DOI: 10.1148/rg.262055039
RadioGraphics 2006;26:373-388
© RSNA, 2006
Imaging Characteristics of Bone Graft Materials1
Francesca D. Beaman, MD,
Laura W. Bancroft, MD,
Jeffrey J. Peterson, MD,
Mark J. Kransdorf, MD,
David M. Menke, MD and
James K. DeOrio, MD
1 From the Departments of Radiology (F.D.B., L.W.B., J.J.P., M.J.K.), Pathology (D.M.M.), and Orthopedics (J.K.D.), Mayo Clinic, 4500 San Pablo Rd, Jacksonville, FL 32224-3899; and Department of Radiologic Pathology, Armed Forces Institute of Pathology, Walter Reed Army Medical Center, Washington, DC (M.J.K.). Recipient of Cum Laude and Excellence in Design awards for an education exhibit at the 2004 RSNA Annual Meeting. Received March 4, 2005; revision requested May 2 and received July 1; accepted July 5. All authors have no financial relationships to disclose.
Address correspondence to M.J.K. (e-mail: kransdorf.mark{at}mayo.edu).
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Abstract
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Bone graft materials are widely used in reconstructive orthopedic procedures to promote new bone formation and bone healing, provide a substrate and scaffolding for development of bone structure, and function as a means for direct antibiotic delivery. Bone graft materials include autografts, allografts, and synthetic substitutes. An autograft (from the patient’s own bone) supplies both bone volume and osteogenic cells capable of new bone formation. The imaging appearance of an autograft depends on its type, composition, and age. Autografts often appear as osseous fragments at radiography. At computed tomography (CT), autografts appear similar to the adjacent cortical bone. At magnetic resonance (MR) imaging, however, autografts have a variable appearance as a consequence of the viable marrow inside them, a feature not present in other graft materials. An allograft (from cadaveric bone) has an appearance similar to that of cortical bone on radiographs and CT images. An allograft in the form of bone chips or morsels does not show those features on radiographs and CT images, but instead appears as a conglomerate with medium to high opacity and attenuation within the bone defect. In the immediate postoperative period, allografts appear hypointense on both T1- and T2-weighted MR images. Hematopoietic tissue replaces the normal fatty marrow in the later phases of graft incorporation. Synthetic bone substitutes are much more variable in imaging appearance. As the use of bone allografts and synthetic substitutes increases, familiarity with postoperative imaging features is essential for differentiation between grafts and residual or recurrent disease.
© RSNA, 2006
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LEARNING OBJECTIVES FOR TEST 3
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After reading this article and taking the test, the reader will be able to:- Identify the different types of allografts and synthetic bone graft materials.
- Describe the imaging appearance of bone graft materials at radiography, computed tomography, and magnetic resonance imaging.
- Recognize bone grafts that mimic pathologic processes.
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Introduction
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Bone grafts are rapidly gaining acceptance through their wide availability and utility in a myriad of reconstructive procedures for osseous defects. Bone grafts promote new bone formation and bone healing, provide scaffolding for these processes, and function as substrates for direct antibiotic delivery. To avoid misinterpreting the appearance of a bone graft on images as that of residual or recurrent disease, radiologists need to develop a familiarity with the imaging features of such materials. In this article, the authors describe their experience with various bone graft materials, with an emphasis on the appearance of each material type on radiographs and other radiologic images.
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Principles of Bone Grafting
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The primary function of bone graft material is to promote the healing of osseous defects through new bone formation and structural support. Bone graft material provides a latticework or scaffolding on which new bone can grow through osteogenesis, osteoinduction, and osteoconduction.
Graft osteogenesis results from the transplantation of osteogenic precursor cells that are capable of new bone formation from the graft or the host bed. The cellular elements within the graft must be transplanted, remain viable through incorporation, and produce new bone at the recipient site. Types of grafts that are capable of invoking osteogenesis at the transplantation site include cancellous and cortical bone and vascularized bone segments (1,2).
Osteoinduction is the process through which pluripotential mesenchymal cells are recruited from the surrounding tissue and differentiate into osteoblasts. This transformation is mediated in part by growth factors within the graft—specifically, by bone morphogenic proteins, glycoproteins that are located in the bone matrix (1–3).
Osteoconduction occurs when the resorbable or permanent implant functions as a scaffold to facilitate the ingrowth of vessels and the migration of host cells capable of osteogenesis. As new bone is formed, the graft may be partially or completely resorbed through a process described as creeping substitution (2).
Successful incorporation of bone graft material in any site depends on new bone formation, structural incorporation of the graft, and adaptive remodeling of the skeleton in response to mechanical stress (4). These processes take place in sequential phases similar to those in fracture healing. The length of time until incorporation depends on the native bone environment, the type of graft material, and the structure of the graft (2).
Bone graft procedures are used in a myriad of clinical settings and include osseous fusion (spinal and extremity arthrodesis); fracture stabilization (in cases of acute delayed union or nonunion of fractured bones); and repair of cavitary, segmental, osteochondral, and arthroplasty-related osseous defects (4).
