1 Introduction

Total hip arthroplasty (THA) is widely recognised as one of the most effective and frequently performed procedures in orthopaedic surgery, reliably providing pain relief, restoring joint function, and improving quality of life in patients with advanced degenerative hip disease.¹ Over the past decade, the direct anterior approach (DAA) has gained increasing popularity, largely due to its utilisation of a true intermuscular and internervous plane. This muscle-sparing technique minimises soft-tissue disruption and has been associated with reduced early postoperative pain, faster functional recovery, and earlier mobilisation compared with traditional posterolateral or anterolateral approaches.²

Despite the growing adoption of the DAA, controversy remains regarding optimal patient positioning during surgery. The approach may be performed with the patient in either the supine (S-DAA) or lateral decubitus (L-DAA) position, each offering distinct technical advantages and limitations.³ Supine positioning is traditionally favoured due to improved intraoperative assessment of leg length, facilitated use of fluoroscopy, and reduced risk of pelvic tilt, potentially enhancing the accuracy of component positioning. However, S-DAA typically requires specialised traction or extension tables and may limit femoral exposure, particularly during the early learning phase of the approach, potentially increasing technical difficulty and complication risk.⁴

Conversely, L-DAA can be performed on a standard operating table and may improve access to the proximal femur through gravity-assisted soft-tissue retraction, which may be particularly advantageous in patients with larger body habitus. Lateral positioning may also be familiar to surgeons accustomed to lateral-based posterior or anterolateral approaches and may facilitate femoral preparation. However, concerns persist regarding pelvic stability, variability in pelvic tilt/rotation, and reduced reliability of fluoroscopic assessment, which may influence apparent acetabular orientation and the assessment of leg length and offset when compared with S-DAA.⁵

However, the available literature reports inconsistent findings regarding the influence of patient positioning on outcomes.^6,7 Some authors advocate supine positioning for improved radiographic precision, particularly when fluoroscopy is used, whereas others report comparable clinical outcomes between positions. Interpretation of these findings is limited by small sample sizes, heterogeneity in surgical technique and imaging protocols, and the predominance of retrospective study designs. Comparisons are further confounded by differences in table type, use of fluoroscopy or navigation, implant systems, and surgeon experience, all of which may influence intra-operative workflow, femoral exposure, and complication risk independent of patient position. To date, only a single prospective randomised controlled trial comparing L-DAA and S-DAA has been published,¹ and the absence of robust pooled evidence contributes to ongoing uncertainty regarding the optimal positioning strategy.

This systematic review and meta-analysis aimed to compare clinical, radiographic, and perioperative outcomes of L-DAA and S-DAA in primary THA. We hypothesised that clinical outcomes would be comparable, and that any observed differences would relate primarily to operative workflow (femoral exposure, table setup) and the reliability of intra-operative measurement strategies (fluoroscopy/navigation), rather than consistent differences in final component positioning.

2 Methods

3 Results

3.1

3.1 Study selection and characteristics

A total of 126 records were identified, with 47 duplicates removed, leaving 79 records for title and abstract screening. Of these, 71 studies were excluded and 8 full-text articles were assessed for eligibility. Reasons for full-text exclusion are presented in Fig. 1. Five studies met the inclusion criteria and were included in the final systematic review and meta-analysis.

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Fig. 1 Prisma diagram.

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The 5 studies^1,3,11–13 included in this systematic review comprised one prospective double-blinded randomised controlled trial and four retrospective comparative cohort studies, analysing a total of 375 hips (189 L-DAA, 186 S-DAA). Outcomes were reported and analysed at the level of hips rather than patients in most studies. Sample sizes ranged from 39 to 89 hips, with mean age between 56.9 and 72.3 years. Body mass index (BMI) was reported in four studies and varied between groups, with the highest mean BMI observed in the lateral decubitus cohort reported by Zhao et al. Reporting of sex distribution was inconsistent, with male representation ranging from 2.1% to 79%. All studies evaluated primary THA performed for degenerative hip disease or avascular necrosis. Follow-up ranged from 3 months to a mean of 45 months, with one study not reporting duration. Surgical technique and imaging varied across studies: S-DAA was typically performed using specialised traction or radiolucent tables with intraoperative fluoroscopy, whereas L-DAA was performed on a standard table with variable imaging use. Lateral positioning was reported to facilitate femoral exposure, while supine positioning was favoured for pelvic stability and intraoperative leg length assessment. Study characteristics are summarised in Tables 1 and 2.

Table 1 Characteristics of included studies comparing lateral decubitus versus supine positioning for direct anterior approach total hip arthroplasty.

