Abstract
Purpose
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Leg length discrepancy (LLD) is a common complication following total hip arthroplasty (THA). The direct anterior approach (DAA) for THA is gaining popularity due to its advantages, but there is limited research on the incidence and size of LLD. This systematic review aims to explore the differences in LLD between DAA and other approaches, as well as the techniques to control LLD in DAA.
Methods
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A comprehensive literature search was conducted to identify relevant studies comparing THA by DAA with other surgical approaches and investigating methods to control LLD in DAA, following PRISMA guidelines and a priori registration on PROSPERO (CRD42023412644). The quality of the included studies was assessed. Data on preoperative and postoperative LLD and other relevant outcomes were extracted and analyzed descriptively.
Results
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In total, 29 studies were included in this systematic review. The majority (86%) were classified as level IV evidence. Comparisons between DAA and posterior approach (PA) or anterolateral approach (ALA) showed DAA had lower rates of LLD >10 mm compared to PA and ALA. Different pre- and intra-operative techniques were evaluated, but no consensus on the best method for preventing LLD in DAA was reached.
Conclusion
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DAA shows comparable or superior results in the prevention of LLD compared to other surgical approaches. Supine patient placement, direct leg measurement, and the use of IF contribute to these outcomes. Intraoperative fluoroscopy with a grid and preoperative planning offers a good option, especially for training purposes, but its role in preventing LLD by experienced DAA surgeons needs further investigation.
Introduction
Leg length discrepancy (LLD) is one of the most frequent complications after total hip arthroplasty (THA) (1). LLD is related to severe dissatisfaction of the patient, causing problems like limping, low-back pain, instability, trochanteric pain, and nerve palsy (2, 3, 4, 5). For these reasons, it is one of the most frequent causes of litigation (6). There is debate over the degree of LLD that is clinically acceptable after THA. While some studies indicate that most patients could tolerate LLD up to 10 mm, others claim that even a slight difference could cause unhappiness (3). In fact, subjective patient dissatisfaction can emerge at different length thresholds, explaining why there are different views in the literature (7, 8, 9).
THA by direct anterior approach (DAA) is gaining increasing popularity among orthopedic surgeons (10) due to the many advantages resulting from the use of an intermuscular approach: decreased bleeding, reduced hospitalization stay, together with lower postoperative dislocation rates, all contributed to its diffusion (11, 12, 13). The possibility of performing the procedure with the patient supine allows the surgeon to rely on natural pelvic anatomic landmarks, helping with the proper positioning of the implants. Moreover, with the patient supine, it is possible to manually verify leg length, whereas when traction tables are used, it is possible to employ fluoroscopy to intraoperatively check for LLD (14, 15).
There is currently plenty of research about functional outcomes between DAA and other surgical approaches, as well as between DAA performed with and without a traction table; however, there is a lack of research examining the differences in the incidence and size of LLD in DAA patients.
On the other hand, several methods have been proposed to ease preoperative and intraoperative measurement of LLD in DAA: preoperative planning with manual or digital systems, the use of navigation systems and robot-assisted surgical techniques, intraoperative fluoroscopy (IF) with or without the grids, and a combination of these.
Despite the variety of applied procedures, there is currently no consensus on a method, and rather it depends on the surgeons’ preference, the type of implants used, and whether radiolucent tables and tractions are used. The main purpose of this systematic review is to explore the differences between DAA and other surgical approaches in the risk to developing LLD. Moreover, the techniques to control LLD and correct component positioning and sizing were compared to answering the following questions: i) Are there any differences in the incidence and size of LLD between DAA, posterior approach (PA) and anterolateral approach (ALA)? ii) Are there any differences in the incidence and size of LLD in DAA with the use of a traction table (DAA-TT) or with a standard table (DAA-ST)? iii) What are the best preoperative and intraoperative techniques and tips to avoid LLD in THA performed by DAA?
Materials and methods
Literature search
This systematic review was a priori registered with the International Prospective Register of Systematic Reviews (PROSPERO) with code CRD42023412644, and we had an agreement detailing our search strategy, inclusion and exclusion criteria, and the data we wished to assess before we started our research. The review process was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.