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Bone Graft Materials
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The three main types of bone graft materials are autografts (grafts from the patient’s own bone stock), allografts (grafts from cadaveric bone stock), and synthetic bone graft substitutes (Table) (5).
Autografts
Autogenous cancellous, cortical, and corticocancellous bone particles and bone marrow aspirate have historically been the mainstays of bone grafting. Autografts have the main advantage of supplying not only bone volume but also osteogenic cells capable of new bone formation through osteogenesis, osteoinduction, and osteoconduction (1,6,7). The primary sources of bone autografts are the iliac crest and the fibula, but graft materials also may be harvested from the other long bones, the femoral head, and the ribs. Physical forms include paste, morsels, chips, strips, matchsticks, blocks, and segments (4).
Focal chondral and osteochondral defects located on the weight-bearing surfaces of bones may cause significant disability and are hypothesized to be precursors of osteoarthritis (8). Several methods may be employed in treatment of these lesions, including arthroscopic débridement (9), abrasion arthroplasty (10), subchondral drilling and/or microfracture (11), periosteal graft (12), autogenous chondrocyte implantation (13–15), and autologous osteochondral mosaicplasty (16,17). Mosaicplasty is a procedure in which several small cylindric osteochondral grafts are obtained from the weight-bearing periphery of the femoral condyles at the level of the patellofemoral joint and transplanted in the critical lesion (17). Over time, the graft may be incorporated into the native bone (Fig 1).
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Figure 1a. Osteochondral autograft transfer in a 27-year-old man. (a) Coronal reconstruction CT image of the left ankle shows a talar dome osteochondral defect (arrow). (b) Anteroposterior radiograph, obtained 2 months after surgical osteochondral autograft transfer, shows the graft as a bone fragment in the talar dome (arrowheads).
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Figure 1b. Osteochondral autograft transfer in a 27-year-old man. (a) Coronal reconstruction CT image of the left ankle shows a talar dome osteochondral defect (arrow). (b) Anteroposterior radiograph, obtained 2 months after surgical osteochondral autograft transfer, shows the graft as a bone fragment in the talar dome (arrowheads).
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The imaging appearance of a bone graft depends on the type, composition, and age of the graft. Chip autografts initially look like osseous fragments on radiographs. Healed osteochondral transfer autografts are barely perceptible on conventional radiographs, and, on MR images, show minimal signal heterogeneity, with signal nearly isointense to that in the adjacent marrow and cartilage (Fig 2). Vascularized fibular autografts maintain the appearance of tubular bones, with defined cortices and medullary canal (Fig 3).
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Figure 2a. Osteochondral autograft transfer in a 52-year-old woman. Sagittal turbo spin-echo proton density–weighted MR images (repetition time msec/echo time msec, 2500/26) obtained after osteochondral autograft transfer show minimal signal heterogeneity and cartilage thickening over the right medial femoral condylar defect (arrowheads in a) and the donor site of the osteochondral autograft (arrow in b).
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Figure 2b. Osteochondral autograft transfer in a 52-year-old woman. Sagittal turbo spin-echo proton density–weighted MR images (repetition time msec/echo time msec, 2500/26) obtained after osteochondral autograft transfer show minimal signal heterogeneity and cartilage thickening over the right medial femoral condylar defect (arrowheads in a) and the donor site of the osteochondral autograft (arrow in b).
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Figure 3a. Vascularized fibular autograft in a 20-year-old man. (a) Anteroposterior radiograph of the left humerus shows humeral bone loss from multiple débridements for a nonunited grade 2 open fracture secondary to a motor vehicle accident, as well as osteomyelitis. The external fixator was placed at an outside institution. (b) Anteroposterior radiograph obtained 18 days after placement of a vascularized fibular autograft (arrow) shows new bone bridging the damaged native humeral segments. (c) Anteroposterior radiograph obtained 2 months after the procedure shows increased consolidation of the new periosteal bone (arrows).
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Figure 3b. Vascularized fibular autograft in a 20-year-old man. (a) Anteroposterior radiograph of the left humerus shows humeral bone loss from multiple débridements for a nonunited grade 2 open fracture secondary to a motor vehicle accident, as well as osteomyelitis. The external fixator was placed at an outside institution. (b) Anteroposte-rior radiograph obtained 18 days after placement of a vascularized fibular autograft (arrow) shows new bone bridging the damaged native humeral segments. (c) Anteroposterior radiograph obtained 2 months after the procedure shows increased consolidation of the new periosteal bone (arrows).
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Figure 3c. Vascularized fibular autograft in a 20-year-old man. (a) Anteroposterior radiograph of the left humerus shows humeral bone loss from multiple débridements for a nonunited grade 2 open fracture secondary to a motor vehicle accident, as well as osteomyelitis. The external fixator was placed at an outside institution. (b) Anteroposte-rior radiograph obtained 18 days after placement of a vascularized fibular autograft (arrow) shows new bone bridging the damaged native humeral segments. (c) Anteroposterior radiograph obtained 2 months after the procedure shows increased consolidation of the new periosteal bone (arrows).
