Load-bearing increases new bone formation in impacted and morselized allografts

The effects of mechanical loading on the incorporation of morselized impacted grafts were addressed in this study. Twelve skeletally mature rabbits were surgically treated. Six rabbits received a proximal tibial joint replacement with a tibial tray and a load-bearing 25-mm long stem. The tibia was packed with fresh frozen, morselized, cancellous rabbit bone. No cement was used. In six other rabbits only the stem was inserted, without a tibial tray, leaving the stem and the likewise impacted bone graft mechanically unloaded. The rabbits were euthanized after 6 weeks, and the tibias were sectioned and analyzed by histomorphometric examination. In the loaded specimens the graft was resorbed and replaced by new bone (30% of area of interest) to a larger extent than in the unloaded specimens. Mechanical loading of an impacted, morselized graft surrounding a conical uncemented stem, increased the amount of new bone that replaced the graft. The ability of morselized impacted grafts to allow mechanical stimulation of ingrown tissue appears to be a principal cause for the success of this grafting procedure.     

Rapid bone and blood flow formation in impacted morselized allografts

5 patients were revised with impaction of morselized frozen allograft and a cemented total hip arthroplasty (THA) because of loosening and osteolysis of a primary hip arthroplasty. Plain film radiographs of the stems showed stable implants in all patients 15-24 months after surgery. The clinical results were good. We used: 1) Positron Emission Tomography (PET) to evaluate vascularization and new bone formation in the allograft, 2) kinetic [18F]-fluoride PET to produce quantitative images, interpreted as new bone formation in the allograft surrounding the femur stem, 3) [15O]-water PET to quantify bone blood flow, and 4) [15O]-carbon monoxide to determine blood volume. After surgery, all patients were evaluated twice: at 1-8 days and 12 months and 3 patients were also studied at 4 months. As early as at 8 days after surgery, blood flow and bone formation had increased greatly adjacent to the allograft. At 4 months blood flow and bone formation were about the same, but activity was highest in the graft material. At 1 year after surgery, blood flow had declined to the levels of the contralateral femur diaphysis in most of the graft bed. These findings using the PET technique showed that angiogenesis and new bone formation occurred early after impaction of morselized bone allografts around the femoral component in revision THA. We found that PET is a sensitive method for evaluating neovascularization and bone formation in the graft beds.     

Rinsing morselized allografts improves bone and tissue ingrowth

Bone defects in revision hip surgery can be reconstructed with impacted morselized bone grafts. Rinsing these trabecular allografts may enhance graft incorporation by washing out immunogenic factors present in blood, marrow, and fat. However, it has been proposed that impaction of the graft releases biologically active factors, which can provide sufficient activity to stimulate new bone formation. Rinsing before impaction could enhance bone allograft incorporation, but rinsing after impaction could diminish the incorporation process of impacted bone graft. To study the effect of rinsing and impaction of morselized bone grafts on bone ingrowth, a bone chamber study was done in goats. Autografts and allografts were divided into three treatment groups: (A) impacted; (B) rinsed and impacted; and (C) rinsed, impacted, rinsed, and impacted again. Ten goats received three bone chambers in each proximal tibia. The chambers were filled with either allograft or autograft, yielding six different implants per goat. After 6 weeks, histologic analyses were done and bone and tissue ingrowth were measured. New bone and total tissue ingrowth were higher in autografts than in allografts, especially in the nonrinsed group. With rinsing, total tissue ingrowth increased in the allograft group to approach that of autografts. Rinsing after impaction did not additionally alter bone ingrowth. The current findings show that incorporation of allografts can be improved by rinsing the grafts before impaction.     

