INTRODUCTION

Total Hip Arthroplasty (THA) is among the most common surgical orthopaedical procedures¹. This procedure was first described in the 60s, with the  introduction of the Charnley low-friction arthroplasty by Sir John Charley². Nowadays, following decades of improvements, this surgery has excellent results in terms of pain improvement and in restoring the function and patient’s range of motion³. THA can be performed by several approaches with the posterior, the direct lateral and the direct anterior being the three most commonly used approaches⁴. 

However, there is evidence that the posterior approach can result in a higher risk of dislocation, especially when soft tissues are not repaired, although there is no high level evidence demonstrating it^5,6. Therefore, in our practise we use the direct anterior approach (DAA) and the modified direct lateral approach (MDLA). The DAA has the advantage of being a truly intermuscular and internervous approach⁷. Thus, its advocates state that it is associated with less postoperative pain and a faster  recovery than its counterparts due to less muscle damage⁸. However, there is contradictory evidence in the literature and meta-analysis have concluded  that there is not sufficient evidence to consider any of the approaches superior to the other^9-12. The DAA is associated with a shorter hospitalization period than the lateral approach, an improved functional rehabilitation and lower pain during the early postoperative period. On the other hand, DAA is associated with a longer surgery time. The 2 approaches have the same rates of perioperative surgical complications and transfusions, as well as similar radiographic results.

Since Lewinnek et al described the “Lewinnek safe zone”, there have been a variety of studies supporting their findings, which state that the  acetabular cup should be positioned in 40°±10° of abduction and 15°±10° of anteversion¹³. Yet, there is a scarcity of data on the influence of the approach on component positioning. It is our belief that, when using the DAA, cup anteversion tends to be higher than that of the DLA.

The objective of this study was to compare the short-term clinical and positioning results after THA performed either by the DAA or the MLDA. Our hypothesis is that the DAA leads to a better functional outcome than the DDA.

METHODS

We conducted a retrospective study in a tertiary care hospital in March 2019. The selected patients were submitted to surgery by the same surgeon, who has 10 years of experience in hip surgery. We do not usually perform the DAA in patients who are either short, obese or have coxa profunda or dysplasia, so, when the proposal to perform a THA is done, the eligibility to a DAA is assessed and registered. Even though, in these patients, a DAA is not always performed. So, for this study, the inclusion criteria were a diagnosis of primary osteoarthritis, eligibility to a DAA approach and at least 24 months of follow-up. Patients were excluded if they had a secondary cause for osteoarthritis (for example, femoral head avascular necrosis) or if they were not deemed eligible to a DAA approach by a combination of factors such as Body Mass Index (BMI) >35, height < 155cm, coxa profunda, dysplasia or coxa vara. The study was approved by the institution’s ethics committee (protocol nº 0468) and informed consent was obtained from all patients.

Surgeries were conducted under general or regional anaesthesia. We perform the DAA in the supine position and start by developing the internervous  plane between the sartorius and the tensor fasciae latae superficially. Subsequently, we dissect the plane between the rectus femoris and the gluteus medius until the capsule is exposed. In the MDLA, done in the lateral decubitus position, we start by developing the Gibson interval between the fascia latae and the gluteus maximus. With the vastus lateralis and the gluteus medius exposed, we divide the anterior forth and the posterior ¾  of gluteus medius muscle fibers with an omega incision¹⁴. We then detach the gluteus minimus from the great trochanter (with preservation of the  piriformis muscle) and expose the articular capsule. Regarding cup positioning, we aim for an acetabular anteversion of 10º and an acetabular abduction of 45º. No drains were used. Tranexamic acid was also not used. Low-molecular-weight heparin (0.4 mL) was administered subcutaneously to all patients 12 hours after the surgery and was continued for 28 days afterwards for antithrombotic prophylaxis.

The patient clinical file was consulted to assess age, sex, weight and height, the hip side intervened, the admission and discharge dates, the last appointment date, complications such as infection, hip dislocation, neurovascular lesions, periprosthetic fracture or prosthetic loosening. The surgical report was also assessed to register the length of surgery, estimated blood loss, haemoglobin drop, red blood cell (RBC) concentrate units used and intra-operative complications such as femoral and/or acetabular fractures and neurovascular lesions. A telephonic interview was done to assess the Visual Analogue Scale (VAS) before and after surgery, satisfaction with the surgery, physiotherapy duration, crutches’ use duration, limb length difference feeling and limping. It was also applied the modified “Harris Hip Score” (mHHS), before and after the surgery, at last follow-up (motion not assessed).

