Abstract
Introduction
Robotic assisted total knee arthroplasty has become an increasingly popular technique over the past several years. Manual total knee arthroplasty can be associated with acute blood loss anemia. Instrumentation of the femoral canal with the alignment guide may in part contribute to this blood loss. Because the femoral canal is not entered during robotic assisted total knee arthroplasty, the blood loss may be lower compared to that seen in manual total knee arthroplasty. The purpose of this study was to determine if acute blood loss is greater in manually instrumented total knee arthroplasty versus robotic assisted total knee arthroplasty.
Materials and methods
This retrospective cohort study was performed in a large tertiary academic hospital network by two fellowship trained surgeons. Patients underwent either robotic assisted or manually instrumented total knee arthroplasty and were assessed for postoperative acute blood loss anemia, defined as hemoglobin <13 g/dL for males or <12 g/dL for females plus a 2 g/dL drop from preoperative levels, as well as postoperative drop in hemoglobin.
Results
A total of 75 patients were included in each study arm. There was no significant difference (p > 0.05) in postoperative hemoglobin in robotic assisted (2.1 g/dL) compared to manually instrumented total knee arthroplasty (2.1 g/dL). There was no significant difference in the incidence of postoperative acute blood loss anemia between robotic assisted (45 %) and manually instrumented total knee arthroplasty (39 %). Higher BMI and increased age were protective against postoperative drop in hemoglobin. These protective effects were not significant when controlling for confounding variables. Surgical time was significantly longer for robotic assisted (99 min) versus manually instrumented total knee arthroplasty (86 min) (p < 0.001).
Conclusions
There is no significant difference in acute blood loss when comparing patients undergoing robotic assisted and manually instrumented total knee arthroplasty.
Keywords: Anemia, Total knee, Robotic
1. Introduction
Conventional (manual) total knee arthroplasty (TKA) can result in substantial blood loss during and immediately after surgery resulting in postoperative anemia. Acute blood loss anemia has been associated with several postoperative complications including acute kidney injury, prolonged recovery, higher readmission rates, increased morbidity, and potential thrombo-embolic events.1, 2, 3, 4 The need for transfusion further negatively impacts outcomes by increasing length of stay, infection rates and cost of admission.5, 6, 7 Cost of care is also impacted by post-operative acute blood loss anemia as these patients may be assigned an ICD-10-CM code of 62D (“acute posthemorrhagic anemia”) which is both a billable and reimbursable code. As such, patients assigned the diagnosis of “acute posthemorrhagic anemia” may incur a higher cost of care.
Several institutions have implemented comprehensive blood management programs aimed at optimizing patients in the perioperative window to minimize postoperative complications related to acute blood loss anemia. Documented strategies include preoperative laboratory analysis to identify pre-existing anemia, cessation of medications which may induce bleeding, consideration for spinal and/or hypotensive anesthesia and use of antifibrinolytics.8
Robotic assisted total knee arthroplasty (RATKA), a popular alternative to manually instrumented total knee arthroplasty (MITKA),9 does not require insertion of intramedullary femoral or tibial guides. This has the theoretical benefit of decreasing blood loss associated with medullary canal violation. Therefore, the aim of our study is to determine if RATKA is associated with less acute postoperative blood loss compared to MITKA.