An extensive search of English journal articles was performed with the terms ‘leg length discrepancy’ OR ‘LLD’ OR ‘leg length inequality’, AND ‘total hip arthroplasty’ OR ‘THA’ OR ‘total hip replacement’ OR ‘THR’, AND ‘direct anterior approach’ OR ‘DAA’ by consulting the major scientific databases such as PubMed/Medline, Scopus, Web of Science, and the Cochrane Library on November 16, 2022. The limit regarding the year of publication was set at 10 years, and all journals were considered. The investigation produced 91 findings after removing duplicates, including case reports, letters, communications, clinical trials, and prospective and retrospective studies. This study included all publications on comparison studies between THA by DAA vs PA, DAA vs ALA, and between the DAA-TT and the DAA-ST. Moreover, all studies regarding the prevention and/or treatment of LLD during THA by DAA in any population group were included as well.
Exclusion criteria included studies on revision total hip replacement, primary hemiarthroplasty, primary THA by the direct lateral approach, and severely dysplastic hip (Crowe III and IV hips) cases. Additionally, cadaveric and/or radiographic-only studies and studies where LLD was not evaluated in the results were excluded. The study design was also an exclusion criterion, as case reports, letters, and communications were not considered in the study.
Two authors (LT, MB) read the abstracts and excluded the articles that were unrelated to the topic of the study. In case of doubt regarding the inclusion of an article, the senior authors (ADM, CF) made the final decision. Based on the year of publication, title, abstract, and study design, 49 articles were excluded.
The full-text version of the remaining articles was obtained. The content of the resulting articles was discussed by all the coauthors and was assessed for their relevance and methodology. Twenty-nine of the studies were considered eligible for inclusion in this review. A PRISMA flowchart was used to summarize the selection procedure of the reviewed papers (Fig. 1).
PRISMA flowchart showing the selection of selected papers for the systematic review.
Citation: EFORT Open Reviews 9, 8; 10.1530/EOR-23-0116
Qualitative assessment
The level of evidence and the quality of the studies included were evaluated using the modified Coleman methodological score (MCMS) by two authors independently (LT, VR).
The MCMS is a tool used to evaluate the methodological quality of clinical trials. It was developed by Coleman et al. in 2000 as an update to the original Coleman Methodological Score. It assesses ten key areas of a clinical trial's methodology, each scored on a scale of 0–2, with a total maximum score of 26. The ten key areas evaluated are: study design, method of patient selection, the definition of inclusion criteria, definition of exclusion criteria, allocation concealment, blinding, outcome measures, follow-up, statistical analysis, and sample size calculation. A score of 0 indicates poor methodology, a score of 1 indicates fair methodology, and a score of 2 indicates good methodology. The total score is then used to determine the overall methodological quality of the trial, with scores of 0–14 considered poor, 15–19 considered fair, and 20–26 considered good (16).
Statistical analysis
The selected studies were analyzed, and the information of interest was extracted into a database created using Microsoft Excel for Microsoft Mac (v16.73, Microsoft). The following data were recorded, if available: number of patients, age, gender, body mass index (BMI), performed surgical approach, use of a traction table and of IF, indications for surgery, preoperative LLD, postoperative LLD, number of LLD <10 mm, LLD >10 mm, and length of follow-up. The extracted data were reported using descriptive statistics. Data with negative numbers were expressed with a minus sign, positive numbers without any sign. Continuous variables were reported as averages and standard deviations. Categorical variables were reported as frequencies and percentages.
Preoperative and outcome measures
The primary evaluated measures were the average preoperative and postoperative LLD and the number of LLD cases up to and above <10 mm.
Results
Search results
The research included 29 papers for review. Among these, nine compared DAA and PA, three regarded DAA and ALA, and four were eligible to compare DAA with a traction table or with a standard table. Sixteen articles were inherent to the preoperative and intraoperative methods to control implant positioning in DAA (with and without a traction table), and these were analyzed systematically as well.
Study quality assessment
Of the 29 articles included in the systematic review, 25 were of level IV of evidence (86%), three of level III (10%), and only one of level I (4%). All articles were published between 2012 and 2022. According to the MCMS score evaluation system, only one study was rated excellent, none were rated good, nine were rated fair, while all the remaining 19 studies resulted poor.
