A large amount of researches have been done on the comparison of direct anterior approach with other approaches, demonstrated that patients undergoing the DAA for THA had slightly shorter incision length and blood loss. Zhao Wang et al. researched a meta-analysis about 184 cases of DAA and 175 cases of PA, demonstrated that the average incision length of DAA for THA was 3.51cm less than posterior approach . Klasan et al. compared DAA with anterolateral approach, demonstrated that the blood transfusion rate was statistically decreased in DAA group, with 5.8% of 14.1% lower compared to anterolateral approach . Whereas, DAA could be performed in lateral decubitus position or supine position, and there were few studies conducted on comparison these two different positions of DAA for THA.
The supine position is the position in which most surgeons begin to learn DAA, and it is also described in most studies, especially in the posterolateral position. Malahias et al. believe that simultaneous bilateral THA at the same time is effective and safe . In order to reduce the operation time, lateral position should be avoided when the patient requires bilateral surgery. While the supine position can be placed once to complete the operation, which greatly saves the operation time. According to Guler et al, supine surgery is advantageous in terms of anesthesia . Meanwhile, c-arm machine is more acceptable, the photography is more accurate, theoretically, it is easier to locate the anatomical position of the pelvis, and acetabular cup implantation is more accurate. In 1985, Robert and Judet et al used a traction bed during the DAA operation. Moreau et al. proposed that DAA was originally performed in the supine position on a specialized traction bed . However, Camenzind et al. believed that the use of traction bed in the supine DAA greatly increased the incidence of postoperative complications. Therefore, 138 patients were selected to exprience THA with supine position DAA, and only 3 patients had complications, with an incidence of 2.1%. Combining with the 24-months follow-up, it was believed that the DAA in supine position with trecion bed showed better early clinical efficacy . Sarraj et al. compared DAA with use of a traction bed and a standard operating bed, and concluded that the standard operating bed and traction bed had similar clinical outcomes and complication rates. Using the standard operating bed had more advantages, including reduced blood loss, shorter operating time, and fewer intraoperative fractures rates . Meanwhile, it also has disadvantages such as the need for more assistants, the difficulty in the femur exposing, and the possibility of additional soft tissue injury. Lovell et al. believe that DAA with a standard surgical bed has potential advantages, including the position of the operated limb doesn't need to adjust during the procedure, and it's easier to access hip stability, range of motion and limb length . Therefore, there are few studies on the selection of surgical beds, which are mainly determined by the preference and habits of surgeons, as well as by the factors such as cost and technology.
As we know, the traditional position of the classic posterolateral surgery is lateral position. When the operative limb is in overextension, abduction and external rotation, it is more likely to expose the femur and enter the medullary space, which can reduce the incidence of complications, and in the lateral decubitus position, the abdominal adipose tissue can be removed from the incision and surgical field due to gravity, besides, Slotkin et al. suggested that the lateral position causes pelvic orientation changes that may affect the implantation of the acetabular prosthesis, whereas the supine position produces less pelvic orientation changes [8, 9, 21].
Within our cohort, Operative data (like Operation time/Length of stay/CK-MB/Hb values) showed no statistical significance. This could be due to the reason that DAA is a minimally invasive surgery with small incision and using a muscle gap approach, which makes less injure and bleeding. Although showing no difference, we believe that it’s relevant to the insufficient number of cases in the whole study. We understand In DAA no muscles were cut ,but considerable traction had to be applied to obtain good exposure Some authors believe that in the lateral position, the soft tissue around the incision can make full use of the advantages of gravity to expose the surgical area better and reduce blood loss [22, 23]. Of course, we still need further research on whether lateral position can reduce blood loss and muscle injury.
Clinical scores also appear not to depend on position. There is no evidence that either lateral or supine position can recover faster or better. Although, on our study, no difference was showed in clinical scores between the two groups, all patients obtained significantly excellent functional scores and improved quality of life during the last follow-up.
