Are robotic-assisted and computer-navigated total hip arthroplasty associated with superior outcomes in patients who have hip dysplasia?

Abstract

Introduction

Robotic-assisted (RA) and computer-navigated (CN) total hip arthroplasty (THA) have been demonstrated to improve component placement accuracy compared to manual THA (mTHA) for primary osteoarthritis. As hip dysplasia presents several additional challenges in component placement accuracy and leg length discrepancy (LLD) correction during THA, a systematic review was conducted to evaluate whether utilizing these platforms may be associated with superior outcomes over mTHA in patients who have hip dysplasia.

Methods

PubMed, Medline, EBSCOhost, and Google Scholar were searched on September 13, 2023 to identify comparative studies published after January 1, 2000 that evaluated outcomes of RA-THA or CN-THA in patients who have hip dysplasia. The query yielded 197 unique articles, which were screened for alignment with the study aims. After screening, 10 studies fulfilled all inclusion criteria, comprising 946 patients. Risk of bias was evaluated via the Methodological Index for Nonrandomized Studies tool, and the mean score was 21.2 ± 1.5.

Results

Both RA-THA and CN-THA were not associated with improved acetabular anteversion and inclination when evaluating Crowe I-IV types altogether compared to mTHA, but studies reported improved accuracy for each Crowe I and II cases when assessed individually. While studies reporting acetabular cup placement within the Lewinnek and Callanan safe zones consistently found higher odds of accurate positioning for RA-THA versus mTHA, accuracy in achieving targeted center of rotation was mixed. Also, studies reported no difference in LLD restoration for RA-THA and CN-THA compared to mTHA. While operative time may be increased when utilizing these platforms, they may also expedite specific sequences, offsetting most of the increase in operative time.

Conclusion

This review highlights the advantages of RA-THA and CN-THA for patients who have DDH, particularly when treating Crowe I and II types as superior radiographic outcomes were achieved with these intraoperative technologies. However, there remains a need for studies to investigate whether this results in patient-reported outcome measures.

1. Introduction

Accurate component placement is a critical factor in restoring hip biomechanics and attaining favorable long-term outcomes via total hip arthroplasty (THA). Poor component positioning has been associated with accelerated wear, worse function, and joint instability.1, 2, 3, 4 Considering this, robotic-assisted (RA) and computer-navigated (CN) THA platforms have been developed, aiming to increase the precision of and individualize implant positioning, leading to improved patient outcomes compared to manual THA (mTHA).^5,6 These platforms have been shown to increase acetabular component placements in the Lewinnek and Callanan safe zones and improve radiographic measures such as acetabular inclination and anteversion.7, 8, 9, 10 However, RA and CN platforms has also been associated with increased operative time^9,10 and have mixed results for whether they lead to increased blood loss^11,12 and improved patient outcomes.^7,9, 10, 11

Due to acetabular deformities such as an inadequate roof, double floor, retroverted or anteverted acetabulum,¹³ and the presence of osteophytes on the acetabular rim, achieving optimal cup placement in patients with secondary osteoarthritis to developmental dysplasia of the hip (DDH) is challenging. These deformities interfere with selecting the acetabular reaming target point for cup placement, which may result in cup malpositioning, and subsequently poorer outcomes, particularly in more severely dysplastic Crowe III or IV cases.14, 15, 16 Additionally, patients who have dysplastic hips often have substantial leg length discrepancies.^14,17 As superior cup positioning has been demonstrated with primary osteoarthritis patients who underwent RA-THA or CN-THA, utilizing these platforms with dysplastic hip patients may help surgeons overcome anatomic challenges common with DDH to improve placement accuracies. While several studies have investigated the utility of RA-THA and CN-THA with patients who have hip dysplasia, most studies have only reported a limited set of outcomes, making evaluations difficult regarding their potential benefit.

Therefore, a systematic review of the literature was conducted to assess the utility of RA and CN platforms for patients who have hip dysplasia undergoing primary THA. Specifically, we asked: Does RA-THA and CN-THA result in more accurate 1) inclination and anteversion accuracy and components placed within safe zones as well as 2) center of rotation placement accuracy compared to mTHA? 3) Additionally, are these platforms associated with improved correction of leg length discrepancies? 4) Do RA-THA and CN-THA have similar intraoperative workflows and postoperative adverse event profiles as mTHA?

