Ultrasonographic changes associated with the healing process in a fracture of the distal phalanx in a cow.

A female Holstein cow presented with lameness in the left hind-limb, having suffered a fracture within the distal phalanx distal to the distal interphalangeal joint. The lesion was visualized as a radiolucent gap on a lateral radiograph and a hypoechoic gap on an ultrasonogram in which the hyperechoic bony line disappeared. Using regular ultrasonographic examinations, the healing of the fracture could be characterized by increased echogenicity inside the gap and the formation of a hyperechoic bony bridge. Ultrasonography can provide earlier evidence compared with that provided by radiography of the healing process of a fractured distal phalanx.

Fractures of the distal phalanx are comparatively rare claw injuries that typically occur within the inner claw of the foreleg in cattle [8]. Radiography is the most accurate diagnostic tool in such cases because it can provide definite proof of a fracture of the distal phalanx, commonly visualized as a radiolucent gap running in the proximal–distal direction and distal to the distal interphalangeal joint [5, 8]. However, diagnosis using a lateral radiogram has the disadvantage of superimposition of the inner and outer claws, therefore use of the oblique view is recommended for diagnosis of this type of fracture [5, 6]. Currently, ultrasonography is used to measure the thickness of the sole horn and the soft tissue layers [7] and to diagnose fractures in the extensor process of the distal phalanx in lame cattle [6]. However, there have been no previous reports describing ultrasonographic findings of a typical fracture of the distal phalanx affecting the area distal to the distal interphalangeal joint in cattle. Furthermore, ultrasonography has not previously been used to evaluate the healing process following the application of a claw block, which is the most suitable approach for the management of this type of fracture [1, 3, 8], although follow-up radiography has been successful in showing changes over time during recovery [8]. This study describes changes in radiographic and ultrasonographic findings indicative of bone union in a fracture of the distal phalanx in a cow.

A female Holstein cow aged four years and nine months presented with sudden weight-bearing lameness in the left hind-limb. Twelve days after the sudden onset of lameness (Day 1), the cow exhibited a pain response in the heel region of the outer claw following deep palpation. There were no gross abnormalities on the sole surface or in the interdigital space after trimming, although the coronet was severely swollen. A claw block was applied to the sound (inner) claw, resulting in an immediate improvement in gait. On Day 13, the cow continued to exhibit weight-bearing lameness. Throughout this study, imaging devices were used to visualize the affected claw by placing the cow in a treatment stall and lifting the claw while the animal was in a standing position. A portable radiographic device (PX-20BT; KenkoTokina Co., Tokyo, Japan) was used with an X-ray condition of 60 kV and 2 mAs. From the lateral radiograph, a radiolucent gap was observed within the distal phalanx distal to the distal interphalangeal joint. The gap led to separation of the three parts of the distal phalanx (two dorsal parts and one plantar part). The plantar bone fragment was dislocated toward the plantar direction, resulting in the proximal width of the gap being extended. On Day 38, the cow could walk using a claw block but showed slight weight-bearing lameness in her left hind-limb. A 5-MHz linear transducer with a portable ultrasound device (HONDA HS-101V; HONDA Electronics, Tokyo, Japan) was applied to the sole surface of the affected outer claw, which had been trimmed prior to examination. When visualized by ultrasonogram on Day 38, the line of the ventral surface of the distal phalanx (DP line) was comparatively smooth and hyperechoic in the dorsal region; it was intact where it disappeared between the deepest concave site and the flexor tuberosity due to interruption of the gap (Fig. 1A). The gap appeared as a homogenous hypoechoic trapezoid-shaped structure, in which the hyperechoic line was evident and ran parallel with the DP line in the deeper site; this line possibly indicated the ventral surface of the middle phalanx. In this study, the structures of the fractured distal phalanx visualized using ultrasonograms were quantitatively analyzed using imaging software (ImageJ 1.42; NIH, USA). The deeper and ventral widths of the gap (DWG and VWG) were estimated to be 7.3 and 13.2 mm, respectively. By Day 154, the cow was walking normally. A second radiographic examination on Day 154 revealed decreased widths in both the proximal and ventral sites of the gap, despite the gap being clearly visible (Fig. 2A). The radiopacity inside the gap had not changed much in comparison with that of the first examination. A second ultrasonographic examination on Day 154 revealed that heterogeneously hyperechoic areas were scattered throughout the hypoechoic gap (Fig. 1B). A small hyperechoic line was evident near the dorsal edge of the gap in the DP line. The situation deeper within the gap was unclear. Based on an ultrasonogram, the VWG was estimated to be 10.3 mm, although the DWG could not be measured. On Day 301, the radiopacity inside the gap had increased, according to the lateral radiograph (Fig. 2B). The widths of the gap were slightly less in both the proximal and ventral sites compared with the widths seen in the second examination on Day 154. On the ultrasonogram, the gap appeared to be triangular in shape because the hyperechoic line of the deeper site was shorter compared with that of the first examination on Day 38 (Fig. 1C). The gap had been filled with a mixture of both hypoechoic and hyperechoic structures. A hyperechoic and thickened line had formed in the space between the dorsal and plantar edges of the gap and was intermittently connected with the dorsal and plantar edges of the gap in the DP line. The VWG could not be accurately estimated. On Day 742, the gap appeared as a small hollow outlined by the hyperechoic DP line on the ultrasonogram (Fig. 1D). Radiography revealed that the gap was embedded with radiopaque structures throughout two-thirds of the proximal end, although there was a small gap remaining in the ventral part (Fig. 2C). The lameness had completely disappeared, and the cow was kept for milking.