2. Methods
2.1. Patient demographics
This is a retrospective cohort study performed at a large multihospital network. Two fellowship trained orthopaedic surgeons performed all the operations. Both surgeons are experienced in manually instrumented TKA and robotic assisted TKA, and have undergone cadaveric training on the robotic arm assisted device. An Institutional Review Board exemption was granted given the retrospective nature of the study. Consecutive RATKA cases were compared to consecutive MITKA cases collected from April of 2021 to December of 2021 performed by both surgeons. Seventy-five patients were in the RATKA arm and 75 in the MITKA arm. Average age for the total cohort was 67.5±8.3 years, 60.1 % were female, 60.1 % were ASA 2 and the remaining 39.9 % were ASA 3. Demographic characteristics for each technique are summarized in Table 1. Patients undergoing primary total knee arthroplasty for the diagnosis of knee osteoarthritis aged 18 years and older who were not anemic prior to surgery and had documented preoperative and postoperative complete blood counts with differential (CBC w/diff) were included in the study. Those undergoing revision surgery, lacking pre-operative or postoperative CBC w/diff, or were preoperatively anemic were excluded. Anemia was defined as a hemoglobin (Hgb) of <12.0 g/dL in females and <13.0 g/dL in males according to the World Health Organization's (WHO).10 Patients were assigned the diagnosis of post-operative acute blood loss anemia (PABLA) if they met the following criteria: 1) exhibited a drop in Hgb >2.0 g/dL and 2) met the WHO definition of anemia. A flow chart summarizing the patient selection process is seen in Fig. 1.
Table 1.
Demographics of study groups.
| Characteristics | Total | Technique |
p-value | |
|---|---|---|---|---|
| RATKA | MITKA | |||
| Number of knees | 150 | 75 | 75 | – |
| Age (years) | 67.5 ± 8 | 68.2 ± 9 | 66.8 ± 8 | 0.32 |
| Gender (Male/Female) | 73/78 | 44/31a | 28/47a | 0.001a |
| BMI | 31.5 ± 4.9 | 31.2 ± 4.6 | 31.8 ± 5.2 | 0.44 |
| Pre-op Hgb (g/dL) | 13.8 ± 1.2 | 13.9 ± 1.1 | 13.8 ± 1.3 | 0.53 |
| Pre-op Hct (%) | 42.8 ± 3.4 | 43.0 ± 3.2 | 42.6 ± 3.7 | 0.46 |
| ASA Score | ||||
| 2 | 91 | 49 | 42 | 0.24 |
| 3 | 59 | 26 | 33 | |
RATKA- Robotic assisted total knee arthroplasty, MITKA- Manually instrumented total knee arthroplasty, BMI- Body mass index, ASA- American Society of Anesthesiologists, Hgb- Hemoglobin, Hct- Hematocrit.
Significant difference, more males underwent robotic assisted total knee arthroplasty.
Fig. .1.
2.2. Perioperative course
Patients on anticoagulation regimens with direct oral anticoagulants (DOAC) were instructed to discontinue medications 3 days prior to surgery. Those on warfarin were confirmed to have international normalized ratios (INR) < 1.5 and those on antiplatelet medications were allowed to continue medication throughout their clinical course.
All patients received spinal anesthesia with a regional adductor canal block and propofol infusion for sedation. All patients received 1g of tranexamic acid within 1 h of incision. All patients were placed in supine position and a tourniquet was used in all cases. A medial parapatellar approach was performed in all cases. For the MITKA cohort, the intramedullary alignment jig was inserted into the femur. In the RATKA cohort, the Velys robotic arm (DePuy Synthes, Warsaw, IN) was used to achieve all bone cuts. Two femoral and two tibial navigation pins were placed through the incision into bone. In all patients the patella was resurfaced and a cemented Attune knee (DePuy Synthes, Warsaw, IN) was implanted. After the cement was dry, the tourniquet was released. Patient were admitted to the orthopaedic floor overnight for observation and discharged the next day unless they were waiting on placement in a rehabilitation facility. Hemoglobin and hematocrit were measured in the morning of postoperative day one. If the patient required a longer stay hemoglobin and hematocrits were followed daily. All patients received low molecular weight heparin 12 h after surgery completion for DVT chemoprophylaxis.
3. Outcomes and covariates
Primary outcomes were the post-operative incidence of PABLA and the day one drop in Hgb. Potential confounders included age, gender, body mass index (BMI), preoperative Hgb and hematocrit (Hct), American Society of Anesthesiologists (ASA) classification, length of surgery and whether the patient was on a preoperative anticoagulation regimen. Length of surgery was defined as the duration between pre-incision time-out and final wound closure.