2. Methods

2.1. Search strategy

PubMed, Medline, EBSCOhost, and Google Scholar were searched on September 13, 2023 to identify all comparative studies published between January 1, 2000 and September 13, 2023 that evaluated outcomes of RA-THA or CN-THA in patients who have hip dysplasia. The following keywords and Medical Subject Headings (Mesh) terms were used in combination with the “AND” or “OR” Boolean operators: “Arthroplasty, Replacement, Hip"[Mesh] OR “Arthroplasty, Replacement"[Mesh] OR “total hip arthroplasty" OR “THA") AND “Robotics"[Mesh] OR “robotic*" OR “Surgery, Computer-Assisted"[Mesh] OR “Robotic Surgical Procedures"[Mesh] OR “robotic arm" OR “computer navigated" AND “Developmental Dysplasia of the Hip"[Mesh] OR “Hip Dislocation, Congenital"[Mesh] OR “DDH” OR “Dysplasia” OR “Acetabular dysplasia”. This study was considered exempt from review by the Cleveland Clinic Foundation ethical review board because of the public nature of all data included and the lack of protected health information.

2.2. Eligibility criteria

Articles were included if 1) English full-text manuscripts were available and 2) the study investigated either RA-THA or CN-THA outcomes for patients who have hip dysplasia, and 3) the study had a comparison group, most often mTHA. Additionally, the following were excluded from our analysis: 1) case reports; 2) systematic reviews; 3) editorials; 4) duplicate studies; 5) preprint articles; and 6) abstracts.

2.3. Study selection

This review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (PROSPERO registration of the study protocol: CRD42023459236, September 13, 2023).¹⁸ Each article was evaluated for eligibility by two independent reviewers (CJH, JRP). To settle disagreements, a third independent reviewer (KAM) was consulted. After removing duplicates, the remaining 197 articles were screened for alignment with the study purpose. Upon title and abstract screening, 17 studies remained, in which the full text of each article was reviewed, with 10 fulfilling all inclusion criteria. No further articles were retrieved via examining each study's reference list (Fig. 1).

Fig. 1.

This PRISMA diagram depicts the selection process.

2.4. Data extraction and analyses

The resulting studies were searched for study design characteristics and the outcomes of RA-THA and CN-THA. To evaluate the utility of these intraoperative technologies, data was extracted for cup placement accuracy metrics, LLD, operative time, complications, and blood loss. Data extraction was performed in duplicate by two independent reviewers (CJH, JRP) and findings were compared for verification by a third reviewer (KAM). Due to heterogeneity in study design, implants utilized, and surgical approach, a meta-analysis was not conducted, and we presented a narrative summary of the results.

2.5. Study characteristics

A total of five retrospective cohort,19, 20, 21, 22, 23 three retrospective case control,24, 25, 26 one crossover,²⁷ and one randomized controlled trial²⁸ were included, comprising 946 patients who received their index THA for DDH between 2006 and 2022 (Table 1). Six studies evaluated outcomes after RA-THA,19, 20, 21^,23,25,26 all utilizing the MAKO platform, while six studies reported on CN-THA.22, 23, 24^,26, 27, 28 All ten studies evaluated acetabular anteversion and inclination as well as component placement within the safe zones,19, 20, 21, 22, 23, 24, 25, 26, 27, 28 while seven reported on the accuracy of achieved center of rotation.20, 21, 22, 23, 24, 25, 26 Also, three studies investigated leg length discrepancy,^19,20,28 and six studies reported on intraoperative events (operative time and bleeding) and complications.19, 20, 21^,24,25,28

Table 1.

Characteristics of studies included in the final analysis.