LLD in surgical approaches
DAA vs PA
The studies (17, 18, 19, 20, 21, 22, 23, 24) comparing the DAA and PA included 3937 hips, 2751 THAs performed by DAA (70%), and 1171 by PA (30%) (Table 1). All analyzed studies were retrospective cohort studies except for one randomized clinical trial. These studies reported the results of at least two cohorts of patients, one undergoing THA by DAA and one by PA. Only one study compared DAA with a modified minimally invasive PA according to the SuperPath technique (22). In most cases, the indication for surgery was primary osteoarthritis (6/9; 66.7%). One study focused soley on femoral neck fractures, and two studies included patients with secondary osteoarthritis of the hip (i.e. rheumatoid arthritis and avascular necrosis of femoral head).
Characteristics and findings of included studies comparing DAA and PA.
| Reference/approach | Study design | Indication to surgery | Hips | DAA | PA | Age (years) | Women (%) | BMI | Leg length discrepancy (mm) | |||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Pre-op | Post-op | <10, n | >10, n | |||||||||
| Schwartz et al. (24) | RCS | Primary OA, RA, ANFH, FNF | 412 | 211 | 201 | |||||||
| DAA | 66.3 ± 11 | 62.1 | 29.6 ± 5.9 | −4.4 ± 2.3 | 0.6±6.5 | 27 | ||||||
| PA | 66.6 ± 13.7 | 57.7 | 30.1 ± 6.5 | −4.4 ± 2.5 | 0.9 ± 7 | 27 | ||||||
| Shemesh et al. (15) | RCS | Primary OA, secondary OA to ANFH | 148 | 75 | 73 | |||||||
| DAA | 62.4 ± 13.1 | 59 | 26.6 ± 3.3 | −4.9 ± 4 | 1.3 ± 1.3 | |||||||
| PA | 60.9 ± 15.8 | 62 | 29.8 ± 5.8 | −3.7 ± 3 | 2.5 ± 1.7 | |||||||
| Lin et al. (21) | RCS | Primary OA | 194 | 108 | 86 | |||||||
| DAA | 61.2 ± 12.6 | 58 | 27.8 | 108 | ||||||||
| PA | 60.7 ± 12.2 | 47 | 29.9 | 86 | ||||||||
| Taunton et al. (18) | RCT | Primary OA | 116 | 52 | 49 | |||||||
| DAA | 65 ± 10 | 49 | 29 ± 2.2 | 1 ± 4 | ||||||||
| PA | 64 ± 11 | 49 | 30 ± 4 | 0 ± 6 | ||||||||
| Pujol et al. (17) | RCS | Primary OA | 371 | 187 | 184 | |||||||
| DAA | 64.3 ± 1 | 34 | 26.4 ± 0.3 | 181 | 6 | |||||||
| PA | 65.9 ± 1.1 | 58 | 30.4 ± 0.4 | 169 | 15 | |||||||
| Metzger et al. (23) | RCS | Primary OA | 2452 | 2007 | 445 | |||||||
| DAA | 62.9 | 53.3 | 28.9 | 0.3 ± 2 | ||||||||
| PA | 62,2 | 45.6 | 29.8 | 1 ± 2.1 | ||||||||
| Chung et al. (19) | RCS | FNF | 67 | 36 | 31 | |||||||
| DAA | 78.2 ± 9.4 | 91 | 22.6 ± 2.3 | 1 | ||||||||
| PA | 76.4 ± 6.8 | 83 | 22.2 ± 5.8 | 1 | ||||||||
| Belyea et al. (20) | RCS | Primary OA | 97 | 35 | 62 | |||||||
| DAA | 61 | 33 | 6.7 | |||||||||
| PA | 63 | 80 | 5.7 | |||||||||
| Busch et al. (22) | ||||||||||||
| DAA | RCS | Primary OA | 80 | 40 | 40 | 68.6 ± 8.7 | 60 | 26.1 ± 2.1 | −1.9 ± 4.9 | 4.8 ± 5.6 | ||
| PA | 68.8 ± 8.7 | 77.5 | 25.2 ± 1.8 | −3.2 ± 5.4 | 1.5 ± 5.4 | |||||||
| Total | 3937 | 2751 | 1171 | |||||||||
| DAA | 289 | 34 | ||||||||||
| PA | 255 | 43 | ||||||||||
ANFH, avascular necrosis of the femoral head; BMI, body mass index; DAA, direct anterior approach; FNF, femoral neck fracture; OA, osteoarthritis; PA, posterior approach; RCS, retrospective cohort study; RCT, randomized clinical trial; RA, rheumatoid arthritis.