3.1. Data analysis
A priori power analysis was performed to determine sample size. The average postoperative day one drop in Hgb was obtained from a sample of 20 patients who had undergone MITKA and was found to be 2.1 ( ± 0.86) g/dL. Sample size calculations required 66 patients per arm in order to detect a 20 % improvement in postoperative day one Hgb with an alpha of 0.05 and 80 % power.
Patient data was collected from hospital EMR and statistical analysis was performed using Excel (Microsoft, Redmond, WA). Categorical variables were compared using chi squared analysis and continuous variables were compared with student t-tests and Pearson's correlation coefficient. Any variable found to be significant (p < 0.05) on univariate analysis was included in a multivariate analysis to control for confounding factors.
4. Results
A total of 150 patients were included in this study with 13 patients being excluded (9 revision procedures, 3 patients with preoperative anemia and 1 without a preoperative CBC w/diff). A summary of this data can be found in Fig. 1. There was no significant difference in post-operative Hgb drop between RATKA versus MITKA (2.13 g/dL vs. 2.10 g/dL respectively, p = 0.83). Similarly, there was no significant difference in the incidence of postoperative acute blood loss anemia (PABLA) between RATKA and MITKA (OR = 1.32, 95 % CI [0.69, 2.52], p = 0.42) (Table 2). Univariate analysis revealed that elevated BMI and increased age were protective against postoperative drop in Hgb (BMI: r(148) = −0.26, p = 0.001, Age: r(148) = −0.19, p = 0.02), but this relationship failed to remain significant in multivariate analysis when controlling for confounding variables (P = 0.26, P = 0.16 respectively) (Table 3). Surgical time was significantly longer for RATKA versus MITKA (98.9 versus 85.7 min, P < 0.001). Overall, no measured variable was an independent risk factor for PABLA or greater drop in postoperative Hgb.
Table 2.
Postoperative Hemoglobin and PABLA after RATKA vs MITKA.
| Comparison | Technique |
p-value | OR | |
|---|---|---|---|---|
| RATKA | MITKA | |||
| Drop in Hgb | 2.1 ± 0.8 | 2.1 ± 0.9 | 0.83 | – |
| PABLA Rate (%) | 45.3 | 39.2 | 0.41 | 1.31 |
RATKA- Robotic assisted total knee arthroplasty.
MITKA- Manually instrumented total knee arthroplasty.
Hgb- Hemoglobin.
PABLA- Postoperative acute blood loss anemia.
OR- Odds ratio.
Table 3.
Pearson correlation coefficient and MLR for confounding variables.
| Comparison | PCC | p-value | MLR p-value |
|---|---|---|---|
| Pre-op Hbg vs Hbg Drop | 0.3 | <0.001a | 0.01a |
| Surgery Duration and Hgb Drop | −0.04 | 0.66 | 0.96 |
| BMI vs Hgb Drop | −0.26 | 0.001a | 0.26 |
| Age vs Hgb Drop | −0.19 | 0.02a | 0.16 |
| Pre-op Hct vs Hct Drop | 0.29 | 0.001a | 0.02a |
PCC- Pearson Correlation Coefficient.
Hgb- Hemoglobin.
BMI- Body mass index.
Hct- Hematocrit.
MLR- Multivariate logistic regression.
Significant difference, BMI and age were inversely correlated with postoperative Hgb drop. This relationship failed to remain significant after MLR.
5. Discussion
Postoperative anemia in total knee arthroplasty is associated with increased patient morbidity and has prompted investigation into several methods to reduce intraoperative blood loss. In this cohort study of 150 patients, we were unable to show a significant difference in the incidence of PABLA or improvement in postoperative Hgb in RATKA versus MITKA. Furthermore, no other covariate predisposed patients to PABLA or significant drops in postoperative Hgb.