Author (Year)	Study Design	Data Source	Sample Size (n)	Study Years	Sex (%F)	Age	BMI	Follow Up	RA or CN	Platform Utilized	Surgical Approach	# of Surgeons	Implants Utilized	Crowe Classification (n)	Comparison Cohort	Matching	MINORS Scorea
Ando et al. (2021)26	Retrospective Case Control	Single Institution	58	2018–2019	95	67 ± 8 RA-THA	23 ± 4 RA-THA	2–12 weeks	Both	MAKO, Stryker CT-Hip System	Anterolateral and posterolateral	5	Cup: Trident	I – 45	RA-THA, CN-THA	1:1, age, sex, BMI, surgical approach	20
						64 ± 8 CN-THA	64 ± 8 CN-THA						Stem: Accolade II, Exeter	II – 13
Chai et al. (2022)19	Retrospective Cohort	Single Institution	54	2017–2019	100	43 ± 9 RA-THA	24 ± 5 RA-THA	2 years	RA	MAKO	Posterolateral	N/A	Cups: Trident, Combicup or Pinnacle	III - 16	mTHA	1:1, age, sex, BMI, ASA score, laterality, Crowe type	22
						45 ± 10 mTHA	23 ± 3 mTHA						Stem: S-ROM Modular	IV - 38
Hayashi et al. (2021)20	Retrospective Cohort	Single Institution	69	2018–2019	93	61 ± 11 DDH	23 ± 6 DDH	1 year	RA	MAKO	Anterolateral and posterior	2	Cup: Trident Stem: Accolade II or Exerter v40	I - 14 II - 5 III - 10 IV - 1	Non-DDH RA-THA	N/A	22
						61 ± 11 non-DDH	23 ± 6 non-DDH
Kaku et al. (2021)27	Crossover	Single Institution	36	2018–2019	81	66 ± 11	24 ± 3	N/A	CN	Vector Vision Hip	Posterior	1	Cup: SQRUM/HA	I - 26 II - 10	mTHA	N/A	24
Sato et al. (2023)21	Retrospective Cohort	Single Institution	168	2019–2020	99	66 ± 8 RA-THA	24 ± 3 RA-THA	3 months	RA	MAKO	Anterolateral	9	Cup: Trident Stem: Accolade II	I - 161	mTHA	1:1, age, sex BMI, Crowe type, CE angle.	21
						66 ± 8 mTHA	24 ± 5 mTHA							II - 7
Tamaki et al. (2022)23	Retrospective Cohort	Single Institution	104	2018–2022	85	65 ± 9 RA-THA	25 ± 4 RA-THA	1 week	Both	MAKO, Aquilion 16	Anterolateral	N/A	Cup: Trident or Trident II	I - 89 II - 15 III, IV - 0	RA-THA, CN-THA	1:1, age, sex, BMI	22
						66 ± 10 mTHA	25 ± 4 mTHA
Tsutsui et al. (2017)22	Retrospective Cohort	Single Institution	249	2006–2014	90	66 (range, 38–88)	24 (range, 16–36)	3 weeks	CN	Aquilion 16	Direct lateral	N/A	Cups: Trident, TriAD, Tritanium, Triology	I - 186 II - 44 III, IV - 19	mTHA	N/A	19
Uekoa et al. (2019)24	Retrospective Case Control	Single Institution	68	2006–2018	88	69 ± 6 Crowe IV	23 ± 5 Crowe IV	5 year	CN	Stryker CT-Hip System	Posterolateral	1	Cup: Trident	I - 34 IV - 34	Crowe I vs IV	1:1, age, sex, BMI	21
						67 ± 7 Crowe I	23 ± 4 Crowe I
Zhang et al. (2011)28	Randomized Controlled Trial	Single Institution	22	2007–2008	45	49 ± 7 CN-THA	N/A	1 year	CN	N/A	Posterior	N/A	N/A	I - 22	mTHA	N/A	22
						49 ± 5 mTHA
Zhou et al. (2021)25	Retrospective Case Control	Single Institution	118	2019–2020	75	50 ± 11 RA-THA	25 ± 3 RA-THA	4 weeks	RA	MAKO	Posterolateral	3	N/A	I - 72 II, III - 26 IV - 10	mTHA	1:1, age, sex, BMI, Crowe type, operation date	20
						50 ± 12 mTHA	25 ± 3

BMI = body mass index; RA = robotic-assisted; CN = computer-navigated; MINORS = methodological index for non-randomized studies; N/A = not applicable; mTHA = manual total hip arthroplasty; ASA = American Society of Anesthesiologists; DDH = developmental dysplasia of the hip; CE = center edge.

