1. Introduction
Total hip arthroplasty (THA) is perceived as the most effective treatment for end-stage hip osteoarthritis (OA). It can be performed through a number of different approaches, including, direct lateral (LA; Bauer), posterior (PA; Kocher-Langenbeck), posterolateral (PLA; Gibson-Moore), anterolateral (ALA; Rottinger), and direct anterior (DAA; Smith-Petersen; Hueter, Matta) [
1,
2]; however, the superiority of a surgical approach over the others for THA performance is a controversial issue. DAA for THA has gained popularity over the last few years [
3,
4,
5,
6,
7,
8,
9].
Carl Hueter described the use of the interval between the tensor fasciae latae and the sartorious muscle to gain access to the hip joint in his 1817 German manuscript “Der Grundriss der Chirurgie [
10]”, to manage war injuries and infectious diseases of the femoral head. Smith-Petersen popularized the approach throughout the English-speaking scientific community after describing its use for the open reduction of congenital dislocation of the hip, in 1917.
The modern anterior minimally invasive surgical approach, or AMIS, (Medacta, Switzerland) was developed by F. Laude in 90′ in Paris [
6]. This technique was brought and further modified later on in the United States by Matta [
2]. The modern anterior minimally invasive surgical approach could require the use of a traction table and dedicated instrumentation with curved retractors, off-setted handles for acetabular reaming and cup implantation, and curved handles for femoral preparation and stem implantation, designed to minimize the extension of the surgical exposure for THA performance through DAA. The evolution in instrumentation was parallel to the evolution of the design of implants; a short corail-type stem has been proposed [
11,
12]. More recently, this surgical technique has been described for difficult cases once considered less suitable to it [
13,
14].
The aim of this retrospective study was to analyze the clinical and radiological outcomes of a series of 1000 consecutive THAs performed by a modified minimally-invasive DAA in a single high volume center between 2012 and 2017, (1) to determine survival at a minimum 5 year follow up, (2) to evaluate radiological and clinical outcomes, and perioperative complications.
4. Discussion
The most important findings of the study were a 7-year survival of 95.3% and a rate of revision surgery during follow up of 2.3%. The overall complication rate both intra- and postoperatively was 9.4% with neuroapraxia of the LFC nerve and implant dislocation being the two most common.
Several limits of the current study should be acknowledged. First and most important, being the current study a report of the first 1000 implants, surgeons were at the beginning of their practice and learning curve; therefore, a higher rate of complications could be observed; however, this is consistent with the real practice of orthopedic surgeons. Moreover, the study cohort was extremely heterogeneous, still representing a good sample of the surgical population commonly referring to an orthopedic surgeon.
DAA for THA has gained popularity among hip surgeons in recent years; however, surgeons still fear the learning curve [
19], which was estimated to be between 50 and 100 surgeries [
20].
In order to assess the outcomes of DAA in a high-volume orthopedic center in terms of survival, causes of failures, intraoperative complications, and radiographic outcomes, the current study reports on the first 1000 consecutive THAs carried out using uniform surgical technique and implants. When the study’s enrollment concluded in 2017, DAA was used to treat primary and secondary hip osteoarthritis, as well as femoral neck fractures, in the great majority of cases (98% of all primary THA implants). Prior to 2012, every senior surgeon in the department had received extensive education in posterolateral or direct lateral approaches to the hip. Starting in 2012, their whole DAA learning curve was covered by the current study.
Abundance of scientific literature about the risks and benefits of DAA pushed towards the implementation of DAA at the Authors’ institution. Indeed, many studies showed that early postoperative functional recovery was faster [
21] when compared to other approaches [
22,
23], recognizing that after a few months the differences in functional recovery disappear [
24,
25]. In fact, in the prospective randomized clinical study by Barrett et al. [
24], THAs performed by DAA and PL approach were compared, and they showed how post-operative recovery was faster with DAA in the first 6 weeks after surgery, although differences completely disappeared at 6 months. Moreover, a lower incidence of bleeding, reduced physical therapy and hospitalization time were demonstrated when DAA was compared to PL and DL approaches [
26,
27,
28,
29].
