Posterior approach total hip replacement

Overview

The posterior approach splits gluteus maximus in the line of its fibres, takes down the short external rotators and the posterior capsule, and dislocates the hip posteriorly by flexion, adduction and internal rotation. It is extensile, it is the approach most registrars will learn first, and the quality of the capsular and rotator repair at the end is what the patient’s early stability depends on.

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 patient-specific and provides a neck-cut guide. A pelvic-pin leg-length caliper is used where leg length is critical.

Equipment

Trays

• Mayo table
• Acetabular reamers and handles; cup impactor and trial shells; trial liners (and dual-mobility trials where planned)
• General instrument and retractor tray
• Patient-specific neck-cut guide from the pre-operative plan
• Femoral broaches and femoral instruments for the planned stem
• On hand, unopened: acetabular screw tray, offset reamer handles, liner removal instruments

On the Mayo table

• Knife: #21 blade, with a longer handle available
• Sponges × 2
• Cobb elevator
• Long Gillies forceps, Metzenbaum scissors, Kocher forceps
• Posterior Charnley retractor
• Small self-retaining retractor
• Hohmanns: long and extra-long, standard, and a blunt standard retractor for the pubis
• Braided non-absorbable sutures loaded in a needle holder (rotator stay sutures)
• Blue-handled femoral neck elevator

Power, suction and energy

• Suction with a revision sucker
• Diathermy with a medium-length tip
• Pulse lavage

1. Positioning, landmarks and draping

1. Lateral decubitus. Round posterior support at the sacrum, a double anterior support at the anterior superior iliac spines, and a sandbag at the shin.
2. Check that the pelvis is neutral and square to the table, neither rolled forward nor back. Every cup orientation reading later in the case assumes it.
3. Mark the incision: centred over the greater trochanter with the hip flexed to 40°, extended proximally and distally as the exposure requires.
4. If the leg-length caliper is to be used, expose and prepare the iliac crest for its pin.
5. Alcoholic chlorhexidine preparation.
6. Drape: two head drapes, two adhesive U-drapes, stockinette and cohesive bandage on the foot, a hip drape with pouches, then two large iodine-impregnated incise drapes, groin first, and an isolation drape.
7. Connect suction, diathermy and pulse lavage before the knife.

2. Approach

1. Skin. Sharp dissection through skin and subcutaneous tissue.
2. Fascia. Incise the fascia lata distally and continue proximally into the fascia over gluteus maximus, in line with its fibres.
3. Muscle. Split gluteus maximus bluntly along its fibres. Identify the sciatic nerve by palpation in the fat posterior to the rotators and keep it protected throughout; it is never dissected out.
4. Short external rotators. Identify piriformis and the conjoined tendon of the obturator internus and gemelli. Tag each with a braided non-absorbable stay suture, then release them at their trochanteric insertion. Clip and cut. The stays retract the rotators backwards over the nerve and are the handles for the repair at the end.
5. Capsule. L-shaped posterior capsulotomy, preserving a flap that can be repaired.
6. Dislocation. Flex, adduct and internally rotate the hip, with gentle traction, to dislocate the head posteriorly.

3. Femoral neck cut and head removal

1. Blunt Hohmann on the inferior neck.
2. Clear the saddle (the junction of neck and greater trochanter) of soft tissue with forceps and knife, so the guide seats on bone.
3. Seat the patient-specific guide, pin it, and drill.
4. Cut the neck with the saw held upside down against the guide.
5. Drill out the pins and remove the guide.
6. Complete the cut with a wide osteotome and mallet.
7. Corkscrew into the head if it helps delivery (optional).
8. Deliver the head and measure it.

4. Acetabular preparation

1. Long Hohmann anteriorly over the anterior wall.
2. Standard Hohmann beneath tensor fasciae latae.
3. Small self-retainer on the capsule.
4. Excise the labrum and the ligamentum teres to expose the true floor.
5. Ream sequentially, starting 2 mm under the measured head size and finishing 4 mm over it, or to the plan.
6. Watch the quadrilateral plate: it is the medial limit.

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 lipped liner is placed with the lip postero-inferior.
6. Remove rim osteophytes with an osteotome where they would impinge.

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. Femoral exposure and preparation

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

1. The assistant holds the leg vertical, with the hip flexed and internally rotated and the knee flexed, so the cut surface of the neck faces the surgeon.
2. Blue-handled double-prong retractor under the calcar to deliver the neck cut into the wound.
3. 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.
4. Broach sequentially. Use the powered impactor for the cementless stem.
5. If the fit is tight, have a guidewire and flexible reamers available to ream the canal.

7. Trial reduction and stability

1. Trial neck and head.
2. Reduce with traction and external rotation.
3. Posterior stability: hand under the knee, flex the hip to 90° and internally rotate. Note the degree of internal rotation at which the hip levers.
4. Leg length: clinically against the other side, or with the pelvic-pin caliper if it was placed.
5. Shuck test for axial stability.
6. Anterior stability: extend and externally rotate.
7. Dislocate for the definitive stem.

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. Definitive head and reduction

1. Trial head, plus or minus a size, and repeat the stability tests if anything has changed.
2. Definitive femoral head on a clean, dry taper. Reduce.

10. Closure

1. Repair the capsule and the short external rotators back to the trochanter with the braided non-absorbable stays on a Mayo needle, through drill holes or to the tendinous insertion. This repair is the posterior hip’s stability; do it properly.
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

• Pelvic position. A pelvis that has rolled forward reads as anteversion that is not there. Check it before the cup and again if the patient has been moved.
• Sciatic nerve. Palpate it, protect it with the retracted rotators, and keep retractors off it. Never place a Hohmann blindly behind the acetabulum.
• The saddle. Clear it properly so the guide sits on bone and the cut is where the plan put it.
• Quadrilateral plate. The reamer stops at the medial wall. Depth is the plan, not the feel.
• The repair. The capsule and rotators are repaired every time. The precautions the patient follows afterwards protect this repair while it heals.

Post-operative protocol

Full weight bearing from day one. Posterior precautions for about six months in this practice: no hip flexion past 90°, no crossing the midline, no internal rotation. The patient-facing program is the posterior hip rehabilitation guide.