^aThe MINORS scale is from 0 to 16 for noncomparative studies and 0 to 24 for studies with control groups. Higher scores represent better study quality.

2.6. Risk of bias in individual studies

Using the Methodological Index for Nonrandomized Studies (MINORS) tool, two independent reviewers (CJH, JRP) evaluated the risk of bias. With higher scores indicating higher research quality, this is a validated assessment method that rates comparative studies from 0 to 24 based on 12 criteria related to study design, data analyses, outcomes examined, and follow-up. Each item domain receives a score of 0 if not reported, 1 if reported but insufficient, and 2 if reported and sufficient. Grading disagreements were settled by consulting a third reviewer (KAM) to reach consensus. The mean MINORS score was 21.2 ± 1.5.

3. Results

3.1. Accuracy of component placement

No difference in accuracy was reported by both studies that grouped Crowe types I through IV patients together to compare acetabular anteversion and inclination accuracy for RA or CN-THA versus mTHA (Table 2).^24,25 However, one retrospective cohort study showed markedly increased accuracy for Crowe I patients with RA-THA versus mTHA,²¹ and another similar study reported moderately increased accuracy in achieving desired anteversion and inclination for both Crowe type I and II patients undergoing CN-THA versus mTHA.²² Notably, one study that compared cup alignments before and after screw placement versus the preoperative target found that cup screw placement eliminated the slight increase in accuracy that CN-THA had achieved.²⁷ Likewise, evaluating only Crowe I patients, the randomized controlled study by Zhang et al. showed slightly improved accuracy with CN-THA compared to mTHA.²⁸ Also, one study found that mean absolute discrepancies in cup inclination and anteversion for Crowe I and II cases were slightly reduced in the RA-THA cohort compared to the CN-THA cohort.²³ Both studies reporting acetabular cup placement within the Lewinnek and Callanan safe zones found higher odds of accurate positioning in RA-THA versus mTHA, across Crowe types.^19,25

Table 2.

Key findings from studies evaluating the acetabular anteversion and inclination as well as placement within the Lewinnek and Callanan safe zones for RA-THA and CN-THA in patients who have hip dysplasia.

