The introduction of new approaches and instruments can be expected to temporarily be associated with complications, such as neurovascular injury and component malposition. It is important to have information about the risk for various complications and predisposing factors. This study is based on non-selected, consecutive, primary unilateral total hip replacements. The very reason to use this approach is the possibility to minimize surgical soft tissue injury and to maintain normal muscle function and stability of the hip [1, 7, 9–13]. The approach is internervous and does not include the release of muscles or tendons. In the literature there is little evidence for a higher complication rate with the direct anterior approach compared to lateral approaches. It is however of interest to demonstrate and discuss the hardships involved when the technique is adopted by a team of surgeons with mixed experience.
Overall the distribution of complications was fairly even among the 200 cases included in the study. Aside from the first 10 cases, this study does not well delineate a learning curve. An almost linear reduction in intraoperative blood loss was noted among the first 10 cases; in two of them cracks occurred in the proximal femur – this was not seen in cases done later.
Access to the femoral canal can be expected to be difficult especially in patients with a short and varus angulated femoral neck and where the range of motion is restricted due to fibrosis of the joint capsule. Other authors [3, 12, 14, 15] have reported fractures in the proximal femur with this approach. In our series the major predisposing factor seems to have been pronounced osteoporosis. With the currently used offset handle, broaching is safer than with a standard straight handle as in the present series. The risk for fracture of the proximal femur is further minimized by adequate posterolateral capsule release so that an elevator can be placed around the tip of the trochanter while the hip is extended, adducted and externally rotated. However, if the surgeon excessively releases soft tissues from the proximal femur (which is not necessary) instability could result. This was possibly the reason for the dislocations that were seen in cases 118, 189 and 192 in our series. Even if no instability occurs, the release of tendons from the proximal femur counteracts the objective of this approach. Case number 169 was a patient with dysplasia (Figure 5) where the necessary medialization of the femur and not excessive soft tissue release led to postoperative instability. The end result of that operation was excellent.
The direct anterior approach subjects the lateral femoral cutaneous nerve and the femoral nerve to higher risk than lateral approaches. Even though the posterior branch of the lateral femoral cutaneous nerve can be injured [2, 12, 16] the technique described here seems to be effective in avoiding clinically relevant damage to the nerve. This is important since dysesthesia due to injury of this nerve may lead to considerable discomfort in the thigh for several months. Injury to the femoral nerve with the anterior approach has been mentioned by others [3, 17, 18]. We believe that it can be caused by the retractor placed anteriorly so that the iliopsoas muscle and the femoral nerve are compressed against fascial structures. This retraction should be directed cranially, towards the opposite shoulder and not transversely. In addition we have also constructed a retractor which sits around the ilium at the level of the anterior inferior iliac spine. This instrument is useful in difficult cases such as patients with pronounced abdominal obesity. Fortunately, femoral nerve injury seems to have a good prognosis and should resolve completely within a few months.
We decided to use the direct anterior approach even in cases with morbid obesity and in cases with grade 1 and 2 acetabular dysplasia. In obese patients we found that there was a specific problem in positioning the acetabular component. A high BMI was also associated with a longer operative time but not with a significantly higher intraoperative blood loss.