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On CT scans, the attenuation of an autograft is similar to that of the adjacent cortical bone (Fig 4a). However, autografts have a variable postoperative MR imaging appearance. On T1-weighted MR images, solid fusion of the autograft with native bone may be evidenced by normal marrow signal intensity that extends throughout the surgical site and by an intact cortical margin (Fig 4b). The signal in the autograft may be hyperintense on T1-weighted MR images and hypointense on T2-weighted MR images, relative to the signal intensity of skeletal muscle. The MR imaging appearance of autografts is a consequence of the viable marrow inside them, a feature not present in other graft materials. Low signal intensity on T1-weighted images and isointensity to hyperintensity on T2-weighted images, features that histologically correlate with necrosis and ingrowth of granulation tissue, also may be present in autografts (7). Vascularized fibular autografts should maintain T1- and T2-weighted signal intensity similar to that of bone marrow; in the absence of this similarity, vascular and therefore graft compromise may be suspected (19–21).
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Figure 4a. Iliac crest autografts. (a) Sagittal reconstruction CT image of the right foot shows subtalar fusion (arrows) 1 year after iliac crest autograft placement in a 71-year-old man. (b) Axial spin-echo T1-weighted MR image (550/13) shows solid fusion of the posterior vertebral arch from L4 to S1 in a 68-year-old woman, 22 years after placement of an iliac crest autograft. Note the normal marrow signal (*) that extends throughout the surgical site and the intact cortical margin.
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Figure 4b. Iliac crest autografts. (a) Sagittal reconstruction CT image of the right foot shows subtalar fusion (arrows) 1 year after iliac crest autograft placement in a 71-year-old man. (b) Axial spin-echo T1-weighted MR image (550/13) shows solid fusion of the posterior vertebral arch from L4 to S1 in a 68-year-old woman, 22 years after placement of an iliac crest autograft. Note the normal marrow signal (*) that extends throughout the surgical site and the intact cortical margin.
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Allografts
Because of morbidity associated with autograft harvesting and because of limited donor site availability, alternatives to autografts have been extensively investigated. Allografts (cadaveric bone transplants) are popular substitutes for autografts but provide mainly an osteoconductive matrix that lacks osteoinductive properties. The graft is surrounded by fibrovascular granulation tissue and undergoes vascular and osteogenic precursor cell invasion. The interface between allograft transplant and host fibrovascular tissue is the site of osteoclastic activity and bone resorption. The balance between osteolysis and osteogenesis must be maintained for graft incorporation to occur (22). Bone allografts face specific limitations, which include the possibility of disease transmission, procurement cost, host immune response and graft rejection, and inconsistent incorporation. The risk of disease transmission is negligible because of tissue sterilization and processing procedures (1,2,6).
Allograft functions may include those of a bone void filler, an in vivo antibiotic delivery system (23,24), a composite graft (Fig 5) (25), and an onlay graft (26). Onlay or strut allografts function as long-bone scaffolds in cases of periprosthetic fracture (Fig 6) or large en bloc bone resection (27). Strut graft complications may include fracture nonunion or graft fracture (Fig 7). In surgical reconstructions, bone allografts are often placed in tandem with implants and fixation devices; however, graft failure allows excessive mechanical force to be placed on the hardware, which may result in hardware failure (Fig 8).
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Figure 5a. Proximal femoral allograft in a 40-year-old woman. (a) Anteroposterior radiograph of the left proximal femur shows a grade 1 chondrosarcoma. (b) Postoperative anteroposterior radiograph of the left femur shows an allograft-prosthesis composite.
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Figure 5b. Proximal femoral allograft in a 40-year-old woman. (a) Anteroposterior radiograph of the left proximal femur shows a grade 1 chondrosarcoma. (b) Postoperative anteroposterior radiograph of the left femur shows an allograft-prosthesis composite.
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Figure 6a. Onlay allograft in a 73-year-old woman. (a) Photograph shows a syringe that contains demineralized bone matrix putty (MTF DBX Putty; Dentsply) used to secure the allograft to the fractured femur. (b) Anteroposterior radiograph shows the allograft (arrowheads) and cerclage wires placed to correct a right periprosthetic femur fracture distal to the tip of the femoral stem (arrow).
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Figure 6b. Onlay allograft in a 73-year-old woman. (a) Photograph shows a syringe that contains demineralized bone matrix putty (MTF DBX Putty; Dentsply) used to secure the allograft to the fractured femur. (b) Anteroposterior radiograph shows the allograft (arrowheads) and cerclage wires placed to correct a right periprosthetic femur fracture distal to the tip of the femoral stem (arrow).
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Figure 7a. Radial osteochondral allograft in a 24-year-old woman. (a) Anteroposterior radiograph of grade 1 osteosarcoma of the distal right radius. (b) Coronal spin-echo T1-weighted MR image (483/23) shows heterogeneity and hypointensity of signal in the mass relative to that in skeletal muscle, information useful for defining the tumor extent within the diaphysis. (c) Immediate postoperative anteroposterior radiograph shows placement of the radial osteochondral allograft (arrowhead), with middle and distal radial plate and screw fixation and with suture anchors in the radial styloid. (d) Ten-month follow-up anteroposterior radiograph shows interval fracture of the distal radial graft (arrowhead) with half-shaft anterior displacement of the distal fracture fragment and moderately severe anterior angulation at the fracture site.