Hip revisions with impacted morselized allograft bone and cement

No Abstract available     

Rapid bone and blood flow formation in impacted morselized allografts: positron emission tomography (PET) studies on allografts in 5 femoral component revisions of total hip arthroplasty

5 patients were revised with impaction of morselized frozen allograft and a cemented total hip arthroplasty (THA) because of loosening and osteolysis of a primary hip arthroplasty. Plain film radiographs of the stems showed stable implants in all patients 15-24 months after surgery. The clinical results were good. We used: 1) Positron Emission Tomography (PET) to evaluate vascularization and new bone formation in the allograft, 2) kinetic [18F]-fluoride PET to produce quantitative images, interpreted as new bone formation in the allograft surrounding the femur stem, 3) [15O]-water PET to quantify bone blood flow, and 4) [15O]-carbon monoxide to determine blood volume. After surgery, all patients were evaluated twice: at 1-8 days and 12 months and 3 patients were also studied at 4 months. As early as at 8 days after surgery, blood flow and bone formation had increased greatly adjacent to the allograft. At 4 months blood flow and bone formation were about the same, but activity was highest in the graft material. At 1 year after surgery, blood flow had declined to the levels of the contralateral femur diaphysis in most of the graft bed. These findings using the PET technique showed that angiogenesis and new bone formation occurred early after impaction of morselized bone allografts around the femoral component in revision THA. We found that PET is a sensitive method for evaluating neovascularization and bone formation in the graft beds.     

Incorporation of morselized bone grafts: a study of 24 acetabular biopsy specimens

Animal studies have shown almost complete incorporation of impacted morselized bone grafts. To determine whether this also is true in humans, 24 acetabular bone biopsy specimens from 21 hips of 20 patients were examined. Biopsy specimens were obtained 3 months to 15 years after acetabular reconstruction in primary and revision total hip arthroplasties in combination with a cemented cup. Histologic examination showed rapid revascularization of the graft, directly followed by osteoclastic resorption and woven bone formation on the graft remnants. New bone also was formed on fibrin accumulations or without any scaffold in the fibrous stroma tissue that had invaded the graft. Thereafter the mixture of graft, new bone, and fibrin was remodeled completely into a new trabecular structure, with normal lamellar bone and only scarce remnants of graft material. Localized areas of nonincorporated bone graft surrounded by fibrous tissue remained, irrespective of the followup period. Large nonincorporated fragments of cartilage also were found, particularly in cases in which femoral head bone chips were produced by a bone mill. In general, impacted trabecular bone chips incorporate by a mechanism that is similar to that previously observed in animal studies. In some patients, however, areas of nonincorporated bone graft remained and long-term alterations were found, probably related to the loosening process.     

No augmentation of morselized and impacted bone graft by OP-1 in a weight-bearing model

Introduction: Impacted morselized bone allograft is thought to be remodeled to a great extent. We have previously shown that load-bearing increases the remodeling of impacted morselized bone allografts in a rabbit knee prosthesis model. Bone Morphogenic Proteins (BMPs) also stimulate bone formation and bone allograft remodeling. In this study, our aim was to determine whether it was possible to increase further the remodeling of impacted morselized bone allografts by combining load-bearing with a BMP. Experiment: A solution of Osteogenic Protein-1 (OP-1, also called BMP-7) was added to freeze-dried bone allograft chips before impaction grafting in our rabbit knee prosthesis model. 23 skeletally mature rabbits received an uncemented tibial knee prosthetic component inserted into a bed of impacted morselized bone allograft. 12 rabbits were given OP-1-treated allograft (50 µg OP-1 per gram allograft), and 11 rabbits vehicle-treated allograft. Each rabbit received mean 0.53 g graft. The rabbits were killed after 3 or 6 weeks and the grafted region was examined by histomorphometric assessment of the volume fraction of newly formed bone and remaining graft. Results and interpretation: We found that OP-1 did not increase the bone density (graft plus new bone) to any substantial extent. However, we can not exclude that this might be due to a carrier problem, since the OP-1 was added as a solution directly to the dry graft.     