	Key Findings
Ando et al. (2021)26	Among Crowe I and II cases, RA-THA was associated with lower deviation between postoperative and target inclination compared to CN-THA, but there was no difference in anteversion achieved. All RA-THA cases were within Callanan's safe zone, while 2 CN-THA cases were outliers.
Chai et al. (2022)19	No difference in cup inclination accuracy for Crowe III or IV RA-THA patients compared to mTHA. Average cup anteversion was modestly higher in mTHA for both Crowe III and IV. The ratio of the acetabular cup within both the Lewinnek and Callanan safe zones was 37% mTHAs and compared to 96% of RA-THAs. RA-THA for either Crowe classifications III and IV resulted in markedly increased odds of accurate placement within the safe zones.
Hayashi et al. (2021)20	Compared to RA-THA patients without hip dysplasia, no difference in mean absolute difference of preoperative plan versus postoperative radiograph values for cup inclination or anteversion were found with RA-THA patients who have dysplasia. The RA-THA Crowe I and II cases had lower absolute differences in inclination versus III and IV. No difference in anteversion between Crowe class I and II versus III and IV.
Kaku et al. (2021)27	Among patients who have hip dysplasia, the inclination and anteversion angle errors between the target angle and the intraoperative installation were modestly smaller with CN-THA compared to mTHA. No difference in error based on BMI, bilateral superior anterior iliac spine distance, absolute value of pelvic tilt angle, Crowe classification (I vs II), and presence of double-floor osteophytes.
Sato et al. (2023)21	With the vast majority of cases being Crowe I, the average difference between preoperative target inclination and anteversion versus postoperative measurements were largely reduced with RA-THA compared to mTHA.
Tamaki et al. (2022)23	Across three comparisons (preoperative plan vs intraoperative record, intraoperative record vs postoperative measurement, preoperative plan vs postoperative measurement) for Crowe I and II, the mean absolute discrepancies in cup inclination and anteversion were slightly reduced in the RA-THA cohort compared to the CN-THA cohort. As an exception, there was no difference in the intraoperative record versus postoperative measurement between the cohorts for the mean discrepancy in cup inclination.
Tsutsui et al. (2017)22	The proportion of implants within the combined target zone (inclination and anteversion) was 98% in the overall CN-THA cohort and 61% in the mTHA cohort. However, upon evaluating Crowe classifications I-IV separately versus mTHA, only Crowe I and II showed modestly higher accuracy than mTHA.
Uekoa et al. (2019)24	Comparing Crowe classification I versus IV that underwent CN-THA, there were no differences in cup anteversion or inclination angle deviations between preoperative plan and postoperative measurement between the two cohorts. Notably, there were no cup angle deviations greater than five degrees in either cohort.
Zhang et al. (2011)28	For Crowe I, mean deviation between preoperative planned and postoperative cup inclination and anteversion at one year follow up were modestly lower for CN-THA cases compared to mTHA.
Zhou et al. (2021)25	Across Crowe classifications I-IV, the acetabular components of the RA-THA cohort had significantly more cases located within the Lewinnek (95 vs. 80%) and Callanan (75 vs. 51%) safe zones than mTHA. No difference in cup anteversion or inclination angle for RA-THA versus mTHA when evaluating Crowe classifications I-IV combined.

RA-THA = robotic-assisted total hip arthroplasty; CN-THA = computer-navigated total hip arthroplasty; mTHA = manual total hip arthroplasty; BMI = body mass index.

3.2. Center of rotation achieved

There were mixed results on the likelihood of achieving the targeted center of rotation (Table 3), with one matched cohort RA-THA study showing no difference in odds,²⁵ while another matched cohort study found RA-THA was slightly better in aligning the center of rotation versus mTHA.²¹ No difference in center of rotation accuracy was reported by three studies comparing Crowe types to each other.^20,22,24 Likewise, one article reported no difference in center of rotation accuracy achieved between RA and CN-THA.²³ Another study that compared RA-THA versus CN-THA in Crowe I and II type patients found that the absolute error of the COR in the anteroposterior and superoinferior directions was slightly less in the RA-THA cohort, but no difference in the mediolateral direction.²⁶

Table 3.

Key findings from studies evaluating the center of rotation achieved for RA-THA and CN-THA in patients who have hip dysplasia.

	Key Findings
Ando et al. (2021)26	No difference in achieved postoperative versus targeted COR between RA-THA and CN-THA cohorts for Crowe I and II types. However, the absolute error was slightly lower for the RA-THA cohort in the anteroposterior and superoinferior directions. No difference in absolute error in the mediolateral direction.
Hayashi et al. (2021)20	Comparing RA-THA patients who have hip dysplasia versus those who do not, there were no differences in the accuracy of 3-D cup positioning (coronal and axial planes) between preoperative plan and postoperative measurements. Also, no differences were reported based on anterolateral versus posterior operative approach or between Crowe classification I, II versus III, IV.
Sato et al. (2023)21	The RA-THA cohort had modestly less difference between preoperatively planned target COR and postoperatively measured COR in the anteroposterior and mediolateral directions. However, there was no difference reported in the superoinferior direction compared to mTHA.
Tamaki et al. (2022)23	No differences reported in transverse, longitudinal, or sagittal COR mean discrepancies when comparing preoperative targets to postoperative measurements between RA-THA and CN-THA cohorts.
Tsutsui et al. (2017)22	No differences reported in transverse, longitudinal, or sagittal COR mean discrepancies (preoperative plan versus postoperative measurements) when comparing Crowe I versus IV classification with CN-THA. Mean discrepancies for each of the three axes were within 3 mm per Crowe classification.
Uekoa et al. (2019)24	No differences in the mean deviations between preoperative target and postoperative measurements of the transverse, longitudinal, and sagittal axes for Crowe I versus Crowe IV dysplasia patients who underwent CN-THA.
Zhou et al. (2021)25	No difference in RA-THA versus mTHA COR accuracy in the transverse or longitudinal directions. The study did not report sagittal direction discrepancies.

