Revision THA — Femoral Impaction Bone Grafting

Surgical Indications

Absolute Indications

• Contained cavitary femoral bone loss (Paprosky Type II or IIIA) in a patient younger than 65 years where restoration of bone stock is a priority for future revisions
• Failed primary or revision stem with contained osteolysis and adequate proximal femoral support for impaction
• Need for biological reconstruction rather than mechanical distal fixation in a physiologically young patient

Relative Indications

• Paprosky Type IIIA defects with greater than 4 cm of intact isthmus when combined with mesh containment of any segmental component
• Patient preference for bone-stock restoration over an extensively porous-coated stem that sacrifices proximal bone
• Revision of a cemented stem where the cement mantle has failed but the surrounding bone is cavitary rather than segmental

Contraindications

Absolute:

• Uncontained segmental defects (Paprosky IIIB or IV) without ability to contain with mesh or strut allograft
• Active periprosthetic joint infection
• Inadequate distal femoral isthmus (less than 4 cm) for stable trial impaction

Relative:

• Elderly low-demand patient where an uncemented modular fluted tapered stem offers faster recovery
• Severe osteoporosis with cortical thickness less than 2 mm (high fracture risk)
• Previous pelvic radiation or poor soft-tissue envelope increasing infection risk

Evidence for Impaction Bone Grafting

Principle and Rationale

• Fresh-frozen morcellised allograft impacted around a polished tapered cemented stem restores proximal femoral bone stock by creeping substitution
• The polished stem is deliberately non-bonded to cement and subsides within the mantle to achieve a self-locking wedge; this is the opposite philosophy to a roughened stem that requires immediate cement interlock
• The Exeter and Nijmegen (Slooff) groups pioneered the technique with greater than 85 percent survivorship at 10-15 years when performed for contained defects

Comparison with Alternative Femoral Reconstructions

Key Evidence

Paprosky Femoral Defect Classification

Type I

Minimal bone loss with intact metaphyseal and diaphyseal bone; primary stem or simple cementless revision is sufficient. Impaction grafting is not indicated.

Type II

Contained cavitary bone loss with intact proximal femoral support; the isthmus is intact and greater than 4 cm of diaphyseal bone is available for distal stem fixation. This is the classic indication for impaction bone grafting.

Type IIIA

Greater than 4 cm of intact isthmus with contained cavitary loss; impaction grafting with mesh containment of any segmental component remains feasible. The distal isthmus provides rotational stability for the trial stem during impaction.

Type IIIB

Less than 4 cm of intact isthmus; impaction grafting alone is unreliable because the trial stem cannot achieve rotational stability. A modular fluted tapered stem or structural allograft-prosthetic composite is preferred.

Type IV

Complete loss of the proximal femur with no supportive isthmus; custom tumour prosthesis, allograft-prosthetic composite or proximal femoral replacement is required. Impaction grafting is contraindicated.

Relevant Surgical Anatomy for Impaction Grafting

Proximal Femoral Bone Stock

• The medial calcar and anterior and posterior metaphyseal cortices provide the contained envelope for graft impaction
• In revision surgery the calcar is often deficient or sclerotic; mesh or strut augmentation is required to restore containment
• The greater trochanter must be preserved or reconstructed because abductor function determines stability and gait

Femoral Canal Dimensions

• The isthmus is the narrowest point of the diaphysis and provides the distal anchor for the trial stem during impaction
• A minimum 4 cm of intact isthmus is required for stable trial seating; shorter isthmus mandates a different reconstruction strategy
• The anterior bow of the femur must be respected when selecting stem length; a stem that is too long risks anterior cortical perforation

Neurovascular Structures at Risk

• The sciatic nerve lies immediately posterior to the greater trochanter and is tethered by scar in revision surgery; it must be identified and protected throughout exposure and reconstruction
• The femoral nerve and profunda femoris artery lie anteriorly and are at risk during anterior column exposure or mesh placement
• The superior gluteal neurovascular bundle is at risk during extended trochanteric osteotomy or abductor reconstruction

Soft-Tissue Envelope

• Previous incisions and scar tissue alter the tissue planes; the posterior approach is most commonly used because it allows extensile exposure and sciatic nerve identification
• The abductor mechanism may be deficient or detached; repair or augmentation with a constrained liner or dual-mobility construct is often required

Positioning and Preparation

Patient position: Lateral decubitus position on a radiolucent table with the operative hip uppermost. The pelvis is stabilised with pubic and sacral supports to allow free movement of the limb and accurate leg-length assessment. The entire leg is prepped and draped free to allow full range of motion and traction.

Approach: Posterior (Moore-Southern) approach is standard for impaction grafting because it provides extensile access to the femur and acetabulum and allows direct visualisation and protection of the sciatic nerve. An extended trochanteric osteotomy is added when distal cement removal or femoral deformity correction is required.

Anaesthesia: Regional (spinal or epidural) plus general anaesthesia is preferred for muscle relaxation and controlled hypotension. Invasive arterial monitoring is used in lengthy revisions. Tranexamic acid (1 g IV at induction and 1 g at closure) reduces blood loss.