We assessed implant survival, reasons for failure, and radiographic and clinical outcomes with a minimum of five years of follow-up, concentrating our investigation on both early and long-term outcomes. Lower than earlier findings, the overall failure rate in the current study that necessitated reoperation was reported to be 2.3%. An analysis of the DAA results was subsequently conducted on a comparable cohort of 1329 hips. Aggarwal et al. [
30] conducted a retrospective cohort study comparing the five techniques utilized for THA at their institution (PL, DAA, DL, AL, and Northern). Comparable but higher than our findings (2.3%), they discovered that DAA was linked to a failure rate (requiring reoperation) in 8.5%.
The most frequent complications that were encountered included injury to the femoral-cutaneous nerve, dislocations and intraoperative femoral fractures. Injury to LFCN is relatively frequent, because it typically crosses the incision, and can be severed [
31]. According to the modified DAA technique by Faldini et al. [
13], the incision of the fasciae is performed over the TFL muscle belly, preventing an accidental lesion of LCFN which in most patients lies alongside the sartorius muscle. This can be responsible for the relatively low complication rate in our patients’ population (0.5%). A similar procedure was described by Den Hartog in 2015, that reported a 0.8% rate of LFCN lesion, similar to our findings [
32]. Regarding intraoperative femoral fractures, in the systematic review of Lee et al. [
33], an intraoperative fracture rate of approximately 2% was observed on 11,000 THAs performed by DAA, higher than our reported incidence of 1.2%.
As regards dislocation, only 0.6% required reoperation, a data which is comparable with previous findings in literature, averaging 0.5% [
2,
34].
There are some drawbacks in the surgical technique, such as femoral exposure and difficulty in performing straight reaming [
35]. Moreover, when using a straight tapered stem, DAA may be associated with a high incidence of varus stem alignment, mainly during the learning curve [
36]. This may also be determined by an insufficient capsule release, which makes femur exposure more challenging. In the current study, only 5 patients (0.5%) presented a varus stem, and 2 had valgus alignment (0.2%), all outside the tolerance range. Such a low incidence of stem malpositioning, justifies the use of dedicated instrumentation with offset handles, in addiction mid-size and dedicated stem allow an easier placement and promote implant positioning and alignment [
37].
In DAA, either the standard bed or the traction bed can be used for surgery [
38]. The outcomes and complications of the standard table and the traction table DAA are similar [
39]. In a standard table, it is possible to perform a manual check of leg length discrepancy (LLD), but an additional scrubbed assistant is required; when using a traction table instead, it is possible to indirectly check LLD by intraoperative fluoroscopy, and an unscrubbed assistant operates the traction: we routinely used this latter option. Sarraj et al. [
38] published the only systemic review comparing DAA THA with and without an orthopedic traction table. They did not observe side effects from the use of a traction table, including pudendal nerve palsy; moreover, limb length discrepancy was not analyzed in their review. In our study, overall, 8 patients had LLDs above 1 cm, with only 2 patients (0.2%) requiring reoperation probably because of the meticulous preoperative workout and accurate templating [
15].
Some patients might be less suitable for DAA in unexperienced hands, and these include adults with outcomes of developmental dysplasia of the hip, Legg-Calvè-Perthes disease and Slipped capital femoral epiphysis. As outlined by Laude in 2020, THA for DAA on patients with Crowe grade III and IV dysplasia is demanding, but in experienced hands it is associated with satisfactory clinical and radiographic results [
14,
40]. DAA can also be used efficiently in obese patients due to the reduced anterior width of the body fat at the tight [
41]. As highlighted in a previous study, THA performed by DAA is safe in obese patients and shows a low rate of complications and satisfying clinical outcomes [
13].