Anteroposterior hip radiographies were consulted by a study author (orthopaedic surgeon) to assess limb length difference, vertical and horizontal  centre of rotation position, lateral acetabular abduction, femoral stem alignment and heterotopic calcification, as described by Vanrusselt et al¹⁵. The acetabular anteversion was calculated using the Lewinnek’s method (Figure 1)^13,16.

Regarding the statistical analysis, continuous variables were presented as the mean (± Std Deviation). To compare them, the t-student or the  Mann-Withney test were used, according to the data distribution. The proportions were expressed for nominal variables. To compare them we used the  Pearson Chi-Square test or the Fisher’s Exact Test, according to the data distribution. A p value less than 0,05 was considered significant. The statistical analysis was done with SPSS version 21, SPSS Inc., Chicago, EUA.

RESULTS

A total of 72 patients that filled the inclusion criteria were identified and included in the study. The study population included 49 men (68,1%) and 23 women (31,9%) and the mean age was 69,9 ± 8,3 (42 - 83) years. The right hip was intervened in 37 (51.4%) patients. In forty-two patients, a DAA was performed whether in the remaining 30 patients, a MDLA was done. Mean follow-up time was of 44.9 ± 13.2 (24 - 71) months.

There were no demographic differences between the 2 groups (Table 1).

The length of surgery was shorter in the DAA group by 17,7 minutes (100,5 ± 3,4 vs 118,2 ± 7,7 minutes (p=0,025)). Surgical complications were not  significantly different between the groups, although they were more frequently seen in the DAA (11.9% vs 6.6%, p=0,203) (Table 2). The only neurovascular lesion occurred in the DAA group and consisted of femoral cutaneous paraesthesias that resolved during the follow-up period.

The length of hospital stay, after excluding outliers, was also significantly shorter by 2,2 days in the DAA group compared to the MDLA group (5,9 ± 0,5 days vs 8,1 ± 0,9 days, p=0,014). Regarding the post-operative follow-up period, results are presented in Table 3. There was only one surgical reintervention, in the DAA group, due to a periprosthetic fracture.

Concerning the post-operative radiographic evaluation, only the acetabular anteversion was significantly different between the approaches (3,2º ± 1,23º (0,75-5,66), p=0,01), with 10,58º ± 4,82º (2 – 21) in the DAA group vs 7,37º ± 5,60º (2 - 19) in the MDLA group. Regarding Lewinnek safe zone, 7 patients in the DAA group (16,7%) had an anteversion of less than 5º, whereas in the MDLA group that happened in 14 patients (46,7%). Acetabular abduction did not significantly differ between the groups. It was higher than 50º in 2 patients (4,7%) in the DAA group (32 - 52º). The other parameters were similar between both approaches (Table 4).

Regarding the follow up telephonic interview, the duration of physiotherapy was significantly shorter within the DAA group compared to the MDLA group (2,9 ± 0,8 vs 7,7 ± 2,8 weeks, p=0,019). The mHHS before and after surgery were not significantly different in both groups (p=0,053 and p=0,923) although, preoperatively, it was higher  in patients submitted to a DAA. Other follow-data is summarized in Table 5. Ninety-six percent of patients report that they would repeat the surgery.

DISCUSSION

THA is a procedure that has a great impact on the patients’ quality of life, a fact that is also made clear with this study that showed a great improvement in patients hip scores. However, there is still debate about whether the surgical approach can influence the results and this study aimed to cover that issue^9,17.

Regarding the surgical procedure, we found a difference in the length of surgery, which was significantly shorter in the DAA group. Several studies, however, show that using the DAA implies a longer surgery as was also our initial belief⁵. This difference was of 17,7 minutes and could be related to the closure time that is shorter in the DAA group. It is our hypothesis that the patients that could otherwise take a long time to be operate on via the DAA, were the ones with advanced and very deformed osteoarthritis that were excluded from the study. So, although the DAA could generally take longer to perform, there is a subset of patients that could benefit the most from this approach, so patient selection seems crucial.

We found no significant difference in the surgical blood loss in both groups. Others studies state that it is hard to exclusively correlate the blood loss with the surgical approach because there are several factors playing a role in fluids loss during surgery, although there are some studies that report less blood loss with the DAA⁵.

Intraoperative fractures can occur during THA and have an important role in the duration of surgery and postoperative mobilization and recovery⁸. The intraoperative fractures were not significantly different between the groups, although they were present more frequently in the DAA approach. Even so, the DAA was found to last less time than MDLA and the patients appear to recover faster. The literature shows that intraoperative fractures occur more commonly around the femoral than the acetabular component, with an incidence between  1,4% and 2,3% in the DAA (11,9% in our study) and of about 4% in the DLA approach (3,3 in our study)^5,15,18-20.

