Direct anterior approach total hip replacement

Overview

The direct anterior approach uses the internervous plane between tensor fasciae latae (superior gluteal nerve) and sartorius and rectus femoris (femoral nerve). The patient is supine on a traction table with the operated leg in a positioner, so the surgeon controls exposure through traction, rotation, extension and adduction of the limb rather than through the assistant. Mastery of the approach is largely mastery of three things: the fascial window over tensor, the capsular releases that let the femur come up into the wound, and the table.

In this practice the standard construct is a cementless hemispherical cup with a highly cross-linked polyethylene liner, and a cemented polished taper stem. A cementless proximally coated stem is used in selected patients, and the differences are noted at each step. The pre-operative plan is a patient-specific one: a planning study generates the cup orientation targets, the neck-cut level and a neck-cut guide.

Equipment

Trays

• Mayo table
• Acetabular reamers and handles; cup impactor and trial shells; trial liners (and dual-mobility trials where planned)
• Patient-specific neck-cut guides from the pre-operative plan
• General retractor and instrument tray: rat-tail rasp, retractors, corkscrew
• Femoral broaches and offset broach handles
• Anterior-approach retractor tray
• Table attachments: traction leg positioner, gluteal bolster

On the Mayo table

• Knife: #21 blade on a standard handle for skin, long handle for depth
• Sponges × 2
• Rake retractors × 2
• Large articulating self-retaining retractor
• Cobb elevator
• Right-angled forceps × 2, loaded with #1 braided absorbable ties (or a bipolar sealer, if available)
• 0 braided absorbable suture on a small needle, in a needle holder (capsular stay)
• Gillies forceps, Metzenbaum scissors, Kocher forceps
• Anterior retractors: blunt Hohmann, double-bent Hohmann × 2, cobra retractor, blue-handled femoral neck elevator

Power, suction and energy

• Yankauer suction, with a revision sucker for later in the case
• Diathermy with a medium-length tip
• Pulse lavage
• Bipolar sealer where available
• Image intensifier available in the room

1. Positioning, landmarks and draping

1. Cohesive bandage on both feet. Supine, with the operated leg in the traction positioner.
2. Level the pelvis and set the hips symmetrically abducted. Set the operated limb in 30° of external rotation. Check patella height against the other side as a baseline for leg length.
3. Mark the incision: start 2 cm distal and 2 cm lateral to the anterior superior iliac spine and run it distally toward the head of the fibula, over the belly of tensor fasciae latae. Starting lateral to the spine keeps the lateral femoral cutaneous nerve medial to the wound.
4. Alcoholic chlorhexidine preparation.
5. Drape: two head drapes, two adhesive U-drapes, two iodine-impregnated incise drapes as the isolation layer.
6. Connect suction, diathermy, pulse lavage and the bipolar sealer before the knife.

2. Approach

1. Skin and subcutaneous tissue along the marked line.
2. Tensor fascia. Identify the fascial sheath of tensor fasciae latae and spread it to confirm the fibre direction before opening it. Open the sheath in line with the fibres, staying on the tensor side so the lateral femoral cutaneous nerve stays protected in the medial fascial leaf.
3. Sweep a finger (“slippery finger”) medially under the fascia, between tensor and sartorius, down to the intermuscular plane. Place the large self-retainer vertically.
4. Place a double-bent Hohmann superiorly to check the release and feel the iliac crest. If more exposure is needed, release the origin of tensor off the crest.
5. The fatty layer. Look for the red-white-yellow sequence (tensor muscle, its fascia, the fat over the capsule) and release the fascia at the white-yellow junction.
6. Turn the self-retainer to the horizontal so it now retracts rectus femoris medially.
7. Divide the delicate fascial floor beneath.
8. Circumflex vessels. Use the Cobb elevator to isolate the ascending branches of the lateral femoral circumflex artery, which cross the field in the fat at the lower end of the window. Tie and divide them, or seal them with the bipolar sealer. Unsecured, they are the commonest source of early bleeding in this approach.
9. Place a blunt Hohmann on the inferior femoral neck and a double-bent Hohmann on the superior neck at the acetabular margin.
10. Clear the precapsular fat with the Cobb and diathermy, sweeping laterally and inferiorly, until the anterior capsule is clean.
11. Rotate the limb a few degrees in each direction while watching the field (“wiggle-wiggle”): the acetabulum-head interface declares itself as the line that does not move.
12. Capsulotomy. Make an L-shaped capsulotomy. Identify the reflected head of rectus femoris and the acetabular margin as you go, and move the blunt Hohmann from outside to inside the capsule once the joint is open.
13. Place a 0 braided absorbable stay suture on a small needle in the superior capsular flap, then complete the superior capsulotomy. Clip the stay and cut.
14. Check that the inferior capsule and the saddle (the junction of neck and greater trochanter) are released.
15. Pin the patient-specific guide to the anterior neck with two pins.

3. Femoral neck cut and head removal

1. Apply fine traction on the table, about 20 mm, to open the joint a little.
2. Cut the neck with the saw held upside down against the guide, so the blade angle matches the planned cut. Complete the cut with an osteotome and mallet.
3. Drive a corkscrew into the head.
4. Externally rotate the limb to 50°, which turns the cut head towards the wound and assists its delivery.
5. Remove sharp fragments. Divide the remaining posterior capsular attachments to the head with rongeurs to hand.
6. Deliver the head. Measure it, and check the cut against the guide and the plan.

