Hybrid Total Hip Replacement (Cemented Stem, Uncemented Cup)

Indications for Hybrid THA

Patient Selection

• Age greater than 70 years with Dorr B or C femoral morphology
• Osteopenic or osteoporotic bone where uncemented stem fixation is unreliable
• Previous femoral osteotomy or deformity favouring cemented stem
• Surgeon preference based on registry-proven cemented stem durability in older patients

Absolute Indications

• Failed previous fixation with significant bone loss requiring cemented reconstruction
• Pathological fracture or metastatic disease requiring immediate stable fixation
• Neuromuscular conditions with high dislocation risk where constrained or dual-mobility options are planned

Relative Indications

• Age 65-75 with mixed bone quality
• Inflammatory arthritis with poor bone stock
• Prior radiation to the proximal femur

Contraindications

Absolute:

• Active infection
• Severe acetabular bone deficiency preventing press-fit cup stability
• Known severe allergy to bone cement or antibiotics in cement

Relative:

• Young active patients (less than 60) with good bone quality — consider fully uncemented
• Severe cardiopulmonary disease where cement implantation syndrome risk is prohibitive

Registry Evidence for Hybrid Fixation

Hybrid constructs demonstrate excellent long-term survivorship in multiple national registries. Cemented stems maintain greater than 95 percent survival at 15 years in patients older than 75, while modern porous-coated cups achieve greater than 98 percent osseointegration at 10 years across all age groups. The combination avoids the higher early revision rates seen with fully uncemented stems in older patients and the late cup loosening seen with older cemented cup designs.

Key Evidence

Relevant Surgical Anatomy for Hybrid THA

Acetabulum

The acetabulum is a hemispherical socket formed by ilium, ischium and pubis. The posterior wall is thicker and provides the primary buttress for cup fixation. The posterosuperior quadrant is the safest zone for screw placement. The anterior wall is thinner and lies immediately posterior to the external iliac vessels. The quadrilateral surface is thin (2-4 mm) and must not be penetrated by screws.

Proximal Femur

The femoral neck-shaft angle averages 125-135 degrees. The calcar femorale is a dense cortical strut on the medial neck that provides critical support for the cemented stem. Dorr classification describes canal morphology: Type A (champagne flute, thick cortices), Type B (intermediate), Type C (stovepipe, thin cortices). Hybrid THA is particularly indicated for Dorr B and C femurs where uncemented stem fixation may be unreliable.

Sciatic Nerve

The sciatic nerve exits the pelvis through the greater sciatic notch, passes posterior to the acetabulum and courses distally along the ischium. In the posterior approach it lies 1-2 cm posterior to the greater trochanter at the level of the piriformis. Identification and protection are mandatory before posterior capsulotomy.

Blood Supply

The medial femoral circumflex artery is the primary blood supply to the femoral head and must be preserved during capsular exposure. The superior gluteal artery exits the greater sciatic notch and supplies the abductor musculature. The inferior gluteal artery and sciatic nerve travel together in the greater sciatic notch.

Safe Intervals

The posterior approach exploits the interval between gluteus maximus (inferior gluteal nerve) and the abductors (superior gluteal nerve). The short external rotators (piriformis, gemelli, obturator internus, quadratus femoris) are divided close to their insertion to protect the medial femoral circumflex artery and allow later repair.

Positioning and Preparation

Patient position: Lateral decubitus on a radiolucent table with beanbag or pegboard support. The operative leg is draped free. Confirm the table can accommodate fluoroscopy if needed. Apply sequential compression devices and antibiotic prophylaxis (cefazolin 2 g IV or vancomycin if MRSA risk).

Anaesthesia: Spinal or general anaesthesia with arterial line monitoring in high-risk patients. Maintain normovolaemia throughout. Have vasopressors (phenylephrine, ephedrine) immediately available for cement implantation syndrome.

Consent: Discuss dislocation risk (1.5-2.5 percent), leg-length discrepancy, cement implantation syndrome, infection (less than 1 percent), nerve injury (less than 1 percent), and the need for possible blood transfusion.

Posterior Approach — Step-by-Step

Step 1: Incision and Superficial Dissection

Make a 12-15 cm curved incision centred over the greater trochanter, extending proximally along the gluteus maximus fibres and distally along the femoral shaft. Divide the fascia lata in line with the skin incision. Split the gluteus maximus fibres bluntly in the direction of their orientation, protecting the inferior gluteal neurovascular bundle.

