Diagnostic analgesia of the equine digit

Abstract

Summary Analgesia usually occurs within 5 min after administration of local anaesthetic solution into joints or around nerves in the distal portion of the limb. Gait should be assessed within 10 min after diagnostic regional analgesia of the distal portion of the limb because rapid diffusion of anaesthetic solution can result in anaesthesia of other nerve branches, thus confusing results of the examination. A palmar digital nerve block (PDNB) anaesthetises most of the foot, including the distal interphalangeal (DIP) joint (coffin joint), rather than just the palmar half of the foot, as was once commonly believed. To avoid partially anaesthetising the proximal interphalangeal joint (pastern joint), the palmar digital nerves should be anaesthetised near or distal to the proximal margin of the collateral cartilages. Clinicians should be aware that an abaxial sesamoid nerve block (ASNB) may ameliorate or abolish pain within the metacarpo/metatarso‐phalangeal joint (fetlock joint). Mepivacaine administered into the DIP joint desensitises the DIP joint and probably the palmar digital nerves to also cause anaesthesia of the navicular bursa, the navicular bone, the toe region of the sole, the digital portion of the deep digital flexor tendon (DDFT) and the distal portions of the collateral ligaments of the DIP joint. When a large volume of mepivacaine HCl (e.g. 10 ml) is administered, the heel region of the sole may also be desensitised. Only a small percentage of horses with disease of the collateral ligament(s) of the DIP joint show a significant improvement in lameness after intra‐articular analgesia of the DIP joint, and no horse is likely to improve after intrabursal analgesia of the navicular bursa. A PDNB, however, improves lameness substantially in most horses that are lame because of disease of the collateral ligament(s) of the DIP joint, and all affected horses are likely to become sound after an abaxial sesamoid nerve block. The degree of improvement in lameness associated with injury to one or both collateral ligaments of the DIP joint after PDNB is determined by the extent of the injury and the level at which the palmar digital nerves are anaesthetised. The further proximal the level of the injury within the collateral ligament, the less likely that lameness is ameliorated by analgesia of the DIP joint or a PDNB. Verschooten's technique appears to be the most accurate technique for centesis of the navicular bursa. Even though analgesia of the DIP joint results in analgesia of the navicular bursa, analgesia of the navicular bursa does not result in analgesia of the DIP joint. Pain arising from the DIP joint can probably be excluded as a cause of lameness when lameness is attenuated by analgesia of the navicular bursa. Analgesia of the digital flexor tendon sheath (DFTS) is likely to desensitise only structures that are contained within or border on the sheath itself (i.e. the superficial and deep digital flexor tendons, the straight and oblique distal sesamoidean ligaments, the annular ligaments of the fetloc...

Where does it hurt? Problems with interpretation of regional and intra‐synovial diagnostic analgesia

“…The use of video gait analysis systems and inertial measurement units as objective measures of degree of lameness may well revolutionise lameness investigation in the future, but have not so far permeated into widespread use in general practice. The pros and cons of various local anaesthetic solutions available have been well reviewed elsewhere (Schumacher et al . ), but we strongly recommend mepivacaine hydrochloride. The speed of onset of action is good (5–10 min, depending on site) and the duration of action is sufficient (1–3 h) (Bidwell et al .…”

Agreement between a body-mounted inertial sensors system and subjective observational analysis when evaluating lameness degree and diagnosticanalgesia response in horses with forelimb lameness

“…The palmar digital (PD) and abaxial sesamoid (AS) nerve blocks were performed as previously described (Dyson 1984, Schumacher et al 2004, Schumacher et al 2013) using 2 ml of 2 % mepivacaine (Scandicain ® ) b per site (Schumacher et al 2004). For the distal interphalangeal (DIP) joint block, the injection site was aseptically prepared and 5 ml of 2 % mepivacaine were injected into the joint using the dorsal approach (Schumacher et al 2004).…”

“…Local anaesthesia (blocking) helps to isolate the focus of pain within the limb in horses with lameness (Adam 1974, Schumacher et al 2004, Schumacher et al 2013). This requires the veterinarian to assess the amplitude of lameness by observing the horse in motion before and after the nerve block (Adam 1974).…”

Comparison of lameness scores after a low 4‐point nerve block to lameness scores after additional desensitisation of the dorsal metatarsal nerves in horses with experimentally induced pain in the metatarsophalangeal joint

“…Objective re‐evaluation of the subject's gait revealing significant amelioration of lameness was further indication of success of the nerve block (Schumacher et al . ).…”