Anatomic Markers for Intraoperative Identification of the Heuter Interval in the Direct Anterior Approach to the Hip

Direct anterior approach (DAA) has been shown to have many benefits for patients undergoing total hip replacement. These include less soft tissue damage, a low dislocation rate, and earlier postoperative recovery compared with other approaches.1,2 The accurate identification of the Smith-Peterson interval is vital to minimize unnecessary soft tissue dissection, as well as to avoid injury to nearby structures. It also allows for an internervous approach, between the sartorius muscle (femoral nerve) and the tensor fascia latae muscle (superior gluteal nerve). This has been shown to lead to improved postoperative pain control and decreased length of hospital stay.3 The interval is accessed by incising the fascia over the tensor fascia lata muscle. It is the identification of this muscle that is the key element in ensuring safe exposure of the hip. A comprehensive understanding of the anterior hip anatomy is essential when acquiring exposure to the joint. Anterior mobilization of the femur is necessary for exposure for reaming, broaching, and femoral implant positioning. Specific releases are described in detail by Rodriguez et al,4 which allow the proximal part of the femur and the greater trochanter to be elevated anteriorly in front of the acetabulum with minimal force applied to the femur. The senior author has used the DAA in over 2500 cases to date and has identified 4 constant markers that aid in identifying the Smith-Peterson interval. TECHNIQUE After incision through the skin and subcutaneous fat, the tensor fascia muscle can be identified using the following markers (Figs. 1–3): Lateral to a line drawn from the anterior superior iliac spine to the head of the fibula. Oblique orientation of the muscle fibers running from the anterior superior iliac spine proximally in an inferolateral direction distally. Presence of perforating vessels in the fascia of the tensor fascia lata. Fat streak between tensor and sartorius medially. FIGURE 1: Right hip direct anterior approach. Anatomic landmarks for identifying the Heuter interval. ASIS indictes anterior superior iliac spine; TFL, Tensor fascia lata.FIGURE 2: Once the plane is identified, the fascia overlying the bulk of the tensor fascia muscle is incised and retracted to allow for access to the Heuter Interval.FIGURE 3: Anatomical landmarks for identifying the Heuter interval. The patient consented to clinical photography, available on request. ASIS indictes anterior superior iliac spine; TFL, Tensor fascia lata.Expected Outcomes The Heuter interval can be difficult to identify. However, using these 4 markers can allow surgeons to be confident with their approach. Once identified, the fascia overlying the bulk of the tensor fascia muscle is incised and retracted to allow for access to the Heuter interval and the hip capsule with minimal soft tissue disruption. The steep learning curve to the DAA can be aided by the identification of these markers. COMPLICATIONS The lateral femoral cutaneous nerve (LFCN) is at risk during a DAA. It is a purely sensory nerve. Careful dissection and identification are important to reduce the risk of damage. Incision of the fascia overlying the tensor fascia muscle limits the risk to the LFCN. The incidence of LFCN lesions varies in the literature.5 Despite the risk, the long-term effects of LFCN damage do not limit function.6 The presence and number of the tensor fascia lata perforators can vary. Cadaveric studies show that it may be absent in 5% of cases, and the number of perforators can range from 0 to 5.7,8