Femoral Impaction Bone Grafting

Femoral impaction bone grafting (IBG) was popularised in Exeter (Gie, Ling) and Nijmegen (Slooff, Schreurs) in the late 1980s to early 1990s. It addresses the central problem of femoral revision in the young patient: every alternative strategy consumes or bypasses bone, whereas IBG rebuilds it.

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How the strategies differ. The strategy in a deficient femur is chosen by whether bone stock must be rebuilt, bypassed or substituted. Impaction grafting with a cemented polished taper rebuilds it; a distally fixed stem bypasses the proximal femur and accepts proximal stress-shielding and a harder re-revision; a proximal femoral replacement or allograft-prosthesis composite substitutes for it, which is salvage rather than restoration.

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Who it is for. The decision turns on infection status, the Paprosky defect type, whether the cortical tube is contained or can be made so, and what the patient will demand of the reconstruction. The younger, higher-demand patient in whom re-revision is anticipated is the one in whom restoring bone stock is strategically valuable; the elderly, low-demand patient favours a quicker construct, because IBG is technically demanding and time-consuming.

Indications. The defect must be contained or containable, and the patient must stand to gain from the bone:

• Paprosky type II and IIIA cavitary or ectatic defects with an intact cortical tube, the classic indication
• Paprosky IIIB and selected IV, and Vancouver B3 periprosthetic fractures, provided the tube can be reconstituted with mesh, cerclage and/or strut allograft to contain the graft
• Wide, capacious "stove-pipe" canals where a cemented stem alone would have an excessive mantle and an uncemented stem cannot obtain fit

Contraindications. Do not graft into infection, and do not graft into a defect you cannot close:

• Active infection: staged reconstruction only after eradication
• Segmental loss that cannot be converted to a contained defect
• Inability to source adequate allograft, typically 2 to 4 fresh-frozen femoral heads
• Very elderly or low-demand patients, where a quicker distally fixed stem or proximal femoral replacement is more pragmatic

Morsellised, impacted fresh-frozen allograft behaves quite differently from structural bulk allograft, which remains largely a dead scaffold with only superficial creeping substitution. Incorporation is real, but it is partial and slow, and it should be described that way.

What incorporation needs. A contained defect, a viable vascular host bed, rigid mechanical stability of the graft mass, compressive rather than shear loading, absence of infection, and graft of adequate quality, free of fat and soft tissue.

Source. Fresh-frozen femoral head allograft from a licensed bone bank, typically 2 to 4 heads for a femur. All cartilage, cortical shell remnants and soft tissue are stripped before milling.

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Chip size by zone. The distal canal takes 8 to 10 mm chips, milled with a bone mill or rongeurs. Large chips interlock and resist axial and shear load where distal stability is most critical; chips milled too fine distally lose interlock and allow subsidence. The last proximal layers use finer chips of roughly 3 to 5 mm, which pack around the tamps into metaphyseal irregularities and fill the proximal cavity densely. The proximal pitfall is over-milling to a slurry or paste, which has no mechanical interlock at all.

Washing. Washed graft is now preferred: warmed saline pulsed lavage over a sieve, drained, and impacted slightly damp. Washing removes marrow fat, blood and immunogenic cellular debris; fat acts as a lubricant, so washed graft achieves higher shear strength and impaction density in bench testing, and washing may reduce immunogenic load and fat embolisation. Chip size is set at milling and is unchanged by washing. Two pitfalls: impacting sodden rather than damp graft, and leaving fat in situ and blaming the tamps for poor density.

The case for unwashed graft. The classic Exeter series milled and impacted the graft directly, and the results carded below were obtained with unwashed graft. Unwashed graft retains marrow elements and theoretically osteoinductive proteins, and its published results are historically excellent; against it, fat lubrication limits the achievable impaction density, and that mechanical argument now dominates in most units. The case for washing rests on laboratory and practice-based reasoning, not on a clinical comparison.

Antibiotic in the graft. Some surgeons add antibiotic powder, for example vancomycin, to the graft in higher-risk cases for local elution at the graft bed. The evidence is limited; elution data are supportive, but this is adjunctive and no substitute for debridement and systemic cover.

