Background

Surgical approaches are anatomic dissections of tissue planes that use anatomic knowledge to limit the amount of dissection required to perform the procedure while avoiding nerve and vessel damage.1 A variety of surgical approaches including anterior, anterolateral, direct lateral, transtrochanteric and posterior, have been utilized for performance of total hip arthroplasty (THA). Each approach has advantages and disadvantages. Postoperative dislocation following the posterior approach and prolonged abductor recovery following anterolateral and direct lateral approaches are concerning. The direct anterior approach utilizes an internervous and intermuscular plane to the hip-the interval between the sartorius and tensor fascia lata.

The Direct Anterior Approach for Total Hip Arthroplasty

History of the Anterior Approach

The first written description of the anterior approach comes from Carl Hueter, a German surgeon. He published "Der Grundriss der Chirurgie" (The Compendium of Surgery) in 1881 to describe this approach. Marius N. Smith-Petersen (1886-1953), an American surgeon, spread the use of this approach to the English-speaking world.2 Sometimes, the approach is also commonly referred to as the "Smith-Petersen" approach. The anterior approach, with slight modifications, has been used to treat various conditions of the hip including developmental dysplasia, femoroacetabular fractures, impingement, uncemented and cemented THA and resurfacing. However, difficulty in gaining proper access to the femoral canal might have limited its use in hip arthroplasty. In 1985, the Judet brothers described the use of an "orthopedic table" to perform THA through the anterior approach.2 Over the last decade or so, some surgeons have championed its use in THA as a true muscle-sparing approach. In this era of minimally invasive surgery, THA through the anterior approach has attracted widespread interest among surgeons and patients alike.

Patient Positioning and Set-up (Fig. 8.1)

The operation can be performed with or without the use of a specialized fracture table. We have been performing the surgery without the use of the special table and this technique would be described. The patient is positioned supine with the pelvis squared on a standard table such that a transverse line drawn through the anterior superior iliac spines is perpendicular to the long axis of the table. The operating table should be capable of attaining a Trendelenburg's position and lowering its foot-end at the level of the break. The most

Figure 8.1: Patient positioning

Total Hip Arthroplasty

prominent point of the greater trochanter is positioned at the level of the break in the table, so that hip extension results when the foot-end is lowered. The contralateral leg can be positioned in abduction on a Mayo stand at the time of femoral preparation such that the operative hip can be adducted. Use of a C-arm image intensifier is optional but is recommended. The C-arm should be draped sterile and positioned at right angles to the long axis of the operating table on the opposite side and is advanced when needed. The operative hip and both lower limbs are prepared and draped in the normal sterile fashion. An elastic compression bandage is used from the foot to the mid thigh bilaterally to minimize venous pooling. Typically, 2 assistants are adequate (1 of the assistants is mostly responsible for limb positioning at the time of femoral preparation).

Applied Anatomy and Surgical Technique

The present-day direct anterior approach for THA utilizes only the distal part of the original Hueter or Smith-Petersen approach. Instead of entering the interval between the fascia of the tensor and sartorius muscles, the direct anterior approach involves a more lateral entry to avoid damage to the lateral femoral cutaneous nerve. The incision is approximately 10 cms long starting 2 cms lateral (posterior) and distal to the anterior superior iliac spine and extended distally and laterally (directly over the belly of tensor muscle) (Fig. 8.2). The subcutaneous tissue and fat is incised to expose the fascia of the tensor fascia lata muscle, which is incised in the direction of its fibers. The medial portion of the incised fascia is the grasped with an Allis forceps and blunt dissection is performed to separate the fibers of the tensor muscle from the internal aspect of its fascia (Fig. 8.3). The lateral femoral cutaneous nerve is therefore protected by the medial part of the fascia of the tensor muscle. The tensor

Figure 8.2: Incision is marked starting 2 cms lateral (posterior) and distal to anterior superior iliac spine

The Direct Anterior Approach for Total Hip Arthroplasty

Figure 8.3: Tensor fascia lata muscle is seen after its fascia is opened. Medial fascial flap is held with Allis forceps

Figure 8.4: Branches of the lateral circumflex vessels visualized after retracting tensor fascia lata laterally and rectus femoris medially

Figure 8.5: Fat pad overlying the anterior hip capsule

muscle is retracted laterally and the rectus femoris is retracted medially (Fig. 8.4). Blunt dissection is continued to reveal the branches of the lateral circumflex femoral vessels which are coagulated, ligated or transected depending on surgeon preference. The fascial plane lateral to the rectus femoris and inferior to the tensor muscle is then entered and released all the way up to the acetabular margin. This reveals the fat pad overlying the anterior hip capsule and proximal aspect of origin of vastus intermedius muscle (Fig. 8.5), which is excised.

Total Hip Arthroplasty

Figure 8.6: Anterior hip capsule after fat pat removal. Capsulotomy is marked

Figure 8.7: Inverted T-shaped capsulotomy with Ethibond suture tags

Two cobra retractors are then placed, one medial and the other lateral to the femoral neck to expose the anterior hip capsule (Fig. 8.6). The medial retractor is placed under the rectus femoris and iliocapsularis muscles.