Regarding LLD, the pre- and postoperative means and s.d. are reported in Table 1. The number of patients with postoperative LLD < 10 mm was 289 (10.5%) in the DAA group and 255 (22%) in the PA group; 34 (1.2%) DAA patients and 43 (3.7%) PA patients had LLD > 10 mm. The average follow-up of the reviewed studies was 7.8 ± 13.4 months.
DAA vs ALA
The studies (25, 26, 27) comparing DAA and ALA included 410 hips, with 217 THAs performed by DAA (53%) and 193 by ALA (47%) (Table 2). Only one study compared DAA with a modified minimally invasive ALA (MIS) (25). All reviewed articles were retrospective cohort studies. In two studies, the indication for surgery was primary osteoarthritis, while in one study, the indication also included osteoarthritis secondary to avascular necrosis of the femoral head (ANFH) and Crowe I dysplasia. The absolute number of patients with LLD > 10 mm was 6 (2.8%) in the DAA group, while 22 (11.4%) were in the ALA group. The average follow-up was 1 ± 1.7 months.
Characteristics and findings of included studies comparing DAA and ALA.
| Study/Approach | Study design | Indication to surgery | Hips | DAA | ALA | Age (years) | Women (%) | BMI | Leg length discrepancy (mm) | ||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Pre-op | Post-op | >10, n | |||||||||
| Debi et al. (26) | RCS | Primary OA | 172 | 78 | 94 | ||||||
| DAA | 64.5 ± 11 | 42.3 | 28.7 ± 4.4 | 0.9 ± 1.4 | 0 | ||||||
| ALA | 64.8 ± 10.3 | 61.7 | 29.2 ± 4.9 | 2.4 ± 3.1 | 2 | ||||||
| Dunn et al. (27) | RCS | Primary OA | 121 | 69 | 52 | ||||||
| DAA | 60.6 | 43.4 | 30 | 4.5 | 6 | ||||||
| ALA | 65 | 61.5 | 30.1 | 7.7 | 20 | ||||||
| Luger et al. (25) | RCS | Primary OA, secondary OA, ANFH, Crowe I dysplasia | 117 | 70 | 47 | ||||||
| DAA | 65.9 ± 11.6 | −3.6 ± 5.5 | 0 ± 4.5 | ||||||||
| ALA | 65 ± 11.3 | −3.7 ± 6 | 1.1 ± 5.1 | ||||||||
| Total | 410 | 217 | 193 | ||||||||
| DAA | 6 | ||||||||||
| ALA | 22 | ||||||||||
ALA, anterolateral approach; ANFH, avascular necrosis of the femoral head; BMI, body mass index; DAA, direct anterior approach, OA, osteoarthritis; RCS, retrospective cohort study.
DAA-TT vs DAA-ST
The comparative studies (28, 29, 30, 31) between DDA with TT and DAA with ST included 929 hips, with 470 performed using the traction table (50.6%) and 459 with the standard table (49.4%). Demographic data e results are reported in Table 3. All reviewed articles were retrospective cohort studies, except one that was a retrospective matched case–control study. In two studies, the indication for surgery was primary osteoarthritis, and two also included secondary osteoarthritis in ANFH patients. All the studies compared one cohort of THA performed by DAA with a traction or extension table versus a cohort of THA with a standard table.
Characteristics and findings of included studies comparing DAA with traction table and DAA with standard table.
| Study/Approach | Study design | Indication to surgery | Hips | DAA-TT | DAA-ST | Age (years) | Women (%) | BMI | Leg length discrepancy (mm) | |||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Pre-op | Post-op | <10, n | >10, n | |||||||||
| Knoth et al. (28) | RCS | Primary OA, ANFH | 324 | 161 | 163 | |||||||
| DAA-TT | 71 (61–77)* | 45 | 27 (25–31)* | 2 (0–4)* | ||||||||
| DAA-ST | 72 (62–78)* | 51 | 28 (25–31)* | 1 (0–3)* | ||||||||
| Wernly et al. (30) | RMCCS | Primary OA | 150 | 75 | 75 | |||||||
| DAA-TT | 70 ± 13.4 | 26 ± 4.7 | 3.7 ± 3.1 | 15 | 2 | |||||||
| DAA-ST | 66 ± 15.2 | 25 ± 4 | 2.4 ± 2 | 8 | 0 | |||||||
| Moslemi et al. (31) | RCS | Primary OA, secondary OA, ANFH | 266 | 137 | 129 | |||||||
| DAA-TT | 65 ± 13.1 | 54 | 25.1 ± 4.8 | −3.5 ± 7.5 | 1.6 ± 7.3 | 0 | 4 | |||||
| DAA-ST | 64.8 ± 14 | 59 | 25.3 ± 5 | −3.5 ± 7.2 | 0.5 ± 6.9 | 6 | 4 | |||||
| Lenze et al. (29) | RCS | Primary OA | 189 | 97 | 92 | |||||||
| DAA-TT | 52.5 | 1.7 ± 4.8 | ||||||||||
| DAA-ST | 51 | 1.8 ± 5 | ||||||||||
*Median (range).