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Figure 7b. Radial osteochondral allograft in a 24-year-old woman. (a) Anteroposterior radiograph of grade 1 osteo-sarcoma of the distal right radius. (b) Coronal spin-echo T1-weighted MR image (483/23) shows heterogeneity and hypointensity of signal in the mass relative to that in skeletal muscle, information useful for defining the tumor extent within the diaphysis. (c) Immediate postoperative anteroposterior radiograph shows placement of the radial osteo-chondral allograft (arrowhead), with middle and distal radial plate and screw fixation and with suture anchors in the radial styloid. (d) Ten-month follow-up anteroposterior radiograph shows interval fracture of the distal radial graft (arrowhead) with half-shaft anterior displacement of the distal fracture fragment and moderately severe anterior an-gulation at the fracture site.
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Figure 7c. Radial osteochondral allograft in a 24-year-old woman. (a) Anteroposterior radiograph of grade 1 osteo-sarcoma of the distal right radius. (b) Coronal spin-echo T1-weighted MR image (483/23) shows heterogeneity and hypointensity of signal in the mass relative to that in skeletal muscle, information useful for defining the tumor extent within the diaphysis. (c) Immediate postoperative anteroposterior radiograph shows placement of the radial osteo-chondral allograft (arrowhead), with middle and distal radial plate and screw fixation and with suture anchors in the radial styloid. (d) Ten-month follow-up anteroposterior radiograph shows interval fracture of the distal radial graft (arrowhead) with half-shaft anterior displacement of the distal fracture fragment and moderately severe anterior an-gulation at the fracture site.
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Figure 7d. Radial osteochondral allograft in a 24-year-old woman. (a) Anteroposterior radiograph of grade 1 osteo-sarcoma of the distal right radius. (b) Coronal spin-echo T1-weighted MR image (483/23) shows heterogeneity and hypointensity of signal in the mass relative to that in skeletal muscle, information useful for defining the tumor extent within the diaphysis. (c) Immediate postoperative anteroposterior radiograph shows placement of the radial osteo-chondral allograft (arrowhead), with middle and distal radial plate and screw fixation and with suture anchors in the radial styloid. (d) Ten-month follow-up anteroposterior radiograph shows interval fracture of the distal radial graft (arrowhead) with half-shaft anterior displacement of the distal fracture fragment and moderately severe anterior an-gulation at the fracture site.
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Figure 8a. Cancellous bone allograft resorption with hardware loosening and failure in a 46-year-old woman. (a) Lateral radiograph obtained on postoperative day 1 shows the allograft (*) as an area of high opacity in the C4-C5 interspace and C4-C5 anterior cervical plate (Atlantis Vision; Medtronic Sofamor Danek, Memphis, Tenn). The graft was coated with injectable bone paste (Osteofil; Regeneration Technologies. (b) One-year follow-up radiograph shows focal allograft resorption, hardware loosening, and failure of the inferior screw (arrow).
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Figure 8b. Cancellous bone allograft resorption with hardware loosening and failure in a 46-year-old woman. (a) Lateral radiograph obtained on postoperative day 1 shows the allograft (*) as an area of high opacity in the C4-C5 interspace and C4-C5 anterior cervical plate (Atlantis Vision; Medtronic Sofa-mor Danek, Mem-phis, Tenn). The graft was coated with injectable bone paste (Osteofil; Regeneration Technologies. (b) One-year follow-up radiograph shows focal allograft resorption, hardware loosening, and failure of the inferior screw (arrow).
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Allografts have opacity or attenuation similar to that of cortical bone on radiographs or CT scans. CT or conventional tomography may be employed to evaluate both autografts and allo-grafts in situations of suspected graft failure. After placement, strut grafts initially appear as tubular bones with a defined cortex and medullary canal. Grafts in the form of chips or morsels do not retain these characteristics at imaging, but instead appear as high-attenuating conglomerates within the bone defects. The discrete boundary between host and graft is initially identifiable; however, as union progresses, the graft-host junction is obliterated as a result of trabecular ingrowth, and the medullary canal is replaced by fibrous tissue.
In the immediate postoperative period, allo-grafts have signal hypointensity on both T1- and T2-weighted MR images. MR imaging is also useful for ascertaining the presence or absence of marrow signal intensity, which indicates graft incorporation or failure, respectively. The replacement of normal fatty marrow by hematopoietic tissue in the later phases of graft incorporation is manifested by the presence of a red-marrow signal. A persistent signal intensity lower than that of marrow on T1- and T2-weighted images suggests fibrous replacement and a lack of complete graft incorporation (19,28).
Graft combinations are often used to obtain both osteoconductive and osteoinductive properties. Allografts may be mixed with autologous platelet-rich plasma, a concentration of human platelets in a small volume of plasma, which encourages osteoinduction by supplying fundamental growth proteins that are secreted by the platelets and that initiate wound healing. Cell adhesion molecules of fibrin, fibronectin, and vitro-nectin also are present in the plasma (29). The combination of platelet-rich plasma with an allo-graft affords both structural integrity and growth factors. Only the allograft material is detectable on radiographs, because platelet-rich plasma is radiolucent (Fig 9).
