated that 73.1% of users utilized robotics for increased precision; however, nearly 20% used robotics primarily for nonclinical reasons of peer pressure, marketing, and administrative pressure. Most respondents said they felt RTKA increased operative time (76.5%) and was not cost-effective compared to traditional methods (78.7%). Nonusers also indicated that they were equally likely to consider marketing as increased precision in deciding whether to adopt RTKA [
Robotic surgery in total joint arthroplasty: a survey of the AAHKS membership to understand the utilization, motivations, and perceptions of total joint surgeons.
]. Finally, a recent literature review reported that 97% of studies supporting robotic joint arthroplasty have been published by authors receiving financial compensation from industry [
Making the transition from traditional to robotic-arm assisted TKA: what to expect? A single-surgeon comparative-analysis of the first-40 consecutive cases.
Robotic-arm assisted total knee arthroplasty has a learning curve of seven cases for integration into the surgical workflow but no learning curve effect for accuracy of implant positioning.
], we excluded the first 20 cases of all surgeons. All surgeons used Stryker TKA implants to minimize the effect of implant variability; however, our data filter lacked the granularity to distinguish cruciate-retaining vs posterior-stabilized or cemented vs cementless implants.
Acute Stay Metrics
We observed RTKA operative times to be longer than MTKA operating times. The greatest difference was in in-room/out-of-room time (+32 minutes). Procedure time was also longer for RTKA (+8 minutes). Thus, we observed that while surgical time for RTKA approached “time neutral” with MTKA, as predicted by Sodhi et al [
], the preoperative set up time for the robot and other equipment made RTKA a longer procedure. We did not observe the improvement in OR efficiency that others have forecast with RTKA [
]. Since the greatest portion of additional operating time is not during the open procedure, it is unlikely that this presents a greater risk of complications to the patient, as reported by others [
Robotic-arm assisted total knee arthroplasty is associated with improved early functional recovery and reduced time to hospital discharge compared with conventional jig-based total knee arthroplasty.
] reported a 28-hour shorter median time to hospital discharge for 40 RTKA patients, compared to 40 prior MTKA patients. Others have suggested that reduced soft tissue trauma in RTKA may be responsible for these differences [
]. We observed no difference in median time to hospital discharge between RTKA and MTKA in our study. Although the mean LOS for RTKA (42.3 hours) was significantly shorter than for MTKA (44.2 hours, P = .0408), the difference of 1.9 hours is not felt to be clinically significant.
Cost Analysis
In this series, median total cost for RTKA was $2941 per case greater than MTKA. This included greater supply costs for RTKA (+$1199), primarily attributable to the cost of the robot itself, and greater labor costs for RTKA (+$536), primarily accrued in the OR due to longer in-room/out-of-room times. It is also noteworthy that our cost analysis did not consider the cost of the preoperative CT scan required for RTKA.
] performed 30-day, 60-day, and 90-day episode-of-care cost analyses of Medicare payment data for 519 RTKAs and 2595 MTKAs. They observed the total episode payment for RTKA to be lower at each interval, and they reported the 90-day postoperative cost for RTKA to be $2392 less than MTKA. However, as a Medicare payment study, they did not consider the cost of the robot, maintenance agreement, and disposables. Our study examined only acute stay costs but did account for all costs associated with the robot.
Complications
Earlier studies have reported either a higher rate of complications in RTKA than MTKA [
]. Basic science studies of RTKA have suggested that the stereotactic boundary of the robot arm may prevent surgical injury and reduce complications. Kayani et al [
Iatrogenic bone and soft tissue trauma in robotic-arm assisted total knee arthroplasty compared with conventional jig-based total knee arthroplasty: a prospective cohort study and validation of a new classification system.
] reported less damage to the posterior cruciate ligament with RTKA than MTKA in cadaveric models. However, in this study there was no difference in complication rates between RTKA and MTKA. Specifically, there were no mechanical complications. Pin site complications, which are unique to RTKA and a potential source of morbidity and added cost, were not specifically recorded in this study. However, no fractures were observed in this series, and overall, infections and wound complications were infrequent in both cohorts.
Utilization of Postacute Services
The percentage of patients discharged directly home in this study was equal in both cohorts (95%), with only 5% in each cohort discharged to an SNF. However, 9% more RTKA patients were discharged home with HHC than MTKA patients.
Fewer 30-day readmissions occurred after RTA (1.2%) than MTKA (4.9%). Our findings differ from those of Mont et al [
], who observed lower utilization of all postacute services after RTKA. However, higher rates of readmission were also observed after MTKA in that study.
