Biological restoration of femoral bone stock in revision hip arthroplasty using morsellised allograft, layered retrograde impaction and a cemented polished double-taper stem
- Impaction grafting is the only revision femoral technique that RESTORES bone stock rather than bypassing it — its principal indication is the young patient with cavitary bone loss who will likely need further revision.
- The construct works only with a force-closed, polished, collarless, double-tapered stem (Exeter philosophy): controlled subsidence at the stem-cement interface generates radial compressive (hoop) load that stimulates graft incorporation; the graft-cement composite itself must be rigidly stable.
- Graft: fresh-frozen morsellised femoral head allograft, cleared of soft tissue and cartilage; larger chips distally for axial stability, finer proximally; vigorous layered retrograde impaction over a guidewire with sized tamps/phantoms builds a neomedullary canal.
- Segmental (uncontained) defects must be converted to contained defects with metal mesh and cerclage before impaction; an incompetent tube cannot resist hoop stress.
- Prophylactic cerclage wiring of thin or ectatic cortex before vigorous impaction is the key manoeuvre to prevent intraoperative fracture (reported up to 10-15 percent).
- Retrieval and biopsy studies show genuine incorporation: revascularisation, osteoclastic resorption and remodelling of graft to viable trabecular bone with a normal cortex-like shell over years.
- “Distinguish acceptable stem subsidence WITHIN the cement mantle (design feature of a polished taper, usually 1-2 mm) from catastrophic subsidence of the cement-graft construct (technical failure from inadequate impaction).
- “Never use a composite-beam (shape-closed, roughened or collared) stem with impaction grafting — subsidence at a bonded stem-cement interface is failure, not function.
- “If the femoral tube cannot be reconstructed to a stable contained cylinder even with mesh, abandon impaction grafting for a distally fixed tapered fluted stem or proximal femoral replacement.
The biomechanics depend on a polished, collarless, double-tapered stem engaging its cement mantle as a taper, converting axial load into radial compression of the graft. A matt, collared or shape-closed stem loads the construct in shear, causes graft resorption and early massive subsidence.
Vigorous impaction against a thinned, ectatic or perforated cortex fractures the femur in up to 10-15 percent of cases. Prophylactically cerclage any suspect segment, bypass cortical defects with mesh, and impact against a protected tube — never rely on feel alone.
The commonest mechanical failure is massive early subsidence from under-impaction. The phantom stem must be rotationally and axially stable in the neomedullary canal before cementing — if you can twist or push it, keep impacting.
Segmental defects (Paprosky IIIB/IV cortical loss, ballooned Vancouver B3 femora) must be converted to contained defects with stainless-steel mesh and cerclage first. Impacting into an uncontained defect extrudes graft and leaves an unstable construct.
Rationale and Patient Selection
Femoral impaction bone grafting (IBG), popularised in Exeter (Gie, Ling) and Nijmegen (Slooff, Schreurs) in the late 1980s to early 1990s, addresses the central problem of femoral revision in the young patient: every alternative strategy consumes or bypasses bone, whereas IBG rebuilds it.
Strategic comparison of femoral revision options:
- Fixation principle
- Force-closed taper in cement on compacted allograft
- Effect on bone stock
- Restores — graft remodels to host bone
- Best-suited patient
- Young patient, cavitary loss, containable tube
- Fixation principle
- Distal press-fit in diaphysis
- Effect on bone stock
- Bypasses proximal femur; proximal stress-shielding
- Best-suited patient
- Most Paprosky III defects; workhorse in many units
- Fixation principle
- Distal scratch-fit, needs 4-5 cm isthmus
- Effect on bone stock
- Bypasses; risk of stress-shielding and difficult re-revision
- Best-suited patient
- Type II-IIIA with adequate isthmus
- Fixation principle
- Megaprosthesis or allograft-prosthesis composite
- Effect on bone stock
- Sacrifices or substitutes proximal femur
- Best-suited patient
- Elderly, low demand, non-reconstructable Type IV
- Younger, higher-demand patient in whom future re-revision is anticipated and bone stock restoration is strategically valuable
- Paprosky type II and IIIA cavitary/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
- Active infection (staged reconstruction only after eradication)
- Segmental loss that cannot be converted to a contained defect
- Inability to source adequate allograft (typically 2-4 fresh-frozen femoral heads)
- Very elderly/low-demand patients where a quicker distally fixed stem or PFR is more pragmatic — IBG is technically demanding and time-consuming
"Impaction grafting is chosen when the priority is to leave the femur with more bone than you found — a biological reconstruction for the patient who will outlive this revision."
Biology of Graft Incorporation
Morsellised, impacted fresh-frozen allograft behaves quite differently from structural bulk allograft (which remains largely a dead scaffold with only superficial creeping substitution).
The impacted graft is initially a dead, mechanically stable particulate scaffold. Host haematoma infiltrates; inflammatory cells and vascular buds begin to invade from the endosteal surface and any bleeding host bone contact points.
Osteoclasts resorb dead trabecular fragments while osteoblasts lay new woven bone on graft surfaces — classical creeping substitution, but far more complete than in bulk graft because the particulate structure is fully permeable to vascular ingrowth. Mechanical stability (rigid impaction) and compressive load (taper-slip stem) are prerequisites; micromotion produces fibrous encapsulation instead.
Woven bone remodels to lamellar trabecular bone orientated along load lines. Radiographs show trabecular remodelling and cortical repair/thickening. Nijmegen and Exeter biopsy/retrieval studies (e.g. Linder; Ullmark) confirm viable new bone with residual graft islands — a true composite of living host bone and diminishing graft.