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Figure 9a. Cancellous bone allograft and autologous platelet-rich product used for left ankle fusion in a 53-year-old man. (a) Photograph shows the autologous blood concentrate product (Symphony; DePuy/Johnson & Johnson). (b, c) Lateral radiographs of the left ankle, obtained 2 months (b) and 4 months (c) after graft placement, show progressive resorption of the graft material (arrowhead) and deposition of bone (arrow).
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Figure 9b. Cancellous bone allograft and autologous platelet-rich product used for left ankle fusion in a 53-year-old man. (a) Photograph shows the autologous blood concentrate product (Symphony; DePuy/Johnson & Johnson). (b, c) Lateral radiographs of the left ankle, obtained 2 months (b) and 4 months (c) after graft placement, show progressive resorption of the graft material (arrowhead) and deposition of bone (arrow).
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Figure 9c. Cancellous bone allograft and autologous platelet-rich product used for left ankle fusion in a 53-year-old man. (a) Photograph shows the autologous blood concentrate product (Symphony; DePuy/Johnson & Johnson). (b, c) Lateral radiographs of the left ankle, obtained 2 months (b) and 4 months (c) after graft placement, show progressive resorption of the graft material (arrowhead) and deposition of bone (arrow).
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Synthetic Substitutes
Because of the inherent disadvantages of bone autografts and allografts, interest in synthetic substitutes has intensified. Synthetic substitutes may be classified into three primary groups: demineralized bone matrix, ceramics, and composite materials (2).
Demineralized bone matrix is created from cortical or corticocancellous bone through an acid extraction process that produces a composite of noncollagenous proteins, bone growth factors, and collagen (18). Demineralized bone matrix implants act in an osteoinductive manner to stimulate bone healing in 3–6 months and have been reported to show no significant resorption in patients 7 years after implantation (30,31). Disadvantages of demineralized bone are the loss of structural rigidity (because of processing) and the inability to visualize the material radiographically (because of its inherent radiolucency) (32).
A formulation that is favored at our institution is demineralized bone matrix putty (Grafton DBM Putty; Osteotech), a malleable substance that can be packed into bone voids (Fig 10) and that is barely perceptible on postoperative radiographs. Demineralized bone matrix putty also may be combined with a cancellous bone allograft to obtain both osteoconductive and osteoinductive properties. On both immediate postoperative and subsequent radiographs, the combination of putty and allograft chips appears to have a density between that of medullary and cortical bone (Fig 11). On CT scans, the combination has attenuation in the range of 500–1000 HU, between those of medullary and cortical bone (Fig 12). Diffuse enhancement of signal intensity in the postoperative bed is an expected finding on MR images, presumably because of the calcium content of bone graft material and the ingrowth of vascularized granulation tissue (Fig 13).
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Figure 10a. Demineralized bone matrix putty used in tibial plateau reconstruction in a 55-year-old man. (a) Photograph shows the putty. (b) Anteroposterior postoperative radiograph, obtained 1 month after reconstruction of the tibial plateau with mechanical elevation of native bone fragments and putty placement, shows slight opacity at the graft site (*) in the lateral tibia.
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Figure 10b. Demineralized bone matrix putty used in tibial plateau reconstruction in a 55-year-old man. (a) Photograph shows the putty. (b) Anteroposterior postoperative radiograph, obtained 1 month after reconstruction of the tibial plateau with mechanical elevation of native bone fragments and putty placement, shows slight opacity at the graft site (*) in the lateral tibia.
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Figure 11a. Cancellous bone allograft and demineralized bone matrix putty used to repair the hip bone in a 77-year-old man. (a) Anteroposterior radiograph of the left hip shows superior acetabular osteolysis (*) due to particle disease (polyethylene osteolysis). (b) Anteroposterior radiograph, obtained 1 year after placement of a cancellous bone allograft and putty (Grafton DBM Putty; Osteotech) in the bone void (*), shows opacity at the site of the graft that is similar to that of adjacent bone.
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Figure 11b. Cancellous bone allograft and demineralized bone matrix putty used to repair the hip bone in a 77-year-old man. (a) Anteroposterior radiograph of the left hip shows superior acetabular osteolysis (*) due to particle disease (polyethylene osteolysis). (b) Anteroposterior radiograph, obtained 1 year after placement of a cancellous bone allograft and putty (Grafton DBM Putty; Osteotech) in the bone void (*), shows opacity at the site of the graft that is similar to that of adjacent bone.
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Figure 12a. Cancellous bone allograft and putty used to repair the left femur in a 29-year-old man. (a) Sagittal reconstruction CT image, obtained on postoperative day 1, shows bone graft material placed in a void in the left medial femoral condyle after giant cell tumor curettage. Note that the attenuation of the graft is similar to that of bone. (b) Anteroposterior radiograph, obtained 1 month after graft placement, shows faint callus formation (arrowheads), a nondisplaced fracture that extends through the articular surface (arrow), and K-wires that traverse the epiphysis. (c) Anteroposterior radiograph, obtained 3 years after graft placement, shows solid bone bridging the medial defect (arrowheads) and the near invisibility of the fracture.