Capsulotomy or capsulectomy is then performed depending on surgeon preference. We routinely perform an inverted "T-shaped" capsulotomy to raise medial and lateral flaps (Fig. 8.7]. The capsulotomy starts at the anterior wall of the acetabulum (at the same time releasing partially the reflected head of the rectus femoris) and brought down along the superior 1/3rd of the neck upto the intertrochanteric line. The fibers of the vastus intermedius (inferiorly) and gluteus minimus (laterally) are protected. Adequate release of the superolateral capsule up to the posterior-superior aspect of the greater trochanter and femoral neck is performed. Medial capsule is released adequately so that the lesser trochanter can be palpated with a finger. Ethibond suture tags are passed through the capsule to facilitate capsular maneuvering (Fig. 8.7). The cobra retractors are then repositioned intracapsularly around the femoral neck. The level of the neck resection is determined (keeping the lesser trochanter as a reference) as per pre-operative planning (may be confirmed with fluoroscopy). Care should be taken not to damage the greater trochanter with the saw. The head can then be extracted with a cork-screw device. Alternately, some surgeons perform a "napkin-ring" neck-cut, which is removed with a threaded Steinmann pin. Adequacy of capsular release is assessed based on the mobility of the proximal femur with a bone hook placed at the calcar to deliver an anterior force to femur. Residual posterosuperior capsule can limit the amount of anterior translation of the femur and should be released judiciously before proceeding further. Part of the gluteus minimus insertion lies on the superior capsule3 and this has to

The Direct Anterior Approach for Total Hip Arthroplasty

Figure 8.8: Acetabular exposure

Figure 8.9: Fluoroscopic image showing cup placement

be released to create a plane between the capsule and gluteus minimus. The superior capsular flap should appear triangular at the end of this release. With this, it should be possible to bring the posterior greater trochanter out from behind the acetabulum to at least the center of the socket.

The acetabulum is exposed by placing a sharp retractor anteroinferiorly (over the anterior acetabular wall-4 o'clock position for the right and 8 o'clock for the left hip). Another cobra retractor is placed on the ischium posterior to the acetabulum (8 o'clock position for right hip and 4 o'clock position for the left hip) (Fig. 8.8). Inferior capsule is released, if tight. Labrectomy is performed followed by removal of the pulvinar and residual capsule in the way of acetabular preparation. Sequential reaming is performed and confirmed fluoroscopically. The acetabular component is then implanted in the appropriate orientation under fluoroscopic guidance (Fig. 8.9). Acetabular screws may be inserted if desired and the liner is impacted in place.

A special table-mounted elevator is then used for femoral preparation (Omni-Tract Surgical, St Paul, Minnesota). The traction hook of the elevator is placed around the proximal femur, just distal to the lesser trochanter and the device is mounted on the bed (Fig. 8.10). The contralateral lower-limb is now placed on the padded Mayo stand in abduction and the

Total Hip Arthroplasty

Figure 8.10: Table-mounted femoral elevator (Omni Tract) and leg positioning. Note that the hip has been extended by lowering the foot-end of the table

Figure 8.11: Leg positioning for femoral preparation

operative side is placed in extension, adduction and external roration (Fig. 8.11). This is made possible by dropping the foot end of the table and placing the table in Trendelenberg's position. Slight flexion of the knee may occur, but extreme flexion may result in tightening of the rectus femoris muscle thereby making the femoral exposure difficult. Anterolateral traction is now applied with the Omni-Tract elevator. A blunt retractor is placed medially around the calcar and another blunt cobra retractor is placed under the greater trochanter to assist in further lifting the femur anteriorly. If the femur is inadequately mobilized despite releasing the posterosuperior capsule (as may happen in muscular males) partial or complete tenotomy of the conjoint tendon (Fig. 8.12) and/or the pyriformis may also be needed. The obturator externus tendon should be preserved.

Femoral preparation is then started in the standard fashion by taking bone from the posterolateral neck with a midas-rex high speed burr or box-osteotome. A curved canal finder is inserted to judge the direction of the medullary canal and sequential broaching is performed (Figs 8.13A and B). Special double-offset broach handles may make femoral broaching easier, although we find a single-offset broach to be most reproducible. It is advisable to keep the broach handle close to the patient's abdomen so as to get a straight shot down the medullary canal and prevent posterior cortical perforation. The final broach is left in place and trial neck and head are inserted. The traction on the femoral elevator is released, the calcar and greater trochanteric retractors removed, and the hip is brought to neutral alignment and reduced by linear traction and internal rotation by an assistant while the surgeon's fingers guide the head into the socket. The C-arm can then be used to check for stem sizing, positioning, restoration of leg-length and offset (Fig. 8.14). Since the patient

The Direct Anterior Approach for Total Hip Arthroplasty

Figure 8.12: Conjoint tendon release at its insertion in the piriformis fossa. Rectus femoris (medial), tensor fascia lata (lateral) and vastus intermedius (distal) are also visualized

Figures 8.13A and B: Femoral preparation with the use of a single-offset broach handle

Figure 8.14: Fluoroscopic image obtained after trial reduction demonstrating adequate sizing and satisfactory positioning of the broach. The length and offset is compared with a fluoroscopic image obtained of the contralateral hip

is supine, the medial malleoli can be palpated (Fig. 8.15) and leg-length corroborated with the fluoroscopy. Forced external rotation can be performed to check stability with the hip in neutral as well as in hyperextension.

