This study demonstrated a very low dislocation rate with rTHA performed via the DDA. Only dislocation occurred in the patients receiving a trochanteric osteotomy as index surgery. We believe that this complication happened because of insufficient repair of the abductor mechanism that was damaged by fracture, hence unbalancing the soft-tissue tension. Damage to the abductor mechanism is strongly related to dislocation rates . The intermuscular DAA is abductor-sparing and reduces trauma to the soft tissues, thus making it more attractive in the setting of multiple revision surgery, specifically after another primary approach. What is even more interesting is that, by using the DAA in patients receiving posterior index surgery, we preserved the posterior neocapsule, thus avoiding eliminating this additional stability factor. As in our series, 46% of index surgeries (n = 39) were PA or trochanteric osteotomy approach, which reinforces our belief that revision through the DAA may offer protection from dislocations. Regarding dislocations after rTHA through posterior approach, higher rates were reported in the literature. If the posterior capsule is not repaired, which is mostly the case because of extensive capsular release, dislocation rates could reach up to 10% [13, 14], higher than rates reported in rTHA through the DAA. Thaler et al. reported a 7% dislocation rate in their series of 165 femoral revisions and 3% in another one of 64 acetabular revisions through the DAA [15, 16]. Prodinger et al. reported 3% dislocations in their prospective series of 61 acetabular revisions through the DAA . Other reports described dislocation rates between 0 and 5% [11, 18,19,20]. Moreover, dislocation is a significant complication leading to another hospitalization with a high risk for re-revision. Yu et al. found that instability, as an indication for re-revision THA, was a statistically significant (P = 0.038) indicator of re-revision failure, with a relative risk of 1.9 (1.0–3.4) . The 2020 Australian Orthopedic Association national joint replacement registry annual report described instability as the major diagnosis for a second revision. Regarding revision for infection, we did not report any dislocation of either the spacer or the definitive implants. The studies that compared the outcomes between the anterior and the posterior approaches for rTHA were scanty. Kurkis et al. have found a decreased dislocation rate of two percent compared to 13% in the PA group (P = 0.002) and a significantly increased risk of wound complications in the DAA cohort (7% vs. 0.5%), and the findings remain valid after multivariate regression analysis. In addition, a trend towards more overall 90-day complications was seen in the PA group (OR 1.71) . We believe, by externally rotating and extending the hip, abductor muscle insertions on the greater trochanter are excluded from the surgical field. It may help avoid damaging them. To our knowledge, no study evaluated the muscle damage patterns after rTHA. In another series, Baba et al. found significantly less blood loss and total complications in acetabular revisions through the DAA compared to the PA . Our study reported one wound dehiscence and one surgical wound infection, which yielded a total rate of 3% of wound complications that was in line with the rates of 1% and 12% previously reported in primary THA [23,24,25]. As these complications happened in two obese patients, we strongly believe that care must be taken when rTHA is done in this patient population. Preoperative aqueous chlorhexidine gluconate (4%) shows, the day before the operation, appropriate antibiotic prophylaxis before incision and daily wound care are essential to reduce this risk [26,27,28].
In addition, this study also demonstrated a good postoperative function in terms of the Oxford Hip Score. The use of patient-reported outcome measures (PROMs) to evaluate the clinical effect of procedures helps clinicians gain unique insight into the patients' actual and perceived physical benefits of rTHA. Our findings are in line with recent reports about functional outcomes following rTHA [29, 30]. Poor PROMs were associated with revision for infection, periprosthetic fracture or dislocation. Revision for aseptic loosening scored better on functional scores compared to revision for fracture, infection or dislocation [30, 31]. In our series, OHS functional scores in the setting of revision for infection were significantly lower compared to OHS in the setting of periprosthetic fracture, aseptic loosening and dislocation. Median comparisons between these three last groups did not yield any significant difference.
The deep infection rate in our series was comparable with published infection rates after rTHA through different approaches, ranging from 1 to 8% [22, 32]. In the setting of our study, we cannot extrapolate any conclusion about the superiority of the DAA to other approaches with respect to deep infection rates. On the other hand, in the United States Medicare population, infection is shown to be the most common complication after revision surgeries, with a total rate of 17% in 3555 revised hips between 1998 and 2011 . When comparing revisions through the DAA and the PA, literature revealed no difference in the deep infection rate [18, 22]. Revision surgery is associated with longer operative time, an independent risk factor for surgical site infection and a high infection rate .
Regarding the risk of intraoperative fracture through the DAA, we noticed two fractures of greater trochanter tips with posterior retractor placement and one acetabular fossa fracture during cup impaction. No osteosynthesis material was used. They were treated conservatively with a protected weight-bearing protocol. These numbers are in concordance with the result reported by Thaler et al. who described 4 intraoperative femoral fractures (2%) in his series of 165 femoral revisions through the DAA . These numbers suggest that revision through the DAA may have a low risk of intraoperative femoral fracture.
In some cases, issues like acute acetabular fractures, anterior defects or acetabular protrusion need to be addressed. With the patient assuming supine position and draped from chest to knee, all proximal and distal extensions are possible. The Stoppa approach, as well as the Levine extension of the Smith-Peterson approach, provide excellent exposure of the anterior column and could be used to treat the above-mentioned issues . If needed, the distal extension provides direct visualization of the whole femur for fracture fixation, extended trochanter osteotomy or trans-femoral Wagner osteotomy for well-fixed stems . Femoral retroversion makes intraoperative dislocation more challenging and acetabular exposure less easy. Moreover, other relative contraindications for rTHA through the DAA might be overweight patients with excessive skinfolds, multiple lateral incisions and the need to access the posterior column for osteosynthesis or hardware removal.
The present study has limitations due to its retrospective design and lack of a control group. Although the patient populations are comparable between the two hospitals situated in a 65-km radius where the two surgeons used the same technique, grouping bias was observed. Moreover, anesthesia and rehabilitation protocols differed from one institution to the other, introducing confounding bias that has to be taken into consideration. Furthermore, the OHS was collected by the principal investigator and not filled in by the patient, which introduced a bias and, for some patients, it was collected a year after their operations and even longer with others. The score is also sensitive to the activity level of the patient as well as the use of pain medications. We could not compare the score to a preoperative one because none was collected. Finally, when analyzing the indications throughout time, we observed that surgeons started revision through the DAA with relatively straightforward indications (acetabular cup revision) and complexity increased with time (revision of both components). This added a selection bias and showed the limitations of such an approach regarding its steep learning curve.