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Figure 12b. Cancellous bone allograft and putty used to repair the left femur in a 29-year-old man. (a) Sagittal reconstruction CT image, obtained on postoperative day 1, shows bone graft material placed in a void in the left medial femoral condyle after giant cell tumor curettage. Note that the attenuation of the graft is similar to that of bone. (b) Anteroposterior radiograph, obtained 1 month after graft placement, shows faint callus formation (arrowheads), a nondisplaced fracture that extends through the articular surface (arrow), and K-wires that traverse the epiphysis. (c) Anteroposterior radiograph, obtained 3 years after graft placement, shows solid bone bridging the medial defect (arrowheads) and the near invisibility of the fracture.
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Figure 12c. Cancellous bone allograft and putty used to repair the left femur in a 29-year-old man. (a) Sagittal reconstruction CT image, obtained on postoperative day 1, shows bone graft material placed in a void in the left medial femoral condyle after giant cell tumor curettage. Note that the attenuation of the graft is similar to that of bone. (b) Anteroposterior radiograph, obtained 1 month after graft placement, shows faint callus formation (arrowheads), a nondisplaced fracture that extends through the articular surface (arrow), and K-wires that traverse the epiphysis. (c) Anteroposterior radiograph, obtained 3 years after graft placement, shows solid bone bridging the medial defect (arrowheads) and the near invisibility of the fracture.
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Figure 13a. Cancellous bone allograft placement in the hand of a 16-year-old girl. (a) Anteroposterior radiograph, obtained 7 months after surgery for a recurrent giant cell tumor, shows a persistent region of lucency (*) despite bone ingrowth in part of the void (arrows). To aid bone repair, demineralized bone matrix putty (Grafton DBM Putty; Osteotech) was used along with a demineralized bone matrix graft (Opteform; Exactech, Gainesville, Fla, and Regeneration Technologies, Alachua, Fla) that contains a collagen gelatin for thermoplasticity of the graft. (b) Coronal fast spin-echo inversion recovery MR image (3480/39), obtained 4 months after graft placement, shows the heterogeneous signal of the bone graft materials and vascularized granulation tissue (*). (c) Contrast material–enhanced coronal spin-echo fat-saturation T1-weighted image (444/16) from the same MR examination as b shows heterogeneous enhancement of the graft materials and vascularized granulation tissue (*).
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Figure 13b. Cancellous bone allograft placement in the hand of a 16-year-old girl. (a) Anteroposterior radiograph, obtained 7 months after surgery for a recurrent giant cell tumor, shows a persistent region of lucency (*) despite bone ingrowth in part of the void (arrows). To aid bone repair, demineralized bone matrix putty (Grafton DBM Putty; Osteotech) was used along with a demineralized bone matrix graft (Opteform; Exactech, Gainesville, Fla, and Regeneration Technologies, Alachua, Fla) that contains a collagen gelatin for thermoplasticity of the graft. (b) Coronal fast spin-echo inversion recovery MR image (3480/39), obtained 4 months after graft placement, shows the heterogeneous signal of the bone graft materials and vascularized granulation tissue (*). (c) Contrast material–enhanced coronal spin-echo fat-saturation T1-weighted image (444/16) from the same MR examination as b shows heterogeneous enhancement of the graft materials and vascularized granulation tissue (*).
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Figure 13c. Cancellous bone allograft placement in the hand of a 16-year-old girl. (a) Anteroposterior radiograph, obtained 7 months after surgery for a recurrent giant cell tumor, shows a persistent region of lucency (*) despite bone ingrowth in part of the void (arrows). To aid bone repair, demineralized bone matrix putty (Grafton DBM Putty; Osteotech) was used along with a demineralized bone matrix graft (Opteform; Exactech, Gainesville, Fla, and Regeneration Technologies, Alachua, Fla) that contains a collagen gelatin for thermoplasticity of the graft. (b) Coronal fast spin-echo inversion recovery MR image (3480/39), obtained 4 months after graft placement, shows the heterogeneous signal of the bone graft materials and vascularized granulation tissue (*). (c) Contrast material–enhanced coronal spin-echo fat-saturation T1-weighted image (444/16) from the same MR examination as b shows heterogeneous enhancement of the graft materials and vascularized granulation tissue (*).
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The majority of ceramics currently used are synthetic and composed of calcium sulfate, hydroxyapatite, tricalcium phosphate, or a combination of hydroxyapatite and tricalcium phosphate. Ceramics provide an osteoconductive lattice on which host osteogenesis can take place, but they lack osteoinductive properties (2). Ceramics are available in a variety of forms, including pellets, cement, and injectable paste. Ceramics are radiopaque and formulated for use in spaces that are not intrinsic to the stability of the bone structure. The design of these products allows for creeping substitution, which involves the resorption of the ceramic and its replacement by bone during the healing process.