No augmentation of morselized and impacted bone graft by OP-1 in a weight-bearing model

INTRODUCTION: Impacted morselized bone allograft is thought to be remodeled to a great extent. We have previously shown that load-bearing increases the remodeling of impacted morselized bone allografts in a rabbit knee prosthesis model. Bone Morphogenic Proteins (BMPs) also stimulate bone formation and bone allograft remodeling. In this study, our aim was to determine whether it was possible to increase further the remodeling of impacted morselized bone allografts by combining load-bearing with a BMP. EXPERIMENT: A solution of Osteogenic Protein-1 (OP-1, also called BMP-7) was added to freeze-dried bone allograft chips before impaction grafting in our rabbit knee prosthesis model. 23 skeletally mature rabbits received an uncemented tibial knee prosthetic component inserted into a bed of impacted morselized bone allograft. 12 rabbits were given OP-1-treated allograft (50 microg OP-1 per gram allograft), and 11 rabbits vehicle-treated allograft. Each rabbit received mean 0.53 g graft. The rabbits were killed after 3 or 6 weeks and the grafted region was examined by histomorphometric assessment of the volume fraction of newly formed bone and remaining graft. RESULTS AND INTERPRETATION: We found that OP-1 did not increase the bone density (graft plus new bone) to any substantial extent. However, we can not exclude that this might be due to a carrier problem, since the OP-1 was added as a solution directly to the dry graft.     

A combination of bisphosphonate and BMP additives in impacted bone allografts

OP-1 increases bone ingrowth distance of new bone into allografts (T?gil et al. 2000), but the bone density after incorporation may be reduced by an increase in resorption (H?istner et al. 2000). Bisphosphonates inactivate osteoclasts and can be used to increase allograft bone density after incorporation (Aspenberg and Astrand 2002). A combination of locally-applied bisphosphonate and OP-1 in the graft could therefore be expected to increase both new bone ingrowth and density. We tested this by using a rat bone chamber model. OP-1 alone increased the ingrowth distance of bone. Clodronate increased final bone density greatly, but reduced the ingrowth distance of new bone into grafts that were extremely impacted. This reduction was improved by adding OP-1. Regardless of graft density, combinations of OP-1 and clodronate included a high final bone density, but the ingrowth distances were shorter than with OP-1 alone. These data indicate that new bone and tissue ingrowth into a compacted graft depends on resorption and that resorption is a prerequisite for the stimulating effect of OP-1 in this experimental set-up. Although the problems associated with the use of OP-1 in impaction grafting may be solved by adding a bisphosphonate, some of the benefits of OP-1 can be lost.     

A combination of bisphosphonate and BMP additives in impacted bone allografts

OP-1 increases bone ingrowth distance of new bone into allografts (Tägil et al. 2000), but the bone density after incorporation may be reduced by an increase in resorption (Höstner et al. 2000). Bisphosphonates inactivate osteoclasts and can be used to increase allograft bone density after incorporation (Aspenberg and Åstrand 2002). A combination of locally-applied bisphosphonate and OP-1 in the graft could therefore be expected to increase both new bone ingrowth and density. We tested this by using a rat bone chamber model. OP-1 alone increased the ingrowth distance of bone. Clodronate increased final bone density greatly, but reduced the ingrowth distance of new bone into grafts that were extremely impacted. This reduction was improved by adding OP-1. Regardless of graft density, combinations of OP-1 and clodronate included a high final bone density, but the ingrowth distances were shorter than with OP-1 alone. These data indicate that new bone and tissue ingrowth into a compacted graft depends on resorption and that resorption is a prerequisite for the stimulating effect of OP-1 in this experimental set-up. Although the problems associated with the use of OP-1 in impaction grafting may be solved by adding a bisphosphonate, some of the benefits of OP-1 can be lost.     