RA-THA = robotic-assisted total hip arthroplasty; CN-THA = computer-navigated total hip arthroplasty; mTHA = manual total hip arthroplasty; COR = center of rotation.

3.3. Leg length discrepancy correction

Of the two studies comparing LLD correction between RA and CN-THA versus mTHA, there was consensus that utilization of these technologic platforms was not associated with improved LLD correction (Table 4).^19,28 One study assessing DDH versus non-DDH patients who underwent RA-THA found that the non-DDH cohort had a slightly lower mean postoperative LLD.²⁰

Table 4.

Key findings from studies evaluating leg length discrepancy correction during RA-THA and CN-THA in patients who have hip dysplasia.

	Key Findings
Chai et al. (2022)19	No difference in LLD correction between RA-THA and mTHA cohorts for both Crowe III and IV classifications.
Hayashi et al. (2021)20	While there was no difference between the absolute difference of leg length (postoperative measurement versus preoperative plan) between non-DDH and DDH patients who underwent RA-THA, postoperative mean leg length discrepancy was slightly less in the non-DDH cohort.
Zhang et al. (2011)28	No difference in mean decrease in LLD after mTHA versus CN-THA.

RA-THA = robotic-assisted total hip arthroplasty; CN-THA = computer-navigated total hip arthroplasty; DDH = developmental dysplasia of the hip; mTHA = manual total hip arthroplasty.

3.4. Occurrence of intraoperative events and complications

Two retrospective matched cohort studies reported increased operative time associated with RA-THA compared to mTHA (Table 5).^19,21 However, another similar study found no difference,²⁵ noting that operative time was likely saved while reaming the acetabulum to the targeted position due to robotic assistance, particularly in cases of severe dysplasia. In contrast, a randomized controlled trial found that CN-THA had slightly lower operative time than mTHA.²⁸ While one study found increased blood loss for RA-THA compared to mTHA, this was explained by conducting the robotic registration after femoral rasping, prolonging medullary bleeding time.²¹ Other studies reporting on blood loss showed either comparable loss²⁵ or slightly decreased loss.²⁸ No intraoperative complications occurred in the RA or CN-THA cohorts across three reporting studies.^19,20,24 Likewise, no postoperative complications were reported through two-year follow-up by one study.¹⁹

Table 5.

Key findings from studies evaluating intraoperative events and complications RA-THA and CN-THA in patients who have hip dysplasia.

	Key Findings
Chai et al. (2022)	The RA-THA cohort had a longer operative time compared to mTHA (133 ± 45 vs. 115 ± 20 min). There were no intraoperative complications or dislocations and nerve injuries through two-year follow up in either cohort.
Hayashi et al. (2021)	No intraoperative or one-year timeframe complications in either the DDH or non-DDH RA-THA cohorts.
Sato et al. (2023)	The RA-THA cohort had a longer duration of surgery compared to mTHA (63 ± 13 vs. 45 ± 11 min). Blood loss in the RA-THA cohort was higher than mTHA (136 ± 52 vs. 114 ± 27 mL). No complications intraoperatively or in the 3-month postoperative period.
Uekoa et al. (2019)	Crowe IV CN-THA patients had a modestly higher likelihood of postoperative dislocation than Crowe I. No difference in infection, deep vein thrombosis, nerve palsy, or fracture.
Zhang et al. (2011)	Average operative time for CN-THA was slightly less than mTHA (119 vs 125 min), and CN-THA patients had less blood loss (155 versus 98 mL).
Zhou et al. (2021)	No difference in operative time or blood loss between RA-THA and mTHA cohorts.

RA-THA = robotic-assisted total hip arthroplasty; CN-THA = computer-navigated total hip arthroplasty; mTHA = manual total hip arthroplasty; DDH = developmental dysplasia of the hip.

