COMPLICATIONS OTHER THAN PAINFUL NEUROMAS FOLLOWING A POSTERIOR DIGITAL NEURECTOMY

A painful neuroma occurs following 25% of routine equine neurectomies unless special neurosurgery is done. There are at least five other complications that one may encounter: (1) A change of gait such as stumbling or forging has been noted, especially when the neurectomy has been done in one leg; (2) A vascular compromise has been found if there had been any complications in wound healing or excessive tissue insult. Excessive scar formation surrounding both the digital vein and artery can compromise the blood supply to the foot. When the posteriod digital nerves are severed the autonomic nerves are also interrupted. This results in a vasodilatation which may be responsible for faster hoof growth; (3) If the navicular bone had undergone osteolytic changes before the neurectomy it may fracture as soon as the horse starts to use the foot; (4) The deep flexor tendon may rupture where it passes over the navicular bone. This is especially true where adhesions between the bone and tendon were present; (5) Infections in the sole, bulbs of heel, frog, navicular bursa or coffin joint often go unattended because the horse does not show a lameness.     

Variation in foot conformation in lame horses with different foot lesions

Foot conformation in the horse is commonly thought to be associated with lameness but scientific evidence is scarce although it has been shown in biomechanical studies that foot conformation does influence the forces acting on the deep digital flexor tendon (DDFT) and the navicular bone (NB). The aim of this study was to determine the relationships between foot conformation and different types of lesion within the foot in lame horses. It was hypothesised that certain conformation parameters differ significantly between different types of foot lesions. Conformation parameters were measured on magnetic resonance images in the mid-sagittal plane of 179 lame horses with lesions of their deep digital flexor tendon (DDFT), navicular bone (NB), collateral ligaments of the distal interphalangeal joints and other structures.Conformation parameters differed significantly between lesion groups. A larger sole angle was associated with combined DDFT and NB lesions, but not with NB lesions alone. A more acute angle of the DDFT round the NB was associated with DDFT and NB lesions, and a lower heel height index with DDFT injury. The larger the sole angle the smaller the likelihood of a DDFT or NB lesion with odds ratios of 0.86 and 0.90, respectively. This study shows an association between foot conformation and lesions but it does not allow the identification of conformation as causative factor since foot conformation may change as a consequence of lameness. Future studies will investigate foot-surface interaction in lame vs. sound horses, which may open a preventative and/or therapeutic window in foot lame horses.     

Penetrating injuries of the foot

Penetrating injuries to the foot are potentially serious injuries in the horse. Diagnosis is usually straightforward and a combination of radiography (including positive contrast studies) and synoviocentesis usually is necessary to determine which structures within the foot are involved. Superficial punctures usually carry a good prognosis but involvement of deep structures such as the distal phalanx or deep digital flexor tendon and navicular bursa adversely influence this. Knowledge of wound healing in the foot and a rational approach to antimicrobial selection and surgical intervention are all necessary for successful case management.     

Subjective and quantitative scintigraphic assessment of the equine foot and its relationship with foot pain

It was hypothesised that in solar bone images of the front feet of clinically normal horses, or horses with lameness unrelated to the front feet, there would be less than a 10% difference in the ratio of uptake of radiopharmaceutical in either the region of the navicular bone, or the region of insertion of the deep digital flexor tendon (DDFT), compared to the peripheral regions of the distal phalanx. Nuclear scintigraphic examination of the front feet of 15 Grand Prix show jumping horses, all of which were free from detectable lameness, was performed using dorsal, lateral and solar images. The results were compared with the examinations of 53 horses with primary foot pain, 21 with foot pain accompanying another more severe cause of lameness and 49 with lameness or poor performance unrelated to foot pain. None of the horses with foot pain had radiological changes compatible with navicular disease. All the images were evaluated subjectively. The solar views were assessed quantitatively using regions of interest around the navicular bone, the region of insertion of the deep digital flexor tendon and the toe, medial and lateral aspects of the distal phalanx. In 97% of the feet of normal showjumpers, there was <10% variance of uptake of the radiopharmaceutical in the navicular bone, the region of insertion of the DDFT and the peripheral regions of the distal phalanx. There was a significant difference in uptake of radiopharmaceutical in the region of the navicular bone in horses with foot pain compared to normal horses. There was a large incidence of false positive results related to the region of insertion of the DDFT. Lateral pool phase images appeared more sensitive in identifying potentially important DDFT lesions. There was a good correlation between a positive response to intra-articular analgesia of the distal interphalangeal joint and intrathecal analgesia of the navicular bursa and increased uptake of radiopharmaceutical in the region of the navicular bone in the horses with primary foot pain. It is concluded that quantitative scintigraphic assessment of bone phase images of the foot, in combination with local analgesic techniques, can be helpful in the identification of the potential source of pain causing lameness related to the foot, but false positive results can occur, especially in horses with low heel conformation.