Histology of vancomycin-supplemented impacted bone allografts in revision total hip arthroplasty

Vancomycin-supplemented allografts provide biological restoration of bone stock and sound fixation with a low incidence of re-infection. Experimental incorporation of these grafts is similar to allografts without vancomycin. However, the underlying biology remains unknown. We report the first histological observations of vancomycin-supplemented impacted bone allografts in two reconstructions performed 14 and 20 months after revision surgery because of a periprosthetic fracture. Areas of active bone remodelling (creeping substitution), as well as calcified bone trabeculae and graft particles embedded in dense fibrous tissue, were observed with osteoid and fibroconnective tissue surrounding polymethylmethacrylate particles.These pathological findings are similar to those reported in allografts without vancomycin and support the hypothesis that high levels of vancomycin do not affect the incorporation of bone graft.     

Irradiation has no effect on the incorporation of impacted morselized bone: a bone chamber study in goats

Background Gamma irradiation has been widely used for sterilization of bone allografts. However, gamma irradiation alters proteins. This is favorable when it reduces immunogenicity, but is undesirable when osteoinductive proteins are damaged. Although the effect of gamma irradiation on BMPs has been studied, the effect of irradiation on the process of incorporation of morselized bone chips remains unclear. We studied the effects of sterilization by gamma irradiation on the incorporation of impacted morselized allografts.

Methods Bone chambers with impacted allografts, rinsed impacted allografts, allografts that were rinsed and subsequently irradiated, and an empty control were implanted in proximal medial tibiae of goats. Incorporation was evaluated using histology and histomorphometry.

Results Histology revealed evidence of bone graft incorporation, which proceeded in a similar way in unprocessed, rinsed, and both rinsed and irradiated bone grafts. After 12 weeks, no difference in bone and tissue ingrowth was found between the unprocessed, the rinsed, and the rinsed and subsequently irradiated allografts. The amount of unresorbed graft remnant was highest in the unprocessed bone grafts.

Interpretation We conclude that sterilization with gamma irradiation does not influence the incorporation of impacted rinsed bone allografts.     

Rapid bone and blood flow formation in impacted morselized allograftsPositron emission tomography (PET) studies on allografts in 5 femoral component revisions of total hip arthroplasty

5 patients were revised with impaction of morselized frozen allograft and a cemented total hip arthroplasty (THA) because of loosening and osteolysis of a primary hip arthroplasty. Plain film radiographs of the stems showed stable implants in all patients 15-24 months after surgery. The clinical results were good. We used: 1) Positron Emission Tomography (PET) to evaluate vascularization and new bone formation in the allograft, 2) kinetic [18F]-fluoride PET to produce quantitative images, interpreted as new bone formation in the allograft surrounding the femur stem, 3) [15O]-water PET to quantify bone blood flow, and 4) [15O]-carbon monoxide to determine blood volume. After surgery, all patients were evaluated twice: at 1-8 days and 12 months and 3 patients were also studied at 4 months. As early as at 8 days after surgery, blood flow and bone formation had increased greatly adjacent to the allograft. At 4 months blood flow and bone formation were about the same, but activity was highest in the graft material. At 1 year after surgery, blood flow had declined to the levels of the contralateral femur diaphysis in most of the graft bed. These findings using the PET technique showed that angiogenesis and new bone formation occurred early after impaction of morselized bone allografts around the femoral component in revision THA. We found that PET is a sensitive method for evaluating neovascularization and bone formation in the graft beds.     

Femoral and acetabular revision using impacted nondemineralized freeze-dried bone allografts

Background  Favorable results have been obtained by the use of deep-frozen bone allografts in total hip arthroplasty. However, owing to the shortage of deep-frozen allografts and the risk of infectious disease, other materials have been studied, such as sterile nondemineralized freeze-dried allografts. The aim of this study was to describe midterm clinical outcomes and radiographic bone incorporation of human freeze-dried bone grafts in 42 revision total hip arthroplasty procedures using cancellous impacted bone grafting. Methods  This report presented clinical and radiographic evidence of allograft incorporation in 42 hip reconstructions performed between 1996 and 2002. The patient group included 13 (31%) men and 29 (69%) women with mean ± SD age of 63 ± 14 years (range 28–80 years). Meanfollow-upwas 82 months (range 63–127) months. Clinical analysis was based on the D’Aubigné-Postel score. Radiographic incorporation was defined according to specific criteria. Results  The D’Aubigné and Postel criteria showed adequate outcome in 38 (90%) of the patients. The radiographic evaluation revealed that allograft remodeling and incorporation were found in 39 (93.0%) and 36 (86.5%) of acetabular and femoral cases, respectively. The overall graft survival rate at an average follow-up of 8 years (range 5–10 years) was 90%. Conclusions  Bone grafts obtained by the lyophilization process developed and carried out in our tissue bank provide suitable grafts for revision total hip arthroplasty. Clinical and radiographic midterm results were excellent, indicating that nondemineralized freeze-dried bone allografts are suitable for replacing deep-frozen grafts.     

