Total hip arthroplasty (THA) is one of the most commonly performed surgical procedures, with an estimated prevalence in the United States of 0.83%.1 This considerable impact on public health has been largely positive, as good results have been reported well into the long term.2,3 However, issues and failure of THA do persist. Dislocation and loosening of implants are the most common postoperative complications, resulting in the necessity of revision surgery.4 Other problems, such as leg-length discrepancy (LLD), also remain an issue after THA.5
As in many fields, advances in computer and robotic technology have offered the opportunity to improve accuracy and precision in THA implantation. Robotic-arm assisted (RAA) THA has been shown to result in significantly more accurate positioning of implants in vivo.6 Other studies have suggested RAA reduces LLD and allows for smaller, bone-preserving implants in THA.7
What has yet to be determined, however, is how RAA THA translates into clinical outcomes. The additional financial costs and learning curve associated with surgical robotic systems demand a clear benefit to the patient to justify their use. The literature on outcomes of RAA THA compared with the conventional manual technique is relatively scarce.
The purpose of this study was to compare RAA THA and manual THA at minimum 2-year follow-up. The authors compared the following patient-reported outcomes: Harris Hip Score (HHS), Forgotten Joint Score (FJS-12), pain on a visual analog scale (VAS), and satisfaction. Complication rates and subsequent surgeries also were compared. The hypothesis was that patients who underwent RAA would have better outcome scores and lower rates of postoperative complications and reoperations.
Materials and Methods
Prospective data were collected for the study period from July 2011 to January 2015. Patients were included in the study if they underwent primary THA to treat idiopathic osteoarthritis that was performed by the senior author (B.G.D.) with RAA. At a minimum of 2 years after surgery, outcome data were collected prospectively and reviewed retrospectively through questionnaires distributed during office visits, by encrypted email, or via telephone.
Complete follow-up included collection of the HHS and FJS-12 patient-reported outcome measures, VAS pain score on a scale ranging from 0 to 10, and patient satisfaction on a scale ranging from 0 to 10.8,9 In addition, any postoperative complications or subsequent ipsilateral hip surgeries were noted. Radiographs also were obtained for all patients following surgery. From the supine anteroposterior pelvic image, cup inclination, cup version, LLD, and global offset were measured using TraumaCad software (Brainlab Inc).
Each patient who underwent RAA THA was matched to a patient who, within this same date range, underwent primary THA by the senior author (B.G.D.) using freehand technique without robotic assistance. Patients were matched 1:1 for age of ±5 years, sex, body mass index ±5 kg/m2, and whether the anterior or posterior approach was used. All patients participated in the Hip Reconstruction Registry. Although the current study represents a unique analysis, data on some patients in this study may have been reported in other studies. All data collection received institutional review board approval.
Total hip arthroplasty was indicated in patients with advanced osteoarthritis causing significant pain and disability in activities of daily living. After administration of general anesthesia and intravenous tranexamic acid (10 mg/kg), each patient was prepared and draped in the conventional sterile manner.
The hip joint was accessed using either the direct anterior or the mini-posterior approach, as previously described.10,11 At the beginning of the study period, the senior author (B.G.D.) primarily used the posterior approach. In 2014, he transitioned to the anterior approach except for cases in which the posterior approach was indicated by a gluteus medius repair or the need for hardware removal. TraumaCad software was used preoperatively to plan all THAs, both manual and RAA. This planning used preoperative radiographs to measure offset, leg length, and component sizing. In addition, all patients in the RAA group had a preoperative computed tomography (CT) scan that was used for preoperative planning and intraoperative registration.
Control cases were performed using conventional manual technique, with free-hand placement of implants. Leg length and offset were measured intraoperatively; leg length was measured from the center of the femoral head to the lesser trochanter, and offset was measured from the center of the femoral head to the greater trochanter. The surgeon aimed to replicate these measurements with the components in place. For patients who underwent a direct anterior approach, intraoperative fluoroscopic guidance also was used to assess these measurements. The RAA cases used the MAKO Robotic-Arm Interactive Orthopedic (RIO) System (MAKO Surgical Corp), as previously described.12,13
Pelvic and femoral arrays were placed and used to register the acetabulum and femur based on preoperative CT scans. This produced a live 3-dimensional computer model specific to the patient's anatomy. With this model, the robotic arm provided haptic guidance of the acetabular reaming and cup implantation. The system also provided information on the femoral neck cut, broaching, and stem implantation. After implantation and final reduction, the robotic system calculated final numbers for cup inclination and version, leg length, and offset. A deep Hemovac drain was placed, and the surgical wound was closed and dressed in conventional fashion.
