Introduction: Bone is unique with a vast potential for regeneration from cells with stem cell characteristics. With an increasing aging population, clinical imperatives to augment and facilitate tissue repair have highlighted the therapeutic potential of harnessing mes-enchymal populations from bone. We describe laboratory and clinical findings from two clinical cases, where different proximal femoral conditions (AVN, bone cyst) were treated with impacted allograft augmented with marrow-derived allogeneic progenitor cells. Methods: Marrow was aspirated from the posterior superior iliac crest and seeded onto prepared washed morsellised allograft. The seeded graft was left for 40 minutes to allow adherence of the marrow-derived osteoprogenitor cells prior to impaction into the defect. Samples of the impacted graft were taken for in-vitro analysis of cell viability, histology and biochemical analysis of cell number and osteogenic enzyme activity. The total force imparted during impaction was calculated using a load cell, with three independent surgeons performing a laboratory simulation of the impaction technique. Results: Both patients made a rapid clinical recovery after an overnight stay. Imaging confirmed filling of the defects with increased density on plain radiographs suggesting good impaction of the graft composite. Immu-nohistochemical staining of graft samples demonstrated that a living composite graft with osteogenic activity had been introduced into the defects as evidenced by cell tracker green viability and alkaline phosphatase (osteogenic marker) expression and specific activity. The average peak forces during impaction were 0.7kN corresponding to average peak stresses within the graft of 8.3MPa. Similar forces were seen between operators. Discussion: Replacement of bone loss remains a major challenge in orthopaedic practice. Although allograft remains the gold standard where large volumes preclude autograft, allograft has little osteoinductive potential. We demonstrate that marrow-derived cells can adhere to highly washed morsellised allograft, survive the impaction process, and are of the osteoblastic phenotype creating a living composite. Thus we conclude, impacted allograft seeded with autologous marrow cells allows the delivery of a biologically active scaffold for the treatment of bone deficiency. In addition this is a novel straightforward technique, surgeon independent and with applications in a number of orthopaedic scenarios

Acetabular component loosening and pelvic osteolysis continue to be a significant clinical challenge in revision hip arthroplasty. We present results of 339 cases of acetabular reconstruction with impacted allograft. All patients who under went acetabular reconstruction with impaction allograft between July 1995 and July 1999 were included. Clinical and radiographic data was collected prospectively. There were 339 patients identified. Average age was 71 years. The majority were first time revisions (201) but the group includes 2nd, 3rd and 4th revisions with 34 two-stage revisions and 44 primary arthroplasties. There were multiple surgeons with 2/3 being consultants and 1/3 fellows. Pre and post-operative clinical assessment included Oxford and Harris hip scores, and a modified Charnley score for pain, function and range of movement. Pre-operative radiographs were classified with the Paprosky classification. Follow up radiographs were assessed for graft thickness, component migration, graft reabsorption and lucent lines. There were 10 grade I, 205 grade II, and 103 grade III defects with 3 pelvic discontinuities. Reconstruction methods included impaction only, rim and/or medial mesh, KP plate fixation and reinforcement cages. Follow up average was 6.1 years (4.3 – 8.4) and no patient was lost. Infection was identified in 13 patients (5 recurrent 89% eradication and 8 new 2.6%). There were 6 nerve injuries, 2 remain unresolved and 13 patients dislocated (3.8%). There have been 46 deaths in the group with 3 being peri-operative. There have been 18 re-operations for aseptic loosening. 7 KP plates fractured, 1 cage migrated and 10 rim meshes failed. Factors associated with aseptic loosening include use of a large rim mesh particularly with an allograft thickness of > 2cm. We conclude that impaction allografting is a reliable method for acetabular reconstruction. Careful consideration should be given when allograft thickness will be > 2cm and a large rim mesh is required

Introduction Bone graft supply for impaction grafting can be problematic due to the supply of graft, sterilisation, which alters the biological properties of the graft, and the immunogencity of the graft which may lead to graft rejection. Reducing the amount of graft can be accomplished by using increased amounts of synthetic materials such as hydroxyapatite (HA). This study evaluated the effect of using mixtures of porous HA (Apapore™) with allograft for cemented impaction allografting of the femoral stem in an ovine model. The aim was to test the hypothesis that increased quantities of Apapore™ will be stable and induce similar bone remodelling to that where a 50:50 mixture with allograft was used.