Total Hip Arthroplasty

Figure 8.15: Assessment of leg-length

The hip is dislocated with a combination of linear traction and external rotation (by the assistant) and a small bone hook around the trial neck with the surgeon pulling distally, laterally and anteriorly. The limb is again placed in extension-adduction-external rotation and femoral elevator, calcar and greater trochanteric retractors are applied. The trial implants are removed and final components are implanted. The hip is then reduced and checked under fluoroscopy. The traction hook is removed and bed is leveled. A drain can be left if desired. The wound is irrigated and closure is initiated. The fascia of the tensor muscle is sutured first (taking care not to suture too medial for risk of lateral femoral cutaneous nerve entrapment), followed by fat and subcutaneous tissue, followed by skin. The quality of closure can be significantly improved by suturing the skin in a subcuticular fashion, especially due to the thin nature of skin in this region.

Rehabilitation

Dislocation precautions are unnecessary because posterior musculotendinous structures are either partially or completely intact. No abduction pillow or high chair is needed. Immediate weight-bearing and activities as tolerated are permitted. Patients can walk with a walker or crutches on the day of surgery. A multi-modal analgesic protocol is usually utilized and most patients are discharged from the hospital on postoperative day three, or when they have met physical therapy goals. Patients progress to walking with a cane in about two weeks, which they gradually wean-off in 4 to 6 weeks. Postoperative physical therapy requirements are minimal after 2 weeks.

Complications

These have been well summarized by Barton and Kim4 and complications specific to this approach shall be briefly enlisted.

1. Approach related complications: The commonest complication is lateral femoral cutaneous nerve damage with resultant numbness of the anteolateral thigh. About 40 to 50% patients report transient numbness over the anterolateral thigh just distal to the incision, which may persist in a small percentage of patients. Injury to the femoral nerve can also occur

   due to incorrect positioning of the medial or anterior acetabular retractor. If the proper surgical plane is not identified, the sartorius can be confused with the tensor fascia lata with the potential for entering the femoral triangle with resultant risk of damage to the femoral neurovascular bundle. This can be avoided by correct identification of the tensor fascia lata based on its fascial sheath (which thickens posteriorly towards the gluteus minimus). Intraoperative bleeding and postoperative hematoma formation can also occur if the lateral femoral circumflex vessels are not cauterized or ligated well. Problems with incision healing are more likely in obese patients with a large abdominal pannus overlying the surgical site predisposing to poor local hygiene. The pannus keeps local skin moist, making wound care difficult and predisposing to infection.

2. Access related complications: These include malpositioning of components, especially the acetabular cup. Levering the reamer on the anterior femoral shaft entails the risk of reaming away the anterior acetabular wall. Surgeons transitioning from the posterior approach may put the cup in too much anteversion than is ideal for the anterior approach with resultant risk of posterior impingement and/or anterior dislocation. Femoral perforation may occur if the true direction of the femoral canal is not identified. Most common sites of perforation are lateral (extreme varus broach positioning) and posterior as described earlier. In addition, failure to adequately mobilize the femur and use of sharp retractor to elevate the greater trochanter may lead to fracture of the trochanter, especially in patients with poor bone quality.

3. Traction table related complications: These include ankle fractures as a result of overzealous rotation and pudendal nerve neuropraxia as a result of prolonged traction against the perineal post.

4. Dislocation after anterior approach THA: Reported dislocation rates have been in the range of 0.61 to 1.5 percent.5-8 It is evident that the dislocation rates are somewhat higher in the initial part of an individual surgeon's learning curve.5

5. Heterotopic ossification: This is the only intermediate-term complication reported in literature so far. It is considered to happen secondary to muscle damage most likely as a result of retraction. However, there is little data on this at present.

   The Direct Anterior Approach for Total Hip Arthroplasty

   Advantages

   A cadaver study has revealed less abductor muscle damage with the anterior approach, although there is increased potential for damage to tensor fascia lata and rectus femoris muscles.9 The direct anterior approach has been compared clinically to the lateral and mini-posterior approaches approaches in primary THA and has been found to be advantageous in terms of early functional recovery.10,11 Biomechanical studies comparing the anterior approach to the posterior and anterolateral approaches have shown no significant differen-ces.12,13 A prospective study done at our center confirms an early, transient benefit compared to the posterior approach with parity maintained at 6 and 12 weeks postoperatively [unpublished data]. It is a true intermuscular approach with limited potential for hip abductor injury as well as minimal to no damage to the posterior hip stabilizers. Since the femoral vessels are not distorted (compared to the posterior approach), risk of thromboembolic complications may be theoretically lower. Moreover, patients are much relieved to have no hip dislocation precautions, even in the early postoperative period. In summary, the anterior approach is an excellent and rewarding approach for surgeons and patients, at least for primary THA, allowing reproducible component positioning and rapid rehabilitation.