Radiology

Radiography is essential to supplement clinical assessment of fracture healing. Radiographic interpretation of fracture healing or prediction of failure of fracture healing begins with knowledge of the blood supply to the organ bone.

The main blood supply is via one or more nutrient arteries; within the medullary cavity, it branches into ascending and descending vessels that anastomse with epiphyseo-metaphyseal vessels; having distributed throughout the bone giving branches to supply the bone marrow and cancellous bone and ultimately the cortical bone through Haversian system and finally exit the bone via muscle attachments.

The major blood supply is therefore centrifugal from the medullary space to the cortical surfaces. The periosteum is a highly vascular membrane during the embry onic development of bone and can rapidly regenerate to provide an extra-medullary blood supply when required. The anastomoses are important for adequate perfusion to the metaphyseal arteries which compensate the principal nutrient artery that has been get ruptured by the fracture. (Figs 1,2).

Once the fracture has been reduced and provided blood supply to the fragments is intact, the main requirement for successful healing is the provision of adequate immobilization. Primary or direct union of bone can occur when reduction of the fragments results in stable fixation of an anatomical reduction. Anatomical reduction indicates that cortical margins are apposed and the medullary cavity of the fragments is in contact. Healing fracture margins occur simultaneously by direct osteonal remodeling. (Figure 3).

Radiographically, a slow filling of the fracture with bone density material. Internal and external callus are minimum or absent, and there is absence of osteopenic remodeling of the bone at the fracture margins or distal to the fracture.

Primary bone healing of fracture may be not recognizing as normal healing. There may be some concern that healing is not progressing satisfactorily unless miner evidence of secondary bone healing is found. This reinforces the idea that the assessment of fracture healing should be made by the appropriate examination method, which is clinical examination and palpation of the fracture site. Absence of pain or motion at the fracture site should be regarded as evidence of normal bone healing. (Figs 4, 5, 6, 7, 8, 9).

Secondary bone healing is the usual event in veterinary patients. Extensive soft tissues damage, large haematoma location of the fracture (diaphyseal vs. metaphyseal) displacement, interposition of soft tissues and extent of fragmentation may be used to predict a slower rate of healing.

The sequence of events associated with secondary fracture repair can be followed on radiographs based on the expected time line of events. At 5 to 7 day following trauma following trauma, liquefactive necrosis of bone occurs; osteoctast and phagocytosis begin removing dead bone. This occurs at the fracture margins, where bone losses mineral, the margins lose sharpness and are indistinct or smudged, and the fracture gap may appear to have increased. The indistinct fracture margins and widening of fracture gap extend up to 2 weeks. At 4-6 weeks, unstructured and patchy mineralization of bridging callus were seen and the fracture line still visible. At 6-9 weeks, bridging callus of even density and smooth borders. Fracture line Faintly visible (can remove some of fixation; e.g., pin from external fixation).At 8-12 weeks, dense callus of reduced size; Fracture line barely visible, early corticomedullary remodeling were seen (stage of early clinical union). At 10 weeks or more further condensation of callus; distinct corticomedullary separation due to remodeling; fracture line not visible. (Figs 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20).

The rate of union in terms of clinical union with different primary methods of fixation was seen in table

Age of animal	External skeletal and intramedullary pin fixation	Fixation with bone plates
Under 3 months	2-3 weeks	4 weeks
3-6 months	4-6 weeks	2-3 months
6-12 months	5-8 weeks	3-5 months
Over 1year	7-12 weeks	5 months-1year

In young dogs and cats, fracture line may heal past the point of radiographic detection within two weeks. In older patients with severely displaced fracture, the fracture line may still be easily seen 12 weeks following injury. Certain bones heal more slowly than other. Fracture lines in the third phalanx of cattle were seeing on radiographs taken 78 weeks after injury. Healing of fracture lines in the third phalanx of horse may require 12 to 18 months.

The fracture line then becomes more prominent than it was immediately after the injury. (Figs 21, 22).

Because the uncalcified cartilaginous or osteoid callus is not visible radiographically, this important stage in fracture healing and the degree of early immobilization of the fragment can not be evaluated.

Visualization of the calcified periosteal callus is the most reliable radiographic evidence of beginning bone healing.

The callus first appears as a faint hazy area of increased density developing adjacent to and directly overlying the fracture site (2 weeks).

When it appears as a continuous zone stemming from one fragment to another it is good evidence that a solid union is occurring eventually the callus becomes larger and more dense with distinct margin.

At 3 weeks callus bridges the fracture lines and the fracture line can not be identified.

The amount of visible periosteal callus varies greatly and is extensive in fractures in which there is great displacement of the fragments as in mid shaft femoral fractures of dogs where it may cover almost the entire length of the shafts of the femurs. Comminuted fractures also cause extensive periosteal callus formation. Certain bones such as the proximal sesamoid bones and the third phalanx of the horse heal with the formation of little or no periosteal callus. (Figs 23, 24).

The amount of periosteal callus is much greater in cases in which reduction was incomplete and is greatest in cases in which some degree of motion or infection was present during healing rigid stabilization plus compression of the fragments into an anatomic reduction results in primary bone healing with no periosteal callus noted on the radiograph

Although its radiographic visualization is not clear because of the surrounding periosteal callus, the endosteal callus is extremely important in normal fracture healing. Endosteal callus at its greatest causes complete filling of the medullary cavity. Radiographically endosteal callus contributes greatly to the disappearance of the fracture line causing it to become less and distinct and finally impossible to identify.

The late radiographic signs of bony union are the reforming of the normal trabecular pattern, obscuring the fracture line and remodeling and restoration of the continuity of the medullary cavity and cortex. The radiographic appearance of complete bony union does not occur until after the time of immobilization devices could actually be removed and indicated. The best method for adequate fracture healing is through clinical examination of the fractured bone for movement at the fracture site and for pain response. (Figs 25, 26, 27, 28, 29, 30).

Last Updated May 2006