Study (Year)	Design	N hips (L-DAA/S-DAA)	Mean Age Years (L-DAA/S-DAA)	Mean BMI (L-DAA/S-DAA)	Gender % Male (L-DAA/S-DAA)	Follow-up
Xiao et al. (2022)	Prospective, Double-blinded, Randomized Clinical Trial	36/54	56.9/57.5	23.4/24.0	67/56	Mean 10.9 months (Range 6–14 months)
Chen et al. (2023)	Retrospective Comparative Study (Fluoroscopy-Guided)	38/38	63.5/62.3	23.1/22.9	50/45	3 months post-op for HHS
Maeda et al. (2015)	Comparative Study (CT-based Navigation, Mechanical Guide)	47/34	63.1/61.6	22.9/22.7	15/2.1	Not reported on clinical follow-up
Rogers et al. (2022)	Retrospective Cohort Study	22/17	63 across both groups	Unspecified	79 across both groups	Average 45 months (Range 17–81 months)
Zhao et al. (2021)	Retrospective Comparative Study	46/43	72.3/71.9	29.8/24.7	52.2/21.2	Mean 15.6 months (Range 8–23 months)

Table 2 Summary of positioning techniques, intra-operative imaging methods, and reported advantages and disadvantages of supine and lateral decubitus direct anterior approach total hip arthroplasty.

Study	Group	Positioning & Equipment Used	Intra-operative Imaging/Guidance Method	Pros (Authors' Findings)	Cons (Authors' Findings)
Rogers et al. (2022)	S-DAA	Medacta™ traction table; leg manipulated via hydraulic arm.	Intra-operative C-arm fluoroscopy.	Allows visualization of anatomy and implant position.	Higher rate of intra-operative fractures; requires specialised table and radiographer.
	L-DAA	Standard operating table; lateral decubitus clamps.	None (Manual checks & pre-op planning).	Familiar position; uses existing implants; no specialised table/radiographer needed.	Requires a third assistant to hold the leg.
Zhao et al. (2021)	S-DAA	Supine; operative leg placed under non-operative leg for exposure.	Visual comparison (Direct visualization of limb lengths).	Fixed pelvic position allows accurate direct comparison of leg lengths.	Harder to expose proximal femur; higher rate of femoral fracture; limited in obese patients.
	L-DAA	Lateral decubitus.	Intra-operative fluoroscopy (Used to measure LLD based on landmarks).	Shorter op time; less blood loss; easier femoral exposure (gravity retracts tissue).	Fluoroscopic landmarks are less accurate for comparing leg length than direct vision.
Chen et al. (2023)	S-DAA	Supine on radiolucent table.	Intra-operative C-arm fluoroscopy.	Higher accuracy and consistency in component positioning (LLD, offset, inclination).	No significant difference in long-term function compared to L-DAA.
	L-DAA	Lateral decubitus with hammered sacral/pubic positioners.	Intra-operative C-arm fluoroscopy.	N/A (Comparative study focused on S-DAA accuracy).	Significant discrepancy between intra-op fluoro and post-op measurements due to pelvic shift.
Xiao et al. (2022)	S-DAA	Supine.	Not explicitly specified (Discussion notes C-arm is facilitated/accurate in this position).	More reliable/consistent pelvic positioning; easier anesthesia.	Longer operative time; higher incidence of complications.
	L-DAA	Lateral decubitus.	Not explicitly specified.	Lower complication rate; gravity aids soft tissue retraction.	Pelvic orientation changes more severely than in supine.
Maeda et al. (2015)	S-DAA	Supine on horizontal table.	Mechanical cup alignment guide (Verified with CT-based navigation).	No difference in cup angle accuracy compared to lateral position when using mechanical guide.	Pelvis extension and rotation increased during cup procedures (instability similar to lateral).
	L-DAA	Lateral decubitus; trunk along longitudinal axis.	Mechanical cup alignment guide (Verified with CT-based navigation).	No difference in cup angle accuracy compared to supine.	Cup anteversion was significantly larger than the target angle.

3.2

3.2 Outcomes

3.2.1

3.2.1 Functional outcomes

Three studies (255 hips)^1,3,11 reported Harris Hip Score (HHS) at one month. Pooled analysis demonstrated no significant difference between lateral and supine positioning (MD −0.39; 95% CI −1.41 to 0.63; I² = 0%) (Fig. 2). At final follow-up (3-6 months), results remained comparable (MD −0.61; 95% CI −1.97 to 0.76; I² = 15%) (Fig. 3). Other patient-reported outcome measures (PROMs), including the Oxford Hip Score, WOMAC, SF-12, and VAS, were not pooled due to inconsistent reporting timepoints and incomplete availability across studies. Nevertheless, individual studies similarly demonstrated comparable functional outcomes between groups across these measures (Xiao et al.; Zhao et al.; Rogers et al.). Chen et al. reported a transient early difference favouring supine positioning at one week; however, this difference was not sustained at subsequent follow-up.