4. Acetabular preparation

1. Move the large self-retainer deeper so it holds back the anterior capsule and the capsular flap.
2. Excise the labrum and the ligamentum teres to expose the true floor. The bipolar sealer controls the bleeding from the pulvinar.
3. Ream sequentially, starting 2 mm under the measured head size and finishing 4 mm over it, or to the plan.
4. Bring in the image intensifier for the last reamer if there is any doubt that the reamer is down to the teardrop (optional).

5. Definitive cup

1. Change gloves.
2. Load the cup on the impactor with the orientation guide attached.
3. Check inclination and anteversion against the plan before impacting (see note).
4. Infiltrate 20 ml of local anaesthetic.
5. Insert the liner: a neutral (0°) liner in the standard construct.

Note on targets. The written workflow records an inclination check of 50 and anteversion of 20 at impaction. Confirm with Dr Broadhead whether these are the intended cup angles or the reading on the orientation guide, and record the plan’s own targets for each patient; the patient-specific plan takes precedence.

6. Delivering the proximal femur

This is the step that separates the anterior approach from the others, and it is done in order, slowly, with the surgeon calling the table movements aloud.

1. Traction off. Externally rotate to 120° if the hip allows (optional), then bring the limb back to 90°.
2. Check that the pubofemoral ligament is released.
3. Place the large bone hook around the neck and lift.
4. Release the iliofemoral ligament.
5. Release the posterior capsule and clear the piriformis fossa only if the femur still will not come up. Work from 12 o’clock around to 3 or 9 o’clock gradually, releasing only as much as the exposure needs.
6. Extend the hip on the table. Go slowly, call out each increment, and stop halfway to check: the greater trochanter must clear the acetabular rim.
7. Adduct 20° to 40°.

The femur is delivered when the neck cut faces the surgeon with the greater trochanter clear of the posterior rim and the calcar visible without force.

7. Femoral preparation and trial reduction

Have the cement or the powered broach impactor ready before starting.

1. Open the canal: box chisel at the piriformis fossa, then the rat-tail rasp, nibblers and a curette. Lateralise with the saw where the stem’s shoulder needs room, as the polished taper stem does.
2. Broach sequentially, with the offset broach handles. Use the powered impactor for the cementless stem.
3. If the fit is tight, have a guidewire and flexible reamers available to ream the canal.
4. Trial the neck and head with the leg brought half way back up.
5. Adduction off; bring the leg up to neutral.
6. Reduce: traction up to 5 to 7 cm with internal rotation. Do not force a reduction; if it will not go, something is in the way.
7. Test stability: externally rotate to 90° and drop the limb into 10° of extension.
8. Shuck test for axial stability.
9. Image intensifier and a long straight instrument to check leg length and offset against the other side (optional at this stage, routine at the next).
10. Dislocate for the definitive stem: external rotation, extension and adduction.

8. Definitive stem

Cemented polished taper stem (standard)

1. Cement restrictor from the preparation kit, sized to the canal.
2. Load an 8 to 10 mm centraliser onto the stem.
3. Pack the canal with hydrogen peroxide on gauze, then suction dry.
4. Antibiotic-loaded high-viscosity bone cement, vacuum mixed, inserted retrograde and pressurised.
5. Insert the stem, using a Trethowan spike to hold it laterally in the canal while the cement sets.
6. Trial head and leg-length check (optional).

Cementless proximally coated stem (selected patients)

1. Final broach to the planned size; the broach’s seating is the guide to the stem’s seating.
2. Impact the definitive stem to the same level.

9. Final trial, definitive head and reduction

1. Trial head on the stem.
2. Image intensifier with the long straight instrument: compare leg length and offset with the other side.
3. Externally rotate to 90° and drop into 10° of extension to confirm stability with the definitive stem.
4. Definitive femoral head on a clean, dry taper. Reduce.

10. Closure

1. Repair the capsule with 0 braided absorbable suture on a small needle (optional).
2. Wash out with dilute povidone-iodine, then pulse lavage.
3. Local anaesthetic infiltration.
4. Layered closure: 0 barbed absorbable suture for the fascia, 2-0 barbed absorbable for the subcutaneous layer, 3-0 monofilament absorbable for the skin.
5. Mesh-reinforced skin adhesive, then a transparent film dressing, with a dated sticker for removal at 14 days, and an iodine-impregnated drape over the top.

Pitfalls

• Lateral femoral cutaneous nerve. It lives in the medial leaf of the tensor fascia. Open the sheath on the tensor side and never on the sartorius side.
• Circumflex vessels. Find them before they find you. They sit in the fat at the inferior end of the window.
• The femur that will not come up. Release in order: pubofemoral, iliofemoral, then posterior capsule and the piriformis fossa, and only as far as needed. Extension and adduction on the table do the rest. Forcing the femur with the hook breaks the trochanter.
• The table. Every movement is called aloud, in increments. Traction is on for the neck cut and the reduction only; it is off for the femoral releases.
• The reduction. Traction and internal rotation, never force. A hip that will not reduce has soft tissue, a trial or an osteophyte in the way.

Post-operative protocol

There are no routine posterior-type precautions after this approach. The limb is kept out of extension with external rotation for six weeks. Full weight bearing from day one. The patient-facing program is the anterior hip rehabilitation guide.