Position and approach. Lateral decubitus on a supported table. The posterior approach is most common because it is extensile and allows an extended trochanteric osteotomy if needed; an anterolateral approach is acceptable according to surgeon preference.

Imaging and equipment. Full-length femoral radiographs are templated for a stem that bypasses distal defects by at least two cortical diameters where possible, and an image intensifier is available for guidewire and plug position and for fracture surveillance. The dedicated X-change (or equivalent) instrumentation comprises:

• Intramedullary plug and central guidewire
• Cannulated distal impactors
• Modular proximal tamps and phantom stems, sized one size up from the definitive stem to create the cement mantle space
• Slap hammer
• Mesh and cable or cerclage set
• Cement gun with long revision nozzles

Preparation and clearance. Infection is excluded preoperatively with inflammatory markers and aspiration where indicated, and multiple deep tissue samples are taken at surgery. Remove the failed stem, then meticulously clear all cement, membrane and fibrous tissue from the endosteum back to bleeding host bone, because retained membrane blocks graft incorporation. Culture the membrane.

Assess the tube and contain it. Probe for occult perforations and thin segments; old cement-removal tracks are notorious. A segmental defect is converted to a contained one by applying stainless-steel mesh over the calcar or diaphyseal deficiency, secured with cerclage wires or cables, recreating a cylindrical tube; strut allograft with cables may reinforce a grossly deficient diaphysis. Place prophylactic cerclage around thin or ectatic segments before any impaction begins.

Distal plug and guidewire. Insert the intramedullary restrictor, a threaded plug with a guidewire eyelet in the X-change system, approximately 2 cm distal to the planned stem tip, and confirm the level on the image intensifier. The plug defines the cement mantle length and gives the distal graft column something to impact against. Pass the central guidewire through it: every cannulated impactor and phantom runs over this wire, which keeps the neomedullary canal centred and prevents varus malposition.

Distal layered impaction. Deliver the 8 to 10 mm chips and impact them retrogradely in layers with cannulated distal impactors of decreasing then appropriate diameter, striking firmly; this is deliberately vigorous. Build a dense distal column above the plug.

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Proximal impaction with phantoms. Switch to the modular proximal tamps and phantom stems, oversized replicas of the stem. Add the finer chips and impact around and with the phantom, working proximally layer by layer and packing graft into metaphyseal cavities and against the mesh.

The stability test. The final phantom must sit at the templated level and be absolutely stable to axial push and rotational torque; any movement means further impaction. This single step determines whether the reconstruction succeeds. The product is a neomedullary canal, a tube of densely compacted allograft sized to accept the definitive stem plus a circumferential cement mantle of roughly 2 mm.

Cementation. Remove the phantom and guidewire without disturbing the graft. Do not pulse-lavage the neomedullary canal, which would wash out graft; pack and dry it gently. Gun-inject standard-viscosity antibiotic-loaded cement retrogradely in a slightly earlier, doughier phase than for a primary, then pressurise with a proximal seal. Cement interdigitates into the graft to form a cement-graft composite, and some penetration into the graft is expected and desirable.

The stem. Insert the polished, collarless, double-tapered stem (Exeter) slowly to templated depth in correct version, with a centraliser, and hold until cure. The centraliser maintains the distal mantle and accommodates taper subsidence.

At risk. The sciatic nerve behind a posterior approach; a thin cortex, which fractures or perforates during impaction; and the circulation, during both impaction and pressurisation.

Closure and aftercare. Check stability, repair the capsule and short external rotators, and close in layers. Weight-bearing is traditionally protected, touch to partial, for 6 to 12 weeks, progressing with radiographic evidence of a stable construct; earlier weight-bearing protocols exist, but the graft-cement composite is most vulnerable early. Serial radiographs at 6 weeks, 3, 6 and 12 months monitor subsidence and remodelling.

What actually fails. Impaction grafting essentially does not fail by loosening. In Halliday's 226 hips, survivorship at 10 to 11 years was 99.1% with reoperation for symptomatic aseptic loosening as the endpoint and 90.5% with any further femoral operation as the endpoint, and ten of the twelve aseptic reoperations were for femoral fracture. The gap is fracture, and containment, cerclage and a stem long enough to bypass compromised bone are the technical answers to it.