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Fig. 2 Harris hip score at 1 Month postoperatively.

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Fig. 3 Harris hip score at final reported follow-up.

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3.2.2

3.2.2 Radiographic outcomes

Four studies^1,3,11,12 evaluated radiographic parameters, including acetabular cup inclination/anteversion and measures of biomechanical reconstruction (LLD and offset). Quantitative pooling was not performed because studies used heterogeneous imaging modalities (plain radiographs, intra-operative fluoroscopy, CT-based navigation) and non-uniform measurement definitions and units; radiographic findings were therefore synthesised descriptively. Final postoperative cup inclination and anteversion were broadly comparable between L-DAA and S-DAA across studies, including the CT-validated navigation study by Maeda et al. In fluoroscopy-guided cohorts, differences were more apparent in measurement reliability, defined as agreement between intra-operative fluoroscopic estimates and postoperative measurements. Chen et al. reported no significant discrepancy in the supine group, whereas the lateral group demonstrated significant discrepancies for inclination (P < 0.001) and anteversion (P = 0.009). Findings for restoration of LLD and offset were mixed: Chen et al. and Zhao et al. reported smaller absolute postoperative discrepancies in supine cohorts, while Rogers et al. and Xiao et al. reported no significant between-group differences.

3.2.3

3.2.3 Length of hospital stay

Three studies^1,3,12 reported length of hospital stay, including 218 hips. Pooled analysis demonstrated no significant difference between L-DAA and S-DAA (MD −0.30 days; 95% CI −1.09 to 0.48; P = 0.45), with moderate heterogeneity (I² = 38%) (Fig. 4).

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Fig. 4 Length of hospital stay.

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3.2.4

3.2.4 Positioning advantages and disadvantages in either the supine or lateral position

Across included studies, operative setup and imaging strategies differed between S-DAA and L-DAA (Table 2). S-DAA was commonly performed using traction or radiolucent tables, frequently with intra-operative fluoroscopy or alignment guides. Authors reported that this setup facilitated pelvic stabilisation and intra-operative assessment of leg length and component orientation, but several cohorts described increased technical difficulty with femoral exposure and reported intra-operative femoral complications in the supine group. L-DAA was generally performed on a standard table with variable use of fluoroscopy. Authors reported improved femoral exposure attributed to gravity-assisted retraction, and some cohorts reported shorter operative time and reduced blood loss. In fluoroscopy-guided lateral cohorts, greater variability in pelvic orientation and discrepancies between intra-operative estimates and postoperative measurements were reported.

4 Discussion

This systematic review and meta-analysis suggests that patient positioning during DAA THA is not associated with clinically meaningful differences in short-to mid-term functional recovery. Pooled analyses of Harris Hip Score at one month and at final follow-up demonstrated no between-group differences between S-DAA and L-DAA, consistent with the randomised trial by Xiao et al.¹ and comparative cohort data, including Rogers et al..¹² Similar conclusions have been reported in broader THA positioning literature across multiple approaches, where clinical outcomes and length of stay were generally comparable between supine and lateral positioning.^6,14 However, confidence in these estimates remains limited by the small number of studies and the predominance of non-randomised cohorts at serious-to-critical risk of bias; accordingly, findings are best interpreted as supportive of clinical equivalence rather than superiority.

Radiographic findings were more heterogeneous and could not be pooled due to substantial differences in imaging modality, measurement technique, and reporting units. Across studies, final postoperative acetabular inclination and anteversion were generally comparable between positions^12,13 suggesting that acceptable component orientation can be achieved with either setup in experienced hands. Differences were more apparent in the reliability of intra-operative measurement, particularly when fluoroscopy was used. In the fluoroscopy-guided study by Chen et al., intra-operative fluoroscopic estimates more closely agreed with postoperative measurements in the supine group, whereas larger discrepancies were observed in the lateral group for both inclination and anteversion.¹¹ Similarly, restoration of LLD and offset was reported as more accurate in some supine cohorts,^3,11 although other studies found no between-group differences. These observations align with the concept that pelvic stabilisation and control of pelvic tilt/rotation may influence fluoroscopic landmark fidelity and thereby the consistency of intra-operative assessment.⁶ Importantly, Maeda et al. reported comparable accuracy between positions when using a mechanical alignment guide verified with CT-based navigation,¹³ suggesting that the intra-operative reference method and pelvic control may be more influential than patient position alone.