ANFH, avascular necrosis of the femoral head; BMI, body mass index; DAA-TT, direct anterior approach with traction table; DAA-ST, direct anterior approach with standard table; OA, osteoarthritis; RCS, retrospective cohort study; RMCCS, retrospective matched case–control study.
The DAA-TT group reported 15 patients with LLD <10 mm (3.2%) and six above (1.3%); the group of DAA-ST reported 14 cases of LLD <10 mm (3%) and four above (0.9%).
The average follow-up was 12 ± 14.9 months.
How to prevent LLD in DAA
Preoperative planning
Four studies focused on the importance of preoperative planning to predict component malposition and determine LLD (Table 4). Sariali et al. (35) compared the accuracy and clinical relevance of 3D preoperative planning vs conventional 2D templating in THA performed by DAA with a traction table. They found that 3D preoperative planning had higher accuracy compared to 2D templating regarding implant size and positioning; in terms of LLD, the 3D group achieved a higher accuracy compared to the 2D templating group, −1.8 ± 3.6 mm (3D) vs 1.37 ± 6.4 mm (2D), and reporting no LLD > 10 mm in either groups. Lecoanet et al. (33) used intraoperative limb length control based on intraoperative visualization of anatomical landmarks (anterosuperior iliac spine and medial malleoli) in association with 3D EOS imaging software to assess pre- and postoperative LLD in THA by DAA without a traction table. They obtained that 8.9% of patients experienced a symptomatic increase in limb length after the procedure, and 14.2% of patients had a radiographic LLD > 10 mm. Peng et al. (34) used standard AP pelvis radiographs for preoperative planning in association with IF to perform THA by minimally invasive DAA on a standard table. They obtained an average postoperative LLD of 4.4 mm, with 11.5% of patients showing an LLD equal to or exceeding 10 mm. Free et al. (32) used standard preoperative planning with calibrated plain radiographs before surgery and performed DAA on a traction table on 204 hips. They reported a 27% incidence of LLD > 5 mm and found that an increased center-edge (CE) angle was a significant predictor for a postoperative LLD.
Characteristics and findings of the studies regarding the use of preoperative planning to prevent LLD.
| Study | Hips, n | Women, % | Age (years) | BMI | Approach | TT | Primary method | IF assistance (%) | Grid | LOE | Outcome measures | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| LLD, mm | LLD > 10 mm | |||||||||||
| Sariali et al. (35) | 60 | 26.6 | 58.6 ± 14 | 26.4 ± 5.2 | DAA | Yes | Pre-op templating (2D vs 3D) without IF | 0 | NO | III | 3D: −1.8 ± 3.6; 2D: 1.37 ± 6.4 |
None |
| Lecoanet et al. (33) | 56 | 58.9 | 62.8 | 25.8 | DAA | No | Pre-op use of EOS 3D with software calculation | 100 | NO | IV | 14.2% | |
| Peng et al. (34) | 96 | 75 | 70 | DAA | No | Pre-op templating | 100 | NO | IV | 4.4 mm | 11.5% | |
| Free et al. (32) | 204 | 51 | 65.9 | 30.1 | DAA | Yes | Pre-op X-ray and IF | 22.1 | NO | IV | >5 mm: 27% | |
BMI, body mass index; DAA, direct anterior approach; IF, intraoperative fluoroscopy; LLD, leg length discrepancy; LOE, level of evidence; TT, traction table.