Not only the tamp. In Te Stroet's long-stem series, intraoperative fractures or fissures occurred in 24% of patients but none occurred during impaction of the graft, which puts the exposure and the extraction, rather than the impactor alone, under suspicion.

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• Global variation: IBG is most established in the United Kingdom, the Netherlands and Scandinavia, reflecting the Exeter and Nijmegen heritage and strong bone-banking infrastructure. In North America, distally fixed uncemented tapered fluted stems dominate femoral revision; IBG is a niche technique in selected young patients.
• Registry evidence: revision-of-revision data from the National Joint Registry (UK), Swedish Hip Arthroplasty Register and Dutch (LROI) registries confirm cemented revision with impaction grafting as a durable option in appropriate defects, while also documenting the worldwide shift toward uncemented modular and monoblock tapered fluted stems for most femoral revisions. Registries consistently show revision outcomes are unit- and volume-dependent — IBG in particular is a technique with a documented learning curve.
• Society guidance: no society mandates a single femoral revision strategy. BOA/BHS revision hip networks in the UK recommend complex femoral bone loss be managed in specialist revision units with access to bone banking and the full range of implants. EFORT and AAOS revision instructional material present IBG as the bone-stock-restoring option for contained defects in younger patients.
• Resource considerations: IBG requires a licensed bone bank, fresh-frozen allograft supply, dedicated instrumentation and considerable theatre time. In settings without bone banking, alternatives include distally fixed stems, or (with caution) processed/irradiated allograft with inferior mechanical and biological properties. Cost of allograft versus modular revision implants varies by region and can favour either strategy.

Force-closed, or taper-slip. The polished Exeter-type stem is not bonded to cement. Under load it subsides minutely within the cement mantle, wedging as a taper, and that converts axial load into radial compressive hoop stress transmitted through cement into the impacted graft and out to host cortex. Compressive loading of graft is osteogenic, Wolff's law applied to allograft incorporation, and Tagil's loaded grafts remodelled faster than unloaded ones; shear loading causes resorption and fibrous tissue.

Why a shape-closed stem cannot do it. A composite-beam stem, whether matt, roughened or collared, is bonded to its cement. Any subsidence at a bonded interface represents interface failure, and the load it transfers to the graft is predominantly shear, which resorbs graft and produces early massive subsidence. Choosing the wrong stem is a design-stage error, and an avoidable one.

Two interfaces, two meanings of subsidence. Expected behaviour is early subsidence of the stem at the stem-cement interface of the order of 1 to 2 mm, then stabilisation: a design feature, mirrored in RSA studies of primary Exeter stems, seen on the radiograph as the centraliser space closing with no migration of the cement mantle and no lucency at the cement-graft or graft-host levels. Pathological behaviour is subsidence at the cement-graft or graft-host interface, the whole composite migrating, which indicates inadequate impaction or an uncontained defect and predicts failure.

• Washing the graft: mechanically superior and now majority practice, but the historic Exeter results were achieved unwashed; whether washing removes clinically meaningful osteoinductive signal remains debated.
• IBG versus tapered fluted stems in Paprosky III: fluted stems are faster, forgiving and reliable but stress-shield the proximal femur; IBG restores bone but is slower with higher fracture risk. Most units reserve IBG for the young; direct comparative data are limited and largely observational.
• Weight-bearing protocols: traditional protected weight-bearing for 6 to 12 weeks versus earlier loading to stimulate graft — no high-level evidence; practice varies.
• Graft substitutes and extenders: mixing allograft with tricalcium phosphate/hydroxyapatite granules or bioactive glass to economise allograft shows promising series but long-term equivalence to pure allograft is unproven.
• Vancouver B3 fractures: IBG with a long stem and mesh is described with good results in specialist hands, but most surgeons prefer distal fixation in the fracture setting.
• Chip size and vibration/standardised impaction devices: optimal particle size distribution and force-controlled impaction systems remain research topics; current practice is craft-based.

Related pages. The choice this technique competes in: Femoral Bone Loss and Revision Stems sets out the Paprosky grading and the distal-fixation alternatives, and Revision THA is the parent operation. Acetabular Bone Loss (Paprosky) is where the same impaction principle is applied on the other side of the joint.