Several studies state that the length of stay is not related to the approach since there are several factors playing a role in the discharge time^21,22. We discharge patients when a sufficient walking autonomy is achieving and there are no complications. In our study, the length of hospital stay was significantly shorter in the DAA group compared to the MDLA group, despite the non-significant higher rate of complications. This could be related to the faster recovery in the DAA group, as a whole, provided by a muscle sparing approach.

The only neurovascular lesion occurred in the DAA group. In this case, it consisted of femoral cutaneous paraesthesia that resolved during  the follow-up period. The main neurovascular complications associated with THA are the lesion of superior gluteal, lateral femoral cutaneous, sciatic  and femoral nerves⁵. Of all of those structures, the superior gluteal nerve is the most commonly injured, especially during DLA, what can be related  with a postoperative limp^5,8,23.

Infection is a relatively uncommon, but a well-known, complication of THA. It has an estimated prevalence between 0,2% and 1,2% that seems to  be higher in revision arthroplasties^24,25. Despite the importance of this complication, there are minimal data comparing infection rates between the several approaches²⁵. In our study, we just had one late infection in the DAA group that corresponds to a prevalence of 1,4%.

Dislocation or loosening are the most common cause of failure in non-infected THA and can be early diagnosed by imagiologic studies even  before the patient relate any pain²⁴. Although there are several studies that don’t report difference of dislocation rates with these approaches, there is  some data that favours DLA, although both of these approaches have low dislocation rates^5,25,26. In our study we found no difference between both groups. We do not perform posterior approaches in this setting because we feel the risk of incomplete soft tissues is higher and can lead to a greater dislocation risk. Interestingly, Abdel et al showed that, although the posterior approach was correlated with a better acetabular positioning than the anterolateral approach, it was associated with an increased risk of dislocation²⁷.

Concerning the radiographic analysis, only the acetabular anteversion was significantly different in both groups, being higher in the DAA group. Although there is a paucity of data concerning the acetabular anteversion variation according to the approach, a study showed a tendency of the same  amount (3º) to antevert the acetabular cup when performing THA using the DAA²⁸. This difference can probably be related with the spatial view within each approach. Finally, although the MDLA group had a greater proportion of patients with a cup anteversion of less than 5º, the minimum observed anteversion was of 2º. This probably happened because we aim for 10º of anteversion, instead of the 15º suggested by Lewinnek, although it does not appear to result in a higher rate of dislocation, especially in an approach that preserves posterior soft tissues. Interestingly, there are some studies that show that most THAs that dislocate are within the Lewinnek safe zone^27,29. The stability of a THA, rather than relying purely on positioning criteria, is an interplay between component positioning, specific patient anatomy and proper restoration of soft tissue tension and balance. Furthermore, acetabular anteversion should not be analysed on its own, as a study by Jolles et al found that only combined femoral and acetabular anteversion could predict dislocation risk and not either on its own³⁰.

Regarding the functional status of the patients in the follow up period, neither the mHHS nor the VAS showed significant differences in both groups,  showing improvement in both groups from baseline³¹. The duration of physiotherapy was significantly shorter in the DAA group, in accordance with several studies that state that the immediate and short-term recovery post-surgery seems to be slightly better with the DAA, what could be related with the lower muscular lesion during the procedure^32-34. This difference between approaches disappears with time with studies showing no difference at 2 years follow up, as was also the case in our study^{5,21,22,34,35}.

Our study had some limitations that need to be addressed. Given the fact that we do not perform the DAA in every patient, this data cannot be applied to every patient, although some group of patients can benefit from it. This was a retrospective study, so it has the inherent limitations in data collection. Some functional scales (VAS and mHHS) were applied retrospectively and are then subjected to recall bias. We did not investigate interobserver or intraobserver reliability when measuring radiographic parameters. Finally, although we mention complications such as prosthetic failure, the primary objective of the study and therefore its design was not made to identify such outcomes whose incidence rises with longer follow-ups.

Concluding, the findings of the present study suggest an advantage of the DAA for THA concerning length of surgery, length of hospital stay and postoperative recovery. Acetabular anteversion seems to be higher with the DAA.

Main Points

• There is no definitive evidence of superiority of a surgical approach in THA over another
• Few studies investigate the influence of surgical approach on acetabular cup positioning
• The anterior approach seems to be associated with a shorter surgery, a shorter hospital stay and shorter physiotherapy duration
• The above benefits of the anterior approach might only be true for a selected group of patients
• Acetabular anteversion seems to be higher with the anterior approach

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