Fig. 1.

Ultrasonograms of the fractured distal phalanx of a female Holstein cow at Day 38 (A), Day 154 (B), Day 301 (C), and Day 742 (D). (A) The fracture gap (FG) is represented by a hypoechoic structure, in which the hyperechoic ventral line of the distal phalanx (DP line) disappears at the ventral site. The hyperechoic line seen at the deeper site possibly corresponds with the distal articular surface of the middle phalanx. (B) Hyperechoic spots (asterisk) can be seen within the FG; they incompletely cover the interrupted DP line. (C) Hyperechoic spots occupy most the FG, which is attributed to the newly formed DP line (suggestive of remodeling). (D) The FG is imaged as a small hollow (asterisk) outlined by the hyperechoic line of the ventral surface of the distal phalanx. SH, sole horn; S-S line, borderline between the sole horn and soft tissue layers; ST, soft tissue layers; DWG, deeper width of the gap; VWG, ventral width of the gap. Scale bar=10 mm.

Fig. 2.

Lateral radiographs of the fractured distal phalanx at Day 154 (A), Day 301 (B), and Day 742 (C) (A) Radiopacity of the fracture gap (FG) gradually increases, but the FG is still discernible because it is radiolucent compared with the bone body of the distal phalanx. (B) Radiopacity of the FG is similar to that on Day 154 (shown in Fig. 2A). (C) The FG is embedded with radiopaque structures in two-thirds of the dorsal end (arrow). DP, distal phalanx; MP, middle phalanx; SB, sesamoid bone.

Radiography is a conventional imaging tool that can provide valuable evidence for the diagnosis of fractures in the extensor process and the distal phalanx, despite the superimposition of the inner and outer claws in a lateral radiogram [5, 6, 8]. A lesion in a claw can be detected without this superimposition by taking a radiograph when the radiographic plate or cassette-less film is placed between the inner and outer claws [2]. However, it may be hard to fully visualize a fracture line running distal to the distal interphalangeal joint using interdigital radiographic techniques because the radiographic plate or film cannot be placed intact in the interdigital cavity in the plantar location. Compared with a radiographic image, an ultrasonographic image of the affected claw is not superimposed with that of the opposite claw. It is possible to perform the examination at any time, in any place, and to obtain images in real-time, although a degree of forced restriction is required. Prior to the application of ultrasonography for bovine sole horn, the claw should be trimmed slightly to ensure the sole surface is flat, enabling good visualization of sole structures [7]. Trimming decreases the width of the sole horn, which is recommended to be less than 10 mm; a sole horn thickness of more than 10 mm can lead to poor visualization of the sole structures in an ultrasonogram [7]. In addition, the use of a 5-MHz transducer allows increased visualization of sole structures characterized by three echogenic lines of the line of the sole surface, the borderline between the sole horn and the soft tissue layers, and the DP line, compared with the visualization obtained using a 6.5-MHz transducer, although a slightly better image quality can be obtained with the latter [7]. The use of a lower frequency transducer is recommended for the observation of pathological osseous changes in the bovine claws, because it provides a rough but more hyperechoic image of the DP line [7].