Method Twelve hemi-arthroplasty femoral components were inserted into the right hip of skeletally mature female commercially cross-bred sheep weighing between 65 and 80kg. Femoral components were manufactured from Cobalt Chromium alloy and cemented in place following impaction of the femoral canal. Animals were randomly placed into one of two groups according to the allograft-apapore mixture used. Group 1: Apapore:allograft mixed 50:50. Group 2: Apapore: allograft mixed 90:10. Six animals were investigated in each group. Implants remained in vivo for 6 months. In order to quantify bone formation rates, oxytetracycline injections were given 2 months post-surgery and 3 weeks later, followed by a third administration in the fifth month post-surgery and 3 weeks later. Animals were walked over a force plate pre-operatively and at 8, 16 and 24 weeks post-operatively. Twelve readings of maximum force (Fmax, N/m2) were taken and average values of right over left were calculated as a percentage (%AR/AL) and represented how well the animal used its operated leg where 100% represents full weight-bearing. Thin sections (~70μm thick) were prepared through four regions of the femur. The proximal, mid and tip of the femoral component region and one distal to the implant tip were analysed where bone area, Apapore™ area, Apapore™-bone contact and cement mantle thickness were quantified and compared using image analysis techniques.

Results In both groups, the use of graft resulted in the formation of a cancellous network of bone on the endosteal surface which incorporated the Apapore™ granules. When all regions were compared, femoral bone turnover results demonstrated significantly increased rates in group 1 (0.0021mm day-1) when compared with group 2 (0.0015mm day-1) (p< 0.05). No significant differences were identified when the proximal, mid and tip regions in the two groups were compared however, significantly increased turnover was identified in the distal region in group 1 (0.0027 mm day-1) when compared with group 2 (0.0013mm day-1) (p< 0.05). In both groups increased turnover was observed in the proximal, tip and distal regions with least in the mid region of the stem. Ground Reaction Force (GRF) results demonstrated no significant differences between the two experimental groups at 8, 16 and 24 weeks postoperatively. In both groups, a significant decline in function was demonstrated 8 weeks post-op when compared with pre-operative values and in both groups function gradually increased over time. Results for new bone area demonstrated significantly increased new bone in the proximal and distal regions in both groups (proximal =7.94mm2 and 7.13mm2; distal =7.03mm2 and 8.17mm2, group 1 and 2 respectively) with least new bone in the mid region of the stem (4.53mm2 and 4.79mm2). No significant differences in any of the regions were demonstrated when group 1 and 2 were compared. In both groups, significantly increased amounts of Apapore™ was observed in the proximal and distal regions of the femoral stem with least in the mid and tip region. No significant difference in cement mantle thickness was identified between the two groups.

Discussion Results demonstrated that hips maintained functional stability when a higher amount of Apapore™ mixture was used. Results for bone turnover rates and the amount of new bone formation in the 90:10 mixture demonstrated Apapore™ to be a comparable and suitable alternative to replace allograft in impaction grafting of a femoral component.

Twenty-nine patients (30 hips) with uncemented acetabular impaction allografting contained behind a metal backed component screwed to the pelvis at revision hip arthroplasty were reviewed at 12 to17 years (average 15.3 years) follow up. Five patients had died with the prosthesis in situ, 4 patients were lost to follow up, 13 patients had failed requiring further revision (only one failed prior to 5 years) and 9 survivors were minimally asymptomatic. The mean time to failure warranting further surgery was 9 years.

Analysis of available serial radiographs (24 cases) demonstrated signs of loosening (migration, progressive radiolucent lines, screw breakage) in 54% of the latest radiographs of all cases. Removing those lost to follow up or deceased, 72% were radiologically loose (in the intact asymptomatic group 57% could be defined as loose). Additionally, in 70% of the cases the acetabular component tended to fail in a varus manner as the medial wall remodelled.

These results indicate as previously published, short term results for this technique are satisfactory but in the long term they are not. Factors associated with this include the pressfit nature of the polyethylene liner which has been implicated in disappointing long term results for this prosthesis in primary applications, but not of the level of failure encountered in the current series. This experience suggests that the reliance on screw fixation over a bed of allograft in the absence of cement supplementation does not provide sufficient stability for reliable bone graft incorporation.

The method reported above should be abandoned.

