IMPACTION MORCELLIZED ALLOGRAFTING AND CEMENT

1. IMPACTION MORCELLIZED ALLOGRAFTING AND CEMENT • AAOS Instructional Course Lectures, Vol 48 • Tom J. J. H. Slooff, MD • B. Willem Schreurs, MD • Pieter Buma • Jean W. M. Gardeniers, MD

2. INTRODUCTION • Most Total Hip Arthroplasties (THA), cemented and cementless, fail because of aseptic loosening • Key problems in revision surgery: • Management of periprosthetic bone loss • Achieving long-lasting stability • Restoring hip biomechanics

3. INTRODUCTION • The authors of this lecture prefer the use of impaction allografting with cement for reconstruction of failed THA acetabular components

4. GENERAL ISSUES • Graft material: • Autograft - Bone that is transplanted from one location to another within the same individual • Allograft - Bone from another individual, but the same species • Xenograft - Bone from another species

5. GENERAL ISSUES • The graft material goes through a series of processes in which the donor bone and host become closely interconnected. • Host supplies the blood vessels and viable bone cells • Graft stimulates the host’s cellular activity, ultimately leading to new bone formation in and around the graft

6. GENERAL ISSUES • Factors that influence the success of incorporation of the graft material: • Firm fixation of the bone graft to the bone bed of the host • Extent of surface area between the graft and host bone • Vascularity of the surrounding host tissue • Load pattern of the graft

7. GENERAL ISSUES • Structural vs morcellized allografts • Compact structural bone grafts are very dense, which strongly compromises the ingrowth of blood vessels • In the early stages, only the contact surface of the graft undergoes breakdown to create space for revascularization • Subsequently, the inner part of the graft remains dead bone and weakens due to fatigue fractures and graft resorption

8. GENERAL ISSUES • Structural vs morcellized allografts • Morcellized allografts are incorporated more uniformly and completely • Blood vessels can easily penetrate, which means rapid bone apposition of dead trabeculae without any loss of mechanical strength

9. GENERAL ISSUES • Since 1984, the authors (Slooff and assoc) have advocated their technique of dealing with acetabular segmental defects. • Acetabular segmental defects were closed with corticocancellous slices or with flexible metal wire meshes. • The contained acetabulum was tightly packed with allograft chips • The cup was inserted after pressurizing the cement directly onto the graft

10. GENERAL ISSUES • The previous treatment sought to accomplish the following • Repair hip mechanics by positioning the cup at the level of the anatomic acetabulum (teardrop) • Close segmental defects with metal wire mesh to achieve containment • Replace the periprosthetic bone loss by augmenting the cavitary defect with morcellized allograft • Restore stability by impacting the chips and using bone cement

11. SURGICAL TECHNIQUE • Posterolateral approach is used • Fluid and tissue are always sent to the lab to rule out infection as the cause of the loosening • All components and cement are removed • The transverse acetabular ligament is identified, and the socket is reconstructed from this level up • Cultures are also taken from this deep tissue as well

12. SURGICAL TECHNIQUE • The acetabular floor and walls are examined closely for any hidden medial and/or peripheral segmental defects • A flexible stainless steel mesh is trimmed and adapted to fit any of the defects and is rigidly fixed to the iliac wall with at least 3 screws • Defects are filled by tightly packing allograft chips into the areas • A 5mm layer of graft is placed circumferentialy in the area of the new cup

13. SURGICAL TECHNIQUE • Cement is pressurized and placed over the allograft, then the cup is held in position until the cement has hardened

14. SCIENTIFIC STUDIES • Histologic analysis was performed to evaluate graft incorporation • At 1 month postrevision, no signs of graft incorporation were found • At 4 months, a front of new bone was found penetrating the avascular graft • At 8 months, various amounts of graft remnants were embedded in a new trabecular structure • At 15 months, bone closely resembled normal trabecular bone

15. CLINICAL RESULTS • Short term results: • 1984 study • 40 patients with 43 acetabular reconstructions • 21 primary, 22 revisions • After 2 years (0.5 to 5.5 years), there were no revisions, but 5 cases demonstrated radiolucent lines

16. CLINICAL RESULTS • Midterm results: • 1993 study • 80 patients with 88 acetabular revisions • 5.7 year follow-up (2 to 11 years) • 42 cases for cavitary, 38 combined segmental/cavitary • 4 acetabular re-revisions (2 for infection) • Post op Harris Hip Score went from 44 to 87

17. CLINICAL RESULTS • Long-term results: • The most reliable criterion in long-term follow-up of primary and revision THA’s is the survival rate of the prosthesis • 60 hips • 37 defects cavitary, 23 combined • 11.8 year f/u (10 -15 years) • 5 re-revisions were performed (2 infections) • Overall survival rate 90%

18. CONCLUSIONS • Experimental and clinical studies have shown that impacted morcellized allografts lead to a predictable result, with complete and rapid incorporation of the graft without impairing strength during the process • In contrast to structural allografts, which incorporate incompletely with unpredictable results • The use of wire meshes can be used in conjunction with allograft to fill segmental defects

19. CONCLUSIONS • Impaction of the morcellized graft results in a stable and rough surface that improves the mechanical cement-bone interlock • Rigid impaction reduces gap formation between the host and graft, promoting the union process