In the first ultrasonogram taken of this case, the fracture gap appeared to be trapezoid-shaped, because there was a large separation between the dorsal and plantar edges of the deeper site, as seen in the first radiograph. These findings might represent pathological osseous change due to osteoclastic bone resorption along fracture edges, as well as dislocation of the plantar bone fragment associated with tension from the deep digital flexor tendon [8]. The VWG and DWG measured on the first ultrasonogram were very large compared with a previous case, where the widths of the fracture gaps at the proximal and ventral sites, which were 2 to 3 mm and 4 to 5 mm, respectively, on the radiographs of a fractured distal phalanx distal to the distal interphalangeal joint [8]. This suggests that the present case might have involved a refractory lesion. During the fracture healing process, high quality osteosynthesis appears to be associated with adequate stabilization and a short distance between both edges of the fracture gap [1]. On the other hand, the DWG on Day 154 was small compared with that in the first ultrasonogram. In addition, the fracture gap had changed shape and had become triangle-shaped in the third ultrasonogram taken on Day 301. This suggests that when the weight-bearing load on the affected outer claw was effectively reduced by the application of a claw block for the inner, sound claw, in this case it may have helped return the dislocated plantar bone fragment to its original position. Ultrasonography appears to be useful for the clear visualization of changes in the shape of the gap associated with the positional repair of a distal phalanx plantar bone fragment, in a similar way to radiography.

Ultrasonography may provide earlier evidence of fracture healing compared with that provided by radiographic examination, which can have a delay of weeks to months before clinical union can be detected [1, 4]. On Day 154, the content inside the fracture gap could be visualized by the heterogeneously increased echogenicity on the ultrasonogram but was unchanged on a radiogram taken on the same day. In human medicine, ultrasonography is used to evaluate three phases of fracture healing, comprising the reactive phase (such as inflammatory cell influx), the reparative phase (such as calcification), and the remodeling phase, while radiography can only provide evidence of the reparative and remodeling phases [4]. On the other hand, use of an ultrasonogram may make it difficult to evaluate whether an irregular DP line is associated with bone union, such as bridge formation, or carious change due to osteomyelitis, which represents a causative background that predicts the possibility of serious damage [3, 8]. Radiography is far superior to ultrasonography for the detection of carious change and bone destruction associated with deep infection and osteomyelitis, which are also causes of fracture [3, 6, 8]. However, in this case the relationship between the degree of healing based on clinical signs (soundness states) and imaging results was not high synchronous. Frequently used imaging devices may be more useful for making a prognosis compared with making a judgment with regard to healing, because they can provide subjective evidence for pathological osseous changes and any delays in the fracture healing phases.

Ultrasonography can provide supplemental information for the definitive diagnosis of fractures of the distal phalanx made using radiography [6], including the degree of destruction in the sole horn or the soft tissue layers in addition to changes inside the fracture gap due to healing. In ultrasonography of bovine claws, the dorsal wall or the sole horn is commonly used as an ultrasound window for observation of the distal phalanx [6, 7]. Trans-solar ultrasonography of the bovine claw can provide a sagittal section of the inside structures that corresponds with a lateral radiograph; however, it provides poor quality of imaging of the deeper structures because of the attenuation of the ultrasound wave as it passes through the sole horn [7]. On the other hand, ultrasonography may reveal the depth of a fracture gap and the formation of a callus or bone union in deeper sites of the gap when a transducer is applied for the abaxial wall at the plantar location, although this technique has never previously been reported. In addition, this technique can be performed with standing animals, although slight trimming of the horn is required for concave or irregular surfaces. For diagnosis of a fractured distal phalanx, it is recommended to scan the bovine claw using multiple ultrasound windows. In addition, the use of color Doppler ultrasonography enables the visualization of blood flow in a fracture site and may be used to predict the degree of bone union and form a prognosis [4].