Introduction:. The reconstructive hip surgeon is commonly faced with complex cases where severe bone loss makes conventional revision techniques difficult or impossible. This problem is likely to increase in future, as there is a good correlation between the degree of bone loss seen and number of previous total hip operations. In such situations, one alternative is the use of impaction allografting with cement. History:. The first clinical reports of impaction allografting on the femoral side were in relation to revision with cementless stems. The use of morselised bone with cement on the femoral side was first reported by the Exeter group. Biology:. The great enthusiasm with which this technique has been received is related to its biological potential to increase bone stock. The rapid revascularization, incorporation and remodeling of morselised compacted cancellous allograft differs dramatically from structural allografting where bone ingrowth usually is limited to 2mm to 3mm. Histological evidence for bony reconstitution has been presented from postmortem retrievals, and from biopsies at the time of trochanteric wire removal. Type of bone:. The size of the bone chips used as morselised allograft is important. The graft behaves as a friable aggregate and its resistance to complex forces depends on grading, normal load and compaction. It is recommended that particles of 3–5mm in diameter make up the bulk of the graft. A bone slurry, such as that produced by blunted bone mills, or by the use of acetabular reamers or high speed burrs would not give satisfactory stability. A wide range of particle sizes is recommended in order to achieve the greatest stability. The cement mantle:. A satisfactory cement mantle is required to ensure the longevity of any cemented stem. The primary determinant of cement mantle thickness is the differential between the graft impactors and the final stem. All femoral impaction systems require careful design to achieve a cement mantle that is uninterrupted in its length and adequate in its thickness. Stem design:. The technique of impaction allografting on the femoral side was first and most successfully reported using a highly polished stem with a double tapered geometry and no collar. It is thought to be ideal for this technique as it can subside within the cement mantle, thus generating hoop stresses on the cement which creeps, potentially maintaining physiological loads on the supporting bone. The extension of this technique to other stems has led to some controversy. Confounding factors such as surgical technique, the impaction system available, the type and size of allograft bone used, and the extent of the preoperative bone loss, will undoubtedly continue to influence such comparisons. It appears that the exact stem configuration may not be as critical as its surface finish, the amount of graft impaction possible and the cement mantle produced. The introduction of longer stems and impactors in the last decade has undoubtedly further increased the scope of this technique. Conclusion:. Impaction allografting is the only technique currently available that reverses the loss of bone stock seen in a revision hip arthroplasty. Moreover, this technique does not sacrifice host tissue, and could facilitate further surgery. Impaction allografting, performed with great attention to detail using appropriate equipment, represents an exciting reconstructive solution for contained femoral defects

AIM. Avascular necrosis (AVN) of the femoral head is a potentially debilitating disease of the hip in young adults. Impaction bone grafting (IBG) of morcellised fresh frozen allograft is used in a number of orthopaedic conditions. This study has examined the potential of skeletal stem cells (SSC) to augment the mechanical properties of impacted bone graft and we translate these findings into clinical practice. STUDY DESIGN. We have examined the effect of SSC density on augmentation of bone formation. An in vitro model was developed to replicate the surgical IBG process. Plain allograft was used as the control, and the SSC's seeded at a density of 5×103, 5×104 and 2×105 cells per cc of allograft for the experimental groups. All samples were cultured for 2 weeks and mechanically tested to determine shear strength using the Mohr Coulomb failure curve. The approach was translated to 3 patients with early avascular necrosis (AVN) of the femoral head. The patient's bone marrow was concentrated in theatre using a centrifugation device and the concentrated fraction of SSC's were seeded onto milled allograft. The patient's necrotic bone was drilled, curetted and replaced with impacted allograft seeded with SSC's. Osteogenic potential of concentrated and unconcentrated marrow was simultaneously compared in vitro by colony forming unit assays. RESULTS. The mechanical properties of the impacted allograft was significantly improved as a function of increasing SSC density. The difference compared to the control plain allograft was highly significant at the 2×105 level (p=0.001). Autologous SCC's on impacted bone allograft was subsequently applied in 3 patient cases and up to two year follow up demonstrates no deleterious effect. Critically the analysis of concentrated marrow demonstrated a higher SSC count in vitro than plain marrow aspirate. DISCUSSION. We have demonstrated the potential of skeletal stem cells to augment the mechanical properties of impacted bone allograft in a laboratory model and subsequently translated these findings into a new technique for the treatment of AVN of the femoral head. Such an approach provides not only improved mechanical support to the overlying cartilage but critically improved biology for new bone formation. The early clinical results are encouraging and indicate potential use also in fracture non-unions and void filling of bone defects