As total knee arthroplasty continues to migrate to the outpatient surgical setting, it is imperative to remember that these are major operative procedures which can be associated with substantial blood loss. The incidence of blood transfusion in TKA often ranges from 11 to 18 %.11, 12, 13 Blood transfusions are associated with significant morbidity and mortality, and increased health care expenditure. Patients who receive blood transfusions have an increased hospital cost of $2500 and utilization of hospital resources.14 Transfusion of blood products has rare but serious risks of death, HIV and hepatitis C transmission, transfusion-related acute lung injury, transfusion-associated circulatory overload, and many other complications.15, 16, 17 In order to mitigate the risk for blood transfusion after major orthopaedic surgery, several blood management strategies have been published aimed at guiding perioperative optimization. These strategies include preoperative testing, minimization of intra-operative blood loss and higher transfusion thresholds.17 Our institution has a standardized protocol for optimizing patients including preoperative laboratory testing, intraoperative use of tranexamic acid and post-operative hydration protocols. None of the 150 patients included in this study required a blood transfusion.
The underlying hypothesis that RATKA would confer a lower risk for PABLA and postoperative drop in Hgb was predicated on the fact that robotic assistance does not require instrumentation of either the femoral or tibial intramedullary canals for placement of cutting guides. This idea has been explored with computer assisted total knee arthroplasty (CATKA). A 2016 meta-analysis by Han et al. included 12 studies which evaluated intraoperative blood loss, post-operative Hgb levels and transfusion rates after CATKA. They found that CATKA improved calculated blood loss and post-operative Hgb drop but did not significantly reduce the rate of transfusion.18 Similarly, a series by Khan et al., in 2021 found that RATKA significantly reduced calculated intraoperative blood loss and improved postoperative Hgb concentration compared to MITKA but did not improve rates of transfusions.19 Conversely, a more recent retrospect cohort comparing conventional TKA or robotic assisted TKA found no differences in postoperative hemoglobin changes or the need for postoperative blood transfusions.20 Puri et al. retrospectively reviewed 14,890 TKA performed at a single institution over 4 years. Robotic or computer assisted TKA accounted for 28 % of the sample size and was not associated with decreased transfusion rates and had negligible differences in blood loss.21
There are several limitations to this study. The retrospective design can introduce selection bias. In addition, the patients sampled came only from a single multi-hospital system that serves a single region of the country. The consecutive time frames over which the sample groups were taken introduces the opportunity for systematic variation in hospital operations to affect results. This effect could be reduced if the two arms of the study had been conducted concomitantly. Finally, it has been shown that patients often do not reach their lowest Hgb and Hct levels until four days postoperatively.22 This study only included Hgb and Hct counts obtained on postoperative day one, thus we may have underestimated post-operative drops in these values.22
6. Conclusion
By obviating the need for instrumentation of the femoral and tibial canals, we hypothesized that patients undergoing RATKA would exhibit smaller postoperative drops in Hgb and fewer incidences of PABLA. The current study demonstrates that RATKA and MITKA have similar rates of PABLA and changes in postoperative Hgb. This finding is in accordance with other recently published studies.
Funding
None.
Patient consent
No patient consent needed due to retrospective nature and public database.
Ethical approval
IRB exemption due to retrospective nature and public database Authors’ contribution.
Credit author statement
JD- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
MD- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
AM-Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
NW- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing. MM- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
PI- Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
AS-Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
AK-Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
PB-Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; and Writing - review & editing.
Declaration of competing interest
JD- None.
MD- AAOS Now editorial or governing board.
AM-receives support from American Orthopaedic Association: Board or committee member, American Orthopaedic Society for Sports Medicine: Board or committee member, Arthrex, Inc: Other financial or material support, Arthroscopy: Editorial or governing board, B Braun: Other financial or material support, BMC Musculoskeletal Disorders: Editorial or governing board.
NW- None.
PI- None.
AS- paid consultant for DePuy, A Johnson & Johnson Company.
AK- None.
PB- None.
Acknowledgements
None.
Footnotes
This article has not been published elsewhere and that it has not been simultaneously submitted for publication elsewhere. All tables and figures are your original work and no permissions are required. The authors have no conflict of interest.
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