The invasiveness of robot-assisted total hip replacement is similar to that of conventional surgery

Robot-assisted total hip arthroplasty (R-THA) is increasingly being performed throughout the world. The invasiveness of this operation is unknown. We retrospectively reviewed the cohort of consecutive osteonecrosis of the femoral head (ONFH) patients who received primary R-THA or manual THA (M-THA) from January 2020 to January 2022 in our institution. One experienced surgeon performed all procedures. We calculated the propensity score to match similar patients in different groups by multivariate logistic regression analysis for each patient. We included confounders consisting of age, sex, body mass index (BMI), and operation time. Preoperative serum markers and Harris hip scores (HHS), postoperative serum markers at first day and third day, complications rate, postoperative HHS and Forgotten Joint Score (FJS) at 6 months after surgery of different cohorts were compared. We analyzed 218 ONFH patients treated with THA (98 R-THA patients, and 120 M-THA patients). After propensity score matching, we generated cohorts of 95 patients in R-THA and M-THA groups. We found no significant difference in preoperative serum markers and HHS. In the R-THA cohort, the PLT count was significantly lower on the postoperative day 1 (192.36 ± 41.72 × 109/L Vs 210.47 ± 72.85 × 109/L, p < 0.05). The Hb level was significantly lower on the postoperative third day in the R-THA cohort (98.52 ± 12.99 g/L Vs 104.74 ± 13.15 g/L, p < 0.05). There was no significant difference in the other serum markers between the cohorts on postoperative day 1 and 3 (p > 0.05). The FJS was significantly higher in the R-THA than M-THA group (p = 0.01). There was no significant difference in the postoperative HHS or complication rate between the groups (p > 0.05). The R-THA is not associated with a serious invasiveness compared to M-THA. Patients who underwent R-THA had a better early function compared to those who underwent M-THA.


Background
Robot-assisted total hip arthroplasty (R-THA) is increasingly being performed worldwide.Previous studies have suggested that R-THA is more accurate, provides better component positioning, reduces leg length discrepancy, and yields better functional outcomes [1][2][3].However, several studies have shown that R-THA leads to longer surgery times and an increased risk of blood loss, and anesthesia accidents [4,5].Concerns have been raised about the safety and invasiveness of the procedure.To our knowledge, the invasiveness of THA is difficult to measure, no previous studies have compared the surgical invasiveness of M-THA and R-THA.
The specific enzymes and inflammation serum markers released during surgical dissection have been proposed as a measure of muscle damage in lumbar spine and hip surgery [6][7][8].The immediate surgical insult in patients has been quantified and demonstrated to be unbiased and sensitive using systemic inflammatory markers [9][10][11][12].Therefore, we compared the postoperative systemic inflammatory response between patients who underwent R-THA and M-THA using postoperative serum markers of inflammation and muscle damage.
Mingyang Ma and Zheng Cao have contributed equally to this work.

Eligibility criteria
Institutional Review Board approval was obtained for this study.Consecutive patients who received R-THA or M-THA between January 2020 and January 2022 had their records examined.Patients with ONFH who received R-THA or M-THA performed by one surgeon and had complete medical records were included in the study.
Patients chose the operation (R-THA or M-THA) to be performed, according to their specific condition and preference.R-THA was suggested for all patients.The patients who chose R-THA had to wait for 2 weeks after the computed tomography (CT) scan before receiving their customized surgical plan.This was time-consuming for patients who lived far from the hospital.The surgeon had no preference regarding the technique or any particular patient group.In practice, the surgeon would take each patient's opinion into full consideration and decide on the optimal surgical approach for that particular patient.At our institution, R-THA does not add to the patient's costs; thus, patients are free to choose R-THA or M-THA.All of the benefits and risks of performing R-THA are introduced to the patients, so that they can decide on the appropriate surgical procedure for their situation.
Participants who diagnosis with rheumatoid disease, abnormal preoperative inflammatory markers, bilateral simultaneous THA, a history of surgery or infection in the operative hip, neuromuscular dysfunction that affected lower limb function, coagulation dysfunction, liver or muscle disease, or a "complicated" postoperative hospital stay were all excluded from the study.A total of 218 patients were included in this study, including 120 and 98 in the M-THA and R-THA groups, respectively.