The reconstructive hip surgeon is commonly faced with complex cases where severe bone loss makes conventional revision techniques difficult or impossible. This problem is likely to increase in future, as there is a good correlation between the degree of bone loss seen and number of previous total hip operations. In such situations, one alternative is the use impaction allografting with cement. This has captured the attention of the orthopaedic community because of its potential for reconstituting femoral bone stock. The first clinical reports of impaction allografting on the femoral side were in relation to revision with cementless stems. The use of morsellised bone with cement on the femoral side was first reported by the Exeter group. The great enthusiasm with which this technique has been received is related to its biological potential to increase bone stock. The rapid revascularisation, incorporation and remodelling of morsellised compacted cancellous allograft differs dramatically from structural allografting where bone ingrowth usually is limited to 2–3mm. Histological evidence for bony reconstitution has been presented from postmortem retrievals, and from biopsies at the time of trochanteric wire removal. The size of the bone chips used as morsellised allograft is important. The graft behaves as a friable aggregate and its resistance to complex forces depends on grading, normal load and compaction. It is recommended that particles of 3–5mm in diameter make up the bulk of the graft. A bone slurry, such as that produced by blunted bone mills, or by the use of acetabular reamers or high speed burrs would not give satisfactory stability. A wide range of particle sizes is recommended in order to achieve the greatest stability. Future considerations will include the potential for either adding biomaterials to the allograft, or ultimately substituting it completely. A satisfactory cement mantle is required to ensure the longevity of any cemented stem. The primary determinant of cement mantle thickness is the differential between the graft impactors and the final stem. All femoral impaction systems require careful design to achieve a cement mantle that is uninterrupted in its length and adequate in its thickness. The technique of impaction allografting on the femoral side was first and most successfully reported using a highly polished stem with a double tapered geometry and no collar. It is thought to be ideal for this technique as it can subside within the cement mantle, thus generating hoop stresses on the cement which creeps, potentially maintaining physiological loads on the supporting bone. The extension of this technique to other stems has led to some controversy. Confounding factors such as surgical technique, the impaction system available, the type and size of allograft bone used, and the extent of the pre-operative bone loss, will undoubtedly continue to influence such comparisons. It appears that the exact stem configuration may not be as critical as its surface finish, the amount of graft impaction possible and the cement mantle produced. Impaction allografting is the only technique currently available that reverses the loss of bone stock seen in a revision hip arthroplasty. Moreover, this technique does not sacrifice host tissue, and could facilitate further surgery. Impaction allografting, performed with great attention to detail using appropriate equipment, represents an exciting reconstructive solution for contained femoral defects. Its role in larger and combined defects remains open to scrutiny. Careful observation and cautious optimism are necessary as further refinements may well improve the predictability of the clinical results and expand the indications for this important addition to the armamentarium of the revision surgeon

Impaction allografting is increasingly used for the treatment of failed total hip replacements. In six human cadaveric femurs the impaction allografting procedure was performed to comprehensively describe the postoperative morphology of impaction allografting. After the procedure, the specimens were sectioned and prepared for histomorphometric analysis. The graft porosity was lowest in Gruen zone four (52%) and highest in Gruen zone one (76%). At the level of Gruen zone six and two, virtually the entire cross-section was filled with bone cement. The presented data will serve as a baseline for future investigations of the impaction allografting. Impaction allografting is an attractive procedure for the treatment of failed total hip replacements. The purpose of this study was to comprehensively describe the morphology of impaction allografting post operatively to form a baseline for further investigations. Three experienced surgeons performed the impaction allografting procedure on six cadaveric femurs. After the procedure, the femurs were cut in 6mm thick transverse sections and processed for histomorphometric analysis. The porosity of the impacted graft was highest proximally in Gruen zone one (76%) and lowest in Gruen zone four (52%). Below the tip of the stem (Gruen zone four), the mean cement penetration was significantly lower compared to the proximal part of the femur. The averaged residual impacted graft layer in Gruen zone six and two was (0.5mm SD 0.4mm) significantly thinner compared with Gruen zone’s one, 7/1, and four. In the region of Gruen zone six and two the entire cross-section was penetrated with bone cement with almost no residual graft layer (Figure). Even the simulated lytic defects in this region were filled with the graft cement composite which may not be remodelled by the host bone. The graft porosity was found to be highest proximally and lowest distally. In the region of Gruen zone six and two the entire cross-section was penetrated with bone cement with almost no residual graft layer. This investigation will serve as a baseline for future studies of the mechanical and biological processes that make the impaction allografting a successful procedure. Funding: Stryker Howmedica and DePuy for provided implants and instruments. Please contact author for figures and/or diagrams

