Many scholars have tried to define the learning curve of DAA technique using various data, including procedure time, implanted position, fluoroscopy time, complication rate[19–23]. The learning curve has been previously described as 50–100 cases[10,23−25]. But previous literature has focused on the transition from posterolateral approach to DAA. So we have attempted to add to the literature defining the learning curve of a single surgeon's transition from DLA to DAA by this retrospective study.
The PT changed most obviously in the first and second intervals, and then decreased slowly. The PT over the 90–100 DAA case interval was 10.37% less than the DLA PT, but the difference was not statistically significant. According to Andrea et al, the PT of DAA was significantly shorter than that of the posterior approach after 850 surgeries. We believe that the PT of DAA will further decrease with the extension of surgical cases.
Because of different surgical techniques and different preoperative preparation steps, OPT is bound to differ. We found that trend of OPT was significantly different from that of PT. First of all, the increase of the first interval is obviously greater than that of PT, reaching 57.69%. Secondly, the decline in increase is slower. Although the mean OPT was gradually approaching with the extension of surgical cases, it was always longer than that of the DLA. We considered that the preoperative preparation for DAA technique was more complicated, requiring simultaneous disinfection on both sides. Standardized skin preparation and draping procedures would take more time. What’s more, in the whole process of surgery, the surgeon can play a good control, the surgeon's proficiency and state are the most important influencing factors of PT. There are a large number of participants in the process of preoperative preparation, and the influencing factors of personnel are larger.
The DAA requires more like special surgical tools, intraoperative fluoroscopy, foldable operating table, and an experienced surgical team. Because DAA technique had never been performed before, the entire team was built from scratch, including surgical technologists, nursing staff, anesthesia staff, and radiology technicians. The learning curve of DAA does not only belong to a single surgeon, but also for the entire surgical team. A nurse is required to fold the operating table for getting better exposure and convenience of prosthesis implantation. The radiology technician is also important. Using intraoperative fluoroscopy enabled us to gain clear anteroposterior radiographs of the pelvis and lateral radiographs of the femur, so as to select a more appropriate neck length of the femoral prosthesis and better femoral off-set to achieve the limb-length equality. It was not until approximately 80 cases were completed before the ORT of DAA was shorter than that of DLA. Fortunately, there were no intraoperatie injuries such as ankle fractures happen in the operating room[26, 27].
The major complication rate of DAA in the learning curve has been reported to be 1.6–10%[10, 29, 30]. The complication rate was 3%, which is similar to previous reports. The patient with lateral femoral cutaneous nerve injury complained of obvious hypesthesia in the anterolateral aspect of the thigh 6 weeks after surgery. Improvement of symptoms was seen in the seventh month after takeing mecobalamin tablets (0.5mg TID) for 2 months. The patient with femoral nerve injury had difficulty in walking in the outpatient review at the third month. The quadriceps muscle strength assessed by Lovett scale score was 3. It was considered that the injury was caused by excessive pulling of the hook at the superior ramus of the pubis. The patient received drug treatment (mecobalamin tablets ,0.5mg TID) for 2 months and rehabilitation program. The muscle strength returned to normal one year later. The greater trochanter fracture of the femur occurred in a patient with poliomyelitis sequelae. Muscle atrophy, osteoporosis and inadequate exposure of the greater trochanter led to fracture. The patient was fixed with wire strapping intraoperatively and was instructed to delay weight-bearing and ambulation until 4 weeks. Maratt et al reviewed 2147 THA via DAA. Dislocation occurred in 17 cases and the rate was 0.84%. According to Kong et al, the dislocation rate was 2%(2/100) including the learning curve. In our study, there was no dislocation case. Firstly, the surgeon was experienced and was aware of protecting the obturator external tendon. Secondly, by using intraoperative fluoroscopy, a more appropriate neck length could be selected. The acetabulum and femoral prosthesis could be placed in a safer position. Thirdly, our surgical technique adopted articular capsule to cover the outer musculature and to protect the tensor fasciae lata muscle carefully. At last, the anterior capsule was re-sutured closed to improve the stability and to reduce the risk of dislocation. Hallert et al reported 2.5% (5/200) early revisions while no case in this study needed revision surgery. It might be related to the short follow-up time.
For the first 50 DAA cases, 64.94%(50/77) cases were performed via DAA, while 35.06%(27/77) were performed via the original approach due to various factors. The change of surgical approach is not a simple switch from A to B, but requires a long process of adaptation. We believed that a deeper understanding of DAA had been gained after the completion of 50 DAA cases and most hip joint diseases could be solved by DAA technique. There were statistically significant differences in blood loss, PT, OPT and ORT between group 2 and group 3. All the 3 complications occurred in group 2. A steady state came out after 50 DAA cases.
Shorter length of stay has always been an advantage of DAA over posterolateral and DLA [33, 34]. However, the difference among three groups was not statistically significant. It may be related to the older age of patients in this group, which leads to more underlying diseases, longer time of routine preoperative medical testing, and slower postoperative recovery.
This study is designed for a single experienced joint reconstruction surgeon and may potentially limit the generalizability of the study. Inexperienced surgeons may have a longer period of learning curve, a higher complication rate, longer PT, OPT and ORT. Visiting experienced DAA surgeons, attending cadaver courses, and restudying possible problems after completing several DAA cases can help a lot [20, 28, 29]. If possible, we recommend continuing medical education for the entire surgical team.
There are limitations to this study. This is a retrospective study. The overall number of cases was small, the follow-up time was not long, and the diseases of THA patients were not further subdivided, which may not accurately present the learning curve confounding variables. The advantage of this study is that it completely presents the learning curve of THA when transitioning from DLA to DAA. By studying PT, OPT, ORT, blood loss, blood transfusion, length of stay and complications, some interesting trends were found. The learning curve is influenced not only by the individual surgeon, but also by the entire surgical team.