A standardized postoperative protocol was followed, as previously described.13 Immediately after surgery, each patient received another dose of 10 mg/kg of tranexamic acid and reinfusion of salvaged red blood cells. Pain management during recovery consisted of intravenous ketorolac and hydromorphone, or oral hydrocodone/acetaminophen (7.5 mg/325 mg) tablet. Intravenous ondansetron and metoclopramide were administered to control nausea and vomiting.
At discharge, patients were given a hydrocodone/acetaminophen (7.5 mg/325 mg) prescription for pain management. Additionally, instructions for 1 to 2 weeks of home physical therapy and nursing care were provided. Patients were scheduled for clinical and radiographic follow-up at postoperative week 2, month 3, and year 1, and annually thereafter.
Data were analyzed using Excel (Microsoft) with the Real Statistics Resource Pack add-in. Categorical variables were compared using Pearson's chi-square test. The F test was applied to all distributions of continuous variables. Based on these results, the study groups were compared using either a paired Student t test or the nonparametric Wilcoxon signed rank test. An a priori power analysis found a sample size of 22 would be necessary to reach 90% power to detect a difference in HHS between groups of 10 with SD of 15.
A total of 353 eligible RAA THAs were performed during the study period; 295 (83.6%) of these RAA THAs had complete minimum 2-year follow-up. Eighty-five RAA THAs were successfully pair-matched to controls. Mean age was 57.0 years in the RAA group and 56.6 years in the control group (P=.798). Mean body mass index was 28.2 kg/m2 in the RAA group and 28.1 kg/m2 in the control group (P=.777). Both groups consisted of 48 females and 37 males.
The anterior approach was used in 43.5% of cases, and the posterior approach was used in 56.5% of cases. Gluteus medius repairs were not performed for any RAA patient and were required for only 1 manual THA patient (P>.999). There were no statistically significant differences in demographic factors between the study groups (Table 1), indicating adequate control by the pair-matching process.
Patients who underwent THA with RAA had significantly higher scores than patients in the control group for both HHS (P<.001) and FJS-12 (P=.003). The RAA THA patients also had 2.4 times higher odds of reaching an FJS-12 of 60 or above than manual THA patients (P=.0196). In addition, RAA THA patients trended toward having lower VAS scores, although these differences were not statistically significant (P=.120). There was no difference in patient satisfaction between the 2 groups (P=.591). Outcome data are illustrated in Figures 1–2.
Patient-reported outcomes for Harris Hip Score (HHS) and Forgotten Joint Score (FJS-12) at minimum 2-year follow-up. Abbreviation: RAA, robotic-arm assisted.
Patient pain and satisfaction ratings at minimum 2-year follow-up. Abbreviations: RAA, robotic-arm assisted; VAS, visual analog scale.
Of the 85 RAA patients, 84 (98.8%) patients were in the Lewinnek safe zone for cup orientation; this was a significantly higher proportion than for the manual THA cases, with 67 (78.8%) patients in the Lewinnek safe zone (P<.001). Similarly, a higher proportion of RAA patients were in the Callanan safe zone for cup orientation; 79 (92.9%) RAA patients were in the safe zone compared with 51 (60.0%) manual THA patients (P<.001). Figures 3–5 show the proportion of patients in the safe zones for acetabular component placement.
Proportion of patients in the safe zone for acetabular component positioning. Abbreviation: RAA, robotic-arm assisted.
Robotic-arm assisted (RAA) total hip arthroplasty patients in the safe zone for acetabular component placement.
Manual total hip arthroplasty (THA) patients in the safe zone for acetabular component placement.