A detailed analysis of readmissions was beyond the scope of this study. In addition, our study coincided with Centers for Medicare and Medicaid Services decision to remove TKA from the inpatient only list, effective January 1, 2017, and this may have affected our findings. Because this accelerated the transition to outpatient TKA, steadily greater utilization management resources were assigned to TKA patients during this 3-year period. Since more of the RTKA cases were performed later in the study period (Fig. 6), they may have been exposed to more utilization management influence than the MTKA cohort, which was evenly distributed throughout the study. This may have affected both the utilization of HHC and the rate of readmissions in the cohorts. As a result, we can only report the association of higher HHC utilization after RTKA and more frequent 30-day readmissions after MTKA, without determining causality.
Overall, the high rate of home discharge and low rates of readmission for both cohorts observed in our study are consistent with contemporary arthroplasty practices, including preoperative patient optimization and careful utilization management. The association of higher HHC utilization with a lower rate of readmission seen after RTKA has been observed previously in a study of different arthroplasty populations [
Extremes of body mass have significant impacts on complications, readmissions, and utilization of post-acute services after primary total hip arthroplasty.
] and suggests that HHC may confer some protection against readmission in selected patients.
Strengths and Limitations
The primary strength of this study is the large number of patients studied. To the authors’ knowledge, this is the largest series comparing RTKA and MTKA reported to date. By selecting only high volume surgeons, we sought to compare optimal results in both groups. By selecting a single manufacturer, we attempted to minimize implant-specific variability. In addition, detailed cost data, including all costs related to the use of the robot, allowed a thorough comparison of the 2 groups. Finally, a major strength of the study is that it was performed free of industry influence.
There are limitations to this study to be considered. As a retrospective database study, it is potentially subject to coding error and selection bias. Our database lacked the granularity to discern specific implant choices (posterior stabilized vs cruciate retaining; cemented vs cementless) which could potentially affect cost or recovery. (The cost of a cementless Stryker implant in our system is approximately $450 greater than cemented, with no cost difference between posterior stabilized and cruciate retaining implants. Even if all implants in one cohort had been cementless and the other had all been cemented, only the magnitude of cost difference would be different, not the conclusion that RTKA cost was greater than MTKA.)
Only costs of the acute stay were examined, and associated costs of the preoperative CT scan, postoperative utilization of services, and readmissions were not considered. All surgeries were performed in acute care hospitals, and it is unclear if the results can be extrapolated to the ambulatory surgical setting. Details of anesthetic, pain management, and postoperative rehabilitation protocols were also beyond the scope of our database.
Finally, the greatest limitations of this study are the lack of patient-reported outcome measures and radiographic assessments. Although our cost data and quality measures give considerable insight into the differences between these 2 procedures, patient outcomes are essential elements in the comparison.
Conclusions
In this series of propensity-score matched patients, RTKA was observed to be a longer and costlier procedure than MTKA, without clinically significant differences in LOS or complications. HHC was more frequently utilized after RTKA than MTKA, but readmissions occurred more frequently after MTKA. Longer term follow-up studies, including PROMs, will be required to determine if the added cost of RTKA is warranted by better functional outcomes and/or lower revision rates.
Acknowledgments
The authors wish to acknowledge Erin Rogers and Rebecca Valderrama for their assistance in this study.
Improved mediolateral load distribution without adverse laxity pattern in robot-assisted knee arthroplasty compared to a standard manual measured resection technique.
Robotic-assisted total knee arthroplasty combined with a robotic tensioning system can help predict and achieve accurate postoperative ligament balance.
Iatrogenic bone and soft tissue trauma in robotic-arm assisted total knee arthroplasty compared with conventional jig-based total knee arthroplasty: a prospective cohort study and validation of a new classification system.
Making the transition from traditional to robotic-arm assisted TKA: what to expect? A single-surgeon comparative-analysis of the first-40 consecutive cases.
Robotic-arm assisted total knee arthroplasty is associated with improved early functional recovery and reduced time to hospital discharge compared with conventional jig-based total knee arthroplasty.
Patient-reported functional and satisfaction outcomes after robotic-arm-assisted total knee arthroplasty: early results of a prospective multicenter investigation.
Robotic-arm assisted total knee arthroplasty has a learning curve of seven cases for integration into the surgical workflow but no learning curve effect for accuracy of implant positioning.
Robotic surgery in total joint arthroplasty: a survey of the AAHKS membership to understand the utilization, motivations, and perceptions of total joint surgeons.
Extremes of body mass have significant impacts on complications, readmissions, and utilization of post-acute services after primary total hip arthroplasty.
One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to https://doi.org/10.1016/j.arth.2021.12.018.
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