Intraoperative fluoroscopy assistance
Most of the reviewed studies focused on the use of IF (Table 5). Hasegawa et al. (41), performed DAA THA with IF and external grids, not performing preoperative templating; they achieved an average postoperative LLD of 2.9 ± 2.2 mm, with no patients experiencing LLD > 10 mm. Thorne et al. (15, 39) compared the results of two types of grids, manual or digital, for THA by DAA using a traction table. The manual grid group showed average postoperative LLD values of 2.9 ± 2.5 mm, with 0.8% of patients experiencing LLD > 10 mm; otherwise, the digital grid group registered an average 3.1 ± 2.5 mm LLD, with 1.1% of patients experiencing LLD > 10 mm. Caus et al. (36) measured LLD with a single IF image and reported a LLD of 2.4 ± 2.1 mm, with 1.2% of patients with LLD > 10 mm. Herrero et al. (38) used real-time fluoroscopic navigation with digital overlay, comparing anteversion, inclination, and leg length after the performance of non-navigated fluoroscopic assisted DAA THA. They found an LLD of 4.5 ± 3.2 mm without fluoroscopic navigation and 1 ± 1.2 mm when navigation with digital overlay was used. Bechler et al. (40) used a software app-based measurement technique to control implant position and leg length. Measurements were made on C-arm screenshots during supine anterior THA. They obtained a postoperative LLD of 0.9 mm (range: −5–6 mm), compared to an intraoperative value of 0.6 mm (range −4 to 5 mm). Dejesus et al. (37), retrospectively evaluated two cohorts of patients undergoing IF-assisted THA by DAA with and without the use of an adjustable grid (AG). They found a postoperative LLD of 3.7 ± 3.4 mm and a LLD > 10 mm in 3.5% of IF-only patients. In the IF AG group, LLD measured 3.2 ± 2.6 mm, with 0.9% of patients showing LLD >10 mm. Thorne et al. (39) compared digital grid and digital overlay to assess component placement in DAA THA, finding a LLD of 3.1 ± 2.3 mm with no LLD > 10 mm when a manual grid was used, and a LLD of 3.3 ± 2.7 mm with 1.6% of LLD > 10 mm when digital overlay was used.
Characteristics and findings of the studies regarding the use of intraoperative fluoroscopy to prevent LLD.
| Study | Hips, n | Women (%) | Age (years) | BMI | Approach | TT | Primary Method | IF assistance (%) | Grid | LOE | Outcome measures | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| LLD (mm) | LLD >10 mm | |||||||||||
| Hasegawa et al. (41) | 304 | 53 | 66.0 ± 10.7 | 26.9 ± 4.6 | DAA | Yes | IF-only, no pre-op templating | 100 | Yes | IV | 2.9 ± 2.2 | None |
| Thorne et al. (15) | 533 | 51 | 66.2 ± 9.8 | 27.2 ± 5.1 | DAA | Yes | IF, digital vs manual grid | 100 | Yes | IV | Digital: 3.1 ± 2.5 | Digital: 1.1% |
| Manual: 2.9 ± 2.5 | Manual: 0.8% | |||||||||||
| Caus et al. (36) | 182 | DAA | Yes | IF with single image only | 100 | No | IV | 2.4 ± 2.1 | 1.2% | |||
| Herrero et al. (38) | 75 | 61,3 | 65.7 ± 9.1 | 27.2 ± 5.2 | DAA | No | IF, navigation (overlay software) vs no navigation | 100 | Yes | IV | No navigation: 4.5 ± 3.2 | |
| With overlay: 1 ± 1.2 | ||||||||||||
| Bechler et al. (40) | 93 | 71 | 65.2 ± 9.6 | DAA | Yes | IF and IPad-app software | 100 | No | III | Intra-op: 0.6 (−4 to 5) | ||
| Post-op: 0.9 (−5 to 6) | ||||||||||||
| DeJesus et al. (37) | 784 | 51,7 | 66.1 ± 11.3 | 27.2 ± 5.2 | DAA | Yes | IF with and without grid | 100 | Yes | IV | No grid: 3.7 ± 3.4) | No grid: 3.5% |
| With grid: 3.2 ± 2.6 | With grid: 0.9% | |||||||||||
| Thorne et al. (39) | 534 | 50,6 | 66.2 ± 9.6 | 27.1 ± 5.3 | DAA | Yes | IF, manual vs digital overlay | 100 | Yes | IV | Manual: 3.1 ± 2.3 | Manual: 0% |
| Overlay: 3.3 ± 2.7 | Overlay: 1.6% | |||||||||||
BMI, body mass index; DAA, direct anterior approach; IF, intraoperative fluoroscopy; LLD, leg length discrepancy; LOE, level of evidence; TT, traction table.