The mean LLD was 3.0±2.6 mm in RAA patients, which was significantly lower than the mean LLD of 4.0±2.7 for manual THA patients (P=.013). However, this difference may not be of clinical importance. No patient in either group had greater than 1 cm LLD. There was no significant difference between groups in mean global offset (P=.310) (Table 2).
In the RAA THA group, 7 (8.2%) patients had minor postoperative complications. Six patients had superficial infections of the surgical site. In 5 patients, these infections resolved after treatment with antibiotics, and 1 patient required a superficial scar revision. The seventh patient had a deep venous thrombosis.
In the control group, there were 2 superficial infections, 2 cases of subjectively noted lateral femoral cutaneous nerve numbness, 1 case of numbness around the incision scar, and 1 case of a calcar split, which was protected with a cerclage wire, for a minor complication rate of 7.1%. The difference in complication rate was not statistically significant between groups (P=.773), and the difference in superficial infections also was not statistically significant (P=.15).
One (1.1%) RAA patient required revision THA for femoral stem loosening 8.7 months after primary THA. Three (3.5%) patients in the control group required revision THA at a mean of 25.1 months postoperatively; these revisions were all for femoral stem loosening. The revision rates between groups were not statistically significant (P=.621).
This study reported clinical outcomes after a minimum of 2 years of follow-up for patients who underwent RAA THA compared with patients who underwent manual THA. Eighty-five THAs performed with RAA were pair-matched to THAs performed freehand for age, sex, body mass index, and approach. The findings demonstrated statistically higher scores after a minimum follow-up of 2 years for RAA THAs using 2 separate patient-reported outcome measures. The RAA group demonstrated a higher proportion of patients in the cup placement safe zones. This study also demonstrated no significant difference between RAA and manual THA regarding VAS score, patient satisfaction, complication rate, and revision rate.
Correct positioning of implants during THA is essential for achieving a good patient outcome. Previous studies have suggested difficulty in consistent implant placement using the freehand technique. Callanan et al14 reviewed radiographs of 1823 THAs and hip resurfacings in the Massachusetts General Hospital joint registry and found only 50.3% of acetabular cups were within the safe zone for both abduction and version. In their study of 200 THAs performed by 3 orthopedic surgeons and 9 residents, Bosker et al15 found 70.5% had accurate placement. Component malposition has been shown to be associated with serious negative consequences, such as increased polyethylene wear, osteolysis, and dislocations.16–18
Surgical robotic systems developed in recent years to assist implantation in THA have offered the ability to improve accuracy and precision. Nawabi et al19 studied 12 cadaveric cup implantations and found the robotic system was significantly more accurate to planned cup orientation; they concluded that robotic assistance has the potential to reduce human error in THA.
Domb et al6 compared the postoperative radiographs of 50 RAA THAs with a pair-matched control group of conventional posterior THAs performed by the same surgeon. They found cup components implanted with robotic assistance were significantly more likely to be positioned within the safe zone as defined by both Lewinnek et al20 and Callanan et al.14 The cup components were placed with 100% accuracy, as defined by the Lewinnek safe zone.
A review of 1980 THAs performed by 6 surgeons at the same institution found techniques using computer navigation or robotic-arm assistance were significantly more accurate to the safe zones.21 Suarez-Ahedo et al22 also found robotic-arm assistance allowed for relatively smaller component sizes, suggesting greater preservation of native bone stock. Illgen et al23 reported on 100 RAA THAs compared with manual THAs performed both early and late in clinical practice. They found robotic-arm assistance led to a 71% increase in accuracy of cup component placement and a significantly lower rate of dislocations.
The current authors previously examined a part of this patient population and reported a case series on 162 RAA THA with minimum follow-up of 2 years.24 Mean VAS score was 0.7, satisfaction was 9.3, HHS was 91.1, and FJS-12 was 83.1. No LLD more than 10 mm or dislocations were reported. In addition, 2 other previous studies from the current group demonstrated high accuracy of component placement with the use of robotics in THA.25,26
Although data were not collected for the current study, the relative costs and benefits of RAA THA is an important consideration. Studies of other robotic assistance systems have suggested high front-end costs associated with development and acquisition of the technology, maintenance, and preoperative imaging.27 However, these initial investments eventually could be outweighed by the savings associated with potential improved outcomes or decreased complication rates. It also is conceivable that as the field of RAA THA develops, efficiency of production and technique will improve, and increasing returns to scale will ultimately result in a favorable cost-benefit ratio. Analysis and optimization from this financial perspective remains a topic for future study.