On radiographs, ceramics appear denser than the adjacent native bone. In the initial postoperative period, a lucent band is identifiable at the graft-host junction, and the margins and internal architecture of the graft are sharply defined. Osseous ingrowth begins soon after surgery, with subsequent obliteration of the radiolucent area that once surrounded the implant and with loss of definition of the implant margins and internal architecture on radiographs. These changes in appearance are believed to result from osteoclastic activity and osseous ingrowth (19).
An example of such a ceramic is the calcium sulfate bone void filler MIIG (Minimally Invasive Injectable Graft) X3 (Wright Medical Technology). On CT scans obtained immediately after placement, the calcium sulfate ceramic has attenuation similar to that of cortical bone; however, follow-up scans demonstrate rapid resorption, with near-complete radiolucency by 2 months (Fig 14).
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Figure 14a. Calcium sulfate ceramic bone graft substitute used for joint repair in a 42-year-old man. (a) Photograph of the ceramic graft material. (b) Preprocedural axial CT image shows a unicameral bone cyst (*) in the right posterior ilium at the level of the superior sacroiliac joint. (c) Axial CT image, obtained 1 month after graft placement, shows partial resorption of the graft material (arrow). (d) Axial CT image, obtained 2 years after graft placement, shows complete resorption of the graft material and minimal ingrowth of bone (arrows).
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Figure 14b. Calcium sulfate ceramic bone graft substitute used for joint repair in a 42-year-old man. (a) Photograph of the ceramic graft material. (b) Preprocedural axial CT image shows a unicameral bone cyst (*) in the right posterior ilium at the level of the superior sacroiliac joint. (c) Axial CT image, obtained 1 month after graft placement, shows partial resorption of the graft material (arrow). (d) Axial CT image, obtained 2 years after graft placement, shows complete resorption of the graft material and minimal ingrowth of bone (arrows).
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Figure 14c. Calcium sulfate ceramic bone graft substitute used for joint repair in a 42-year-old man. (a) Photograph of the ceramic graft material. (b) Preprocedural axial CT image shows a unicameral bone cyst (*) in the right posterior ilium at the level of the superior sacroiliac joint. (c) Axial CT image, obtained 1 month after graft placement, shows partial resorption of the graft material (arrow). (d) Axial CT image, obtained 2 years after graft placement, shows complete resorption of the graft material and minimal ingrowth of bone (arrows).
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Figure 14d. Calcium sulfate ceramic bone graft substitute used for joint repair in a 42-year-old man. (a) Photograph of the ceramic graft material. (b) Preprocedural axial CT image shows a unicameral bone cyst (*) in the right posterior ilium at the level of the superior sacroiliac joint. (c) Axial CT image, obtained 1 month after graft placement, shows partial resorption of the graft material (arrow). (d) Axial CT image, obtained 2 years after graft placement, shows complete resorption of the graft material and minimal ingrowth of bone (arrows).
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Calcium sulfate also is available in the form of pellets. According to manufacturer-provided information, one such formulation (Osteoset; Wright Medical Technology) is resorbed in 30–60 days. The dense pellets are clearly visible on initial postoperative radiographs but are imperceptible on radiographs obtained 67 days after surgical placement (Fig 15). Potential pitfalls exist in MR imaging of a graft that contains calcium sulfate pellets, which, regardless of the MR sequence used, appear hypointense and masslike, features that could lead physicians to mistake the graft for residual or recurrent tumor (Fig 16).
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Figure 15a. Calcium sulfate pellets used to repair a calcaneal defect in a 79-year-old woman. (a) Photograph shows the graft material. (b) Intraoperative radiograph obtained after placement of the pellets (arrows) in the left foot, in a posterior calcaneal defect that resulted from resection for osteomyelitis. (c) Lateral radiograph, obtained 5 months after graft placement, shows complete resorption of the pellets and resultant remodeling of the calcaneus, with minimal ingrowth of bone (*).
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Figure 15b. Calcium sulfate pellets used to repair a calcaneal defect in a 79-year-old woman. (a) Photograph shows the graft material. (b) Intraoperative radiograph obtained after placement of the pellets (arrows) in the left foot, in a posterior calcaneal defect that resulted from resection for osteomyelitis. (c) Lateral radiograph, obtained 5 months after graft placement, shows complete resorption of the pellets and resultant remodeling of the calcaneus, with minimal ingrowth of bone (*).
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Figure 15c. Calcium sulfate pellets used to repair a calcaneal defect in a 79-year-old woman. (a) Photograph shows the graft material. (b) Intraoperative radiograph obtained after placement of the pellets (arrows) in the left foot, in a posterior calcaneal defect that resulted from resection for osteomyelitis. (c) Lateral radiograph, obtained 5 months after graft placement, shows complete resorption of the pellets and resultant remodeling of the calcaneus, with minimal ingrowth of bone (*).
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Figure 16a. Calcium sulfate pellets mimic recurrent pigmented villonodular synovitis in a 51-year-old woman. (a, b) Sagittal T1-weighted spin-echo (589/18) (a) and sagittal fat-saturated T2-weighted turbo spin-echo (4000/78) (b) MR images show a large ill-defined area with hypointense T1 and T2 signal (arrow) that mimics recurrent PVNS, adjacent to the calcaneus and the cuboid, navicular, middle cuneiform, and lateral cuneiform bones. (c) Photomicrograph (original magnification, x40; hematoxylineosin stain) shows foci of calcium deposition (arrows) surrounded by new bone with surface osteoblastic activity (arrowhead).