Robotic assistance and handheld navigation
Stewart et al. (42) used robotic assistance to perform THA by DAA and compared patients with an IF-assisted control group. They showed a difference between pre- and postoperative LLD of 3.8 ± 3.1 mm with the use of IF and LLD of 3.8 ± 2.9 mm in the robotic group. Kolodychuk et al. (43) used a handheld navigation system to estimate the intraoperative accuracy of acetabular component placement and postoperative leg length and offset. They observed an LLD of 3.4 ± 3.3 mm and a LLD > 10 mm in 5% of IF-assisted DAA THA cases, and 1.6 ± 1.7 mm and no LLD > 10 mm in the group of patients using navigation (Table 6).
Characteristics and findings of the studies regarding the use of robotic assistance and handheld navigation system to prevent LLD.
| Study | Hips, n | Women,% | Age(years) | BMI | Approach | TT | Primary method | IF assistance (%) | Grid | LOE | Outcome measures | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| LLD (mm) | LLD > 10 mm | |||||||||||
| Stewart et al. (42) | 200 | 57 | 60.4 ± 7.7 | 30.2 ± 5.5 | DAA | No | IF vs robotic assistance | 50 | No | IV | IF only: 3.8 ± 3.1 | |
| Robotic: 3.8 ± 2.9 | ||||||||||||
| Kolodychuk et al. (43) | 159 | 50.9 | 64.1 ± 10.8 | 26.8 ± 5.2 | DAA | Yes | IF vs handheld navigation system | 50 | No | IV | Conventional: 3.4 ± 3.3 | Conventional: 5% |
| Navigation: 1.6 ± 1.7 | Navigation: 0 % | |||||||||||
BMI, body mass index; DAA, direct anterior approach; IF, intraoperative fluoroscopy; LLD, leg length discrepancy; LOE, level of evidence; TT, traction table.
Discussion
In recent years, DAA for THA has grown in popularity (44). Shorter hospital stays, a higher percentage of patients being sent home after discharge, and better immediate postoperative results are all considered to be related to its muscle-sparing principles. Overall, conventional techniques for THA are not associated with higher complication rates (45).
DAA patients may perform early postoperative functional rehabilitation and show reduced levels of subjective pain and shorter hospital stays, according to a recent meta-analysis comparing DAA with other approaches (46). The failure of fixation, instability, and damage to soft tissues caused by trauma associated with surgery are some of the causes of postoperative pain, which prevents patients from returning to full function and activity, according to the network meta-analysis by Putananon et al. (47), that compared all the surgical approaches for THA. The positioning of the acetabular cup and the postoperative LLD, crucial for assessing the success of the surgical technique, were less emphasized in their report. Therefore, due to the lack of evidence, it seems important to study the extent and incidence of LLD among surgical approaches, a complication that has become increasingly prominent for both patients and orthopedic surgeons.
It is important to consider an important limitation of this systematic review: the studies analyzed were all retrospective cohort studies, except for one randomized clinical trial. This type of study design carries some limitations, including potential selection bias and confounding variables. Additionally, the relatively short follow-up period may not accurately reflect the long-term outcomes and complications.
Are there any differences in the incidence and size of LLD between the DAA, PA, and ALA?
In the majority of cases, studies comparing DAA vs PA were performed for primary osteoarthritis, with some patients being operated on for femoral neck fracture or secondary osteoarthritis due to other diseases. DAA had a lower incidence of LLD > 10 mm, with only 1.2% of cases compared to 3.7% for PA. It is important to note that in the study where a comparison was performed in THA after FNF (19), no preoperative LLD assessment or preoperative planning was performed, unlike the remaining studies taken into consideration (67 hips out of 3927, approximately 1.7% of the total).
Smaller numbers were instead taken into consideration in studies comparing DAA vs ALA. Another possible bias in the comparison is given by the presence of a study comparing a minimally invasive variant of ALA vs DAA (25), where only the mean pre- and postoperative LLD was taken into account, but not the number of LLD > 10 mm. The incidence of LLD > 10 mm was 11.4% in ALA compared to 2.8% in DAA patients. However, the average follow-up period was relatively short (1 ± 1.7 months).