Impaction grafting is an excellent option for acetabular revision. It is technique specific and very popular in England and the Netherlands and to some degree in other European centers. The long term published results are excellent. It is, however, technique dependent and the best results are for contained cavitary defects. If the defect is segmental and can be contained by a single mesh and impaction grafting, the results are still quite good. If, however, there is a larger segmental defect of greater than 50% of the acetabulum or a pelvic discontinuity, other options should be considered. Segmental defects of 25–50% can be managed by minor column (shelf) or figure of 7 structural allografts with good long term results. Porous metal augments are now a good option with promising early to mid-term results. Segmental defects of greater than 50% require a structural graft or porous augment usually protected by a cage. If there is an associated pelvic discontinuity then a cup cage is a better solution. An important question is does impaction grafting facilitate rerevision surgery? There is no evidence to support this but some histological studies of impacted allograft would suggest that it may. On the other hand there are papers that show that structural allografts do restore bone stock for further revision surgery. Also the results of impaction grafting are best in the hands of surgeons comfortable with using cement on the acetabular side, and one of the reasons why this technique is not as popular in North America

Femoral revision in cemented THA might include some technical difficulties, based on loss of bone stock and cement removal, which might lead to further loss of bone stock, inadequate fixation, cortical perforation or consequent fractures. Cemented THA has become an extremely successful operation with excellent long-term results. Although showing decreasing popularity in North America, it always remained a popular choice for the elderly patients in Europe and other parts of the world. Various older and recent studies presented excellent long-term results, for cemented fixation of the cup as well as the stem. Besides optimal component orientation, a proper cementing technique is of major importance to assure longevity of implant fixation. Consequently a meticulous bone bed preparation assures the mechanical interlock between the implant component, cement and the final bone bed. Pre-operative steps as proper implant sizing/ templating, ensuring an adequate cement mantle thickness, and hypotensive anaesthesia, minimizing bleeding at the bone cement interface, are of major importance. Additionally, femoral impaction grafting, in combination with a primary cemented stem, allows for femoral bone restoration due to incorporation and remodeling of the allograft bone by the host skeleton. Historically, it has been first performed and described in Exeter in 1987, utilizing a cemented tapered polished stem in combination with morselised fresh frozen bone grafts. The technique was refined by the development of designated instruments, which have been implemented by the Nijmegen group from Holland. Indications might include all femoral revisions with bone stock loss, while the Endo-Clinic experience is mainly based on revision of cemented stems. Cavitary bone defects affecting meta- and diaphysis leading to a wide or so called “drain pipe” femora, are optimal indications for this technique, especially in young patients. Contraindications are mainly: septical revisions, extensive circumferential cortical bone loss and noncompliance of the patient. The cement mantle is of importance, as it acts as the distributor of force between the stem and bone graft and seals the stem. A cement mantle of at least 2 mm has shown favorable results. Originally the technique is described with a polished stem. We use standard brushed stems with comparable results. Relevant complications include mainly femoral fractures due to the hardly impacted allograft bone. Subsidence of tapered polished implants might be related to cold flow within the cement mantle, however, could also be related to micro cement mantle fractures, leading to early failure. Subsidence should be less than 5 mm. Impaction grafting might technically be more challenging and more time consuming than cement-free distal fixation techniques. It, however, enables a reliable restoration of bone stock which might especially become important in further revision scenarios in younger patients

Introduction. The reconstructive hip surgeon is commonly faced with complex cases where severe bone loss makes conventional revision techniques difficult or impossible. This problem is likely to increase in future, as there is a good correlation between the degree of bone loss seen and number of previous total hip operations. In such situations, one alternative is the use impaction allografting with cement. This has captured the attention of the orthopaedic community because of its potential for reconstituting femoral bone stock. History. The first clinical reports of impaction allografting on the femoral side were in relation to revision with cementless stems. The use of morselised bone with cement on the femoral side was first reported by the Exeter group. Biology. The great enthusiasm with which this technique has been received is related to its biological potential to increase bone stock. The rapid revascularization, incorporation and remodelling of morselised compacted cancellous allograft differs dramatically from structural allografting where bone ingrowth usually is limited to 2–3 mm. Histological evidence for bony reconstitution has been presented from postmortem retrievals, and from biopsies at the time of trochanteric wire removal. Impaction allografting, performed with great attention to detail using appropriate equipment, represents an exciting reconstructive solution for contained femoral defects. Its role in larger and combined defects remains open to scrutiny. A number of technical issues with regards to allograft preparation and prosthetic design have been resolved over the past decade. The necessary intra-operative precautions are now appreciated, and the high complication rates seen in some centers have been explained in simple terms. Careful observation and cautious optimism are necessary as further refinements may well improve the predictability of the clinical results and expand the indications for this important addition to the armamentarium of the revision surgeon. The technique of impaction allografting of the femur has great potential, and is here to stay as a reconstructive solution to the deficient proximal femur in revision hip arthroplasty. Although many questions remain unanswered, the capacity for impaction allografting to act as a truly biologic augmentation of the proximal femur makes this technique the modern bridge from revision arthroplasty to reconstructive hip surgery

