FEMORAL STEM IMPACTION GRAFTING: EXTENDING THE ROLE OF CEMENT

Abstract

Femoral revision in cemented THA might include some technical difficulties, based on the loss of bone stock and cement removal, which might lead to further loss of bone stock, inadequate fixation, cortical perforation or consequent fractures. Femoral impaction grafting, in combination with a primary cemented stem, allows for femoral bone restoration by incorporating and remodeling the allograft bone of the host skeleton. Historically, this was first performed and described in Exeter in 1987.

Indications might include all femoral revisions with bone stock loss, while the Endo-Clinic experience is mainly based on revision of cemented stems. Nowadays our main indication is the Paprosky Type IIIb and Type IV. Contraindications are mainly: septical revisions, extensive circumferential cortical bone loss and noncompliance of the patient. Generally the technique creates a new endosteal surface to host the cemented stem by reconstruction of the cavitary defects with impacted morselised bone graft. This achieves primary stability and restoration of the bone stock. It has been shown, that fresh frozen allograft shows superior mechanical stability than freeze-dried allografts.

Technical steps include:

1. –

   removal of failed stem and all cement rests

2. –

   reconstruction of segmental bone defects with metal mesh (containment)

3. –

   preparation of fresh frozen femoral head allografts with bone mill

4. –

   optimal bone chip diameter 2 to 5 mm, larger chips for the calcar area (6–8 mm)

5. –

   insertion of an intramedullary plug including central wire, 2 cm distal the stem tip

6. –

   introduction of bone chips from proximal to distal

7. –

   impaction started by distal impactors over central wire, then progressive larger impactors proximal

8. –

   insertion of a stem „dummy“ as proximal impactor and space filler

9. –

   removal of central wire

10. –

    retrograde insertion of bone cement (0.5 Gentamycin) with small nozzle syringe, including pressurisation

11. –

    insertion of standard cemented stem

The cement mantle is of importance as it acts as the distributor of force between the stem and bone graft while sealing the stem. A cement mantle of at least 2 mm has shown favourable results. Post-operative care includes usually touch down weight bearing for 6–8 weeks, followed by 4–6 weeks of gradually increased weightbearing with a total of 12 weeks on crutches. Relevant complications include mainly femoral fractures due to the hardly impacted allograft bone. Subsidence of tapered polished implants might be related to coldflow within the cement mantle, however, it could also be related to micro cement mantle fractures, leading to early failure. Subsidence should be less than 5 mm.

Survivorship with a defined endpoint as any femoral revision after 10-year follow-up has been reported by the Exeter group at over 90%. While survivorship for revision defined as aseptic loosening is even greater at above 98%. Within the last years various other authors and institutions reported similar excellent survivorships, above 90%. In addition a long-term follow-up by the Swedish arthroplasty registry in more than 1180 patients reported a cumulative survival rate of 94% after 15 years and 99% with the endpoint aseptic loosening.

Impaction grafting is technically more challenging and more time consuming than cement free distal fixation techniques. However, it enables a reliable restoration of bone stock.