Complications can arise during fracture healing. These can include infections, hyperemia, ischemia, and avascular necrosis, all of which can lead to delayed union or nonunion. Nonunion can also be caused by instable immobilization and excessive distraction or compression.1 Nonunion fractures are those in which healing has ceased, whereas delayed union fractures are those in which healing requires longer than expected.2,3
Early recognition of complications is important to enable clinicians to take immediate corrective actions. Clinical characteristics of delayed union or nonunion fractures include lack of rigidity, crepitation, abnormal movement in the fracture region, signs of pain during manipulation of the fracture region, inability or unwillingness to bear weight, deformity of the limb, disuse atrophy of the limb, and an abnormal callus (profuse or total lack of a callus).1,3,4
Classically, nonunion fractures have been delineated into viable and nonviable categories. Viable nonunion fractures are described as hypertrophic, slightly hypertrophic, and oligotrophic. All are caused by instability. Nonviable nonunion fractures have an interruption of the blood supply and are classified as dystrophic, necrotic, defect, and atrophic.1
Radiography is the imaging method traditionally used for the assessment of fracture healing. The main radiographic signs of nonunion include a visible fracture gap, clearly defined fracture ends, obliteration of the marrow cavity, and a callus (if evident) that does not bridge the fracture gap.2 Classification into viable and nonviable categories is based primarily on whether there is a callus. In hypertrophic viable nonunion fractures, abundant callus formation is visible but the callus does not bridge the fracture gap. Fractures with evidence of a small amount of nonbridging callus have been termed slightly hypertrophic1 but are also classified as viable. In atrophic nonunion fractures, minimal or no callus formation is evident.1,2,4 There is less uniformity in the appearance of the fracture ends, other than the amount of callus formation. According to 1 source,2 sclerotic ends are an indication for a nonviable nonunion fracture. However, another author4 believes that sclerotic ends should be classified as viable and sharp tapered ends classified as nonviable. This illustrates the difficulty that exists when radiography is used to predict the type of nonunion.
Classification into nonviable and viable is necessary for determining a plan of treatment because debridement is necessary for nonviable nonunion fractures, whereas rigid immobilization (with or without autograft placement) is used for viable nonunion fractures. However, authors in 1 study5 reported that induced atrophic nonunion fractures in rabbits were vascularized. Therefore, assessment of vascularization, rather than estimating the vascular supply, may be more useful in radiographic evaluation of the type of nonunion fracture.
Scintigraphy has been used to examine vascularization of nonunion fractures6 and in an attempt to predict the development of nonunions.7 Venous osseography has also been evaluated experimentally to test the validity of the method for use in assessing vascularization of fractures.8 However, it would require that an animal be sedated or anesthetized to perform scintigraphy and venous osseography, which would make them less desirable options.
Investigators have used CT to reconstruct a multiplanar image of a nonunion site,9 and MRI has been used to predict the development of delayed union in a group of 12 patients, 5 of which had a delayed union.10 In that report, differences were visible between images obtained from normally healing fractures and those that developed delayed union at 3 to 6 weeks after the trauma. However, CT and MRI are not yet universally available in veterinary medicine. Furthermore, CT and MRI cannot be used on surgically treated fractures because implants will create numerous artefacts. Additionally, it would require that an animal be anesthetized to perform CT or MRI procedures.
Ultrasonographic images of delayed unions and nonunion fractures in humans have been reported.11,12 A lack of developing callus in the fracture gap, with an initial increase in nonhomogenicity and a subsequent increase in hyperechogenicity, is an early indication of delayed union.11 In another report,12 investigators describe nonunion as a lack of a bony bridge consisting of several bony fragments with poor alignment or a structure with an extreme nonhomogeneous tissue echogenicity.
In addition, B-mode (brightness mode) ultrasonography has been used to classify the types of nonunion fractures. Hypertrophic and atrophic nonunion fractures both have characteristic ultrasonographic features. Hypertrophic nonunion fractures will be visible as structures with a hypoechoic to anechoic, nonhomogeneous tissue echogenicity filling the fracture gap with no progression to hyperechogenicity over time. No callus formation is visible in atrophic nonunions. Also, an image with rounded, extremely smooth bony edges is indicative of atrophic nonunion.11
Laser Doppler ultrasonography has been used to assess the viability of bone fragments,13 and color Doppler14 and power Doppler15 ultrasonography have been used to assess fracture healing. Our hypothesis for the study reported here was that power Doppler ultrasonography would be a better modality than radiography to assess vascularization of nonunion fractures in dogs. Histologic evaluation was used to assist in comparison of the imaging techniques.
Magnetic resonance imaging
HFG series A, Varian, Salt Lake City, Utah.
HF R105, Ralco, Milan, Italy, distributed by Verachtert equipment, Antwerp, Belgium.
GE Logiq 7, M12L (7 to 14 MHz), General Electrics, Milwaukee, Wis.
Aquasonic, Parker Laboratories Inc, Fairfield, NJ.
Monoclonal mouse anti-human CD31 clone JC70A, DakoCytomation, Glostrup, Denmark.
SAS, version 9.1, SAS Institute Inc, Cary, NC.
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Kuhlman JE, Fishman EK & Magid D, et al. Fracture nonunion: CT assessment with multiplanar reconstruction. Radiology 1988;167:483–488.
Tervonen O, Junila J, Ojala R. MR imaging in tibial shaft fractures. A potential method for early visualization of delayed union. Acta Radiol 1999;40:410–414.
Hannesschlager G, Reschauer R. Sonographic follow-up of secondary fracture healing. Initial experiences with morphologic and semiquantitative assessment of periosteal callus formation. Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 1990;153:113–119.
Maffulli N, Thornton A. Ultrasonographic appearance of external callus in long-bone fractures. Injury 1995;26:5–12.
Herzog L, Huber FX & Meeder PJ, et al. Laser Doppler flow imaging of open lower leg fractures in an animal experimental model. J Orthop Surg (Hong Kong) 2002;10:114–119.
Caruso G, Lagalla R & Derchi L, et al. Monitoring of fracture calluses with color Doppler sonography. J Clin Ultrasound 2000;28:20–27.
Risselada M, Kramer M & van Bree H, et al. Power Doppler assessment of the neovascularization during uncomplicated fracture healing of long bones in dogs and cats. Vet Radiol Ultrasound 2006;47:301–307.
Risselada M, Kramer M, van Bree H. Approaches for ultrasonographic evaluation of long bones in the dog. Vet Radiol Ultrasound 2003;44:214–220.
Martinoli C, Derchi LE & Rizzatto G, et al. Power Doppler sonography: general principles, clinical applications, and future prospects. Eur Radiol 1998;8:1224–1235.
Nyland TG, Mattoon JS & Herrgesell EJ, et al. Physical principles, instrumentation, and safety of diagnostic ultrasound. In: Nyland TG, Mattoon JS, eds. Small animal diagnostic ultrasound. Philadelphia: WB Saunders Co, 2002;1–18.
Mukai K, Yoshimura S & Anzai M, et al. Effects of decalcification on immunoperoxidase staining. Am J Surg Pathol 1986;10:413–419.
Semiquantitative system used to score 3 categories of power Doppler ultrasonography signals. Each category was scored on a scale of 0 to 3.
|Color||No signal||Red or purple|
|Vessel area (mm2)||No signal||< 5|
|No. of vessels||No signal||< 5|