Femoral revision in cemented THA might include some technical difficulties, based on 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 due to incorporation and remodelling of the allograft bone by the host skeleton. Historically it has been first performed and described in Exeter in 1987, utilizing a cemented tapered polished stem in combination with morselised fresh frozen bone grafts. The technique was refined by the development of designated instruments, which have been implemented by the Nijmegen group from Holland. Indications might include all femoral revisions with bone stock loss, while the Endo-Clinic experience is mainly based on revision of cemented stems. Cavitary bone defects affecting meta- and diaphysis leading to a wide or so called “drain pipe” femora, are optimal indications for this technique, especially in young patients. 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. Incorporation of these grafts has been described in 89%. Technical steps include: removal of failed stem and all cement, reconstruction of segmental bone defects with metal mesh (if necessary), preparation of fresh frozen femoral head allografts with bone mill, optimal bone chip diameter 2–5 mm, larger chips for the calcar area (6–8 mm), insertion of an intramedullary plug including central wire, 2 cm distal the stem tip, introduction of bone chips from proximal to distal, impaction started by distal impactors over central wire, then progressive larger impactors proximal, insertion of a stem “dummy” as proximal impactor and space filler, removal of central wire, retrograde insertion of low viscosity cement (0.5 Gentamycin) with small nozzle syringe, including pressurization, and 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 and seals the stem. A cement mantle of at least 2 mm has shown favorable results. Post-operative care includes usually touch down weightbearing 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 cold flow within the cement mantle, however, 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 being over 90%, while survivorship for revision as aseptic loosening being above 98%. Within the last years various other authors and institutions reported about 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. Impaction grafting might technically be more challenging and more time consuming than cement-free distal fixation techniques. It, however, enables a reliable restoration of bone stock which might especially become important in further revision scenarios in younger patients

Impaction allografting is a bone reconstruction technique currently used in lower limb revision arthroplasty. Demineralisation and addition of osteogenic protein-1 (OP-1) can improve the osteoinductivity of the allograft however recent reports indicate significant allograft resorption when it is combined with OP-1 during impaction. Our hypothesis was that hydroxyapatite (HA) and OP-1 could effectively replace demineralised allograft. The objective was to evaluate human mesenchymal stem cell (h-MSC) proliferation (tritiated thymidine incorporation, total DNA Hoechst 33258 and scanning electron microscopy) and osteogenic differentiation (alkaline phosphatase activity) in human demineralised bone matrix (h-DBM) and HA, with or without OP-1. Cell proliferation on HA+OP-1 was significantly higher compared to HA at all time points (p< 0.05) and to DBM alone (day 1, p=0.042; day 14, p< 0.001). Cell proliferation was higher in DBM+OP-1, at all time points compared to HA+OP-1 but only in absolute values. Cell differentiation was significantly higher in HA+OP-1 compared to HA (p< 0.05) but comparable to DBM alone. Differentiation was significantly higher on DBM+OP-1 at all time points compared to HA (p< 0.05) and to HA+OP-1 (p< 0.05). HA is a potential graft expander in impaction allografting. When combined with OP-1 is comparable to DBM alone and being non absorbable may support the impacted graft in the early stages after the administration of OP-1