Step 2: Identify and Protect the Sciatic Nerve

Palpate the sciatic nerve on the posterior surface of the ischium. Place a vessel loop or Penrose drain around the nerve for identification. Retract the nerve gently medially and protect it throughout the procedure. Never place a retractor deep to the nerve on the ischium.

Step 3: Divide Short External Rotators and Posterior Capsule

Tag and divide the short external rotators (piriformis, superior and inferior gemelli, obturator internus, quadratus femoris) close to their insertion on the greater trochanter. Tag the tendons for later repair. Perform a posterior capsulotomy from the acetabular rim to the femoral neck, preserving as much capsule as possible for repair. Dislocate the hip by flexing, adducting and internally rotating the leg.

Step 4: Femoral Neck Osteotomy and Acetabular Exposure

Perform the femoral neck osteotomy at the pre-planned level using the neck resection guide from the implant system. Remove the femoral head. Place a curved retractor over the anterior acetabular rim to expose the acetabulum. Place a posterior retractor on the ischium (avoiding the sciatic nerve) and an inferior retractor under the transverse acetabular ligament.

Step 5: Acetabular Preparation and Cup Implantation

Remove residual labrum and osteophytes. Identify the true floor of the acetabulum. Ream sequentially with hemispherical reamers, preserving subchondral bone where possible. Under-ream by 1-2 mm for press-fit. Impact the trial cup to assess stability and position (abduction 40-45 degrees, anteversion 15-25 degrees). Select the definitive cup size. Impact the porous-coated acetabular component. Assess primary stability. If needed, add 2-3 screws in the posterosuperior quadrant only, limiting length to less than 25 mm. Confirm extra-pelvic screw placement by palpation or fluoroscopy. Insert the polyethylene liner.

Step 6: Femoral Canal Preparation

Expose the femoral canal by placing the leg in the figure-of-four position. Remove residual femoral neck bone. Use sequential broaches to prepare the canal, aiming for a minimum 2 mm cement mantle on all sides. Confirm the broach size that achieves rotational stability with at least 2 mm clearance for cement. Perform a trial reduction to assess leg length, offset, and stability.

Step 7: Third-Generation Cementing Technique

Place a cement restrictor plug 2 cm distal to the planned stem tip. Perform pulsatile lavage with at least 1 L of saline until the effluent is clear. Dry the canal thoroughly with suction and epinephrine-soaked swabs. Inject low-viscosity cement in retrograde fashion using a pressurised gun while maintaining continuous pressure. Insert the stem with a centraliser to ensure central positioning. Maintain pressurisation until the cement has hardened. Remove excess cement.

Step 8: Final Reduction and Stability Testing

Reduce the hip. Perform stability testing in full flexion, extension, and combined positions. Confirm leg length with a pin or ruler comparison to the contralateral side. Assess offset and abductor tension. Irrigate the wound. Repair the posterior capsule and short external rotators to the greater trochanter using heavy non-absorbable sutures. Close fascia, subcutaneous tissue, and skin in layers. Apply sterile dressing.

Postoperative Protocol

Day 0-2

• Mobilise weight-bearing as tolerated from day of surgery with physiotherapist
• Multimodal analgesia (paracetamol, NSAIDs, gabapentinoids, opioids as needed)
• VTE prophylaxis (enoxaparin 40 mg daily or rivaroxaban 10 mg daily for 28-35 days)
• Hip precautions for 6 weeks if posterior approach (no flexion greater than 90 degrees, no adduction, no internal rotation)

Week 2-6

• Wound review at 10-14 days
• Progressive physiotherapy focusing on abductor strengthening and gait normalisation
• Discontinue hip precautions at 6 weeks if stable

Long-term

• Follow-up at 6 weeks, 3 months, 1 year, then annually or biennially
• Radiographs at each visit to assess component position and fixation
• Return to low-impact activities (swimming, cycling, walking) at 3 months; higher-impact activities discussed individually

Registry Outcomes and Global Practice

Hybrid THA demonstrates excellent long-term durability. AOANJRR 2023 data show 96.8 percent survival at 10 years for hybrid constructs in patients older than 70. NJR data confirm greater than 94 percent survival at 15 years with third-generation cementing. The combination of a cemented stem and uncemented cup is particularly effective in older patients with poor bone quality, where fully uncemented stems carry higher early revision risk for fracture and subsidence.

Global guidelines (AAOS, NICE, BOA-BOAST, EFORT) support the use of hybrid fixation in appropriately selected patients. Cemented stems remain the preferred option in patients older than 75 or with Dorr C femurs in most national registries. Modern porous-coated cups have largely replaced cemented acetabular components because of superior long-term fixation.