Laminitis

Laminitis can results in radiographic signs of rotation of the third phalanx and this problem produces little diagnostic challenges to most equine practitioners. While the radiographic signs of secondary changes as loss of normal bone density, prominent hypervascularity, focal region of destruction, increased thickness of soft tissues and sometimes sequestration is the real challenges.

Radiographic Examination

A latero-medial, and dorso-palmar/plantar views of the feet were used to evaluate signs of laminitis. Oblique view was used to evaluate the possible changes of the distal phalanx.

Angiography: is used for studying the normal arteriogram of the normal foot as well as the laminitic one. It is preformed under the effect of deep narcosis using chloral hydrate 10%. Area above the metacarpo/metatarsophalangeal joint of the medial aspect is prepared for aseptic interference. A 3 cm skin incision was made between the deep digital flexor tendon and the suspensory ligament exposing the common digital arteries upon a curved hemostate. The artery was canulated and then a 20 ml of the radio-opaque medium (Urografin 76%) injected rapidly through the canula. An X-ray exposure was made just before the end of the injection.

Postmortem examination:  The affected and normal limbs of the euthanised donkeys were transected at the midmetacrpal/metatarsal regions and sectioned sagittally for comparative studies.

Results of the radiographic measurements on the original radiographic films includes wall thickness (WL), Palmar cortical length (PL), and the wall thickness to the palmar cortical length ratio to overcome the effect of animal size and radiographic magnifications, and the difference between angle 1 and angle 2.

Radiographic signs and measurements of normal feet:    

In donkeys, over two years of age, with normal feet, the wall thickness measure (11-14 mm), the palmar cortical length ranges between (33-35 mm), and the wall thickness/palmar cortical length ratio average (31-42%). Meanwhile these measurements in young donkeys less than 6 months were (9-11 mm), (28- 32 mm), and (28-39%), respectively as shown in (Fig.1).

In horses, over two years of age, the range of wall thickness measure (11-17 mm), the palmar cortical length was (57-70 mm), and the wall thickness/palmar cortical length ratio was (16-29%). While in young foals, less than 6 months of age, the measurements were (9-12 mm), (40-55 mm), and (16-30 %) respectively as in (Figs. 2, 3).

Radiographic  signs  and  measurements of  long-standing laminitic  feet  in donkeys:

The predominant radiographic features of chronic laminitic cases were increase in wall thickness (18-28 mm) with lack of true rotation and distal displacement of the third phalanx in a number of 5 out of 28 feet (18%) as shown in (Fig. 4).

Distal displacement of the third phalanx, an increased the wall thickness and the ratio between the wall thickness and the palmar cortical length (46%). The dorsal surface of the hoof capsule and the dorsal cortex of the third phalanx remain parallel, marked moving of the extensor process of the third phalanx distally in relations to the coronary band which was marked at the end of the metallic wire in a number of 11 out of 28 feet (39.28 %), as shown in (Fig. 5).

Decrease of normal bone density and  focal region of bone destruction to the distal half of the third phalanx were seen in a number of 4 out of 28 feet (14.28 %) as in (Fig. 6). Resorption of a part of the distal phalanx, and it is no longer visible (Fig.7).  The tip of the third phalanx is curled up and it may be fuzzy and indistinct in 7 out of 28 feet (25 %) as in (Fig. 8). Reverse rotation was reported in one foot only (3%).

The results of angiography in long-standing laminitic cases revealed that both medial and lateral digital artery did not filled with contrast material, vessels of the coronary band became irregular. Central obliteration of the terminal arch and dorsal branches of the pedal bone were noticed (Fig. 9).

Sagittal  sections of normal and long-standing laminitic feet  in donkeys:

In normal feet, the top of the extensor process of the distal phalanx measured 5 mm below the top of the dorsal hoof wall, the coronary groove is oval in shape, the dorsal cortex of the distal phalanx is closely parallel to the dorsal hoof wall, the horn tubules in the dorsal hoof wall run in straight lines down to the ground surface, the horny sole is concave (Fig. 10).