Progressive corticalisation around the cement mantle; the reconstructed segment approaches normal bone architecture, making any future revision technically closer to a primary procedure.
Conditions required for incorporation (examiner checklist): contained defect, viable vascular host bed, rigid mechanical stability of the graft mass, compressive (not shear) loading, absence of infection, and adequate graft quality free of fat and soft tissue.
Graft Preparation
- Fresh-frozen femoral head allograft from a licensed bone bank is the gold standard — retains trabecular architecture and mechanical properties better than irradiated or freeze-dried bone. Typically 2-4 heads for a femoral reconstruction.
- Strip all cartilage, cortical shell remnants and soft tissue — retained cartilage and fibrous tissue do not incorporate and create planes of weakness.
- Morsellise with a bone mill or rongeurs. Chip size matters:
- Distal canal: 8-10 mm chips — large chips interlock and resist axial/shear load where stability is most critical.
- Proximal femur: finer chips, roughly 3-5 mm — pack around tamps into metaphyseal irregularities.
- Avoid over-milling to slurry — paste has no mechanical interlock.
Operative Technique (Exeter / X-change)
- Position: lateral decubitus on a supported table; posterior approach most common (extensile, allows ETO if needed); anterolateral acceptable per surgeon preference.
- Imaging/equipment: full-length femoral radiographs templated for stem length (bypass distal defects by at least two cortical diameters where possible); image intensifier available for guidewire, plug position and fracture surveillance. Dedicated X-change (or equivalent) instrumentation: intramedullary plug and guidewire, cannulated distal impactors, modular proximal tamps/phantom stems sized one size up from the definitive stem (to create the cement mantle space), slap hammer, mesh and cable/cerclage set, cement gun with long revision nozzles.
- Preparation: exclude infection preoperatively (inflammatory markers, aspiration where indicated); multiple deep tissue samples intraoperatively. Remove the failed stem, then meticulously clear all cement, membrane and fibrous tissue from the endosteum back to bleeding host bone — retained membrane blocks graft incorporation. Culture the membrane.
Vigorous impaction and long-column cement pressurisation both embolise fat and marrow contents. Communicate with the anaesthetic team before these steps, especially in patients with cardiopulmonary comorbidity — hypotension and desaturation events are well described, analogous to bone cement implantation syndrome.
C-PIG-CSSequence of Femoral Impaction Grafting
Hook:Contain the pig before you cement the stem — you cannot impact into an open field.
Complications: Rates, Prevention, Management
- Approximate rate
- Up to 10-15 percent in reported series
- Prevention
- Prophylactic cerclage of thin cortex; mesh over defects; long stem bypassing defects by two cortical diameters; controlled impaction under fluoroscopic surveillance
- Management
- Intraoperative: cerclage/cables, longer stem, strut allograft. Postoperative: treat as periprosthetic fracture — fix if construct stable, revise to long distally fixed stem if unstable
- Approximate rate
- Technique-dependent; the signature failure of under-impaction
- Prevention
- Vigorous layered impaction; phantom must be axially and rotationally rock-stable; adequate chip size distally; washed graft for better interlock
- Management
- Minor and stabilising: observe. Progressive with symptoms/instability: revision, usually to a distally fixed tapered fluted stem
- Approximate rate
- Comparable to other complex revisions, broadly 2-5 percent
- Prevention
- Exclude infection preoperatively; antibiotic-loaded cement; consider antibiotic-supplemented graft; meticulous asepsis with large allograft volumes
- Management
- Standard periprosthetic joint infection principles — usually two-stage exchange; infected graft must be fully removed
- Approximate rate
- Elevated versus primary hip arthroplasty, as for all revisions
- Prevention
- Careful version during stem insertion, soft-tissue repair, appropriate head size/dual mobility in high-risk patients
- Management
- Closed reduction, address cause; revise for recurrent instability
- Approximate rate
- Uncommon but recognised during impaction and pressurisation
- Prevention
- Washed graft (less fat), staged communication with anaesthetist, vigilance in cardiac patients
- Management
- Supportive resuscitation; pause impaction/pressurisation
FISTFailure Modes of Impaction Grafting
Hook:Impaction grafting fails by FIST — every element is preventable at the table.
Guidelines, Registries & Global Practice
- 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.
Biomechanics: Why the Polished Taper Is Essential
- Force-closed (taper-slip) design: the polished Exeter-type stem is not bonded to cement. Under load it subsides minutely within the cement mantle, wedging as a taper. This 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); shear loading causes resorption and fibrous tissue.
- Expected behaviour: early subsidence of the stem at the stem-cement interface of the order of 1-2 mm, then stabilisation — a design feature, mirrored in RSA studies of primary Exeter stems.
- Pathological behaviour: subsidence at the cement-graft or graft-host interface — the whole composite migrating — indicates inadequate impaction or an uncontained defect and predicts failure.
- A shape-closed (composite-beam) stem bonded to cement cannot do this: any subsidence represents interface failure, and load transfer to graft is predominantly shear.
Question: A follow-up radiograph after impaction grafting shows 2 mm of stem subsidence at one year. Concerned? Answer: Identify WHERE. Subsidence of the polished stem within an intact cement mantle (centraliser space closing, no cement mantle migration, no graft-level lucency) is expected taper-slip behaviour. Migration of the cement-graft construct relative to host bone is failure of impaction and demands close surveillance or revision.
Controversies & Areas of Uncertainty
- 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.