Several meta-analyses evaluating the results and complications of direct anterior and posterior methods for THA have been reported in recent years (46, 48, 49, 50, 51, 52). However, they were not designed to test differences in LLD. A recent study (53), however, explored differences in primary instability between DAA and PA, but it did not show significant differences in terms of dislocation rate, cup inclination or anteversion, or in LLD among the groups.
Overall, the results of the current study suggest that DAA may be associated with a lower incidence and smaller entity of LLD when compared to PA. When compared with ALA, DAA appeared more reliable, although these results are not comparable with other studies available in the literature.
Are there any differences in the incidence and size of LLD in DAA with the traction table (DAA-TT) and DAA with the standard table (DAA-ST)?
The results show that the incidence of LLD <10 mm was similar between the two groups (3.2% for DAA-TT and 3% for DAA-ST), while the incidence of LLD >10 mm was slightly higher in the DAA-TT group (1.3%) compared to the DAA-ST group (0.9%). Other secondary outcomes were evaluated in the only systematic review on DAA THA with and without a traction table performed by Sarraj et al. (54), which showed similar outcomes and complications between the two techniques. Unfortunately, the study did not assess LLD among the groups. Overall, DAA with a traction table has similar outcomes in terms of absolute LLD and LLD > 10 mm.
What are the best preoperative and intraoperative techniques to avoid LLD in THA by DAA?
Several methods have been reported to prevent LLD during THA by DAA. These include methods related to preoperative planning, those related to IF assistance with or without the use of a grid or navigation system, and those related to robotic assistance or handheld navigation. An algorithm is therefore proposed, collecting the resulted procedures from this review, in order to minimize the incidence of LLD in the DAA (Fig. 2).
Algorithm showing currently suggested techniques to avoid LLD in the DAA.
Citation: EFORT Open Reviews 9, 8; 10.1530/EOR-23-0116
Preoperative planning is routinely performed by orthopedic surgeons, utilizing software with digitally or analogically calibrated X-rays. Within these categories, planning methods may differ in terms of the type of X-ray projections, calibration, rulers, and anatomical measurements (i.e. LLD, center of rotation of the hip) (55). In DAA, 3D methods appeared to be slightly more reliable than the 2D methods, but the incidence of patients with LLD > 10 mm was substantially similar. In fact, 3D with EOS software (EOS image Inc., France) recorded a 14.2% of LLD >10 mm compared to 11.5% of preoperative 2D planning combined with IF.
Intraoperative fluoroscopic assistance during surgery is widely used during THA, independently from the surgical approach (56). It is a cost-effective solution, and it is useful when direct measurement of the legs cannot be performed when these latter are bound to a traction table. The major shortcoming of this method is the exposure to radiation and the lengthening of the surgical time. In DAA, methods involving the use of IF can be further subdivided into those without and with a calibrated grid (manual or digital integrated into the machine software). Digital and navigation systems have contributed to improving the reliability of IF: considering the inevitable vertical distortion of this method, they reached an average combined distortion of 10 mm (57). Although they can achieve higher levels of accuracy, this method did not show significant differences from manual or IF-only systems.
The most recent technologies implemented in clinical practice are represented by surgical robots and handheld navigation systems. These show very high levels of accuracy and rely on careful preoperative planning, but they require expensive equipment and a non-negligible learning curve for the technique. They are becoming increasingly popular among orthopedic surgeons and appear to offer accuracy over traditional IF systems, helping to reduce radiation dose and time. However, long-term results in terms of reliability, LLD reduction, cost-effective analysis, and their effect on revision surgery rates at follow-up are yet to be demonstrated.
Conclusion
In terms of size and incidence of LLD, DAA is associated with results similar to or better than the other surgical approaches, both in conventional and minimally invasive surgery. Supine patient placement with direct measurement of LLD and the use of IF may contribute to these results. The use of a traction table in DAA is not associated with poorer outcomes in terms of LLD. Given the variability of surgical techniques used to perform DAA, there is currently no superiority of one method over the others in controlling LLD. This rather depends on traction, software, imaging technology available at the individual orthopedic center, and in most cases, the surgeon's experience. IF with the use of a grid in association with standard digital preoperative planning represents a promising, affordable method in terms of reliability and economic sustainability: it could be used to support the learning curve of young surgeons, but its role in prevention of LLD by skilled hip surgeons at the end of the learning curve of DAA is yet to be demonstrated.
ICMJE Conflict of Interest Statement
The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of this review.
Funding Statement
This work did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.
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