Traditional THA for Crowe type III-IV DDH typically employs a fluted modular stem or extensively porous-coated stem via a posterolateral approach. Most studies have shown satisfactory middle- to long-term clinical results.18,19 However, some limitations in this approach have been recognized, such as invasion of the short external rotators increasing dislocation,20 and interruption of the medial femoral circumflex branch of the femoral artery impairing osteointegration on bone-prothesis interface and bone union at the osteotomy site.21 These deficiencies could be properly addressed by DAA as we proposed in our previous publication,22 and this inference was fully substantiated by prior uncontrolled study.23
To our knowledge, there are very few studies reporting THA via the DAA in treating Crowe type III-IV DDH. Oinuma did report the early outcomes of 9 patients (12 hips) diagnosed with Crowe IV dysplasia by DAA with STO, functional improvement seemed to be satisfactory at a mean follow-up period of 3.7 years.10 Our series demonstrates similar functional improvements, but with a decreased surgery duration and blood loss even for those patients who underwent a STO compared to this study. Another uncontrolled study reported an average 8.4-year outcomes of 23 case series treated with DAA in supine position on a traction table. The improvement of HHS and WOMAC scores were satisfactory, but three hips were revised due to wear-induced loosening at an early stage after surgery.9
This study presented a single surgeon series of patients treated with DAA THA for Crowe III-IV DDH, by evaluating the effectiveness and benefit-risks of DAA compared to traditional approach. We demonstrated a clinically important difference in the increase of the HHS and WOMAC when performing the surgery via a DAA with a low complication rate comparable to the PLA. Our result did have a lower rate of complications as compared to the select patients in the study by Cameron who underwent THA via the DAA for DDH.24 We do report an increased EBL in the DAA compared to the PLA; however, this did not result in an increased rate of transfusion. In addition, despite the non-significant difference in surgical time between the two cohorts, the average increase for the DAA cohort was 21 minutes more than PLA cohort in our well trained and experienced surgical team. Since the chance of infection increases with surgical time,25 careful planning and advanced practice are advised to those who may think of trying direct anterior approach in Crowe III-IV DDH, in case of increased occurrence of surgical site infection.
The DAA spares the abductor complex, which may already be weak in these patients. Kawasaki et al found damages to the gluteus minimus, obturator internus and tensor fascia latae in the case series with DDH underwent DAA, but sparing of the gluteus medius and piriformis.26 We demonstrated no clinically relevant injury to the hip flexors as measured by muscle strength in patients who underwent the DAA as compared patients who underwent the PLA and a more rapid improvement in hip flexor and abductor strength.
The lumbar-pelvic-hip complex also plays a key role in decision-making for Crowe type III-IV DDH.6,27 DAA in the supine position is advantageous to reproducibly gain a functional pelvic position, which is beneficial for accurate sizing and safe positioning of the component.28,29 As we reported in our series, both the clinical outcomes and radiographic analyses demonstrated comparable results between the DAA and the PLA. `
The limitations of this study include a small sample size, retrospective study design, and long-term clinical data are unavailable at present. This limitation needs to be addressed by conducting a multicenter, prospective cohort study with a large sample population of our undergoing work.
The strengths of the study are: first, it is a single surgeon case series with consistent surgical procedure and follow-up program, which avoids the subjective bias in the comparative study performed by multiple surgeons. Second, this study also includes a precise radiographic review of the postoperative radiographs (especially rotation center deviation and stem subsidence) comparing DAA to PLA. Third, this is also the first paper to our knowledge to quantitatively measure postoperative hip abductor and flexor muscle strength after DAA in high-dislocated hip dysplasia.