In long standing laminitic feet the top of the extensor process of the digital phalanx measure (10-11mm) below the top of the dorsal hoof wall, insensitive epidermal  laminae and dermal sensitive laminae are easily separated by gentle traction and the third phalanx is only attached at the coronary band and digital cushion region. The horny sole is flat, hemorrhagic and congested laminae. The tip of the third phalanx was curled up, increased wall thickness and distal displacement of the third phalanx, with reverse rotation were recorded (Figs. 11-12).

Figure 1: Diagrammatic representation of the normal split foot Stippled area = coronary corium; hatching = laminar corium. The three phalangeal bones (P, M & D) are a straight line. The top of the pedal bone (e) for extensor process is slightly below the coronary band. The coronary corium is oval in shape; the solid dots represent the circumflex artery of the pedal bone (at the front) and blood vessels within the solar corium. Note that the frog extends in front of the area of attachment of the deep digital flexor tendon (t).

Figure 2: Diagrammatic representation of the laminitic split foot stippled area = coronary corium; hatching = laminar corium. The three phalangeal bones (P, M & D) are not straight line. The top of the pedal bone (e) for extensor process is slightly below the coronary band. The coronary corium is oval in shape. The front of the pedal bone and of the hoof are not longer parallel. Difference between angel (1) and angel (2) is the degree of rotation (Eustace, 1992).   

Figure 3: Latero-medial radiograph of a normal donkey foot. The phalanges are in straight line and the wire marker is parallel to the front of the pedal bone. The wall thickness measures 12 mm and the palmar cortical length (PL) measures 35 mm

Figure 4: Latero-medial radiograph of a normal foot in a drafting horse, the phalanges are in a straight line and the wire marker is parallel to the front of the pedal bone. The wall thickness measures 13 mm and the palmar cortical length (PL) measures 60 mm.

Figure 6: Lateral radiograph in chronic laminitic foot in a donkey showing chronic degenerative changes in os pedis. Notice increased width between the outer surface of the hoof and the dorsal cortical surface (Wall thickness=18 mm) without pedal rotation.

Figure 7: Lateral radiograph in chronic laminitic foot in a donkey showing distal displacement of the third phalanx without pedal rotation, and increased wall thickness/palmar cortical length ratio.

Figure 8: Dorso-palmar and lateral radiographs showing chronic pedal ostitis, loss of normal bone density and focal region of bone destruction in a case of long-standing chronic laminitis in 6 years-old donkey (black arrows)

Figure 9: Dorso-palmar and lateral radiographs in long-standing case of laminitis in 6 years-old donkey showing mis-shapen of the hoof, osteoperosis of os pedis and the distal half of the distal phalanx is no longer visible.

Figure 10: Lateral radiograph in long-standing of chronic laminitis in 7 years old donkey showing flaring of the dorsal solar border of pedal bone. The tip of the pedal bone has a distinct appearance (curled up), black arrows.

Figure 11: Angiographic appearance in a case of chronic laminitis showing that both medial and lateral digital artery did not filled with contrast material,  obliteration of the terminal arch and rami of the third phalanx.

Figure 12: Sagittal section of a normal foot. The coronary groove (a) is oval, phalanges are in straight line; dorsal cortex of pedal bone (b) is parallel to the dorsal hoof wall; horn tubules (c) run in straight line with concave horny sole and the tip of the extensor process of the distal phalanx (d) is 5 mm below the top of the dorsal hoof wall.

Figure 13, 14: Sagittal sections in a chronic laminitic feet. The coronary groove (a) is not more oval, phalanges are not in typical straight line, and the horny sole (b) is flat. The laminae (c) are severely hemorrhagic and congested. The tip of the third phalanx (d) is curled up with clear distal displacement of the third phalanx (e).