A critical consideration is confounding by operative platform and surgeon experience. In the included literature, patient position was closely linked to table type (traction/radiolucent versus standard), imaging strategy (fluoroscopy versus navigation or none), and surgeon workflow, all of which may independently affect exposure, operative time, and complication profiles.¹⁵ Furthermore, the DAA learning curve-particularly for femoral preparation and avoidance of intra-operative femoral events-may differ depending on whether surgeons adopt S-DAA with traction tables or perform L-DAA on a standard table..^7,16 These factors are difficult to adjust for using aggregate data and likely contribute to between-study variability.

Peri-operative differences between positioning strategies reflected predictable technical trade-offs. L-DAA was frequently associated with improved femoral exposure, plausibly related to gravity-assisted soft-tissue retraction and limb maneuverability, and some cohorts reported shorter operative time and reduced blood loss.³ In contrast, S-DAA may facilitate pelvic stabilisation and fluoroscopic assessment of leg length and component orientation,^11,17,18 but femoral exposure may be more constrained, particularly early in the learning curve. Consistent with this, intra-operative femoral complications were reported more often in some supine cohorts,^3,12 although interpretation is limited by confounding and selection bias. Overall, the available evidence supports that both strategies can be performed safely when surgeon experience, table setup, and intra-operative referencing are optimised.¹⁹

This review has several limitations. First, the evidence base is small (one RCT and four retrospective cohorts) with modest sample sizes and variable follow-up, limiting precision and precluding robust subgroup analyses. Second, multiple cohorts were judged at serious-to-critical risk of bias, primarily due to confounding and selection bias, which limits causal inference regarding position as an independent determinant of outcome. Third, outcomes were frequently reported per hip rather than per patient, and potential within-patient correlation could not be accounted for using aggregate data. Fourth, PROMs beyond HHS and several complication outcomes were inconsistently reported by timepoint, limiting quantitative synthesis. Finally, radiographic outcomes were measured using heterogeneous modalities and definitions (fluoroscopy, radiographs, CT/navigation), precluding pooling and reducing comparability. Publication bias cannot be excluded; formal assessment was not feasible given the small number of studies. Accordingly, the certainty of evidence supporting equivalence between S-DAA and L-DAA should be interpreted as moderate for functional outcomes and low for radiographic and perioperative outcomes.

Despite these limitations, the consistency of functional outcomes across studies suggests that patient positioning during DAA THA does not materially influence early clinical recovery. In practice, both S-DAA and L-DAA can be performed effectively, with position selection guided by surgeon experience, patient anatomy, and available resources. Supine positioning may offer advantages when fluoroscopy or navigation is utilised, whereas lateral positioning may facilitate femoral exposure and operative efficiency in selected patients.²⁰ Importantly, the benefits of supine positioning are closely linked to the availability of specialised traction tables and intra-operative fluoroscopy, which may not be universally accessible across healthcare systems. In such settings, performing the DAA in the lateral decubitus position on a standard operating table may represent a pragmatic alternative, offering improved femoral exposure without compromising postoperative functional outcomes.

Future research should prioritise adequately powered multicentre randomised trials with standardised operative platforms (table type), imaging protocols, and radiographic definitions. Key endpoints should include radiographic outliers using consistent measurement methodology, complications (particularly intra-operative femoral events and dislocation), validated PROMs across uniform follow-up intervals, and longer-term outcomes such as revision risk and implant survivorship.

5 Conclusion

Available comparative evidence suggests that direct anterior approach total hip arthroplasty performed in either the lateral decubitus or supine position yields similar short-to mid-term functional outcomes and length of hospital stay. Radiographic component orientation appears broadly comparable between positions; however, when fluoroscopy is utilised, supine positioning may provide more consistent intra-operative measurement agreement, whereas lateral positioning may facilitate femoral exposure and operative efficiency in selected patients. Given the limited number of available studies and the predominance of retrospective cohort designs, these findings should be interpreted as supportive of clinical equivalence rather than superiority. In practice, patient positioning during DAA THA should therefore be individualised according to surgeon experience, operative setup, and available resources.

Guardian/patient's consent

Not applicable.

Ethical considerations

Not applicable.

Consent for publication

Not applicable.

Credit author information

Dimitrios Nikos: Conceptualization, Methodology, Investigation, Visualization, Writing – original draft, Writing – review & editing.

Nicholas Dominguez: Conceptualization, Methodology, Data curation, Formal analysis, Investigation, Writing – original draft, Writing – review & editing.

Christopher Wilson: Supervision, Methodology, Writing – review & editing.

Ethical statement

Ethical approval was not required for this study as it is a systematic review and meta-analysis of previously published studies.

Funding statement

The author(s) received no financial support for the research, authorship, and/or publication of this article.