The findings of the current literature seem to indicate that robotic assistance leads to superior positioning of components in THA. However, there is less scholarship available on the clinical outcomes of RAA THA, particularly for systems designed to guide acetabular reaming and cup implantation such as that used in the current study. Substantial and durable improvement in patient-reported outcome scores due to robotic assistance in THA has yet to be established.
For femoral-side systems that assist in femoral broaching and stem implantation, results have been inconclusive and somewhat mixed. Bargar et al28 and Schulz et al29 did not find statistically significant differences in patients who underwent THA with ROBODOC (THINK Surgical) in HHS and Merle d'Aubigné-Postel scores, respectively. Honl et al30 and Nakamura et al31 reported significantly higher scores for ROBODOC using patient-reported outcome measures such as the Mayo hip score, HHS, and Japanese Orthopaedic Association score, but the differences were not statistically significant. It may be postulated that although the difference in component placement accuracy is not substantial enough to confer lower dislocation rates in the short term, specifically in studies that are not powered to this end, the higher accuracy does improve patients' subjective pain and function by better restoring the native spatial relationship of the joint.
Strengths and Limitations
This study used a matched-pair design to compare study groups. This technique allowed for control of confounders related to age, sex, and body mass index of patients, as well as the surgical approach used. Two independent patient-reported outcome measures, a VAS score for pain and satisfaction, were used to assess outcomes. This allowed for a multimodal comparison of study groups.
The sample size was well above that necessary according to an a priori power analysis. All of the procedures were performed by the senior surgeon (B.G.D.), controlling for potential differences due to surgical technique or experience. However, there were some limitations to this study. Preoperative baseline scores and outcomes data were not collected. Thus, differences in preoperative status or magnitude of improvement between groups could not be evaluated. This also limits the ability to compare the baseline status of the groups, perhaps introducing selection bias. However, the authors attempted to mitigate this bias by performing a matched study, based on age, sex, body mass index, and surgical approach.
Another disadvantage was the retrospective nature of this study, which introduced the potential for bias. However, the prospective collection of data reduces selection bias and excludes recall bias. With a minimum follow-up of 2 years, this was a relatively short-term study. Longer-term studies are needed to investigate the durability of outcomes.
Because all of the procedures were performed by a single surgeon, the generalizability of this study's findings may be limited. One variable that was not recorded consistently enough to make an adequate comparison was surgical time, which could have been informative for the reader.
Finally, although a statistically significant difference was demonstrated in all patient-reported outcomes, the difference in HHS between groups did not exceed the minimal clinically important difference.32 However, when the goal is to differentiate between a good outcome and a great outcome, the HHS suffers from a ceiling effect. The FJS, on the other hand, was specifically designed to detect clinical differences between good and great. Although in this study the FJS showed a difference that was statistically significant and larger than the HHS, the authors could not find a minimal clinically important difference for this.
Performing THA with RAA yielded improved short-term patient outcomes compared with manual THA and higher likelihood of cup placement in the safe zones. There were no differences regarding VAS, satisfaction, the rate of complications or subsequent revisions between groups.