R-THA surgical technique
R-THA was assisted by the MAKO robotic arm interactive orthopedic system (MAKO Rio Robot).The Accolade II femoral stem (Stryker) and Trident acetabular cups (Stryker) were used, along with a tapered cementless stem and cementless acetabular cups.The surgery was performed under general anesthesia using a standardized posterolateral approach.To fix the pelvic array, three pins were implanted at the anterior superior iliac spine during R-THA.An intraoperative assessment of leg length was then performed using fixed adhesive electrodes attached to the patella.To determine leg length and offset, the pelvic array was attached and a locating pin was placed at the outer edge of the greater trochanter.Joint dislocation and femoral neck osteotomy followed.By inserting a pelvic checkpoint screw outside the acetabulum, the acetabulum was registered.Three acetabular direction points, 32 registration points, and eight confirmation points were involved in acetabular registration.We constructed a three-dimensional computed tomography (CT) model of the bone structure prior to surgery.According to the preoperative plan, robotic-assisted acetabular reaming and acetabular cup implantation were performed under realtime three-dimensional navigation (Fig. 2).Implantation of the acetabular screws and liner, and manual preparation of the femur were performed.It was confirmed that the hip joint was stable throughout its full range of motion.The landmarks that were used to determine the leg length and offset were marked.Finally, the femoral stem and head were implanted.

M-THA surgical technique
M-THA uses the same approach and implant design as the R-THA, but the acetabular surgery was manually performed.The acetabular bottom was prepared with the smallest available reamer, and the acetabulum was prepared using larger reamers before the acetabular cup was implanted (Fig. 3).

Rehabilitation treatment
The patients in both groups received the same treatment, including intravenous and topical tranexamic infusions, as well as antibiotics within 24 h of surgery.

Data collection
The levels of CRP, IL-6, hemoglobin (Hb), creatine kinase (CK), lactate dehydrogenase (LDH), alkaline phosphatase (ALP), platelet count (PLT), white blood cell count (WBC), neutrophil rate, and lymphocyte rate, as well as the erythrocyte sedimentation rate (ESR), as evaluated preoperatively and on postoperative days 1 and 3, were compared between the two groups.The operative time was defined as that between making and closing the incision.The postoperative HHS and FJS were collected 6 months in all patients.The complications, including fracture, infection, dislocation, nerve injury, aseptic loosening, and osteolysis, were recorded.
Fig. 2 In the R-THA group, the acetabular component was positioned with the aid of a robotic arm Fig. 3 In the R-THA group, the acetabular component was positioned by traditional tools

Statistical analysis
To improve the comparability between the two groups, the propensity score matching (PSM) was used to identify a cohort of patients with similar characteristics.Patients in the R-THA groups were matched with M-THA group.When calculating the propensity score by multivariate logistic regression analysis for each patient, we included confounders of age at the time of surgery, sex, body mass index (BMI) and operation time.In the matched cohort, paired comparisons were performed using McNemar's test for binary variables and a paired Student's t test or paired-sample test for continuous variables.Descriptive statistics are presented as mean ± standard deviation.All reported P values are twosided and have not been adjusted for multiple testing.All statistical tests were performed at a probability level of 95% (α = 0.05) using SPSS software (version 25.0;IBM Corp., Armonk, NY, USA).

Results
We performed analysis on total of 218 patients were included in this study, including 120 and 98 in the M-THA and R-THA groups.Propensity score matching was performed between the two groups.Based on the propensity scored, we generated 1:1 matched cohorts to facilitate comparison between two groups.We matched the patients using the nearest neighbor technique, with a predefined caliper width equal to 0.05 of the standard deviation of the logit of the propensity score, after propensity score matching.A total of 95 patients were included for the propensity scorematched analysis in each group.The cohorts were comparable in terms of age, gender, BMI and preoperative HHS (all p > 0.05; Table 1).
Preoperative serum inflammatory markers were not significantly different between groups (Table 2); on the first day after the surgery, the PLT count was significantly lower in the R-THA than M-THA group (192.36 ± 41.72 × 10 9 /L Vs 210.47 ± 72.85 × 10 9 /L, p < 0.05).However, there was no significant difference in CRP, IL-6, Hb, ALP, CK, or LDH level, neutrophil rate, WBC or ESR on the first postoperative day between the groups (all p > 0.05).On the third day after the surgery, the Hb level was significantly lower in the R-THA than M-THA group (98.52 ± 12.99 g/L Vs 104.74 ± 13.15 g/L, p < 0.05).However, there was no significant difference in CRP, PLT count, IL-6, ALP, CK, or LDH level, neutrophil rate, WBC or ESR on the first postoperative day between the groups (all p > 0.05).
HHS at 6 months after surgery did not differ significantly between groups.The FJS was significantly higher in the R-THA than M-THA group (p < 0.01).One patient in M-THA group readmitted for surgery within 90 days due to postoperative infection.No other complications occurred (Table 3).