Radiographic outcomes after surgery have been linked to clinical outcomes. We measured cup abduction、cup anteversion、LLD、femoral anteversion and offset as described by Lewinnek, Acceptable cup abduction was defined as between 30°and 50°,acceptable cup anteversion angle was defined as between 5°and 25° . In our study, postoperative radiological outcomes showed that the prosthesis of the two groups was in a good position. LLD value was equal to operative side minus the other side, which was denoted as positive if the operative extremity is longer than the contralateral side. In fact, some clinical articles didn't measure offset and LLD, while smaller offset was regarded as a significant risk factor for LFCN injury following THA via a DAA [25, 26]. Although our findings showed radiographic outcomes were no statistical differences, generally each was improved by surgery. Nowadays, in terms of functional recovery, it has still not been demonstrated which radiographic date are most important, each parameter is meaningful.
The pelvic position is more reliable when in the supine position, leading to more consistent orientation of the acetabular component . For two case of Ankylosing Spondylitis, we decide to choose the lateral position, because it is difficult for the patients to lie flat and anesthesia. The patient is in the lateral position, the exposure would be better for greater back extension and limb adduction .
We are all too familiar with the complications of DAA. Many clinicians have done research about complications of DAA. Comparing to the other approaches, DAA has the higher incidence of complications . The most common complication after DAA was nerve dysfunction followed by intraoperative fractures, including intraoperative trochanter and femoral fractures, especially [30, 31]. Moreover, several studies have reported that complication rates of DAA may relate to the so-called “learning-curve period” for the surgeon After 50 or more procedures need to be performed, the rate of revision would reach a steady level . In Chinese patients, analysis showed that complication rates and operating time normalize after 88 cases and 72 cases respectively . However, there was no significant relationship between femoral nerve palsy and surgeon's experience of DAA . Paul et al. also showed that using ceramic-on-ceramic implant through DAA made a good clinical results and implant survival rates at a mean follow-up of 31.9 months,111 hips (96%) were perceived no serous complication . In our study, few complications happened after the operation. In the lateral position, only 1 case of dislocation occurred postoperatively. While in the supine position, 1 case of dislocation and 1 case of greater trochanter fracture occurred intra-operatively ,2 cases were due to difficult exposure during operation.;1 case of unexplained recurrent fever, 1 case of dislocation and 1 case of poor hip flexion occurred after operation. Although it is theoretically considered that the dislocation rate of DAA is lower than other approaches, dislocation still occurred in both positions. For the case of intraoperative dislocation, we have taken to reduce the femoral anteversion and then dislocation didn't happen again. And we still experienced one case of greater trochanteric fracture occurring during the exposure process, which is considered to be caused by osteoporosis. Nevertheless, the results showed that the incidence of complications in the lateral position was lower than that in the supine position, but this result should be verified in a larger sample to ensure it is not due to inadequate statistical power.
Making a summary to sum up the above points. The lateral position has the following advantages:
- Proximal femoral exposure is more convenient;
- The incision exposure is more convenient for the reason that muscular adipose tissue won’t hidden the incision;
- Special traction bed and special surgical instruments are not required, it's no need to adjust intraoperative the operating bed intraoperatively;
- For most surgeons who study the posterolateral approach firstly, the habit of acetabular process does not change;
- There is no need to change the position when posterior lateral incision is needed, in the case of greater trochanter fracture.
- the incidence of complications are lower.
- Pelvic fixation is needed before operation;
- It is inconvenient to compare the length of bilateral limbs during the operation.
The supine position has the following advantages:
- Simultaneous surgery can be performed on both sides without changing body position.
- It is convenient to compare the length of bilateral limbs during the operation.
- Facilitating intraoperative fluoroscopy, reducing the risk of anesthesia, increasing the safety of surgery.
- In theory, acetabular prosthesis implantation is more accurate.
- Special traction bed and special surgical instruments are needed.
- Proximal femoral exposure is difficult and greater trochanteric fractures are more likely to happen.