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Figure 16b. Calcium sulfate pellets mimic recurrent pigmented villonodular synovitis in a 51-year-old woman. (a, b) Sagittal T1-weighted spin-echo (589/18) (a) and sagittal fat-saturated T2-weighted turbo spin-echo (4000/78) (b) MR images show a large ill-defined area with hypointense T1 and T2 signal (arrow) that mimics recurrent PVNS, adjacent to the cal-caneus and the cuboid, navicular, middle cuneiform, and lateral cuneiform bones. (c) Photomicrograph (original magnification, x40; hematoxylin-eosin stain) shows foci of calcium deposition (arrows) surrounded by new bone with surface osteoblastic activity (arrowhead).
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Figure 16c. Calcium sulfate pellets mimic recurrent pigmented villonodular synovitis in a 51-year-old woman. (a, b) Sagittal T1-weighted spin-echo (589/18) (a) and sagittal fat-saturated T2-weighted turbo spin-echo (4000/78) (b) MR images show a large ill-defined area with hypointense T1 and T2 signal (arrow) that mimics recurrent PVNS, adjacent to the cal-caneus and the cuboid, navicular, middle cuneiform, and lateral cuneiform bones. (c) Photomicrograph (original magnification, x40; hematoxylin-eosin stain) shows foci of calcium deposition (arrows) surrounded by new bone with surface osteoblastic activity (arrowhead).
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Composite grafts incorporate the favorable attributes of ceramics and demineralized bone matrix in a single compound. The ceramic provides an osteoconductive matrix, while the demineralized bone matrix affords osteoinductive properties. Mixtures also may be created at the surgical table to accomplish similar goals. As is the case with other mineral-containing synthetic bone grafts, the composite grafts appear radiopaque on postoperative radiographs and CT scans (Fig 17) and over time may be incorporated into the skeletal structure.
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Figure 17a. Tricalcium phosphate granules combined with demineralized bone matrix putty in a 61-year-old woman. (a) Photograph shows the tricalcium phosphate granules (Conduit; DePuy/Johnson & Johnson) before they were mixed with the putty (Grafton DBM; Osteotech). (b) Axial CT image obtained 1 day after the graft placement shows the individual high-attenuation granules (arrow) filling the bone void. (c) Anteroposterior radiograph of the left distal femur, obtained 1 month after enchondroma curettage and insertion of the combined graft materials, shows individual tricalcium phosphate granules (arrow).
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Figure 17b. Tricalcium phosphate granules combined with demineralized bone matrix putty in a 61-year-old woman. (a) Photograph shows the tricalcium phosphate granules (Conduit; DePuy/Johnson & Johnson) before they were mixed with the putty (Grafton DBM; Osteotech). (b) Axial CT image obtained 1 day after the graft placement shows the individual high-attenuation granules (arrow) filling the bone void. (c) Anteroposterior radiograph of the left distal femur, obtained 1 month after enchondroma curettage and insertion of the combined graft materials, shows individual tricalcium phosphate granules (arrow).
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Figure 17c. Tricalcium phosphate granules combined with demineralized bone matrix putty in a 61-year-old woman. (a) Photograph shows the tricalcium phosphate granules (Conduit; DePuy/Johnson & Johnson) before they were mixed with the putty (Grafton DBM; Osteotech). (b) Axial CT image obtained 1 day after the graft placement shows the individual high-attenuation granules (arrow) filling the bone void. (c) Anteroposterior radiograph of the left distal femur, obtained 1 month after enchondroma curettage and insertion of the combined graft materials, shows individual tricalcium phosphate granules (arrow).
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Complications
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The possible complications of bone graft placement include nonunion or delayed union of bone fragments, graft fracture, graft extrusion, and infection (Figs 7, 18–20). The failure of osseous union is depicted radiographically as persistent lucency at the graft-host junction with sclerosis, erosion, and fragmentation (19). Possible complications at an autograft donor site include increased duration of surgery, blood loss, wound infections, chronic pain, scarring, and local sensory loss (2,6). Possible complications related to allografts include disease transmission and mild rejection (4).
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Figure 18. Failure of an autograft in the wrist of a 24-year-old man. Anteroposterior radiograph shows a Herbert screw that bridges an old nonunited scaphoid fracture deformity (arrow), accompanied by evidence of scapholunate advanced collapse. The autograft that was initially placed to aid in fracture union has failed and cannot be seen. The proximal pole of the scaphoid is diminutive and not well defined, and there is marked cystic change of the capitate (*) and distal radius, with ulnar positive variance.
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Figure 19a. Failure of a vascularized fibular autograft in a 49-year-old man. Anteroposterior radiograph (a) and coronal reconstruction CT image (b) show a subtrochanteric transverse fracture of the right femur and an associated fracture of the vascularized fibular autograft (*). The linear area of opacity in a is a K-wire placed for graft fixation.
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Abstract
LEARNING OBJECTIVES FOR TEST...