4. Discussion

Robotic-assisted and computer-navigated THA have been demonstrated to improve component placement accuracy compared to mTHA in cases of primary osteoarthritis. As hip dysplasia presents several challenges in component placement accuracy and LLD correction during THA, utilizing these platforms may also show superior outcomes in this patient population. Therefore, our study sought to assess the utility of RA and CN platforms for patients who have hip dysplasia undergoing primary THA. We found that RA-THA and CN-THA were not associated with improved acetabular anteversion and inclination when evaluating Crowe I-IV types altogether, but studies reported improved accuracy for each Crowe I and II cases when assessed individually. While studies reporting acetabular cup placement within the Lewinnek and Callanan safe zones consistently found higher odds of accurate positioning for RA-THA versus mTHA, accuracy in achieving targeted center of rotation was mixed, with no differences noted across Crowe I-IV types. Also, studies consistently reported no difference in LLD restoration between RA-THA and CN-THA compared to mTHA. While operative time may be increased when utilizing these platforms, they may also expedite specific intraoperative sequences during THA. These results may assist surgeons in determining whether the benefits outweigh the limitations for RA-THA and CN-THA for specific patients who have DDH, particularly distinguishing Crowe I and II types as achieving more favorable outcomes with utilizing these intraoperative technologies. Likewise, surgeons need to balance component placement accuracy to not only restore proper acetabular inclination, anteversion, and hip center of rotation, but also factor in acetabular coverage for optimal kinematics, stability, and longevity of the implant.

4.1. Potential limitations

This study is not without limitations. Most articles included were retrospective in design and comprised relatively small samples, in which more prospective and higher-powered studies are needed. Also, the study was were unable to assess differences among implants utilized, surgeon experience, and perioperative care regimens due to heterogeneity and lack of reporting. Similarly, due to a lack of reporting, patient reported outcome measures were not able to be evaluated. As some studies only analyzed Crowe types I-IV as a total cohort, the strength of conclusions about the utility of RA and CN platforms for THA per each Crowe type were limited.

4.2. Accuracy of component placement

There were no reported differences in the accuracy of component placement for RA and CN-THA versus mTHA overall, but there was improved accuracy noted for Crowe I and II types with RA or CN-THA compared to mTHA. This benefit noted for Crowe I and II types is likely due to less severe dysplasia, as more dysplastic hips are often deficient with an elongated and shallow shape, contributing to difficulty placing the acetabular cup.^13,29 A common pitfall in conducting THA on dysplastic hips is pursuing the psuedoacetabulum, resulting in a lateral, high, and oversized cup that contributes to prosthetic instability.^30,31 Another explanation may be that cup alignment may change upon screw placement, particularly in more severe hip dysplasia cases, as one study that compared alignments before and after screw placement versus the preoperative target found that cup screw placement eliminated the slight benefit that CN-THA had achieved. This calls for future studies to investigate cup alignment both before and after screw placement to isolate for the effect of technology on accurate cup placement. Therefore, aligning with the findings of this review, Crowe I and II types with less severe dysplasia are likely associated with greater feasibility of obtaining accurate implant positioning.²⁷ This review also found higher odds of accurate positioning in the Lewinnek and Callanan safe zones for RA-THA versus mTHA for all Crowe types. This finding is especially important, as positioning within safe zones is key to mitigate dislocations,³² particularly in patients who have DDH.³³

4.3. Center of rotation achieved

Mitigating deviances from the targeted center of rotation is likely not improved by using RA or CN-THA compared to mTHA, with no differences found when comparing between Crowe types as well. Restoring the hip center of rotation as close as possible to the approximate femoral head center (AFHC) has been shown to improve gait and implant stability, as well as reduce aseptic loosening and cup revision after THA in patients who have DDH.^25,34,35 However, the included studies noted that in addition to approximating the true center of rotation, some cases had a purposeful elevation of the cup center of rotation to also optimize coverage. This contributed to large variations in the actual target and therefore achieved centers of rotation, making the results less clear, as the patients who had THA assisted by technological platforms may have had more cup elevation.^23,25,26 Due to balancing acetabular coverage with achieving the targeted center of rotation in patients who have DDH, the deviance from targeted and achieved COR may be a misleading metric when taken into consideration in isolation of other component placement metrics.