Discussion
In this paper, surgical invasiveness was measured using serum markers, which could represent an objective method of determining the invasiveness of a surgical procedure [13][14][15].It reflects the extent of soft tissue injury during THA [16,17].As compared to M-THA at 24 h, patients in the R-THA group were associated with a lower level of PLT count.The difference in variation resolved within 3 days.On postoperative day 3, patients in the R-THA group have a lower level of Hb.However, the FJS of the R-THA group was significantly higher than that of the M-THA group (p < 0.01) at 6 months after surgery.Several variables that could have influenced the measurements, such as age and BMI to be comparable between cohorts.THA is one of the most successful surgical operations, but it's not perfect [18][19][20].The application of roboticassisted operation enables the THA under the guidance of simulated image and gives surgeon more information besides operative field of vision [21].Some studies have shown that R-THA is associated with a smaller incision, less retractor compression, better preservation of the periarticular soft tissue envelope, and improved accuracy of component positioning compared to M-THA [22][23][24].However, there have been several concerns about muscle and tissue damage brought by additional pin placement, mechanical traction for post-operative pain and rehabilitation in R-THA patients [25][26][27].To our knowledge, there is no study has compared the surgical invasiveness of R-THA with M-THA in terms of serum markers of inflammation and muscle degradation.
In contrast to M-THA, which involves the use of a manually controlled reamer, R-THA uses stereotactic boundaries to ensure that the reamer acts within the surgical plan, which reduces the risk of unintentional periarticular injury.Theoretically, R-THA tends to cause less bone trauma than M-THA.However, we found that R-THA was associated with similar soft tissue damage compared to M-THA, in current technical.Our research results may suggest that more accurate implant positioning is associated with more red blood cell loss and platelet decline.The improvement of the patient's postoperative function was due to the improvement of the implant position.
Our variations changes in a robotic-assisted surgery are similar to other robotic-assisted studies published in the literature.Kayani et al. [11] revealed that robotic-assisted total knee arthroplasty (R-TKA) was associated with a transient reduction in the early systemic inflammatory response, with lower levels of IL-6, tumor necrosis factor-α, CRP, ESR, LDH, and CK.Their results showed less trauma to the periarticular soft tissue and bone, as well as a smaller immediate postoperative inflammatory response, with R-TKA compared to conventional TKA.We only found significant difference in PLT count and Hb level.R-THA and R-TKA are two distinct surgical procedures, which could be the explanation.Patients in our research who got THA were younger and recovered sooner after surgery.Probably concealing the discrepancies between the two groups.Larger sample studies are likely needed to detect a statistically significant difference in CK levels.Previous studies showed that systemic inflammation is closely related to the PLT count and Hb level [16,28].PLTs have also been implicated in the pathogenesis of several inflammatory diseases [29].Some correlative data suggest that low platelet counts are associated with the much worse prognosis and much greater likelihood of infection.The PLT count on day 1 after surgery was different between the two cohorts.There was no significant difference in PLT count between the two groups 3 days after operation indicates that R-THA is safe.Previous studies have pointed out that Hb decline affects patients' functional recovery after surgery [30].In our study, although patients in the R-THA group had lower Hb 3 days after surgery, the difference was statistically significant, however, the difference was not clinically significant.The FJS at 6 months after operation showed that R-THA group had more advantages.
Our results show a statistically significant improvement of FJS in the R-THA group.One explanation of why there was a clinically significant difference in the FJS but not in the HHS between R-THA and M-THA is that there may be an intrinsic property of these scoring measures.The FJS has a greater postoperative measurement range due to the low postoperative ceiling effect and twice the effect size of the HHS.Clement et al. [22] study comes to similar conclusions.
The main strength of our study is that it is the first study to evaluate the levels of systemic inflammatory markers as indicators of the invasiveness after R-THA.We selected similar patients in the two groups for comparison through PSM, which increased the comparability of the two groups.Patients with different characteristics underwent surgery using a standardized operation; the same implant design was used in both treatment groups.The postoperative functional scores of the two groups were also compared to provide additional reference for R-THA.There were also certain limitations to this study.First, it was a retrospective design.Second, the study follow-up period was short.It would have been better if these serum biomarkers were monitored more than 3 days after the operation.Third, there was just one disease in this research.A study with a large sample and long-term follow-up is needed to verify our conclusion.

Conclusion
The results of this study showed that R-THA associated with a similar invasiveness compared to M-THA.Short-term functional outcomes were better with R-THA compared with M-THA.Further studies are needed to compare the mediumand long-term outcomes.

Fig. 1
Fig.1The fowchart shows the total number of THAs performed during the study period and the numbers of THAs performed in each cohort

Table 1
Patient demographics

Table 3
Postoperative patient outcomes