Impaction allografting is a bone tissue engineering technique currently used in lower limb reconstruction orthopaedic surgery. Our hypothesis was that biological optimisation can be achieved by demineralisation and addition of osteogenic protein-1(OP-1) to the allograft. The objective of our in vitro study was to evaluate human mesenchymal stem cell (MSC) proliferation (Alamar Blue assay, titrated thymidine assay, total DNA Hoechst 33258 and scanning electron microscopy) and osteogenic differentiation (alkaline phosphatase assay) in two types of impacted carrier, namely demineralised bone matrix (DBM) and insoluble collagenous bone matrix (ICBM), with or without OP-1. The objective in vivo was to compare the osteogenic potential of impacted DBM with or without OP-1, with that of impacted fresh frozen allograft (FFA), again with or without OP-1. DBM+OP-1 optimized osteoinduction and significantly improved (p< 0.05) proliferation and differentiation in comparison to the majority of all other graft preparation in vitro. In addition DBM+OP-1 was significantly superior, with regard to osteogenesis, compared to the impacted FFA alone (p< 0.001), FFA+OP-1 (p=0.01) and DBM alone (p=0.02) in vivo. We propose that partial demineralisation and addition of OP-1 provides a good method for improving the osteoinductive properties of fresh allograft currently used in the impaction grafting technique

A large series of animal experiments in goats was performed in relatevely simple bone chamber models and in very realistic loaded pre-clinical models. In this paper the focuss is on two experiments. In exp 1 we analysed the effect of rinsing of allograft bone on bone ingrowth into the bone induction chamber. We found that rinsing improves the ingrowth capacity to a level that is comparable to that of autologous bone. In experiment 2 we analysed the effect of two different reconstruction methods, e.g., a mesh or a strut graft, on the revascularization of impacted allograft bone in a femoral reconstruction. We found that new vessels can enter the impacted bone through the mesh and that this promotes an early revascularization of the bone graft. In patients we analysed 24 biopsies of 20 patients and quantitated the amount of non-incorporated graft (remnants of original material), graft in the process of incorporation, incorporated graft (=new bone) and fibrous tissue. With increasng follow up peripods after the revision operation the amount of normal bone increased upto ca 90%. The remaining 10% consists of non-incorpated bone and fibrous tissue

Impaction allograft using cement is commonly used in revision surgery for filling bone defects and provides a load bearing interface. However, the variable regeneration of new bone within the defect makes clinical results inconsistent. Previous studies showed that addition of mesenchymal stem cells (MSCs) seeded on allograft can enhance bone formation in the defect site. The purpose of this study is to test the hypothesis that heat generated during cement polymerization will not affect viability of the human MSCs. The temperatures and durations were taken from previous studies that recorded the maximum temperature generated at the bone-cement interface. Temperatures of below 30 degrees Celsius to over 70 degrees Celsius have been detected and the duration of elevated temperature varies from 30 seconds to 5 minutes. In this study the viability of MSCs cultured at different temperatures was assessed. Ten groups were studied with three repeats (Table 1). A control group in which cells were cultures normally was used. Culture medium was heated to the required temperature and added to the cells for the required duration. The metabolism of MSCs was measured using the alamar Blue assay, cell viability was analysed using Trypan Blue and cell apoptosis and necrosis were tested using Annexin V and Propidium Iodide staining. Results showed that cell metabolism was not affected with temperatures up to 48 degrees Celsius for periods of 150s, while cells in the 58 degrees Celsius group eventually died (Fig. 1). Similar results were shown in Trypan Blue analysis (Fig. 2). When comparing the group of cells heated to 48 degrees Celsius for 150s with the control group for apoptosis and necrosis, no significant difference was observed. The study suggests that human MSCs seeded to allograft can be exposed to temperatures up to 48 degrees Celsius for 150s, which covers many of the situations when cement is used. This indicates that the addition of mesenchymal stem cells to cemented impaction grafting can be carried out without detrimental effects on the cells and that this may increase osteointegration

Aims: This study reports the results of all patients from our centre who underwent femoral impaction grafting more then five years previously. As a consequence of our experience our technique has been modified and the indications for impaction grafting have become clearer. Methods: 226 hips underwent femoral impaction grafting in 207 patients. No deaths were attributable to the revision surgery. 33 patients with 35 functioning hips died with less than 5 years follow up. Only one patient was lost to follow-up. There were two (1%) acute infections. Twelve stems underwent a further surgical procedure for aseptic failure – 10 for treatment of femoral fracture and 2 for mechanical loosening in the absence of fracture. Results: Survivorship with any femoral re-operation for any cause as the end point is 90.5% (Confidence Interval 82–98%) at 10–11 years. Using femoral re-operation for symptomatic aseptic mechanical loosening as the endpoint the survivorship was 99.1% (Confidence Interval 96–100%) at the same follow-up. Conclusions: As a consequence of our experience in this series our technique has been modified with an increased use of longer stems with impacted allograft. Long stems are indicated when the host bone around a short stem is significantly compromised, in cases of severe bone stock loss, or when a fracture occurs