Acetabular reconstruction with impacted morselized cancellous allografts in cemented hip arthroplasty: A histological and biomechanical study on the goat

Bone defects in total hip arthroplasty revision surgery can be restored with different types of bone graft. The use of impacted morselized allograft chips in combination with cement is the treatment of our choice. To establish the incorporation capacity of the grafts and mechanical stability of the implant, an animal model in the goat was developed. An acetabular defect was created and restored with morselized grafts and a cemented cup. Postoperative performance of the reconstruction was followed both histologically and biomechanically. Histology showed that consolidation of the graft with the host bone bed had occurred within 3 weeks. In the following period a front of vascular sprouts infiltrated the graft. Graft resorption, woven bone deposition, and subsequent remodeling resulted in a new trabecular structure. This structure contained only scarce remnants of the original dead graft material. At the graft-cement interface, graft resorption and new bone formation had resulted in areas of direct vital bone-cement contact. Locally, a soft tissue interface was present. After longer follow-up periods, progressive interface formation and loosening of the cups were found in most animals. Mechanical testing showed that the stability of the reconstruction increased during the first 12 postoperative weeks. Thereafter, the stability decreased, probably by soft-tissue interface formation at the graft cement-interface. We conclude that cemented morselized allografts have a high capacity to incorporate. Initial cup stability is adequate to provoke graft incorporation with decreasing stability after the incorporation process has been completed.     

Vancomycin-supplemented impacted bone allografts in infected hip arthroplasty. Two-stage revision results

Bone allografts can store and release high levels of vancomycin. We present our results of a two-stage treatment for infected hip arthroplasty with acetabular and femoral impaction grafting using vancomycin-loaded allografts. We treated 29 patients (30 hips) by removal of the implants, meticulous debridement, parenteral antibiotic therapy and second-stage reconstruction using vancomycin-supplemented impacted bone allografts and a standard, cemented Charnley femoral component. The mean follow-up was 32.4 months (24 to 60). Infection control was obtained in 29 cases (re-infection rate of 3.3%; 95% confidence interval 0.08 to 17) without evidence of progressive radiolucent lines, demarcation or graft resorption. One patient had a further infection ten months after revision caused by a different pathogen. Associated post-operative complications were one traumatic periprosthetic fracture at 14 months, a single dislocation in two hips and four displacements of the greater trochanter. Vancomycin-supplemented allografts restored bone stock and provided sound fixation with a low incidence of further infection.     

Migration of the acetabular component after revision with impacted morselized allografts: a radiostereometric 2-year follow-up analysis of 21 cases

In a consecutive series of hip revisions due to mechanical loosening, using impacted morselized allografts and cement, we followed 21 acetabular components by radiostereometric analysis (RSA) during 2 years. All but 1 acetabular component migrated in the proximal direction (median 2.1 (0.5-6.4) mm). 6 components migrated in the medial direction (median 0.8 (0.4-1.2) mm) and 6 in the lateral (median 0.8 (0.4-2.0) mm). 14 components migrated in the posterior direction (median 0.8 (0.3-2.3) mm) and 1 in the anterior 0.6 mm. The migration rate gradually decreased in all directions, but 7 acetabular components still migrated in at least 1 direction (median 0.3-0.6 mm) between 1.5 and 2 years postoperatively.