- Maradit Kremers H, Larson DR, Crowson CS, et al. Prevalence of total hip and knee replacement in the United States. J Bone Joint Surg Am. 2015;97(17):1386–1397. doi:10.2106/JBJS.N.01141 [CrossRef] PMID:26333733
- Callaghan JJ, Albright JC, Goetz DD, Olejniczak JP, Johnston RC. Charnley total hip arthroplasty with cement: minimum 25-year follow-up. J Bone Joint Surg Am. 2000;82(4):487–497. doi:10.2106/00004623-200004000-00004 [CrossRef] PMID:10761939
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- Gwam CU, Mistry JB, Mohamed NS, et al. Current epidemiology of revision total hip arthroplasty in the United States: National Inpatient Sample 2009 to 2013. J Arthroplasty. 2017;32(7):2088–2092. doi:10.1016/j.arth.2017.02.046 [CrossRef] PMID:28336249
- Desai AS, Dramis A, Board TN. Leg length discrepancy after total hip arthroplasty: a review of literature. Curr Rev Musculoskelet Med. 2013;6(4):336–341. doi:10.1007/s12178-013-9180-0 [CrossRef] PMID:23900834
- Domb BG, El Bitar YF, Sadik AY, Stake CE, Botser IB. Comparison of robotic-assisted and conventional acetabular cup placement in THA: a matched-pair controlled study. Clin Orthop Relat Res. 2014;472(1):329–336. doi:10.1007/s11999-013-3253-7 [CrossRef] PMID:23990446
- Chahal J, Thiel GSV, Mather RC, Lee S, Salata MJ, Nho SJ. The minimal clinical important difference (MCID) and patient acceptable symptomatic state (PASS) for the modified Harris hip score and hip outcome score among patients undergoing surgical treatment for femoroacetabular impingement. Orthop J Sports Med. 2014;2(7suppl2):2325967114S0010. doi:10.1177/2325967114S00105 [CrossRef]
- Harris WH. Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty: an end-result study using a new method of result evaluation. J Bone Joint Surg Am. 1969;51(4):737–755. doi:10.2106/00004623-196951040-00012 [CrossRef] PMID:5783851
- Behrend H, Giesinger K, Giesinger JM, Kuster MS. The “forgotten joint” as the ultimate goal in joint arthroplasty: validation of a new patient-reported outcome measure. J Arthroplasty. 2012;27(3):430–436.e1. doi:10.1016/j.arth.2011.06.035 [CrossRef] PMID:22000572
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- Tarwala R, Dorr LD. Robotic assisted total hip arthroplasty using the MAKO platform. Curr Rev Musculoskelet Med. 2011;4(3):151–156. doi:10.1007/s12178-011-9086-7 [CrossRef] PMID:21728013
- Domb B, Rabe S, Walsh JP, Close MR, Chaharbakhshi EO, Perets I. Outpatient robotic-arm total hip arthroplasty surgical technique. Surg Technol Int. 2016;29:235–239. PMID:27466866
- Callanan MC, Jarrett B, Bragdon CR, et al. The John Charnley Award. Risk factors for cup malpositioning: quality improvement through a joint registry at a tertiary hospital. Clin Orthop Relat Res. 2011;469(2):319–329. doi:10.1007/s11999-010-1487-1 [CrossRef] PMID:20717858
- Bosker BH, Verheyen CCPM, Horstmann WG, Tulp NJA. Poor accuracy of freehand cup positioning during total hip arthroplasty. Arch Orthop Trauma Surg. 2007;127(5):375–379. doi:10.1007/s00402-007-0294-y [CrossRef] PMID:17297597
- Kennedy JG, Rogers WB, Soffe KE, Sullivan RJ, Griffen DG, Sheehan LJ. Effect of acetabular component orientation on recurrent dislocation, pelvic osteolysis, polyethylene wear, and component migration. J Arthroplasty. 1998;13(5):530–534. doi:10.1016/S0883-5403(98)90052-3 [CrossRef] PMID:9726318
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|RAA THA||Manual THA|
| Female||48 (56.5%)||48 (56.5%)|
| Male||37 (43.5%)||37 (43.5%)|
| Left||42 (49.4%)||37 (43.5%)|
| Right||43 (50.6%)||48 (56.5%)|
| Anterior||37 (43.5%)||37 (43.5%)|
| Posterior||48 (56.5%)||48 (56.5%)|
|Outcome||RAA THA||Manual THA||P||Odds ratio|
|LLD, mean±SD, mm||3.0±2.6||4.0±2.7||.013|
|Global offset, mean±SD, mm||3.8±3.0||4.7±4.1||.310|
|Inclination and version, No.|
| Lewinnek safe zone||84 (98.8%)||67 (78.8%)||<.001||22.6|
| Callanan safe zone||79 (92.9%)||51 (60.0%)||<.001||8.8|