Introduction: The long term success of impaction grafting depends on the remodelling process during incorporation. This project was designed to characterise any differences in the biochemical markers of bone turnover following revision hip arthroplasty performed with or without impaction grafting. Methods: 87 patients undergoing revision hip arthroplasty were entered into this prospective study and grouped according to whether impaction allograft was used or not. Biochemical markers of bone turnover were assessed pre-operatively and post-operatively on day 2, day 9, week 6, 6 months and 1 year. Osteocalcin, pro-collagen type-I N-terminal propeptide and bone specific alkaline phosphatase were measured as bone formation markers. C-telopeptide, pyridinoline and deoxypyridinoline were measured as bone resorption markers. Results: All patients had a successful radiological and clinical outcome at one year. 50 patients with radiologically defined host-graft union were compared with 37 patients who did not receive allograft. Markers of bone formation tended to rise by day 9 but the rise in osteocalcin was delayed in the graft group and was significantly lower at 6 months in comparison to the non-graft group (p=0.002). Alkaline phosphatase levels remained significantly elevated at one year in the graft group (p=0.027) whilst levels in the non-graft group had normalised. Markers of bone resorption also rise in both groups but with no significant differences between the groups. Discussion: Following impaction grafting, new bone formation may be delayed in comparison to revisions performed without graft. The pattern of markers of bone resorption did not differ significantly between the groups suggesting that there is no large scale resorption of the impacted allograft in these cases. These results provide a biochemical insight into the bone formation and bone resorption processes during allograft incorporation

Introduction: Impaction allografting is a technique that is used at revision where the bone stock in the femur is poor. Femoral heads are ground to create morsellised bone, which is impacted down the femur prior to the cementing a new stem into the canal. The results of this technique are variable and there is a high incidence of stem migration. This variation in results may be due to the degree of bone loss or the techniques used to impact the graft. The aim of this study was to quantify the forces currently used in revision hip surgery with impaction allografting. Methods: To enable these measurements the Exeter slap hammer (Stryker Howmedica) was altered to include a load washer. The load washer had a special cable welded to it so that sterilisation could still be conducted in an autoclave. During surgery the end of the load washer cable is passed to the operator, who is able to connect it to a laptop computer. A specially written Labview program is then used to store the data and determine the impaction forces. The load washer is mounted within the hammer at the point of impact between the sliding mass and the hammer, consequently it is reading the force transmitted to the hammer, not that transmitted to the graft chips. Calibration was performed in an in vitro experiment with a second load washer, which found that the force in the hammer is three times that in the impactor. The force is so much less because it is taken up in the hammer’s inertia. Conclusions: The impaction forces have been measured during eight operations performed by three different surgeons. The study shows variability between surgeons, and variability between patients operated on by the same surgeon. These readings show that the forces travelling through the impactor range between three to eleven time body weight

Introduction: The long term success of impaction grafting depends on the remodelling process during incorporation. This project was devised to characterise any differences in the biochemical markers of bone turnover following revision hip arthroplasty performed with or without impaction grafting. Methods: 87 patients were entered into this prospective study and grouped according to whether impaction allograft was used or not. Biochemical markers of bone turnover were assessed pre-operatively and post-operatively on day 2, day 9, week 6, 6 months and 1 year. Osteocalcin, procollagen type-I N-terminal propeptide and bone specific alkaline phosphatase were measured as bone formation markers. C-telopeptide, pyridinoline and deoxypyridinoline were measured as bone resorption markers. Results: All patients had a successful outcome at one year. 50 patients with radiologically defined host-graft union were compared with 37 patients who did not receive an allograft. Markers of bone formation tended to rise by day 9 but the rise in osteocalcin was delayed in the graft group and was significantly lower at 6 months in comparison to the non-graft group (p=0.002). Alkaline phosphatase levels remained significantly elevated at one year in the graft group (p=0.027) whilst levels in the non-graft group had normalised. Markers of bone resorption also rise in both groups but with no significant differences between the groups. Discussion: Following impaction grafting, new bone formation may be delayed in comparison to revisions performed without graft. The pattern of markers of bone resorption did not differ significantly between the groups suggesting that there is no large scale resorption of the impacted allograft in these cases. These results provide a biochemical insight into the bone formation and bone resorption processes during allograft incorporation