4.4. Leg length discrepancy correction

No differences were found between LLD correction for RA and CN-THA versus mTHA. Restoring the acetabular component positioning is critical in adjusting offset and leg length, especially in patients who have DDH who have subluxation and LLD frequently. As multiple studies noted placing the acetabular component more superiorly than planned to balance acetabular coverage with approximating the true center of rotation,^23,25,26 the impact of these intraoperative changes likely influenced the accuracy of the LLD results. Therefore, other variables that are not directly altered by intentional intraoperative deviations from originally planned targets, may be more of a deciding factor in utilization of RA or CN-THA in patients who have DDH. For example, the only comparative study evaluating RA-THA patient-reported outcome measures (Hospital for Special Surgery Knee Score [HSS] and Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC]) found no difference in improvements at 2-year follow-up compared to mTHA for both Crowe III and IV cases.¹⁹ More data is needed comparing patient-reported outcomes for patients who have DDH specifically between conventional and technology assisted THA. As data for LLD correction are likely confounded, additional variables may help determine whether technology-assisted or conventional methods should be used in performing THA on patients who have DDH.

4.5. Occurrence of intraoperative events and complications

The use of RA or CN-THA compared to mTHA was associated with similar complication rates and blood loss but slightly higher overall operative time. Some studies, however, found no differences in operative time or even a decrease in operative.^25,28 Although increased operative time is typically associated with increased blood loss,³⁶ there was comparable blood loss with RA and CN-THA versus mTHA. This is supported by a recent systematic review comparing RA-THA to mTHA that found similar blood loss between cohorts, despite slightly increased operative times.³⁷ This is likely because while RA and CN-THA involve technically advanced equipment that may require increased time to use, but certain aspects of the procedure can be accelerated, such as the reaming of the acetabulum, which can offset any additional operative time.²⁵

5. Conclusion

This systematic review highlights the benefits of RA and CN-THA in patients who have DDH in the attaining targeted anteversion and inclination values and safe zone placement, while also noting its equivalence to mTHA in achieved accuracy of center of rotation and LLD restoration. This data can assist surgeons in weighing the advantages and drawbacks of utilizing novel platforms patients who have DDH, while also calling for the reporting of patient-reported outcomes in patients who have DDH that underwent RA or CN-THA.

Funding

None.

Ethical committee approval

Ethical approval was waived as our analysis does not contain human data.

Study location

This study was performed at Cleveland Clinic Foundation, Cleveland, OH.

Registration

PROSPERO registration of the study protocol: CRD42023459236, September 13, 2023.

Guardian/patient's consent

No consent was needed as no patients or human data were included in this study.

CRediT authorship contribution statement

Christian J. Hecht: were involved in, Conceptualization, Methodology, Formal analysis, Visualization, Writing – original draft, and, Writing – review & editing. Victoria J. Nedder: were involved in, Conceptualization, Methodology, Formal analysis, Visualization, Writing – original draft, and, Writing – review & editing. Joshua R. Porto: were involved in, Conceptualization, Methodology, Formal analysis, Visualization, Writing – original draft, and, Writing – review & editing. Kerry A. Morgan: were involved in, Conceptualization, Methodology, Formal analysis, Visualization, Writing – original draft, and, Writing – review & editing. Atul F. Kamath: was involved in, Conceptualization, Methodology, Project administration, Formal analysis, Visualization, Writing – original draft, Writing – review & editing, and, Supervision.

Declaration of competing interest

A.F.K. reports the following disclosures: paid presenter or speaker (Zimmer Biomet), paid consultant (Zimmer Biomet, BodyCad, Ortho Development, United Ortho), stock or stock options (Zimmer Biomet, Johnson & Johnson, and Procter & Gamble), IP royalties (Innomed), and board or committee member (AAOS, AAHKS, and Anterior Hip Foundation). CJH, VJN, JRP, and KAM have nothing to disclose.