Equipment: Have available a full revision hip set, cerclage wires or cables, mesh (titanium or tantalum), fresh-frozen morcellised allograft (minimum 4-6 femoral heads), distal cement restrictors, polished tapered cemented stem system (Exeter or equivalent), and a backup modular fluted tapered stem.

Consent: Discuss risk of intraoperative fracture (5-15 percent), subsidence, dislocation (5-10 percent), infection (2-5 percent), sciatic nerve injury (1-3 percent), leg-length discrepancy, and the possibility of switching to an alternative reconstruction if impaction grafting proves unstable intraoperatively.

Step-by-Step Operative Technique

Step 1: Exposure and Component Removal

The posterior approach is developed through the previous incision when possible. The sciatic nerve is identified and protected with a vessel loop or Penrose drain. The posterior capsule and short external rotators are tagged and preserved for later repair. The femoral stem and cement are removed using standard techniques (cement extraction system, ultrasonic cement removal, or extended trochanteric osteotomy if required).

The acetabulum is addressed first if both components are being revised. The femur is then delivered into the wound with gentle traction and external rotation. Any remaining cement, membrane or debris is meticulously removed from the femoral canal with curettes and a high-speed burr. The canal is irrigated and dried.

Step 2: Defect Assessment and Containment

The femoral defect is classified according to Paprosky. Any segmental or uncontained defect (anterior, medial or posterior wall) is contained with titanium mesh or strut allograft secured with cerclage wires or cables. The mesh must be stable and must convert the defect into a contained cavity before any graft is introduced.

A distal cement restrictor is placed 2 cm beyond the planned length of the definitive stem. This prevents graft from escaping distally and allows pressurisation of the cement column.

Step 3: Graft Preparation and Impaction

Fresh-frozen femoral heads are morsellised into 5-8 mm chips using a bone mill or rongeurs. The chips are lightly packed but not washed excessively to preserve osteoinductive factors. The graft is introduced into the contained defect in layers beginning distally.

Sequential impaction is performed with increasing-diameter trial stems. Each trial is advanced with firm axial blows until it seats at the planned level and demonstrates axial and rotational stability. The process is repeated with the next larger trial until the final trial is stable. The trial is then removed and the canal is inspected for any areas of inadequate graft density.

Step 4: Cementing the Polished Tapered Stem

Once the final trial is stable, the canal is again irrigated and dried. Polymethylmethacrylate cement is mixed and introduced in a retrograde fashion with a cement gun. The cement is pressurised thoroughly to interdigitate with the impacted graft. The definitive polished tapered stem (collarless Exeter-type) is inserted to the predetermined depth and held in position until the cement has fully polymerised.

The stem is deliberately not bonded to the cement; it will subside 1-3 mm within the mantle over the first year to achieve a self-locking wedge. This subsidence is expected and desirable.

Step 5: Trial Reduction, Stability Assessment and Closure

A trial head is applied and the hip is reduced. Leg length, offset and stability are assessed in all positions. Abductor tension is evaluated; if deficient, a constrained liner or dual-mobility construct is considered. The posterior capsule and short external rotators are repaired to the greater trochanter. Drains are placed. The wound is closed in layers.

Post-operative Protocol

Early Phase (Day 0-14)

• Protected weight-bearing: Touch weight-bearing or 20 kg partial weight-bearing for the first 6 weeks, then 50 percent weight-bearing until 12 weeks
• Hip precautions: Posterior hip precautions for 12 weeks (no flexion greater than 90 degrees, no adduction, no internal rotation beyond neutral)
• DVT prophylaxis: Low-molecular-weight heparin or direct oral anticoagulant for 35 days
• Wound care: Drain removal at 24-48 hours; staples or sutures at 14-16 days

Return to Function

• Driving: When safe to perform an emergency stop (usually 6-8 weeks)
• Work: Sedentary work at 3 months; manual work at 6 months
• Sports: Low-impact activities only after 6 months; avoid running or jumping indefinitely

Radiographic Surveillance

• 6 weeks, 3 months, 6 months, 1 year, then annually for 5 years, then every 2 years
• Assess graft incorporation (hazy interface becoming trabecular by 6-12 months), stem subsidence (acceptable 1-3 mm; concerning greater than 5 mm), cement mantle integrity, and any lucent lines

Graft Incorporation and Long-Term Outcomes

Radiographic Incorporation

• At 3 months the graft-host interface appears hazy; this represents early creeping substitution
• By 6-12 months the graft shows trabecular continuity with host bone in successful cases
• Complete incorporation with remodelling to normal bone density occurs by 2-3 years in the majority of contained defects

Survivorship Data

• 85-95 percent free of aseptic loosening at 10-15 years in contained defects when performed in high-volume centres
• Outcomes are inferior when mesh is required for segmental defects or when intraoperative fracture occurs
• The polished tapered stem philosophy (deliberate subsidence within the cement mantle) is associated with lower rates of cement mantle fracture than roughened or precoated stems

Future Revision Considerations

• Successful impaction grafting restores proximal femoral bone stock, making subsequent revisions technically easier and preserving options for the patient
• Failed impaction grafting with stem loosening usually requires conversion to a modular fluted tapered stem or structural allograft-prosthetic composite